Patent Publication Number: US-8528508-B2

Title: Individual rocker shaft and pedestal mounted engine brake

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the priority of provisional application Ser. No. 61/301,645 filed Feb. 5, 2010 and relates to, is a continuation in part of, and claims the priority of U.S. patent application Ser. No. 12/611,297 filed Nov. 11, 2009 entitled “Rocker Shaft Mounted Engine Brake,” which is a continuation in part of, and claims the priority of U.S. patent application Ser. No. 12/076,173 filed Mar. 14, 2008 entitled “Engine Brake Having An Articulated Rocker Arm And A Rocker Shaft Mounted Housing,” which relates to, and claims the priority of U.S. Provisional Patent Application Ser. No. 60/895,318 filed Mar. 16, 2007, which is entitled “Engine Brake Having an articulated Rocker Arm and a Rocker Shaft Mount Housing.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a system and method for providing engine braking in an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines typically use either a mechanical, electrical, or hydro-mechanical valve actuation system to actuate the engine valves. These systems may include a combination of camshafts, rocker arms and push rods that are driven by the engine&#39;s crankshaft rotation. When a camshaft is used to actuate the engine valves, the timing of the valve actuation may be fixed by the size and location of the lobes on the camshaft. 
     For each 360 degree rotation of the camshaft, the engine completes a full cycle made up of four strokes (i.e., expansion, exhaust, intake, and compression). Both the intake and exhaust valves may be closed, and remain closed, during most of the expansion stroke wherein the piston is traveling away from the cylinder head (i.e., the volume between the cylinder head and the piston head is increasing). During positive power operation, fuel is burned during the expansion stroke and positive power is delivered by the engine. The expansion stroke ends at the bottom dead center point, at which time the piston reverses direction and the exhaust valve may be opened for a main exhaust event. A lobe on the camshaft may be synchronized to open the exhaust valve for the main exhaust event as the piston travels upward and forces combustion gases out of the cylinder. Near the end of the exhaust stroke, another lobe on the camshaft may open the intake valve for the main intake event at which time the piston travels away from the cylinder head. The intake valve closes and the intake stroke ends when the piston is near bottom dead center. Both the intake and exhaust valves are closed as the piston again travels upward for the compression stroke. 
     The above-referenced main intake and main exhaust valve events are required for positive power operation of an internal combustion engine. Additional auxiliary valve events, while not required, may be desirable. For example, it may be desirable to actuate the intake and/or exhaust valves during positive power or other engine operation modes for compression-release engine braking, bleeder engine braking, exhaust gas recirculation (EGR), or brake gas recirculation (BGR). FIG. 19 of co-pending application Ser. No. 11/123,063 filed May 6, 2005, which is hereby incorporated by reference, illustrates examples of a main exhaust event 600, and auxiliary valve events, such as a compression-release engine braking event 610, bleeder engine braking event 620, exhaust gas recirculation event 630, and brake gas recirculation event 640, which may be carried out by an exhaust valve using various embodiments of the present invention to actuate exhaust valves for main and auxiliary valve events. 
     With respect to auxiliary valve events, flow control of exhaust gas through an internal combustion engine has been used in order to provide vehicle engine braking. Generally, engine braking systems may control the flow of exhaust gas to incorporate the principles of compression-release type braking, exhaust gas recirculation, exhaust pressure regulation, full cycle bleeder and/or partial bleeder type braking. 
     During compression-release type engine braking, the exhaust valves may be selectively opened to convert, at least temporarily, a power producing internal combustion engine into a power absorbing air compressor. As a piston travels upward during its compression stroke, the gases that are trapped in the cylinder may be compressed. The compressed gases may oppose the upward motion of the piston. As the piston approaches the top dead center (TDC) position, at least one exhaust valve may be opened to release the compressed gases in the cylinder to the exhaust manifold, preventing the energy stored in the compressed gases from being returned to the engine on the subsequent expansion down-stroke. In doing so, the engine may develop retarding power to help slow the vehicle down. An example of a prior art compression release engine brake is provided by the disclosure of the Cummins, U.S. Pat. No. 3,220,392 (November 1965), which is hereby incorporated by reference. 
