Patent Publication Number: US-9896933-B1

Title: Continuously variable displacement engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-In-Part of U.S. patent application Ser. No. 14/829,442, filed on Aug. 18, 2015, entitled CONTINUOUSLY VARIABLE DISPLACEMENT ENGINE, which issues on Jan. 10, 2017, as U.S. Pat. No. 9,540,932. U.S. application Ser. No. 14/829,442 is a Continuation-In-Part of U.S. patent application Ser. No. 13/368,198, filed on Feb. 7, 2012, entitled CONTINUOUSLY VARIABLE DISPLACEMENT ENGINE, which issued on Aug. 18, 2015, as U.S. Pat. No. 9,109,446. U.S. application Ser. No. 13/368,198 claims benefit of U.S. Provisional Application No. 61/462,700, filed on Feb. 7, 2011, entitled CONTINUOUSLY VARIABLE DISPLACEMENT ENGINE. U.S. patent application Ser. Nos. 14/829,442, 13/368,198 and 61/462,700, and U.S. Pat. Nos. 9,109,446 and 9,540,932 are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an internal combustion piston engine having a wobble plate or swash plate. In particular, it relates to a wobble plate engine in which the piston displacement can be continuously varied over a range of displacements while maintaining a constant compression ratio, or while varying the compression ratio in predetermined relation to the selected displacements. 
     BACKGROUND 
     Current internal combustion engines typically use one or more pistons in single, opposed, in-line or V arrangements. They use a crankshaft where the piston is connected to a crankshaft through a connecting rod. The crankshaft has one or more bearings offset from the center of the shaft that drive the pistons back and forth as the shaft turns to ingest and exhaust gases contained by the piston in a cylindrical space in the engine block. They operate with a constant displacement and constant compression ratio. Thus they are essentially constant displacement engines. Some attempts (such as in some Cadillac and Honda automobiles) have been made to vary displacement by inactivating use of certain cylinders in a multi-piston engine. The engine displacement is changed in discontinuous steps limiting fuel efficiency over a continuously variable displacement engine. Also, the frictional losses are not reduced in this design at reduced power and engine control becomes more complex. 
     Aircraft engines have also been designed with multiple pistons arranged in a radial manner around a single offset bearing on the crank shaft. This arrangement is used when high torque is required and the engine speed (rotations per minute) is not very high. 
     High speed rotary compressors and turbines have also been used in engine designs, primarily in aircraft applications, where air is drawn through the engine, mixed with fuel and combustion is internal to the engine. These applications are generally not suitable for land vehicle or industrial uses because of cost and low fuel efficiency. 
     Many factors affect the useful power that is produced by an internal combustion engine. The five main variables for a piston engine are the engine displacement, speed (rotations per minute), compression ratio, inlet air pressure and fuel-to-air ratio. Thermodynamic principles indicate that for an internal combustion engine of fixed displacement, maximum fuel efficiency (ratio of useful power to fuel consumed) of traditional engines occurs near the conditions of maximum inlet air pressure, which is also near the maximum power setting for a given engine speed. In internal combustion engine applications, the common method of controlling power produced is to lower intake pressure until the desired power level is produced. Thus the engine is normally operating at reduced efficiency. 
     U.S. Pat. No. 5,553,582, issued to Speas, shows an engine based on the wobble plate concept wherein the engine design is capable of varying engine displacement, cylinder compression ratio, valve timing and valve travel. The Speas design may be considered very complex, and may not be practical for an operational engine. The complex mechanisms in the Speas patent required to achieve all the variables are not needed in a fuel efficient engine and may prevent the design from being implemented. 
     SUMMARY 
     One embodiment comprises a 4-stroke piston engine with one or more cylinders arranged around a central straight power shaft. The axes of the cylinders are parallel to the axis of the power shaft. A piston control mechanism is linked to the power shaft at a variable angle with respect to the power shaft axis. The piston control mechanism transforms the forces from the piston(s) into torque to turn the power shaft. As the displacement is continuously varied, the top of the piston stroke is automatically varied to maintain a constant compression ratio throughout the full range of displacement. Maintaining a constant compression ratio throughout the range of piston displacement permits the engine to maintain full intake air pressure and maximum fuel efficiency over a wide range of power demand. 
     In a preferred embodiment, the range of engine displacement can be continuously and smoothly varied over at least a range of 3:1. In another preferred embodiment, lesser power demand is met by restricting intake air flow and fuel (limiting intake air pressure) at minimum displacement. Variations in valve timing are readily achieved by a simple actuation mechanism. This combination of engine features improves fuel efficiency over conventional designs in applications wherein the engine will routinely operate at various power demands. 
     In still other embodiments, an engine is provided having numerous advantages over conventional designs in addition to those previously described. In some embodiments, the engine requires a small spatial envelope. In other embodiments, the engine weight is reduced by the structural efficiency of the straight power shaft, structural efficiency of the engine block and reduction of weight in the pistons and connecting rods due to lower side forces. In other embodiments, the inertial forces are also lower because of the reduced weight and the feature that the primary inertial mode is balanced in multi-piston engine configurations. 
     In still other embodiments, an engine is provided that is readily scalable and is readily adapted to other piston control mechanism configurations. In various embodiments, the engine can accommodate up to five cylinders with little change in engine spatial envelope over a single cylinder design. In other embodiments, the engine competes favorably with much more complicated and costly hybrid power trains (i.e., combined internal combustion and electrical) in automotive engine systems. In other embodiments, the engine provides improved fuel efficiency may be even more important in large truck applications, especially for long cross-country routes where fuel costs are a high part of the transportation cost. In other embodiments, two or more sets of pistons can also be grouped together in various arrangements. 
     In still other embodiments, hydraulically powered valve lifters (rather than conventional cams) and/or a hydraulic piston replacement for the mechanical piston control mechanism actuator may offer further improvements. In other embodiments, hydraulic valve actuation permits an electronic engine control unit to vary valve timing and/or valve open duration and/or rate of valve opening and closing and/or valve travel. 
     In another embodiment, an engine comprises an engine block, an elongated power shaft rotatably supported by the engine block, the power shaft having a longitudinal axis, and at least one cylinder supported by the engine block. Each cylinder has a bore defining a bore axis aligned substantially parallel to the longitudinal axis of the power shaft. The engine of this embodiment further comprises one or more pistons corresponding in number to the number of the cylinders, each respective piston being slidably disposed within the bore of a respective cylinder. The engine of this embodiment further comprises a wobble plate assembly having a generally annular configuration defining a central opening through which central opening the power shaft passes, the wobble plate assembly including a central support member, a first ring portion, a second ring portion and a ring bearing assembly. The central support member is longitudinally slidably mounted on the power shaft and defines a pivot axis for the wobble plate assembly. The pivot axis intersects the longitudinal axis of the power shaft in a perpendicular orientation and rotates with the power shaft. The first ring portion is pivotally mounted on the central support member such that the first ring portion pivots about the pivot axis and rotates with the central support member. The second ring portion is concentrically disposed adjacent the first ring portion and has mounted thereon one or more connecting rod bearings corresponding in number to the number of the cylinders. The ring bearing assembly is connected between the first ring portion and the second ring portion so as to allow the first ring portion to rotate about the common center relative to the second ring portion while constraining the second ring portion to remain parallel to the first ring portion. The wobble plate assembly, when viewed in a direction parallel to the pivot axis, defines a wobble plate inclination plane and a wobble plate inclination angle θ, the wobble plate inclination plane being seen as a line passing through the center of the pivot axis and the center of the connecting rod bearing(s), when viewed in a direction parallel to the pivot axis, and the wobble plate inclination angle θ being the angle of intersection between the wobble plate inclination plane and a line perpendicular to the longitudinal axis of the power shaft, when viewed parallel to the pivot axis. The engine of this embodiment further comprises a displacement actuator operatively connected between the engine block and the central support member, the displacement actuator selectively moving the central support member along the power shaft so as to longitudinally position the pivot axis of the wobble plate assembly at a user-selectable distance d from a theoretical zero displacement point on the longitudinal axis. The engine of this embodiment further comprises a piston control linkage operatively connected to the wobble plate assembly, the piston control linkage setting the wobble plate inclination angle θ as the distance d changes so as to maintain a linear relationship between d and sin(θ) such that d=W sin(θ), where W is a constant. The engine of this embodiment further comprises an anti-rotation assembly having a first portion operatively connected to the second ring portion of the wobble plate assembly and a second portion operatively connected to the engine block, the anti-rotation assembly preventing rotation of the second ring portion of the wobble plate assembly relative to the engine block. The engine of this embodiment further comprises a torque assembly having a first portion operatively connected to the first ring portion of the wobble plate assembly and a second portion operatively connected to the power shaft, the torque assembly transmitting torque between the first ring portion and the power shaft to cause rotation of the power shaft relative to the engine block when the first ring portion rotates relative to the engine block. The engine of this embodiment further comprises one or more connecting rods corresponding in number to the number of cylinders, each respective connecting rod having an upper end connected to a respective piston and a lower end connected to a respective connecting rod bearing on the second ring member of the wobble plate assembly such that reciprocation of the piston(s) within the cylinder bore(s) results in rotation of the power shaft. Operation of the displacement actuator to selectively change the pivot axis-to-zero point distance d within a range between a maximum distance dmax and a minimum distance dmin, where the ratio of dmax/dmin=N, correspondingly changes the piston displacement DP of the engine within a range between a maximum displacement DPmax and a minimum displacement DPmin having a ratio DPmax/DPmin=N, while the piston control linkage maintains the compression ratio of the engine at a substantially constant value as the displacement changes within the range between DPmax and DPmin. 
     In another embodiment, an engine comprises an engine block supporting a plurality of cylinders spaced apart around a rotatably mounted central power shaft having a longitudinal axis, each respective cylinder having a respective bore defining a bore axis aligned substantially parallel to the longitudinal axis and having a respective piston slidably disposed therein, each respective piston having connected thereto an upper end of a respective connecting rod also having a lower end. The engine of this embodiment further comprises a wobble plate assembly mounted on the power shaft, the wobble plate assembly including a first ring portion, a second ring portion and a ring bearing assembly. The first ring portion is operatively mounted on the power shaft such that the first ring portion rotates with the power shaft and pivots about a pivot axis intersecting the longitudinal axis of the power shaft in a perpendicular orientation and rotating with the power shaft. The second ring portion is concentrically disposed adjacent the first ring portion and has mounted thereon a plurality of connecting rod bearings corresponding in number to the number of the cylinders, each respective connecting rod bearing being connected to the lower end of a respective connecting rod, the second ring portion being operatively connected to the engine block so as to prevent the second ring portion from rotating relative to the engine block. The ring bearing assembly is connected between the first ring portion and the second ring portion so as to allow the first ring portion to rotate about the common center relative to the second ring portion while constraining the second ring portion to remain parallel to the first ring portion. Reciprocation of the pistons within the cylinder bores results in rotation of the power shaft. The wobble plate assembly, when viewed in a direction parallel to the pivot axis, defines a wobble plate inclination plane and a wobble plate inclination angle θ, the wobble plate inclination plane being seen as a line passing through the center of the pivot axis and the center of the connecting rod bearings, when viewed in a direction parallel to the pivot axis, and the wobble plate inclination angle θ being the angle of intersection between the wobble plate inclination plane and a line perpendicular to the longitudinal axis of the power shaft, when viewed parallel to the pivot axis. The engine of this embodiment further comprises a displacement actuator operatively connected between the engine block and the wobble plate assembly, the displacement actuator selectively moving the wobble plate assembly along the power shaft so as to longitudinally position the pivot axis of at a user-selectable distance d from a theoretical zero displacement point on the longitudinal axis. The engine of this embodiment further comprises a piston control linkage operatively connected to the wobble plate assembly, the piston control linkage setting the wobble plate inclination angle θ as the distance d changes such that d=W sin(θ), where W is a constant. Operation of the displacement actuator to selectively change the pivot axis-to-zero point distance d within a range between a maximum distance dmax and a minimum distance dmin, where the ratio of dmax/dmin=N, correspondingly changes the piston displacement DP of the engine within a range between a maximum displacement DPmax and a minimum displacement DPmin having a ratio DPmax/DPmin=N, while the piston control linkage maintains the compression ratio of the engine at a substantially constant value as the displacement changes within the range between DPmax and DPmin. 
     In another embodiment, an engine comprises an engine block supporting a plurality of cylinders spaced apart around a rotatably mounted central power shaft having a longitudinal axis, each respective cylinder having a respective bore defining a bore axis aligned substantially parallel to the longitudinal axis and having a respective piston slidably disposed therein, each respective piston having connected thereto an upper end of a respective connecting rod also having a lower end. The engine of this embodiment further comprises a wobble plate assembly mounted on the power shaft, the wobble plate assembly including a first ring portion, a second ring portion and a ring bearing assembly. The first ring portion is operatively mounted on the power shaft such that the first ring portion rotates with the power shaft and pivots about a pivot axis intersecting the longitudinal axis of the power shaft in a perpendicular orientation and rotating with the power shaft. The second ring portion is concentrically disposed adjacent the first ring portion and has mounted thereon a plurality of connecting rod bearings corresponding in number to the number of the cylinders, each respective connecting rod bearing being connected to the lower end of a respective connecting rod, the second ring portion being operatively connected to the engine block so as to prevent the second ring portion from rotating relative to the engine block. The ring bearing assembly is connected between the first ring portion and the second ring portion so as to allow the first ring portion to rotate about the common center relative to the second ring portion while constraining the second ring portion to remain parallel to the first ring portion. Reciprocation of the pistons within the cylinder bores results in rotation of the power shaft. The wobble plate assembly, when viewed in a direction parallel to the pivot axis, defines a wobble plate inclination plane and a wobble plate inclination angle, the wobble plate inclination plane being seen as a line passing through the center of the pivot axis and the center of the connecting rod bearings, when viewed in a direction parallel to the pivot axis, the wobble plate inclination angle being the angle of intersection between the wobble plate inclination plane and a line perpendicular to the longitudinal axis of the power shaft, when viewed parallel to the pivot axis. The engine of this embodiment further comprises a displacement actuator operatively connected between the engine block and pivot axis, the displacement actuator selectively moving the wobble plate assembly along the power shaft so as to longitudinally position the pivot axis within a range of positions along the longitudinal axis. The engine of this embodiment further comprises a piston control linkage operatively connected to the wobble plate assembly, the piston control linkage setting the wobble plate inclination angle as the longitudinal position of the pivot axis changes to maintain a constant compression ratio. Operation of the displacement actuator to selectively change the longitudinal position of the pivot axis within a range between a first position and a second position correspondingly changes the piston displacement of the engine within a range between a maximum displacement and a minimum displacement. 
     In another aspect, a variable-displacement engine comprises an engine block, power shaft and rotating cylinder block. Pistons and connecting rods mounted in the cylinder block connect to a wobble plate having a rotating ring portion and non-rotating ring portion connected to allow relative rotation therebetween while constraining the portions to remain parallel. The wobble plate defines an inclination plane, pivot axis and wobble plate angle θ. A piston control mechanism includes axial lift, control lever supported by the lift and by an axially fixed anchor bearing, and links connecting the control lever to the wobble plate. Axial movement of the lift changes the axial position of the control lever pivot and changes the control lever angle, in turn changing, via the connecting links, the wobble plate angle θ and the axial position of the wobble plate pivot axis. This changes the piston displacement of the engine while maintaining substantially constant compression ratio. 
