Abstract:
An engine compression braking system having a rocker lever and reset valve assembly to operate an engine in both normal power and braking modes while effectively controlling opening and closing of the exhaust valve for compression braking. The reset valve assembly includes a reset pin mounted in a passage of the rocker arm and movement of the reset pin in the compression mode of braking is controlled by contact of the reset pin with a support shaft which the rocker arm rotates around.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to and the benefit of the filing date of U.S. Provisional App. No. 61/730,395 filed on Nov. 27, 2012, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This invention relates to a reset actuation device which uses a cam profile to reduce and control reset pin motion for a compression relief brake. 
     BACKGROUND 
     Compression braking is known in the art and is used for many applications, including braking heavy vehicles. Compression brakes convert an internal combustion engine cylinder to a compressor by cutting off the fuel flow and opening an exhaust valve of the cylinder near the end of the compression stroke. This allows the power generated in the piston to escape to the atmosphere, rather than continuing to power the vehicle. One type of compression braking system is shown in U.S. Pat. No. 6,253,730 to Gustafson. 
     An early technique for accomplishing compression braking is disclosed in U.S. Pat. No. 3,220,392 to Cummins, where a slave hydraulic piston located over an exhaust valve opens the exhaust valve near the end of the compression stroke of an engine piston with which the exhaust valve is associated. To place the engine into braking mode, solenoids are energized which cause pressurized lubricating oil to flow through a control valve, creating a hydraulic link between a master piston and a slave piston. The master piston is displaced inward by an engine element (such as a camshaft mechanism) periodically in timed relationship with the compression stroke of the engine. A typical modern compression braking system may include exhaust valves operated during the engine&#39;s power mode by an exhaust rocker lever. 
     The system may also include a reset valve which operates to cause the slave piston to retract after an initial opening of the exhaust valve during braking. As a result, the exhaust valve is closed prior to the end of the expansion stroke and before the hydraulic pressure drops due to a return motion of the master piston. This design advantageously avoids shock or asymmetric loading of the valve or valve crosshead by the exhaust rocker arm at the start of the main opening event of the exhaust valve following the initial opening event. 
     The modern compression braking system has been further improved by the system disclosed in Gustafson, wherein the engine compression braking system has an integral rocker lever and reset valve capable of effectively avoiding asymmetric loading of a valve crosshead while providing accurate and predictable compression braking. However, further improvements in this technological area are desired. 
     SUMMARY 
     Systems, apparatus, and methods are disclosed herein to improve the operation of a reset pin in a compression brake assembly. 
     The systems, apparatus and methods disclosed herein present an alternative approach and enhancement to the rocker lever compression brake disclosed in U.S. Pat. No. 6,253,730 to Gustafson, the entire contents of which are hereby incorporated by reference. Although the function is similar to the device disclosed in U.S. Pat. No. 6,253,730, such as shown in  FIGS. 1   a  and  1   b , the reset actuation device of the present disclosure includes a reset pin that is actuated via a cam shaped surface on the rocker shaft, such as shown in the rocker lever of  FIGS. 2-11  of the present disclosure. 
     Controlling motion of the reset pin by the cam surface on the rocker shaft separates the reset pin motion from the base camshaft profile lift. Shorter lift reduces the reset ball total travel and allows for improved reset spring design. In addition, the cam surface can increase the lift of the reset pin after the reset event and exhaust valve closure to enhance filling of the slave piston. 
     This summary is provided to introduce a selection of concepts that are further described below in the illustrative embodiments. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are cross-sectional illustrations of a prior art compression relief brake reset mechanism with an integral rocker lever and reset valve operated by a reset pin in conjunction with a reset pin contact pad on a pedestal mount. 
         FIG. 2  is a cross-sectional illustration of a rocker lever assembly with a rocket lever connected with a cam at one end and an exhaust valve of a cylinder at an opposite end, the rocker lever being pivotally mounted about a support shaft with a cam surface that contacts a reset pin of a reset actuation device for compression relief braking. 
