Abstract:
The timing or phasing of port openings and closings during operation of an opposed-piston engine is varied in response to changing engine speeds and loads by changing crankshaft phasing.

Description:
RELATED APPLICATIONS 
       [0001]    This Application contains subject matter related to the subject matter of commonly-assigned U.S. application Ser. No. 13/385,539, filed Feb. 23, 2012 for “Dual Crankshaft, Opposed-Piston Engine Constructions.” 
     
    
     BACKGROUND 
       [0002]    The subject matter relates to a dual-crankshaft, opposed-piston engine equipped for variable crankshaft phasing in order to change port timing and/or port phasing in response to changing engine conditions. Particularly, the subject matter relates to an opposed-piston engine with two crankshafts coupled by a gear train in which a phasing mechanism coupled to at least one crankshaft varies port timing in the engine by changing the rotational phasing between the crankshafts, an operation referred to as “crank phasing”. 
         [0003]    In an opposed-piston engine, a pair of pistons is disposed for opposed sliding motion in the bore of at least one ported cylinder. Each cylinder has exhaust and intake ports, and the cylinders are juxtaposed and oriented with exhaust and intake ports mutually aligned. Each port is constituted of one or more arrays or sequences of openings disposed circumferentially in the cylinder wall near a respective end of the cylinder. The engine includes two crankshafts rotatably mounted at respective exhaust ends and intake ends of the cylinders, and each piston is coupled to a respective one of the two crankshafts. The reciprocal movements of the pistons control the operations of the ports. In this regard, each port is located at a fixed position where it is opened and closed by a respective piston at predetermined times during each cycle of engine operation. Those pistons that control exhaust port operation are termed “exhaust pistons” and those that control intake port operation are called “intake pistons”. 
         [0004]    Typically in opposed-piston engines the exhaust piston is phased in relation to the intake piston so as to enhance exhaust gas purging and scavenging during the later portion of the power stroke. 
         [0005]    Piston phasing is normally fixed by positioning the exhaust piston connecting rod at some advanced angle on the crankshaft to which it is connected (“the exhaust crankshaft”) ahead of the intake piston connecting rod position on the crankshaft to which it is connected (“the intake crankshaft”). In such a configuration, as the pistons move away from top center (TC) positions after combustion, both ports (intake and exhaust) are closed by their respective pistons. As the pistons approach bottom center (BC) positions the exhaust port is opened first to begin exhaust gas purging and then the intake port opens some preset time later to allow pressurized air into the cylinder chamber to provide scavenging of the remaining exhaust gasses. Then, as the pistons reverse direction, the exhaust port closes first, allowing pressurized air into the cylinder chamber through the still open intake port until it too closes and a compression cycle begins. 
         [0006]    It is desirable to be able to vary the timing or phasing of port openings and closings during engine operation in order to dynamically adapt the time that a port remains open to changing speeds and loads that occur during engine operation. 
         [0007]    It is desirable to be able to vary the timing or phasing of port openings and closings during engine operation in order to maintain optimal blowdown, uniflow scavenging, and/or supercharger operations in the face of changing engine operating conditions. 
         [0008]    Some opposed-piston engine designs do not utilize the pistons for port control. Instead, these engines are equipped with reciprocating sleeves that slide axially along the cylinder sidewall to open and close ports. Such arrangements are termed “sleeve valves” and port timing depends upon control of sleeve valve position and movement. Port phasing in sleeve valve engines presents very complicated control challenges that have to provide for timing the movements of crankshafts, pistons, and valve sleeves. Moreover, an important advantage of opposed-piston engines is the relative simplicity of engine construction: an opposed-piston engine dispenses with cylinder heads and many moving parts associated with valves and valve train mechanisms of single-piston engines. Much of this simplification is surrendered by the sleeve valve constructions. 