     In yet another aspect, a variable-displacement engine comprises an engine block and an elongated power shaft rotatably supported by the engine block, the power shaft having a longitudinal axis defining an axial direction and being fixed axially relative to the engine block. A rotating cylinder block defines at least one cylinder, each cylinder having a bore defining a bore axis aligned substantially parallel to the power shaft axis, with the cylinder block being fixedly mounted to the power shaft such that when the power shaft rotates, the cylinder block rotates around the power shaft axis and each bore axis revolves around the power shaft axis. One or more pistons are provided corresponding in number to the number of the cylinders, each respective piston being slidably disposed within the bore of a respective cylinder. One or more connecting rods are provided corresponding in number to the number of cylinders, each respective connecting rod having an upper end connected to a respective piston and a lower end connected to a respective connecting rod bearing. A wobble plate assembly is provided having a generally annular configuration defining a central opening through which the power shaft passes, the wobble plate assembly including a rotating first ring portion, the first ring portion including one or more bearing mounting arms formed thereon, corresponding in number to the number of the connecting rods, each bearing mounting arm having a respective connecting rod bearing mounted thereon, and a non-rotating second ring portion, the second ring portion being rotatably slidably connected to the first ring portion so as to allow the first ring portion to rotate relative to the second ring portion about a common ring center line while constraining the second ring portion to remain parallel to the first ring portion. A rotation-locking assembly is provided connected between the first ring portion and the power shaft to rotationally lock the first ring portion to the power shaft while allowing the first ring portion to vary an angle of inclination with respect to the power shaft axis. The wobble plate assembly defines a wobble plate inclination plane being a plane passing through the centers of the connecting rod bearings, a wobble plate pivot axis being a line lying in the wobble plate inclination plane and intersecting the longitudinal axis of the power shaft in a perpendicular orientation and rotating with the power shaft, and a wobble plate angle θ being an angle of intersection between the wobble plate inclination plane and a plane normal to the power shaft axis when viewed in a direction parallel to the pivot axis. A piston control mechanism is provided, including a lift mechanism slidably mounted on the engine block for axial movement along the power shaft axis, a control lever supported at a first location by pivot bearings mounted to the lift mechanism along a normal line passing through the power shaft axis parallel to the wobble plate pivot axis and supported at a second location by an anchor bearing disposed at an axially fixed position, thereby defining a control lever centerline passing through the centers of the pivot bearing and the anchor bearing and an control lever angle being an angle between the control lever centerline and a plane normal to the power shaft axis when viewed in a direction parallel to the pivot axis, and two or more spaced-apart connecting links, each connecting link having a first end connected to the second ring portion of the wobble plate and a second end connected to the control lever. Operation of the lift mechanism to selectively change the axial position of the control lever pivot bearings selectively changes the control lever angle, which in turn selectively changes, via the connecting links, the wobble plate angle θ and the axial distance d between the wobble plate pivot axis and a theoretical zero angle point, which in turn selectively changes the piston displacement of the engine while maintaining the compression ratio of the engine at a substantially constant value. 
     In one embodiment, the rotation-locking assembly is a constant velocity joint including an inner joint portion connected to the power shaft and having a plurality of radially outward facing races formed thereon, an outer joint portion connected to first ring portion of the wobble plate and having a plurality of radially inward facing races formed thereon, each race of the outer joint portion facing a corresponding race on the inner joint portion, and a plurality of race balls, each race ball captured between the corresponding inward facing and outward facing races of the respective joint portions. 
     In another embodiment, the anchor bearing supporting the control lever at the second location is mounted in a slider block and the slider block is slidingly mounted to the engine block to move in a radial direction along a normal line extending from the power shaft axis but is constrained against movement in the axial direction and constrained against movement in a circumferential direction around the power shaft axis. 
     In still another embodiment, the anchor bearing supporting the control lever at the second location is mounted to the engine block at a fixed axial location, at a fixed radial distance from the power shaft axis and at a fixed circumferential location and the outer end of the control lever includes a slot slidingly engaged over the anchor bearing to allow sliding movement of the outer end of the control lever along the anchor support bearing. 
     In a further embodiment, the wobble plate assembly, connecting links and control lever are configured to maintain the wobble plate inclination plane parallel to the centerline of the control lever such that the wobble plate angle θ is equal to the angle of intersection between the control lever centerline and a plane normal to the power shaft axis. 
     In yet another embodiment, the wobble plate assembly, connecting links and control lever are configured such that the wobble plate inclination plane is not parallel to the centerline of the control lever, but changing the angle of intersection between the control lever centerline and a plane normal to the power shaft axis changes the wobble plate angle θ. 
     In still another embodiment, the piston control mechanism is operatively connected to the wobble plate assembly to set the wobble plate inclination angle θ as the axial distance d between the position of the wobble plate pivot axis and a theoretical zero angle point changes so as to maintain a linear relationship between d and sin(θ) such that d=K·sin(θ), where K is a constant. 
     In another aspect, a variable-displacement engine comprises an engine block and an elongated power shaft rotatably supported by the engine block, the power shaft having a longitudinal axis defining an axial direction and being fixed axially relative to the engine block. A rotating cylinder block is provided defining at least one cylinder, each cylinder having a bore defining a bore axis aligned substantially parallel to the power shaft axis, the cylinder block being fixedly mounted to the power shaft such that when the power shaft rotates, the cylinder block rotates around the power shaft axis and each bore axis revolves around the power shaft axis. One or more pistons are provided corresponding in number to the number of the cylinders, each respective piston being slidably disposed within the bore of a respective cylinder. One or more connecting rods are provided corresponding in number to the number of cylinders, each respective connecting rod having an upper end connected to a respective piston and a lower end connected to a respective connecting rod bearing. A wobble plate assembly is provided having a generally annular configuration defining a central opening through which the power shaft passes. The wobble plate assembly includes a rotating first ring portion, the first ring portion including one or more bearing mounting arms formed thereon, corresponding in number to the number of the connecting rods, each bearing mounting arm having a respective connecting rod bearing mounted thereon. A non-rotating second ring portion is rotatably slidably connected to the first ring portion so as to allow the first ring portion to rotate relative to the second ring portion about a common ring center line while constraining the second ring portion to remain parallel to the first ring portion. A rotation-locking assembly is connected between the first ring portion and the power shaft to rotationally lock the first ring portion to the power shaft while allowing the first ring portion to vary an angle of inclination with respect to the power shaft axis. The wobble plate assembly defines a wobble plate inclination plane being a plane passing through the centers of the connecting rod bearings, a wobble plate pivot axis being a line lying in the wobble plate inclination plane and intersecting the longitudinal axis of the power shaft in a perpendicular orientation and rotating with the power shaft, and a wobble plate angle θ being an angle of intersection between the wobble plate inclination plane and a plane normal to the power shaft axis when viewed in a direction parallel to the pivot axis. A piston control mechanism is provided including a lift mechanism mounted on the engine block and operatively connected to a first location on the non-rotating second ring portion to selectively move the first location on the second ring portion in an axial direction, and an axial anchor arm extending from a second location on the non-rotating second ring portion to an outer end connected to a bearing anchor point mounted on the engine block at an axially fixed position. Operation of the lift mechanism to selectively change the axial position of the first location of the second ring portion selectively changes the wobble plate angle θ and the axial distance d between the wobble plate pivot axis and a theoretical zero angle point, which in turn selectively changes the piston displacement of the engine while maintaining the compression ratio of the engine at a substantially constant value. 
     In one embodiment, the rotation-locking assembly is a constant velocity joint including an inner joint portion connected to the power shaft and having a plurality of radially outward facing races formed thereon, an outer joint portion connected to first ring portion of the wobble plate and having a plurality of radially inward facing races formed thereon, each race of the outer joint portion facing a corresponding race on the inner joint portion, and a plurality of race balls, each race ball captured between the corresponding inward facing and outward facing races of the respective joint portions. 
     In another embodiment, the bearing anchor point supporting the outer end of the axial anchor arm is mounted in a slider block and the slider block is slidingly mounted to the engine block to move in a radial direction along a normal line extending from the power shaft axis but is constrained against movement in the axial direction and constrained against movement in a circumferential direction around the power shaft axis. 
     In yet another embodiment, the bearing anchor point is mounted to the engine block at a fixed axial location, at a fixed radial distance from the power shaft axis and at a fixed circumferential location, and the outer end of the axial anchor arm includes a slot slidingly engaged over the bearing anchor point to allow sliding movement of the outer end of the axial anchor arm along the bearing anchor point. 
     In another aspect, a variable-displacement engine is provided comprising an engine block and an elongated power shaft rotatably supported by the engine block, the power shaft having a longitudinal axis defining an axial direction and being fixed axially relative to the engine block. A cylinder block is fixedly mounted to the engine block, the cylinder block defining at least one cylinder, each cylinder having a bore defining a bore axis aligned substantially parallel to the power shaft axis. One or more pistons are provided corresponding in number to the number of the cylinders, each respective piston being slidably disposed within the bore of a respective cylinder. One or more connecting rods are provided corresponding in number to the number of cylinders, each respective connecting rod having an upper end connected to a respective piston and a lower end connected to a respective connecting rod bearing. A wobble plate assembly has a generally annular configuration defining a central opening through which the power shaft passes, the wobble plate assembly including a non-rotating first ring portion, the first ring portion including one or more bearing mounting arms formed thereon, corresponding in number to the number of the connecting rods, each bearing mounting arm having a respective connecting rod bearing mounted thereon. A rotating second ring portion is provided, the second ring portion being rotatably slidably connected to the first ring portion so as to allow the second ring portion to rotate relative to the first ring portion about a common ring center line while constraining the second ring portion to remain parallel to the first ring portion. A rotation-locking assembly is connected between the first ring portion and the engine block to rotationally lock the first ring portion to the engine block while allowing the first ring portion to vary an angle of inclination with respect to the power shaft axis. The wobble plate assembly defines a wobble plate inclination plane being a plane passing through the centers of the connecting rod bearings, a wobble plate pivot axis being a line lying in the wobble plate inclination plane and intersecting the longitudinal axis of the power shaft in a perpendicular orientation and rotating with the power shaft, and a wobble plate angle θ being an angle of intersection between the wobble plate inclination plane and a plane normal to the power shaft axis when viewed in a direction parallel to the pivot axis. A piston control mechanism is provided including an anchor support member attached to the power shaft to rotate with the power shaft and extending radially outward from the power shaft to an outer end. A lift mechanism is slidably mounted on the power shaft for axial movement along the power shaft axis. A lever beam is supported at a first location by pivot bearings mounted to the lift mechanism along a normal line passing through the power shaft axis parallel to the wobble plate pivot axis and is supported at a second location by an axial anchor bearing carried by the anchor support member, thereby defining a lever beam centerline passing through the centers of the pivot bearing and the axial anchor bearing and an lever beam angle being an angle between the lever beam centerline and a plane normal to the power shaft axis when viewed in a direction parallel to the pivot axis. Two or more spaced-apart connecting links are provided, each connecting link having a first end connected to the second ring portion of the wobble plate and a second end connected to the lever beam. Operation of the lift mechanism to selectively change the axial position of the lever beam pivot bearings selectively changes the lever beam angle, which in turn selectively changes, via the connecting links, the wobble plate angle θ and the axial distance d between the wobble plate pivot axis and a theoretical zero angle point, which in turn selectively changes the piston displacement of the engine while maintaining the compression ratio of the engine at a substantially constant value. 
     In one embodiment, the rotation-locking assembly is connected to the engine block by a tubular support extending into the center of the wobble plate assembly. 
     In another embodiment, the rotation-locking assembly is a constant velocity joint including an inner joint portion connected to the tubular support and having a plurality of radially outward facing races formed thereon, an outer joint portion connected to first ring portion of the wobble plate and having a plurality of radially inward facing races formed thereon, each race of the outer joint portion facing a corresponding race on the inner joint portion, and a plurality of race balls, each race ball captured between the corresponding inward facing and outward facing races of the respective joint portions. 
     In yet another embodiment, the rotation-locking assembly is a constant velocity joint including an inner joint portion connected to the first ring portion of the wobble plate and having a plurality of radially outward facing races formed thereon, an outer joint portion connected to engine block surrounding the first ring portion and having a plurality of radially inward facing races formed thereon, each race of the outer joint portion facing a corresponding race on the inner joint portion, and a plurality of race balls, each race ball captured between the corresponding inward facing and outward facing races of the respective joint portions. 
     In a further embodiment, the outer end of the anchor support member forms a radially-oriented passageway, a block is slidingly mounted in the passageway, and the axial anchor bearing is mounted in the slider block to be movable in a radial direction along a normal line extending from the power shaft axis but constrained against movement in the axial direction and constrained to move in a circumferential direction around the power shaft axis with the anchor support member. 
     In another embodiment, the axial anchor bearing is fixedly mounted in the outer end of the anchor support member, and the outer end of the lever beam includes a slot slidingly engaged over the axial anchor bearing to allow sliding movement of the outer end of the lever beam along the anchor support bearing while being constrained to move in a circumferential direction around the power shaft axis with the anchor support member. 
     In yet another embodiment, the wobble plate assembly, connecting links and lever beam are configured to maintain the wobble plate inclination plane parallel to the centerline of the lever beam such that the wobble plate angle θ is equal to the angle of intersection between the lever beam centerline and a plane normal to the power shaft axis. 
     In still another embodiment, the wobble plate assembly, connecting links and lever beam are configured such that the wobble plate inclination plane is not parallel to the centerline of the lever beam, but changing the angle of intersection between the lever beam centerline and a plane normal to the power shaft axis changes the wobble plate angle θ. 
     In a further embodiment, the piston control mechanism is operatively connected to the wobble plate assembly to set the wobble plate inclination angle θ as the axial distance d between the position of the wobble plate pivot axis and a theoretical zero angle point changes so as to maintain a linear relationship between d and sin(θ) such that d=K·sin(θ), where K is a constant. 
     In a further aspect, a variable-displacement engine comprises an engine block, an elongated power shaft rotatably supported by the engine block, the power shaft having a longitudinal power shaft axis defining an axial direction and being fixed axially relative to the engine block. A cylinder block is fixedly mounted to the engine block, the cylinder block defining at least one cylinder, each cylinder having a bore defining a bore axis aligned substantially parallel to the power shaft axis. One or more pistons are provided corresponding in number to the number of the cylinders, each respective piston being slidably disposed within the bore of a respective cylinder. One or more connecting rods are provided corresponding in number to the number of cylinders, each respective connecting rod having an upper end connected to a respective piston and a lower end connected to a respective connecting rod bearing. A wobble plate assembly has a generally annular configuration defining a central opening through which the power shaft passes, the wobble plate assembly including a non-rotating first ring portion, the first ring portion including one or more bearing mounting arms formed thereon, corresponding in number to the number of the connecting rods, each bearing mounting arm having the respective connecting rod bearing mounted thereon, and a rotating second ring portion, the second ring portion being rotatably slidably connected to the first ring portion so as to allow the second ring portion to rotate relative to the first ring portion about a common ring center line while constraining the second ring portion to remain parallel to the first ring portion. A rotation-locking assembly is connected between the first ring portion and the engine block to rotationally lock the first ring portion to the engine block while allowing the first ring portion to vary an angle of inclination with respect to the power shaft axis. The wobble plate assembly defines a wobble plate inclination plane being a plane passing through the centers of the connecting rod bearings, a wobble plate pivot axis being a line lying in the wobble plate inclination plane and intersecting the longitudinal power shaft axis in a perpendicular orientation and rotating with the power shaft, and a wobble plate angle θ being an angle of intersection between the wobble plate inclination plane and a plane normal to the power shaft axis when viewed in a direction parallel to the pivot axis. A piston control mechanism includes an anchor support member attached to the power shaft to rotate with the power shaft and extending radially outward from the power shaft to an outer end, the outer end of the anchor support member forming a radially-oriented passageway wherein at least a portion of the passageway is non-perpendicular with respect to the power shaft axis. A slider block is slidingly mounted in the passageway and constrained to move along a path defined by the passageway. A lift mechanism is slidably mounted on the power shaft for axial movement along the power shaft axis. A lever beam is supported at a first location by pivot bearings mounted to the lift mechanism along a normal line passing through the power shaft axis parallel to the wobble plate pivot axis and is supported at a second location by an anchor bearing carried by the anchor support member, thereby defining a lever beam centerline passing through the centers of the pivot bearing and the anchor bearing and an lever beam angle being an angle between the lever beam centerline and a plane normal to the power shaft axis when viewed in a direction parallel to the pivot axis. One or more connecting links are provided, each connecting link having a first end connected to the second ring portion of the wobble plate and a second end connected to the lever beam. The anchor bearing is mounted in the slider block to be movable in a radial direction along the path defined by the passageway extending from the power shaft axis, the path having components in both the radial and axial directions and constrained to move in a circumferential direction around the power shaft axis with the anchor support member. Operation of the lift mechanism to selectively change the axial position of the lever beam pivot bearings selectively changes the lever beam angle, which in turn selectively changes, via the connecting links, the wobble plate angle θ and an axial distance d between the wobble plate pivot axis and a theoretical zero angle point, which in turn selectively changes the piston displacement of the engine while maintaining the compression ratio of the engine at a substantially constant value. 
