Abstract:
An engine braking method includes the steps of engaging a cam roller( 235 ) of an internal combustion engine with an engine power cam( 230 ) for an engine power operation; disengaging the cam roller( 235 ) from the engine power cam( 230 ); losing a motion from the engine power cam( 230 ) and a motion of an engine valve( 301 ) associated with the motion from the engine power cam( 230 ); engaging the cam roller( 235 ) with an engine braking cam( 2302 ) for an engine braking operation; transmitting a motion from the engine braking cam( 2302 ) to the engine valve( 301 ); and generating an engine valve motion for the engine braking operation. An engine braking system includes an engine power cam( 230 ) of an internal combustion engine; an engine braking cam( 2302 ) of the internal combustion engine; and a cam roller( 235 ) that is designed to engage with the engine power cam( 230 ) for an engine power operation and to engage with the engine braking cam( 2302 ) for an engine braking operation.

Description:
FIELD OF THE INVENTION 
       [0001]    The present application relates to engine braking, particularly to an engine braking method and system. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the prior art, conventional valve actuation for a vehicle engine is well known and its application has more than one hundred years of history. It uses a conventional valve actuator to control engine valve motion, including the normal exhaust valve motion and normal intake valve motion, for engine power operation. However, due to the additional requirements on engine emission and engine braking, more and more engines need to produce an auxiliary engine valve event, such as an exhaust gas recirculation event or an engine braking event, in addition to the normal engine valve event. The engine brake has gradually become the must-have device for the heavy-duty commercial vehicle engines. 
         [0003]    The engine braking technology is also well known. During engine braking, the engine is temporarily converted to an air compressor, and in the conversion process, fuel supply is cut off, and the exhaust valve is opened near the end of the compression stroke of the engine piston, thereby allowing the compressed gases (being air during braking) to be released. The energy absorbed by the compressed gases during the compression stroke cannot be returned to the engine piston at the subsequent expansion stroke, but is dissipated by the engine exhaust and cooling systems, which results in an effective engine braking and the slow-down of the vehicle. 
         [0004]    An example of engine brake devices in the prior art is disclosed by Cummins in U.S. Pat. No. 3,220,392. The invention utilizes a hydraulic linkage to transfer the motion from the nearby injection cam or exhaust cam to an engine valve, creating a compression release braking valve event in addition to the conventional engine valve event. The invention produces only a compression-release braking in each four-stroke engine cycle. 
         [0005]    U.S. Pat. No. 4,572,114 (1986) discloses two-stroke engine braking devices and methods in a four-stroke engine. Thus, for each two-stroke or each crankshaft rotation of the engine, one engine braking is generated. Theoretically, the braking power from two compression releases of the two-stroke braking in each engine four-stroke cycle would be twice that of conventional four-stroke braking power. However, since the invention uses two hydraulic actuation systems with great structural complexity, there is no practical application. 
         [0006]    U.S. Pat. No. 5,537,976 (1996) discloses another two-stroke engine braking apparatus and method using a cam drive, hydraulic linkage, high-speed solenoid valve and electronic control means, to achieve the valve motion. Because within each cycle, the solenoid valve is required to open at least once, the solenoid valve has a particularly high reliability and durability requirements. Plus other issues with the hydraulically actuation, such as valve seating velocity control, engine cold start, etc., the invention has no real application. 
         [0007]    U.S. Pat. No. 6,293,248 (2001) discloses yet another two-stroke engine braking apparatus and method. In order to achieve the two-stroke engine braking on a four-stroke engine, in addition to the four cams, four rocker arms must be used: two exhaust rocker arms (one for firing and the other for braking) and two intake rocker arms (one for firing and the other for braking). The structure and the control are complex. Also, hydraulic actuation is used to open the engine valves. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to provide an engine braking method and system to solve the technical problems in the prior art, such as complex structure and control, poor reliability and durability of hydraulic valve actuation, and limited applications. The mechanical loading (through solid contact) of the present invention also eliminates the failure modes of hydraulic loading (through liquid volume), such as high oil pressure, high leakage and high compliance. 
         [0009]    According to one aspect of the present invention, a new engine braking method comprises the following steps:
       1. engaging a cam roller of an internal combustion engine with an engine power cam for an engine power operation;   2. disengaging the cam roller from the engine power cam;   3. losing a motion from the engine power cam and a motion of an engine valve associated with the motion from the engine power cam;   4. engaging the cam roller with an engine braking cam for an engine braking operation;   5. transmitting a motion from the engine braking cam to the engine valve; and generating an engine valve motion for the engine braking operation.       
 
         [0015]    Further, the step of engaging the cam roller with the engine power cam includes using an axial cam roller driver to move the cam roller axially on a roller shaft of the engine to a first axial position on the roller shaft, and wherein the step of engaging the cam roller with the engine braking cam includes using the axial cam roller driver to move the cam roller axially on the roller shaft of the engine to a second axial position on the roller shaft. 
         [0016]    Further, the axial cam roller driver is integrated into a valve actuator of the engine. 
         [0017]    Further, the axial cam roller driver comprises a piston-spring mechanism in the valve actuator, said piston-spring mechanism being engaged with one end of a linkage or a sliding fork, the other end of the linkage or the sliding fork being engaged with the cam roller. 
         [0018]    Further, the axial cam roller driver is placed outside of a valve actuator of the engine, said axial cam roller driver moving the cam roller axially on the roller shaft through a linkage or a sliding fork. 
         [0019]    Further, the cam roller is designed to have a tendency to separate radially from the cam shaft to enhance the axial motion of the cam roller on the roller shaft. 
         [0020]    Further, the engine power cam and the engine braking cam are located on a common cam shaft, are adjacent to each other, and have the same or substantially the same inner base circle. 
         [0021]    Further, the engine braking method comprises a transition mechanism that assists the cam roller to move between the engine power cam and the engine braking cam. 
