Abstract:
Apparatus for modifying engine valve lift to produce an engine valve event in an internal combustion engine, the engine including at least one exhaust valve and an exhaust valve lifter for cyclically opening and closing the at least one exhaust valve, includes (a) an actuator for operating the at least one exhaust valve to produce said modified engine valve lift, said actuator having an inoperative position and an operative position; in said inoperative position said actuator being disengaged from the operation of the at least one exhaust valve, and in said operative position said actuator opening the at least one exhaust valve for said engine valve event; and (b) a controller for moving said actuator between said inoperative position and said operative position.

Description:
This application is a continuation of application Ser. No. 12/217,813, filed Jul. 9, 2008 now U.S. Pat. No. 7,789,065. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates generally to the modification of engine valve lift for producing an engine valve event in an internal combustion engine, particularly to engine braking apparatus and methods 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 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 engine valve event for the normal engine operation. 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 cam 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 valve lift, which normally generates a bleeder type engine brake; and   (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 which is reciprocated in a master piston bore by a mechanical input from the engine, such as the pivoting movement of the fuel injector rocker arm. Hydraulic fluid in the circuit transmits the motion of the master piston 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. This is a Type I engine brake. 
     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 systems have certain inherent disadvantages that have limited their application to primarily larger vehicles such as heavy duty trucks (and typically, on engines having a displacement of about 10 liters or more), and their retrofit to existing engines is largely impossible without substantial modification of the engine cylinder head. 
     One of the disadvantages associated with the conventional prior art CREB system is due to the fact that the load from engine braking is supported by the engine components. Because the engine braking load is much higher than the normal engine operation load, many parts of the engine, such as the rocker arm, the push tube, the cam, etc. must be modified to accommodate the engine braking system. Thus, the overall weight, height, and cost of using the prior art CREB system are likely to be excessive, and limit its commercial application. 
     Another disadvantage associated with the conventional prior art CREB system is the high and unique noise generated by the releasing of high-pressure gas or “blow down” through the exhaust valve(s) during the compression stroke, near the top dead center position of the engine piston. 
     Additional disadvantages of the prior art systems reside in their relative complexity and the necessity for using precision components because they require accurate timing and hydraulic actuators capable of opening the exhaust valves precisely when required. Thus they may be comparatively expensive and difficult or impossible to install on certain engines. 
     Yet another disadvantage associated with the conventional prior art CREB system of hydraulic type is the compliance of the braking system, which may cause the braking valve lift to collapse at the peak braking load (near compression top dead center (TDC) of the engine piston) and further increase the braking load. The large reduction of braking valve lift due to compliance will reduce the braking performance and excessive braking load may cause engine damage. 
     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. An example of BTEB system and method is provided by the disclosure of the present inventor, U.S. Pat. No. 6,594,996, which is hereby incorporated by reference. 
     Usually, the initial opening of the braking valve(s) in a bleeder braking operation is far in advance of the compression TDC and then the braking valve lift is held constant for a period of time. As such, a BTEB may require much lower force to open the valve(s) due to early valve actuation, and generates less noise due to continuous bleeding instead of the rapid blow down of the CREB. Moreover, a BTEB often requires fewer components and can be manufactured at a lower cost. Thus, a BTEB can overcome some of the disadvantages of the CREB. Indeed, the BTEB systems have achieved certain commercial success, especially in the application to smaller vehicles, such as the middle and light duty trucks (and typically, on engines having a displacement of less than 10 liters). Following are some BTEB systems that are currently on the market. 
     (a) BTEB Operated by Rocker Arm with Eccentric Shift 
     U.S. Pat. No. 5,335,636 discloses a bleeder type engine brake (BTEB) system wherein the pivot center of the engine exhaust rocker arm is displaced or shifted in a downward direction by an eccentric that is connected to a hydraulic piston/actuator by a level arm. The displacement or shift of the rocker arm pivot center causes the exhaust valves to open during braking operation of the engine to create a partial cycle bleeder braking event. This is a Type IV engine brake. 
     The BTEB system of the type described above requires an extra mechanical component between the hydraulic piston or actuator and the rocker arm. The system also requires intermediate arms, a second rocker arm eccentric bore, features on the small end of the actuation/pivot arm and features on the mechanical actuation end of the piston. These parts and features all add cost and complexity, and reduce system reliability. Also, the system is integrated into the engine exhaust valve train. Load from engine braking by opening both exhaust valves is so high that other parts of the engine, such as the rocker arm, the push tube, the cam, etc. must be redesigned. Finally, such type of engine brakes cannot be retrofitted into existing engines. 
     (b) BTEB Operated by a Dedicated Engine Braking Valve 
     U.S. Pat. No. 5,168,848 discloses a bleeder type engine brake (BTEB) system that has an extra exhaust valve in addition to the normal engine exhaust valve(s). The extra exhaust valve is dedicated to engine braking and opened exclusively during braking operation of the engine. The dedicated engine braking valve is actuated by pneumatic or hydraulic means and held open to create a full cycle bleeder braking event. This is a Type V engine brake. 
     The BTEB system of the type described above is integrated into the cylinder head of the engine, thereby substantially conditioning its design and manufacture. The engine braking device is therefore dedicated to a particular type of engine. Moreover, the introduction of the extra exhaust valve creates an extra pocket in the combustion chamber, which increases engine emission. Also, such type of engine brakes can not be used in existing engines. 
     (c) BTEB Operated by Engine Valve Floating 
     U.S. Pat. No. 5,692,469 and U.S. Pat. No. 7,013,867 disclose a bleeder type engine brake (BTEB) system for engines with one and two exhaust valves per cylinder. The BTEB system includes 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 not consistent, 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. Again, such type of engine brakes may not be able to retrofit into existing engines. 
