Abstract:
Compression brake systems using “back-fill” between combustion cylinders or requiring an exhaust valve to be opened twice during a braking cycle require brake actuation systems able to maintain control over the exhaust valve during different loading conditions. In a first opening event where a piston is at or near bottom dead center, pressures in the combustion cylinder are low. During a second opening event near top dead center pressures are higher. Movement of the exhaust valve may be slowed during the first opening event by controlling fluid leaving a second actuator volume opposite a first actuator volume providing opening force on an exhaust valve.

Description:
DESCRIPTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates generally to an engine retarding device for an internal combustion engine and more particularly to a method and system for compression brake actuation.  
           [0003]    2. Background Art  
           [0004]    Compression brakes or engine retarders are used to assist and supplement wheel brakes in slowing heavy vehicles, such as tractor-trailers. Compression brakes are desirable because they help alleviate wheel brake overheating. As vehicle design and technology have advanced, hauling capacity of tractor-trailers has increased, while at the same time rolling resistance and wind resistance have decreased. Thus, there is a need for advanced engine braking systems in today&#39;s heavy vehicles.  
           [0005]    Known engine compression brakes convert an internal combustion engine from a power generating unit into a power consuming air compressor. Typically, an exhaust valve located in a combustion cylinder opens when a piston in the cylinder nears a top dead center (TDC) position on a compression stroke.  
           [0006]    In an effort to maximize braking power, some systems open the exhaust valve of each cylinder during a first opening event and a second opening event. In this manner, pressure released from a first cylinder into the exhaust manifold is used to boost the pressure of a second cylinder. Thereafter, the pressure in the second cylinder is further increased during the upstroke of the associated piston so that retarding forces are similarly increased. This mode of operation is termed “back-filling” and is disclosed in U.S. Pat. No. 5,724,939 issued to Faletti et al on Mar. 10, 1998.  
           [0007]    Systems employing “back-filling” may require opening the exhaust valves twice during the compression or exhaust cycles. During a first opening event, the piston is at or near bottom dead center (BDC). During a second opening event, the piston is at or near TDC and pressures in the cylinder typically are higher than pressures in the cylinder during the first opening event. Forces required to move the exhaust valve during the second opening event are greater than those in the first opening event. Systems are typically designed to meet the higher opening forces required in the second opening event. Operating the exhaust valve with these higher opening forces may cause an exhaust valve actuating device to impact the exhaust valve or loose contact with exhaust valve during when acting against the lower opening forces present in the first opening event. Loosing contact between the exhaust valve and valve actuating device or “overshoot” reduces controllability of the valve opening events. Further, impact between the exhaust valve and valve actuating device may cause premature wear of both the valve actuating device and the valve.  
           [0008]    The present invention is directed to overcoming one or more of the problems as set forth above.  
         DISCLOSURE OF THE INVENTION  
         [0009]    In one aspect of the present invention a compression brake actuation device for an internal combustion engine has a brake actuator cylinder with a brake actuator piston. The brake actuator piston has a first actuating surface and a second actuating surface. The brake actuator cylinder and the first actuating surface define a first actuator volume. The brake actuator cylinder and the second actuating surface define a second actuator volume. A first fluid conduit is in fluid communication with the first actuator volume. The second fluid conduit is in fluid communication with the second actuator volume.  
           [0010]    In another aspect of the present invention a method of operating a compression brake actuation system discloses pressurizing a first actuator volume. Fluid is controllably drained from a second volume. A brake actuator moves the brake actuator piston in response to the pressurizing and draining steps. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a sketch of a compression brake system incorporating the method of the present invention; and  
         [0012]    [0012]FIG. 2 is a sketch showing an alternative embodiment of the compression brake system. 
     
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
       [0013]    In FIG. 1 a compression brake system  10  is shown having 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 the brake actuator cylinder  14  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 seal  24  also separates the first actuator volume  20  from the second actuator volume  22 . The brake actuator piston 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 .  
