Engine compression release method and apparatus

Abstract

The present invention comprises apparatus and methods for releasing internal combustion engine compression during cranking to reduce cranking effort and the size and weight of the starter motor and battery. It is particularly suitable for fuel conservation systems that stop the engine when the vehicle is stopped in traffic, and restart the engine when the driver steps on the accelerator petal, since such systems place heavy demands on the starter motor and battery. The apparatus provides a means for automatically shifting the valve gear such that exhaust and/or inlet valves are held slightly open during the intake compression strokes to reduce compression torque during initial cranking, and restoring the valves to normal operation before the first firing event. The method provides a sequence of steps executed by the engine electronic control module to control the compression release apparatus to carry out the engine starting process safely and reliably.

What is claimed is: 
     
         1 . A method for reducing the cylinder compression pressure of a rotating non-firing internal combustion engine on demand comprising adding a lift increment to the normal lift motion of at least one valve of at least one cylinder, wherein the lift increment is substantially independent of engine rotational position, thereby preventing complete valve closure and permitting gas flow form the cylinder during the compression stroke. 
     
     
         2 . The method of  claim 1  wherein fuel delivery, ignition or both are disabled to achieve a non-firing condition in a rotating engine before adding the valve motion lift increment, and re-enabled in a rotating engine only after the valve motion lift increment is removed. 
     
     
         3 . The method of  claim 1  wherein a sensing and control module is utilized to:
 Measure operating parameters, e.g. engine RPM, load, temperature, and valve motion lift increment status, and operator inputs including brake, accelerator or clutch status; 
 Determine a requirement to reduce the cylinder compression pressure, and send a control command sequence comprising:
 Disable engine firing; and 
 Add valve motion lift increment; or 
 
 Determine a requirement to restore the cylinder compression pressure, and send a control command sequence comprising:
 Remove valve motion lift increment; 
 
 Measure and confirm that the valve motion lift increment is removed; and
 Restore engine firing. 
 
 
     
     
         4 . A mechanism for adding a lift increment to the normal motion of at least one valve of at least one cylinder of an internal combustion engine by using an actuator to shift the position of the pivot of the rocker arm that opens the valve in a direction such that the valve remains open when the cam follower that actuates the rocker arm engages the base circle of the cam. 
     
     
         5 . The mechanism of  claim 4  wherein the rocker arm pivot is the external ball element of the plunger of a conventional lash adjuster comprising a cylindrical body and plunger assembly mounted in a cylindrical pocket in the cylinder head structure;
 The actuator energized to shift the lash adjuster axially within the cylindrical pocket, thereby shifting the rocker pivot position closer to the cam such that the lift increment is added to the normal valve lift motion to initiate compression relief; and 
 The actuator de-energized to return the lash adjustment to its original position to remove the lift increment to restore normal valve lift motion and eliminate compression relief. 
 
     
     
         6 . The mechanism of  claim 5  wherein the actuator comprises a two-position shift cam controlling the lash adjuster axial position such that in a first position the lift increment is added to the valve motion and in a second position no lift increment is added, and a motor means for causing the shift cam to move between the first and second positions upon demand. 
     
     
         7 . The mechanism of  claim 5  wherein the actuator comprises a conduit through which pressurized fluid is introduced to the cylindrical pocket to move the lash adjuster in the axial direction to a first position in which the lift increment is added to the valve motion, and through which the pressurized fluid is removed from the pocket to return the lash adjuster to a second position in which no lift increment is added, the mechanism further comprising a controlled fluid source connected to the conduit for introducing and removing the pressurized fluid upon demand. 
     
     
         8 . The mechanism of  claim 7  wherein a mechanical stop limits the maximum axial motion of the lash adjuster under the influence of the pressurized fluid. 
     
     
         9 . The mechanism of  claim 7  wherein the pressurized fluid delivered by the controlled fluid source is the lubricating oil circulating in the engine. 
     
     
         10 . The mechanism of  claim 9  wherein the engine lubricating oil pressurized fluid is increased to a pressure higher than supplied to the engine components by a supplemental pump incorporated in the controlled fluid source. 
     
     
         11 . The mechanism of  claim 10  wherein a hydraulic accumulator charged by the supplemental pump stores pressurized engine lubricating oil to move the lash adjuster in the axial direction, a controllable valve is connected between the hydraulic accumulator and the conduit, wherein the valve may be operated to introduce or remove the pressurized fluid upon demand.