Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
2001-04-02
2003-07-01
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
C123S568120
Reexamination Certificate
active
06584954
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to valve actuation in internal combustion engines that include compression release-type engine retarders. In particular, it relates to a valve actuation system that uses both compression release and exhaust gas recirculation (“EGR”) to improve compression release braking performance and to assist in cleaning the EGR valve and system.
BACKGROUND OF THE INVENTION
Compression release-type engine braking or retarder systems are well-known in the art. Engine retarders temporarily convert an internal combustion engine of the compression ignition type into an air compressor in order to slow the engine. A compression release retarder decreases the kinetic energy of an engine by opposing the upward motion of the engine's pistons on the compression stroke. As a piston travels upward on its compression upstroke, the gases that are trapped in the cylinder are compressed. The compressed gases oppose the upward motion of the piston. When the piston nears the top of its stroke, an exhaust valve is opened to release the compressed gasses. After the pressure has been released from the cylinder, the piston cannot recapture the energy stored in the compressed gases on the subsequent expansion downstroke.
The braking system provides the operator with increased control over the vehicle. Properly designed and adjusted compression release-type engine retarders can generate retarding power equal in magnitude to a substantial portion of the power generated during positive power operations. Compression release-type retarders of this type supplement the braking capacity of the primary vehicle wheel braking system. Engine retarders may substantially extend the life of the primary wheel braking system of the vehicle.
The hydraulic valve control systems of compression release engine retarders have a number of components. A solenoid valve is typically provided to control the supply of engine oil to the hydraulic circuit of the compression release engine retarder. A master piston engages the hydraulic valve control system, typically at a rocker arm or cam. The master piston is linked to a slave piston through a hydraulic circuit. The slave piston is connected to an exhaust valve of the engine. When the compression release retarder is actuated, the rocker arm or cam lobe pushes against the master piston. The motion of the master piston is transferred to the slave piston through the hydraulic circuit, causing the slave piston to actuate and open the exhaust valve at a point near the end of the compression stroke.
Much of the potential energy created by compressing the gas in the cylinder is not recovered during the subsequent expansion or power stroke of the engine. Instead, it is dissipated through the exhaust and radiator systems of the engine. By dissipating the energy developed by compressing the cylinder charge, the compression release-type retarder slows the vehicle down.
As the market for lost motion-type compression release retarders has developed, engine manufacturers have sought ways to improve compression release retarder performance and efficiency. Environmental restrictions, in particular, have forced engine manufacturers to explore a variety of new ways to improve the efficiency of their engines. These changes have forced a number of engine modifications. Engines have become smaller and more fuel efficient. Yet, the demands on retarder performance have often increased, requiring the compression release engine retarder to generate greater amounts of retarding horsepower under more limiting conditions.
The focus of engine retarder development has been toward a number of goals: securing higher retarding horsepower from the compression release retarder, working with, in some cases, lower masses of air deliverable to the cylinders through the intake system; and the inter-relation of various collateral or ancillary equipment, such as: silencers; turbochargers; and exhaust brakes. In addition, the market for compression release engine retarders has moved from the after-market, to original equipment manufacturers. Engine manufacturers have shown an increased willingness to make design modifications to their engines that would increase the performance and reliability and broaden the operating parameters of the compression release engine retarder.
One way of increasing the braking power of compression release engine retarders is to carry out EGR in combination with the compression release braking. EGR denotes the process of briefly opening the exhaust valve at the beginning of the compression stroke of the piston. Opening of the exhaust valve at this time permits higher pressure exhaust gas from the exhaust manifold to recirculate back into the cylinder. The recirculated exhaust gas increases the total gas mass in the cylinder at time of the subsequent compression release event, thereby increasing the braking effect realized by the compression release event.
The effectiveness of engine braking can be improved through the use of EGR. The exhaust gas may be recirculated into the cylinder at the time when the cylinder's piston is at or near Bottom Dead Center (“BDC”) at the beginning of the normal compression stroke. EGR allows a greater volume of air to be admitted to the cylinder. Consequently, the engine works harder compressing the denser air volume, and superior braking is achieved. EGR may also be employed during normal positive power operation. The benefits derived from positive power EGR are primarily reduced exhaust gas emissions.
Engine efficiency and performance may be maximized through the use of variably timed positive and negative power EGR events. Similarly, braking performance may be enhanced through two-cycle braking. A lost motion system may be used to implement these operations. In a lost motion system, working fluid is drained and added at precise times to the hydraulic link between the master piston and slave piston. The engine valve profile may be modified by modifying the motion of the master piston, which follows a cam, prior to its transfer to the slave piston. In this way, variable timing is achieved. Variable timed positive and negative power EGR, as well as two-cycle braking, may be difficult to achieve on an exhaust valve cam already crowded with a main exhaust event lobe and a compression release brake event lobe because of inadequate base circle “residence time.” Residence time refers to the amount of time at which the cam presents a zero lift profile to the cam follower or master piston. This time is generally proportional to the amount of space on the cam not taken up by different lobes.
An example of a lost motion system and method used to obtain retarding and exhaust gas recirculation is provided by the Gobert, U.S. Pat. No. 5,146,890 (Sep. 15, 1992) for a Method And A Device For Engine Braking A Four Stroke Internal Combustion Engine, assigned to AB Volvo, and incorporated herein by reference. Gobert discloses a method of conducting exhaust gas recirculation by placing the cylinder in communication with the exhaust system during the first part of the compression stroke and optionally also during the latter part of the inlet stroke. Gobert uses a lost motion system to enable and disable retarding and exhaust gas recirculation, but such system is not variable within an engine cycle.
Currently external EGR systems are being provided by turbo design and manufacturing businesses. There have been other attempts to redirect the exhaust gases directly with a dedicated by-pass for engine braking. This is described as a difficult problem by the industry. EGR systems are needed that can utilize existing hardware for EGR and to also adapt braking gas recirculation (“BGR”) where braking pulses may be used to charge engine cylinders through the use of engine back-pressure and an auxiliary exhaust opening event.
EGR systems (valves, inter-coolers, and passages) tend to become very sooted over their life-cycle. Soot accumulation will reduce the overall performance of the system, and could actually make the EGR valve
Fuchs Neil
Janak Robb
Castro Arnold
Yuen Henry C.
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