Patent Publication Number: US-7909015-B2

Title: Apparatus and method for engine braking

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of application Ser. No. 12/228,901, filed on Aug. 18, 2008, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates generally to the braking of an internal combustion engine, specifically to engine braking apparatus and method for converting an internal combustion engine from a normal engine operation to an engine-braking operation. 
     2. Prior Art 
     It is well known in the art to employ an internal combustion engine as brake means by, in effect, converting the engine temporarily into a compressor. It is also well known that such conversion may be carried out by cutting off the fuel and opening the exhaust valve(s) at or near the end of the compression stroke of the engine piston. By allowing compressed gas (typically, air) to be released, energy absorbed by the engine to compress the gas during the compression stroke is not returned to the engine piston during the subsequent expansion or “power” stroke, but dissipated through the exhaust and radiator systems of the engine. The net result is an effective braking of the engine. 
     An engine brake (or engine retarder) is desirable for an internal combustion engine, particularly for a compression ignition type engine, also known as a diesel engine. Such engine offers substantially no braking when it is rotated through the drive shaft by the inertia and mass of a forward moving vehicle. As vehicle design and technology have advanced, its hauling capacity has increased, while at the same time rolling and wind resistances have decreased. Accordingly, there is a heightened braking need for a diesel-powered vehicle. While the normal drum or disc type wheel brakes of the vehicle are capable of absorbing a large amount of energy over a short period of time, their repeated use, for example, when operating in hilly terrain, could cause brake overheating and failure. The use of an engine brake will substantially reduce the use of the wheel brakes, minimize their wear, and obviate the danger of accidents resulting from brake failure. 
     There are different types of engine brakes. Typically, an engine braking operation is achieved by adding an auxiliary engine valve event called an engine braking event to the normal engine valve event. Depending on how the engine valve event is produced, an engine brake can be defined as:
         (a) Type I engine brake—the engine braking event is produced by importing motions from a neighboring cam, which generates the so called “Jake” brake;   (b) Type II engine brake—the engine braking event is produced by altering existing cam profile, which generates a lost motion type engine brake;   (c) Type III engine brake—the engine braking event is produced by using a dedicated valve lifter for engine braking, which generates a dedicated cam (rocker) brake;   (d) Type IV engine brake—the engine braking event is produced by modifying the existing engine valve lift, which normally generates a bleeder type engine brake;   (e) Type V engine brake—the engine braking event is produced by using a dedicated valve train for engine braking, which generates a dedicated valve (the fifth valve) engine brake.       

     The engine brake can also be divided into two big categories, i.e., the compression release engine brake (CREB) and the bleeder type engine brake (BTEB). 
     Compression Release Engine Brake (CREB) 
     Conventional compression release engine brakes (CREB) open the exhaust valve(s) at or near the end of the compression stroke of the engine piston. They typically include hydraulic circuits for transmitting a mechanical input to the exhaust valve(s) to be opened. Such hydraulic circuits typically include a master piston that is reciprocated in a master piston bore by a mechanical input from the engine, for example, the pivoting motion of the injector rocker arm. Hydraulic fluid in the circuit transmits the master piston motion to a slave piston in the circuit, which in turn, reciprocates in a slave piston bore in response to the flow of hydraulic fluid in the circuit. The slave piston acts either directly or indirectly on the exhaust valve(s) to be opened during the engine braking operation. 
     An example of a prior art CREB is provided by the disclosure of Cummins, U.S. Pat. No. 3,220,392 (“the &#39;392 patent”), which is hereby incorporated by reference. Engine braking systems based on the &#39;392 patent have enjoyed great commercial success. However, the prior art engine braking system is a bolt-on accessory that fits above the overhead. In order to provide space for mounting the braking system, a spacer may be positioned between the cylinder head and the valve cover that is bolted to the spacer. This arrangement may add unnecessary height, weight, and costs to the engine. Many of the above-noted problems result from viewing the braking system as an accessory to the engine rather than as part of the engine itself. 
     As the market for compression release-type engine brakes (CREB) has developed and matured, there is a need for design systems that reduce the weight, size and cost of such retarding systems. In addition, the market for compression release engine brakes has moved from the after-market, to original equipment manufacturers. Engine manufacturers have shown an increased willingness to make design modifications to their engines that would increase the performance and reliability and broaden the operating parameters of the compression release-type engine brake. 
     One possible solution is to use a dedicated valve lifter for the engine braking U.S. Pat. No. 5,626,116 (“the &#39;116 patent”) discloses a dedicated engine braking system (a Type III engine brake) including a rocker arm having a plunger, or braking piston, positioned in a cylinder integrally formed in one end of the rocker arm wherein the plunger can be locked in an outer position by hydraulic pressure to permit braking system operation. A solenoid valve or control valve is also integrated into the dedicated rocker arm. A cam designed exclusively for engine braking has only the small cam lobes for engine braking Therefore, the engine braking performance can be optimized without interfering with the valve lift profile design for the normal engine operation. During the normal engine operation, the control valve sits in a dent on the rocker shaft and the engine braking rocker arm stays in a neutral position. There are one gap between the rocker arm and the cam and another gap between the rocker arm and the valve bridge. 
     Although the engine brake system disclosed in the &#39;116 patent has enjoyed considerable commercial success due to its high performance and compact size, it has some drawbacks. One of the drawbacks is that the engine braking rocker arm could get away from the neutral position and contact the cam and the valve bridge during the normal engine operation. The braking piston in the rocker arm would be hammered and get loose to cause serious engine damage. 
     Additional disadvantages of the prior art system reside in their relative complexity and the necessity for using precision components because of the need of accurate control of the rocker arm position and the braking piston stroke. Thus the system is comparatively expensive and difficult or impossible to install on certain engines. 