         FIG. 3  is a cross-sectional illustration of the rocker lever of  FIG. 2  with the position of the rocker lever and reset pin at zero lift. 
         FIG. 4  is a cross-sectional illustration of the rocker lever of  FIG. 2  with the position of the rocker lever and reset pin at peak lift. 
         FIG. 5  is a cross-sectional illustration of the rocker lever of  FIG. 2 . 
         FIG. 6  is a cross sectional view of the rocker lever along line  6 - 6  of  FIG. 5  with reset pin in the brake on position. 
         FIG. 7  is the cross sectional view of the rocker lever of  FIG. 6  with reset valve in the brake off position. 
         FIGS. 8 and 9  are perspective view illustrations of the rocker lever. 
         FIG. 10  is a perspective view of the support shaft of the rocker lever. 
         FIG. 11  is a top elevation view of the rocker lever. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, any alterations and further modifications in the illustrated embodiments, and any further applications of the principles of the invention as illustrated therein as would normally occur to one skilled in the art to which the invention relates are contemplated herein. 
     Referring to  FIGS. 1A and 1B , a compression relief braking system  120  is shown similar to that disclosed in U.S. Pat. No. 6,253,730 to Gustafson. In this system, a rocker lever  140  is provided on a support shaft  170 . Rocker lever  140  includes a reset pin  192  slidably mounted in a bore  190 , where the upper end of reset pin  192  is immediately adjacent the valve seat for abutment by reset valve head  194 . Reset pin  192  is positioned to contact and move valve head  194  against the force of bias spring  196 . Valve head  194  is positioned to open and close bore  190 , which separates low pressure fluid circuit  164  from high pressure fluid circuit  166 . A reset pin contact pad  122  is mounted on an engine component, for example a pedestal  124 , immediately adjacent a lower end of reset pin  192 . During the initial pivoting movement of rocker lever  140 , reset pin  192  will contact reset pin contact pad  122  mounted on pedestal mount  124 , causing reset pin  192  to move upwardly, thereby moving reset valve head  194  off its seat from a closed position into an open position, shown in  FIG. 1B . In this prior art embodiment, the amount of travel of the reset pin  192  at peak lift is shown in  FIG. 1B . 
       FIG. 2  illustrates an embodiment of the compression relief brake apparatus  20  of the present invention. Apparatus  20  includes a rocker lever  40  operably connected at one end to a cam  30  that pivots or rotates rocker lever  40  about a support shaft  70  to control opening and closing of at least one exhaust valve  26  of engine cylinder  28 . A reset valve assembly  90  is housed in an obliquely oriented bore  98  of the rocker lever  40 , and a portion of bore  98  also serves as a fluid passage  62 . Passage  62  is in flow communication with a slave piston  32 , which is coupled to exhaust valve  26 , and a fluid supply  86 . Slave piston  32  reciprocates between a lower position, in which exhaust valve  26  is open and an upper position, in which exhaust valve  26  is closed, the distance between the lower and upper positions of slave piston  32  is represented schematically as a distance D in  FIG. 2 . Slave piston  32  may also be connected to crosshead  22  that is connected to a second exhaust valve of cylinder  28 . 
     Reset valve assembly  90  includes a reset pin  92  slidably mounted in bore  98 , where a second or upper end of reset pin  92  is immediately adjacent the valve seat  78  for abutment by reset valve head  94 . In the illustrated embodiment, reset valve head  94  is a ball valve, although other valve types are not precluded. Reset pin  92  is positioned to contact and move valve head  94  against the force of bias spring  96 . When the reset valve  90  is in the closed position, with reset valve head  94  seated in the valve seat  78 , fluid is trapped in the slave piston  32  under high pressure, which enables slave piston  32  to hold exhaust valve  26  open, which in turn enables a compression brake event in a compression braking mode of operation. 