         [0022]    Further, the engine braking method comprises a transition mechanism, wherein the transition mechanism includes an inclined line or surface transition between a first height on the engine power cam and a second height on the engine braking cam. 
         [0023]    Further, the step of engaging the cam roller with the engine power cam includes using an axial cam driver to move both the engine power cam and the engine braking cam axially on the camshaft to a first axial position on the camshaft, and wherein the step of engaging the cam roller with the engine braking cam includes using the axial cam driver to move both the engine power cam and the engine braking cam axially on the camshaft of the engine to a second axial position on the camshaft. 
         [0024]    Further, the cam roller is placed on a rocker arm of the engine, and the step of engaging the cam roller with the engine power cam includes using an axial rocker arm driver to move the rocker arm axially on a rocker shaft of the engine to a first axial position on the rocker shaft, and wherein the step of engaging the cam roller with the engine braking cam includes using the axial rocker arm driver to move the rocker arm axially on the rocker shaft of the engine to a second axial position on the rocker shaft. 
         [0025]    Further, the cam roller comprises an exhaust cam roller, said engine power cam comprises a normal exhaust cam, and said engine braking cam comprises a braking exhaust cam. 
         [0026]    Further, the engine braking method comprises the following steps:
       1. engaging the exhaust cam roller with the normal exhaust cam for the engine power operation;   2. disengaging the exhaust cam roller with the normal exhaust cam;   3. losing a motion from the normal exhaust cam and a motion of an engine exhaust valve associated with the motion from the normal exhaust cam;   4. engaging the exhaust cam roller with the braking exhaust cam for the engine braking operation;   5. transmitting a motion from the braking exhaust cam to the engine exhaust valve; and   6. generating an engine exhaust valve motion for the engine braking operation.       
 
         [0033]    Further, the braking exhaust cam comprises three braking exhaust cam lobes, the first braking exhaust cam lobe being the first compression release cam lobe and associated with a location near the engine compression top dead center, the second braking exhaust cam lobe being the second compression release cam lobe and associated with a location near the engine exhaust top dead center, the third braking exhaust cam lobe being the exhaust gas recirculation cam lobe and associated with a location mainly in the engine expansion stroke, immediately following the first compression release cam lobe or directly connecting to the first compression release cam lobe. 
         [0034]    Further, the cam roller comprises an exhaust cam roller and an intake cam roller, said engine power cam comprises a normal exhaust cam and a normal intake cam, and said engine braking cam comprises a braking exhaust cam and a braking intake cam. 
         [0035]    Further, the engine braking method comprises the following steps:
       1. engaging the exhaust cam roller with the normal exhaust cam for the engine power operation, and engaging the intake cam roller with the normal intake cam for the engine power operation;   2. disengaging the exhaust cam roller with the normal exhaust cam, and disengaging the intake cam roller with the normal intake cam;   3. losing a motion from the normal exhaust cam and a motion of an engine exhaust valve associated with the motion from the normal exhaust cam, and losing a motion from the normal intake cam and a motion of an engine intake valve associated with the motion from the normal intake cam;   4. engaging the exhaust cam roller with the braking exhaust cam for the engine braking operation, and engaging the intake cam roller with the braking intake cam for the engine braking operation;   5. transmitting a motion from the braking exhaust cam to the engine exhaust valve, and transmitting a motion from the braking intake cam to the engine intake valve; and   6. generating an engine exhaust valve motion for the engine braking operation, and generating an engine intake valve motion for the engine braking operation.       
 
         [0042]    Further, the braking exhaust cam comprises at least two braking exhaust cam lobes, the first braking exhaust cam lobe being the first compression release cam lobe and associated with a location near the engine compression top dead center, the second braking exhaust cam lobe being the second compression release cam lobe and associated with a location near the engine exhaust top dead center. 
         [0043]    Further, the braking intake cam comprises at least two braking intake cam lobes, the first braking intake cam lobe being associated with a location mainly in the engine&#39;s intake stroke, and the second braking intake cam lobe being associated with a location mainly in the engine&#39;s expansion stroke. 
         [0044]    Further, the engine has a valve actuator, said valve actuator comprising a rocker arm and a valve bridge, one end of the rocker arm being engaged with the engine power cam or the engine braking cam through the cam roller, the other end of the rocker arm being over the valve bridge, the two ends of the valve bridge being engaged respectively with an inner valve that is close to the cams and with an outer valve that is away from the cams, wherein said engine braking method further comprises the following steps:
       1. disengaging the rocker arm from the center of the valve bridge while the engagement of the cam roller to the engine power cam is being switched to the engine braking cam,   2. opening the inner valve by the rocker arm while the outer valve being kept closed,   3. transmitting the motion of the engine braking cam to the inner valve, and generating the engine braking operation.       
 
         [0048]    Further, a lost motion mechanism is provided to disengage the rocker arm from the center of the valve bridge, said lost motion mechanism being integrated into the valve actuator. 
         [0049]    Further, the lost motion mechanism comprises a hydraulic piston mechanism integrated with the rocker arm, said hydraulic piston mechanism including an auto lash adjusting system. 
         [0050]    Further, the lost motion mechanism comprises a mechanical linkage mechanism integrated with the rocker arm, said rocker arm comprising a full rocker arm for actuating the inner valve and a half rocker arm for actuating both the inner valve and the outer valve, one end of the full rocker arm being engaged with one of the two cams through the cam roller, the other end of the full rocker arm being engaged with the inner valve, the half rocker arm and the full rocker arm being rotationally placed on a common rocker shaft, the end of the half rocker arm being over the center of the valve bridge, and the two rocker arms being linked through the mechanical linkage mechanism. 