     During bleeder type engine braking, in addition to, and/or in place of, the main exhaust valve event, which occurs during the exhaust stroke of the piston, the exhaust valve(s) may be held slightly open during remaining three engine cycles (full-cycle bleeder brake) or during a portion of the remaining three engine cycles (partial-cycle bleeder brake). The bleeding of cylinder gases in and out of the cylinder may act to retard the engine. Usually, the initial opening of the braking valve(s) in a bleeder braking operation is in advance of the compression TDC (i.e., early valve actuation) and then lift is held constant for a period of time. As such, a bleeder type engine brake may require lower force to actuate the valve(s) due to early valve actuation, and generate less noise due to continuous bleeding instead of the rapid blow-down of a compression-release type brake. 
     Exhaust gas recirculation (EGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during positive power operation. EGR may be used to reduce the amount of NO x  created by the engine during positive power operations. An EGR system can also be used to control the pressure and temperature in the exhaust manifold and engine cylinder during engine braking cycles. Generally, there are two types of EGR systems, internal and external. External EGR systems recirculate exhaust gases back into the engine cylinder through an intake valve(s). Internal EGR systems recirculate exhaust gases back into the engine cylinder through an exhaust valve(s). Embodiments of the present invention primarily concern internal EGR systems. 
     Brake gas recirculation (BGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during engine braking operation. Recirculation of exhaust gases back into the engine cylinder during the intake and/or early compression stroke, for example, may increase the mass of gases in the cylinder that are available for compression-release braking. As a result, BGR may increase the braking effect realized from the braking event. 
     SUMMARY OF THE INVENTION 
     Applicants have developed an innovative system for actuating an engine valve comprising: a rocker shaft having a hydraulic fluid supply passage; a lost motion housing having a collar surrounding the rocker shaft, an actuator piston bore, and an internal hydraulic circuit extending from the actuator piston bore to the hydraulic fluid supply passage; means for securing the lost motion housing in a fixed position relative to the rocker shaft; and an actuator piston slidably disposed in the actuator piston bore. In the foregoing system, the hydraulic fluid supply passage extends internally through the rocker shaft. Further, the lost motion housing may have two collars surrounding the rocker shaft. Still further, a control valve bore may be provided in the lost motion housing, wherein said control valve bore communicates with the internal hydraulic circuit and a control valve is disposed in the control valve bore. Still further, a check valve may be disposed in the control valve. Still further, the means for securing may be provided on a side of the lost motion housing which is distal from the actuator piston, on a side of the lost motion housing which is proximal to the actuator piston, or on both the side of the lost motion housing distal from the actuator piston and the side of the lost motion housing proximal to the actuator piston. Still further, the means for securing the lost motion housing may comprise a boss extending from the lost motion housing collar and a bolt extending from the boss into an engine component. Still further, the means for securing the lost motion housing may comprise a flange extending from the lost motion housing proximal to the actuator piston and a bolt extending from said flange into an engine component. Still further, the system may further comprise a solenoid valve adapted to control the supply of hydraulic fluid to said hydraulic fluid supply passage. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference, and which constitute a part of this specification, illustrate certain embodiments of the invention and, together with the detailed description, serve to explain the principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to assist the understanding of this invention, reference will now be made to the appended drawings, in which like reference characters refer to like elements. The drawings are exemplary only, and should not be construed as limiting the invention. 
         FIG. 1  is a pictorial view of an engine brake system having an articulated rocker arm and a rocker shaft mounted housing for master and slave pistons constructed in accordance with a first embodiment of the present invention and disposed in an internal combustion engine. 
         FIG. 2  is an overhead exploded pictorial view of an engine brake system having an articulated rocker arm, rocker shaft mounted housing, and a rocker arm return spring in accordance with the first embodiment of the present invention. 
         FIG. 3  is an overhead exploded pictorial view of the underside of the engine brake system shown in  FIG. 2  as arranged in accordance with the first embodiment of the present invention. 
         FIG. 4  is a cross-sectional side view of a rocker shaft mounted housing of  FIGS. 2 and 3  which shows the master and slave pistons arranged in accordance with the first embodiment of the present invention. 
         FIG. 5  is a second cross-sectional side view of the rocker shaft mounted housing of  FIGS. 2 and 3  which shows the control valve in hydraulic communication with the rocker shaft and the master and slave pistons as arranged in accordance with the first embodiment of the present invention. 
