Patent Publication Number: US-6213091-B1

Title: Engine compression brake system

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an engine compression brake system, and particularly, to an engine compression brake system of the type wherein the pivot center of the exhaust rocker arm is displaced. 
     Various types of engine compression brake systems are known. In one type of engine compression brake system, a lost motion device is included in an end of the rocker arm or in the links connecting the rocker arm to the cam lobe or valve (push rod or lifter) to allow a control mechanism to react to or ignore a portion of the cam lobe profile. Another type of engine compression brake system is shown in U.S. Pat. No. 5,647,319, issued in 1997 to Uehara et al. and U.S. Pat. No. 3,367,312, issued in 1966 to Jonsson. Both of these systems have engine brake mechanisms wherein the pivot center of the exhaust rocker arm is displaced or shifted by an eccentric which is connected to an hydraulic piston/actuator by a lever arm. 
     However, these mechanisms require an extra mechanical component between the hydraulic piston/actuator and the rocker arm. Also, the various actuation arms and levers of these systems are subject to tension and bending loads, which increases the probability of stress failures. These additional links, arms and actuators also increase the manufacturing tolerance requirements of many of the components. These systems also require intermediate arms, a second rocker arm eccentric bore, features on the small end of the actuation/pivot arm and features on the mechanical actuation end of the piston. These parts and features all add cost and complexity, and reduce system reliability. Finally, these systems result in an assembly which is not as compact as desired, and could result in increased engine height. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide an engine compression brake mechanism with few components. 
     A further object of the invention is to provide such an engine compression brake mechanism wherein the parts are not subject to tension and bending loads. 
     A further object of the invention is to provide such an engine compression brake mechanism which does not increase the manufacturing tolerance requirements of many of the components. 
     A further object of the invention is to provide such an engine compression brake mechanism with reduced complexity, lower cost and increased system reliability. 
     A further object of the invention is to provide such an engine compression brake mechanism which avoids increasing engine height. 
     These and other objects are achieved by the present invention, wherein an engine compression braking system includes an exhaust rocker arm pivotally supported on a rocker shaft. One end of the rocker arm carries a roller which engages a camshaft which has a lost motion bump formed thereon. The other end of the rocker arm engages an exhaust valve stem assembly. A part of the rocker shaft engages a pressure operated piston. Extension of the piston moves the rocker shaft transversely to its axis, so that the rocker arm can selectively react to or ignore the lost motion portion bump. A pressure control system includes a solenoid operated valve controlled by an operator controlled switch, so that the piston selectively applies a light force or a very high force to the rocker arm rocker shaft, thus shifting the pivot point of the rocker arm 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The sole FIGURE is a view of an engine compression braking system according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to the sole FIGURE, the engine compression braking system  10  includes an exhaust rocker arm  12  pivotally supported by rocker shaft  14  which is received by rocker shaft bore  15 . The rocker shaft  14  has a diameter which is smaller than that of the rocker shaft bore  15  by a small amount such as 0.030 inches. One end of the rocker arm  12  carries a roller  16  which engages a camshaft  18  which has a lost motion bump  20  formed thereon. The other end of the rocker arm  12  engages an exhaust valve stem assembly  22 . Because of the bias of the springs of the valve stem assembly  22 , normally, the rocker arm  12  will be in engagement with the bottom side of the rocker shaft  14 , viewing the Figure. The rocker arm  12  includes a tab  24  which projects therefrom. The tab  24  has partially cylindrical convex outer surface  26 . A piston  28  engages the tab  24  and has cylindrical concave surface  29  which mates with the convex surface  26  of tab  24 . As clearly shown in the sole FIGURE, the piston  28  slides along an axis which extends through the rocker shaft  14 . 
     The piston  28  is slidably received in a piston bore  30  formed in a housing  32 , which is preferably part of the piston housing of a Diesel engine (not shown). The piston  28  and a wall of the bore  30  enclose a pressure chamber  34 . The pressure in chamber  34  is preferably controlled by a pressure control assembly  36 , preferably also enclosed in the housing  32 , such as is known from “FAQs: Engine Brake Theory”, by Jacobs Vehicle Systems, 1996. 
     The pressure control assembly  36  preferably includes a solenoid operated valve (not shown), and energization of the solenoid valve is controlled by an operator controlled switch  46 , which is preferably connected to the vehicle battery  48  via a fuel pump switch  50 , clutch switch  52  and fuse  54 . Pressurization of the pressure chamber  34  causes the piston  28  to move towards the rocker shaft  14  and thereby moves the central portion of the rocker arm  12  until the wall of bore  15  engages an upper part of the rocker shaft  14 , thus shifting the pivot axis of the rocker arm  12 . 
     Thus, this system  10  uses electronically controlled hydraulics to control the pivot position the exhaust rocker arm  12  for engine retarding or braking. Controlling the pivot position of the exhaust rocker arm  12  allows the selective transfer of some or all the exhaust lobe profile/motion of the camshaft  18  to be transferred to the exhaust valve stem assembly  22 . The selective transfer of some or all the cam lobe motion to the valves, in conjunction with engine fueling level, determines the engines capability to generate positive power or absorb (braking) power. 
     Extension of the piston  28  moves the rocker arm pivot point transversely to its axis, so that the rocker arm  12  can selectively react to or ignore the lost motion bump  20 . The pressure on the piston  28  can be controlled so that the piston  28  selectively applies a light force or a very high force to the rocker arm  12 , thus controlling the pivot point of the rocker arm  12 . A light piston force allows the rocker arm  12  to operate in its normal location, such as when the engine (not shown) is under load. This normal position prevents the rocker arm  12  from reacting to the lost motion bump  20 , and transmitting forces to the exhaust valve assembly  22 , since the lost motion bump  20  is small enough to be “lost” in the valve lash clearance. A high piston force displaces and holds the rocker arm  12  down against the top of the rocker shaft  14 , causing the rocker arm  12  to react to the lost motion bump  20 , and transmit forces to the exhaust valve assembly  22 , since the rocker arm  12  has an effective zero valve lash clearance. 
     The system above does not have an extra mechanical component between the hydraulic piston/actuator and the rocker arm, resulting in improved function, reliability and reduced cost. Since the piston  28  exerts only a compressive force on the rocker arm  12 , bending loads are avoided and the probability of failure is reduced. Fewer parts results in lowered manufacturing tolerance requirements components other than the hydraulic piston/bore and the rocker arm bore. Finally, this design permits a compact engine of low height. 
     While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.