Patent Publication Number: US-11384698-B2

Title: Self-contained compression brake control module for compression-release brake system of an internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
     This application is a continuation of application Ser. No. 16/952,483 filed Nov. 19, 2020, which is now U.S. Pat. No. 11,149,659, issued on Oct. 19, 2021, the entire disclosure of which is incorporated herein by reference and to which priority is claimed. The present invention also claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Ser. No. 62/938,595 filed on Nov. 21, 2019, which is hereby incorporated by reference in its entirety and to which priority is claimed. 
    
    
     1. Field of the Invention 
     The present invention relates to compression-release brake systems for internal combustion engines in general, and, more particularly, to a self-contained compression-release brake control module for a compression-release engine brake system of an internal combustion engine. 
     2. Background of the Invention 
     For internal combustion engines (IC engine), especially diesel engines of large trucks, engine braking is an important feature for enhanced vehicle safety. Consequently, the diesel engines in vehicles, particularly large trucks, are commonly equipped with compression-release engine brake systems (or compression-release retarders) for retarding the engine (and thus, the vehicle as well). The compression release engine braking provides significant braking power in a braking mode of operation. For this reason, the compression-release engine brake systems have been in North America since the 1960&#39;s and gained widespread acceptance. 
     The typical compression-release engine brake system opens an exhaust valve(s) just prior to Top Dead Center (TDC) at the end of a compression stroke. This creates a blow-down of the compressed cylinder gas and the energy used for compression is not reclaimed. The result is engine braking, or retarding, power. A conventional compression-release engine brake system has substantial cost associated with the hardware required to open the exhaust valve(s) against the extremely high load of a compressed cylinder charge. Valve train components must be designed and manufactured to operate reliably at both high mechanical loading and engine speeds. Also, the sudden release of the highly compressed gas comes with a high level of noise. In some areas, typically urban, engine brake use is not permitted because the existing compression-release engine brake systems open the valves quickly at high compression pressure near the TDC compression that produces high engine valve train loads and a loud sound. It is the loud sound that has resulted in prohibition of engine compression release brake usage in certain urban areas. 
     Typically, the compression-release engine brake systems up to this time are unique, i.e., custom designed and engineered to a particular engine make and model. The design, prototype fabrication, bench testing, engine testing and field testing typically require twenty four (24) months to complete prior to sales release. Accordingly, both the development time and cost have been an area of concern. 
     Exhaust brake systems can be used on engines where compression release loading is too great for the valve train. The exhaust brake mechanism consists of a restrictor element mounted in the exhaust system. When this restrictor is closed, backpressure resists the exit of gases during the exhaust cycle and provides a braking function. This system provides less braking power than a compression release engine brake, but also at less cost. As with a compression release brake, the retarding power of an exhaust brake falls off sharply as engine speed decreases. This happens because the restriction is optimized to generate maximum allowable backpressure at rated engine speed. The restriction is simply insufficient to be effective at the lower engine speeds. 
     U.S. Pat. No. 8,272,363 describes a self-contained compression brake control module (CBCM) for controlling exhaust valve motion, primarily for, but not limited to, the purpose of engine retarding. The CBCM described in U.S. Pat. No. 8,272,363 is often required to operate with a significant axial offset between a longitudinal axis of the CBCM and a longitudinal valve axis of an exhaust valve it acts upon, as illustrated in FIGS. 2A-C of the U.S. Pat. No. 8,272,363. 
     The CBCM described in U.S. Pat. No. 8,272,363 comprises an actuation piston retaining ring and seal engaging the same bore within a single casing of the CBCM. This causes an increased diameter requirement in a portion of the bore due to assembly concerns with passing a seal past a retaining ring groove. The CBCM of U.S. Pat. No. 8,272,363 utilized a casing that contained the actuation piston while still requiring a support housing, adding diameter to the overall assembly. These contributors to a required offset generates a side force acting on the actuation piston of the CBCM, which causes a risk of wear and/or jamming of the actuation piston in its bore. Practical applications for the CBCM often dictate both a reduction in overall height and diameter in order to fit within existing engine packages without interference or undesired changes to other components. It is therefore advantageous to be able to reduce the size of the CBCM module, to both better center it over the loading generated by the exhaust valve, and to package it into tighter space constraints. 
     Thus, while known compression-release engine brake systems have proven to be acceptable for various vehicular driveline applications, such devices are nevertheless susceptible to improvements that may enhance their performance and cost. With this in mind, a need exists to develop improved compression-release engine brake systems that advance the art, such as a self-contained compression brake control module for a compression-release brake system of an internal combustion engine that is easier to assemble, is more robust and compact when assembled, enhances performance and significantly reduces the development time and cost of the compression-release engine brake system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a compression-release brake system for an internal combustion including a more compact self-contained compression brake control module in the form of a hydraulically expandable linkage that is integrated with mounting hardware into the valve train of the I.C. engine. The compact design results in easier device assembly; and, a more robust and compact device when assembled. 
