A work machine, such as a construction work machine, an agricultural work machine or a forestry work machine, typically includes a prime mover in the form of an internal combustion (IC) engine. The IC engine may either be in the form of a compression ignition engine (i.e., diesel engine) or a spark ignition engine (i.e., gasoline engine). For most heavy work machines, the prime mover is in the form of a diesel engine having better lugging, pull-down and torques characteristics for associated work operations.
An IC engine may be coupled with an IVT which provides continuous variable output speed from 0 to maximum in a stepless fashion. An IVT typically includes hydrostatic and mechanical gearing components. The hydrostatic components convert rotating shaft power to hydraulic flow and vice versa. The power flow through an IVT can be through the hydrostatic components only, through the mechanical components only, or through a combination of both depending on the design and output speed.
One example of an IVT for use in a work machine is a hydromechanical transmission which includes a hydraulic module coupled with a planetary gear set. Another example of an IVT for a work machine is a hydrostatic transmission which includes a hydraulic module coupled with a gear set.
The deceleration rate with an IVT can be more abrupt than a traditional torque
converter powershift transmission when the ground speed control pedal is fully released. The IVT ratio of input to output speed increases as the speed control pedal is released and the vehicle inertia back drives the engine and abruptly slows down the vehicle. This brings the vehicle to a stop quickly and is undesirable to the operator.
What is needed in the art is a work machine with an IVT which is configured and controlled to allow the work machine to be slowed down or stopped without abrupt and objectionable deceleration.