         FIG. 6  is a cross-sectional front view of the rocker shaft mounted housing of  FIGS. 2 and 3  showing the control valve and the slave piston as arranged in accordance with the first embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of the engine brake system of  FIGS. 2 and 3  showing the articulated rocker arm, rocker shaft mounted housing, and cam lobe as arranged in accordance with the first embodiment of the present invention when the engine brake system is turned off. 
         FIG. 8  is a cross-sectional side view of the engine brake system of  FIGS. 2 and 3  showing the articulated rocker arm, rocker shaft mounted housing, and cam lobe as arranged in accordance with the first embodiment of the present invention when the engine brake system is turned on and rocker arm is contacting the cam base circle. 
         FIG. 9  is a cross-sectional side view of the engine brake system of  FIGS. 2 and 3  showing the articulated rocker arm, rocker shaft mounted housing, and cam lobe as arranged in accordance with the first embodiment of the present invention when the engine brake system is turned on and the rocker arm is contacting the cam compression-release bump. 
         FIG. 10  is a cross-sectional side view of an engine brake system showing the articulated rocker arm, rocker shaft mounted housing, and cam lobe as arranged in accordance with a second embodiment of the present invention when the engine brake system is turned off. 
         FIG. 11  is an exploded pictorial view of an engine brake system having an articulated rocker arm, rocker shaft mounted housing, and a rocker arm return spring in accordance with the second embodiment of the present invention. 
         FIG. 12  is a cross-sectional side view of the engine brake system of  FIGS. 2 and 3  showing the oil passage schematic between the engine oil supply passage, solenoid valve and rocker shaft. 
         FIG. 13  is an overhead pictorial view of a valve actuation system that may be used for bleeder braking in particular, having a rocker shaft mounted housing in accordance with a second embodiment of the present invention. 
         FIG. 14  is a pictorial view of the underside of the valve actuation system shown in  FIG. 13  as arranged in accordance with the second embodiment of the present invention. 
         FIG. 15  is a cross-sectional side view of a rocker shaft mounted housing of  FIGS. 13 and 14  which shows an alternative or additional flange for securing the rocker shaft mounted housing in a fixed position in accordance with an alternative embodiment of the present invention. 
         FIG. 16  is a second cross-sectional side view of the rocker shaft mounted housing of  FIGS. 13 and 14  which shows the control valve in hydraulic communication with the rocker shaft and the actuator piston as arranged in accordance with the second embodiment of the present invention. 
         FIG. 17  is a cross-sectional front view of the rocker shaft mounted housing of  FIGS. 13 and 14  showing the control valve and the actuator piston as arranged in accordance with the second embodiment of the present invention. 
         FIG. 18  is a cross-sectional side view of the valve actuation system of  FIGS. 13 and 14  showing the rocker shaft mounted housing and actuator piston as arranged in accordance with the second embodiment of the present invention when the actuator piston is separated by a lash space from the sliding pin/engine valve. 
         FIG. 19  is a cross-sectional side view of the valve actuation system of  FIGS. 13 and 14  showing the rocker shaft mounted housing and actuator piston as arranged in accordance with the second embodiment of the present invention when the system is turned on and the actuator piston has actuated the engine valve. 
         FIG. 20  is a cross-sectional side view of the valve actuation system of  FIGS. 13 and 14  illustrating control of hydraulic fluid supply by a solenoid valve. 
         FIG. 21  is a cross-sectional side view of a valve bridge disposed between an actuator piston and an engine valve in accordance with an alternative embodiment of the present invention. 
         FIG. 22  is a cross-sectional view of an alternative actuator piston in accordance with an alternative embodiment of the present invention. 
         FIG. 23  is a pictorial view of an engine brake system having an individual rocker shaft and rocker shaft pedestal assembly, two articulated rocker arms (an exhaust rocker arms and an intake rocker arms), rocker arm shaft mounted brake housing, and a solenoid valve mounted in the solenoid valve bore in accordance with an embodiment of the present invention and disposed in an internal combustion engine. 
         FIG. 24  is a pictorial view of an engine brake system having two individual rocker shaft and rocker shaft pedestal assemblies, four articulated rocker arms (two exhaust rocker arms and two intake rocker arms), and rocker arm shaft mounted brake housing in accordance with an embodiment of the present invention and disposed in an internal combustion engine. 