     The compression-release brake system comprises a self-contained compression brake control module (CBCM) operatively coupled to the exhaust valve for controlling a lift and a phase angle thereof. The CBCM includes a casing defining an actuator cavity, an actuation piston disposed outside the casing so as to define an actuation piston cavity between the casing, the actuation piston, and the bore into which the CBCM has been installed. The CBCM further includes a check valve provided between the actuation piston cavity and a compression brake actuator disposed in the actuator cavity. The actuation piston reciprocates relative to the casing and the bore. The compression brake actuator includes an actuator element and a biasing spring. The actuator element selectively engages the check valve when deactivated to unlock fluid contained within the actuation piston cavity and disengages from the check valve when activated so as to lock fluid within the actuation piston cavity. 
     The present invention provides advantages owing to its relatively smaller and more compact design. This design fits under valve train covers without major modification of existing fuel injection or valve train components and minimum increased valve cover height. In addition, the compact size enables design flexibility to install the CBCM even on engines configurations with a single valve cover per cylinder. 
     By virtue of the compact design and inclusion of an internal check valve, locking pressurized hydraulic fluid in a similarly compact actuation piston chamber, the present device provides a design using a minimum fluid volume thereby reducing the compliance of the trapped hydraulic fluid. The compactness thus yields a stiffer system to more readily maintain a constant exhaust valve(s) lift at higher engine loading in the CBCM engine braking mode. The compactness also creates the possibility of closer axial alignment between the CBCM and an underlying actuated exhaust valve. 
     The compact design can more easily be accommodated to more engine configurations and hardware with the same CBCM integrated hardware design and can be accomplished with much lower engineering design costs and time, prototype fabrication and validation testing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, wherein: 
         FIGS. 1A and 1B  are schematic views of an internal combustion engine including a compression-release brake system according to an exemplary embodiment of the present invention; 
         FIG. 2A  is an enlarged schematic view of the portion of the compression-release brake system according to the exemplary embodiment of the present invention with exhaust valves closed; 
         FIG. 2B  is an enlarged schematic view of the portion of the compression-release brake system according to the exemplary embodiment of the present invention with exhaust valves open by an exhaust rocker assembly; 
         FIG. 2C  is an enlarged schematic view of the portion of the compression-release brake system according to the exemplary embodiment of the present invention with the exhaust valves floating due to backpressure in an exhaust manifold; 
         FIGS. 3A and 3B  are sectional views of a hydraulically actuated compression brake control module of the compression-release brake system according to the exemplary embodiment of the present invention in a depressurized condition; 
         FIGS. 4A and 4B  are sectional views of the hydraulically actuated compression brake control module of the compression-release brake system according to the exemplary embodiment of the present invention in a pressurized condition. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to exemplary embodiments and methods of the invention as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the drawings. It should be noted, however, that the invention in its broader aspects is not limited to the specific details, representative devices and methods, and illustrative examples shown and described in connection with the exemplary embodiments and methods. 
     This description of exemplary embodiment(s) is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “upper”, “lower”, “right”, “left”, “top” and “bottom”, “front” and “rear”, “inwardly” and “outwardly” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. The term “integral” (or “unitary”) relates to a part made as a single part, or a part made of separate components fixedly (i.e., non-moveably) connected together. The words “smaller” and “larger” refer to relative size of elements of the apparatus of the present invention and designated portions thereof. Additionally, the word “a” and “an” as used in the claims means “at least one” and the word “two” as used in the claims means “at least two”. 
       FIGS. 1A and 1B  schematically depict a compression-release (or weeper) brake system  12  according to an exemplary embodiment of the present invention, provided for an internal combustion (IC) engine  10 . Preferably, the IC engine  10  is a four-stroke diesel engine, comprising a cylinder block  14  including a plurality of cylinders  14 ′. However, for the sake of simplicity, only one cylinder  14 ′ is shown in  FIGS. 1A and 1B . Each cylinder  14 ′ is provided with a piston  16  that reciprocates therein. Each cylinder  14 ′ is further provided with two intake valves  17   1  and  17   2 , and two exhaust valves  18   1  and  18   2 , each provided with a return spring  17 ′ or  18 ′, respectively, and a valve train provided for lifting and closing of the intake and exhaust valves  17  and  18 . The intake valves  17   1  and  17   2  as well as exhaust valves  18   1  and  18   2  are substantially structurally identical in this embodiment. In view of these similarities, and in the interest of simplicity, the following discussion will sometimes use a reference numeral without a letter to designate both substantially identical valves. For example, the reference numeral  17  will be sometimes used when generically referring to each of the intake valves  17   1  and  17   2 , while the reference numeral  18  will be sometimes used when generically referring to each of the exhaust valves  18   1  and  18   2  rather than reciting all two reference numerals. It will be appreciated that each cylinder  14 ′ may be provided with one or more intake valve(s) and/or exhaust valve(s), although two of each is shown in  FIGS. 1A and 1B . The engine  10  also includes an intake manifold  19  and an exhaust manifold  20  both in fluid communication with the cylinder  14 ′. The IC engine  10  is capable of performing a positive power operation (normal engine cycle) and an engine brake operation (engine brake cycle). The compression-release brake system  12  operates in a compression brake mode (during the engine brake operation) and a compression brake deactivation mode (during the positive power operation). 