     (d) BTEB Operated by High-Pressure Oil 
     U.S. Pat. No. 6,866,017 and U.S. Pat. No. 6,779,506 disclose a bleeder type engine brake (BTEB) that is actuated and controlled by high-pressure hydraulic fluid, or oil. The hydraulic fluid is supplied from a hydraulic rail, or oil rail, to a respective fuel injector at each engine cylinder to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber during normal engine operation. A hydraulic actuator in the engine brake uses the already available high-pressure oil to actuate and hold one exhaust valve open to create a full cycle bleeder braking event. This is also a Type IV engine brake. 
     The BTEB system of the type described above is dedicated to a particular type of engine that has high-pressure oil rail (source), which greatly limits its application. Sophisticated electronic control is needed to eliminate excessive oscillations of the shared common high pressure source and to ensure a smooth transition between engine braking operation and normal engine operation. Also, such type of engine brakes cannot be retrofitted into existing engines. 
     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 can only be installed on a particular type of engines; 
     (b) The system cannot be retrofitted to existing engines; 
     (c) The engine braking load is carried by the engine components; 
     (d) The system installment needs redesign of the engine or engine components; 
     (e) The system has too many components and is too complex; 
     (f) The system increases the manufacturing tolerance requirements and is too costly; 
     (g) The system is not reliable and only work at certain engine speeds; and 
     (h) The system affects normal engine performance (emission, oil rail pressure, etc.). 
     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 can be installed on all types of engines, especially on smaller size engines. 
     Another object of the present invention is to provide an engine braking apparatus that can be retrofitted to existing engines. 
     Yet another object of the present invention is to provide an engine braking apparatus wherein the engine (valve train) components are not subject to the heavy engine braking loads so that the installment of the engine braking apparatus does not need redesign of the engine or engine components. 
     Still another object of the present invention is to provide an engine braking apparatus with fewer components, reduced complexity, lower cost, and increased system reliability. 
     A further object of the present invention is to provide such an engine braking apparatus that contains a braking valve lash adjusting mechanism so that it does not increase the manufacturing tolerance requirements of many of the components. 
     Still a further object of the present invention is to provide an engine braking apparatus that is rugged and simple in construction, easy to install, reliable in operation and effective at all engine speeds. 
     Yet a further object of the present invention is to provide engine brake actuation means that transmit force, or the engine braking load, through mechanical linkage means that does not have high compliance and overloading problems associated with hydraulic means. The mechanical linkage means includes rotatable devices, slidable devices, ball-locking devices, and a toggle device. 
     Still another object of the present invention is to provide an engine braking apparatus that will not interfere with the normal engine operation. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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. 
         FIG. 2  is a schematic diagram of an engine braking apparatus with an exhaust valve train of the engine according to a first embodiment of the present invention. 
         FIG. 3  is a schematic diagram of an engine braking apparatus according to a second embodiment of the present invention. 
         FIG. 4A  is a schematic diagram of an engine braking apparatus according to a third embodiment of the present invention. 
         FIG. 4B  is a schematic diagram of a slidable plunger contained in the engine braking apparatus shown in  FIG. 4A . 
         FIG. 5A  is a schematic diagram of an engine braking apparatus according to a fourth embodiment of the present invention. 
         FIG. 5B  is a schematic diagram of a slidable plunger contained in the engine braking apparatus shown in  FIG. 5A . 
         FIG. 6  is a schematic diagram of an engine braking apparatus with an exhaust valve train of the engine according to a fifth embodiment of the present invention. 
         FIGS. 7A and 7B  are schematic diagrams of an engine brake control mean at its “on” or “feeding” position and its “off” or “drain” position according to at least one embodiment of the present invention. 
         FIG. 8A  is a schematic diagram of an engine braking apparatus according to a sixth embodiment of the present invention. 
         FIG. 8B  is a schematic diagram of a slidable plunger contained in the engine braking apparatus shown in  FIG. 8A . 
         FIGS. 8C and 8D  are schematic diagrams of a spring used in the engine braking apparatus shown in  FIG. 8A . 
         FIG. 8E  is a schematic diagram showing the relationship between the spring shown in  FIGS. 8C and 8D  and the slidable plunger shown in  FIG. 8B . 
         FIG. 9A  is a schematic diagram of an engine braking apparatus with an exhaust valve train of the engine according to a seventh embodiment of the present invention. 
         FIG. 9B  is a schematic diagram of a slidable plunger assembly contained in the engine braking apparatus shown in  FIG. 9A . 
         FIG. 10  is a schematic diagram of an engine braking apparatus with an exhaust valve train of the engine according to an eighth embodiment of the present invention. 
         FIGS. 11A and 11B  are schematic diagrams of an engine brake actuation means at its “off” and “on” position for an engine braking apparatus according to a ninth embodiment of the present invention. 
         FIGS. 12A and 12B  are schematic diagrams of an engine brake actuation means at its “off” and “on” position for an engine braking apparatus according to a tenth embodiment of the present invention. 
         FIGS. 13A and 13B  are schematic diagrams of an engine brake actuation means at its “off” and “on” position for an engine braking apparatus according to an eleventh embodiment of the present invention. 
         FIGS. 14A and 14B  are schematic diagrams of engine brake actuation means at its “off” and “on” position for an engine braking apparatus according to an twelfth embodiment of the present invention. 
         FIGS. 15A and 15B  are schematic diagrams of engine brake actuation means at its “off” and “on” position for an engine braking apparatus according to an thirteenth 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 at least one exhaust valve  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 , which takes place after the exhaust valve  300  is actuated by the exhaust valve lifter  200 . 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 valve  300 . 