     In one embodiment, the radially-oriented passageway of the anchor support member is oriented at a non-perpendicular angle β with respect to the power shaft axis such that the path of movement of the anchor bearing as the axial position of the lever beam pivot bearing changes is along a straight line intersecting the power shaft axis at the non-perpendicular angle β. 
     In another embodiment, the radially-oriented passageway of the anchor support member is curved such that the path of movement of the anchor bearing as the axial position of the lever beam pivot bearing changes is along a curved line. 
     In yet another embodiment, the radially-oriented passageway of the anchor support member is curved such that the path of movement of the anchor bearing as the axial position of the lever beam pivot bearing changes is along a circular path having a radius θ about a control point disposed adjacent to the power shaft axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a simplified cross-sectional top view of an engine according to one embodiment taken along line  1 - 1  of  FIG. 2 ; 
         FIG. 2  is a cross-sectional side view of the engine of  FIG. 1  taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a cross-sectional side view of the engine block portion of the engine of  FIG. 2 ; 
         FIG. 4  is a cross-sectional side view of the cylinder head portion of the engine of  FIG. 2 ; 
         FIG. 5  is a schematic side view of an engine in accordance with another aspect illustrating the geometry of the wobble plate assembly at different values of displacement; 
         FIG. 6 - a  is a schematic side view of an engine in accordance with another aspect illustrating the geometry of the engine reference plane; 
         FIG. 6 - b  is a schematic view of gear tooth profiles illustrating one embodiment of the anti-rotation assembly; 
         FIG. 7  is a cross-sectional side view of an engine block portion of an engine according to another embodiment (“first variation”) illustrating aspects of a hydraulic displacement actuator; 
         FIG. 8  is a cross-sectional side view of a cylinder head portion of an engine according to another embodiment (“second variation”) illustrating aspects of hydraulic valve actuators; 
         FIG. 9  is a cross-sectional side view of an engine block portion of an engine according to another embodiment (“fourth variation”) illustrating aspects of an alternative connecting rod configuration; 
         FIG. 10  is a cross-sectional side view, taken along line  10 - 10  of  FIG. 11 , of an engine block portion of an engine according to another embodiment (“fifth variation”) illustrating aspects of a universal joint anti-rotation mechanism; 
         FIG. 11  is a partial top view of the engine of  FIG. 10 , further illustrating aspects of the anti-rotation mechanism; 
         FIG. 12  is a partial cross-sectional side view of the engine of  FIG. 10 , taken along line  12 - 12  of  FIG. 11 , still further illustrating aspects of the anti-rotation mechanism; 
         FIG. 13  is a cross-sectional side view of an engine block portion of an engine according to another embodiment (“seventh variation”) illustrating aspects of an alternative piston control linkage; 
         FIG. 14A  is a partial cross-sectional side view of an engine block portion of a variable-displacement engine according to another embodiment (“eighth variation”) illustrating aspects of an alternative engine and piston control mechanism; 
         FIG. 14B  is a partial view, similar to  FIG. 14A , of a variable-displacement engine having an alternative piston control mechanism according to another embodiment; 
         FIG. 15  is an enlarged perspective view, with portions broken away, of the wobble plate mechanism of  FIG. 14A ; 
         FIG. 16  is a partial cross-sectional side view of an engine block portion of another variable-displacement engine according to another embodiment (“ninth variation”) illustrating aspects of another alternative engine and piston control mechanism; 
         FIG. 17  is a partial cross-sectional side view of an engine block portion of still another variable-displacement engine according to another embodiment (“tenth variation”) illustrating aspects of another alternative engine and piston control mechanism; 
         FIG. 18  is an enlarged partial cross-sectional side view of a piston-control mechanism using a shoe and slot mechanism similar to that shown in  FIG. 14A , wherein the beam anchor bearing is carried in a slider block moving in a slot defined by the shoe along a path perpendicular to the centerline of the power shaft; 
         FIG. 19  is a partial schematic side view of another variable-displacement engine similar to the engine of  FIG. 14A , but having a different cylinder-to-wobble plate geometric configuration exemplified by the scaled connection of the upper ring portion of the wobble plate to a representative piston (depicted at top-dead-center) and connecting rod positioned within the associated cylinder; 
         FIG. 20  is a graph showing variations in engine compression ratio as a function of wobble plate angle (and thus also engine displacement) for three different configurations of variable-displacement engine having the cylinder-to-wobble plate geometry shown in  FIG. 19 , namely, Case 1 being an engine having the perpendicular straight-line piston-control mechanism of  FIG. 18 , Case 2 being an engine having an inclined straight-line piston-control mechanism as illustrated in  FIG. 21  and Case 3 being an engine having the curved-line piston-control mechanism as illustrated in  FIG. 22 ; 
         FIG. 21  is an enlarged partial cross-sectional side view of another piston-control mechanism using a shoe and slot mechanism wherein the anchor bearing travels along a straight-line path that is non-perpendicular to the centerline of the power shaft; 
         FIG. 22  is an enlarged partial cross-sectional side view of another piston-control mechanism using a shoe and slot mechanism wherein the anchor bearing travels along a curved-line path having a center of curvature disposed axially between the piston and the anchor bearing; 
         FIG. 23  is an enlarged partial cross-sectional side view of another piston-control mechanism using a shoe and slot mechanism wherein the anchor bearing travels along a curved-line path and wherein the anchor bearing is disposed axially between the piston and the center of curvature of the curved-line path; and 
         FIG. 24  is a graph showing variations in engine compression ratio as a function of wobble plate angle (and thus also engine displacement) for a variable-displacement engine having the cylinder-to-wobble plate geometry shown in  FIG. 19  and having the curved-path piston control mechanism of  FIG. 23 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, wherein like reference numbers are used herein to designate like elements throughout, the various views and embodiments of continuously variable displacement engine are illustrated and described, and other possible embodiments are described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated and/or simplified in places for illustrative purposes only. One of ordinary skill in the art will appreciate the many possible applications and variations based on the following examples of possible embodiments. 
     Description of a First Exemplary Embodiment 
     Referring to  FIGS. 1-4 , there is illustrated a variable displacement engine  100  in accordance with a first exemplary embodiment of the invention.  FIG. 1  provides a simplified cross-sectional top view of the engine  100 ,  FIG. 2  provides an overall cross-sectional side view of the engine  100 ,  FIG. 3  provides a cross-sectional side view of the engine block assembly  102  including the cylinders, power shaft and piston control mechanism and  FIG. 4  shows the cylinder head assembly  104  and its internal components. 
     Referring now specifically to  FIG. 1 , engine  100  comprises an engine block  106 , a power shaft  108  rotatably supported by the engine block and at least one cylinder  110  supported by the engine block. The elongated power shaft  108  defines a longitudinal axis  112  running through both the power shaft and the engine block  106 . Each cylinder  110  has a bore  114  defining a bore axis  116  aligned substantially parallel to the longitudinal axis  112  of the power shaft  108 . The engine  100  illustrated in  FIG. 1  has five cylinders  110  evenly spaced around the central shaft  108 ; however, other embodiments of the engine may have different numbers of cylinders (including a single cylinder) and/or have the cylinders spaced differently around the power shaft. 
     Referring now also to  FIG. 2 , the illustrated engine  100  is configured with the cylinder head assembly  104  mounted on top of the engine block assembly  102 . In the illustrated embodiment, the power shaft  108  extends from the engine block assembly  102  into the cylinder head assembly  104 ; however, in other embodiments of the engine the power shaft may be differently arranged. A piston  118  is slidably disposed within the bore  114  of each respective cylinder  110 . 
     Referring now to  FIG. 3 , the engine block assembly  102  is illustrated in more detail. The engine block  106  (also called the “cylinder block”) is the major support structure for the internal components and may include coolant passages  120  for the cylinders  110 . An outer wall  122  of the cylinder block  106  may have a cylindrical configuration for structural efficiency. The power shaft  108  may be mounted in the cylinder block  106  by bearings  124  and  126 . The pistons  118  are attached to a non-rotating portion of a ring-like wobble plate assembly  128  by connecting rods  130 . In  FIG. 3 , three of the connecting rods  130  are visible. Spherical connecting rod bearings  132  and  134  are provided at the respective upper and lower ends of each connecting rod  130  to permit the necessary freedom of relative motion for the connected components. In  FIG. 3 , one piston (denoted  118 ′) is illustrated at the bottom of its stroke, and another piston (denoted  118 ″, shown partially in hidden line) is illustrated near the top of the stroke. 
     The wobble plate assembly  128  has a generally annular (i.e., ring-like) configuration defining a central opening  136 . In the illustrated embodiment, the power shaft  108  passes through the central opening  136 . The wobble plate assembly  128  includes a central support member  138 , a first ring portion  140 , a second ring portion  142  and a ring bearing assembly  144 . The central support member  138  is longitudinally slidably mounted on the power shaft  108 , but rotates around the longitudinal axis  112  with the power shaft. The central support member  138  defines a pivot axis  146  for the wobble plate assembly  128 . The pivot axis  146  intersects the longitudinal axis  112  in a perpendicular orientation and also rotates with the power shaft  108 . The first ring portion  140  is pivotally mounted on the central support member  138  such that the first ring portion  140  pivots (as denoted by arrow  148 ) about the pivot axis  146 ; however, the first ring portion also rotates around the longitudinal axis  112  with the central support member  138  and the power shaft  108 . The second ring portion  142  is concentrically disposed adjacent the first ring portion  140 . Mounted on the second ring portion  142  are the lower connecting rod bearings  134 . As will be further described herein, the second ring portion  142  does not rotate around the longitudinal axis  112  with the power shaft  108 . The ring bearing assembly  144  is connected between the first ring portion  140  and the second ring portion  142  so as to allow the first ring portion to rotate about the common center relative to the second ring portion while constraining the second ring portion to remain parallel with the first ring portion. 
     Referring still to  FIG. 3 , the wobble plate assembly  128 , when viewed in a direction parallel to the pivot axis  146 , defines a wobble plate inclination plane (denoted by reference number  150 ) and a wobble plate inclination angle θ. When viewed in a direction parallel to the pivot axis  146 , the wobble plate inclination plane  150  is seen as a line passing through the center of the pivot axis  146  and the center(s) of the lower connecting rod bearings  134 ; however, that line corresponds to the edge of the wobble plate plane  150  collectively defined by the centers of the lower connecting rod bearings  134 . The wobble plate inclination angle θ is the angle of intersection between the wobble plate inclination plane  150  and a plane (denoted by reference number  152 ) perpendicular to the longitudinal axis  112  of the power shaft  108 , when viewed parallel to the pivot axis. As will be further described herein, the wobble plate inclination angle θ determines the engine displacement (also called “piston displacement”) of the engine  100  for each full rotation of the power shaft  108 . 
     As previously described, the second ring portion  142  of the wobble plate assembly  128  does not rotate with the power shaft  108 . Rotation of the second ring portion  142  is prevented by an anti-rotation assembly  154  having a first anti-rotation portion  156  operatively connected to the second ring portion and a second anti-rotation portion  158  operatively connected to the engine block  106 . In the embodiment of  FIG. 3 , the first anti-rotation portion  156  includes a first plurality of teeth  160  disposed on the outer rim  162  of the second ring portion  142 , and the second anti-rotation portion  158  includes a second plurality of teeth  164  disposed on a stationary ring gear  166  fixedly mounted on the engine block  106 . In the illustrated embodiment, the engagement of the teeth  160  and  164  occurs substantially where the wobble plate inclination plane  150  intersects a control plane (denoted by reference number  168 ), the control plane  168  being a plane oriented perpendicular to the longitudinal axis  112  positioned at the theoretical zero displacement point (denoted by reference number  170 ). Determination of the position of the theoretical zero displacement point  170  is further described herein, e.g., in relation to  FIG. 5 . That the intersection of teeth  160  and  164  may occur in the control plane  168  and at the same distance from the center of the second ring portion  142  is further described below. As the power shaft  108  rotates, the highest part the second ring portion  142  remains continuously engaged with the ring gear  166  and prevents the second ring portion from rotating relative to the engine block  106 . It will be appreciated that the teeth  160  and  164  may have non-standard profile(s) so as to accommodate differences in the pitch of the teeth of outer rim  162  and gear  166 . The tooth profiles may also need to accommodate the change in angle and radial location of the outer rim  162  as the wobble plate inclination angle θ changes to vary piston displacement. An example of gear tooth configurations to accommodate the difference in tooth pitches is described in connection with  FIG. 6 - b.    
     Referring still to  FIG. 3 , the non-rotating second ring portion  142  of the wobble plate assembly  128  is attached by the ring bearing assembly  144  to the first ring portion  140 , which rotates with the power shaft  108  as previously described. The first ring portion  140  is pivotally attached to the central support member  138  defining the pivot axis  146 . In the illustrated embodiment, the central support member  138  includes a support collar  171  and two pivot bearings  172 , one disposed on each side of the support collar along the pivot axis  146 . The support collar  171  is permitted to slide axially (i.e., longitudinally) along the power shaft  108 . A short arm  174  mounted on the first ring portion  140  extends to a control bearing  176 , which in turn connects the first ring portion to one end of a control link  178 . The other end of the control link  178  is attached to an upper collar  180  by two upper bearings  182 , one on each side of the upper collar. In the illustrated embodiment, the upper bearings  182  are disposed on the longitudinal axis  112  at the theoretical zero displacement point  170 . Upper collar  180  is attached firmly to the power shaft  108  to prevent movement axially and relative rotation about the power shaft. The control link  178  assures that the first ring portion  140  rotates with the drive shaft  108 . 
     The control link  178  between bearings  182  and  176  together with the first ring portion  140  between bearings  176  and  172  forms a three point linkage comprising a piston control linkage  184  for the illustrated embodiment. The piston control linkage  184  changes the wobble plate inclination angle θ as the pivot axis  146  moves along the longitudinally axis  112  so as to maintain a constant compression ratio independent of engine displacement. The specific dimensions and/or positions of the elements making up the piston control linkage  184  may be determined by considering the minimum desired combustion chamber volume (i.e., with the pistons  118  at maximum upward travel), piston diameter, maximum wobble plate inclination angle, and the distance from the longitudinal axis  112  (i.e., center of power shaft  108 ) to the lower connecting rod bearings  134 . An example of this determination is described in connection with  FIG. 5 . 
