This invention relates in general to a mechanical governor for an internal combustion engine, and more particularly to a cam shaft torque controlling device for an all-speed type of mechanical governor for a Diesel engine fuel injection pump in which the engine speed control range is set or determined by the position of a movable control lever.
As is well known, in existing governor assemblies, especially those for Diesel engines adapted to construction vehicles, speed control is implemented in the same manner for lower loads or lower torque ranges as it is for maximum load and torque conditions during a construction operation.
FIG. 3 shows a plot of engine rotation speed N versus the position of the injection pump control rod R, which represents the amount of load exerted on or torque exerted by the engine. The rotation speed N.sub.B and the corresponding position of the control rod R.sub.B for a maximum engine output under full load setting is plotted, as is a predetermined low rotation speed N.sub.C, which is 50% lower than the rated speed, and the position of the control rod R.sub.C for a maximum engine output under full-load. In a conventional governor assembly, when the load is lower than R.sub.B speed control is effected as in an ordinal type of all-speed mechanical governor. If the load exceeds R.sub.B, however, the control rod must be shifted a distance Q (from R.sub.B to R.sub.C) in accordance with the speed deceleration curve from N.sub.B to N.sub.C in order to prevent the engine from suddenly stopping or stalling due to the increased (over capacity) load. This sharp speed slowdown alerts the operator to the overload, and enables him to back the machine off and/or shift to a lower gear ratio before the engine stalls. To implement this control function a torque spring is usually employed in the governor assembly. This presents a drawback, however, in that since the torque spring is operable or functioning at all times and for all load conditions, engine output shortages are unnecessarily caused thereby even during partial or reduced load operations.