       FIG. 2  is a schematic diagram of an engine braking apparatus with an engine exhaust valve train according to one embodiment of the present invention. A typical truck engine has two exhaust valves  300   a  and  300   b  per engine cylinder. The two valves are biased upwards against their seats  320  on the engine cylinder head  500  by engine valve springs  310   a  and  310   b  to seal gas (air, during engine braking) from flowing between the engine cylinder and the exhaust manifolds  600 . The exhaust valve lifter  200  includes a rocker arm  210  pivotally mounted on a rocker shaft  205  for transmitting a mechanical input from a cam  230  to the exhaust valves through a cam follower  235  and a valve bridge  400 . The cam contains a lift profile  220  above the Cain inner base circle  225  for cyclically opening and closing the exhaust valves during the normal engine operation. 
     With continued reference to  FIG. 2 , the engine brake actuation means  100  includes a brake housing  125  that is fixed on the engine block (not shown). In the brake housing there is a bore  120 , in which a rotatable device  135  with a stem  115  rotates. Underneath the rotatable device there are two surfaces  140  and  145  that have a height difference  130 . The first surface  140  is commensurate with the operative position for the engine braking operation and the second surface  145  commensurate with the inoperative position for the normal engine operation. The rotatable device  135  is biased to the inoperative position by an engine brake control means  50  that is also fixed on the engine block. The control means  50  comprises an electromechanical system that may contain an electric motor  51 , such as the well-known step motor, which has a predetermined rotational angle  53 . The electric motor is turned on and off by electric current through the positive and negative terminals  55  and  57  on the electric motor. 
     The actuation means  100  as shown in  FIG. 2  is at its inoperative position and the engine brake is disengaged from the engine operation. When engine brake is needed, the control means  50  is turned on, which tends to rotate the actuation means  100  into the operative position. However, there is an intervention between the rotatable device  135  and the valve bridge  400  when the exhaust valve  300   a  is at or near its seat  320 . The actuation means  100  is waiting for the lift or opening of the exhaust valve. Only after the exhaust valve  300   a  is pushed down by the exhaust valve lifter  200 , the actuation means  100  can be rotated into its operative position at which the first surface  140  will be over the valve bridge surface  405 . When the exhaust valve  300   a  returns, the valve bridge surface  405  will contact the first surface  140  on the actuation means  100 . Due to the height difference  130  between the first surface  140  and the second surface  145 , the exhaust valve  300   a  pushed out by the exhaust valve lifter  200  cannot close or return to its seat  320  but is held open to create an engine braking event. 
     The engine brake according to the embodiment shown in  FIG. 2  is a bleeder type or Type IV engine brake. The engine braking event is produced by modifying the existing engine valve lift. The modified lift of the engine braking valve  300   a  by the actuation means  100  during non-exhaust strokes (intake stroke, compression stroke, and expansion or power stroke) is approximately 0.5 to 3.0 millimeters, much smaller than the lift of the same engine valve by the exhaust valve lifter  200  during the engine exhaust stroke. Such a small lift is within the regular valve seating ramp and the impact load between the actuation means  100  and the braking valve  300   a  is small. However, we can further reduce such impact load by improving the existing exhaust valve lift profile with an even slower seating ramp starting before the valve  300   a  contacts the actuation means  100 . 
     The load generated by the engine braking event according to the embodiment of the present invention is not passed to the exhaust valve lifter  200 , but to the engine block through a lash adjusting screw  110  that is secured to the brake housing  125  by a lock nut  105 , which avoids the excessive overall engine weight, height, and cost that were experienced with some prior art engine braking systems whose load is carried by the engine components. 
     A lash adjusting system with the lash adjusting screw  110  and the rotatable device  135  that is also slidable in the housing is designed for setting a lash between the actuation means  100  and the braking valve  300   a . The braking valve lash adjustment is necessary due to engine valve growth and manufacturing tolerance. The height difference  130  between the first surface  140  and the second surface  145  minus the braking valve lash determines the braking valve lift for the engine braking event or operation. Also, the lash adjusting screw  110  sits in a circumferential groove  150  in the rotatable device  135 , which forms a motion limiting means that can be used to control the rotational angle between the inoperative position and operative position. 
     Since the engine braking valve lift is controlled through the lash adjustment, not by a stroke limited piston, it is much less affected by the dimensional tolerance of the engine brake components. Therefore, the engine braking apparatus according to the embodiment of the present invention avoid using high cost precision components that some prior art engine braking systems require. 
       FIG. 3  shows a similar embodiment to that shown in  FIG. 2  except that the engine brake control means  50  is an electrohydromechanical system that contains a three-way solenoid valve  51   a . The solenoid valve  51   a  has a spool  58  with a predetermined stroke  53   a  and is turned on and off by an electric current through the positive and negative terminals  55  and  57 . The control means  50  could be remotely located and used for controlling multiple cylinder engine brakes. A fluid circuit is formed in the engine brake actuation means  100  and in the engine for transmitting hydraulic fluid, for example, engine oil, from the control means  50  to the actuation means  100 . When the spool  58  slides in the brake housing  125 , it opens or closes a port (an orifice)  11  or  22  to allow the engine oil into or out of the fluid circuit including a flow passage  126  in the brake housing  125 . There is an annular cut or groove  127  on the stem  115  through which the pressurized engine oil can pass to a flow passage  128  and spray out of a bleeding orifice  129  in the rotatable device  135  when the engine brake is turned on. 
     The rotatable device  135  is biased against the adjusting screw  110  to the inoperative position by a spring  118  that can provide both compressional and torsional preload. One end of the spring  118  is fixed in the brake housing  125  and the other end in the rotatable device  135 . When the liquid flows out of the bleeding orifice  129 , it generates a jet propulsion force opposite to the flow jet direction, which overcomes the torsional preload by the spring  118  and rotates the rotatable device  135  from the inoperative position into the operative position when the engine braking valve is pushed down by the exhaust valve lifter  200 . The angle of rotation is controlled by a motion limiting means defined by the circumferential groove  150  in the rotatable device  135 , which has stop surfaces against the adjusting screw  110 . 