         [0051]    The present invention is also a new engine braking system, which comprises an engine power cam on a camshaft of an international combustion engine; an engine braking cam on the camshaft of the internal combustion engine; and a cam roller that is designed to engage with the engine power cam for an engine power operation and to engage with the engine braking cam for an engine braking operation. 
         [0052]    Further, the new engine braking system comprises an axial cam roller driver, and a roller shaft, wherein the cam roller is rotationally placed on the roller shaft, wherein the cam roller is also axially slidable along the roller shaft between a first axial position and a second axial position, in said first axial position, the cam roller being engaged with the engine power cam for the engine power operation, and in said second axial position, the cam roller being engaged with the engine braking cam for the engine braking operation. 
         [0053]    Further, the axial cam roller driver comprises a piston-spring mechanism integrated into a valve actuator of the engine, said piston-spring mechanism being engaged with one end of a linkage or a sliding fork, the other end of the linkage or the sliding fork being engaged with the cam roller. 
         [0054]    Further, the axial cam roller driver is placed outside of a valve actuator of the engine, and wherein said axial cam roller driver moves the cam roller axially on the roller shaft through a linkage or a sliding fork. 
         [0055]    Further, the cam roller is designed to have a tendency to separate radially from the cam shaft to enhance the axial motion of the cam roller on the roller shaft. 
         [0056]    Further, the engine power cam and the engine braking cam are located on a common cam shaft, are adjacent to each other and have the same or substantially the same inner base circle. 
         [0057]    Further, the new engine brake system comprises a transition mechanism that assists the cam roller to move between the engine power cam and the engine braking cam. 
         [0058]    Further, the new engine brake system comprises a transition mechanism, wherein the transition mechanism includes an inclined surface transition between a first height on the engine power cam and a second height on the engine braking cam. 
         [0059]    Further, the new engine brake system comprises an axial cam driver, wherein both the engine power cam and the engine braking cam are axially slidable along the camshaft between a first axial position and a second axial position, in said first axial position, the cam roller being engaged with the engine power cam for the engine power operation, and in said second axial position, the cam roller being engaged with the engine braking cam for the engine braking operation. 
         [0060]    Further, the new engine brake system comprises an axial rocker arm driver, wherein the cam roller is placed on a rocker arm of the engine, and said rocker arm is axially slidable along a rocker shaft of the engine between a first axial position and a second axial position, in said first axial position, the cam roller on the rocker arm being engaged with the engine power cam for the engine power operation, and in said second axial position, the cam roller on the rocker arm being engaged with the engine braking cam for the engine braking operation 
         [0061]    Further, the engine power cam comprises a normal exhaust cam, and said engine braking cam comprises a braking exhaust cam. 
         [0062]    Further, the braking exhaust cam comprises three braking exhaust cam lobes, the first braking exhaust cam lobe being the first compression release cam lobe and associated with a location near the engine compression top dead center, the second braking exhaust cam lobe being the second compression release cam lobe and associated with a location near the engine exhaust top dead center, the third braking exhaust cam lobe being the exhaust gas recirculation cam lobe and associated with a location mainly in the engine expansion stroke, immediately following the first compression release cam lobe or directly engaging with the first compression release cam lobe. 
         [0063]    Further, the engine power cam comprises a normal exhaust cam and a normal intake cam, and said engine braking cam comprises a braking exhaust cam and a braking intake cam. 
         [0064]    Further, the braking exhaust cam comprises at least two braking exhaust cam lobes, the first braking exhaust cam lobe being the first compression release cam lobe and associated with a location near the engine compression top dead center, the second braking exhaust cam lobe being the second compression release cam lobe and associated with a location near the engine exhaust top dead center. 
         [0065]    Further, the braking intake cam comprises at least two braking intake cam lobes, the first braking intake cam lobe being associated with a location mainly in the engine&#39;s intake stroke, and the second braking intake cam lobe being associated with a location mainly in the engine&#39;s expansion stroke. 
         [0066]    Further, the engine braking system comprises a lost motion mechanism, wherein said lost motion mechanism is integrated into the engine&#39;s valve actuator, wherein when said lost motion mechanism is actuated, the engine&#39;s rocker arm is disconnected to the center of the engine&#39;s valve bridge, said valve bridge having two ends being engaged respectively with the inner valve that is close to the cams and with an outer valve that is away from the cams, and there being also a single valve linkage mechanism between the rocker arm and the inner valve. 
         [0067]    Further, lost motion mechanism comprises a hydraulic piston mechanism integrated with the rocker arm, said hydraulic piston mechanism being also an auto lash adjusting system. 
         [0068]    Further, the lost motion mechanism comprises a mechanical linkage mechanism integrated with the rocker arm, said rocker arm comprises a full rocker arm for actuating the inner valve and a half rocker arm for actuating both the inner valve and the outer valve, one end of the full rocker arm being engaged with one of the two cams through the cam roller, the other end of the full rocker arm being engaged with the inner valve, the half rocker arm and the full rocker arm are rotationally placed on a common rocker shaft, the end of the half rocker arm being over the center of the valve bridge, and the two rocker arms being linked through the mechanical linkage mechanism. 
         [0069]    Further, the engine braking system comprises an anti-no-follow mechanism, wherein said anti-no-follow mechanism comprises an elastic part. 
         [0070]    A working principle of the present invention is summarized as follows. When an engine power operation needs to be converted to an engine braking operation, an engagement of a cam roller with an engine power cam is switched to an engine braking cam. The switching is accomplished in one or more of three different ways: (1) using an axial cam roller driver to move the cam roller axially on a roller shaft from a first axial position on the roller shaft where the cam roller is engaged with the engine power cam to a second axial position on the roller shaft where the cam roller is engaged with the engine braking cam; (2) using an axial rocker arm driver to move a rocker arm axially on a rocker arm shaft from a first axial position on the rocker shaft where a cam roller on the rocker arm is engaged with the engine power cam to a second axial position on the rocker shaft where the cam roller on the rocker arm is engaged with the engine braking cam; and (3) using an axial cam driver to move both engine power cam and engine braking cam axially on a camshaft from a first axial position on the camshaft where a cam roller is engaged with the engine power cam to a second axial position on the camshaft where the cam roller is engaged with the engine braking cam. After the switching, the motion from the engine power cam and the motion of an engine valve associated with the motion from the engine power cam are lost, while the motion from the engine braking cam is transmitted to the engine valve for the engine braking operation. 