     The valve train of the present invention includes an intake rocker assembly  22  for operating the intake valves  17 , and an exhaust rocker assembly  24  for operating the exhaust valves  18 . The intake rocker assembly  22  includes an intake cam member  26 , an intake rocker arm  28  mounted about an intake rocker shaft  29  and provided to open the intake valves  17  through an intake valve bridge  27 . Similarly, the exhaust rocker assembly  24  includes an exhaust cam member  30 , an exhaust rocker arm  32  mounted about an exhaust rocker shaft  33  and provided to open the exhaust valves  18  (i.e., the exhaust valves  18   1  and  18   2 ) through an exhaust valve bridge  31 . 
     As further illustrated in  FIGS. 1A and 1B , the compression-release brake system  12  according to the exemplary embodiment of the present invention comprises a self-contained compression brake control module (or CBCM)  40  for selectively controlling a lift and a phase angle of at least one of the exhaust valves  18 . In the preferred embodiment of the present invention, the CBCM  40  is provided for controlling exhaust valve motion, primarily for, but not limited to, the purpose of engine retarding. Specifically, the CBCM  40  is provided primarily for selectively controlling a lift and a phase angle of at least one of the exhaust valves  18   2  which is capable to function as a brake exhaust valve. In other words, the CBCM  40  is provided for selectively controlling a valve lash of the brake exhaust valve  18   2 . The compression brake control module  40  is a hydraulically expandable linkage that is integrated into the valve train of the I.C. engine  10 . The compression brake control module  40  is an essential part of the compression-release brake system  12  that holds the brake exhaust valve  18   2  off the valve seat a preset amount for either the full engine cycle or a partial engine cycle. The compression-release brake system  12  can be combined with an exhaust brake to provide two-cycle braking. The compression brake control module  40  according to the exemplary embodiment of the present invention, is a universal compact mechanism that can be applied to different engine configurations with only slight modifications to mount the compression brake control module  40  to different engine valve train overheads. The CBCM  40  has a longitudinal axis X M , as best shown in  FIGS. 2A and 3A . 
     In the exemplary embodiment, illustrated in  FIGS. 1A and 1B , the compression brake control module  40  is fixed (i.e., non-movably, attached to a stationary part of the engine) so as to be operatively disconnected from and spaced from the exhaust rocker assembly  24 . Specifically, the compression brake control module  40  is disposed adjacent to the exhaust valves  18  and spaced from the exhaust rocker arm  32 . More specifically, as illustrated in details in  FIGS. 3A-3B and 4A-4B , the compression brake control module  40  comprises a hollow casing in the form of a cylindrical single-piece body  42  including a unitary, hollow cylindrical inner portion  53 , which defines a cylindrical valve cavity  44 . The cylindrical single-piece body  42  also defines a cylindrical actuator cavity  45  separated from the cylindrical valve cavity  44  by an inner (or separation) wall  46  and being in fluid communication with each other through a connecting passage  47  through the inner wall  46 . As further illustrated in  FIGS. 3A-3B and 4A-4B , a cylindrical outer peripheral surface  43  of the casing  42  is at least partially threaded so as to be threadedly received in an internally threaded bore of a support member  51  fixed to a cylinder head  15  (or the cylinder block  14 ) of the I.C. engine  10  (as shown in  FIGS. 1 and 2A-2C ). A lock nut  41  is provided to adjustably fasten and non-moveably retain the casing  42  of the CBCM  40  to the support member  51 , i.e., to lock the casing  42  of the CBCM  40  in position relative to the support member  51 . Thus, the casing  42  of the CBCM  40  is non-movably, i.e., fixedly, mounted to the I.C. engine  10 . 
     The CBCM  40  further comprises an actuation piston  48  slidingly mounted to the casing  42  for slidingly reciprocating within a cylindrical bore  98  in the support member  51  (best shown in  FIG. 2A ) and relative to the casing  42  of the CBCM  40  between a collapsed position (shown in  FIGS. 3A-3B ) and an extended position (shown in  FIGS. 4A-4B ) so that the casing  42  and the actuation piston  48  define a variable volume hydraulic actuation piston chamber  50  within the actuation piston  48  between an inner end face  49   a  of the actuation piston  48  and the inner wall  46  of the casing  42 . Moreover, a variable volume hydraulic actuation piston cavity  57  is defined within the cylindrical bore  98  of the support member  51  between the casing  42  and the actuation piston  48 , as best shown in  FIGS. 4A-4B . According to the exemplary embodiment of the present invention, a hydraulic seal  52  is utilized between the actuation piston  48  and the cylindrical bore  98  of the support member  51  to eliminate piston to bore leakage of the pressurized hydraulic fluid. 