     When engine braking is not needed, the three-way solenoid valve  51   a  is turned off and the spool  58  will close the oil supply port  11  and open the drain port  22  ( FIG. 3 ). There will be no oil jet flow out of the bleeding orifice  129  and thus no propulsion force on the rotatable device  135  so that it will return back to the inoperative position by the spring  118 , and the actuation means  100  will be disengaged from the normal engine operation. Note that the drain port  22  may be not needed for turning off the engine brake due to the bleeding orifice  129 . Therefore, a two-way solenoid valve plus the bleeding orifice may be used to replace the three-way solenoid valve  51   a.    
     Alternatively, the rotation of the rotatable device  135  can be achieved by other types of fluid and mechanical interaction, such as jet flow out of the brake housing  125  that impinges on the rotatable device  135  with an impulsion force; hydraulic piston in the brake housing  125  that acts on the rotatable device  135 ; or mechanical means, such as gear system or rope and pulley system; electric means; magnetic means; and a combination of two or more of the above means, such as the electrohydromechanical system. 
       FIG. 4A  is a schematic diagram of an engine braking apparatus according to another embodiment of the present invention, in which the engine brake actuation means  100  contains a slidable device  135   a  that will not rotate but only slide in the bore  120  of the brake housing  125  for the braking valve lash adjustment. The slidable device is biased up by a compression spring  118   a  against the lash adjusting screw  110 . In the slidable device  135   a  there is a horizontal bore  415  in which a braking plunger  136  shown with details in  FIG. 4B  can only slide due to an anti-rotation guide that is formed by two surfaces  136   a  on the braking plunger fitting in a slot  139  cut underneath the bore  415 . The braking plunger contains a first surface  140  commensurate with the operative position and a second surface  145  commensurate with the inoperative position. The two surfaces are located on the protrusion portion of the braking plunger and have a height difference  130 . The braking plunger  136  is biased inwards to the inoperative position by a flat (or leaf) spring  177 . One end of the spring  177  is secured to the slidable device  135   a  by at least one screw  179  and the other end is on the braking plunger surface  136   b  and hooked onto the protrusion  136   c.    
     Note that the slidable device  135   a  can have different shapes. If it is a piston, then there will be a bore  120   a  in the brake housing  125  to match the piston, and also an anti-rotation mechanism that is formed by a hole or a radial groove  150  against the lash adjusting screw  110  for preventing the rotation of the slidable device. If it is a rectangular or square block, then  120   a  will be a flat surface. The stem  115  can also take different shapes as long as it can slide up and down in the brake housing for the lash adjustment between the engine brake actuation means and the engine braking valve. 
     When engine braking is needed, the control means  50  containing the solenoid valve  51   a  ( FIG. 3 ) is turned on. The pressurized engine oil gets into the flow passage  126  in the brake housing  125 , overcomes the preload by the spring  177 , and pushes the braking plunger  136  out after the exhaust valve  300   a  is pushed down by the exhaust valve lifter  200  ( FIG. 4A ). There is a motion limiting means that controls the movement of the braking plunger  136 . The plunger movement or stroke is defined by the distance between the stop surface  420  at the left end of the slot or undercut  139  and the spring  177  whose stop surface contacts the stop surface  136   d  on the braking plunger. Once the first surface  140  on the braking plunger  136  is over the valve bridge top surface  405 , the exhaust valve  300   a  pushed out by the exhaust valve lifter  200  cannot close or return to its seat  320  but is held open to create an engine braking event. 
     The lash adjusting system for this engine braking apparatus comprises the lash adjusting screw  110 , the slidable device  135   a  in the housing  125 , and the plunger  136 . It is designed for setting a lash between the brake actuation means  100  and the braking valve  300   a . The height difference  130  between the first surface  140  and the second surface  145  on the plunger minus the braking valve lash determines the braking valve lift for the engine braking event or operation. 
       FIGS. 5A and 5B  show a similar embodiment to that shown in  FIGS. 4A and 4B  except that the braking plunger  136  is biased to the inoperative position by a compression spring  177   a . One end of the spring sits on the slidable device  135   a  and the other end on the braking plunger. Another difference is the motion limiting means. A pin  142  on the slidable device fits into an axial groove  137  in the braking plunger for controlling the axial motion of the braking plunger. The pin and groove combination also forms an anti-rotation guide for the braking plunger. Also the operative and inoperative surfaces  140  and  145  are undercuts on the braking plunger as shown in  FIG. 5B . 
       FIG. 6  shows another embodiment with a slidable device. Here the brake apparatus further comprises the valve bridge  400 . A braking plunger  136  as shown in  FIG. 4B  now is slidably disposed in a bore  415  in the valve bridge  400 . The plunger  136  is guided by an anti-rotation guide formed by two surfaces  136   a  ( FIG. 4B ) on the plunger and a slot  139  that is cut on top of the bore  415 . The plunger  136  contains a first surface  140  (the operative position) and a second surface  145  (the inoperative position). Facing upwards to the lash adjusting screw  110 , the two surfaces are located on the protrusion portion of the braking plunger  136  and have a height difference  130 . The lash adjusting screw is secured to the brake housing  125  by a lock nut  105 . The braking plunger  136  is biased inwards to the inoperative position by the spring  177 . One end of the spring  177  is secured to the valve bridge  400  by at least one screw  179  and the other end is on the braking plunger surface  136   b  ( FIG. 4B ). 