         FIG. 25  is an overhead pictorial view of an engine brake system having a rocker shaft mounted brake housing in accordance with an embodiment of the present invention. 
         FIG. 26  is an overhead pictorial view of a cam cap showing a solenoid valve bore for receiving a solenoid valve in accordance with an embodiment of the present invention. 
         FIG. 27  is a pictorial cross-sectional view of the rocker shaft mounted brake housing and the solenoid valve mounted in the solenoid valve bore of  FIG. 23  showing the engine oil supply passage to the solenoid valve and the brake actuation oil passage to each rocker shaft and rocker shaft pedestal assembly in accordance to an embodiment of the present invention. 
         FIG. 28  is a pictorial cross-sectional view of the rocker shaft mounted brake housing of  FIGS. 23 ,  24 , and  25  that shows the brake actuation oil passage to each rocker shaft and pedestal assembly and the actuator oil supply passages contained in the rocker shaft mounted brake housing in accordance to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Reference will now be made in detail to a first embodiment of the present invention, an example of which is illustrated in the accompanying drawings. With reference to  FIG. 1 , a system  50  for actuating engine valves arranged in accordance with a first embodiment of the present invention is shown.  FIGS. 2-9  show different views of the system shown in  FIG. 1  and/or its components. The system  50  may include a cam  100 , an articulated half rocker arm  200 , a brake housing  300 , a rocker shaft  400 , and a solenoid valve  500 . The rocker arm  200  may be biased away from (or alternatively towards) the cam  100  by a return spring  210  (see also  FIG. 11 ). The brake housing may be secured in position by a anti-rotation bolt  310 . 
     With reference to  FIGS. 2 and 3 , the rocker arm  200  may further include a cam roller  220 , a lug  230 , and a central collar  240 . The rocker arm return spring  210  may bias the rocker arm  200  towards the brake housing  300  such that the lug  230  contacts the master piston  340 . The brake housing  300  may further include an anti-rotation bolt boss  312 , a control valve  320 , a master piston  340 , a slave piston  350  and rocker shaft collars  360  and  362 . A slave piston return spring  352  may bias the slave piston  350  up into a slave piston bore formed in the brake housing  300 . 
     With reference to  FIG. 4 , the rocker shaft collars  360  and  362  of the brake housing  300  may be mounted on the rocker shaft  400 . The brake housing may be secured in a fixed position relative to the rocker shaft  400  by the anti-rotation bolt  310  (not shown). The brake housing  300  may include a master piston  340  slidably disposed in a master piston bore  302  and a slave piston  350  slidably disposed in a slave piston bore  304 . A master-slave hydraulic fluid passage  306  may extend between the master piston bore  302  and the slave piston bore  304 . The slave piston return spring  352  may bias the slave piston  350  upward and against a slave piston lash adjustment screw  354  which extends into the slave piston bore  304 . The rocker shaft  400  may include a first hydraulic passage  410  adapted to provide lower pressure hydraulic fluid to the rocker arm  200  (not shown in  FIG. 4 ) for lubrication purposes. The rocker shaft  400  may also include a second hydraulic passage  420 , the purpose of which is explained in connection with  FIG. 5 . 
     With reference to  FIG. 5 , adjacent to the slave piston  350  (shown in  FIG. 4 ) the brake housing  300  may further include control valve  320 . The control valve  320  may fill the master and slave bores with hydraulic fluid when low pressure hydraulic fluid is supplied to the lower portion of the control valve via a supply passage  308 . A connection hydraulic passage  422  provided in the rocker shaft  400  may extend between the second hydraulic passage  420  and the supply passage  308  provided in the brake housing  300 . As a result, hydraulic fluid may be supplied to the control valve, and the master and slave bores, by the selective supply of low pressure hydraulic fluid in the second hydraulic passage  420 . 