         [0071]    The present application has positive and significant advantages over the prior art. By changing the engagement of the cam roller from the engine power cam to the engine braking cam, the present invention achieves the conversion between the engine power (firing) operation and the engine braking operation. The simple and compact structure is easy to assemble and manufacture with a wide range of applications and other advantages. Since the engine braking cam and the engine power cam are independent from each other, engine braking performance can be optimized. The present invention uses a solid chain (mechanical linkage) to transfer loads, eliminating the high oil pressure, high compliance and high leakage as well as hydraulic jacking and other disadvantages or failure modes linked to the hydraulic loading of conventional engine brakes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0072]      FIG. 1  is an engine braking control diagram used in the first embodiment of the engine braking method of the present invention. 
           [0073]      FIG. 2  is a schematic view showing an engine braking device (side view) according to the first embodiment of the engine braking method of the present invention. 
           [0074]      FIG. 3  is a schematic diagram showing an axial cam roller driver (partial top view) when the cam roller is in the first axial position according to the first embodiment of the engine braking method of the present invention. 
           [0075]      FIG. 4  is a schematic diagram showing an axial cam roller driver (partial top view) when the cam roller is at the second axial position according to the first embodiment of the engine braking method of the present invention. 
           [0076]      FIG. 5  is a schematic diagram showing the normal cam (or valve) lift profiles. 
           [0077]      FIG. 6  is a schematic diagram showing a braking exhaust cam (or valve) lift profile during the engine braking operation according to the first embodiment of the engine braking method of the present invention. 
           [0078]      FIG. 7  is a schematic diagram showing braking exhaust and braking intake cam (or valve) lift profiles during the engine braking operation according to the second embodiment of the engine braking method of the present invention. 
           [0079]      FIG. 8  is a schematic view showing an engine braking system according to the third embodiment of the engine braking method of the present invention. 
           [0080]      FIG. 9  is a schematic view showing a liquid flow control valve according to the third embodiment of the engine braking method of the present invention. 
           [0081]      FIG. 10  is a schematic view showing an engine braking system according to the fourth embodiment of the engine braking method of the present invention. 
           [0082]      FIG. 11  is a schematic view showing an engine braking system (side view) according to the fifth embodiment of the engine braking method of the present invention. 
           [0083]      FIG. 12  is a top view of the fifth embodiment when the full rocker arm is in the first axial position on the rocker shaft and the cam roller is engaged with the engine power cam. 
           [0084]      FIG. 13  is a top view of the fifth embodiment when the full rocker arm is in the second axial position on the rocker shaft and the cam roller is engaged with the engine braking cam. 
           [0085]      FIG. 14  is a schematic view showing an engine braking system (side view) according to the sixth embodiment of the engine braking method of the present invention. 
           [0086]      FIG. 15  is an engine braking control diagram used in the seventh embodiment of the engine braking method of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
       [0087]      FIGS. 1 to 6  are used to describe the first embodiment of the engine braking method of the present invention.  FIG. 1  is an engine braking control diagram of the invention. The engine power operation  10  follows the solid line arrows on the left in  FIG. 1 . The engine brake controller  50  is turned off (not energized). The axial cam roller driver  100  biases the cam roller  235  to a first axial position. The cam roller  235  is engaged with an engine power cam  230 , and the motion from the engine power cam  230  is transmitted to an engine valve for the engine power operation  10 . When the engine power operation  10  needs to be converted to an engine braking operation  20 , the engine braking control is switched to the right in  FIG. 1  and follow the dashed line arrows. The engine brake controller  50  is now turned on (energized). The axial cam roller driver  100  moves the cam roller  235  from the first axial position to the second axial position. The cam roller  235  is disengaged from the engine power cam  230  and switched to an engagement with an engine braking cam  2302 . The motion from the engine power cam  230  is completely lost, while the motion from the engine braking cam  2302  is transmitted to the engine valve for the engine braking operation  20 . As can be seen from  FIG. 1 , the engine power operation  10  and the engine braking operation  20  are independent of each other. 
         [0088]      FIG. 2  is a schematic diagram (side view) of an engine brake device of the present invention. The engine&#39;s valve actuator  200 , for both intake valve actuator and exhaust valve actuator, includes two cams (an engine power cam  230  and an engine braking cam  2302 ), a cam roller  235  and a roller shaft  231 . The cam roller  235  can rotate on the roller shaft  231 . It can also slide axially along the roller shaft between a first axial position ( FIG. 3 ) and a second axial position ( FIG. 4 ). The engine power cam (cam lobe  220 ) and the engine braking cam (cam lobes  232  and  233 ) have different lift and timing. Note that the engine braking cam lobes  232  and  233  have much lower lifts than the engine power cam lobe  220 . The two cams are located on a common camshaft  225 , adjacent to each other and have the same or substantially the same inner base circle. The valve actuator  200  further includes a rocker arm  210  rotationally mounted on a rocker shaft  205 . There is a flow passage  211  in the rocker shaft  205 . Through a valve lash adjusting mechanism, the rocker arm  210  actuates the engine valve  301  (shown here is a single valve, but the present invention is equally applicable to dual-valve engine, but a valve bridge is needed for actuating two engine valves). The valve  301  is biased by a valve spring  311  on valve seat  320  in the engine block  500  to prevent gases from flowing between the engine cylinder and gas duct  600 . The valve lash adjustment mechanism includes a valve lash adjusting screw  110 , a locking nut  105 , and an elephant foot  114 . 