     The actuation piston  48  is coaxial with the longitudinal axis X M  of the CBCM  40 , as best shown in  FIGS. 2A and 3A . An outer end face  49   b  of the actuation piston  48  is provided to engage the brake exhaust valve  18   2  in the extended position thereof through an exhaust valve pin  25  reciprocatingly mounted to the exhaust valve bridge  31 . In other words, the exhaust valve pin  25  is reciprocatingly movable relative to the exhaust valve bridge  31  so as to make the brake exhaust valve  18   2  movable relative to the exhaust valve  18   1  and the exhaust valve bridge  31 . Moreover, as best shown in  FIG. 2A , the longitudinal axis X M  of the CBCM  40  is offset relative to a longitudinal pin axis X P  of the exhaust valve pin  25 , which, in turn, is coaxial with the brake exhaust valve  18   2 . 
     The actuation piston  48  has an annular retaining ring  58  disposed in a complementary groove in an annular outer peripheral surface of the cylindrical inner portion  53  of the casing  42  of the CBCM  40 . The groove is sufficiently shallow such that a portion of the retaining ring  58  projects radially outwardly from the cylindrical inner portion  53  of the casing  42 . Moreover, a cylindrical inner surface  53  of the casing  42  is formed with an annular piston groove  54  having annular flat, axially opposite outer and inner stop surfaces  55  and  56 , respectively. 
     As shown in  FIGS. 3A-4B , the retaining ring  58  extends into the piston groove  54  between the outer and inner stop surfaces  55  and  56  thereof provided to mechanically limit upward and downward movements of the actuation piston  48 . As illustrated in  FIGS. 3A-4B , the width of the piston groove  54  is substantially larger than the width of the retaining ring  58  so as to allow the actuation piston  48  to reciprocate relative to the casing  42  between the outer and inner stop surfaces  55  and  56  of the piston groove  54 . Thus, the retaining ring  58  limits axial movement of the actuation piston  48  along the longitudinal axis X M  between the collapsed position (shown in  FIGS. 3A-3B ) and the extended position (shown in  FIGS. 4A-4B ) thereof. As a result, the actuation piston  48  can reciprocate relative to the casing  42  of the CBCM  40  and over the cylindrical inner portion  53  of the casing  42  between two mechanical actuation piston stops defining the extended position (shown in  FIGS. 4A, 4B ) and the collapsed position (shown in  FIGS. 3A, 3B ). In other words, the actuation piston  48  can extend outwardly from the casing  42  of the CBCM  40  until the inner stop surface  56  of the piston groove  54  contacts the retaining ring  58 , as illustrated in  FIGS. 4A and 4B , which is defined as the extended position. Similarly, the actuation piston  48  can retract inwardly toward the casing  42  of the CBCM  40  until the outer stop surface  55  of the piston groove  54  contacts the retaining ring  58 , as illustrated in  FIGS. 3A and 3B , which is defined as the collapsed position. Thus, the piston groove  54  functions as a stroke limiting slot. A length of the CBCM  40  in the extended position (illustrated in  FIG. 4A ) is L E , while the length of the CBCM  40  in the collapsed position (illustrated in  FIG. 3B ) is L C  which is smaller than the length L E . 
     The hydraulic seal  52  mounted to an outer peripheral surface of the actuation piston  48  and the retaining ring  58  disposed within the actuation piston  48  provides a decrease in overall CBCM diameter, thereby allowing for a reduction in offset distance between the longitudinal axis of the CBCM  40  and the longitudinal valve axis of the brake exhaust valve  18   2 . 
     The compression brake control module  40  further comprises a supply (or inlet) port  60  formed within the body of the casing  42 . This provides a pressurized hydraulic fluid from a source  34  of the pressurized hydraulic fluid to the hydraulic actuation piston chamber  50  through the connecting passage  47 . This pressure extends the actuation piston  48  to the extended position thereof when there is a gap  6 A between the actuation piston  48  and the exhaust valve pin  25  of the brake exhaust valve  18   2 . This gap can occur such as when the exhaust valves  18  are open by the exhaust rocker assembly  24  (as illustrated in  FIG. 2B ) or when the exhaust valves  18  float due to backpressure in the exhaust manifold  20  acting to back faces of the exhaust valves  18  (as illustrated in  FIG. 2C ). Preferably, the source  34  of the pressurized hydraulic fluid is in the form of an engine oil pump (not shown) of the diesel engine  10 . Correspondingly, in this exemplary embodiment, an engine lubricating oil is used as the working hydraulic fluid stored in a hydraulic fluid sump  35 . It will be appreciated that any other appropriate source of the pressurized hydraulic fluid and any other appropriate type of fluid will be within the scope of the present invention. 
     Thus, the hydraulically activated compression brake control module  40  of the compression-release brake system  12  holds the exhaust valve  18  off the exhaust valve seat at a predetermined setting, i.e., timing and duration, for the compression brake actuation mode of the I.C. engine  10 . 