         [0009]    It is therefore desirable to be able to control port phasing in an opposed-piston engine by relying on piston phasing to dynamically adapt port opening and closing times to changing speeds and loads that occur during engine operation. The objective is to secure the benefits realized by adapting port operation to varying engine operating conditions without sacrificing the simplifications achieved with opposed-piston constructions. 
       SUMMARY 
       [0010]    Port phasing in an opposed-piston engine with two crankshafts is varied to accommodate specific engine loads or operating parameters during engine operation. Preferably, port phasing is controlled by varying the crank angle of at least one crankshaft, where the crank angle is an angle of rotation of the crankshaft with respect to the angle which places a piston connected to the crankshaft at a specific point in its slidable movement. For example, the specific point could be the top center (TC) position of the piston. 
         [0011]    In some aspects, port phasing is enabled by equipping the engine with a phasing mechanism coupled to at least one crankshaft so as to vary the crank angle of the crankshaft, which changes rotational phasing between the crankshafts and a shift in the positions of pistons coupled to the crankshaft relative to the pistons not coupled to the crankshaft. 
         [0012]    In some aspects, an opposed-piston engine with two crankshafts has at least one of the crankshafts equipped with an electronically-controlled, hydraulically actuated movable vane structure for adjusting the rotational position of the crankshaft based upon engine operating parameters so as to thereby vary piston phasing. 
         [0013]    In some aspects, an electronically-controlled, hydraulically-actuated crankshaft phasing mechanism includes a pair of coaxially-disposed vane elements, one fixed to one of the crankshafts and the other mounted to the crankshaft&#39;s output gear. Hydraulic fluid is used to control the relative positions of the vane elements and thus to control the phasing between the crankshafts. Hydraulic pressure between the elements&#39; vanes is electronically controlled to obtain a desired rotational relationship between the two crankshafts, thereby establishing a phase relationship between the opposing pistons. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The below-described drawings are meant to illustrate principles and examples discussed in the following description; they are not necessarily to scale. 
           [0015]      FIG. 1A  is an end view of an opposed-piston engine equipped with an electronically controlled, hydraulically-actuated crank phasing mechanism. 
           [0016]      FIG. 1B  is the end view of the engine of  FIG. 1A , with a cover removed to show a gear train coupling two crankshafts and an end plate removed to show details of a crank phasing mechanism. 
           [0017]      FIG. 1C  is a side elevation view of an arrangement of cylinders, pistons, and crankshafts for an opposed-piston engine equipped with an electronically controlled, hydraulically-actuated crank phasing mechanism such as that shown in  FIG. 1A . 
           [0018]      FIG. 2  is an exploded view of a hydraulically-actuated crank phasing mechanism with a coaxial vane assembly. 
           [0019]      FIG. 3A  is an enlarged, partially schematic side view of the end of a crankshaft showing drillings that form part of a fluid transport system. 
           [0020]      FIG. 3B  is an elevation view of the end of the crankshaft. 
           [0021]      FIG. 4A  is a front end view of an inner member of the coaxial vane assembly of  FIG. 2  showing fluid flow paths. 
           [0022]      FIG. 4B  is a rear end view of the inner member depicting associated fluid flow paths. 
           [0023]      FIGS. 5A ,  5 B,  5 C are perspective section views of a portion of the end of the crankshaft of  FIG. 4A  showing an electronically-controlled valve for supplying hydraulic fluid to actuate the crank phasing mechanism of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]      FIGS. 1A ,  1 B and  1 C show details of an opposed-piston engine  10 . Although the figures show the engine  10  in an essentially vertical orientation, this is for the sake of illustration only; in other aspects the engine could be disposed in other orientations than the vertical one shown. The engine  10  includes an interlinked crankshaft system including two rotatably-mounted crankshafts  12  and  14  disposed in a parallel spaced-apart configuration and a gear train assembly  16  linking the crankshafts and coupling them to an output shaft  18 . Preferably, the crankshafts are co-rotating, although a counter-rotating arrangement can be provided by deletion of one gear from (or addition of another to) the gear train  16 . 