         [0089]      FIGS. 3 and 4  (partial top views) illustrate the axial cam roller driver  100  used in the first embodiment of the engine braking method of the present invention with the cam roller  235  being movable between a first axial position and a second axial position. Near the cam side, there is a gap or open slot in the end of the rocker arm  210  (rocker arm  210  shown here can also be a cam follower of a push-tube engine). A roller shaft  231  is provided across the gap, and on the roller shaft  231  provided with the cam roller  235 . The cam roller  235  can not only rotate on the roller shaft  231 , but also move axially along the roller shaft  231 . The length of the roller shaft  231  in the gap is larger than the width of the cam roller  235 . The cam roller  235  has a first axial position ( FIG. 3 ) and a second axial position ( FIG. 4 ) on the roller shaft  231 . The axial cam roller driver  100  is integrated in the rocker arm  210 , which moves the cam roller  235  between the first axial position and the second axial position through a linkage or a sliding fork  236 . 
         [0090]    One end of the sliding fork  236  includes two spaced prongs, and each of the two prongs has a hole or slot  238  and  239 . The roller shaft  231  passes through the holes or slots  238  and  239  in the two prongs, and the cam roller  235  is placed between the two prongs. The other end  237  of the sliding fork  236  is engaged with the axial cam roller driver  100  (the way of the engagement may vary). The axial cam roller driver  100  shown here is a piston-spring mechanism integrated in the valve actuator (the rocker arm  210 ). The piston-spring mechanism includes a piston  164  disposed within a piston bore  260 , with its axial direction being parallel to the axis of the roller shaft  231 . There is a fluid passage  214  on one side of the piston  164 , and a spring  156  on the other side. Piston  164  is pushed separately by the spring force near the spring side (left side in the Figures) and by a fluid (e.g. engine oil) force near the fluid passage side (right side in the Figures). The two forces have opposite directions and make the piston  164  move axially. The piston-spring mechanism is engaged with one end  237  of the sliding fork  236  (the connection here is that the end  237  of the sliding fork  236  is located in annular groove  126  of the piston  164 , and the connecting end  237  having a guide groove  270  in the rocker arm  210 ). The motion of the piston  164  is transmitted to the cam roller  235  through the sliding fork  136 , and the cam roller  235  being moved between the first axial position ( FIG. 3 ) and the second axial position ( FIG. 4 ) on the roller shaft  231 . 
         [0091]    When the cam roller  235  is in the first axial position, it is engaged with the engine power cam  230  on the camshaft  225  ( FIG. 3 ). When the cam roller  235  is in the second axial position, it is engaged with the engine braking cam  2302  on the camshaft  225  ( FIG. 4 ). Preferably the engine power cam  230  and the engine braking cam  2302  are designed to have the same or substantially the same inner base circle, and to have an axial transition mechanism that assists the cam roller to move between them, such as an inclined surface transition between a first height on the engine power cam  230  to a second height on the engine braking cam  2302 , so that the cam roller  235  could have a smooth and stable transition when the engagement of the cam roller  235  is switched between the two cams. Alternatively, the transition mechanism could include any other suitable mechanism. For example, the transition may be accomplished by switching between the two cams only when the height difference between the engine power cam  230  and the engine braking cam  2302  is below a certain value to reduce any impact during the switch. Also it is better for the cam roller  235  to have a tendency to separate radially from the camshaft  225  to enhance the axial motion of the cam roller  235  on the roller shaft  231 . 
         [0092]    The operation of this embodiment is as follows. Spring  156  biases piston  164  to the bottom surface of piston bore  260  near the side with fluid passage  214  (the right side), The piston  164 , through the sliding fork  236 , pushes the cam roller  235  to the first axial position (the right side in  FIG. 3 ), and the cam roller  235  is engaged with the engine power cam  230 . The motion of the engine power cam  230  is transmitted to the engine valve  301  ( FIG. 2 ), generating the valve motion for engine power operation (see  FIG. 5  for the valve profile  220  (exhaust) or  321  (intake)). When it is desired to convert the engine power operation  10  to the engine braking operation  20 , the engine brake controller  50  is turned on to provide a driving force to the axial cam roller driver  100 . Fluid, such as engine oil through the fluid passages, for example,  211  and  214  in the rocker shaft and rocker arm, flows into piston bore  260 . The oil pressure overcomes the force of spring  156  and moves piston  164  in piston bore  260  to the side with spring  156  (left side), and piston  164  pushes the sliding fork  236  with the cam roller  235  to the second axial position (left side in  FIG. 4 ). The cam roller  235  is disengaged from the engine power cam  230  and engaged with the engine braking cam  2302 . The motion of the engine power cam  230  is lost, while the motion of the engine braking cam  2302  is transmitted to the engine valve  301  for the engine braking operation. 
         [0093]    Note that the above description applies to both the exhaust valve actuation and the intake valve actuation. However, in this embodiment, the engine braking operation  20  simply switches the power operation of the exhaust valve to the engine braking operation, the engine power operation of the intake valve is maintained without any change. The intake valve motion for engine power operation is shown in  FIG. 5  (the intake lift curve  321 ) and the engine braking exhaust valve motion which is from the braking exhaust cam  2302 , as shown in  FIG. 6  as an example, is generated by three braking exhaust cam lobes. The first braking exhaust cam lobe is the first compression release cam lobe  232 , located near the engine&#39;s compression top dead center (0° crank angle); the second braking exhaust cam lobe is the second compression release cam lobe  233 , located near the engine&#39;s exhaust top dead center (360° crank angle); and the third braking exhaust cam lobe is the exhaust gas recirculation cam lobe  231 , mainly located in the expansion stroke of the engine and immediately following the first compression-release cam lobe  232  or directly connecting to the first compression release cam lobe  232  to form a combined cam lobe. 
