Control for a hydrostatic transmission

Claim 2

In a hydrostatic transmission having a variable displacement pump and motor hydraulically interconnected to form a closed circuit for transmitting power therethrough, a reservoir source of fluid, and speed and direction of movement control means connected to at least one of said pump and motor and movable in opposite directions from a neutral center position for controlling displacement to selectively produce forward and reverse direction of drive of said motor when the power flow is from the pump to the motor, the combination therewith, comprising: a pair of high pressure pilot-operated relief valves communicatively connected across opposite sides of said closed circuit and normally closed to fluid flow between opposite sides of said closed circuit but each of which is operable responsive to development of a pressure differential thereacross for shortcircuiting fluid flow between opposite sides of said circuit; said high pressure valves having pilot pressure passages therein open to fluid pressures in opposite sides of said circuit; low pressure valve means; high pressure pilot valve means; first fluid passage means connecting said low pressure valve means and high pressure pilot means together and connecting said latter means to said reservoir; second fluid passage means connecting said low pressure valve means with said pilot pressure passages whereby said low pressure valve means are selectively subjectable to pilot pressures from opposite sides of said closed circuit; valve positioning means adapted to operatively connected with said control means for presetting said low pressure valve means into positions corresponding to said positions of said control means; said low pressure valve means being normally closed to pilot pressure between opposite sides of said circuit, when power flow is from the pump to the motor, but being operatively responsive, when the power flow is from the motor to the pump, to an increase of pilot pressure for short-circuiting a portion of the fluid flow therein bEtween opposite sides of said closed circuit and incident thereto opening a corresponding one of said high pressure pilot operated valves to effect a shortcircuiting of the remainder of the fluid flow in said closed circuit between opposite sides thereof whereby the flow of power through said unit is disrupted; anti-coast valve means disposed in said first fluid passage means and responsive to pressure developed when the power flow is from the motor to the pump to block flow to said high pressure pilot valve means whereby the dynamic braking may continue to be utilized; and dampening means associated with said anti-coast valve means for controlling its rate of movement.

Claim 3

In a hydrostatic transmission having a variable displacement pump and motor hydraulically interconnected to form a closed circuit for transmitting power therethrough, a reservoir source of fluid, and speed and direction of movement control means connected to at least one of said pump and motor and movable at a given rate in opposite directions from a neutral center position for controlling displacement to selectively produce forward and reverse direction of drive of the motor when the power flow is from the pump to the motor, the combination therewith, comprising: a pair of high pressure pilot-operated relief valves communicatively connected across opposite sides of said circuit and normally closed to fluid flow between opposite sides of said circuit, but each of which is operable responsive to development of a pressure differential thereacross for short-circuiting fluid flow between opposite sides of said circuit; one of said high pressure relief valves receiving drive pressure from the pump with the transmission displaced for drive in a reverse direction, when the power flow is from the pump to the motor, and receiving motor pressure from the motor with the transmission displaced for drive in a forward direction, when the power flow is from the motor to the pump; a manually controllable poppet valve means normally blocking communication between said high pressure relief valves and said reservoir but manually movable to permit such communication; anti-coast valve means interposed between and normally permitting fluid communication between said poppet valve means and said high pressure relief valves; a pair of low pressure relief valves normally blocking communication between said high pressure relief valves and said anti-coast valve; valve positioning means associated with said control means for opening the low pressure relief valve associated with said one high pressure relief valve for subjecting said anti-coast valve to the pressure received by said one high pressure relief valve; said anti-coast valve being movable responsive to receiving drive and motoring pressure to block communication with said poppet valve means; and dampening means for controlling the movement of said anti-coast valve so that its rate of movement is no greater than said given rate.