     Another integrated engine braking system for commercial vehicles is known from U.S. Pat. No. 6,234,143 (“the &#39;143 patent”) in which an integrated rocker brake with one-valve opening for engine braking is disclosed. An engine brake actuator is disposed in the rocker arm between the pivot point and the distal end. The rocker arm and the valve bridge of the engine are so arranged that the hydraulic piston of the brake actuator is able to actuate on the inner valve near the pivot point of the rocker arm. By actuating only one of the two exhaust valves, the load from engine braking is greatly reduced. 
     The above integrated engine brake system, however, has the following drawbacks. First, after the braking valve is lifted by the hydraulic piston, the valve bridge is tilted and the followed normal valve actuation on both the braking valve and non-braking valve by the rocker arm is asymmetric or unbalanced. Large side load could be experienced on both valve stems or on the valve bridge guide if the bridge is guided. Second, the brake system can only fit on a particular type of engines that have the “parallel” arrangement of the rocker arm and the valve bridge. 
     U.S. Pat. No. 6,253,730 (“the &#39;730 patent”) discloses an integrated rocker brake with a reset valve trying to avoid the asymmetric loading on the valves or the valve bridge caused by the engine braking operation as disclosed by the &#39;143 patent. The reset valve will reset or retract the braking piston in the rocker arm before the braking valve reaches its peak braking lift so that the braking valve will return back to its seat before the main valve lift event starts, and the rocker arm can act on the leveled valve bridge and open both the braking valve and the non-braking valve without any asymmetric loading. 
     However, resetting the engine brake before the peak braking valve lift is very problematic. First, the duration and magnitude of the valve lift for engine braking is very small and even smaller for resetting. Second, the resetting happens at the peak engine braking load and causes high pressure or large load on the reset valve. The timing for the resetting is critical. If the resetting happens too soon, there will be too much braking valve lift loss (lower lift and earlier closing) and lower braking performance. If the resetting happens too late, the braking valve will not be able to close before the main valve event starts and cause asymmetric loading. Therefore, this type of integrated rocker engine brake may not work well at high engine speeds when the reset duration and height is extremely small and the braking load or pressure on the reset valve is very high. 
     Bleeder Type Engine Brake (BTEB) 
     The operation of a bleeder type engine brake (BTEB) has also long been known. During bleeder type engine braking, in addition to the normal exhaust valve lift, the exhaust valve(s) may be held slightly open during a portion of the cycle (partial-cycle bleeder brake) or open continuously throughout the non-exhaust strokes (intake stroke, compression stroke, and expansion or power stroke) (full-cycle bleeder brake). The primary difference between a partial-cycle bleeder brake and a full-cycle bleeder brake is that the former does not have exhaust valve lift during most of the intake stroke. 
     U.S. Pat. No. 5,692,469 and U.S. Pat. No. 7,013,867 (“the &#39;469 and &#39;867 patents”) disclose a bleeder type engine brake (BTEB) system for engines with one and two exhaust valves per cylinder. The BTEB system works with a throttling device (also known as an exhaust brake) capable of raising exhaust pressure high enough to cause each exhaust valve to float near the end of each intake stroke. In this intermediate opening or floating of the exhaust valve, it is possible to intervene with the braking device so that the exhaust valve, which is about to close after the intermediate opening, is intercepted by a control piston charged with oil pressure and prevented from closing to create a partial cycle bleeder braking event. This is a Type IV engine brake. 
     The BTEB system of the type described above may not be reliable because it depends on the intermediate opening or floating of the braking exhaust valve, which is inconsistent, both in timing and magnitude. As is well known in the art, exhaust valve floating is highly engine speed dependent and affected by the quality and control of the exhaust brake, and also the design of the exhaust manifold. There may be not enough or none valve floating for the actuation of the engine braking device at middle and low engine speeds when the engine brake is highly demanded since the engine is mostly driving at such speeds. It is clear from the above description that the prior-art engine brake systems have one or more of the following drawbacks:
         (a) The system is difficult to stay at a neutral position and could cause engine damage;   (b) The system is difficult to manufacture and has high complexity and cost;   (c) The system is not reliable and only work at certain engine speeds; and   (d) The system has unbalanced load on engine valves.       

     SUMMARY OF THE INVENTION 
     The engine braking apparatus of the present invention addresses and overcomes the foregoing drawbacks of prior art engine braking systems. 
     One object of the present invention is to provide an engine braking apparatus that does not need a neutral position. It will stay at either “off” or “on” position. When the braking apparatus is at the “off” position, it will be biased to the inoperative position and disengaged from the normal engine operation. 
     Another object of the present invention is to provide an engine braking apparatus with fewer components, reduced complexity and manufacturing tolerance, lower cost, and increased system reliability. 
     Still a further object of the present invention is to provide an engine braking apparatus that is simple in construction, easy to install, reliable in operation and effective at all engine speeds. 
     Yet another object of the present invention is to provide an engine braking apparatus that eliminates or greatly reduces the unbalanced load on engine valves during engine braking operation. 
     The apparatus of the present invention converts an internal combustion engine from a normal engine operation to an engine braking operation. The engine includes an exhaust valve train that includes two exhaust valves, a valve bridge and an exhaust valve lifter for cyclically opening and closing the two exhaust valves. The apparatus has an actuation means including a hydraulic system integrated into the exhaust valve train. The hydraulic system contains a hydraulic or braking piston slidably disposed in the valve bridge between an inoperative position and an operative position. In the inoperative position, the braking piston is retracted and the actuation means disengaged from the normal engine operation. In the operative position, the braking piston is extended and the actuation means opens one of the two exhaust valves for the engine braking operation. The apparatus also has a control means for moving the actuation means between the inoperative position and the operative position to achieve the conversion between the normal engine operation and the engine braking operation. 
     The actuation means can also have a dedicated valve lifter. The dedicated valve lifter contains a cam with at least one small cam lobe dedicated to the engine braking operation. The dedicated valve lifter will act on the extended braking piston and open one of the two exhaust valves for the engine braking operation or other auxiliary engine valve events. 