     The compression-release brake system  12  according to the exemplary embodiment of the present invention further includes an external compression brake control valve  36  (shown in  FIGS. 1A and 1B ) provided to selectively fluidly connect the source  34  of the pressurized hydraulic fluid to the compression brake control module  40  through a compression brake fluid passageway  37 . In other words, the compression brake control valve  36  is provided to selectively supply the pressurized hydraulic fluid from the source  34  to the CBCM  40  so as to switch the CBCM  40  between an activated (pressurized) condition (or energized state) (shown in  FIGS. 4A and 4B ) when the pressurized hydraulic fluid is supplied to the CBCM  40  and a deactivated (depressurized) condition (or de-energized state) (shown in  FIGS. 3A and 3B ) when the pressurized hydraulic fluid is not supplied to the CBCM  40 . It should be understood that the compression brake fluid passageway  37  communicates with (is fluidly connected to) the supply port  60  of the CBCM  40 . Preferably, the compression brake control valve  36  is an external three-way solenoid valve activated by an electromagnet (solenoid)  36 ′ supplying the pressurized engine oil to the CBCM  40  during the compression brake actuation mode. To deactivate the compression-release brake system  12 , the external three-way solenoid  36  dumps the engine oil supply back to the hydraulic fluid sump  35 . As further illustrated in  FIGS. 1A and 1B , the compression brake control valve  36  is fixed to a cylinder head  15  or cylinder block  14  of the I.C. engine  10 . Thus, the compression brake control valve  36  of the compression-release brake system  12  is non-movably mounted to the I.C. engine  10 . 
     The connecting passage  47  formed longitudinally through the separation wall  46 , includes a piston opening  47   a , and an actuator opening  47   b . As illustrated in detail in  FIGS. 3A-4B , the hydraulic actuation piston chamber  50  fluidly communicates with the connecting passage  47  in the inner wall  46  through the piston port  47   a , the actuator cavity  45  fluidly communicates with the connecting passage  47  through the actuator port  47   b , and the supply port  60  fluidly communicates with the connecting passage  47  also through the actuator port  47   b . In other words, the connecting passage  47  provides fluid communication between the actuation piston chamber  50  and the actuator cavity  45  of the CBCM  40  and the supply port  60  within the body  42  of the CBCM  40 , thus between the actuation piston chamber  50  and the actuator cavity  45  and the source  34  of the pressurized hydraulic fluid. 
     The CBCM  40  further comprises a check valve  62  provided in the valve cavity  44  of the cylindrical inner portion  53  of the casing  42  between the supply port  60  and the actuation piston chamber  50  to hydraulically lock the actuation piston chamber  50  when a pressure of the hydraulic fluid within the actuation piston chamber  50  exceeds the pressure of the hydraulic fluid from the source  34  during the compression brake actuation mode. In other words, the check valve  62  is disposed in the actuation piston chamber  50  (i.e., between the inner end face  49   a  of the actuation piston  48  and the separation wall  46  of the casing  42 ) to selectively isolate and seal the actuation piston chamber  50 . Preferably, the check valve  62  includes a valve member, preferably in the form of a substantially spherical ball member  64  provided to seal against the piston port  47   a  of the connecting passage  47 . It should be understood that an edge of the separation wall  46  forming the piston port  47   a  defines a valve seat of the ball member  64  of the check valve  62 . Preferably, the ball member  64  is biased against the piston opening  47   a  of the connecting passage  47  by a biasing coil spring  66 . The hydraulically activated CBCM  40  provides a seal to eliminate oil leakage from the high-pressure actuation piston chamber  50  and hold the actuation piston  48  in the retracted position without an additional return spring. 
     The CBCM  40  also comprises a hydraulic compression brake actuator  70  mounted within the actuator cavity  45  of the casing  42 . Actuator  70  selectively engages the ball member  64  of the check valve  62  when the CBCM is deactivated so as to unlock the actuation piston chamber  50  and fluidly connect the actuation piston chamber  50  to the source  34  of the pressurized hydraulic fluid. When activated, actuator  70  disengages the ball member  64  of the check valve  62  so as to lock the actuation piston chamber  50  and fluidly disconnect the actuation piston chamber  50  from the source  34  of the pressurized hydraulic fluid. The compression brake actuator  70  includes a reciprocating actuator element (or control piston)  72  slidingly mounted within the casing  42  for reciprocating within the actuator cavity  45  between a retracted position (shown in  FIGS. 3A and 3B ) and an extended position (shown in  FIGS. 4A and 4B ). The casing  42  and the control piston  72  define a variable volume actuator chamber  74  within an innermost portion of the cylindrical actuator cavity  45  between an inner end (or bottom) face  72 B of the control piston  72  and the separation wall  46  of the casing  42 . An outer end (or top) face  72 T of the control piston  72  is provided to engage an end cap  76  of the casing  42  in the extended position thereof. The compression brake actuator  70  also includes a control piston spring  78  acting between the control piston  72  and the end cap  76  to bias the control piston  72  downwardly toward the retracted position thereof. The control piston  72  is bored so as to form a vent chamber  75  between the control piston  72  and the end cap  76  to receive the control piston spring  78 . The vent chamber  75  formed between the end cap  76  and the control piston  72  is subject to atmospheric pressure through a vent port  77  provided in the end cap  76  so as to expose the outer end (or top) face  72 T of the control piston  72  to atmospheric pressure. The control piston  72  is adapted to reciprocate between the separation wall  46  of the casing  42  and the end cap  76 . As illustrated in  FIGS. 3A-4B , the control piston  72  is formed integrally with a protrusion  73  extending into the connecting passage  47  in the separation wall  46  toward the valve member  64  of the check valve  62 . 