         [0025]    As the figures illustrate, the crankshaft system further includes an electronically-controlled, hydraulically-actuated crank phasing mechanism  20  in operable engagement with at least one of the crankshafts  12 ,  14 . In some aspects the crank phasing mechanism  20  is operably coupled between one of the crankshafts and its associated gear in the gear train assembly: preferably, but not necessarily, the crank phasing mechanism is in operable engagement with the exhaust crankshaft  12  and its associated gear  16   a.    
         [0026]      FIG. 1C  is a schematic representation of an arrangement of cylinders, pistons, and crankshafts in an opposed-piston engine equipped with an electronically controlled, hydraulically-actuated crank phasing mechanism such as that shown in  FIG. 1A . The figure shows a three-cylinder arrangement, although this is not intended to be limiting; in fact, an electronically controlled, hydraulically-actuated phasing mechanism can be applied to opposed-piston engines with fewer, or more, cylinders. As per the example of  FIG. 1C , the opposed-piston engine of  FIGS. 1A and 1B  includes cylinders  30  (or sleeves or liners), each including exhaust and intake ports  32  and  34 . Preferably, the cylinders are fixedly mounted to an engine frame or block (not shown). In this engine construction, a pair of pistons  36 ,  38  is disposed for opposing reciprocal movement in the bore of each cylinder  30 . Each piston  36  is coupled to a respective crank journal  13  of the crankshaft  12  by a connecting rod assembly  37 ; each piston  38  is coupled to a respective crank journal  15  of the crankshaft  14  by a connecting rod assembly  39 . The opening and closing times of the ports  32  and  34  are controlled by opposing movements of the pistons  36  and  37 , respectively. 
         [0027]    With reference to  FIG. 1C , the crank phasing mechanism  20  is operated to adjust the rotational angle of the crankshaft  12  in response to engine operating conditions. Adjustment of the rotational angle of the crankshaft  12  adjusts the phase angle between the crankshafts  12  and  14 . In turn, adjusting the phase angle between the crankshafts  12  and  14  adjusts the phase between the pistons  36  and  38 , which enables variability of port phasing and port timing in the opposed-piston engine  10 . The phasing construction is not necessarily limited to one crankshaft in general or in particular; either or both crankshafts can be equipped with a crank phasing mechanism. Further, those skilled in the art will realize that a phasing mechanism can be provided for one or more of the elements of the interlinked crankshaft system. 
         [0028]      FIG. 2  is an exploded view of a preferred crank phasing mechanism  20 , with which various elements of the mechanism are identified. Generally, the crank phasing mechanism comprises a coaxial vane assembly  100  in which an inner vane element  110  mounted to an end of the crankshaft  12  is positioned within and in coaxial alignment with an annular outer vane element  120  mounted to the gear train element  16   a  that couples the rotary movement of the crankshaft  12  to the gear train  16 . The inner vane element  110  is attached to the end  101  of the crankshaft  12  with threaded bolts  130 , with an end closing plate  144  secured therebetween. The annular outer vane element  120 , hard mounted to the crankshaft gear  16   a,  slides over the inner vane element  110  to provide six chambers  121 , one for each vane  111 , to receive pressurized hydraulic fluid (oil, for example). Torque from the crankshaft  12  is transferred from the vanes  111  to the vanes  122  of the outer vane element  120  by compressing the pressurized hydraulic fluid in the chambers  121 , between the two sets of vanes. Polymer apex seals  131  are seated in slots  132  in the outer edges of the inner vanes  111  and polymer apex seals  133  are seated in slots  135  in the edges of the outer vanes  122 . These seals prevent seepage of pressurized hydraulic fluid from one side of each of the chambers  121  to the other side, which guarantees integrity of respective pressures acting upon the sides of the vanes. Threaded bolts  140  through front and rear closing plates  142  and  144  keep the pressurized hydraulic fluid captive within the coaxial vane assembly  100 , thus maintaining hydraulic pressures within the chambers  121 . The plates  142  and  144 , which maintain these hydraulic fluid pressures without significant distortion, are sealed on their peripheries to prevent leakage of pressurized hydraulic fluid from the coaxial vane assembly  100 . 