     The actuation means can also have a dedicated load supporting system including a housing installed on the engine. The housing will support the extended braking piston and hold one of the two exhaust valves open for the added auxiliary valve lift during the engine braking operation. 
     The braking valve lifter or the braking load supporting system can also be integrated into the existing exhaust valve lifter by modifying the cam and the rocker arm. The cam will have additional small cam lobe(s) for the engine braking operation, and its existing or normal large cam lobe needs to be enlarged to accommodate the integration of the small braking cam lobe(s) so that they can be skipped during the normal engine operation. The rocker arm will have an added braking valve lash adjusting means that is integrated into the actuation means for setting a lash or gap between the actuation means and the braking exhaust valve. An engine brake reset means can be added to modify the valve lift profile produced by the enlarged normal cam lobe so that the unbalanced load on the exhaust valves due to one-valve braking can be eliminated or reduced. 
     The engine braking apparatus according to the embodiments of the present invention have many advantages over the prior art engine braking systems, such as better performance and reliability, fewer components, reduced complexity, and less weight and lower cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages of the present invention will become more apparent from the following description of the preferred embodiments in connection with the following figures. 
         FIG. 1  is a flow chart illustrating the general relationship between a normal engine operation and an added engine braking operation according to one version of the present invention. 
         FIGS. 2A and 2B  are schematic diagrams of an engine brake control mean at its “On” or “feeding” position and its “Off” or “drain” position according to one version of the present invention. 
         FIGS. 3A and 3B  are schematic diagrams of an engine braking apparatus at the “Off” and “On” positions according to a first embodiment of the present invention. 
         FIGS. 4A and 4B  are schematic diagrams of an engine braking apparatus at the “Off” and “On” positions according to a second embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an engine braking apparatus at the “Off” position according to a third embodiment of the present invention. 
         FIG. 6  is a schematic diagram of an engine braking apparatus at the “Off” position according to a fourth embodiment of the present invention. 
         FIGS. 7A and 7B  are schematic diagrams of an engine braking apparatus at the “Off” and “On” positions according to a fifth embodiment of the present invention. 
         FIG. 8  is a schematic diagram of an engine braking apparatus at the “On” position according to a sixth embodiment of the present invention. 
         FIG. 9  is a schematic diagram of an engine braking apparatus at the “On” position according to a seventh embodiment of the present invention. 
         FIG. 10  is a schematic diagram of an engine braking apparatus at the “On” position according to an eighth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation, not limitation, of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  is a flow chart illustrating the general relationship between a normal engine operation  20  and an added engine braking operation  10  according to one version of the present invention. An internal combustion engine contains two exhaust valves  300  and an exhaust valve lifter  200  for cyclically opening and closing the exhaust valve during the normal engine operation  20 . The engine braking operation  10  is achieved through engine brake control means  50  and engine brake actuation means  100  that contains an inoperative position  0  and an operative position  1 . To convert the engine from its normal operation  20  to the braking operation  10 , the control means  50  will move the actuation means  100  from the inoperative position  0  to the operative position  1 . By default, the control means  50  is at its off position, the actuation means  100  at the inoperative position  0 , and the engine brake disengaged from the exhaust valves  300  and the normal engine operation  20 . 
       FIGS. 2A and 2B  are schematic diagrams of an engine brake control means  50  at the “On” and “Off” positions. When engine braking is needed, the control means  50  containing a three-way solenoid valve  51  is turned on by electric current through the positive and negative terminals  55  and  57  as shown in  FIG. 2A . The spool valve  58  is moved down and the port  111  is opened to allow engine oil to a brake fluid circuit containing a flow passage  211  in the rocker shaft  205  of the engine. The engine oil flow passes a radial orifice  212 , through an undercut  213 , and into a flow passage  214  in the rocker arm  210 . Details of the exhaust valve lifter  200  will be shown in the following figures. When engine braking is not needed, the three-way solenoid valve  51  is turned off as shown in  FIG. 2B . The port  111  is closed to stop engine oil to flow into the engine braking fluid circuit, while and at the same time, the port  222  is opened to allow engine oil to flow out of the engine braking fluid circuit. Note that the control means  50  could be remotely located and used for controlling multiple cylinder engine brakes, and the brake fluid circuit may reach other components of the engine. Also, by blocking the port  222 , the three-way solenoid valve  51  is changed to a two-way solenoid valve. 
       FIGS. 3A and 3B  are schematic diagrams of an engine braking apparatus at the “Off” and “On” positions according to one embodiment of the present invention. There are three major sub-systems: the engine brake actuation means  100 , an exhaust valve lifter  200  and two exhaust valves  300 . Also, a valve bridge  400  is needed here for opening the two exhaust valves  300  with one rocker arm  210 . The exhaust valve lifter  200  and the exhaust valves  300  plus the valve bridge  400  form the so called exhaust valve train. The engine brake actuation means  100  in  FIGS. 3A and 3B  contains a dedicated load supporting system, so that the engine braking load is not supported by the exhaust valve lifter  200 . The dedicated load supporting system in this embodiment is a dedicated valve lifter  200   b  to the engine braking operation. Therefore, this is a compression release engine braking (CREB) system with a dedicated valve lifter  200   b  (a Type III engine brake). 
     The exhaust valve lifter  200  has components that include a cam  230 , a cam follower  235 , and a rocker arm  210 . The exhaust cam  230  contains a large lobe  220  above the inner base circle  225  for the normal engine operation. The rocker arm  210  can pivot on the rocker shaft  205 . One end of the rocker arm  210  has a cam follower  235  while the other end contains a lash adjusting screw  110  that contacts the valve bridge  400 . Normally there is an elephant foot attached to the lash adjusting screw  110 , but not shown here for simplicity. The lash adjusting screw  110  contains a flow passage  115  and is secured to the rocker arm  210  by a lock nut  105 . A spring  198  may be used on the top of the adjusting screw  110  or other places to bias the rocker arm  210  against the valve bridge  400  for better sealing of the engine oil. 
     The dedicated braking valve lifter  200   b  includes a dedicated or braking cam  230   b , a cam follower  235   b , a rocker arm  210   b  and a braking valve lash adjusting means. The braking cam  230   b  has two small braking cam lobes  232  and  233  above the inner cam base circle  225   b  for the engine braking operation. The braking rocker arm  210   b  can pivot on the rocker shaft  205   b  and is normally biased away from the exhaust valves  300  to the inoperative position, for example, to the braking cam  230   b  by a spring  198   b . The braking valve lash adjusting means includes a lash adjusting screw  110   b  that is secured to the rocker arm  210   b  by a lock nut  105   b.    
     The two valves  300   a  and  300   b  (or simply  300 ) are biased upwards against their seats  320  on the engine cylinder head  500  by engine valve springs  310   a  and  310   b  (or simply  310 ) to seal gas (air, during engine braking) from flowing between the engine cylinder and the exhaust manifolds  600 . Normally, mechanical input from the normal exhaust cam  230  is transmitted to both exhaust valves  300  through the exhaust valve lifter  200  for their cyclical opening and closing. During engine braking, additional cam motion from the two small braking cam lobes  232  and  233  (one for compression release engine braking and the other for braking gas recirculation) are transmitted through the dedicated valve lifter  200   b  to only one of the exhaust valves, for example,  300   a . The valve lift for engine braking is about 3 millimeters or less, much smaller than the main exhaust valve lift (&gt;10 millimeters) during the normal engine operation. 
     The engine brake actuation means  100  further includes a hydraulic system integrated into the exhaust valve train. The hydraulic system contains a hydraulic or braking piston  160  slidably disposed in the valve bridge  400  between the inoperative position and the operative position. Normally, the braking piston  160  is biased to the inoperative position by a spring  177  and separated from the dedicated valve lifter  200   b  by a lash  132  set by the lash adjusting means when the cam  230   b  is at its inner base circle  225   b  as shown in  FIG. 3A . The lash  132  is about equal to the motion or stroke  130  of the braking piston  160 . Therefore, the engine braking actuation means  100  is disengaged from the exhaust valve  300   a  and has no effect on the normal engine operation. One end of the spring  177  is on the braking piston  160  and the other end is secured on the valve bridge  400  by a screw  179 . There may be other components that are not shown here for simplicity, such as an elephant foot that may be connected to the lower portion of the lash adjusting screw  110   b . The hydraulic system further contains a flow control valve, or, one-way check valve  170  and the brake fluid circuit formed in the exhaust valve train. A bore  420  with larger diameter than the flow passage or drill  410  leads to the pressure chamber under the braking piston  160 . 
     When engine braking is needed, the engine brake control means  50  is turned on ( FIG. 2A ) to allow engine oil to flow to the braking piston  160  through the brake fluid circuit that further includes the flow passage  115  in the lash adjusting screw  110  and a flow passage  410  in the valve bridge  400  as shown in  FIGS. 3A and 3B . The engine oil pushes the one-way check valve  170  open against a pin  175 . Oil pressure overcomes the load of spring  177  and pushes the braking piston  160  out of the bore  190  in the valve bridge  400  to the operative or extended position as shown in  FIG. 3B . The braking piston  160  is stopped at the clip ring  176  with a stroke of  130 , and the lash or gap  132  is taken up (totally eliminated or greatly reduced). As the braking cam  230   b  rotates, the motion from the small braking cam lobes  232  and  233  is transmitted to the exhaust valve  300   a  through the braking piston  160  and the valve bridge  400  for the engine braking operation, since the braking piston  160  is extended and hydraulically locked to the operative position by the one-way check valve  170 . Also the normally opened bleeding orifice  197  in the braking piston  160  is blocked or sealed by the lash adjusting screw  110   b  (or the elephant foot) on the dedicated braking valve lifter  200   b.    
     When engine braking is not needed, the engine brake control means  50  is turned off 
     ( FIG. 2B ) and there will be little or no oil supplied to the brake fluid circuit. The bleeding orifice  197  will open when the braking piston  160  is pushed away from the dedicated valve lifter  200   b  by the exhaust valve lifter  200 . The oil under the braking piston  160  will bleed out of the orifice  197  under the load of spring  177 . The braking piston  160  will retract into the bore  190  and disengage from the dedicated braking valve lifter  200   b  as shown in  FIG. 3A  so that the motion of the small braking cam lobes  232  and  233  is skipped. The engine brake means  100  is now at the inoperative position and disengaged from the exhaust valve  300   a  and the normal engine operation. Therefore, the bleeding orifice  197  and the spring  177  form a flow draining means to help turning off the engine braking operation. With the flow draining means, the three-way solenoid valve  51 , as shown in  FIGS. 2A and 2B , may be replaced with a two-way solenoid valve. 
     The embodiment as shown in  FIGS. 3A and 3B  could be modified or varied without departing from the scope and spirit of the present invention. For instance, the cam shaft for the engine braking cam  230   b  can be a separate one or the same one as for the normal exhaust cam  230 , and the rocker arm shaft for the engine braking rocker arm  210   b  can be a separate one  205   b  or the same one  205  as for the normal rocker arm  210 . The spring  198  or  198   b  can also take a different type than the coil spring, for example, a flat or leaf spring, or a torsion spring. Another spring could be added to bias the one-way check valve  170  to its seat. 
       FIGS. 4A and 4B  show a different version of the embodiment in  FIGS. 3A and 3B  with an added guide piston  165  in the valve bridge  400 , while the hydraulic or braking piston  160  is now slidably disposed in a bore  163  in the guide piston  165  between an inoperative position and an operative position. 
