Abstract:
A ring gear variable valve train device is provided for installation on an internal combustion engine having a rotary input crankshaft provided with a cylindrical eccentric journal having a center offset from the rotational axis of the shaft. A connecting rod disposed on the journal is reciprocated by rotary motion of the input shaft. A frame disposed on the input shaft may be controllably varied to vary the lift and timing of the valve. A rocker arm pivotably disposed on the frame is attached to the connecting rod to oscillate a ring gear portion of the rocker arm in response to rotary motion of the input shaft, which ring gear drives a planetary-geared output cam to actuate an engine intake valve to open and close. The teeth of the ring gear and the planetary gear are axially tapered, and a coil spring disposed on the output shaft is operative axially to displace the planetary gear axially of the ring gear to eliminate gear lash therebetween. In a preferred embodiment, some elements are doubled to control the motion of two parallel valves. Preferably, each cylinder in an internal combustion engine is provided with an apparatus in accordance with the present invention.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 60/184,619 filed Feb. 24, 2000. 
    
    
     TECHNICAL FIELD 
     The present invention is related to variable valve train systems for use on internal combustion engines; more particularly, to devices for controllably varying the lift of valves in such engines; and most particularly, to a variable valve train device driven by an input crankshaft and employing a ring and planetary gear arrangement that controllably varies the lift of the intake valves to control engine load. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engine performance has progressed considerably in the past century. Inventions have yielded cleaner exhaust and enhanced durability, fuel efficiency, and power. Systems for varying the lift and timing of intake valves can further refine and enhance the performance of the internal combustion engine by controllably varying the volume of fuel mix supplied to the combustion chambers as a function of engine load and rotational speed. Fuel economy at part load operation can be increased by promoting more thorough combustion, reducing pumping work done by the pistons, which saps energy, deactivating cylinders, and/or by implementing a lean air/fuel ratio scheme. Matching the intake valve closing time more closely to the engine&#39;s need can enhance driveability of a vehicle by improving engine breathing at full engine load. Moreover, if intake and exhaust events can be controlled sufficiently to vary engine load, speed, and fuel dilution over the entire spectrum of required engine operating conditions, a controllable variable valve train can obviate the need for a throttle valve and EGR valve in a gas or diesel internal combustion engine. 
     A range of variable valve train devices and valve timing mechanisms for enhancing engine performance are known in the automotive art, but commercial use of such devices generally has been impractical because of cost, size, and/or operating limitations which have limited their true value and practicality. For example, variable valve timing (VVT) mechanisms, as disclosed in U.S. Pat. No. 5,937,809 issued Aug. 17, 1999 to Pierik et al. and U.S. Pat. No. 6,019,076 issued Feb. 1, 2000 to Pierik et al., the relevant disclosures of both patents being incorporated herein by reference, employ a segmented single shaft crank rocker (SSCR) for operating individual or multiple engine valves by engaging a linkage with a rotary eccentric, preferably a rotary cam, to drive an oscillatable rocker cam. The disclosed SSCR mechanism has four moving components (two arms, a rocker, and a cam) and thus can be expensive to manufacture and subject to wear and premature failure at a plurality of joints. In addition, in typical prior art VVTs, springs are required to maintain contact between an input cam and a roller follower, which springs tend to increase friction and limit maximum operating speed. 
     It is a principal object of the present invention to provide total authority over intake valve lift, open valve duration, and phasing of intake and exhaust events relative to the motion of an engine&#39;s pistons. 
     It is a further object of the invention to improve peak engine torque and fuel economy. 
     It is a still further object of the invention to controllably vary the engine load directly at the engine cylinder, thereby potentially eliminating the need for prior art throttle body and idle air control devices. 
     It is a still further object of the invention to reduce the size and number of components of the device in comparison with prior art variable valve train devices. 
     It is a still further object of the invention to provide a variable valve train device which can be economically mass-produced for commercial use in vehicles powered by internal combustion engines. 