     It will be appreciated that the configuration of the piston control linkage may be different in other embodiments. However, regardless of the configuration, the piston control linkage produces a constant compression ratio independent of engine displacement by maintaining a linear relationship between a distance d and sin(θ) as the pivot axis  146  moves, where d is the distance (measured along the longitudinal axis  112 ) between the location of the pivot axis  146  and the theoretical zero displacement point  170 , and θ is the wobble plate inclination angle. Put another way, the piston control linkage ensures that 0 and d change simultaneously such that d=W·sin(θ), where W is a constant. This relationship assures that the compression ratio is independent of engine displacement, as further illustrated and described in connection with  FIG. 5 . 
     Referring still to  FIG. 3 , the piston displacement of the engine  100  may be varied by moving the pivot axis  146  of the wobble plate assembly  128  axially along the power shaft  108  using a displacement actuator  186 . In the illustrated embodiment, the displacement actuator  186  is a screw jack device and the pivot axis  146  is carried by the support collar  171 ; however, the configuration of these elements may be different in other embodiments. The displacement actuator  186  surrounds the power shaft  108  and is mounted on a base  188  to a lower cover  189  of the engine block  106 . An inner member  190  of the actuator surrounds the power shaft  108  and has external threads. The bottom of the inner member  190  is restrained by a thrust ring  192  that is part of the base  188 . A lower flange  194  of the inner member  190  includes an external gear that is operatively engaged by a screw gear  196  to selective rotate the inner member in order to operate the screw jack and vary the engine displacement. The inner member  190  threadingly engages an internally threaded lift cylinder  198 . The lift cylinder  198  is restrained from rotating by tines or other restraining elements (not shown) that mate with an external housing  200 . The housing  200  is firmly attached to the base  188 , and the base of the housing also restrains the inner member  190  so that it does not lift off the base  188 . The lift cylinder  198  acts against a lift bearing  202 . An outer collar  204  retains the lift cylinder  198  to the lift bearing  202 . The lift bearing is also attached to support collar  171  by an internal collar  206 , which is attached to an extension of the support collar that passes through the inside of the lift bearing. The upper collar  180  and the lift cylinder  198  of the screw jack device  186  also serve as mechanical stops to limit the range of engine displacement. 
     Referring now to  FIG. 4 , the cylinder head assembly  104  of this embodiment is illustrated in more detail. The cylinder head assembly  104  includes a cylinder head  231  that attaches to the engine block assembly  102  (shown in  FIG. 2 ) and defines one or more head cavities  230  to enclose the area above each cylinder  110  of the engine block. For purposes of clarity, the valves and porting structure corresponding to only one cylinder  110  (e.g., for cylinder 1) are shown in  FIG. 4 . The hardware for the remaining cylinders  110  (e.g., for cylinders 2, 3, 4 and 5) is similar and spaced around the power shaft  108  in a similar manner to the cylinders shown in  FIG. 1 . The ignition device  232 , intake valve  233  and exhaust valve  234  are located in the top of the combustion chamber. 
     A cam support structure  235  is attached to the cylinder head  231  concentric to the power shaft  108 . In this embodiment, cam reduction gears  236 ,  237 , and  238  are provided to synchronize the rotation of a cam body  239  with the rotation of the power shaft  108  and reduce the rotation rate of the cam body to one-half the rotation rate of the power shaft as required for a 4-stroke engine. A first cam  240  depresses the exhaust valve  234  for the first cylinder through a push rod  241  and a rocker arm  242 . A second cam  244  depresses the intake valve  233  for the first cylinder through a rocker arm  245 . Corresponding intake and exhaust valves, cams and actuating linkages (not shown) are provided for the remaining cylinders, but are not illustrated in  FIG. 4  for purposes of clarity. 
     During engine operation a fuel/air mixture enters the cylinder head  231  through an intake port  247 . Exhaust gases are discharged through an exhaust port  248 . The top of the cylinder head assembly is enclosed by a valve cover  249 . 
     In the illustrated embodiment, the valve timing may be varied by rotating the position of the cam reduction gear  237  around the power shaft  108 . The cam reduction gear  237  is mounted on a support structure  250 . A bearing  251  permits the support structure  250  with the cam reduction gear  237  to rotate about the support structure  235  and the power shaft  108 . Rotation of the support structure  250  may be controlled by an external actuator  252 . 
     Design Process Example 
     As previously indicated, the details of a mechanism suitable to maintain a constant pressure ratio in an internal combustion engine having a variable displacement depend on several design parameters. An example is now provided to demonstrate the process of calculating the design details for a particular embodiment. This design process example is based on estimated parameters (not optimized) for a gasoline fueled engine with five cylinders and a compression ratio of 4.804 (i.e., pressure ratio of 9.00). The selected pistons and cylinders are 4.00 inches in diameter. The selected distance from the power shaft centerline to the piston/cylinder centerline is 4.00 inches. 
     The selected range of variable displacement of the example design is to allow the engine to operate within a range between a maximum displacement DPmax of 3.0 liters and a minimum displacement DPmin of 1.0 liter, i.e., the “size” of the engine at minimum displacement being ⅓ the size of the engine at the maximum displacement. For the engine operating at the DPmin displacement of 1.0 liter, each piston displacement is calculated to be 12.205 cubic inches, and the corresponding piston stroke is calculated to be 0.971 inches. The required combustion chamber volume at the top of the piston stroke is 3.208 cubic inches (with the top of the piston assumed to be in the same plane as the bottom of the cylinder head). 
     For the engine operating at the DPmax displacement of 3.0 liter, with a piston diameter unchanged at 4.00 inches, the required displacement of each piston is 36.615 cubic inches, and the corresponding stroke for each piston is calculated to be 2.914 inches. The required combustion chamber volume of each cylinder head with the piston at the top of the compression stroke is calculated to be 9.625 cubic inches. Since the combustion chamber volume of the head is only 3.208 cubic inches when the piston top is level with the bottom of the cylinder head (as assumed in the previous step), an additional combustion chamber volume of 6.417 cubic inches must be provided by lowering the top of the piston stroke to 0.511 inches below the cylinder head. 
     Referring now to  FIG. 5 , a schematic diagram is provided of the engine  100  of  FIGS. 1-4  depicting primarily the power shaft and wobble plate assembly.  FIG. 5  shows how the displacement/compression ratio control mechanism (also called the piston control mechanism) described in connection with  FIGS. 1-3  achieves the required characteristics for the design process example. The reference numbers from  FIGS. 1-3  are used to refer to the corresponding features of  FIGS. 1-3 . 
     Point A in  FIG. 5  represents the location of the pivot axis  146  (i.e., the center of the pivot bearing  172 ) on the sliding collar  171  for the engine operating at the minimum piston displacement (DPmin) of 1.0 liter. This location, at the centerline of power shaft  108  (shown by line G-A-F), is selected so that there will be no interference between the parts of the piston control mechanism and the fixed parts of the cylinder block  106 . As previously described, the support collar  171  slides along the power shaft  108 , thereby moving the pivot bearing  172  to vary the engine displacement. At the (DPmin) 1.0 liter level of engine displacement, the stroke of each piston is 0.971 inches. The location of the center of connecting rod lower bearing  134  at the bottom of the piston stroke (i.e., when the section of the wobble plate directly under the rod bearing is lowest) is shown as point B, and the location of the same rod bearing at the top of the piston stroke (i.e., when the section of the wobble plate directly under the rod bearing is highest) is shown hypothetically as point C. The line through points B and C thus represents the wobble plate plane  150  passing through the centers of the connecting rod lower bearings  134  on the second ring portion in  FIG. 3  with the engine operating at 1.0 liter engine displacement. It will be appreciated that in actuality, point C for each cylinder occurs directly above point B after the power shaft/first ring portion of the piston control mechanism has rotated 180 degrees, but for purposes of explanation and illustration it is it represented at the opposite end of the wobble plate line. It was previously assumed that, when the piston is at the top of the stroke for the engine at the 1.0 liter engine displacement, the top of the piston is in the same plane as the bottom of the cylinder head and the combustion chamber volume is 3.208 cubic inches. Since point A is midway between points B and C, the distance between the center of pivot bearing  172  and rod bearing  134  (e. g. points A and B for the 1.0 liter operating level) is always 4.260 inches. Angle G-L-A, which is the angle of inclination θ of the wobble plate line  150  with respect to the plane  152  normal to the centerline of power shaft  108 , is calculated to be 6.55 degrees at 1.0 liter engine displacement. 
     Referring still to  FIG. 5 , the piston stroke for the engine operating at the (DPmax) 3.0 liter engine displacement level requires a piston stroke of 2.914 inches. For the engine to maintain a constant pressure ratio, the combustion chamber volume at the top of piston stroke is required to be 9.625 cubic inches. As explained earlier, a combustion chamber volume of 9.625 cubic inches requires that the top of the piston stroke be 0.511 inches below the top of the cylinder. Thus, the hypothetical location of rod bearing  134  at the top of the stroke for the 3.0 liter engine displacement is shown in  FIG. 5  as point D. Adding the required piston stroke length of 2.914 inches gives the rod bearing  134  location at the bottom of the stroke, which is shown as point E. The location of the pivot bearing  172  at the 3.0 liter operating level is shown as point F. The angle G-J-F, which is also the angle of inclination θ of the wobble plate line  150  with respect to the plane  152  normal to the centerline of power shaft  108  at the 3.0 liter engine displacement, is 20.00 degrees. 
     Accordingly, the distance between point A and point F is 1.482 inches, and this is the distance that support collar  171 /pivot axis  146  must travel for the engine displacement to go from 1.0 liter to 3.0 liters engine displacement while maintaining a constant compression ratio. A linear relationship between collar travel and engine displacement results in a hypothetical location of bearing pivot axis at point G, i.e., 2.223 inches above point F, that will produce zero displacement. This location is also known as the theoretical zero displacement point  170 . 
     A mechanism can now be defined that will maintain constant compression ratio as engine displacement is varied between DPmin of 1.0 liters and DPmax of 3.0 liters. Using the 3.0 liter operating level for analysis, a straight line passing through points D and E represents a plane in the non-rotating second ring portion  142  and the rotating first ring portion  140  in  FIG. 3 . A control link  178  is therefore constructed between the upper bearing  182  on the upper collar  180  and the control bearing  176  on the first ring portion  140 . The center of the upper bearing  182  is located at point G, and point H represents the center of the control bearing  176  of the control link  178 . The location of point H on the line between point D and point E is determined by drawing a line from point G to point H so that the angle H-F-G is the same magnitude as angle H-G-F. By similarity, the distance from point G to point H is the same as the distance from point F to point H, which is 3.250 inches. If the line between point E and point D is extended an additional distance of 3.250 inches from point H to point J, it can be shown by similarity that point J lies on a plane perpendicular to the centerline of power shaft  108  that passes through point G. 
     If the support collar  171  moves along the power shaft  108  so that the center of bearing  172  (i.e., the pivot axis  146 ) moves from point F to point A (engine at the 1.0 liter engine displacement), then the linkage similarity relationships still holds, thereby demonstrating that the engine maintains a constant compression ratio. It should also be noted that if the line between points B and C is extended from point K by the same distance as the distance between points A and K to point L, then point L lies on the same line perpendicular to the power shaft as points G and J. This relationship supports the design concept for gears  160  and  166  described in connection with  FIG. 3 , and further is the basis for an alternate piston control mechanism (Variation 7) described in connection with  FIG. 13 . 
     Referring now to  FIGS. 6 - a  and  6 - b , the tooth profiles to accommodate different tooth pitch in the anti-rotation assembly  154 , e.g., outer rim teeth  160  and the ring gear  166 , in  FIG. 3  are calculated using the previously defined engine design parameters that serve as a basis for design process example. An example of tooth profiles that will meet the requirement for different tooth pitches in parts  160  and  166  are derived in the following description. The derivation is illustrated in  FIGS. 6 - a  and  6 - b  for the engine operating at 3.0 liters piston displacement as shown in  FIG. 3 . 
     Referring first to  FIG. 6 - a , a first imaginary circular plane (denoted A) passing through the centers of the pivot bearing  172  and the control bearing  176  in  FIG. 3  is shown. A second circular plane (denoted B) is perpendicular to the power shaft axis  112  (denoted C) and passes through the center of upper bearing  182 . The point of intersection (denoted D) of these two planes A and B represents the reference plane for engagement of the teeth on parts  160  and  166  in  FIG. 3 . The distance from point D to the power shaft centerline C defines the radii of planes A and B. The point of intersection D traverses a complete circle normal to the power shaft axis  112  as the power shaft  108  rotates one turn. 
     Referring still to  FIG. 6 - a , the first circular plane A is inclined 20 degrees with respect to the second circular plane B. For the baseline 3.0 liter engine of this example, the radius of the first plane A is 6.50 inches and the radius of the second plane B is 6.0 inches. In order for the angle of rotation for the non-rotating second ring portion  142  to be zero, the point of intersection (for the planes A and B) traverses a circle at the same rotational speed as the power shaft  108 . The edge of the first plane A thus represents the line of contact for the gear teeth  160  on the rim  162  of the second ring portion  142  and the edge of plane B represents a line of contact for teeth  164  on the ring gear  166 . There must be the same number of teeth on the outer rim  162  and the ring gear  166 . For this example each “gear” has 60 teeth (one every 6 degrees) and a total height of 0.2 inches (contact line+/−0.1 inches.) The requirement for equal number of teeth means that the tooth pitch on the outer rim  162  and the ring gear  166  are not the same. Such operation is possible only if the differences in tooth pitch are small and the number of teeth engaged at any one time is also sufficiently small. The example given here is for the maximum difference in radii for the outer rim  162  and the ring gear  166 , which occurs at the maximum cylinder displacement as illustrated. 
     Referring now also to  FIG. 6 - b , compatible tooth profiles for the teeth on the outer rim  162  and the ring gear  166  were calculated by comparing the tooth locations near the contact point of planes A and B (of  FIG. 6 - a ). A tooth profile is assumed for one set of teeth. The tooth profile for the second set of teeth can then be calculated. The reference points for this calculation were the center of each tooth tip in the region of interaction between the teeth near the point of intersection D of the two planes A and B. The analysis was accomplished with the tip of the outer rim  162  tooth assumed to be circular with a radius of 0.1 inches (not optimized). The required profile for the teeth on ring gear  166  was calculated as a function of the distance from the point of intersection. The results in a plane normal to and adjacent to the edge of plane B are shown in  FIG. 6 - b . The sides of the teeth on ring gear  166  are defined by the motion of the circular tips of the non-rotating outer rim  162  teeth. The base of the teeth on outer rim  162  only have to be narrow enough to not interfere with the sides of the teeth on ring gear  166 . 
     As the power shaft turns and the contact point progresses to the right, more teeth are engaged to the right of the illustration and an equal number of teeth are disengaged in the left portion of the illustration. Since there are the same number of teeth on outer rim “gear”  162  and ring gear  166 , the point of contact rotates with the same angular rate as the power shaft even though the radii of the ring gear  166  and outer rim gear  162  are not the same. This relationship assures that the outer rim gear  162  (and thus, the second ring portion  142  of the wobble plate assembly) does not rotate. 