     When engine braking is needed, the engine brake control means  50  is turned on ( FIG. 2A ) to allow engine oil to flow to the braking piston  160  through the brake fluid circuit that further includes a flow passage  168  across the guide piston  165  as shown in  FIGS. 4A and 4B . The engine oil pushes the one-way check valve  170  open against a pin  175 . Oil pressure overcomes the load of spring  177  and pushes the braking piston  160  out of the bore  163  in the guide piston  165  to the extended or operative position as shown in  FIG. 4B . The braking piston  160  is stopped at the top of bore  190  in the valve bridge  400  with a stroke of  130 , and the lash or gap  132  is taken up. As the braking cam  230   b  rotates, the motion from the small braking cam lobes  232  and  233  is transmitted to the exhaust valve  300   a  through the braking piston  160  and the guide piston  165  for the engine braking operation, since the braking piston  160  is hydraulically locked to the extended position by the one-way check valve  170  and the sealed bleeding orifice  197  by the loaded braking piston  160  and the dedicated brake valve lifter  200   b.    
     During the normal engine operation or when engine braking is not needed, the engine brake control means  50  is turned off ( FIG. 2B ) and there will be little or no oil supplied to the engine braking fluid circuit. The bleeding orifice  197  will open when the braking piston  160  is pushed away from the dedicated valve lifter  200   b  by the exhaust valve lifter  200 . The oil under the braking piston  160  will bleed out of the orifice  197  under the load of spring  177 . The braking piston  160  will retract and disengage from the dedicated braking valve lifter  200   b  as shown in  FIG. 4A  so that the small braking cam lobes  232  and  233  are skipped. The engine brake means  100  is now at the inoperative position and disengaged from the normal engine operation. 
       FIG. 5  is a schematic diagram of an engine braking apparatus according to another embodiment of the present invention. It is similar to the embodiment shown in  FIGS. 3A and 3B  except that the dedicated load supporting system does not have the dedicated valve lifter  200   b  but a housing  125  fixed on the engine. The housing also includes a valve lash adjusting means containing the lash adjusting screw  110   b  secured on the housing  125  by a lock nut  105   b . Therefore, the braking valve lift is not achieved by the actuation of the small cam lobes  232  and  233 , but by preventing the exhaust valve  300   a  that is opened by the exhaust valve lifter  200  from closing or returning to its seat. 
     When engine braking is needed, oil is supplied to the brake fluid circuit through the control means  50  and pushing the braking piston  160  out of the bore  190  in the valve bridge  400 . However, the braking piston  160  can&#39;t move to the fully extended or operative position when the exhaust valve  300   a  is seated because the piston stroke  130  is larger than the valve lash  132  set by the valve lash adjusting means. The braking piston  160  is waiting for the lift or opening of the exhaust valve  300   a . Only after the exhaust valve  300   a  is pushed down by the exhaust valve lifter  200 , the braking piston  160  can be fully extended and hydraulically locked to the operative position by the one-way check valve  170 . Now the opened exhaust valve  300   a  can&#39;t return to its seat but is held open by the braking piston  160  that is also supported by the housing through the lash adjusting means. Also, the bleeding orifice  197  is blocked or sealed by the loaded braking piston  160  against the housing  125  or the lash adjusting means. The opening or lift of the braking valve  300   a  equals to the difference between the piston motion or stroke  130  and the lash  132 . Therefore, this is a bleeder type engine brake (BTEB). 
     When engine braking is not needed, there will be little or no oil supplied to the brake fluid circuit. The oil under the braking piston  160  will bleed out of the orifice  197  under the load of spring  177  when the braking piston  160  is pushed away from the housing  125  by the exhaust valve lifter  200 . The braking piston  160  will retract into the bore  190  in the valve bridge  400  and separate from the housing  125  or the lash adjusting screw  110   b , and the exhaust valve  300   a  return to its seat  320  as shown in  FIG. 5 . The engine brake actuation means  100  is now at the inoperative position and disengaged from the normal engine operation. 
       FIG. 6  shows a new embodiment formed with the features in  FIG. 5  and  FIGS. 4A and 4B  combined. It has the dedicated load supporting system as shown in  FIG. 5  and the hydraulic system integrated into the exhaust valve train as shown in  FIGS. 4A and 4B . Therefore, its working mechanism and operation are obvious and not explained here for simplicity. 
       FIGS. 7A and 7B  are schematic diagrams of an engine braking apparatus at the “Off” and “On” positions according to another embodiment of the present invention. Instead of using a dedicated load supporting system for the engine braking, such as the housing  125  as shown in  FIGS. 5 and 6 , the braking load supporting system of the engine brake actuation means  100  in  FIGS. 7A and 7B  is integrated into the exhaust valve lifter  200 , which also acts as a braking valve lash adjusting means that contains an adjusting screw  110   b , a lock nut  105   b  and an elephant foot  114   b . Sliding in the regular exhaust valve lash adjusting screw  110  is a lash adjusting piston  112  attached with an elephant foot  114  for the continuous oil supply to the braking piston  160  during engine braking Also, a universal pad  430  is added between one or both valves  300  and the valve bridge  400  for an improved load transmitting during the one-valve braking 
     At the “Off” position as shown in  FIG. 7A , there is a lash or gap  132  between the braking load supporting system or the elephant foot  114   b  and the braking piston  160 , which is about the same as the regular exhaust valve lash. A coil spring  198  pushes the rocker arm  210  against the valve bridge  400  for better fuel sealing that can also be achieved by putting a spring between the lash adjusting screw  110  and the lash adjusting piston  112 . The lash adjusting screw  110  sits on the shoulder of the lash adjusting piston  112  during the normal engine operation. The lash  132  and the exhaust valve train are so designed that the braking load support system or the elephant foot  114   b  will not contact the braking piston  160  when it is at the retracted or inoperative position during the full cycle of engine operation. The engine brake actuation means  100  is disengaged from the exhaust valves  300  and has no effect on the normal engine operation. 