     SUMMARY OF THE INVENTION 
     Briefly described, a ring gear variable valve train device in accordance with the invention is provided for installation on an internal combustion engine having a rotary input shaft positioned substantially as is a camshaft in a conventional engine. The basic mode of operation is similar to that disclosed in the patents incorporated by reference, wherein a variable valve train apparatus is mounted on an input shaft of an engine, such as a camshaft, and is pivotable about the shaft to alter the timing and lift of a valve opening upon an engine&#39;s cylinder. In the present invention, the input shaft, rather than being a conventional camshaft and having an eccentric cam lobe, is provided with a cylindrical eccentric journal having a center offset from the rotational axis of the shaft such that a connecting rod may be disposed conventionally on the journal for deriving reciprocating motion from the rotary motion of the input shaft. A close-fitting frame is rotationally disposed on the camshaft such that the input shaft and journal are free to rotate within the frame. The frame is pivotably connected to an auxiliary control shaft such that the angular orientation of the frame with respect to the input shaft may be controllably varied to vary the lift and timing of the valve. A rocker arm is pivotably disposed on the frame and is attached to the connecting rod to oscillate an arcuate ring gear portion of the rocker arm in response to rotary motion of the input shaft. The ring gear portion meshes with and drives a planetary-geared output cam rotatably disposed on the input shaft to actuate the stem of an engine intake valve to open and then to close the valve conventionally against a valve spring. Preferably, the teeth of the ring gear and the planetary gear are axially tapered in opposite directions, such that a coil spring disposed in compression on the output shaft is operative axially against a side face of the planetary gear to displace the planetary gear axially until all lash is eliminated between the two gears. In a preferred embodiment for controlling the motion of two parallel valves at a single engine cylinder, the elements of the frame, ring gear portion, and output cam are doubled symmetrically about the input shaft journal, and a dual rocker arm cooperates with both ring gear portions for simultaneous and identical actuation thereof. Rotation of the frame about the input shaft serves to alter the timing of the valve opening with respect to the associated piston, the height of the valve lift, and the duration of opening. Preferably, each cylinder in an internal combustion engine is provided with an individual device in accordance with the present invention. The disclosed invention is thus capable of controlling engine load and peak engine torque directly at the cylinder head without resort to a conventional throttle and exhaust gas recirculation (EGR) valve. The invention is also useful for variably controlling the valves of other apparatus incorporating pintle-type valves, for example, compressors for air and other gases. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which: 
     FIG. 1 is a semi-schematic end view of a prior art VVT mechanism directly actuating a single engine valve, showing the mechanism in valve-closed position; 
     FIG. 2 is a view like FIG. 1, showing the mechanism in valve-open position; 
     FIG. 3 is a semi-schematic end view of a VVT mechanism in accordance with the invention directly actuating a single engine valve, showing the mechanism in a valve-closed position, comparable to the view of the prior art VVT mechanism shown in FIG. 1; 
     FIG. 4 is a view like FIG. 3, showing the mechanism in valve-open position, comparable to the view of the prior art VVT mechanism shown in FIG. 2; 
     FIG. 5 is a view like that shown in FIG. 3, showing an alternative and preferred embodiment of an oscillable partial cam; 
     FIG. 6 is a side view of the oscillable partial cam shown in FIG. 5; 
     FIG. 6 a  is a side view of a second embodiment of a partial cam; 
     FIG. 6 b  is an isometric view of a second embodiment of a crankshaft for receiving either of the cam embodiments shown in FIGS. 6 and 6 a;    
     FIG. 7 is an isometric front view of an exemplary embodiment of a variable valve train device in accordance with the present invention, showing the device directly actuating a single engine valve, in the valve-open position, some elements being removed for clarity; 
     FIG. 8 is an isometric front view of the an exemplary device similar to FIG. 7, the device directly actuating two parallel engine valves, in the valve-closed position, some elements being removed for clarity; and 
     FIG. 9 is an isometric front view like that shown in FIG. 8 of an entire VVT device in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The novelty and benefits of a ring gear variable valve train device in accordance with the invention may be better appreciated by first considering an analogous prior art variable valve train device. 