     Variations to the First Exemplary Embodiment 
     Although a first example embodiment of the apparatus, method and system of the present invention has been illustrated in the accompanied drawings and described in the foregoing detailed description, it is understood that other variations, numerous rearrangements, modifications and substitutions can be made without departing from the spirit and the scope of the invention as presented. 
     Additional embodiments are now presented, wherein variations to the first example embodiment are described 
     Variation One—Use of a Hydraulic Piston to Vary Displacement 
     Referring now to  FIG. 7 , there is illustrated an alternative variable displacement engine  700  similar in many respects to the engine  100  described in connection with  FIGS. 1-4 . Only the elements that differ substantially from those describe in  FIGS. 1-4  are renumbered. 
     Variable displacement engine  700  includes a displacement actuator comprising a hydraulic piston  761 , rather than the mechanical screw jack mechanism shown in  FIG. 3 . The piston  761  moves the support collar  171  and pivot bearing  172  in the axial direction along the modified power shaft  762  to increase or decrease the engine displacement. In the embodiment illustrated, the natural forces of pressure on the pistons  118  move the piston control mechanism down to increase displacement. To move the pistons upward and decrease displacement, high-pressure hydraulic fluid flows through the supply tube  763 , through a rotary seal  764 , through a passage in the power shaft  762  and into the upper cavity of the piston  765 . If the fluid supply valve closes so that hydraulic fluid flow is prevented, then the piston  761  remains stationary and the engine displacement is constant. The hydraulic fluid supplied to the piston  761  is regulated by a mechanical and/or electronic engine control. 
     The fluid enters the power shaft  762  at the bottom end so that the high pressure fluid seal will be as small as possible and the passage in the power shaft is reasonably short. Bevel gears  766  and  767  provide a means to transmit power from the power shaft  762  to a location outside of the engine. Bevel gear  767  is supported by drive shaft  768  and bearing  769 . The bearing  769  is supported by an extension of the lower block cover  770 . 
     Variation Two—Replacement of Cams with Hydraulically Driven Valve Actuators 
     Referring now to  FIG. 8 , there is illustrated an alternative variable displacement engine  800  similar in many respects to the engine  100  described in connection with  FIGS. 1-4 . Only the elements that differ substantially from those describe in  FIGS. 1-4  are renumbered. 
     Variable displacement engine  800  includes hydraulically driven actuators for operation of the intake valves  233  and the exhaust valves  234 . A hydraulic actuator  871  opens intake valve  233  for piston 1. A similar actuator is required for each of the remaining intake valves, but these are not shown for clarity. The actuator  871  is held in place by support structure  872 . A hydraulic actuator  873  opens the exhaust valve  234  for piston 1. Similar actuators operate the remainder of the exhaust valves. The actuators  873  are supported by extensions from a modified cylinder head  874 . The cylinder head  874  is the same as cylinder head  231  in  FIG. 4  except for addition of the supports for exhaust valve actuators  873  and deletion of supports for exhaust valve rockers  242  in  FIG. 3 . High pressure hydraulic fluid used to operate the hydraulic actuators is scheduled by a mechanical and/or electronic engine control. This type of valve operation permits variation in valve timing, valve travel, valve open time and rate at which the valves open and close. 
     As noted by a comparison of  FIG. 8  and  FIG. 4 , the use of hydraulic valve actuators  871 ,  873  may greatly reduce the number of parts and complexity of the mechanism contained in the cylinder head of an embodiment which uses cams for valve actuation. The extension of the power shaft  108  into the head is no longer necessary and a shortened power shaft  875  is shown in  FIG. 8 . A flat head cover  876  is shown in  FIG. 8  rather than the domed design  249  shown in  FIG. 4 . 
     Variation Three—Use of Hydraulic Actuation for Both Displacement Actuator (Piston Control Mechanism) and Valve Operation 
     This variation (not shown) combines the features of engines  700  and  800 . All actuators, e.g.,  761 ,  871  and  873 , may use the same source of high pressure hydraulic fluid and/or may be scheduled by a mechanical and/or electronic engine control. 
     Variation Four—Use of Slots and Sliding Mechanism to Control Connecting Rod Motion 
     Referring now to  FIG. 9 , there is illustrated an alternative variable displacement engine  900  similar in many respects to the engine  100  described in connection with  FIGS. 1-4 . Only the elements that differ substantially from those describe in  FIGS. 1-4  are renumbered. 
     Variable displacement engine  900  includes a rectangular vertical slot  981  and a slider mechanism  982  to restrict the lower end of a connecting rod  983  to motion parallel to the centerline of power shaft  108  as shown in  FIG. 9  for piston 1. For this variation, the upper connecting rod bearing  132  (of  FIG. 3 ) is no longer necessary and the connecting rod  983  is firmly attached to a piston  984 . The only difference between the piston  984  and the piston  118  (of  FIG. 3 ) is the method of joining the connecting rod to the piston. The lower end of connecting rod  983  is connected firmly to the upper surface of the arm of slider  982 . The lower side of the arm of slider  982  is a spherical bearing  985 . Bearing  985  connects slider  982  to a second slider mechanism  986 . The changes described for piston one also apply to the remaining pistons. 
     The slider  986  is permitted to slide freely on a flat plate  987 . The flat plate  987  takes the place of the second ring portion  142  of the wobble plate assembly  128  (piston control mechanism) shown in  FIG. 3 . In some embodiments, the plate  987  may be made a rotating part by eliminating the bearing  916 , while in other embodiments bearing  916  is used to allow it to rotate freely. Allowing it to rotate freely will result in minimum friction due to natural processes. The rest of the piston control mechanism described in  FIG. 3  remains unchanged, except that a ring gear  166  ( FIG. 3 ) is not needed. Slot  981  can be made a part of cylinder block  988  or attached to it. 
     Variation 5—Use of a Universal Joint Mechanism in the Anti-Rotation Assembly and Displacement Actuator 
     Referring now to  FIGS. 10-12 , there is illustrated an alternative variable displacement engine  1000  similar in many respects to the engine  100  described in connection with  FIGS. 1-4 . Only the elements that differ substantially from those describe in  FIGS. 1-4  are renumbered. The variable displacement engine  1000  includes a universal joint (“U-joint”) mechanism in the anti-rotation assembly rather than the ring gear  166  and mating outer lip “gear” portion  162  in  FIG. 3 , and also as part of the displacement actuator. 
     Referring first to  FIGS. 10 and 11 , the wobble plate assembly  128  of  FIG. 3  is modified to accommodate a U-joint mechanism comprising four connecting rod bearing blocks  1092  and two connecting rod bearing blocks  1093  (best seen in  FIG. 11 ). The two parts  1093  are mounted opposite to each other on second ring portion  1091 . The four bearing blocks  1092  and one bearing block  1093  are attached to the five connecting rods  130  by bearings  134 . 
     Cylindrical extensions on the outer side of bearing blocks  1093  form the inner surface of bearings  1094  shown in  FIGS. 10 and 11 . The bearings  1094  connect the bearing blocks  1093  to a differential ring  1095  as shown in  FIGS. 10 and 11 .  FIG. 11  shows a top view of part  1095 . 
     Two cylindrical bearing extensions  1096  ( FIG. 11 ) are located on the exterior side of the differential ring  1095 . These extensions  1096  are each located 90 degrees from the two bearings  1094 . Bearings  1099  attach the differential ring  1095  to a support structure  1097  as shown in  FIGS. 11 and 12 . 
     Referring now to  FIG. 12 , the support structure  1097  is shown in detail. Note that the view of  FIG. 12  is turned 90 degrees from that of  FIG. 10 . The structure  1097  is not visible in  FIG. 10  since it is hidden from view by the power shaft  108 . Note that the support structure  1097  moves along power shaft  108  in concert with the support collar  171  in  FIG. 10 . Support structure  1097  helps stabilize the U-joint ring  1094  and assure that the centerlines of the bearings  1099  and the pivot bearings  172  are always in the same plane normal to the centerline  112  of the power shaft  108 . Guide slots  1098  in the cylinder block prevent rotation of the support structure  1097  and permit the arms of the support structure  1097  surrounding the bearings  1099  to move only in a direction parallel to the centerline  112  of the power shaft  108 . Since the support structure  1097  is connected to the part  1091  as shown in  FIG. 11 , the part  1091  is also prevented from rotating. 
     The lift cylinder  198  and the housing  200  of the screw jack mechanism  186  in  FIG. 3  are reconfigured as integral parts of the support structure  1097  in this embodiment as shown in  FIG. 12 . The rest of the screw jack mechanism  186  may be the same as shown in  FIG. 3 . 
     Variation 6—Use of a Constant Velocity Joint (CV-Joint) in the Anti-Rotation Assembly 
     This variation (not shown) substitutes a constant velocity joint (similar to the concept used to power front-wheels in automobiles) for the U-joint of engine  1000 . Details of the constant velocity joint mechanism are not shown. 
     Variation 7—Use of an Arm and a Track in the Piston Control Linkage 
     Referring now to  FIG. 13 , there is illustrated an alternative variable displacement engine  1300  similar in many respects to the engine  100  described in connection with  FIGS. 1-4 . Only the elements that differ substantially from those describe in  FIGS. 1-4  are renumbered. 
     Within the description of the variable displacement engine  100 , it was shown that a specific extension of the second ring portion  142 , specifically the teeth on the outer rim portion  162 , always remained in a single plane perpendicular to the power shaft  108  (see also  FIG. 5  and related description). This variable displacement engine  1300  takes advantage of that feature to provide an alternate design of the piston control mechanism. 
     The variable displacement engine  1300  comprises a wobble plate assembly  1328  that includes a first ring portion  1301  rather than the first ring portion  140  shown in  FIG. 3 . An extension (arm)  1302  extends from the ring portion  1301  to a circular track  1303  that is normal to the axis of power shaft  108  and adjacent to the inner wall of cylinder block  106 . In the illustrated embodiment, the track  1303  is a slot. A follower assembly  1304  is attached the outer end of arm  1302  by a bearing  1305  and is configured to follow the path of the track  1303 . In the illustrated embodiment, the follower assembly  1304  is a bearing block. As the power shaft  108  rotates, the bearing block  1304  traverses a circular path in the slot  1303 . The length of arm  1302  is determined by the distance required to reach the plane normal to power shaft  108  that results in a constant compression ratio as the engine displacement is varied. This plane is shown in  FIG. 5  as the line passing through points G-J-L. The centerline of the bearing  1305  always stays in this plane. 
     In the engine  1300  of the current embodiment, the control bearings  176 , control link  178  and upper bearing  182  of engine  100  in  FIG. 3  are no longer required. The upper collar  180 , which is fixed to power shaft  108 , is no longer required as a part of the piston control mechanism, but may be retained as a mechanical stop to limit minimum engine displacement. The second ring portion  142  in  FIG. 3  is replaced by second ring portion  1306  to accommodate clearances for the arm  1302  and revised gear tooth profiles at its outer rim. A ring gear  1307  replaces the ring gear  166  in  FIG. 3  to accommodate the revised gear tooth profiles. Other significant features of the engine design are unchanged from the engine  100 . 
     In yet another embodiment (not shown) similar to that of engine  1300  in  FIG. 13 , a variable displacement engine  1400  comprises a circular track  1403  disposed on the engine block  106  to define an offset control plane that is oriented normal to the longitudinal axis  112  and intersects the longitudinal axis at an offset distance Y from the theoretical zero displacement point  170 . A follower assembly  1404  including a follower operatively engages the track  1403  to constrain the motion of the follower to the offset control plane. An extension arm  1402  is operatively connected to a first ring portion  1401  of the wobble plate assembly so as to have a distal end positioned along a line parallel to, but longitudinally offset by the distance Y from, the wobble plate inclination plane. The extension arm  1402  is connected at the distal end to the follower assembly and causes the follower assembly to traverse the circular track as the power shaft  108  rotates. The extension arm  1402  is configured such that the distal end is positioned, when viewed in a direction parallel to the pivot axis  146 , along the line parallel to, but longitudinally offset by a distance Y from, the wobble plate inclination plane. 
     Variation 8—Use of a Vertically Fixed, Rotating Shoe in the Piston Control Mechanism (PCM) and Associated Linkage 
     Referring now to  FIGS. 14A, 14B and 15 , there is illustrated an alternative variable-displacement engine  1500  in accordance with another aspect. The engine  1500  includes certain elements substantially similar to those previously described and illustrated herein; and such elements are denoted using the same reference numbers. Elements that differ substantially from those previously described are renumbered. 
     As with the embodiments previously described and illustrated herein, the variable-displacement engine  1500  utilizes a wobble plate mechanism  1528  to convert the reciprocating motion of pistons  118  traveling in cylinders  110  arranged coaxially around a central power shaft  108  (see  FIG. 1 ) into rotary motion of the power shaft. Variable displacement is achieved by increasing or decreasing the stroke of the pistons  118  while simultaneously moving the center point  146  of the wobble plate  1528  to maintain a constant compression ratio. Piston stroke is determined by the wobble plate angle θ, and the compression ratio is determined by the distance d of the wobble plate center point  146  from the point at which the wobble plate angle would be zero, i.e., the theoretical zero displacement point  170 . This relationship is expressed in mathematical terms by the equation d=K sin θ. K is a constant that is determined by the compression ratio and stroke of the pistons at any wobble plate angle θ. As previously described, the wobble plate center point  146  is the point at which the wobble plate line  150  (i.e., the line or plane passing through the centers of the lower connecting rod bearings  126 ) intersects the power shaft axis  112 , and the wobble plate angle θ is the angle between the wobble plate line  150  and a plane  152  normal to the power shaft axis  112 . It will be appreciated that determining the position of the theoretical zero displacement point  170  along the power shaft  108  or power shaft axis  112  does not require the wobble plate  1528  to actually move to a wobble plate angle θ=0 degrees; rather, the position of the theoretical zero displacement point  170  can be determined by simple extrapolation of the wobble plate movement allowed by the linkages of the piston control mechanism. 
     The variable-displacement engine  1500  of this embodiment includes a piston-control mechanism (“PCM”)  1535  wherein pistons  118  and cylinder block  106  are rotationally fixed with relation to the engine mounting structure  102  such that the cylinder block does not rotate with the power shaft  108 . The power generated by the linear motion of the pistons  118  is converted into output power produced by rotation of the power shaft  108 . The piston control mechanism  1535  for this design is further described in the following paragraphs. 
     The wobble plate assembly  1528  includes a non-rotating upper ring portion  1540  that is rotatably slidably connected to a rotating lower ring portion  1542 . This connection allows the lower ring portion  1542  to rotate (i.e., about the power shaft axis  112 ) independent of the upper ring portion  1540 , but constrains the two portions to remain parallel to one another. Stated another way, a change in angle of one portion  1540 ,  1542  always causes an identical change in angle of the other portion. The pistons  118  are connected via connecting rods  130  to fixed locations on the non-rotating upper ring portion  1540  of the wobble plate  1528 . For example, in the illustrated embodiment, the upper ring portion  1540  includes a plurality of mounting arms  1544  projecting radially outward and spaced apart from one another; the lower bearings  126  of the connecting rods  130  are mounted to these mounting arms. As mentioned earlier, the centers of the lower connecting rod bearings  126  lie in a plane  150  that passes through the center point  146  of the wobble plate  1528 . 
