Compression brake system for an internal combustion engine

Improving compression brake systems (10) require better control of timing an actuation event. Numerous systems use complicated electronic controls to achieve such control. Cam actuated compression brake systems may reduce braking power by allowing a valve 32 on an internal combustion engine (30) to remain open well after an optimum crank angle. Using a by-pass port (42), pressure may be increased in a second actuator volume (22) opposite a first actuator volume (20). Increasing pressures in the second actuator volume (22) promotes closing the valve (26) near the optimum crank angle.

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.

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.

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