     A front cross-sectional view of the brake housing  300  is shown in  FIG. 6 . With reference to  FIG. 6 , the control valve  320  is shown in a “brake off” position during which the control valve body  322  is biased into its lower most position by the control valve spring  326 . When the brake is turned on, hydraulic fluid from the second hydraulic passage  420  in the rocker shaft  400  (shown in  FIG. 5 ) may be supplied to the lower portion of the control valve body  322 . The supply of hydraulic fluid may cause the control valve body  322  to move upward until the annular opening provided in the mid-portion of the control valve body registers with the slave bore supply passage  309 . The hydraulic fluid pressure applied to the lower portion of the control valve  320  may be sufficient to push the check valve  324  open so that hydraulic fluid flows into the slave piston bore  304  via the slave bore supply passage  309 . With renewed reference to  FIG. 4 , the hydraulic fluid may further flow from the slave piston bore  304  through the master-slave hydraulic fluid passage  306  into the master piston bore  302 . While the brake is in a “brake on” position, hydraulic fluid may be supplied freely to the master-slave piston circuit by the control valve  320 , while the check valve  324  within the control valve prevents the reverse flow of fluid. As a result, the master-slave hydraulic circuit in the brake housing  300  may experience high hydraulic fluid pressures without substantial back flow of hydraulic fluid. 
     The brake may be returned to the “brake off” position shown in  FIG. 6  by reducing the hydraulic fluid pressure, preferably by evacuating the hydraulic fluid, applied to the lower portion of the control valve  320 . When this happens, the control valve body  322  may slide downward until the slave bore supply passage  309  is exposed to the control valve bore  328 , thereby allowing the hydraulic fluid in the master-slave hydraulic circuit to escape. The selective supply of hydraulic fluid to the control valve  320  may be controlled by the solenoid  500  shown in  FIG. 1 . Alternative placements of the solenoid  500  are considered within the scope of the present invention. 
     The arrangement of the various elements of the system  50  when the engine brake is in a “brake off” position is shown in  FIG. 7 . With reference to  FIG. 7 , the cam lobe  100  is illustrated as having two valve actuation bumps. A first cam bump  102  may provide a compression-release valve actuation event and a second cam bump  104  may provide a brake gas recirculation (BGR) valve actuation event. Alternative cam lobes with more, less, or different cam bumps are contemplated as being within the scope of the present invention. 
     The system  50  is positioned adjacent to an engine valve, such as an exhaust valve  600 . The system  50  may actuate the exhaust valve  600  through a sliding pin  620  that extends through a valve bridge  610 . Use of such a sliding pin and valve bridge arrangement may permit a separate valve actuation system to actuate multiple engine valves for positive power operation and a single engine valve  600  for non-positive power operation, such as engine braking. 
     With continued reference to  FIG. 7 , when the brake is in a “brake off” position, hydraulic fluid pressure in the second hydraulic passage  420  is reduced or eliminated. As a result, there is no hydraulic fluid pressure maintained in the master-slave hydraulic fluid circuit connecting the master piston  340  and the slave piston  350 . Accordingly, the bias of the slave piston return spring  352  may be sufficient to push the slave piston  350  all the way into the slave piston bore against the lash adjustment screw  354 . Furthermore, the bias of the rocker arm return spring  210  may be sufficient to rotate the rocker arm  200  such that the rocker arm lug  230  pushes the master piston  340  all the way into the master piston bore. The rotation of the rocker arm  200  in this manner may create a lash space  106  between the cam roller  220  and the cam lobe  100 . The lash space  106  may be designed to have a magnitude x that is as great or greater than the height of the cam bumps  102  and  104 . Thus, when the system  50  is in a “brake off” position, the cam bumps  102  and  104  may not have any effect on the rocker arm  200  or the master and slave pistons  340  and  350 . 
     The arrangement of the various elements of the system  50  when the engine brake is in a “brake on” position is shown in  FIG. 8 . With reference to  FIG. 8 , when the brake is turned “on,” hydraulic fluid is supplied through the second hydraulic passage  420  to the control valve  320  (not shown) and the master-piston hydraulic circuit in the brake housing. When the cam lobe  100  is at base circle, as shown in  FIG. 8 , the hydraulic fluid pressure in the master-slave hydraulic fluid circuit connecting the master piston  340  and the slave piston  350  may push the master piston  340  out of its bore, overcoming the bias of the rocker arm return spring  210  and rotating the rocker arm  200  backwards until the cam roller  220  contacts the cam lobe  100 . As a result, the lash space  106  may be eliminated. At this time (cam lobe at base circle), the hydraulic pressure in the master-slave hydraulic circuit is not sufficient, however, overcome the bias of the slave piston return spring  352  and push the slave piston  350  out of the slave piston bore. 