     In the illustrated embodiment, the upper ring part  1540  of the wobble plate assembly  1528  is prevented from rotation by employing a constant-velocity joint  1546  (i.e., “CV joint”). The outer portion  1552  of the CV joint  1546  is connected to the upper ring portion  1540  of the wobble plate and the inner portion  1550  of the CV joint is connected to a tubular support  1548  affixed to, and extending from, the cylinder block  106 . The tubular support  1548  surrounds the power shaft  108  and is concentric with it, but does not rotate. As is known in conventional CV joints, the inner and outer portions  1550 ,  1552  of the CV joint  1546  are flexibly connected to one another with a plurality of CV balls  1551  disposed in races  1553  (see  FIG. 15 ) formed on the opposing inward faces of the CV joint. Other components known in conventional CV joints may also be present in the CV joint  1546 , but are not illustrated. The inner portion  1550  of the CV joint  1546  is permitted to slide axially (i.e., along the direction of shaft axis  112 ) along the tubular support  1548 . The center point of the CV joint is common with the center point  146  of the wobble plate  1528 . Rotation of the CV joint  1546  about the tubular support  1548  is prevented by splines  1554 . 
     Although the CV joint  1546  in the illustrated embodiment is disposed radially within the annular space of the ring-shaped wobble plate  1528  (i.e., an “internal CV configuration”), in other embodiments the CV joint used to prevent rotation of upper ring portion  1540  may be disposed radially outside the wobble plate (i.e., an “external CV configuration”). In such external CV configuration, the inner portion of the CV joint may be connected to the upper ring portion  1540  and the outer portion of the CV joint may be secured to a non-rotating structure within the engine block  102  rather than to the tubular support  1548 . 
     The rotating lower ring portion  1542  of the wobble plate  1528  is connected to the lower side of the non-rotating upper ring portion  1540  of the wobble plate (i.e., opposite to the side facing the pistons) by a bearing or bearing surface. This arrangement permits the forces on the pistons  118  generated by combustion of fuel and air to be transferred to the rotating part  1542  of the wobble plate and cause this part of the wobble plate to rotate. These forces can be very large, especially when the pistons  118  are near top-dead-center and the fuel/air mixture is ignited. 
     Referring now in particular to  FIG. 15 , there is illustrated one form of a connection that may be used to rotatably slidably connect the non-rotating upper ring portion  1540  of the wobble plate assembly  1528  to the rotating lower ring portion  1542 . In the embodiment shown, a plurality of restraining straps  1570  are provided along the inner face  1572  of the upper ring portion  1540 . Each retraining strap  1570  has a body portion  1574  that extends axially below the lower edge of the upper ring portion  1540  and a lip portion  1576  that extends radially outward a short distance. The lower ring portion  1542  (shown in broken line for purposes of illustration) is thereby captured on three sides: on the top face by the lower face of the upper ring portion  1540 ; on the inner face by the body portions  1574  of the restraining straps  1570 ; and on the lower face by the lip portions  1576  of the restraining straps. Accordingly, the lower ring portion  1542  can slide in a rotating direction (denoted by arrow  1587 ) relative to the upper ring portion  1540 , but it is constrained to remain in contact with the upper ring portion as the angles of the ring portions change. In the illustrated embodiment, the restraining straps  1574  are connected with mechanical fasteners, however, in other embodiments the restraining straps could be connected by other means, e.g., welding, or formed as integral parts of the upper ring portion. 
     Referring again to  FIG. 14A , after the piston forces are transmitted from the non-rotating upper ring portion  1540  to the rotating lower ring portion  1542 , the forces in the lower ring portion are further transferred to a lever mechanism  1556  comprising another part of the PCM  1535 . The lever mechanism  1556  also constrains the movement/position of the center point  146  of the wobble plate  1528  in accordance with the relationship d=K sin θ. Further still, the lever mechanism  1556  rotationally links the power shaft  108  to the rotating lower ring portion  1542  of the wobble plate  1528  so that the shaft and lower ring portion rotate together. The lever mechanism  1556  is vertically offset below the rotating part  1542  of the wobble plate at a distance sufficient to prevent interference between the lever mechanism and other parts of the PCM  1535 . 
     The lever mechanism  1556  includes a lever beam  1558 , mechanical links  1560  connecting the lever beam to the rotating lower ring portion  1542  of the wobble plate, an anchor support (shoe)  1562 , and a lift mechanism  1564 . The centerline  1566  of the lever beam  1558  may, but is not required to, be parallel to the centerline  150  of the wobble plate  1528  and duplicate the relationship d=K sin θ. The links  1560  transfer the forces from the rotating part  1542  of the wobble plate to the lever beam  1558  and cause the power shaft  108  to rotate with the rotating part of the wobble plate. Link bearings  1561  may be provided at each end of the links  1560  to allow pivotal connection to the wobble plate  1528  and the lever mechanism, respectively. One end (denoted  1559 ) of the lever beam  1558  may be pivotally connected to an anchor point  1568  that interfaces with the anchor support  1562  such that the anchor point  1568  can move rotationally with the power shaft  108  and radially (i.e., normal to the shaft axis  112 ) but cannot move axially (i.e., parallel to the shaft axis  112 ). In the illustrated embodiment, the anchor support  1562  has the form of a shoe defining a passageway  1563  oriented normal to the shaft axis  112 , and the anchor point  1568  is mounted to a block  1569  that is slidably mounted in the passageway. The anchor support/shoe  1562  is attached to the power shaft  108  and rotates with it. Another interface of the lever beam  1558  with the power shaft  108  assures rotation of the lever beam with the power shaft. 
     In the illustrated embodiment, the links  1560  have an upper link bearing  1561 ′ connected to the lower ring portion  1542  and a lower link bearing  1561 ″ connected to the lever beam  1558 . To allow room for the link bearings  1561 ′,  1561 ″ and avoid interference with other components, upper and lower mounting members  1565 ′,  1565 ″ may be provided projecting, respectively, axially below the lower ring portion  1542  and the lever beam  1558  by respective axial offset distances. In the illustrated embodiment, the axial offset distance of (the center of) the upper link bearing  1561 ′ below the wobble plate line  150  is equal to the axial offset distance of (the center of) the lower link bearing  1561 ″ below the beam lever centerline  1566  on the same link. In other words, the axial offset distances for the upper and lower link bearings  1561 ′,  1561 ″ are equal on each individual link; however, the upper axial offset distances on different links may be different from one another and/or the lower axial offset distances on different links may be different from one another. In other embodiments, the axial offset distances may be equal for all links. 
     Axial forces from the pistons  118  and torque forces from the wobble plate  1528  are divided by the lever beam  1558  primarily between the anchor support/shoe  1562  and the lift mechanism  1564 . The lift mechanism  1564  is axially slidably mounted on the power shaft  108  and pivotally connected to an intermediate point on the lever beam  1558 . In the illustrated embodiment, the lift mechanism  1564  is connected at a lift pivot  1578  disposed at the intersection of the lever beam centerline  1566  and the power shaft axis  112 . During operation, a lift collar  1582  of the lift mechanism  1564  slides axially along the power shaft. The lever beam  1558  is pivotally supported by a pair of lift bearings  1579  (shown in broken line) connected to each side of the lift collar  1582  along a line running through the pivot point  1578  and normal to the shaft axis  112 . Thus, raising and lowering the lift collar  1582  moves the pivot point  1578  for the lever beam  1558  axially along the shaft axis  112 , thereby changing the angle of the lever beam  1558  relative to the shaft axis (since the outer end  1559  of the lever beam is axially constrained by anchor points  1568 ). Changing the angle of the lever beam  1558  in turn changes (via the interconnected links  1560 ) the angle of the wobble plate  1528  to set the piston stroke (hence engine displacement) and to change the position of the wobble plate center point  146  to maintain the relationship d=K sin θ. In the illustrated embodiment, the lift mechanism  1564  includes a lift ring  1580  fixedly mounted to the power shaft  108  and a lift collar  1582  slidingly mounted over both the lift ring and the power shaft to form a hydraulic cavity  1584 . Passages  1586  formed in the power shaft  108  may allow hydraulic fluid (from an external source) to flow into and out of the cavity  1584  to form a hydraulic cylinder that can raise and lower the collar  1582  along with the pivot point  1578  mounted on the collar. 
     In other embodiments, the lift mechanism  1564  may include a collar  1582  mounted around the power shaft  108 , a bearing set  1579  that maintains the location of the lever center point  1578  along the centerline  112  of the power shaft  108 , and a hydraulic cylinder  1584  surrounding the power shaft. The collar  1582  is permitted to slide axially along the power shaft  108 . One end of the hydraulic cylinder can be a part of the power shaft so that the forces of the lift are transferred from the lever to the power shaft. The lift mechanism  1564  may be powered by an external source of high pressure hydraulic fluid to control engine displacement. 
     The axial forces produced by the pistons  118  and radial torque forces produced by the PCM  1535  are transferred to the engine block  102  by bearings  124 ,  126  on the power shaft  108  and/or the shoe  1562 . 
     Referring now to  FIG. 14B , in alternative embodiments of the engine (denoted  1500 ′), the axial anchor point  1568  for the lever beam  1558  may be fixed both axially (i.e., in a direction parallel to the shaft axis  112 ) and radially (i.e., in a direction normal to the shaft axis) with respect to the power shaft  108 , although still rotating with the power shaft, rather than being slidably movable in the radial direction. In the illustrated embodiment of  FIG. 14B , the anchor point  1568  is the center of a pin or bearing  1590  fixedly mounted in anchor support  1562 . In such embodiments, the slider block  1569  is not required, and the upper end  1559  of the lever beam  1558  may be provided with a slot  1592  that slidingly engages over the bearing  1590  of the anchor point  1568 . As the lift mechanism  1564  moves the lever beam pivot point  1578  axially along the shaft axis  112  to vary the angle of the lever beam  1558  (and hence, the angle θ of the wobble plate  1528 ) with respect to the shaft axis  112 , the slot  1592  in the end  1559  of the lever beam can move along the bearing  1590  to accommodate the change in distance between the pivot point  1578  and the anchor point  1568 . In different embodiments, the slot  1592  may have a straight or curved path, and may run parallel to the centerline  1566  or be angled with respect to the centerline so as to adjust the relationship between movement of the PCM and wobble plate angle. 
     Small variations in the design of the PCM  1535  in this embodiment can be readily made to permit optimization of engine performance. Some of the factors that might be considered are angle of connecting rods with respect to power shaft centerline, slight variations in compression ratio to reduce emissions, and lowering compression ratio near minimum displacement to reduce starter loads and engine roughness at idle. 
     Variation 9—Use of a Rotating Cylinder Block Rotating with the Power Shaft, and Non-Rotating Piston Control Mechanism (PCM) and Associated Linkage 
     Referring now to  FIG. 16 , there is illustrated an alternative variable-displacement engine  1600  in accordance with another aspect. The engine  1600  includes certain elements substantially similar to those previously described and illustrated herein; and such elements are denoted using the same reference numbers. Elements that differ substantially from those previously described are renumbered. 
     In contrast to previous embodiments wherein the cylinder block  106  is rigidly connected to the engine block  102 , the engine  1600  of this embodiment is a continuously variable displacement engine wherein the cylinders  110  are formed in a separate cylinder block  1606  that can rotate relative to the engine block  102  and external engine structure. In the illustrated embodiment of engine  1600 , the cylinder block  1606  is connected to the power shaft  108  and rotates with the power shaft within the external engine structure  102 . Accordingly, in this embodiment, the pistons  118  reciprocating (in the axial direction) within the cylinders  110  of the cylinder block  1606  also revolve (in a circumferential direction) around the axis  112  of the power shaft  108  as the cylinder block rotates with the power shaft. The piston control mechanism  1635  for the engine  1600  is similar in many respects to the PCM  1535  used in engine  1500  (i.e., the seventh variation); however, it is modified (as described herein) to operate with the rotating cylinder block  1606  and revolving pistons  118 . 
     In particular, referring still to  FIG. 16 , one or more cylinders  110  may be located within the cylinder block  1606  and arranged around the central power shaft  108  that rotates with the cylinder block. The centerlines  116  of the cylinders  110  are nominally parallel to the centerline  112  of the power shaft  108 . A wobble plate mechanism  1628  is used to convert power from the pistons  118  to rotate the central power shaft  108 . 
     In the engine  1600 , variable displacement is achieved by increasing or decreasing the stroke of the pistons  118  while concurrently moving the center point  146  of the wobble plate  1628  so as to maintain a constant compression ratio. Piston stroke is determined by the wobble plate angle θ, and the compression ratio is determined by the distance, d, of the wobble plate center point  146  from the theoretical zero displacement point  170 , i.e., the location at which the wobble plate angle θ would be zero degrees. This relationship is expressed in mathematical terms by the equation d=K sin θ, where K is a constant that is determined by the compression ratio and stroke of the piston at any wobble plate angle θ. It will be appreciated that piston control mechanisms moving according to the d=K sin θ relationship may be used to provide variable displacement and constant compression ratio regardless of whether the cylinders  110  of the engine are fixed with respect to the engine block structure  102  or rotating/revolving with respect to the engine block structure. 
     In the engine  1600 , the power generated by the linear motion of the pistons  118  is converted into output power produced by rotation of the power shaft  108 . The rotating cylinder block  1606  is held to a constant axial position by bearings  1624 . The piston control mechanism (“PCM”)  1635  for the engine  1600  includes a wobble plate assembly  1628  including a rotating upper ring portion  1640  and a non-rotating lower ring portion  1642 . It will be appreciated that the relative positions of the rotating and non-rotating portions of the wobble plate  1628  of engine  1600  are inverted from the arrangement of the rotating and non-rotating portions of the wobble plate  1528  of engine  1500 . 
     In the engine  1600 , each piston  118  is connected to a relatively fixed location on the rotating upper portion  1640  of the wobble plate  1628  by a connecting rod  130  (in this case, the term “relative fixed” is used because the pistons  118  and the upper portion  1640  of the wobble plate both rotate together with the power shaft  108 , and thus do not rotate relative to one another). The connecting rod  130  transfers the axial forces from the piston  118  to the rotating upper portion  1640  of the wobble plate. The center of the lower connecting rod bearing  126  lies in a plane  150  that passes through the center point  146  of the wobble plate  1628 . The upper rotating part  1640  of the wobble plate  1628  is constrained by a constant-velocity (“CV”) joint  1646  to rotate with the cylinder block  1606 . The CV joint  1646  has an inner portion  1650  connecting to the power shaft  108 . The outer portion  1652  of the CV joint  1646  is fixed to the upper portion  1640  of the wobble plate. The inner portion  1650  of the CV joint is permitted to slide axially along the power shaft  108  but is constrained to rotate with the power shaft by splines  1654 . The center point of the CV joint  1646  is held common with the center point  146  of the wobble plate  1628  by the CV balls  1651  linking the two portions  1650 ,  1652  of the CV joint. 
     Although the CV joint  1646  in the illustrated embodiment is disposed radially within the annular space of the ring-shaped wobble plate  1628  (i.e., an “internal CV configuration”), in other embodiments the CV joint used to ensure rotation of upper ring portion  1640  with the power shaft  108  may be disposed radially outside the wobble plate (i.e., an “external CV configuration”). In such external CV configuration, the inner portion of the CV joint may be connected to the upper ring portion  1640  and the outer portion of the CV joint may be secured to a rotating portion of the cylinder block  1606  rather than to the power shaft itself. 