       Second Embodiment 
       [0094]    In this embodiment of the present invention, the intake valve engine braking operation is added to the above-described embodiment. The exhaust valve actuator and the intake valve actuator are both provided with the axial cam roller driver  100 , which has the same working principle and procedure as described in the first embodiment, and is not repeated here. 
         [0095]    The engine power cams in the present embodiment are the same as embodiment one, including both the normal exhaust cam and the normal intake cam, whose lift curves are shown in  FIG. 5  ( 220  for exhaust and  312  for intake). The braking cams include the braking exhaust cam and a braking intake cam, whose lift curves are shown in  FIGS. 7  ( 232  and  233  for exhaust, and  322  and  323  for intake). Therefore, the present embodiment has one more braking intake cam than the first embodiment. When the engine power operation is needed, the axial cam roller driver  100  biases the cam roller  235  to the first axial position, both the intake and exhaust cam rollers are engaged with the normal intake and exhaust cams respectively, whose motions are passed to the engine&#39;s intake and exhaust valves to produce the intake and exhaust valve motions for the engine power operation (see  FIG. 5  for the intake and exhaust lift curves  321  and  220 ). 
         [0096]    When it is desired to convert the engine power operation  10  to the engine braking operation  20 , the engine brake controller  50  is turned on to provide a driving force to the axial cam roller driver  100 , which moves the exhaust cam roller  235  from the first axial position to the second axial position, switching the connection of the exhaust cam roller  235  from the normal exhaust cam  230  to the braking exhaust cam  2302 , losing the normal exhaust cam motion and the corresponding normal exhaust valve motion, generating the engine braking exhaust valve motion. At the same time, the intake cam roller is also moved from the first axial position to the second axial position, switching the connection of the intake cam roller from the normal intake cam to the braking intake cam, losing the normal intake cam motion and the corresponding normal intake valve motion, generating the engine braking intake valve motion. 
         [0097]    As shown in  FIG. 7 , the braking exhaust cam has two braking exhaust cam lobes, one being the first compression-release cam lobe  232  located near the engine&#39;s compression top dead center (0° crank angle), and the other being the second compression release cam lobe  233  located near the engine&#39;s exhaust top dead center (360° crank angle).  FIG. 7  also shows two braking intake cam lobes for the braking intake cam, one being the first braking intake cam lobe  322 , mainly located in the intake stroke of the engine, and the other being the second braking intake cam lobe  323 , mainly located in the expansion stroke of the engine. The first braking intake cam lobe  322  is to charge the engine cylinder prior to the first compression release event, and the first compression release cam lobe  232  to achieve the first stroke braking. The second braking intake cam lobe  323  is to charge the engine cylinder prior to the second compression release event, and the second compression release cam lobe  233  to achieve the second stroke braking. Thus, the four-stroke engine is able to achieve two-stroke braking in one cycle, greatly improving the braking power. Note that the two braking exhaust cam lobes (the first and second compression-release cam lobes  232  and  233 ) are much smaller (lower lift and short duration) than the two braking intake cam lobes. 
       Third Embodiment 
       [0098]      FIGS. 8 and 9  are used to illustrate the third embodiment of the present invention. The present embodiment has two valves  301  and  302  that are biased against the valve seat  320  in the engine block  500  by the two valve springs  311  and  312 . The valve actuator  200  also includes a rocker arm  210  and a valve bridge  400  placed on the two valves. The rocker arm  210  actuates a single engine valve (the first valve or the inner valve close to the cams) through a lash adjusting mechanism (a lash adjusting screw  1102 ), an e-foot  1142 , and a braking bar  116  in the valve bridge  400 . The lash adjusting screw  1102  is fixed on the rocker arm  210  by a lock nut  1052 . The rocker arm  210  contains also a lost motion mechanism that is a hydraulic piston mechanism including a hydraulic piston  160  and a liquid flow control valve  75  (see  FIG. 9  for details of the valve), which happens also to be an auto lash adjusting mechanism. The hydraulic piston  160  is slidably placed in a piston bore  190 . A hydraulic linkage with a liquid column is formed between piston  160  and rocker arm  210  through the liquid flow control valve  75 . The height  234  of the liquid column is automatically adjusted according to the gap between the cam  230  and the bridge  400  or the two valves. The hydraulic piston  160  is engaged with the center of the valve bridge  400  though an e-foot  114 . 
         [0099]    The liquid flow control valve  75  ( FIG. 9  for cross section view) integrated into the rocker arm  210  includes a one-way ball valve  165 , biased upwards by spring  177 . The top of the ball valve  165  is actuated by a funnel shaped piston  58  that is biased downwards by spring  256 . When pressured liquid (for example, engine lube oil) is provided though flow passage  218 , oil pressure overcomes the force of the spring  256  and moves the piston  58  upward. At the same time, oil pressure overcomes the force of the spring  177  and moves the ball valve  165  downwards. Oil is fed into the hydraulic passage  216  as well as all the hydraulic passages and chambers including the piston bore  190  underneath the ball valve  165  to form a hydraulic lock. 