     Thus, the compression brake control module  40  incorporates a system to trap engine hydraulic oil in a actuation piston chamber  50  above the actuation piston  48  to prevent the exhaust valve  18  from returning to the valve seat at the end of the compression stroke. The system assures an absolute minimum trapped oil volume to minimize the bulk modulus compressibility of the trapped oil in the actuation piston chamber  50 . The CBCM  40  is attached to the engine  10  (preferably to a cylinder head) through an attaching hardware that incorporates a stiff mounting hold-down to minimize mechanical hardware flexibility during engine braking operation. Incorporation of minimum oil compliance and hardware deflections provides predictable and optimal engine brake retarding performance. The present invention thus provides a miniaturized CBCM  40  housing package. 
     The compression-release brake system  12  of the I.C. engine  10  can be used in conjunction with a fixed orifice exhaust brake, a pressure regulated exhaust brake or a variable geometry turbocharger (VGT) to incorporate two cycle engine braking. The combination uses the compression and exhaust strokes to produce a quieter system with reduced engine valve train loading while yielding excellent brake retarding power. Thus, the diesel engine  10  further comprises a turbocharger  80  including a compressor  82  and a turbine  83 , and a variable exhaust brake  84  fluidly connected to the turbocharger  80  through an exhaust passage  21 . As illustrated in  FIG. 1 , the compressor  82  is in fluid communication with the intake manifold  19  through an intake conduit  38 , while the turbine  83  is in fluid communication with the exhaust manifold  20  through an exhaust conduit  39 . Conventionally, the exhaust gases from the exhaust manifold  20  rotate the turbine  83  and exit the turbocharger  80  through the exhaust conduit  39  into the exhaust brake  84 . In turn, ambient air compressed by the compressor  82  is carried by the intake conduit  38  to the intake manifold  19  through an intercooler  81  where the compressed charge air is cooled before entering the intake manifold  19 . The charge air enters the cylinder  14  through the intake valve  17  during an intake stroke. During an exhaust stroke, the exhaust gas exits the cylinder  14  through the exhaust valve  18 , enters into the exhaust manifold  20  and continues out through the turbine  83  of the turbocharger  80 . 
     As illustrated in  FIGS. 1A and 1B , the exhaust brake  84  of the exemplary embodiment of the present invention is located downstream of the turbocharger  80 . However, the location of the exhaust brake  84  is not limited to being downstream of the turbine  83  or to the form of a conventional exhaust brake. Alternatively, the exhaust brake  84  may be placed upstream of the turbocharger  80  (the turbine  83 ). Where the exhaust brake  84  is installed upstream of the turbocharger  80 , advantage is taken by generating a high-pressure differential across the turbine  83 . This drives the turbocharger compressor  82  to a higher speed and thereby provides more intake boost to charge the cylinder for engine braking. 
     In accordance with the present invention illustrated in  FIGS. 1A and 1B , the exhaust brake  84  includes a variable exhaust restrictor in the form of a butterfly valve  85  operated by an exhaust brake actuator  86 . Preferably, the butterfly valve  85  is rotated by linkage  85 ′ connected to the exhaust brake actuator  86  in order to adjust the exhaust restriction, thus the amount of exhaust braking. The exhaust brake actuator  86  of the present invention may be of any appropriate type known to those skilled in the art, such as a fluid actuator (pneumatic or hydraulic), an electromagnetic actuator (e.g. solenoid), an electromechanical actuator, etc. Preferably, in this particular example, the exhaust brake actuator  86  is a pneumatic actuator, although, as noted above, other actuating devices could be substituted. 
     The exhaust brake actuator  86  is controlled by a microprocessor (or exhaust brake electronic controller)  87 . The microprocessor  87  controls the variable exhaust restrictor  85 , thus the amount of exhaust braking, based on the information from a plurality of sensors  88  including, but not limited, an pressure sensor and a temperature sensor sensing pressure and temperature of the exhaust gas flowing through the exhaust restrictor  85  of the exhaust brake  84 . It will be appreciated by those skilled in the art that any other appropriate sensors, may be employed. The pneumatic actuator  86  is operated by a solenoid valve  89  provided to selectively connect and disconnect the pneumatic actuator  86  with a pneumatic pressure source (not shown) through a pneumatic conduit  89 ′ in response from a control signal from the microprocessor  87 . 