     When engine braking is needed, the engine brake control means  50  is turned on ( FIG. 2A ) to allow engine oil to flow to the braking piston  160  through the brake fluid circuit that further includes the cross drill  113  in the lash adjusting screw  110 , the flow passage  115  in the lash adjusting piston  112  and a flow passage  410  in the valve bridge  400  as shown in  FIGS. 7A and 7B . The engine oil pushes a flow control valve, or, a one-way check valve  170  open against a pin  175 . Oil pressure overcomes the load of spring  177  and pushes the braking piston  160  out of the bore  190  in the valve bridge  400  against the braking load support system or the elephant foot  114   b  as shown in  FIG. 7B . However, the braking piston  160  can&#39;t move to the fully extended or operative position when the exhaust valve  300   a  is seated because the piston stroke  130  is larger than the valve lash  132 . The braking piston  160  is waiting for the lift or opening of the exhaust valve  300   a . Only after the valve bridge  400  is pushed down by the exhaust valve lifter  200  with the normal large cam lobe  220  to create a separation between the elephant foot  114   b  and the braking piston  160 , the braking piston  160  can be fully extended to a clip ring  176  and hydraulically locked to the operative position by the one-way check valve  170 . Now the opened exhaust valve  300   a  can&#39;t return to its seat but is held open by the braking piston  160  that is supported by the braking load supporting system (or the braking valve lash adjusting means) integrated into the exhaust valve lifter  200 . Also, the bleeding orifice  197  is blocked or sealed by the loaded braking piston  160  against the elephant foot  114   b . The opening or lift  330  of the braking valve  300   a  equals to the difference between the piston stroke  130  and the lash  132 , which is about 1 millimeter or even less. 
     Due to the one valve braking operation, the valve bridge  400  is tilted slightly. For 1 millimeter braking valve lift  330 , there is 0.5 millimeter movement at the center of the bridge, which is the travel  234  of the lash adjusting piston  112  relative to the lash adjusting screw  110  ( FIG. 7B ). The universal pad  430  is added between the valve bridge  400  and one or both of the exhaust valves  300   a  and  300   b  for improving the load transmitting when the exhaust valve lifter  200  pushes the valve bridge  400  to open both of the exhaust valves  300  during the engine braking operation. When engine braking is not needed, the engine brake control means  50  is turned off 
     ( FIG. 2B ) and there will be little or no oil supplied to the brake fluid circuit. The bleeding orifice  197  will open when the braking piston  160  is pushed away with the valve bridge  400  from the braking load supporting system or the elephant foot  114   b  by the normal exhaust cam lobe  220  of the exhaust valve lifter  200 . The oil under the braking piston  160  will bleed out of the orifice  197  under the load of spring  177 . The braking piston  160  will retract into the bore  190  and separate from the braking load supporting system, and the exhaust valve  300   a  return to its seat  320  as shown in  FIG. 7A . The engine brake actuation means  100  is now at the inoperative position and disengaged from the normal engine operation. 
       FIG. 8  is a schematic diagram of an engine braking apparatus at the “On” position according to a different embodiment of the present invention. Instead of using a dedicated valve lifter  200   b  for the engine braking operation as shown in  FIGS. 3A and 3B , the braking valve lifter of the engine brake actuation means  100  in  FIG. 8  is integrated into the exhaust valve lifter  200 . The small braking cam lobes  232  and  233  are integrated with the existing large cam lobe  220  into the existing exhaust cam  230 . The large normal cam lobe  220  needs to be enlarged even more to accommodate for the extra lift by the small cam lobes  232  and  233 . A spring  199   e  is put between the lash adjusting screw  110  and the lash adjusting piston  112  to bias the rocker arm  210  against the cam  230  and to prevent no-follow of the exhaust valve train components. A different type of spring, for example, a flat spring or a torsion spring, can be used and be put at different location as long as the same purposes can be achieved. A gap  234  is designed between the lash adjusting screw  110  and the lash adjusting piston  112  so that the motion of the small braking cam lobes  232  and  233  is skipped (not transmitted to the exhaust valves  300 ) during the normal engine operation. 
     When engine braking is needed, the engine brake control means  50  is turned on ( FIG. 2A ) to allow engine oil to flow to the braking piston  160  in  FIG. 8  through the brake fluid circuit. The engine oil pushes the one-way check valve  170  open against the pin  175  fixed on the valve bridge  400 . Oil pressure overcomes the load of spring  177  and pushes the braking piston  160  out of the bore  190  in the valve bridge  400 . The braking piston  160  is stopped at the clip ring  176  with a stroke of  130 , and the lash or gap  132  between the elephant foot  114   b  and the braking piston  160  is taken up (totally eliminated (≦0) or greatly reduced (&gt;0)). Now the braking piston  160  is fully extended and hydraulically locked to the operative position by the one-way check valve  170 . As the cam  230  rotates, the motion from the small braking cam lobes  232  and  233  is transmitted to the braking exhaust valve  300   a  through the braking valve lash adjusting means and the hydraulic linkage between the braking piston  160  and the valve bridge  400 . The bleeding orifice  197  in the braking piston  160  is blocked or sealed by the elephant foot  114   b  during the engine braking actuation. Note that the motion from the small braking cam lobes  232  and  233  is not transmitted to the other (or non-braking) exhaust valve  300   b  because of the gap  234  between the lash adjusting screw  110  and the lash adjusting piston  112 . 
