Neutral override for servo controlled hydrostatic units

A neutral override system for a hydrostatically propelled vehicle having a brake, the system comprising:

• a variable displacement pump having a casing and being controlled by a displacement control comprising a displacement control valve and a servo;
• the displacement control valve being a three position spring centered neutral biased displacement control valve for supplying control pressure to the servo, the displacement control valve being operatively connected to the servo and having a forward position, a reverse position, and a neutral position that generally corresponds to a neutral position of the displacement control;
• a source of pressurized fluid for charging the pump and supplying fluid to the displacement control valve, the source of charge pressure being operatively connected to the pump and the displacement control valve;
• a brake control valve having first and second ports, the first port being fluidly connected with the casing and the second port being fluidly connected to the source of charge pressure, the brake control valve including a first position in which the first port and the second port are blocked and thereby the brake control valve is closed, the brake control valve including a second position in which the first port and the second port are interconnected through an internal passageway in the brake control valve such that the brake control valve is opened and flow from the source of charge pressure is dumped to the casing to reduce the charge pressure to a predetermined value that is less than a neutral biasing force of the displacement control so that displacement control remains in the neutral position thereof;
• a brake circuit for generating an electrical signal that indicates that the brake has been released;
• a solenoid for moving the brake control valve from the open second position to the closed first position in response to said electrical signal from the brake circuit;
• the brake control valve being located downstream from the source of charge pressure and upstream from the displacement control valve;
• the solenoid-operated brake valve being a two position two port valve.