       FIGS. 7A and 7B  are schematic diagrams of an engine brake control means  50  at its on and off positions. When engine braking is needed, the control means  50  containing a three-way solenoid valve  51   a  is turned on as shown in  FIG. 7A , and the port  11  is opened to allow engine oil to a fluid circuit comprising 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 . Note that the control means  50  could be remotely located and used for controlling multiple cylinder engine brakes, and the fluid circuit may reach other components of the engine. 
     With reference back to  FIG. 6 , the engine oil flows from the rocker arm  210  to a pressure chamber  425  in the valve bridge  400  through a flow passage  410 . The engine oil pressure overcomes the preload of the spring  177 , and pushes the braking plunger  136  out after the valve bridge  400  (and the braking valve  300   a ) is pushed away from the adjusting screw  110  by the exhaust valve lifter  200 . The movement of the braking plunger  136  is controlled by a motion limiting means with a plunger stroke defined by the distance between the stop surface  420  on the valve bridge  400  and the spring  177  whose stop surface contacts the stop surface  136   d  ( FIG. 4B ) on the braking plunger  136 . Once the operative surface  140  is out and under the adjusting screw  110 , the exhaust valve  300   a  pushed out by the exhaust valve lifter  200  cannot close or return to its seat  320  but is held open to create an engine braking event. 
     The lash adjusting system for this engine braking apparatus ( FIG. 6 ) comprises the lash adjusting screw  110 , the valve bridge  400 , and the braking plunger  136  slidable in the valve bridge. The height difference  130  between the first surface  140  and the second surface  145  on the plunger minus the braking valve lash determines the braking valve lift for the engine braking event or operation. 
     When engine braking is not needed, the three-way solenoid valve  51   a  is turned off and the spool  58  will close the oil supply port  11  and open the drain port  22  as shown in  FIG. 7B . Without oil pressure acting on the plunger  136 , it will be pushed back by the spring system  177 . Once the second surface  145  is under the adjust screw as shown in  FIG. 6 , the engine brake means  100  is at the inoperative position and disengaged from the normal engine operation. 
     Note that the bleeding orifice  418  in the valve bridge is optional and used for turning off the engine brake faster or even totally eliminating the need of the drain port  22 . Therefore, a two-way solenoid valve plus the bleeding orifice  418  may be used to replace the three-way solenoid valve  51   a . Also a spring may be desirable to bias the rocker arm  210  against the valve bridge for a better sealing of the fluid from the passage  214  in the rocker arm to the passage  410  in the valve bridge. 
       FIG. 8A  shows a similar embodiment to that shown in  FIG. 6  except that the braking plunger  136  shown with details in  FIG. 8B  is biased to the inoperative position by a special spring device  138  that also acts as a stop and an anti-rotation guide to the braking plunger as shown in  FIGS. 8C ,  8 D and  8 E. Another difference is that the first and second surfaces  140  and  145  are not on the protrusion ( FIG. 4B ) but undercuts on the braking plunger as shown in  FIG. 8B . The bleeding orifice  418  in the valve bridge as shown in  FIG. 6  can still be used but is not shown here. Therefore the three-way solenoid valve with the drain port  22  in  FIG. 7B  is used for turning off the engine brake. 
     With continued reference to  FIGS. 8A and 8B , the braking plunger  136  is slidable in the valve bridge  400  and biased to the inoperative position by a spring  138   a  of the spring device  138  whose details are shown in  FIGS. 8C and 8D . There is an anti-rotation guide and the braking plunger with guiding surfaces  136   a  can only slide between the two legs  138   b  of the spring device that are fixed into the valve bridge  400 . The spring  138   a  acts on surface  136   b  of the braking plunger. The slot or cut  138   c  in the spring fits onto the protrusion  136   c  on the plunger, which can also acts as a guide to the sliding of the braking plunger as shown in  FIG. 8E . A motion limiting means controls the motion of the braking plunger  136 . The plunger stroke is defined by the distance between the stop surface  420  on the valve bridge  400  and the spring legs  138   b  that contact the stop surface  136   d  on the braking plunger as shown in  FIGS. 8B to 8E . 
       FIG. 9A  shows another embodiment with the braking plunger  136  shown with details in  FIG. 9B  sliding in the valve bridge  400 . The plunger  136  contains a first surface  140  commensurate with the operative position and a second surface  145  commensurate with the inoperative position. The two surfaces are on two cylindrical surfaces and have a height difference  130  ( FIG. 9B ). The braking plunger  136  is biased to the inoperative position ( FIG. 9A  where surface  145  is under lash adjusting screw  110 ) by a coil spring  177   a . One end of spring  177   a  sits on a spring seat  176  that is mounted on the braking plunger  136 . The other end of the spring sits on another spring seat  178 . Seat  178  is slidable in the bore  183   a  but normally is stopped against a pin  142  fixed in the valve bridge  400 . There is a slot  137  or axial cut across the bore  183   a  in the braking piston  136 , which has a width slightly larger than the pin  142 . The pin  142  and the slot  137  can form a motion limiting means to control the movement of the braking plunger  136 . 
     When engine braking is needed, the control means  50  is turned on as shown in  FIG. 7A  to allow engine oil to flow through the engine braking fluid circuit and into a pressure chamber  425  in the valve bridge  400  through a flow passage  410  ( FIG. 9A ). The engine oil pressure overcomes the preload of the spring  177   a , and pushes the braking plunger  136  out of the bore  415  after the valve bridge  400  (and the braking valve  300   a ) is pushed away from the adjusting screw  110  by the exhaust valve lifter  200 . When the surface  136   d  in the slot  137  hits the pin  142 , the braking plunger  136  will stop moving. Now the braking plunger  136  is fully out or extended and the operative surface  140  is under the adjusting screw  110 , the exhaust valve  300   a  pushed out by the exhaust valve lifter  200  cannot close or return to its seat  320  but is held open to create an engine braking event. 