         [0029]    With further reference to  FIG. 2 , changing the hydraulic fluid pressures acting against sides of the vanes causes relative movement between the inner vane element  110  and the outer element  120 . This is enabled by a fluid transport system that conducts pressurized hydraulic fluid to the chambers  121  and changes fluid pressures as needed to cause relative clockwise (CW) or counterclockwise (CCW) movement between the inner and outer vane elements  110  and  120 . Relative movement between the inner and outer vane elements advances or retards the rotational position of the crankshaft  12  with respect to the crankshaft  14 . 
         [0030]    One example of such a fluid transport system includes a fluid distribution network with a control valve capable of: 1. enabling pressurized hydraulic fluid to flow in the network, and 2. changing fluid pressures in branches of the network in response to changing engine conditions. With reference again to  FIG. 2 , the fluid distribution network includes a fluid supply ring  150  cooperating with drilled passages in the end  101  of the crankshaft  12 . In this regard, the ring  150  has an inner annular surface in which annular grooves  151  and  152  are formed. Drilled radial passages  153  and  155  extend through the ring  150  to the annular grooves  151  and  152 , respectively. With reference to  FIGS. 2 ,  3 A, and  3 B the end  101  of the crankshaft  12  includes a circumferential array of radial passages  161  and at least one additional radial passage  164  that is axially displaced from the circumferential array. Each of the radial passages  161  intersects a respective axially-aligned passage  162 , and the radial passage  164  intersects a central axial passage  165 . The ring  150  is fixed to a stationary engine support element such as an engine casing (not shown) at a position where it is maintained in coaxial alignment with the end  101  of the crankshaft  12 . At this position, the ring encircles the end  101 , with the groove  151  aligned with the radial passages  161  and the groove  152  aligned with the at least one radial passage  162 . 
         [0031]    Referring now to  FIGS. 2 ,  4 A, and  4 B the inner vane element  110  has a first end surface  170 , which is not visible in  FIG. 2 , and an opposing second end surface  180  which is visible in  FIG. 2 . As best seen in  FIG. 4A , the first end surface  170  has a circular groove  172  with inner radial grooves  171  and outwardly-projecting grooves  173 . A central axial passage  175  through the inner vane element  110  extends from the first end surface  170  to the second end surface  180 . As best seen in  FIG. 4B , the second end surface  180  has a circular groove  182  with outwardly-projecting grooves  183 . One or more diametric grooves run from the central axial drilling  175  to the circular groove  182 . When the coaxial vane assembly  100  is assembled, the first end surface  170  is positioned against and flush with the end face of the crankshaft  12 , the inner radial grooves are aligned with the passages  162  of the crankshaft  12 , and the central axial drilling  175  is aligned with the central axial passage  165  in the crankshaft  12 . Therefore, while the crankshaft  12  rotates, the pressurized hydraulic fluid can be transported into the coaxial vane assembly  100  via a first fluid network branch  153 / 151 / 161 / 162 / 171 / 172 / 173  and via a second fluid network branch  155 / 152 / 164 / 165 / 175 / 184 / 182 / 183 . Note that when the coaxial vane assembly is assembled, and the inner vane member  110  is positioned within the outer vane member  120 , the seals  131  and  133  mutually isolate the chambers  121  and further subdivide each chamber  121  into two mutually isolated, parallel, elongate subchambers. One subchamber is fed through one fluid network branch from the first end surface  170  by a respective one of the outwardly projecting grooves  173 ; the other subchamber is fed through the other fluid network branch from the second end surface  180  by a respective one of the outwardly projecting grooves  183 . 