     With reference to  FIG. 9 , when the cam roller  220  encounters the cam bump  102  (and  104 ), the rocker arm  200  is rotated slightly clockwise. Rotation of the rocker arm  200  may push the master piston  340  into the master piston bore thereby displacing hydraulic fluid through the master-slave hydraulic fluid passage  306  and into the slave piston bore. As a result, the bias of the slave piston return spring  352  is overcome and the slave piston  350  may be displaced downward against the sliding pin  620 , which in turn, may actuate the exhaust valve  600  for a compression-release event or some alternative valve actuation event. 
     An alternative embodiment of the present invention is shown in  FIGS. 10 and 11 . With reference to  FIGS. 10 and 11 , the rocker arm return spring  210  may be provided in the form of a coil spring as opposed to a mouse-trap type spring. Furthermore, the return spring  210  may extend between an overhead element  212  and a rear portion of the rocker arm  200  such that the rocker arm is biased into continual contact with the cam lobe  100  when the system is in a “brake off” position, as shown in  FIG. 10 . As a result, instead of creating a lash space between the cam lobe  100  and the cam roller  220  when the brake is off, a lash space  202  may be created between the rocker arm lug  230  and the master piston  340 . 
     With reference to  FIG. 12 , the communication between an engine oil supply passage  430  and the first and second hydraulic passages  410  and  420  are shown. The solenoid  500  may be disposed between the engine oil supply passage  430  and the rocker shaft  400 . 
     With reference to  FIGS. 13 and 14 , in a second embodiment of the present invention, the rocker arm and master piston may be eliminated. The valve actuation system housing  1300  may include an anti-rotation bolt boss  1312 , a control valve  1320 , an actuator piston  1350  and rocker shaft collars  1360  and  1362 . The rocker shaft collars may surround the rocker shaft providing a means for securely fixing the housing  1300  in a fixed and compact position relative to the engine valves to be actuated. 
     With reference to  FIG. 15 , the rocker shaft collars  1360  and  1362  of the housing  1300  may be mounted on the rocker shaft  1400 . The housing may be secured in a fixed position relative to the rocker shaft  1400  by a first anti-rotation bolt  1310  (not shown) that extends through the anti-rotation bolt boss  1312  and/or by a second anti-rotation bolt  1314  that extends through an anti-rotation flange  1316 . The anti-rotation boss  1312  may be provided distal from the actuator piston  1350  and the anti-rotation flange  1316  may be provided proximal to the actuator piston. The housing  1300  may include an actuator piston  1350  slidably disposed in an actuator piston bore  1304 . An internal hydraulic circuit may include passage  1306  and passage  1308  (shown in  FIG. 16 ). An actuator piston lash adjustment screw  1354  may extend into the actuator piston bore  1304  and provide an upper stop against which the actuator piston  1350  may seat. The rocker shaft  1400  may include a hydraulic fluid supply passage  1420 , the purpose of which is explained in connection with  FIG. 16 . 
     With reference to  FIG. 16 , adjacent to the actuator piston  1350  (shown in  FIG. 15 ) the housing  1300  may further include a control valve  1320 . The control valve  1320  may fill the passage  1306  of the internal hydraulic circuit with hydraulic fluid when low pressure hydraulic fluid is supplied to the lower portion of the control valve via a passage  1308  of the internal hydraulic circuit. A connection hydraulic passage  1422  provided in the rocker shaft  1400  may extend between the hydraulic fluid supply passage  1420  and the passage  1308  provided in the housing  1300 . As a result, hydraulic fluid may be supplied to the control valve and the actuator piston bores by the selective supply of low pressure hydraulic fluid in the hydraulic fluid supply passage  1420 . 