     The lash adjusting system for this engine braking apparatus ( FIG. 9A ) comprises the lash adjusting screw  110 , the valve bridge  400 , and the braking plunger  136  slidable in the valve bridge. The height difference  130  between the first surface  140  and the second surface  145  on the plunger ( FIG. 9B ) minus the braking valve lash  132  ( FIG. 9A ) determines the braking valve lift for the engine braking event or operation. 
     When engine braking is not needed, the control means  50  is turned off and there will be no or little oil supplied to the engine braking fluid circuit. The oil pressure will not be high enough and plunger  136  will be pushed back into the valve bridge  400  by the spring  177   a . Once the second surface  145  is under the lash adjusting screw  110  as shown in  FIG. 9A , the engine brake means  100  is at the inoperative position and disengaged from the normal engine operation. Again, the bleeding orifice  418  in the valve bridge is optional and used for turning off the engine brake. 
       FIG. 10  shows yet another embodiment with the braking plunger  136  slidably disposed in the valve bridge  400 . However, the plunger  136  only contains the first surface  140  commensurate with the operative position, while the second surface  145  commensurate with the inoperative position is on the valve bridge  400  and separated from the lash adjusting screw  110  by a lash  132 . The two surfaces  140  and  145  have a height difference  130 . The braking plunger  136  is biased to the inoperative position by a coil spring  177   a . One end of spring  177   a  is on the braking plunger  136  and the other end on a spring seat  178  that is secured on the valve bridge  400  by at least one screw  179 . Seat  178  is also used as a stop to the braking plunger  136 , which limits the movement of the braking plunger  136 . 
     When engine braking is needed, the control means  50  is turned on ( FIG. 7A ) to allow engine oil to flow through the engine braking fluid circuit and into a pressure chamber  425  in the valve bridge  400  as shown in  FIG. 10 . The engine oil pressure overcomes the preload of the spring  177   a , and pushes the braking plunger  136  out of the bore  415  after the valve bridge  400  (and the braking valve  300   a ) is pushed away from the adjusting screw  110  by the exhaust valve lifter  200 . The braking plunger  136  is stopped at the spring seat  178  and fully out or extended. The operative surface  140  is now under the adjusting screw  110 , and the exhaust valve  300   a  pushed out by the exhaust valve lifter  200  cannot close or return to its seat  320  but is held open to create an engine braking event. 
     The lash adjusting system for this engine braking apparatus ( FIG. 10 ) comprises the lash adjusting screw  110  and the valve bridge  400  that contains the braking plunger  136 . The height difference  130  between the first surface  140  and the second surface  145  minus the braking valve lash  132  determines the braking valve lift for the engine braking event or operation. Instead of a cylindrical surface as shown in  FIG. 10 , the first surface  140  can be a flat surface on the braking plunger  136  as shown in  FIG. 8A . 
     When engine braking is not needed, the control means  50  is turned off and there will be no or little oil supplied to the engine braking fluid circuit. The oil pressure will not be high enough and the plunger  136  will be pushed back into the valve bridge  400  by the spring  177   a . The engine brake means  100  now is at the inoperative position and disengaged from the normal engine operation. 
       FIG. 11A  shows a different embodiment of the engine brake actuation means  100 . It is a ball-locking device over the top surface  405  of the valve bridge  400 . The ball-locking device is contained in a lash adjusting system with the lash adjusting screw  110  secured to the brake housing  125  by a lock nut  105 . Depending on the position of the ball-locking device, a braking piston  160  can extend or retract to generate the operative position or inoperative position commensurate with the engine braking operation or the normal engine operation. 
     When engine braking is needed, the three-way solenoid valve  51   a  ( FIG. 3 ) is turned on and the port  11  will be open to allow engine oil into the fluid circuit comprising a flow passage  126  in the brake housing  125 . The engine oil flows into a chamber  123  through an annular groove  121 , one or more orifices  122  and flow passage  180  as shown in  FIG. 11B . The oil pressure pushes the braking piston  160  downwards with the ball-locking piston  165  against a spring  177   a . The spring is supported by a spring seat  178  that is secured to the lash adjusting screw by screws  179 . The braking piston  160  will slide in a bore  415  and stop at a clip ring  176  when a plurality of balls  175  contained in holes in the braking piston are aligned with an annular groove  170  in the bore  415 . The oil pressure overcomes the preload of spring  199  and pushes the ball-locking piston  165  down to the bottom of the bore  182  in the braking piston, which locks the balls in the groove  170 . Now the braking piston  160  is at its extended position with a lift  130 , and the exhaust valve  300   a  pushed out by the exhaust valve lifter  200  ( FIG. 11A ) cannot close or return to its seat  320  but is held open by the braking piston  160  to create an engine braking event. The engine braking load from the braking piston is passed to the lash adjusting screw  110  through the balls  175 . Note that the bleeding orifice  168  is designed to drain the oil leaked to the backside of the ball-locking piston to avoid hydraulic lock. 
     The lash adjusting system for this engine braking apparatus comprises the lash adjusting screw  110 , the ball-locking system contained in the lash adjusting screw, and the valve bridge  400 . The height difference  130  between the retracted position and the extended position of the ball-locking device minus the braking valve lash determines the braking valve lift for the engine braking event or operation. 
     When engine braking is not needed, the solenoid valve  51   a  is turned off and the spool  58  will close the oil supply port  11  and open the drain port  22  as shown in  FIG. 3 . Without oil pressure acting on the ball-locking piston  165 , it will be pushed upwards by the spring  199  and the balls forced into the recess or annular cut of the ball-locking piston  165  under the upward push of the braking piston  160  by the spring  177   a . Once the balls are out of the annular groove  170  in the bore  415 , the braking piston  160  is free to move up and back to its retracted position when the engine brake actuation means  100  is disengaged from the engine operation, as shown in  FIG. 11A . 