         [0100]    The operation of this embodiment is as follows. The axial motion of the cam roller  235  on the roller shaft  231  is the same as the first embodiment. The axial cam roller driver  100  shown in  FIGS. 3 and 4  has a spring  156  or oil pressure that biases the piston  164  to the bottom surface of piston bore  260  near the side with the fluid passage  214  (the right side). The piston  164 , through the sliding fork  236 , pushes the cam roller  235  to the first axial position (the right side in  FIG. 3 ), and the cam roller  235  is engaged with the engine power cam  230 . Through the roller shaft  231 , the rocker arm  210 , the lost motion mechanism that forms a hydraulic linkage and the valve bridge  400 , the motion of the engine power cam  230  is transmitted to both of the two engine valve  301  and  302  ( FIG. 8 ), generating the valve motion for engine power operation (see  FIG. 5  for the valve lift profile  220  (exhaust) or  321  (intake)). Since the rocker ratio at the e-foot  1142  that opens the inner valve is smaller than the rocker ration at the e-foot  114  that actuates the valve bridge  400  and both of the two valves  301  (inner valve) and  302  (outer valve), the e-foot  1142  will not be loaded or transmit any motion to the inner valve  301 . 
         [0101]    When it is desired to convert the engine power operation  10  to the engine braking operation  20 , the engine brake controller  50  is turned on to provide a driving force to the axial cam roller driver  100 . Fluid, such as engine oil through the fluid passages  211  and  214  in the rocker shaft and rocker arm, flows into piston bore  260  ( FIGS. 3 and 4 ). The oil pressure overcomes the force of spring  156  and moves piston  164  in piston bore  260  to the side with spring  156  (left side), and piston  164  pushes the sliding fork  236  with the cam roller  235  to the second axial position (left side in  FIG. 4 ). The cam roller  235  is disengaged from the engine power cam  230  and engaged with the engine braking cam  2302 . The motion of the engine power cam  230  is lost. 
         [0102]    At the same time, oil to the liquid flow control valve  75  is discharged through fluid passage  218 . Piston  58  moves downwards under the action of spring  256  (see  FIG. 9 ) and pushes the one-way ball valve  165  off its seat. Oil is discharged from the piston bore  190  through the hydraulic passage  216 . The liquid column  234  is now like an air gap and the hydraulic linkage is lost. The motion from the engine braking cam (cam lobes  232  and  233 ) is lost at the e-foot  114  and cannot be transmitted to the two engine valves  301  and  302  through the center of the valve bridge  400 . However, due to the engagement of the rocker arm  210  with the inner valve  301  through the e-foot  1142  and the braking bar  116  in the valve bridge  400 , the motion of the engine braking cam  2302  engaged with the cam roller is transmitted to the inner valve  301  for the engine braking operation with a single valve actuation, which has much lower engine braking load. 
         [0103]    In summary, the present embodiment uses an axial cam roller driver to move the cam roller axially on the roller shaft to switch its connection from the engine power cam to the engine braking cam. The motion of the engine power cam is lost. At the same time, the connection between the rocker arm and the center of the valve bridge is also cut off by a lost motion mechanism, which converts the valve actuator  200  from opening two valves to opening one valve. The motion of the engine braking cam  2302  is transmitted by the rocker arm to one of the two valves, i.e., the inner valve  301  for the engine braking operation with a single valve actuation. 
         [0104]    The clip ring  176  (or other stopping mechanism) inside the piston bore  190  is used to limit the stroke of piston  160  as well as to keep the piston  160  from falling out of the bore (good for shipping and assembly). An anti-no-follow mechanism is added to prevent no-follow of the moving parts due to the gap  234  formed by the lost motion mechanism  250 . The anti-no-follow mechanism includes a spring or an elastic part, such as  117 ,  118  and  198  in  FIG. 8 . The shape, type, installation and location of the springs or elastic parts can be changed to serve the purpose of keeping the moving parts, such as the valve bridge  400 , from having no-follow. The height of the gap  234  is determined by the braking cam lobes to escape (or lose) the motion of the braking cam lobes so that it won&#39;t be transmitted to the valves through the valve bridge  400 . 
       Fourth Embodiment 
       [0105]      FIG. 10  is used to illustrate the fourth embodiment of the present invention. Instead of a single rocker arm in the third embodiment, the present embodiment has two rocker arms: a full rocker arm  210  for opening one valve (the inner valve)  301  and a half rocker arm  212  for opening both of the two valves (the inner and outer valves)  301  and  302 . The lost motion mechanism  250  is now a mechanical linkage mechanism that connects the full rocker arm  210  and the half rocker arm  212 . The full rocker arm  210  is similar to that of the first embodiment and has the cam roller  235  on the roller shaft  231  on its end close to the cams  230  and  2302 . The other end of the full rocker arm  210  is linked to the first valve (the inner valve)  301  through a braking lash adjusting mechanism, an e-foot  1142  and a braking bar  116 . The half rocker arm  212  and the full rocker arm  210  are placed rotationally on the common rocker shaft  205 . For example, the full rocker arm  210  could be placed in the middle while the half rocker arm  212  have a fork shape and be placed on both sides of the full rocker arm  210 . Note that the half rocker arm  212  is not engaged with cam  230  or  2302 . The end of the half rocker arm  212  is engaged with the center of the valve bridge  400  through a valve lash adjusting screw  110  and an e-foot  114 . The valve bridge  400  is engaged with the two valves  301  and  302 . The adjusting screw  110  is fixed on the half rocker arm  212  by a lock nut  105 . The half rocker arm  212  is also engaged with the full rocker arm  210  though the lost motion mechanism (the mechanical linkage mechanism)  250 . The mechanical linkage mechanism  250  includes two links  184  and  186  that are linked through a middle pin  125 . The other (left) end of link  184  is engaged with the full rocker arm  210  through a left pin  122 . The other (right) end of link  186  is engaged with the half rocker arm  212  through a right pin  128 . One end of a returning spring  198  is placed on the extension part of the right end of link  186 . Another end of the returning spring  198  is located on the half rocker arm  212 . 