     A front cross-sectional view of the system is shown in  FIG. 17 . With reference to  FIG. 17 , the control valve  1320  is shown in a “actuator off” position during which the control valve body  1322  is biased into its lower most position by the control valve spring  1326 . When the system is turned on, hydraulic fluid from the hydraulic fluid supply passage  1420  in the rocker shaft  1400  (shown in  FIG. 16 ) may be supplied to the lower portion of the control valve body  1322 . The supply of hydraulic fluid may cause the control valve body  1322  to move upward until the annular opening provided in the mid-portion of the control valve body registers with the passage  1306 . The hydraulic fluid pressure applied to the lower portion of the control valve  1320  may be sufficient to push the check valve  1324  open so that hydraulic fluid flows into the actuator piston bore  1304  via the passage  1306 . While the system is in an “actuator on” position, hydraulic fluid may be supplied freely to the internal hydraulic circuit by the control valve  1320 , while the check valve  1324  within the control valve prevents the reverse flow of fluid. As a result, the internal hydraulic circuit in the housing  1300  may experience high hydraulic fluid pressures without substantial back flow of hydraulic fluid. 
     The system may be returned to the “actuator off” position shown in  FIG. 17  by reducing the hydraulic fluid pressure in the hydraulic fluid supply passage  1420 , and preferably by evacuating the hydraulic fluid applied to the lower portion of the control valve  1320 . When this happens, the control valve body  1322  may slide downward until the passage  1306  is exposed to the control valve bore  1328 , thereby allowing the hydraulic fluid in the internal hydraulic circuit to escape. The selective supply of hydraulic fluid to the control valve  1320  may be controlled by the solenoid  1500  shown in  FIG. 20 . Alternative placements of the solenoid  1500  are considered within the scope of the present invention. 
     The arrangement of the various elements of the system when the engine valve actuator is in an “actuator off” position is shown in  FIG. 18 . With reference to  FIG. 18 , the system is positioned adjacent to an engine valve, such as an exhaust valve  1600 . The system may actuate the exhaust valve  1600  through a sliding pin  1620  that extends through a valve bridge  1610 . Use of such a sliding pin and valve bridge arrangement may permit a separate valve actuation system to actuate multiple engine valves for positive power operation and a single engine valve  1600  for non-positive power operation, such as engine braking. With continued reference to  FIG. 18 , when the system is in an “actuator off” position, hydraulic fluid pressure in the hydraulic fluid supply passage  1420  is reduced or eliminated. As a result, there is no hydraulic fluid pressure maintained in the internal hydraulic fluid circuit connected to the actuator piston  1350 . As a result, the actuator piston  1350  may rest against but not actuate the sliding pin  1620 . Thus, when the system is in an “actuator off” position, the actuator piston may not provide any valve actuation motion to the engine valve. 
     The arrangement of the various elements of the system when it is in an “actuator on” position is shown in  FIG. 19 . With reference to  FIG. 19 , when the system is turned “on,” hydraulic fluid is supplied through the hydraulic passage  1420  to the control valve  1320  (not shown). Hydraulic fluid pressure in the passage  1306  may push the actuator piston  1350  out of its bore so that if it is not already, it does contact the sliding pin  1620 . At this time the hydraulic pressure in the internal hydraulic circuit may not be sufficient, however, to overcome the bias of the engine valve  1600  spring  1602 . When the valve bridge  1610  is moved downward for main exhaust valve actuation event, for example, the low pressure hydraulic fluid in the actuator piston bore  1304  may push the actuator piston  1350  and the sliding pin  1620  downward so that they follow the valve bridge until the actuator piston reaches its maximum downward displacement. As the valve bridge  1610  returns upward at the conclusion of the main exhaust event, the hydraulic fluid in the passage  1306  may become highly pressurized so that the actuator piston  1350  holds the exhaust valve  1600  open for an engine valve event, such as a bleeder braking event. The actuator piston  1350  may continue to hold the exhaust valve  1600  open until the control valve  1320  releases the hydraulic fluid pressure in the passage  1306 . It is appreciated that the valve actuation system may be used for intake and auxiliary engine valve actuation in addition to exhaust valve actuation. 
     With reference to  FIG. 20 , the communication between an engine hydraulic fluid supply passage  1430  and the hydraulic fluid supply passage  1420  is shown. The solenoid valve  1500  may be disposed between the engine hydraulic fluid supply passage  1430  and the hydraulic fluid supply passage  1420  in the rocker shaft  1400 . The solenoid valve  1500  may be provided adjacent to the rocker shaft mounted engine brake system on, for example, a rocker shaft pedestal. 