       FIGS. 12A and 12B  show a similar embodiment to that shown in  FIGS. 11A and 11B  except that the balls  175  of the ball-locking device are contained in holes in the lash adjusting screw  110  and the ball-locking piston  165  is at the outside of the lash adjusting screw. When engine brake actuation means  100  is at its inoperative position, the braking piston  160  is biased up by the spring  177  or the returning braking valve  300   a  and retracted in the bore  415  as shown in  FIG. 12A . Note that the braking piston is part of the lash adjusting system, and the motion limiting means is formed by the ball-locking means. 
     When engine brake is needed, the engine brake control means  50  ( FIG. 3 ) is turned on and oil pressure pushes the braking piston  160  down against the spring  177  to a stop  176  so that the balls are aligned with an annular groove  170   a  on the braking piston. Now the ball-locking piston  165  can be pushed down by the oil pressure against a spring  199   a  and lock the balls into the groove  170   a  as shown in  FIG. 12B . The braking piston  160  is now at its extended position with a lift  130 , and the exhaust valve  300   a  pushed out by the exhaust valve lifter  200  ( FIG. 12A ) cannot close or return to its seat  320  but is held open by the braking piston  160  to create an engine braking event. The engine braking load from the braking piston  160  is passed to the lash adjusting screw  110  through the balls  175 . 
     When engine braking is not needed, the engine brake control means  50  ( FIG. 3 ) is turned off and there will be no oil pressure acting on the ball-locking piston  165 , which will be pushed upwards by the spring  199   a  toward the top of the bore  182 . Once the annular groove  170  on the ball-locking piston  165  is aligned with the balls  175  in the adjusting screw holes, they will move out of the annular groove  170   a  and the braking piston  160  is free to be moved up in the bore  415  by the spring  177  and the upward valve motion. The braking piston  160  is now back to the retracted position and the actuation means  100  is disengaged from the engine operation, as shown in  FIG. 12A . 
       FIGS. 13A and 13B  show another ball-locking device with the balls  175  not contained in holes as in the previous embodiments but restrained by three elements or surfaces. The first surface is the tapered surface  192  on the bottom of the adjusting screw  110 . The second surface is the flat surface on the top of the braking piston  160 . The third surface is on the ball-locking piston  165 , either on the annular groove  170  when the ball-locking device is at the retracted position as shown in  FIG. 13A  or on the bore  415  when the ball-locking device is at the extended position as shown in  FIG. 13B . Note that the braking piston  160  is also part of the motion limiting means incorporated into the ball-locking device. 
     When engine brake is needed, the control means  50  ( FIG. 3 ) is turned on and oil pressure pushes down both the ball-locking piston  165  and the braking piston  160 , while the balls  175  move down and inwards along the tapered surface  192 . Note that the adjusting screw stem  191  is smaller than the braking piston  160  that slides in the bore  415  inside the ball-locking piston. Once the balls are out of the annular groove  170  in the bore  415 , the ball-locking piston can move down further. The total travel of the system is limited by the spring  177  that acts as a spring and a stop. Now the braking piston is at its extended position and locked with the lift  130  as shown in  FIG. 13B , which is finalized by the upward push of the returning braking valve  300   a . The engine braking load is passed from the braking piston  160  to the lash adjusting screw  110  through the balls  175 . 
     The lash adjusting system for the engine braking apparatus comprises the lash adjusting screw  110 , the ball-locking system in the housing, and the valve bridge  400  ( FIG. 11A ). The height difference  130  between the retracted position and the extended position of the ball-locking device minus the braking valve lash determines the braking valve lift for the engine braking event or operation. 
     When engine braking is not needed, the control means  50  ( FIG. 3 ) is turned off and there will be no oil pressure acting on the ball-locking piston  165 , which will be pushed upwards by the spring  199   a  towards the top of the bore  182 . The balls are now aligned with and forced into the annular groove  170  in the ball-locking piston  165  and the braking piston  160  can be pushed up by the spring  177  or the returning braking valve  300   a  and back to its retracted position as shown in  FIG. 13A . 
       FIGS. 14A and 14B  show another ball-locking device with balls  175  restrained by three elements or surfaces. The first surface is the tapered surface  192  on the braking piston  160 . The second surface is the bottom flat surface on the lash adjusting screw  110  and the third surface on the ball-locking piston  165  that slides in a bore  182  in the adjusting screw. Again, the braking piston  160  is part of the lash adjusting system and the motion limiting means is incorporated into the ball-locking device. 
     When engine brake is needed, the control means  50  ( FIG. 3 ) is turned on and oil pressure pushes down the braking piston  160  to a stop  178 , while the balls  175  move outward along the tapered surface  192 . Due to the oil pressure on the ball-locking piston  165 , it is pushed upward against the spring  199 . The venting orifice  168  on top of the adjusting screw  110  is designed to eliminate hydraulic lock of the ball-locking piston  165 . The tapered surface  192  and balls  175  are so designed that when the braking piston  160  is at its extended position, the ball-locking piston  165  is at the highest position and its large diameter surface locks the balls into a position shown in  FIG. 14B . The height difference  130  between the retracted position and the extended position of the ball-locking device minus the braking valve lash determines the braking valve lift for the engine braking event or operation. The engine braking load is passed from the braking piston  160  to the lash adjusting screw  110  through the balls  175 . 
     When engine braking is not needed, the control means  50  ( FIG. 3 ) is turned off and there will be no oil pressure acting on the ball-locking piston  165 , which will be pushed downward by the spring  199  so that the balls  175  can move inward. The braking piston  160  can now slide upward in the bore  415  under the push of spring  177  or the returning braking valve  300   a . Note that the force by spring  177  on the braking piston  160  is higher than that by spring  199  on the ball-locking piston  165  so that the ball-locking device could be back to its retracted position as shown in  FIG. 14A . 
