Automatic Control Means for Infinitely Variable Transmission

Abstract

This invention describes a system of control for a power source-transmission-load system such as might be used on an off-the-road vehicle, for example. The power source is an internal combustion engine having a known optimum characteristic of desired manifold vacuum versus engine speed. The transmission is a hydrostatic or hydromechanical transmission having infinitely variable speed ratio and having a control means for varying said speed ratio. The control system includes a transducer means for measuring engine speed and converting this quantity into an analog fluid pressure proportional to the speed. This analog fluid pressure proportional to speed is modified in a function generator to produce an analog fluid pressure which is proportional to the desired manifold vacuum as a function of engine speed. Means are provided for measuring the actual manifold vacuum and for comparing the actual manifold vacuum with the desired manifold vacuum on a continuous basis. This comparison produces an error signal which is amplified and used to control a hydraulic system to operate the control means in order to vary the transmission ratio of the hydrostatic or hydromechanical transmission to obtain a speed ratio such that will provide optimum engine conditions.