     With one exhaust valve (the braking valve)  300   a  opened and the other (the non-braking valve)  300   b  closed, there is a tilt of the valve bride  400 , which will create an unbalanced loading condition when the elephant foot  114  acts on the valve bridge  400  opening both of the exhaust valves  300 . An engine brake reset means  150  is designed here to address the unbalanced loading issue. When the cam lift reaches certain height, the lash adjusting screw  110  will move down and touch the shoulder of the lash adjusting piston  112 . The gap  234  is eliminated and the flow passage  113  in the lash adjusting screw  110  to the braking piston  160  is blocked. The fluid flow from the control means  50  to the braking piston  160  is stopped. The bleeding orifice  197  will open when the braking piston  160  is pushed away with the valve bridge  400  from the elephant foot  114   b  by the exhaust valve lifter  200  with the enlarged normal cam lobe  220 . The oil under the braking piston  160  will bleed out of the orifice  197  under the load of spring  177  and the braking piston  160  will retract into the bore  190 . The braking valve  300   a  will return to its seat  320  with the same closing timing as the non-braking valve  300   b . If the braking piston  160  were still extended, the braking valve  300   a  would close much later and have a higher lift at the valve exchange top dead center, which may cause engine valve to piston contact. The higher lift and later closing valve lift without resetting are due to the enlarged cam lobe  220  with transition slopes for the small braking cam lobes  232  and  233 . Once the exhaust valves  300  are seated, the rocker arm  210  continues to rotate anti-clockwise, which forms the gap  234  and opens the flow passage  113  so that oil can refill the braking piston  160 . The braking piston  160  will be fully extended before the small braking cam lobes  232  and  233  start to lift the rocker arm  210  so that their motion can be transmitted to the braking valve  300   a , and the engine braking cycle repeats. Therefore, the reset means  150  will modify the valve lift profile produced by the enlarged normal cam lobe  220 , not that by the small braking cam lobes  232  and  233 . The lash adjusting piston  112  is also acting as an engine brake reset piston to block the oil flow to the braking piston  160 , and the bleeding orifice  197  as an engine brake reset flow passage for draining out the oil flow under the braking piston  160 . 
     When engine braking is not needed, the engine brake control means  50  is turned off ( FIG. 2B ) and there will be little or no oil supplied to the brake fluid circuit. The bleeding orifice  197  will open when the braking piston  160  is separated from the elephant foot  114   b . The oil under the braking piston  160  will bleed out of the orifice  197  under the load of spring  177 . The braking piston  160  will retract into the bore  190  and not touch the elephant foot  114   b  during the whole cycle of cam rotation. The engine brake actuation means  100  is now at the inoperative position and disengaged from the engine operation. 
       FIG. 9  shows a different version of the embodiment in  FIG. 8  with a different engine brake reset means  150  that interacts with the engine brake actuation means  100  so that the valve lift profile from the enlarged normal cam lobe  220  can be modified. The reset means contains a reset piston  165   r  that is slidably disposed in the valve bridge  400  below the elephant foot  114 . The reset piston  165   r  as well as the rocker arm  210  is biased to the valve bridge  400  by a spring  198  to prevent no-follow of exhaust valve train components. 
     When engine braking is needed, the engine brake control means  50  is turned on ( FIG. 2A ) to allow engine oil to flow to the reset piston  165   r  and the braking piston  160  through the brake fluid circuit that further includes the flow passage  197   r  in the reset piston  165   r . Oil pressure overcomes the load of spring  198  as well as spring  177  and pushes the reset piston  165   r  as well as the braking piston  160  upwards to rotate the rocker arm  210  anticlockwise towards the cam  230  so that the engine braking apparatus goes to the “On” position as shown in  FIG. 9 . The braking piston  160  is stopped at the clip ring  176  with a stroke of  130  that takes up the lash or gap between the elephant foot  114   b  and the braking piston  160 , while the reset piston  165   r  moves up with a stroke of  234  that takes up the gap existed between the cam follower  235  and the cam  230  during the normal engine operation. Now the braking piston  160  is extended and hydraulically locked to the operative position by the one-way check valve  170 , and the flow draining passage or reset flow passage  167  is blocked by the reset piston  165   r . As the cam  230  rotates, the motion from the small braking cam lobes  232  and  233  is transmitted to the braking exhaust valve  300   a  through the braking valve lash adjusting means and the hydraulic linkage between the braking piston  160  and the valve bridge  400 . The motion from the small braking cam lobes  232  and  233  is not transmitted to the other exhaust valve  300   b  because of the gap  234  between the reset piston  165   r  and the valve bridge  400  as shown in  FIG. 9 . The oil under the reset piston  165   r  is pushed back through the flow passage  197   r . An accumulator may be needed in the braking fluid circuit to absorb the flow pumped back by the reset piston  165   r.    
     When the cam lift produced by the enlarged normal cam lobe  220  is higher than that by the small braking lobes  232  and  233 , the reset piston  165   r  will touch the valve bridge  400  and act on both of the exhaust valves  300   a  and  300   b . Before the reset piston  165   r  touches the valve bridge  400  to block the fluid flow from the control means  50  to the braking piston  160 , it opens a reset flow passage  167  since the reset height  131  is smaller than the gap  234 . The oil under the braking piston  160  will drain out of the passage  167  and the braking piston  160  will retract into the bore  190  under the load of spring  177 . The opened exhaust valve  300   a  will return to its seat  320  and the titled valve bridge  400  will be leveled to eliminate any unbalanced load when the reset piston  165   r  acts on the valve bridge  400 . Now both of the exhaust valves  300   a  and  300   b  will be opened by the enlarged cam lobe  220 . Once the exhaust valves  300  are seated, the rocker arm  210  will continue to rotate anti-clockwise and the reset piston  165   r  will move up in the valve bridge  400  under oil pressure to block the reset flow passage  167  so that oil can refill and push out the braking piston  160 . The braking piston  160  will be fully extended before the small braking lobes  232  and  233  start to lift the rocker arm  210  so that their motion can be transmitted to the braking valve  300   a , and the engine braking cycle repeats. 