     Referring to FIG. 1, numeral  10  generally indicates a prior art embodiment of a VVT device which is operable to vary valve timing and lift in an operating engine  12  having a valve  14  actuated through a direct acting follower  16 . VVT device  10  includes a rotary input cam lobe  18  carried, for example, on a camshaft  19  and rotatable on a rotational primary axis  20 . 
     Device  10  further includes a control frame  22  including a carrier link or lever  23  which is pivotable about the primary axis  20 . Frame  22  is externally drivable by teeth  24  that are engaged by mating teeth  26  formed on a control gear  28  that may be oscillated about an axis  30  parallel to the primary axis. If desired, the control gear  28  could be replaced by a cam or linkage for driving the control frame  22 , substantially as is disclosed in, for example, the incorporated reference U.S. Pat. No. 6,019,076. A primary lever or rocker  32  is pivotably connected at one end with frame  22  at a pivot axis  34  spaced from the primary axis  20 . Rocker  32  has a distal end  36  and an eccentric follower  38  in the form of a roller or other suitable means for engaging cam lobe  18  and acting as a cam follower. 
     A secondary lever  40  has one end mounted on and pivotable about the primary axis  20 . Secondary lever  40  has a distal end  44  spaced from the axis  20  and operatively connected with the distal end  36  of rocker  32 . This operative connection is made by link  46  pivotably interconnecting the two distal ends  44 , 36 . Secondary lever  40  also includes at said one end an oscillating cam  48  having a base circle portion  50  centered on the primary axis  20  and a valve lift portion  52  extending eccentrically outward from the base circle portion. Cam  48  engages the cam follower  16  in a reciprocating motion directly acting upon valve  14  for opening and closing the valve. 
     Referring to FIGS. 1 and 2, in operation, the rotary cam lobe  18  is driven in timed relation with the engine crankshaft by any suitable means, such as a camshaft drive. The control member  22  is positioned in a predetermined orientation which is angularly adjustable to vary valve lift and timing but remains fixed when no change is desired. When the eccentric portion of the cam lobe  18  engages the roller follower  38 , the rocker  32  is pivoted outward (up) about the pivot axis  34  located on the control member  22 . This raises link  46 , causing the secondary lever  40  to rotate clockwise about the primary axis  20  to slide or rock the oscillating cam  48  against the direct acting follower  16 . 
     If the control member  22  is in a first position as shown in FIGS. 1 and 2, the clockwise lever motion causes the valve lift portion  52  of the oscillating cam  48  to actuate the follower  16  downward, opening the valve  14  to its full open position as shown in FIG.  2 . Upon further rotation of the rotary cam  18 , the roller follower  38  rides back down the cam  18  to its base circle. Secondary lever  40  with oscillating cam  48  pivots counterclockwise, allowing valve  14  to close as the follower  16  is again engaged by the oscillating cam base circle portion  50 . 
     To reduce valve lift and valve open time, the control member  22  is rotated counterclockwise, by rotation of the control gear  28 , toward a second position, not shown, of the control member, angularly displaced from the first position. In the second position, the oscillating motion of the cam  48  merely slides its base circle portion  50  against the follower  16  so that the valve remains closed when the device  10  oscillates cam  48 . In intermediate positions of the control member  22 , the valve will be partially opened for a lesser period of time than with the full opening movement, the proportion of full valve opening depending upon the closeness of the control member to the first (full opening) position. 
     Referring to FIGS. 3 through 7, a first exemplary embodiment  110  of a ring gear variable valve train device is shown. Elements of device  110  analogous to elements in prior art device  10  are numbered the same but prefaced with a 1; for example, the prior art rocker is  32 , and the improved rocker is  132 . 