     The compression-release brake system  12  according to the exemplary embodiment of the present invention is controlled by an electronic controller  90  (as illustrated in  FIGS. 1A and 1B ), which may be in the form of a CPU or a computer. The electronic controller  90  operates the electromagnetic compression brake control valve  36  based on the information from a plurality of sensors  92  representing engine and vehicle operating parameters as control inputs, including, but not limited to, an engine speed, an engine load, an engine operating mode, etc. It will be appreciated by those skilled in the art that any other appropriate sensors, may be employed. The electronic controller  90  is programmed to provide a signal  94  to the solenoid  36  of the external three-way control valve  36  to cause them to selectively and independently open or close based on operating demand of the engine  10 . When the compression brake control valve  36  is open, pressurized hydraulic fluid, such as pressurized engine oil, is provided to the hydraulic compression brake actuator  70  of the compression brake control module  40  and the I.C. engine  10  operates in the compression brake mode (engine brake cycle). Correspondingly, when the solenoid compression brake control valve  36  is closed, no pressurized hydraulic fluid is supplied to the hydraulic compression brake actuator  70  of the compression brake control module  40  and the I.C. engine  10  operates in the normal engine cycle. 
     The exhaust brake  84  reads exhaust system pressure and temperature from the sensors  92  at the microprocessor  90  and regulates a signal  89  to the exhaust brake actuator  86  that adjusts the variable exhaust restrictor  85 . The electronic controller  90  also provides a signal  96  to the microprocessor  87  of the exhaust brake  84 . When the engine  10  is operating in engine brake mode, the control signal  96  adjusts the variable exhaust restrictor  85  in order to maintain a desired exhaust backpressure. 
     The braking operation of the I.C. engine  10  of the present invention has two integral components: a compression release (weeper) braking provided by the compression-release brake system  12 , and an exhaust braking provided by the exhaust brake  84 . The compression release braking component is provided by action of the compression brake control module  40  of the compression-release brake system  12 , while the exhaust braking is provided by the exhaust brake  84 . 
     The operation of the compression-release brake system  12  is described in detail below. 
     When the engine  10  performs positive power operation (i.e., operates in the normal engine cycle), the solenoid  36 ′ closes the compression brake control valve  36  and the hydraulic compression brake control module  40  is in the depressurized condition (or de-energized state) so that no hydraulic fluid is supplied to the compression brake control module  40 , and the actuation piston chamber  50  and the actuation piston cavity  57  are filled with hydraulic fluid but not the pressurized hydraulic fluid. In such a condition, shown in  FIGS. 3A and 3B , the control piston  72  is moved to and supported in the retracted position thereof (only by the biasing force of the control piston spring  78 ). In other words, the control piston spring  78  maintains the control piston  72  in this position, which upsets the ball member  64  from the valve seat  47   a  in the casing  42 . Specifically, in this position, the protrusion  73  of the control piston  72  displaces the ball member  64  of the check valve  62  away from the valve seat thereof by overcoming the biasing force of the spring  66  of the check valve  62 , which is lighter than the biasing force of the control piston spring  78  of the compression brake actuator  70 . Thus, the hydraulic fluid is able to flow within the CBCM  40  without causing it to energize, provided that it is not able to reach a pressure high enough to extend the control piston  72  against the control piston spring  78  and allow the ball member  64  to reach the valve seat  47   a.    
     The actuation piston  48  is able to extend if the friction of the hydraulic seal  52  is overcome, but will then retract under load in this state. The de-energized state is utilized during the normal engine operation. The actuation piston  48  is set with an initial spacing (lash) to an exhaust valve or exhaust valve bridge (shown in  FIG. 2A ). The friction of the hydraulic seal  52  is typically enough to maintain this lash. In the case that the friction of the hydraulic seal is insufficient an activation piston return spring can be added to avoid ‘clatter’ of the actuation piston  48  as it extends and is pushed back in during normal exhaust valve motion. 
     During the engine braking operation, when it is determined by the electronic controller  90  based on the information from the plurality of sensors  92  that the braking is demanded, such as when a throttle valve (not shown) of the engine  10  is closed, the exhaust brake  84  is actuated by at least partially closing the butterfly valve  85  in order to create a backpressure resisting the exit of the exhaust gas during the exhaust stroke. Moreover, during the engine braking operation, the electronic controller  90  opens the compression brake control valve  36  to turn on the supply of the pressurized hydraulic fluid to the compression brake control module  40 , thus setting the compression brake control module  40  to the pressurized condition. 
     Pressurized hydraulic fluid enters the CBCM  40  from the support member  51  through the inlet port  60  and passes through machined facets (or ribs) of the control piston  72  of the compression brake actuator  70  to the connecting passage  47 . Consequently, the pressurized hydraulic fluid fills the actuation piston cavity  57 , building pressure in the CBCM  40 , which extends the actuation piston  48  and the control piston  72  until they contact the retaining ring  58  and the end cap  76 , respectively. Moreover, when the pressurized engine oil is supplied to the inlet port  60  of the compression brake control module  40 , the control piston  72  of the compression brake actuator  70  is forced outward by the supply oil pressure allowing the ball member  64  to be seated. The ball member  64  lands on the valve seat  47   a  of the casing  42 , creating the one-way (i.e., check) valve  62  which traps hydraulic fluid in the actuation piston cavity  57 . The energized state is utilized during the engine braking operation. 