       FIGS. 3 and 4  show the effect on reset pin  92  of the rotation or pivoting of rocker lever  40  around support shaft  70 . Cam surface  72  of support shaft  70  has a concave surface portion  74  and a convex surface portion  76 . It should be understood that other profiles of cam surface  72  are also possible in order to achieve the objectives stated herein. When in a compression braking mode of operation, cam surface  72  of support shaft  70  contacts a first end of reset pin  92  and rotation of rocker lever  40  around support shaft  70  causes movement of the first end of reset pin  92  along cam surface  72 . When the first end of reset pin  92  is in contact with the concave surface portion  74  of support shaft  70 , the position of the second end of reset pin  92  adjacent valve head  94  allows valve head  94  to be seated against the valve seat  78 , in a closed position, as shown in  FIG. 3 . When the first end of reset pin  92  is in contact with the convex surface portion  76  of support shaft  70 , the second end of reset pin  92  pushes valve head  94  off of valve seat  78  to an open position, overcoming the force of the reset valve bias spring  96  and any force due to a difference in hydraulic pressure on either side of the valve head  94 , as shown in  FIG. 4 . 
       FIG. 5  is a cross sectional illustration of the rocker lever  40  in a closed position with valve head  94  against valve seat  78 .  FIG. 6  is a cross sectional view of the rocker lever  40  along line  6 - 6  of  FIG. 5  with the reset valve assembly  90  in the brake on position. A detent mechanism  50  includes a detent ball  51  and corresponding spring  52 , which are arranged within a receptacle  53  of rocker lever  40 , which is transverse to bore  98  housing reset pin  92 . There is a recess  56  around reset pin  92 , which provides a seat for detent ball  51  to lock reset pin  92  in an open position when compression braking mode is off, as shown in  FIG. 7 . In an open position, fluid flows from slave piston  32  through fluid passage  62  of bore  98  to and from a fluid supply passage  84  that is connected to a fluid supply  86 . When a compression braking mode of operation is on, as shown in  FIG. 6 , a control fluid pressure  54  pushes detent ball  51  away from recess  56  on the side of reset pin  92 . When detent ball  51  is not seated in recess  56 , reset pin  92  can move freely in bore  98  under bias of spring  96  and in response to a position of cam surface  72  of support shaft  70  relative to the first end of reset pin  90  when rocker lever  40  rotates around support shaft  70 . This allows reset valve head  94  to seat, thereby sealing to valve seat  78  and trapping fluid in slave piston  32 , enabling a compression braking event. It should be noted that in an alternative embodiment, detent ball  51  may be alternatively replaced by a cylindrical detent as disclosed in U.S. Pat. No. 6,253,730 to Gustafson. 
       FIG. 7  shows the position of detent ball  51  and corresponding spring  52  when compression braking mode is off. In this mode control fluid pressure  54  is reduced so detent ball  51  is spring biased into engagement with reset pin recess  56 . Reset pin  92  is thereby locked into a position where it is pushing reset valve head  94  off the valve seat  78  and maintaining the valve head  94  in an open position, regardless of the motion of rocker lever  40  around support shaft  70 . This does not allow fluid pressure to build up in slave piston  32 , allowing exhaust valve  26  to open and close freely in response to the movement of rocker lever  40  in normal operation. 
       FIGS. 8-9  are perspective view illustrations of the rocker lever  40  mounted to support shaft  70 .  FIG. 10  is a perspective view of the rocker lever support shaft  70  showing cam surface  72  formed into an outer surface of support shaft  70  to define concave and convex cam surface portions  74 ,  76 .  FIG. 11  is a top elevation view of the rocker lever  40  mounted about support shaft  70 . 
     The present invention described above advantageously permits the lift of reset pin  92  to be limited as desired by the cam surface  72  formed on support shaft  70 . This has the further advantage of reducing the design requirements of the reset valve bias spring  96 . Moreover, the present brake reset mechanism incorporates an initial negative curvature  74  on the cam surface  72 , which lowers stress when lifting the reset valve head  94  off of the valve seat  78  at high brake cavity pressures at the start of the reset operation. 