     Numeral  110  generally indicates an embodiment of a VVT device in accordance with the invention which is operable to vary valve timing and lift in an operating engine  12  having a valve  14  actuated through a roller finger follower  116 . VVT device  110  includes an eccentric rotary input crank journal  60  carried, for example, on an input crankshaft  62  and rotatable on a rotational primary axis  120 . Journal  60  is conventionally cylindrical and has an axis  64  spaced apart from primary axis  120 . 
     Device  110  further includes a control frame  122  including a carrier link or lever  123  which is pivotable about the primary axis  120 . Frame  122  is pivotably disposed on input crankshaft  62  and is rotationally drivable by a control linkage mechanism shown generally as  66 , substantially as is fully disclosed in incorporated reference U.S. Pat. No. 6,019,076. Alternatively, frame  122  may be equipped and rotationally driven by mating teeth as described above for prior art device  10 . 
     A primary lever or rocker  132  is pivotably connected at one end with frame  122  at a pivot axis  134  spaced from the primary axis  120 . Rocker  132  has a distal end  136  and is pivotably connected at an intermediate location to a connecting rod  68  rotationally disposed on journal  60 . It is a specific advantage of a VVT device in accordance with the invention that the rocker, which is common to many VVT device schemes, is positively connected to the eccentric journal through 360° of input shaft rotation and therefore requires no springs, as are required to maintain contact between a cam follower roller and a rotating cam in prior art VVT devices. Distal end  136  includes a portion of a ring gear  70  having teeth  72  extending inwards generally towards secondary axis  134 . Ring gear  70  is thus oscillatable with rocker  132  about axis  134 . An oscillatable cam  148  is rotatably disposed on input crankshaft  62  radially inward of ring gear portion  70  and has a base circle portion  150  centered on the primary axis  120  and a valve lift portion  152  extending eccentrically outward from the base circle portion. Cam  148  is also a planetary gear and is provided with outwardly-extending gear teeth  74  for engaging the ring gear  70  in a reciprocating motion and therefore directly acting upon follower  16  for opening and closing valve  14 . 
     In operation, the input crankshaft  62  is driven in timed relation with the engine crankshaft by any suitable means, such as a conventional camshaft drive. The control frame  122  is positioned in a predetermined orientation which is angularly adjustable to vary valve lift and timing but remains fixed when no change is desired. As the crank journal  60  of the input crankshaft  60  drives connecting rod  68  outwards, the rocker  132  is pivoted outward (up) about the pivot axis  134  located on the control frame  122 . This raises ring gear  70 , causing the oscillatable cam  148  to rotate clockwise about the primary axis  120  to slide or rock the oscillating cam  148  against the direct acting follower  16 . 
     If the control frame  122  is in a first position as shown, for example, in FIGS. 4,  5 , and  7 , the clockwise cam motion causes the valve lift portion  152  of the oscillating cam  148  to actuate the follower  116  downward, opening the valve  14  from its seat  15  to its full open position as shown in FIG.  4 . Upon further rotation of the input crankshaft  62 , connecting rod  68  is retracted towards primary axis  120 . Rocker  132  and ring gear portion  70  urge oscillating cam  148  to pivot counterclockwise, allowing valve  14  to close against seat  15  as the follower  116  is again engaged by the oscillating cam base circle portion  150 . 
     Referring to FIGS. 5 and 6, a preferred embodiment  148 ′ of oscillating cam  148  is shown. In a multiple cylinder engine having a plurality of journals  60 , a problem arises as to how to install a plurality of cams  148 . One solution employed with prior art VVT devices mountable on camshafts has been to segment the camshaft and to key or otherwise assemble the segments together after installation of each VVT device on each segment. This solution is expensive and cumbersome. Improved oscillating cam  148 ′ solves this problem by being formed in an open U shape having a diameter  149  equal to the outside diameter of input crankshaft  62 , allowing the cam to be installed on the input shaft from a radial rather than axial direction. Because the cam is captured on the crankshaft by the ring gear, and because all radial forces exerted on the cam during operation are inward over a central bearing angle of no more than 180°, the “missing” portion of cam  148  bears no load and may be omitted, as shown in FIG.  5 . If desired, for example, to promote retention of oil on the cam bearing surfaces, a filler block  151 , readily formed as by molding of any suitable plastic or metal, may be provided and installed on cam  148 ′ as shown in FIG. 6 after the cam is mounted on the crankshaft. Thus, a plurality of VVT devices  110  in accordance with the invention may be readily installed on a one-piece input shaft having a plurality of crank journals for operating the valves of a multi-cylinder engine. 