     The PCM  1635  of the engine  1600  further includes the lower, non-rotating portion  1642  of the wobble plate  1628 . In the illustrated embodiment, the lower portion  1642  has a ring-like configuration (disposed around the power shaft  108 ) and is connected to the lower side of the upper, rotating portion  1640  of the wobble plate (opposite from the side facing the pistons) by bearings  1655 . The non-rotating part  1642  of the wobble plate controls the wobble plate angle θ. The non-rotating part  1642  includes a first extension  1657 ′ attached to the (axially) uppermost portion of the non-rotating part and a second extension  1657 ″ attached to the (axially) lowest portion of the part. These extensions  1657 ′,  1657 ″ allow the lower, non-rotating part  1642  of the wobble plate  1628  to be connected to a control lever  1658  through bearings  1661 ′ and  1661 ″ located at each end of control links  1660 . One end  1659  of the control lever  1658  is connected to a slider block  1669  by a bearing  1668 . The slider block  1669  is constrained by a slot  1662  that permits the block to slide a short distance along a radial line extending perpendicularly from the axis  112  of the power shaft  108  (or an extension thereof). The slot  1662  forces the bearing  1668  to become an anchor point at the high end  1669  of the control lever  1658  that constrains this end of the control lever to a single axial position. The slot  1662  may also prevent the control lever  1658  from rotating with the power shaft  108 , and supports a major part of the axial forces produced by the pistons  118 . The control lever  1658  and the two links  1660  prevent rotation of the lower non-rotating portion  1642  of the wobble plate. The slot  1662  is located a sufficient distance from the wobble plate  1628  to avoid any physical interference with the wobble plate. 
     In other embodiments (not shown), the bearing  1668  for the control lever  1658  may be fixed both axially (i.e., in a direction parallel to the shaft axis  112 ) and radially (i.e., in a direction normal to the shaft axis) with respect to the power shaft  108 , rather than being slidably movable in the radial direction. In such embodiments, the slider block  1669  is not required, and the upper end  1659  of the control lever  1658  may be provided with a slot (similar to slot  1592  in  FIG. 14B ) that slidingly engages over the bearing  1668 . As the lift mechanism  1664  moves the control lever pivot point  1678  axially along the shaft axis  112  to vary the angle of the control lever  1658  (and hence, the angle θ of the wobble plate  1628 ) with respect to the shaft axis  112 , the slot in the end  1659  of the control lever can move along the bearing  1668  to accommodate the change in distance between the pivot point  1678  and the anchor point bearing  1668 . In different embodiments, the slot may have a straight or curved path, and may run parallel to the centerline  1666  or be angled with respect to the centerline so as to adjust the relationship between movement of the PCM and wobble plate angle. 
     Referring still to  FIG. 16 , a centerline  1666  through the length of the control lever  1658  may be, but is not necessarily, parallel to the centerline  150  of the wobble plate  1628 . The control lever  1658  and the two links  1660  to the non-rotating portion  1642  of the wobble plate control the wobble plate angle θ. They also control the movement of the center point of the wobble plate along the power shaft to maintain the d=K sin θ relationship discussed earlier as necessary for a constant compression ratio. 
     A support member  1638  whose centerline lies along the extension of the power shaft centerline  112  may be provided to support the bearing  1624  of the power shaft  108 . A lift collar  1682  around the support  1638  constrains a pivot point  1678  on the centerline  1666  of the control lever  1658  to move axially along the centerline  112  of the power shaft  108  as the angle of the control lever (and hence, also the wobble plate angle θ) is changed to vary engine displacement. This feature is provided by the use of two bearing posts  1679  attached to the lift collar  1682  so that their centerline passes through the pivot point  1678  and the power shaft centerline  112  (or extension). These posts  1679  support bearings located along the centerline  1666  of the control lever  1658 . 
     The displacement of engine  1600  is varied by axially moving the lift collar  1682  of the lift mechanism  1664  along the central support member  1638 . The lever beam  1658  is pivotally supported by a pair of lift bearings  1679  (shown in broken line) connected to each side of the lift collar  1682  along a line running through the pivot point  1678  and normal to the shaft axis  112 . Thus, raising and lowering the lift collar  1682  moves the pivot point  1678  for the lever beam  1658  axially along the shaft axis  112 . Since the upper end  1669  of the control lever  1658  is always at a fixed axial position due to the slot  1662 , axially moving the middle portion of the control lever by lifting the collar  1682  and bearing posts  1679  will change the angle of the control lever with respect to the power shaft axis  112 , which in turn similarly changes the wobble plate angle θ by means of the links  1660 . The force necessary to axially move the collar  1682  may be provided by a lift including such devices as a mechanical jack or a hydraulic piston. One configuration to provide the necessary force is to attach a hydraulic piston to the collar  1682 . In the illustrated embodiment, a hydraulic piston surrounds the bearing support  1638  and is powered by high pressure hydraulic fluid (e.g., engine oil) introduced into a hydraulic piston space  1683  through passages  1684  formed in the support, thereby axially moving the lift collar  1682 . 
     Variation 10—Use of a Rotating Cylinder Block Rotating with the Power Shaft, and Alternative Non-Rotating Piston Control Mechanism (PCM) and Associated Linkage 
     Referring now to  FIG. 17 , there is illustrated an alternative variable-displacement engine  1700  in accordance with still another aspect. The engine  1700  includes certain elements substantially similar to those previously described and illustrated herein; and such elements are denoted using the same reference numbers. Elements that differ substantially from those previously described are renumbered 
     The engine  1700  of this embodiment is a continuously variable displacement engine wherein a separate cylinder block rotates within the external engine structure similar to the engine  1600  (“ninth variation”) previously described; however, the engine  1700  includes a simplified piston control mechanism (“PCM”). 
     In engine  1700 , one or more cylinders  110  are located within a cylinder block  1606  and are arranged around a central power shaft  108  that rotates with the cylinder block  1606 . The centerlines  116  of the cylinders  110  are nominally parallel to the centerline  112  of the power shaft  108 . The power shaft  108  is attached firmly to the cylinder block  1606  and does not move axially within the engine block structure  102 . A wobble plate mechanism  1728  is used to convert power from the pistons  118  to rotate the central power shaft  108 . It will be understood in the following description that the singular term “piston” is meant to apply to all pistons in an engine having multiple pistons. 
     Similar to previously described embodiments, variable displacement is achieved in engine  1700  by increasing or decreasing the stroke of the piston  118  while concurrently moving the center point  146  of the wobble plate  1728  so as to maintain essentially a constant compression ratio. Piston stroke is determined by the wobble plate angle θ (measured along the wobble plate centerline  150  relative to a plane  152  normal to the power shaft axis  112 ), and the compression ratio is determined by the distance (denoted d) of the wobble plate center point  146  from the theoretical zero displacement point  170 , i.e., the point at which the wobble plate angle would be zero. The desired relationship is expressed in mathematical terms by the equation d=K sin θ. K is a constant that is determined by the compression ratio and stroke of the piston at any wobble plate angle θ. In some embodiments of engine  1700 , the wobble plate movement produced by the piston control mechanism  1735  does not perfectly match the d=K sin θ relationship, but the error can be made small enough that the resulting variation in compression ratio is acceptable for many applications of the variable displacement engine. 
     The design of a cylinder head (not shown) for mounting on the rotating cylinder block  1606  and the associated supporting structure may be varied in different embodiments to meet the specific requirements of each engine. The illustrated embodiment of engine  1700  features elements that may be required in any design of an engine with a rotating cylinder assembly. Specifically, the end of the power shaft  108  near the wobble plate  1728  is held in place by a bearing  1724  between the power shaft and a support  1738  attached to the exterior frame (e.g., engine block  102 ) of the engine. The centerline of the support  1738  lies along an extension of the centerline axis  112  of the power shaft  108 . The support  1738  may be solid (as illustrated) or hollow, and may permit an extension of the power shaft  108  to pass through to connect to external engine components. 
     As in previous embodiments, the power generated by the reciprocating linear motion of the piston  118  in the engine  1700  is converted into output power by a wobble plate  1728  that produces rotation of the power shaft  108 . The simplified piston control mechanism (PCM)  1735  for this embodiment is further described below. 
     Each piston  118  is connected to a (relatively) fixed location on the upper rotating portion  1640  of the wobble plate  1728  by a connecting rod  130 . The connecting rod  130  transfers the forces from the piston  118  to the rotating wobble plate  1728 . The center of the connecting rod lower bearing  126  (at opposite end from the piston) lies in a plane  150  that passes through the center point  146  of the wobble plate  1728 . The upper rotating part  1640  of the wobble plate is constrained by a constant-velocity (CV) joint to rotate with the cylinder block  1606 . The CV joint  1646  has an inner portion  1650  connected to the power shaft  108 . An outer portion  1652  of the CV joint  1646  is fixed to the upper portion  1640  of the wobble plate. The inner portion  1650  of the CV joint is permitted to slide axially along the power shaft  108  but is constrained to rotate with the power shaft by splines  1654 . The center point of the CV joint  1646  is held common with the center point  146  of the wobble plate by the CV ball bearings  1651  linking races  1653  on the two portions of the CV joint. 
     Although the CV joint  1646  in the illustrated embodiment is disposed radially within the annular space of the ring-shaped wobble plate  1728  (i.e., an “internal CV configuration”), in other embodiments the CV joint used to ensure rotation of upper ring portion  1640  with the power shaft  108  may be disposed radially outside the wobble plate (i.e., an “external CV configuration”). In such external CV configuration, the inner portion of the CV joint may be connected to the upper ring portion  1640  and the outer portion of the CV joint may be secured to a rotating portion of the cylinder block  1606  rather than to the power shaft itself. 
     A lower, ring-like non-rotating part  1742  of the wobble plate  1728  is connected to the lower side of the rotating part  1640  (opposite from the side facing the pistons) by bearings  1655 . The non-rotating part  1742  of the wobble plate  1728  controls the wobble plate angle θ and the movement of the center point  146  of the wobble plate to vary the displacement of engine  1700 . 
     The PCM  1735  of this embodiment includes an axial anchor arm  1759  extending from the non-rotating part  1742  of the wobble plate  1728 . In the illustrated embodiment, the axial anchor arm  1759  extends from the (axially) uppermost position of the non-rotating portion  1742 . A bearing  1768  at the outer end of the anchor arm  1759  pivotally connects the anchor arm to a slider block  1769 . The slider block  1769  is permitted to slide in a slot/path  1763  nominally along a line  1764  normal to the centerline  112  of the power shaft. In the illustrated embodiment, the slider block  1769  is constrained by slot  1763  that is rigidly attached to the engine structure  102 . The slot  1763  is configured to maintain the effective outer end  1768  of the anchor arm  1759  at a nominally constant axial position. However, in some embodiments, the shape of the slot  1763  may be tailored to meet the requirement for essentially constant compression ratio as the displacement is varied. For example, the slot  1763  may be nominally at a constant axial position but may be slightly sloped and/or curved to meet the compression ratio needs of the engine. The slot  1763  also prevents the lower, non-rotating part  1742  of the wobble plate from rotating. The slider block  1769  may slide a short distance from an outermost position at maximum wobble plate angle (θ max ) to an innermost position at minimum wobble plate angle (θ min ). The specific location of the bearing  1768  is normally selected as the location that results in the least variation in compression ratio, but may vary for optimization of the engine design. 
     The PCM  1735  of the engine  1700  may further include a lift arm  1782  extending from another part of the non-rotating portion  1742  of the wobble plate. Typically, the lift arm  1782  is attached on the opposite side of the non-rotating portion  1742  from the anchor arm  1759 . In the illustrated embodiment, the lift arm  1782  extends from the (axially) lowest location of the lower portion  1742 , opposite from the anchor arm  1759 . The outer end  1784  of the lift arm  1782  is connected through bearings and a link  1786  to a lift mechanism  1788 . As the lift mechanism  1788  raises and lowers the lift arm  1782  in the axial direction, the wobble plate angle θ changes (and hence, the engine displacement changes) since the other side of the non-rotating portion  1742  is axially pinned by bearing anchor point  1768  at the outer end of the anchor arm  1759  riding in the slot  1763 . 
     The lift  1788  may be constructed of such devices as a mechanical jack or a hydraulic piston. The hydraulic piston could be powered by high pressure hydraulic fluid such as engine oil. The mechanical jack could be powered by external means. 
     In other embodiments (not shown), the bearing  1768  for the anchor arm  1759  may be fixed both axially (i.e., in a direction parallel to the shaft axis  112 ) and radially (i.e., in a direction normal to the shaft axis) with respect to the power shaft  108 , rather than being slidably movable in the radial direction. In such embodiments, the slider block  1769  is not required, and the end of the anchor arm  1759  may be provided with a slot (similar to slot  1592  in  FIG. 14B ) that slidingly engages over the bearing  1768 . As the lift mechanism  1788  moves the wobble plate center  146  along the shaft axis  112  to vary the angle θ, the slot in the end of the anchor arm  1759  can move along the bearing  1768  to accommodate the change in distance between the wobble plate center  146  and the anchor arm bearing  1768 . In different embodiments, the slot may have a straight or curved path, and may run parallel to the centerline of the anchor arm or be angled with respect to the centerline so as to adjust the relationship between movement of the PCM and wobble plate angle. 
     Referring once again to  FIG. 14A , and also to  FIGS. 18-24 , it will be appreciated that when considering additional aspects of new variable displacement engines and controls therefor, compression ratio is an important parameter in achieving the desired engine characteristics. This parameter (i.e., compression ratio) is especially important in the design of a continuously variable displacement engine because of the challenges involved in keeping the compression ratio in an acceptable range as the displacement is varied. In the embodiment previously disclosed in  FIG. 14A  and the associated written description, a piston control mechanism (PCM)  1535  is utilized having an anchor-point/beam arrangement to maintain an essentially constant compression ratio throughout a wide range of displacement. In the engine design embodiment illustrated in  FIG. 14A , the cylinder centerline  116  is placed at an optimized distance from the power shaft centerline  112 . In one example of such design, the maximum deviation in compression ratio over the displacement range is no more than 0.6 percent. 
     As previously described, in the embodiment illustrated in  FIG. 14A , the anchor-point  1568  in the end of the beam  1558  is constrained to remain at a fixed axial location but is allowed to move (i.e., radially) on a line normal to the power shaft  108  by a slot in a shoe  1562  attached to the power shaft. A second point  1578  along the centerline  1566  of the beam  1558  is then selectively moved axially along the centerline  112  of the power shaft  108 . A third point along the centerline of the beam defines the motion required to achieve the relationship of d=K sin θ where d is the distance of the wobble plate center from a theoretical position at a wobble plate inclination angle (θ) of zero, and K is a constant. The location of this point is defined by the desired compression ratio. The motion of this point is then transferred to the wobble plate by two links  1560 , and then to the piston(s)  118  by connecting rods  130  attached to the wobble plate  1528 . In such embodiments, a slight deviation in the desired compression ratio may be introduced by changes in angle of the connecting rod with respect to power shaft centerline  112  as wobble plate angle θ is varied; however, when the geometry of the design is optimized the effect of this deviation is negligible to engine performance. 
     Whereas engine designs such as those illustrated in  FIG. 14A  may provide an optimized geometry, for example, with respect to the radial spacing of the cylinder axes  116  away from the power shaft axis  112  (e.g., when measured relative to a unit parameter such as the distance from center  146  of the wobble plate  1528  to the center of the lower connecting rod bearing  126 ), the design of an operational engine must also address other considerations, including but not limited to: space for components for valve actuation, fuel injection and ignition; air quality standards; starter power requirements; and smoothness of engine operation. Addressing some of these considerations may require, for example, moving the cylinder axes  116  further away from the power shaft axis  112  (i.e., radially outward from an optimized configuration), which may tend to increase unwanted variation in compression ratio as the displacement varies over the displacement range. Addressing others of these considerations may require the purposeful addition of small predetermined variations in the compression ratio as the displacement is varied over the displacement range. Accordingly, additional aspects are described herein for use in variable displacement engines, namely: 1) Apparatus for minimization of errors in desired compression ratio as displacement varies in variable displacement engines, especially those having a non-optimized mechanical configuration; and 2) Apparatus for the introduction of predetermined variations in the desired compression ratio at predetermined displacements as the displacement varies in variable displacement engines. 