         [0014]    The brake actuator cylinder  14  also has a first fluid port  36  positioned to allow fluid to pass from a first fluid conduit  38  into the first actuator volume  20  and a second fluid port  40  positioned to allow fluid to pass from a second fluid conduit  42  into the second actuator volume  22 . In this embodiment, the first fluid conduit  38  connects to a fluid manifold  44  in this application a hydraulic oil rail being fed by a first oil pump  46 . Preferably the first oil pump  46  will have variable flow rates and an internal pressure regulator as described in U.S. Pat. No. 5,515,829 issued to Wear et al on May 14, 1996. Other fluids such as water, fuel, or air may also be used. A control valve  48  is positioned in the first fluid conduit  38  intermediate the fluid manifold  44  and the first actuator volume  20 . Any conventional valve may be used such as electronic, mechanical, hydraulic, or piezoelectric valves. For this embodiment, the control valve  48  is a electrohydraulically actuated valve such as the upper portion of the hydraulically actuated, electronically controlled unit injector as shown in U.S. Pat. No. 6,014,956 issued to Cowden et al on Jan. 18, 2000. The control valve  48  also connects with a drain line  47  to return fluid to a sump  51 . In this application, the fluid manifold  44  and first oil pump  46  also supply control fluid to a hydraulically actuated fuel system (not shown).  
         [0015]    The second fluid conduit  42  in this embodiment receives fluid from a fluid feed line  50  connected between a second oil pump  49  and the first oil pump  46 . The second oil pump  49  connects to the sump  51 . An orifice  52  or similar flow restriction is positioned in the second fluid conduit  42  intermediate the fluid feed line  50  and the second actuator volume  22 . Optionally, the orifice  52  may include a check valve  54  or orifice by-pass allowing fluid to by-pass the orifice when flowing from the fluid feed line  50  to the second actuator volume  22 .  
         [0016]    Alternatively, FIG. 2 shows the first oil pump  46 ′ (where “′” shows similar structure as found in FIG. 1) supplying the second fluid conduit  42 ′ through a control valve  56  connected to a drain branch  58  and a fill branch  60 . The drain branch  58  connects to second control volume through an orifice  52 ′ to the sump  49 ′. The fill branch connects to the second actuator volume  22  through a pressure regulator  62  or other conventional pressure reduction device to the first oil pump  46 ′.  
       INDUSTRIAL APPLICABILITY  
       [0017]    The compression brake system  10  of the current invention prevents “overshoot” by allowing fluid in the second actuator volume  22  to reduce speed of the brake actuator piston  12 . Reducing “overshoot” improves control of the brake actuation system  10  and reduces wear inherent from the break actuator piston  12  impacting the exhaust valve  26 .  
         [0018]    During a first opening event, the piston is at or near BDC. Pressures in the combustion cylinder  34  at this time are relatively low. Opening the exhaust valve  26  during the first opening requires sufficient to compress the spring  31 . During a second opening event, the piston  32  is at or near top dead center (TDC). Pressure in the combustion cylinder  34  during the second opening event is increased. The opening force for the second event must now overcome both force from the spring  31  along with pressure forces over acting on the valve  26 . Fluid in the fluid manifold  44  is generally at a predetermined pressure. The first actuating surface  16  is generally designed to produce sufficient forces, when exposed to fluid pressures in the fluid manifold  44 , to open the exhaust valve  26  during the second opening event.  
         [0019]    However, the sufficient forces for the second opening event result in overshoot during the first opening event. Restricting fluid flow from the second actuator volume  22  allows fluid to act on the second actuating surface  18  to create additional forces more akin to forces sufficient for the second opening event preventing “overshoot.”  
         [0020]    To actuate the compression brake system  10 , the control valve  48  moves to a first position allowing fluid from the fluid manifold to pass into the first actuator volume  20 . As fluid enters the first actuator volume  20 , pressure on the first actuating surface  16  moves the brake actuator piston  12  against the valve  26 . Fluid in the second actuator volume  22  passes through the second fluid conduit  42  into the lower pressure fluid feed line  50 . The flow restriction  52  limits flow from the second actuator volume  22 .  
         [0021]    To deactivate the compression brake system, the control valve  48  is moved to a second position allowing fluid to exit the first fluid volume  20  through the drain line  47  into a sump  49 . Fluid from the feed line now passes through the check valve  54  by-passing the flow restriction  52  to fill the second actuator volume  22 . Pressure in the second actuator volume  22  along with force from the spring  26  return the valve  26  to close the port  28 .  
         [0022]    The alternative in FIG. 2 replaces the second oil pump  51  with a pressure regulator  62 . The pressure regulator may be variable or fixed and controlled hydraulically, electronically, mechanically, or by some combination thereof. The control valve  56  is movable between a first and second position. In the first position, the control valve directs fluid from the second actuator volume  22  into the drain branch  58  through the restriction  52  into the sump  49 . The second position allows fluid from the first fluid pump  46  to enter the second actuator volume  22  at some predetermined reduced pressure.  
         [0023]    Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims.