Patent Publication Number: US-6701888-B2

Title: Compression brake system for an internal combustion engine

Description:
This application claims the benefit of provisional application No. 60/250,481 filed on Dec. 1, 2000. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to an internal combustion engine and more particularly to operation of engine valves to facilitate engine braking or compression braking. 
     BACKGROUND 
     Compression brakes are well know devices in the industry used to provide additional stopping force especially in large vehicles. In a standard four-cycle operation during a combustion stroke, an exhaust valve is generally in a closed position from near bottom dead center (BDC) to top dead center (TDC) and back to BDC. During a compression brake operation during the combustion stroke, the exhaust valve generally opens as a piston moves from BDC to TDC and closes as the piston moves from TDC to BDC. 
     One manner of controlling operation of the exhaust valve during a brake operation involves using a master piston and a slave piston. As shown in U.S. Pat. No. 4,150,640 issued to Egan on Apr. 24, 1979, the master piston operates in response to movement of a fuel injection cam. Fixing brake actuation to the fuel injection cam may tend to maintain the exhaust valve open for an extended period after the piston reaches TDC. 
     Other systems have added more complicated actuation mechanisms to provide control with less ties to a fixed cam lobe. U.S. Pat. No. 5,526,784 issued to Hakkenbert et al on Jun. 18, 1996 uses electronically controlled hydraulic actuation to control operation of the exhaust valve. These systems provide greater control over brake actuation. Cost and complexity may prevent implementation of these systems in some applications. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention a compression brake system for an internal combustion engine has a master cylinder and a master piston slidably positioned therein. A brake actuator cylinder connects with the master cylinder. A brake actuator piston positioned in the brake actuator cylinder actuates a valve. In a first position, the brake actuator piston limits fluid communication between the master cylinder and a second actuator volume. In a second position, the brake actuator piston allows fluid communication between the master cylinder and the second actuator volume. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an internal combustion having an embodiment of the present invention; and 
     FIG. 2 shows a graph of displacement of an exhaust valve and fuel injector in relation to an engine crank angle for the present invention. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1 a compression brake system  10  has a brake actuator piston  12  and a brake actuator cylinder  14 . The brake actuator piston  12  is slidably positioned in the actuator cylinder  14 . The brake actuator piston  12  has a first actuating surface  16  and a second actuating surface  18  opposite one another. The first actuating surface  16  and brake actuator cylinder  14  define a first actuator volume  20 . The second actuating surface  18  and brake actuator cylinder define a second actuator volume  22 . A seal  24  of any conventional design connects between the brake actuator piston  12  and the actuator cylinder  14 . 
     The brake actuator piston  12  connects with a valve  26  positioned in a port  28  of an internal combustion engine  30 . In this application the valve  26  is an exhaust valve positioned in an exhaust port. A valve spring  31  connects between the engine  30  and valve  26 . The engine  30  may be of any conventional design having a piston  32  moving within a combustion cylinder  34 . 
     The brake actuator cylinder  14  has a cylinder port  36  positioned to allow a fluid  37  to pass from a fluid conduit  38  into the actuator volume  20 . This application uses hydraulic oil as the fluid  37 . Other fluids such as fuel may also be used. A by-pass conduit  40  connects between a by-pass port  42  positioned along the brake actuator cylinder  14  and a return port  44  positioned along the brake actuator cylinder  14  in fluid communication with said second actuator volume  22 . In this embodiment, the fluid conduit  38  connects to a master cylinder  46 . A master piston  48  is slidably positioned in the master cylinder  46 . A cam  50  connects mechanically with the master piston  48 . In this application, the cam  50  is designed to actuate a fuel injector  52  in a conventional manner. 
     While in a first position P 1 , the brake actuator piston  12  blocks the by-pass port  42 . While the brake actuator piston  12  is in a second position P 2 , the by-pass conduit  40  connects the first actuator volume  20  with the second actuator volume  22  through the by-pass port  42  and return port  44  respectively. 
     Operating off the cam  50  designed to actuate the fuel injector  52 , FIG. 2 shows the exhaust valve  26  reaching some predetermined full travel length X ahead of the full travel length Y of the fuel injector  52 . Optimizing braking performance requires the exhaust valve  26  to reach its full travel length X as the piston  32  approaches TDC. Further, the piston  32  should return to a closed range O as quickly as possible, but at least by a crank angle of about sixty degrees after TDC. In contrast, the full travel length Y may not come until about sixty degrees after TDC. 
     Industrial Applicability 
     The compression brake system  10  improves braking performance without added complexity involved in electronic actuation and valving. Instead, the brake actuator piston  12  cooperates with the by-pass port  42  to use hydraulic forces generated by the cam  50  to move the exhaust valve  26  from position O to X and back instead of relying on spring forces to return the valve  26  from X back to O. 
     As the cam  50  rotates to operate the fuel injector  52 , the master piston  48  begins building hydraulic pressure in the master cylinder  46 . During braking, a by-pass valve (not shown) in the fuel injector allows the fluid  37  to by-pass the fuel injector  52 . Instead, the fluid  37  accumulates in the first actuating volume  20  driving the brake actuator piston  12  into engagement with the valve  26 . Through proper design, the valve  26  will reach its full travel length X as the piston  32  reaches TDC. 
     Opening the valve  26  at TDC allows the piston  32  to expend maximum energy compressing gases in the combustion cylinder  34  prior to expending it through the valve  26 . The by-pass port  42  is positioned to begin passing fluid into the second actuator volume  22  near TDC. Fluid in second actuator volume  22  coupled with spring forces will return the valve  26  to position O at around sixty degrees after TDC or sooner. By returning the valve  26  early, the piston  32  may act against a vacuum in the combustion cylinder further retarding the engine  30 . 
     Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims. 
     
       
         
           
               
             
               
                   
               
               
                 LIST OF ELEMENTS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 TITLE: Compression Brake System for an Internal Combustion Engine 
               
               
                 FILE: 00-474 
               
               
                 10 compression brake system 
               
               
                 12 brake actuator piston 
               
               
                 14 brake actuator cylinder 
               
               
                 16 first actuating surface 
               
               
                 18 second actuating surface 
               
               
                 20 first actuator volume 
               
               
                 22 second actuator volume 
               
               
                 24 seal 
               
               
                 26 valve 
               
               
                 28 port 
               
               
                 30 internal combustion engine 
               
               
                 31 valve spring 
               
               
                 32 piston 
               
               
                 34 combustion cylinder 
               
               
                 36 cylinder port 
               
               
                 37 fluid 
               
               
                 38 fluid conduit 
               
               
                 40 by-pass conduit 
               
               
                 42 by-pass port 
               
               
                 44 return port 
               
               
                 46 master cylinder 
               
               
                 48 master piston 
               
               
                 50 cam 
               
               
                 52 fuel injector