       FIGS. 15A and 15B  show a different embodiment of the engine brake actuation means  100 . It is a toggle device that contains two pins  184  and  186 , and a braking piston  160  that slides in a vertical bore  415  in the brake housing  125 . The upper pin  184  has two spherical ends; one engaged with a socket in the adjusting screw  110 , and the other with another socket in the lower pin  186  whose lower end sits in a third socket in the braking piston  160 .  FIG. 15A  shows the retracted position of the toggle device where the two pins guided in the slot  137  that is cut through a pin-locking piston  162  are pushed to the left by the spring  199   a . The pin-locking piston  162  slides in a horizontal bore  182  in the braking housing  125 . There is a smaller pin-locking piston  164  that slides in the larger pin-locking piston  162 . The slot  137  in piston  162  has a width that matches the diameter of the two pins and a length that is smaller than the diameter of the bore  415 . There will be always contact (no separation) among the braking piston, the lower pin, the upper pin, and the adjusting screw due to the upward force of the spring  177  that is secured to the brake housing  125  with at least one screw  179 . 
     When engine brake is needed, the control means  50  ( FIG. 3 ) is turned on and oil pressure can push both pin-locking pistons  162  and  164  to the right against the preload of the spring  199   a . Note that the small pin-locking piston  164  can be moved to the right further to lock the two pins in a vertical position, aligned with the adjusting screw and the braking piston, as shown in  FIG. 15B . Now the toggle device is locked to its extended position. The motion limiting means for this toggle device is unique. The angle between the two pins decides the height difference  130 , while the angle itself is controlled by the two pin-locking pistons. The pin-locking piston  162  has a stroke  131 . The two bleeding orifices  168  and  169  are designed to eliminate hydraulic lock so that the two pistons can move freely. The orifice  169  is in a mounting screw  161  that acts as a spring seat and a stop to the large pin-locking piston  162 . 
     Again, a bleeding orifice could be added to the flow passage  126  in the engine braking fluid circuit for turning off the engine brake faster or even totally eliminating the need of the drain port  22  ( FIG. 3 ), so that a two-way solenoid valve plus the bleeding orifice may be used to replace the three-way solenoid valve  51   a.    
     The lash adjusting system is incorporated into the toggle device. The height difference  130  between the retracted position and the extended position of the toggle device minus the braking valve lash determines the braking valve lift for the engine braking event or operation. The engine braking load is passed from the braking piston  160  to the lash adjusting screw  110  through the two pins  184  and  186 . 
     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:
         (a) The system can be installed on all types of engines;   (b) The system can be retrofitted to existing engines;   (c) The engine braking load is not carried by the engine (valve train) components;   (d) The system has no need for redesign of the engine or engine components;   (e) The system has fewer components, reduced complexity, and lower cost;   (f) The system has a braking valve lash adjusting system;   (g) The system is more rugged and simple in construction, easier to install, more reliable in operation, and effective at all engine speeds; and   (h) The system transmits force, or the engine braking load, through mechanical linkage means that does not have high compliance and overloading problems associated with hydraulic means used by some of the prior art engine brakes.       

     Due to the above advantages, the engine braking apparatus disclosed here can be used not only on truck engines, but also personal car engines; not only to slow down vehicles, but also to enhance vehicle cruise control, braking gas or exhaust gas recirculation control, and other engine or vehicle controls. 
     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, instead of sitting over the top surface  405  of the valve bridge  400  for opening one exhaust valve  300   a  for engine braking as shown in  FIG. 2  and other figures, the engine brake actuation means  100  can sit over the top surface  215  of the rocker arm  210  or under the bottom surface of the rocker arm  210  on the cam follower  235  side for opening two exhaust valves  300  ( 300   a  and  300   b ) for engine braking. The top surfaces could have different shape other than flat surface, for example, a spherical shape. 
     Also, instead of one plunger  136  in one side of the valve bridge  400  for opening one exhaust valve  300   a  for engine braking as shown in  FIG. 6  and other figures, two plungers  136  can be put in both sides of the valve bridge  400  for opening two exhaust valves  300  ( 300   a  and  300   b ) for engine braking. 
     Also, the engine braking apparatus disclosed here can be applied to a push tube type engine (not shown here) instead the overhead cam type engine as shown in  FIG. 2  and other figures, as well as to the engine&#39;s intake valve system (not shown here) instead the exhaust valve system. 
     Also, the engine brake actuation means  100  can be controlled (turned on and off) by other types of control means  50 , like a simple mechanical means, such as the wire control mechanism for a bicycle brake control. And a poppet type control valve could be used to replace the spool type valve  51   a  of the control means  50  as shown in  FIG. 3 . 
     Also, the two surfaces  140  and  145  commensurate with the operative and inoperative positions of the engine brake actuation means  100  as shown in  FIG. 2  and other figures can be combined as one tapered or sloped surface, for example, a wedge type mechanism. And the tapered surface could be actively controlled to generated variable braking valve lift, which could be very useful for different engine braking needs, for example, at different engine speeds. 
     Also, the housing  125  can be different. It can be a rocker arm mounted on a rocker shaft; and there can be a different cam that has more than one lobe. 
     Further, two levels of oil supply pressure could be provided to the fluid circuit as shown in  FIG. 6  so that during engine braking, the oil with full supply pressure flows into the braking circuit to actuate the engine braking actuation means  100 , while during the normal engine operation, the oil flowing through a pressure reduction device, for example, an orifice, into the braking fluid circuit does not have high enough pressure to actuate the actuation means  100  but can be used for system lubrication. 
     Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.