     At the same time, the pressurized hydraulic fluid will flow into the actuation piston chamber  50  and the actuation piston cavity  57 . As the pressurized supply oil fills the actuation piston chamber  50  and the actuation piston cavity  57 , the pressure of the supply oil forces the actuation piston  48  outwardly until the actuation piston  48  contacts the mechanical stop (in the form of the retaining ring  58 ), as shown in  FIGS. 4A and 4B , when the exhaust valves  18  are off the valve seat during the normal exhaust valve lift. The spring-loaded ball member  64  will lock the oil above the actuation piston  48  and prevent the actuation piston  48  from returning to the collapsed position thereof (shown in  FIGS. 4A and 4B ). This provides extended lift and phase angle for the brake exhaust valve  18   2 . The extended open duration lift of the brake exhaust valve  18   2  forms a bleeder (weeper) opening during the engine compression stroke, and the engine  10  performs non-recoverable work as gas is forced out of the cylinder through this opening, which embodies the compression-release brake. 
     In a position illustrated in  FIGS. 4A and 4B , the actuation piston  48  is locked in place by the trapped oil in the actuation piston chamber  50  and the actuation piston cavity  57 , and stops one of the exhaust valves  18  from returning to the valve seat. The location of the actuation piston retaining ring  58 , the stroke limiting slot  54  and the install position of the compression brake control module  40 , determines the amount of distance that the exhaust valve  18  will be held off the valve seat, resulting in a predetermined lift during the complete engine braking cycle. The oil in the actuation piston chamber  50  is hydraulically locked by the ball check valve  62  located above the actuation piston  48  to hold the actuation piston  48  in the extended position. 
     Thus, when the exhaust cam member  30  moves the exhaust valve  18  away during the normal exhaust motion, the actuation piston  48  extends and ‘catches’ the exhaust valve  18  upon its return, in order to hold it open a fixed amount during the remainder of the engine cycle. There is a constant load on the actuation piston  48  from the exhaust valve return spring force, and a varying load due to pneumatic pressure in the engine cylinder acting on a face of the exhaust valve  18 . Hydraulic pressure builds within the trapped oil in the actuation piston cavity  57  to support this load. 
     When the engine braking mode is deactivated, the solenoid valve  36  is turned off to cut the pressurized oil supply to the compression brake control module  40 , thereby resulting in the control piston spring  78  forcing the control piston  72  toward the ball check valve  62 , which unseats the ball member  64  from its seated position. The released oil flows out the actuation piston chamber  50  through the external three-way solenoid valve  36  and back to an oil sump  35 , shown in  FIGS. 1A and 1B . The actuation piston  48  is then forced back to the collapsed position (shown in  FIG. 3 ) in the valve cavity  44  of the casing  42  by the force of the exhaust valve springs  18 ′. The exhaust valve  18  returns to the valve seat to allow for normal engine valve motion. 
     In other words, when hydraulic fluid pressure is removed from the CBCM  40 , the control piston  72  moves back into contact with the ball member  64  until a subsequent normal exhaust valve event, at which point the hydraulic pressure in the actuation piston cavity  57  is reduced sufficiently for the force of the control piston spring  78  to unseat the ball member  64 . The actuation piston  48  is provided with a hydraulic bypass feature (or passage)  59  to prevent the retaining ring  58  from trapping hydraulic fluid within the actuation piston cavity  57  when the CBCM  40  is de-energized. 
     The compression-release brake system  12  with the hydraulically activated compression brake control module  40  holds the exhaust valve  18  off the exhaust valve seat at a predetermined setting for the complete engine brake cycle (weeper brake event). The compression-release brake system  12  can be used in conjunction with a fixed orifice exhaust brake, a pressure regulated exhaust brake or a VGT turbocharger to incorporate two cycle engine braking. The combination uses the compression and exhaust strokes to produce a quieter system with reduced engine valve train loading while yielding excellent brake retarding power. 
     The compression-release brake system  12  used in combination with the pressure regulated exhaust brake  84  provides advantages over using a compression-release brake system with a fixed orifice exhaust brake. When a compression-release brake and exhaust brake combination is designed for maximum exhaust backpressure and the compression-release brake component fails to function for any reason the typical extended exhaust/intake valve overlap condition will be eliminated. The elimination of the extended valve overlap results in much higher exhaust manifold pressures and the engine can experience unacceptable valve seating velocities which can result in major engine damage and excessive valve seat wear. 
     Major engine damage can result from valve seat damage or valve spring failure. Valve spring failure can cause engine valves to drop into the combustion chamber and can cause progressive engine damage. Valve seat damage can progress because the exhaust valve will not adequately seal compression pressures and/or not provide good heat transfer from the exhaust valve to the cylinder head during high positive power engine loading. 
     The pressure regulated exhaust brake that is used in combination with the compression-release brake system has the advantage that the exhaust brake can be used alone on a combination compression-release/exhaust brake engine with no possibility of over-pressurizing the exhaust manifold and thereby avoiding excessive valve floating and unacceptable valve seating velocities. Because the pressure regulated exhaust brake is self-regulating, over-pressurization of the exhaust manifold cannot occur because the restriction orifice in the exhaust brake increases in area automatically to maintain a highest constant exhaust manifold pressure in compliance with engine manufacture specifications. 
     The foregoing description of the preferred embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.