         [0106]    When it is desired to convert the engine power operation  10  to the engine braking operation  20 , the engine brake controller  50  is turned on to provide driving force to the axial cam roller driver  100 . Fluid, such as engine oil through the fluid passage  214 , flows into piston bore  260  ( FIGS. 3 and 4 ). The oil pressure overcomes the force of spring  156  and moves piston  164  in piston bore  260  to the side with spring  156  (left side), and piston  164  pushes the sliding fork  236  with the cam roller  235  to the second axial position (left side in  FIG. 4 ). The cam roller  235  is disengaged from the engine power cam  230  and engaged with the engine braking cam  2302 . The motion of the engine power cam  230  is lost. 
         [0107]    At the same time, the engine brake controller  50  supplies oil to the activation piston  162  in  FIG. 10 . Oil pressure overcomes the action of spring  198  and pushes upwards the activation piston  162  as well as the center of the mechanical linkage mechanism  250  near the middle pin  125 . The half rocker arm  212  rotates anticlockwise and the e-foot  114  is disconnected from the valve bridge  400  and the two valves. The motion from the engine braking cam (cam lobes  232  and  233 ) is lost at the e-foot  114  and cannot be transmitted to the two valves  301  and  302  through the center of the valve bridge  400 . However, due to the connection of the full rocker arm  210  to the inner valve  301  through the e-foot  1142  and the braking bar  116  in the valve bridge  400 , the motion of the engine braking cam  2302  being engaged with the cam roller  235  is transmitted to the inner valve  301  for the engine braking operation with a single valve actuation. 
       Fifth Embodiment 
       [0108]      FIGS. 11 to 13  are used to describe the fifth embodiment of the engine braking method of the present invention. Similar to embodiment four, the present embodiment has also two rocker arms: a full rocker arm  210  and a half rocker arm  212 . However, the full rocker arm  210  of the present embodiment can be moved axially on the rocker shaft  205  between a first axial position ( FIG. 12 ) and a second axial position ( FIG. 13 ). When the full rocker arm  210  is in the first axial position on the rocker shaft  205 , the cam roller  235  on one end of the full rocker arm  210  is engaged with the engine power cam  230  on the camshaft  225  as shown in  FIG. 11 . When the full rocker arm  210  is in the second axial position, the cam roller  235  is engaged with the engine braking cam  2302  as shown in  FIG. 12 . Note that the cam roller  235  on the full rocker arm  210  is not axially movable in the present embodiment. The other end of the full rocker arm  210  is engaged with the half rocker arm  212 . 
         [0109]    An axial rocker arm driver (not shown here)  100  is used to move the full rocker arm  210  axially on the rocker shaft  205  through a linkage, such as a hydraulic piston  162  in the full rocker arm  210 . The axial rocker arm driver  100  is placed outside of the valve actuator of the engine and it can be a hydraulic, pneumatic, electromagnetic, and mechanical mechanism or a combination of the above mechanisms. The motion of the axial rocker arm driver  100  can be synchronized with the motion of the camshaft  225 . 
       Sixth Embodiment 
       [0110]      FIG. 14  is used to describe the sixth embodiment of the engine braking method of the present invention. The present embodiment is similar to the fifth embodiment except that the lost motion mechanism  250  in the third embodiment ( FIG. 8 ) is used here in the half rocker arm  212 . The half rocker arm  212  is also engaged with the inner valve  301  through a braking bar  116 . The operation of the present embodiment is a combination of the fifth embodiment (to move the full rocker arm  212  axially on the rocker shaft  205  between a first axial position and a second axial position so that the cam roller  235  on the full rocker arm  210  will be engaged with the engine power cam  230  or the engine braking cam  2302 ) and the third embodiment (to disengage the half rocker arm  212  from the center of the valve bridge  400  by a lost motion mechanism  250  so that the motion from the engine braking cam  2302  can only be transmitted to the inner valve  301 , not to the outer valve  302 ). 
       Seventh Embodiment 
       [0111]      FIG. 15  is used to describe the seventh embodiment of the engine braking method of the present invention.  FIG. 15  is similar to  FIG. 1  and the present embodiment is an extension of the previous embodiments. The engine power cam  230  and the engine braking cam  2302  are placed on the same camshaft  225  and are axially movable between a first axial position and a second axial position on the camshaft  225 . However, the cam roller  235  of the engine is no longer axially movable. The step of engaging the cam roller  235  with the engine power cam  230  includes using an axial cam driver  100  to move both the engine power cam  230  and the engine braking cam  2302  axially on the camshaft  225  to the first axial position on the camshaft  225 , and the step of engaging the cam roller  235  with the engine braking cam  2302  includes using the axial cam driver  100  to move both the engine power cam  230  and the engine braking cam  2302  axially on the camshaft  225  of the engine to the second axial position on the camshaft  225 . 
         [0112]    While the above description contains many specific embodiments, these embodiments should not be regarded as limitations on the scope of the present invention, but rather as specific exemplifications. Many other variations are likely to be derived from the specific embodiments. For example, the engine braking method or device described herein can be used not only for overhead cam engines, but also for pushtube engines; not only for actuating one engine valve, but also for two engine valves. Also, the present invention involves different cams, such as the intake cam, the exhaust cam, and the braking cam, which include cam lobes that could have different number, size, shape, timing, lift and so on. 
         [0113]    In addition, the axial cam roller driver, the axial rocker arm driver and the axial cam driver described herein can not only be the piston-spring mechanism, but also other mechanism, such as a hydraulic, a pneumatic, a electromagnetic, and mechanical mechanism or a combination of the above mechanisms; it can not only be integrated in the valve actuator (such as with the rocker arm), but also be placed outside of the valve actuator (such as on the engine) to move the cam roller, the rocker arm or the cams axially on the roller shaft, the rocker shaft or the camshaft through a linkage. 
         [0114]    In addition, the lost motion mechanism integrated into the valve actuator could have different type, shape, size and location (such as integrated into a valve bridge), etc. 
         [0115]    Therefore, the scope of the present invention should not be defined by the above-mentioned specific examples, but by the appended claims and their legal equivalents.