     An example of a near-optimized mechanical configuration is illustrated in  FIG. 14A , wherein the cylinders  110  are spaced from the power shaft centerline  112  such that the connecting rods  130  are parallel to the power shaft centerline when the wobble plate angle θ is at the midpoint of the displacement range. A non-optimized mechanical configuration, on the other hand, may have connecting rods  130  that are not parallel to the power shaft centerline  112  at the midpoint of the displacement range. For example, the centerlines  116  of the cylinders  110  maybe located radially outside or inside of the optimized configuration.  FIG. 19  is one example of a non-optimized configuration where the centerlines  116  of the cylinders  110  are moved outside, i.e., radially outward, from the optimized location. The resulting error in compression ratio as displacement changes is shown in  FIG. 20 , Case 1. 
     Referring now specifically to  FIGS. 18, 19 and 20 , one example of using changes in the configuration of the slot  1563  of the shoe  1562  to reduce the deviations of compression ratio is illustrated by examining the effect of moving the centerline  116  of the cylinders  110  outward to create more volume for components located in the head region of the engine.  FIG. 18  is an illustration of a PCM  1800  for a variable displacement engine, which is similar to the PCM  1535  in  FIG. 14A , including a rotating shoe  1562  and lever beam  1558 .  FIG. 19  illustrates the geometry of a variable displacement engine  1900  similar to engine  1500  of  FIG. 14A , except the cylinders  110  are moved outward such that the cylinder bores  116  are moved to the same distance from the power shaft centerline  112  as the distance of the lower connecting rod bearing (point X 3 ) is from the center  146  of the wobble plate  1528 . For purposes of illustration in  FIG. 19 , the piston  118  is shown at top-dead-center with the wobble plate inclination angle (θ) at 30 degrees. When using the PCM  1800  of  FIG. 18  on the engine  1900  having the non-optimized geometry of  FIG. 19 , the effect on the compression ratio of varying the wobble plate inclination angle θ from 9.6 degrees to 30 degrees is shown as Case 1 in  FIG. 20 . The illustrated variation in angle θ within the range from 9.6 degrees to 30 degrees in  FIG. 20  corresponds with a variation in displacement across a range from approximately ⅓ of the maximum displacement value to the maximum displacement value to for the geometry illustrated in  FIG. 19 . Assuming the desired constant compression ratio has a value=10, Case 1 of  FIG. 20  shows the magnitude of the compression ratio error increases continuously as the displacement increases (the compression ratio error being the difference between the desired value of compression ratio and the actual value of compression ratio at a given angle θ or displacement). 
     Referring in particular to  FIG. 18 , there are illustrated selected parts of a piston control mechanism (“PCM”)  1800  similar to the PCM  1535  previously described in connection with  FIG. 14A . The PCM  1800  of  FIG. 18  has no correction for errors in compression ratio (i.e., deviations from the desired compression ratio value caused by non-optimized geometry) as displacement is varied. The PCM  1800  incorporates a shoe  1562  defining a slot (i.e., passage way)  1563  for slidably receiving a slider block  1569 . One end of a lever beam  1558  encompasses an anchor point  1568  that is attached to the slider block  1569 . The slider block  1569  in this embodiment is constrained to movement along a line  1802  normal to the centerline  112  of the power shaft  108 . Another point  1578  (i.e., the lift pivot) on the center line  1566  of the lever beam  1558  is constrained to move axially along the center line  112  of the power shaft  108 . A lift bearing  1579  at the lift pivot  1578  connects the lever beam  1558  to a lift mechanism  1582 . Axial movement of the lift mechanism  1582  along the power shaft  108  changes the inclination angle θ between the lever beam center line  1566  and the line  1802  normal to the power shaft centerline  112 . This PCM design results in the relationship d=K sin θ where d is the distance between the line  1804  and pivot point  1578 , K is the distance between anchor point  1568  and pivot point  1578 , and θ is the inclination angle. This angle θ relationship is transferred to the wobble plate  1528  (see  FIG. 19 ) from the lever beam  1558  by two links  1560  (only partially shown in  FIG. 18 ). This relationship is required in order to maintain a constant compression ratio. 
     Referring now also to  FIGS. 19 and 20 , there is illustrated the mechanical configuration of a variable displacement engine having a non-optimized configuration (i.e., for constant compression ratio), but nevertheless a configuration that may be practical for other considerations. In particular, illustrated are the non-rotating part  1540  and rotating part  1542  of the wobble plate  1528 , the connecting rod  130 , the cylinder  114 , and the piston  118 . In the illustrated embodiment, the cylinder center line  116  is positioned radially away from the power shaft centerline  112  at a distance equal to the distance between the center  146  of the wobble plate  1528  and the center X 3  of the lower connecting rod bearing  126 . The piston  118  is shown at top-dead-center and the wobble plate  1528  is shown at the inclination angle θ. This position determines the compression ratio of the engine. The point  146  follows the relationship d=K sin θ as established by the lever beam  1558  as shown in  FIG. 18  for a constant compression ratio. However, for the engine to maintain a truly constant compression ratio, the distance between the point X 4  (i.e., the point along power shaft axis  112  where a normal line passes through point X 6 , the upper connection rod bearing center) and the point X 5  (i.e., the point along power shaft axis  112  where a normal line passes through point X 3 , the lower connecting rod bearing center) must also remain constant. For the configuration shown in  FIG. 19 , the distance between points X 4  and X 5  is equal to the distance between point X 3  and X 6  times the cosine of angle), where is the angle between the cylinder bore  116  and the centerline  131  of the connecting rod  130 . Since λ is not constant as θ varies, the compression ratio will also vary with θ. The compression ratio error, i.e., how the compression ratio deviates from a constant value for different values of wobble plate angle θ (corresponding to different values of engine displacement), is shown in the graph of  FIG. 20 , and in particular the line “Case 1” shows the error where there is no compensation for the variation in the distance between X 4  and X 5 . 
     In particular,  FIG. 20  is a graph showing the calculated variation in compression ratio as wobble plate angle θ (and corresponding displacement) is varied over the range of 9.6 degrees to 30 degrees for one example of an engine geometry where the distance from the cylinder centerline  116  to the power shaft axis  112  is equal to the distance of the wobble plate center  146  to the center (X 3 ) of the lower connecting rod bearing  126 . Data are presented for three cases of engines having different piston control mechanisms, namely, Case 1 having a PCM  1800  without modifications to the slot in the shoe (i.e., the “straight-line perpendicular path” case); Case 2 having a PCM  2100  wherein the slot is tilted to reduce the deviations in compression ratio as the wobble plate angle θ is changed (i.e., the “straight-line non-perpendicular path” case); and Case 3 having a PCM  2200  wherein the slot is upwardly curved to further reduce deviations in compression ratio as the wobble plate angle θ is changed (i.e., the “curved-line path” case). 
     Referring now to  FIG. 21 , there is illustrated another embodiment of a PCM, which is configured to reduce the compression ratio error caused by non-optimized configurations. The PCM  2100  is this embodiment is similar to PCM  1800  except for the configuration of the slot  1563  in the shoe  1562 . Without compensation (as seen in Case 1 of  FIG. 20 ) the compression ratio becomes lower as the wobble plate inclination angle θ increases. In order to reduce the deviation from a constant compression ratio as the wobble plate inclination angle θ increases, the piston control mechanism may be modified to compensate for the reduction in the distance from X 4  to X 5  (see  FIG. 19 ). In particular, the error in compression ratio can be significantly reduced by angling or tilting the slot  1563  in the shoe  1562  (i.e., relative to a normal line extending from the power shaft axis  112 ). One example of such modification is illustrated in  FIG. 21 . The part of the shoe  2162  forming the slot  2163  is tilted upward by an angle β. As the wobble plate inclination angle θ increases, the slider block  2169  moves along the slant of the slot  2163  and causes the anchor point  1568  to also move along at the same angle β, resulting in the anchor point moving axially upward (i.e., away from the pivot point  1578 ) a short distance. This upward movement of the anchor point  1568  offsets some of the decrease in distance between points X 4  and X 5  ( FIG. 19 ). The compression ratio as a function of wobble plate angle θ for this configuration of the slot is shown as Case 2 in the graph of  FIG. 20 . 
     The alternative PCM  2100  may be used in the variable-displacement engine  1900  (i.e., instead of the PCM  1800 ) to reduce the compression ratio error. As described, the PCM  2100  may be similar to the PCMs  1535  and  1800  except the slot  2163  of the shoe  2162  is inclined an angle β with respect to a normal (i.e., perpendicular) line  2102  extending from the power shaft centerline  112  as shown in  FIG. 21 . The inclined slot  2163  forces the slider  2169  and anchor point  1568  to also move radially at the angle β with respect to another normal line  2104  extending from the centerline  112 . The corresponding effect on compression ratio error versus wobble plate angle θ (and thus displacement) of using PCM  2100  in the engine  1900  is shown as Case 2 in  FIG. 20 . Again assuming the desired constant compression ratio has a value=10, it will be appreciated that Case 2 of  FIG. 20  shows the magnitude of the compression ratio error using the PCM  2100  having an inclined slot  2163  is significantly reduced as displacement increases compared with Case 1 using the PCM  1800  with a perpendicular slot  1563 . 
     Referring now to  FIG. 22 , there is illustrated another alternative PCM  2200  that is configured to reduce compression ratio errors. The PCM  2200  is generally similar to the PCMs previously described except for the configuration of the slot in the shoe and the slider block. In particular, the slot  2263  in the shoe  2262  is modified to include a combination of tilt angle β (which may not be of the same magnitude as in PCM  2100 ) and curvature of radius R. By selecting the appropriate values of β and R, the curved slot  2263  and its matching slider block  2269  may significantly reduce the deviation in compression ratio from the desired value (i.e., the compression ratio error) as the wobble plate inclination angle θ is varied. The resulting compression ratio versus wobble angle θ graph is shown as Case 3 in  FIG. 20 . 
     The alternative PCM  2200  may be used in the engine  1900  (i.e., instead of the PCM  1800  or  2100 ) to reduce the compression ratio error as the displacement varies. The PCM  2200  in the illustrated embodiment is similar to the PCMs  1535 ,  1800  and  2100  except the slot  2263  of the shoe  2262  is upwardly curved about a control point  2250  disposed radially away from the power shaft axis  112  and axially between the pistons  118  and the anchor bearing  1568 . As further described herein, in other embodiments, the slot  2263  may be downwardly curving. It will be appreciated that the radii of the top wall  2251  and the bottom wall  2252  of the slot  2263  will be different from one another since they lie at different distances from the control point  2250 , however, the respective radii are selected to allow a correspondingly curved slider  2269  to move through the shoe  2262  such that the anchor point  1568  travels along a curved-line path  2255  having a radius R about the control point  2250 . In the illustrated embodiment, the anchor bearing  1568  of the slider block  2269  follows a circular-path  2255  around the control point  2250 ; however in other embodiments, other curved paths may be used. The position of control point  2250  may be further specified by a tilt angle β, which may or may not be of the same magnitude as angle β in PCM  2100 ). The corresponding effect on compression ratio error versus wobble plate angle θ (and thus displacement) of using PCM  2200  in the engine  1900  is shown as Case 3 in  FIG. 20 . Again assuming the desired constant compression ratio has a value=10, it will be appreciated that Case 3 of  FIG. 20  shows the magnitude of the compression ratio error using the PCM  2200  having a curved slot  2263  is significantly reduced as displacement increases compared with Cases 1 and 2 using the PCMs  1800  and  2100 , respectively. 
     Referring now to  FIGS. 23 and 24 , other aspects of the design of the slot in the shoe can be used to address other considerations such as lowering the compression ratio near minimum displacement if problems are encountered with smoothness in operation at idle (i.e., at minimum displacement). A PCM for lowering the compression ratio at minimum displacement may use a downwardly curved slot in the shoe and have a control point disposed such that the anchor bearing is disposed axially between the piston and the control point. One example of such a PCM using a downwardly curved slot to provide this feature is PCM  2300  shown in  FIG. 23 . The resulting compression ratio as a function of wobble plate angle θ (i.e., displacement) for the PCM  2300  embodiment of  FIG. 23  is shown in the graph of  FIG. 24 . 
     Referring now particularly to  FIG. 23 , the PCM  2300  may be used in the variable-displacement engine  1900  (i.e., instead of the PCM  1800 ,  2100  or  2200 ) to provide a predetermined variable compression ratio as the displacement varies. As previously discussed, engines with high compression ratios often experience rough engine operation at idle. In some variable-displacement engine designs, the displacement is automatically reduced to minimum displacement at engine idle operation. In such engines, the rough operation problem can be addressed by reducing the compression ratio at minimum displacement, for example by means of a modification to the configuration of a curved slot  2363  and a corresponding curved slider block  2369  ( FIG. 23 ). 
     In further detail, the PCM  2300  may have a downwardly curved slot  2363  in the shoe  2362  defined by a control point  2350  disposed radially away from the power shaft axis  112  and disposed axially such that the anchor bearing  1568  is axially between the piston  118  and the control point. The curved slot  2363  may slidingly receive a corresponding curved slider block  2369 . In the illustrated embodiment, the anchor bearing  1568  of the slider block  2369  follows a circular-path  2355  around the control point  2350 ; however in other embodiments, other curved paths may be used. This configuration may be further defined by a tilt angle β and a radius of curvature R that are different than in previous embodiments. The objective in this design is to reduce the compression ratio at minimum displacement from the nominal design compression ratio of 10 while keeping the compression ratio near 10 over the normal operating range of the engine. 
     Referring now also to  FIG. 24 , there is illustrated the calculated compression ratio as a function of wobble plate inclination angle θ resulting from use of PCM  2300 . The compression ratio at wobble plate angle θ=10 degrees (corresponding to minimum displacement) has a value of 9.0, but rapidly increases as angle θ increases (corresponding to increasing displacement) to produce a compression ratio value of approximately 10 for the upper portion of the displacement range (e.g., for the upper 50% of the displacement range). 
     For embodiments using a curved slot and corresponding curved-path or circular-path anchor bearing movement, the parameters of the curved slot, namely radius R and angle β, maybe determined mathematically or by other techniques including curve fitting. In one example, a first position of the anchor bearing center necessary to get the desired compression ratio at minimum displacement is determined and a second position of the anchor bearing center necessary to get the desired compression ratio at maximum displacement is determined. Next, knowing that the travel path of the anchor bearing center must be circular, an intermediate point at the mid range of the displacement can be determined to give the desired compression ratio. A circular curve is then fitted through the three points to provide the necessary or desired travel path for the of the anchor bearing center. The sinusoidal error produced by the curved slot mechanism can also be scaled to offset the sinusoidal error produced by the angle of the connecting rod, such that the overall error in compression ratio is largely eliminated. 
     It will be appreciated by those skilled in the art having the benefit of this disclosure that this engine provides a continuously variable displacement while maintaining essentially a constant compression ratio over the range of displacements. It should be understood that the drawings and detailed description herein are to be regarded in an illustrative rather than a restrictive manner, and are not intended to be limiting to the particular forms and examples disclosed. On the contrary, included are any further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments apparent to those of ordinary skill in the art, without departing from the spirit and scope hereof, as defined by the following claims. Thus, it is intended that the following claims be interpreted to embrace all such further modifications, changes, rearrangements, substitutions, alternatives, design choices, and embodiments.