     If the radial forces exerted on a cam extend over a central angle greater than 180°, preventing the elimination of a portion as large as the 180° portion as shown in FIG.  6  and represented by filler block  151 , a smaller portion, equivalent to a wide slot  153 , still may be eliminated, as shown in cam  148 ″ in FIG. 6 a.  Such a cam also may be radially installed onto a one-piece shaft  62 ′, as shown in FIG. 6 b,  which is provided with a pair of flats  155  outboard of any operational bearing surface, flats  155  being diametrically separated by a distance no greater than the width of slot  153 . After the cam is centered on the shaft  62 ′ it may then be slid axially to its final location  157 . 
     To reduce and control valve lift and valve open time, the control frame  122  is rotated counterclockwise, analogous to the actuation described hereinabove for prior art VVT device  10 . 
     Referring to FIGS. 7,  8 , and  9 , a preferred embodiment  110 ′ of the invention is adapted for actuating two valves  14 , 14 ′ acting in parallel. 
     In FIG. 7, elements for actuating the first valve are omitted to reveal the crank journal  60  and connecting rod  68  as discussed hereinabove. Wrist pin  69  connecting rocker  132  to connecting rod  68  is extended as shown, as is pin  71  connecting rocker  132  to control frame  122 , permitting substitution of a dual rocker  132 ′ straddling connecting rod  68 , as shown in FIGS. 8 and 9, and first and second ring gear portions  70 , 70 ′ for driving first and second oscillatable cams  148 , 148 ′ for actuating first and second roller finger followers  116 , 116 ′ to open and close first and second valves  14 , 14 ′. 
     In a presently preferred embodiment, an axial passage in input crankshaft  62  is provided as a pressurized oil reservoir, and a network of oil passages is provided in the associated pivoting, reciprocating, and oscillating components in conventional fashion for lubricating force-loaded surfaces. 
     Preferably, the teeth  72  on ring gears  70 , 70 ′ are axially slightly tapered away from crank journal  60  such that the valleys between the teeth are slightly more open on the side away from the crank journal. Teeth  74  on cams  148 , 148 ′ are slightly tapered in the opposite direction. The tapered teeth may be formed on constant pitch circles or on conical pitch circles of conical gears, and teeth of at least one of a pair of mating gears may be crowned to control loading and wear. Axial clearance is provided on the side of each cam abutting the journal and each cam is axially extended on each side away from the journal such that axial compression springs  76 , 76 ′, which are constrained at first ends  78 , 78 ′ by bearing caps (not shown) for input shaft  62 , biasingly urge cams  148 , 148 ′, respectively, axially until the respective teeth of the cams and ring gears are fully engaged axially and all lash between the gears is thus eliminated. Preferably, the taper angles of the teeth and/or the conical pitch circles of the conical gears are made smaller than the friction angle to avoid developing axial gear separation forces greater than the urging forces of the springs. Such a scheme for eliminating gear lash is disclosed with respect to a camshaft phaser in U.S. Pat. No. 5,680,836 issued Oct. 28, 1997 to Pierik, the relevant disclosure of which is herein incorporated by reference. 
     It will be apparent to one of ordinary skill in the art that the ring gear variable valve train device  110 , as illustrated and described herein, and many of its features, could take various forms as applied to other applications and the like. If desired, a device in accordance with the invention could also be applied to the actuation of engine exhaust valves or other appropriate applications and the like. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.