     When engine braking is not needed, the engine brake control means  50  is turned off 
     ( FIG. 2B ) and there will be little or no oil supplied to the brake fluid circuit. When the reset piston  165   r  moves down and opens the reset flow passage  167 , the oil under the braking piston  160  will drain out and the braking piston  160  will retract into the bore  190  under the load of spring  177 . Without oil pressure, the reset piston  165   r  will be biased to the valve bridge  400  by spring  198  to form a gap between the cam follower  235  and the cam  230  to skip the motion from the small braking cam lobes  232  and  233 . The two exhaust valves  300   a  and  300   b  will be opened by the top portion of the enlarged cam lobe  220  through the rocker arm  210 , the reset piston  165   r  and the valve bridge  400 . The retracted braking piston  160  will not touch the elephant foot  114   b  of the braking valve lash adjusting means during the whole cycle of cam rotation. The engine brake actuation means  100  is now at the inoperative position and disengaged from the normal engine operation. 
     With the reset means  150 , the electro-hydro-mechanical system of the engine brake control means  50 , as shown in  FIGS. 2A and 2B , does not need to have a three-way solenoid valve  51  because the reset means  150  is also a flow draining means and will drain out the engine oil under the engine brake actuation means  100  to turn off the engine brake when is needed. Therefore there is no need for the drain port  222 , and the three-way solenoid valve  51  can be replaced with a two-way solenoid valve to open and close the oil supply port  111 . 
       FIG. 10  shows a different version of the embodiment in  FIG. 9  with a different engine brake reset means  150  to interact with the engine brake actuation means  100 . A sleeve  163  with a reset flow passage  164  is inserted in the valve bridge  400 . The reset flow passage  164  will communicate with the reset flow passage  193  in the reset piston  165   r  that slides in the sleeve  163 . Therefore the reset flow from the braking piston  160  does not flow to the outside the valve bridge  400 , but back to the braking fluid circuit. Therefore, an accumulator will be needed in the braking fluid circuit. The operation of the engine braking apparatus shown in  FIG. 10  is almost the same as that shown in  FIG. 9  and not explained here for simplicity. 
     CONCLUSION, RAMIFICATIONS, AND SCOPE 
     It is clear from the above description that the engine braking apparatus according to the embodiments of the present invention have one or more of the following advantages over the prior art engine braking systems. 
     First, the compression release engine brake (CREB) systems disclosed here have fewer components, less complexity, and lower cost. Different from the prior art engine braking system disclosed by the &#39;116 patent, the dedicated brake rocker arm  210   b  is not at the neutral position but biased to the cam. Therefore, the systems disclosed here will not interfere with the normal engine operation. 
     Second, the bleeder type engine brake (BTEB) systems disclosed here have a control means  50  for active control of the engine brake actuation means  100 . Different from the prior art engine braking system disclosed by the &#39; 469  and &#39; 867  patents, the actuation of the engine brake systems disclosed here does not depend on valve floating. Therefore, the BTEB systems disclosed here are more reliable, tolerant with different exhaust brakes, and effective at all engine speeds. 
     Third, the engine brake reset means  150  disclosed here eliminates or greatly reduces the unbalanced load on the exhaust valves  300  by the valve bridge  400 . It also greatly reduces the valve overlap, the braking valve lift at the valve overlap, and the seating velocity of the non-braking exhaust valve  300   b . Therefore, the engine braking performance is better and the potential of contact between the engine valve and piston is eliminated. In addition, the reset means  150  disclosed here is simple, accurate and reliable. 
     While my above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. Many other variations are possible. For example, the rocker arm  210   b  biased to the cam  230   b  can be set to the inoperative position through other mechanism, such as using a spring system to hold the rocker arm  210   b  so that it separates from the cam  230   b  and the braking piston  160 . Different from the prior art engine braking system disclosed by the &#39;116 patent, the hydraulic system disclosed here is not integrated into the dedicated brake rocker arm  200   b . Therefore, there is no such risk that the braking piston  160  would be knocked and get loose to cause engine damage. 
     Also, the apparatus disclosed here can be applied to a push tube type engine instead of the overhead cam type engine as shown in the figures. 
     Also, the apparatus disclosed here can be applied to other engine valve train with different engine valve system and engine valve lifter, such as the intake valve system and the intake valve lifter. 
     Also, the dedicated load supporting system installed on the engine could be different, for example, a housing fixed on the engine, or a rocker arm mounted on a rocker shaft. The system could contain a cam, for example, the braking cam  230   b  for a compression release type (Type III) engine brake, or no cam for a bleeder type (Type IV) engine brake. 
     Also, a poppet type solenoid valve could be used to replace the spool type valve  51  of the control means  50  as shown in  FIGS. 2A and 2B . 
     Also, the apparatus disclosed here can be used to produce other auxiliary valve event. In general, the engine valve lift can be modified to produce an engine valve event that is different from the normal engine operation. The engine valve event could be the engine braking operation, an exhaust valve EGR event or an intake valve EGR event, etc. 
     Also, the two small cam lobes  232  and  233  for the engine braking operation shown in  FIG. 3A  and other figures could take different profiles. They could be individual ones or combined to form a single cam lobe. It could have a substantially constant lift during the engine compression stroke for a partial cycle bleeder brake. The combined single cam lobe can even be extended to be connected to the large cam lobe  220  if the small cam lobes  232  and  233  and the large cam lobe  220  are integrated into the same cam  230  as shown in  FIGS. 8 and 9 . Now the “single” cam lobe is in fact just a transition “step” to the large cam lobe  220 . In summary, there is at least one small cam lobe and the at least one small cam lobe includes the constant lift type for a partial cycle bleeder brake. 
     Also, springs  177 ,  198 , and  199   e  could have different types, for example, a coil spring, a flat spring or a torsion spring, and be put at different locations as long as the same purposes can be achieved. 
     Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.