         [0032]    The direction of relative movement between the inner and outer vane members  110 ,  120  is determined by a hydraulic fluid pressure differential between the annular grooves  151 ,  152  in the fluid supply ring  150 . When the fluid pressure on one side of the vanes is greater than the fluid pressure on the opposite side, the lower pressure hydraulic fluid will tend to move out of its subchamber space and relative movement will be in the direction of the lower pressure. Control of the hydraulic pressure in this regard is provided by a multistate valve under control of an engine control unit (ECU). 
         [0033]    With reference to  FIGS. 5A-5C , an electrically controlled and actuated multi-state valve  200  is provided to control the flow of pressurized hydraulic fluid in the coaxial vane assembly  100  via the fluid control ring  150 . In some aspects, the valve  200  operates in response to signals generated by an ECU  300 ; that is to say, the ECU  300  sets the valve  200  to a state determined by the ECU in response to engine operating parameters. A representative valve for this purpose is a standard 4/3 directional control valve, (4 line, 3 direction valve). Hydraulic fluid is provided to the valve  200  from a fluid source  202  via input (H.P.) and return (L.P.) lines. The valve has two output connections  204  and  205  connected to the passages  153  and  155 , respectively, of the fluid supply ring  150 . 
         [0034]      FIGS. 5A ,  5 B and  5 C show such the valve  200  in respective ones of three possible states.  FIG. 5A  shows the valve  200  in a center position where both of the annular grooves  151 ,  152  in the fluid supply ring  150  are disconnected by the valve  200  from the fluid source  202  so that the vanes are retained in a stationary position last selected by the ECU  300 .  FIG. 5B  shows the valve  200  set to a state in which it connects the return (L.P.) line to the annular ring  152  and the input (H.P.) line to the annular ring  151 . This state increases the fluid pressure on the sides of the vanes in fluid communication with first fluid network branch while decreasing the fluid pressure on the sides of the vanes in fluid communication with the second fluid network branch so that the vanes move (CW, for example) towards the low pressure sides of the chambers.  FIG. 5C  shows the valve  200  set to a state in which it connects the return (L.P.) line to the annular ring  151  and the input (H.P.) line to the annular ring  152 . This state decreases the fluid pressure on the sides of the vanes in fluid communication with first fluid network branch while increasing the fluid pressure on the sides of the vanes in fluid communication with the second fluid network branch so that the vanes move (CCW, for example) towards the low pressure sides of the chambers. 
         [0035]    The ECU  300  (or another controller) regulates port timing and/or port phasing of the opposed-piston engine by controlling the operation of the crank phasing mechanism. Regulation, or control, of port phasing is enabled by the ECU&#39;s control of the operation of the valve  200 . The ECU  300  receives signals that represent values of engine operating parameters. For example the ECU  300  may receive signals representing engine speed, engine load, current crank angle of one or each of the crankshafts, charge air flow and composition, and, possibly, additional data. The ECU processes the signals and subjects the values to an algorithm or procedure for determining a port operating point, and then sets the valve  200  to the second or the third state ( FIG. 5B  or  FIG. 5C ) to change the crankshaft phasing to a set point value that achieves the port operating point. Once the crank phasing set point is achieved, the ECU  300  resets the valve  200  to the first state, which maintains the port operating point until a new one is determined. 
         [0036]    An additional benefit of the crank phasing mechanism is found in the fact that since the total pressures exerted upon the vanes are constant, an automatic damping effect is present at all times. This means that any forces acting upon the vanes due to torsional vibration and/or gear backlash will automatically be mitigated by this damping effect. 
         [0037]    Although principles of crankshaft phasing to control port timing have been described with reference to presently preferred embodiments, it should be understood that various modifications can be made without departing from the spirit of the described principles. Accordingly, any patent protection accorded to the principles is limited only by the following claims.