     Many aspects of the present invention are envisioned. For example, one aspect is directed to a system comprising a compression relief brake apparatus with a rocker lever pivotally mounted on a support shaft with a cam surface and a reset valve assembly. The rocker lever is connected to an exhaust valve of an internal combustion engine cylinder at one end and connected to a cam member that pivots the rocker lever about the support shaft at the other end. The reset valve assembly is housed in a passage of the rocker lever and the passage is in flow communication with a slave piston coupled to the exhaust valve. The passage is also in flow communication with a fluid supply and a reset valve assembly opens and closes the passage with a reset pin. In a compression braking mode of operation, the cam surface of the support shaft contacts one end of the reset pin and rotation of the rocker lever around the support shaft causes movement of the end of the reset pin along the cam surface. This movement positions the reset valve assembly to close the passage and isolate the slave piston from the fluid supply. 
     In one embodiment, one end of the reset pin rides the cam surface of the support shaft to displace the reset pin along the passage to open and close the reset valve assembly. In one refinement of this embodiment, the reset valve assembly includes a reset ball that is positionable with the reset pin to open and close the passage and one end of the reset pin is in contact with the reset ball. In a further refinement, the reset ball is spring biased toward the second end of the reset pin. 
     In another embodiment, closing the reset valve assembly traps fluid in the slave piston to maintain the exhaust valve in an open position for compression braking. In a further embodiment, the cam surface of the rocker lever support shaft includes a concave and a convex portion. One end of the reset pin contacts the concave portion when the reset valve assembly is in a closed position and the end of the reset pin contacts the convex portion when the reset valve assembly is in an open position. In yet a further embodiment, the reset valve assembly is normally locked in the open position with a detent mechanism when the compression mode of braking is off. 
     In one embodiment, the support shaft includes a cylindrical body and the cam surface is formed in an outer surface of the cylindrical body. In another embodiment, the passage includes a first portion between the reset valve assembly and the slave piston and a second portion that houses the reset pin. A fluid supply passage extends from the second portion of the passage to a fluid supply. In one refinement of this embodiment, there is a receptacle in the rocker lever that houses a detent locking mechanism that locks the reset pin and a second fluid supply passage between the receptacle and a fluid supply to unlock the detent mechanism from the reset pin. 
     According to another aspect, the system comprises a compression relief brake apparatus with a rocker lever pivotally mounted on a support shaft with a cam surface and a reset valve assembly. The rocker lever is connected to an exhaust valve of an internal combustion engine cylinder at one end and connected to a cam member that pivots the rocker lever about the support shaft at the other end. The reset valve assembly is housed in a passage of the rocker lever and the passage is in flow communication with a slave piston coupled to the exhaust valve. The passage is also in flow communication with a fluid supply and a reset valve assembly opens and closes the passage with a reset pin. A detent mechanism has a position in engagement with the reset pin to lock the reset valve assembly in an open position when compression mode of braking is off and in a second position disengaged with the reset pin when compression mode of braking is on to allow movement of the reset pin within the passage. In a compression braking mode of operation, the cam surface of the support shaft contacts one end of the reset pin and rotation of the rocker lever around the support shaft causes movement of the end of the reset pin along the cam surface. This movement positions the reset valve assembly to close the passage and isolate the slave piston from the fluid supply. 
     In one embodiment, one end of the reset pin rides the cam surface of the support shaft to displace the reset pin along the passage to open and close the reset valve assembly. In another embodiment, the reset valve assembly includes a reset ball that is spring biased toward contact with the end of the reset pin that is not in contact with the cam surface. In a further embodiment, the detent mechanism is housed in a receptacle of the rocker lever that is in fluid communication with a control fluid. In one refinement of this embodiment, the detent mechanism includes a ball member spring biased into engagement with a recess in the reset pin when compression braking mode is off to maintain the reset valve assembly in an open position. In a further refinement, control fluid is provided to the receptacle to force the ball member out of the recess to unlock the reset pin in the compression braking mode of operation. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain exemplary embodiments have been shown and described. Those skilled in the art will appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.