     With reference to  FIG. 21 , in an alternative embodiment of the system shown in  FIGS. 13-20 , the actuator piston  1350  may act directly on an engine valve  1600  or on an engine valve bridge  1610  instead of acting on a sliding pin. 
     With reference to  FIG. 22 , in another alternative embodiment of the system shown in  FIGS. 13-21 , the solid actuator piston  1350  may be replaced with an auto-lashing actuator piston  1352 . The auto-lashing piston  1352  may include an actuator piston with a hollow interior which receives an adjustable depth lash adjustment screw-plunger  1353 , spring  1355 , and retaining collar  1357 . The adjustable depth lash adjustment screw-plunger may be partially disposed in the hollow interior of the actuator piston  1352  and extend out of the top of the actuator piston bore  1304 . The adjustable depth lash adjustment screw-plunger  1353  may have a lower plunger end and the retaining collar  1357  may be disposed in the hollow interior of the actuator piston  1352  above the lower plunger end. The spring  1355  may be disposed between the retaining collar  1357  and the lower plunger end. The auto-lashing actuator piston  1352  may be maintained out of contact with sliding pin  1620  (as shown in  FIG. 18 ) when the system is in an “actuator off” position. 
     With reference to  FIGS. 23-28 , in another alternative embodiment of the system, the brake housing  2300  may be mounted on individual rocker shaft  2200  and rocker shaft pedestal  2100  (not shown) assemblies. In this embodiment, the brake housing  2300  may be like the brake housing  300  and  1300  described in the preceding paragraph and the drawings. 
     With reference to  FIGS. 23 and 24 , each engine valve may have one individual rocker shaft  2200  and rocker shaft pedestal  2100  (not shown) assembly. Two rocker arms, an intake rocker arm  2201  and an exhaust rocker arm  2202 , may be mounted on each rocker shaft  2200 . The brake housing  2300  may be secured in a fixed position relative to the rocker shaft  2200  by a first bolt  2310  that extends through the rocker shaft pedestal  2100  (not shown) and/or by a second bolt  2320  that also extends through the rocker shaft pedestal  2100  (not shown). The first bolt  2310  and/or the second bolt  2320  may extend through the rocker shaft pedestal  2100  (not shown) and into the cylinder head  800 . Alternatively, the brake housing  2300  may be secured in a fixed position relative to the rocker shaft  2200  by three bolts that extend through the rocker shaft pedestal  2100  (not shown) and/or into the cylinder head  800 . 
     With reference to  FIGS. 23 ,  24 , and  27 , the communication between an engine oil supply passage  2530  and a brake actuation oil passage  2520  is shown. A solenoid valve  2500  may be mounted in the solenoid valve bore  2510 , as shown in  FIGS. 23 and 26 . The solenoid valve  2500  may be provided adjacent to the rocker shaft mounted engine brake system on, for example, a cam cap  2502  or the rocker shaft pedestal  2100  (not shown). The solenoid valve may be connected to the engine oil supply passage  2530  and may selective supply hydraulic oil to a brake actuation oil passage  2520 . The brake actuation oil passage  2520  may be incorporated in the cylinder head  800 . 
     With reference to  FIGS. 25 and 28 , the brake housing  2300  may include actuator piston  2301  slidably disposed in an actuator piston bore  2302  and a control valve  2303 . The brake housing  2300  may also contain actuator oil supply passages  2304  that may selective supply low pressure hydraulic fluid to the actuator piston bore  2302  and the control valve  2303 . The actuator oil supply passages  2304  for each brake housing  2300  may be connected to the brake actuation oil passage  2520 . As a result, hydraulic fluid may be supplied to the control valve  2303  and the actuator piston bore  2302  by the selective supply of low pressure hydraulic fluid in the brake actuation oil passage  2520 . 
     Alternatively, an external physical hydraulic passage, such as, tubes with “banjo” fittings or individual “jumper” tubes between rocker shaft pedestals  2100  (not shown) may be incorporated to selective supply hydraulic fluid to the control valve  2303  and the actuator piston bore  2302  of the brake housing  2300 . 
     It will be apparent to those skilled in the art that variations and modifications of the present invention can be made without departing from the scope or spirit of the invention.