A continuously variable transmission (CVT) provides a continuous range of transmission ratios between an input shaft and an output shaft. In ground-engaging machines, the use of a CVT is well-known for certain applications, and interest in applying such technology to new environments and machine types exists. A variety of different designs are known, including various pulley systems having variable-diameter pulley wheels, belted systems where a drive belt connects rotating cones, hydrostatic or “hystat” transmissions, certain electric drive machines and still others.
CVT's provide certain desirable properties over manual transmissions and over other types of automatic transmissions. For instance, with a CVT it is often possible to maintain engine speed more or less constant, or vary engine speed within a relatively narrow speed range, while torque applied to a load such as a machine driveline is varied principally by adjustment of the transmission ratio. Such properties enable an engine to be operated much of the time at or close to an optimally efficient engine speed, avoiding swings in speed known to occur in other engines where only a finite number of transmission ratios are available. Commonly owned U.S. Pat. No. 9,097,344 to Hoff et al. is directed to an automatic shift control system for a powertrain. In Hoff et al. a control device selectively varies transmission ratio in response to a shift signal, such as where a speed ratio of a transmission is to be adjusted in anticipation of a load change. While Hoff et al. appears well-suited to its intended applications there is always room for improvement.