Claim 4

In a hydrostatic transmission having a variable displacement pump and motor hydraulically interconnected to form a closed circuit for transmitting power therethrough, a reservoir source of fluid, and speed and direction of movement control means connected to at least one of said pump and motor and movable at a given rate in opposite directions from a neutral center position for controlling displacement to selectively produce forward and reverse direction of drive of the motor when the power flow is from the pump to the motor, the combination therewith, comprising: a pair of high pressure pilot-operated relief valves communicatively connected across opposite sides of said circuit and normally closed to fluid flow between opposite sides of said circuit, but each of which is operable responsive to development of a pressure differential thereacross for short-circuiting fluid flow between opposite sides of said circuit; one of said high pressure relief valves receiving drive pressure from the pump with the transmission displaced for drive in a reverse direction, when the power flow is from the pump to the motor, and receiving motor pressure from the motor with the transmission displaced for drive in a forward direction, when the power flow is from the motor to the pump; a manually controllable poppet valve means normally blocking communication between said high pressure relief valves and said reservoir but manually movable to permit such communication; anti-coast valve means interposed between and normally permitting fluid communication between said poppet valve means and said high pressure relief valves; a pair of low pressure relief valves normally blocking communication between said high pressure relief valves and said anti-coast valve; valve positioning means associated with said control means for opening the low pressure relief valve associated with said one high pressure relief valve for subjecting said anti-coast valve to the pressure received by said one high pressure relief valve; said anti-coast valve being movable responsive to receiving drive and motoring pressure to block communication with said poppet valve means; and dampening means for controlling the movement of said anti-coast valve so that its rate of movement is no greater than said given rate.

Claim 5

The combination according to claim 2 wherein said dampening means comprises: a guide pin; said anti-coast valve having a bore mating with and slidable on the guide pin and defining therewith a clearance; said clearance metering the flow of hydraulic fluid into and out of said bore to thereby control the rate of movement of said anti-coast valve.

Claim 6

In a hydrostatic transmission having a pump and motor hydraulically interconnected to form a closed circuit for transmitting power therethrough, at least one of said pump and motor having a variable displacement, a reservoir source of fluid, and speed and direction of movement control means connected to said one of said pump and motor and movable in opposite directions from a neutral center position for controlling displacement to selectively produce forward and reverse direction of drive of said motor when the power flow is from the pump to the motor, the combination therewith, comprising: a pair of high pressure pilot-operaTed relief valves communicatively connected across opposite sides of said closed circuit and normally closed to fluid flow between opposite sides of said closed circuit but each of which is operable responsive to development of a pressure differential thereacross for short-circuiting fluid flow between opposite sides of said circuit; said high pressure valves having pilot pressure passages therein open to fluid pressures in opposite sides of said circuit; low pressure valve means; high pressure pilot valve means; first fluid passage means connecting said low pressure valve means and high pressure pilot means together and connecting said latter means to said reservoir; second fluid passage means connecting said low pressure valve means with said pilot pressure passages whereby said low pressure valve means are selectively subjectable to pilot pressures from opposite sides of said closed circuit; valve positioning means adapted to be operatively connected with said control means for presetting said low pressure valve means into positions corresponding to said positions of said control means; said low pressure valve means being normally closed to pilot pressure between opposite sides of said circuit, when power flow is from the pump to the motor, but being operatively responsive, when the power flow is from the motor to the pump, to an increase of pilot pressure for short-circuiting a portion of the fluid flow therein between opposite sides of said closed circuit and incident thereto opening a corresponding one of said high pressure pilot-operated valves to effect a short-circuiting of the remainder of the fluid flow in said closed circuit between opposite sides thereof whereby the flow of power through said unit is disrupted; anti-coast valve means disposed in said first fluid passage means and responsive to pressure developed when the power flow is from the motor to the pump to block flow to said high pressure pilot valve means whereby the dynamic braking may continue to be utilized; and dampening means associated with said anti-coast valve means for controlling its rate of movement.

Claim 7

In a hydrostatic transmission having a pump and motor hydraulically interconnected to form a closed circuit for transmitting power therethrough, at least one of said pump and motor having a variable displacement, a reservoir source of fluid, and speed and direction of movement control means connected to said one of said pump and motor and movable in opposite directions from a neutral center position for controlling displacement to selectively produce forward and reverse direction of drive of said motor when the power flow is from the pump to the motor, the combination therewith, comprising: a pair of high pressure pilot-operaTed relief valves communicatively connected across opposite sides of said closed circuit and normally closed to fluid flow between opposite sides of said closed circuit but each of which is operable responsive to development of a pressure differential thereacross for short-circuiting fluid flow between opposite sides of said circuit; said high pressure valves having pilot pressure passages therein open to fluid pressures in opposite sides of said circuit; low pressure valve means; high pressure pilot valve means; first fluid passage means connecting said low pressure valve means and high pressure pilot means together and connecting said latter means to said reservoir; second fluid passage means connecting said low pressure valve means with said pilot pressure passages whereby said low pressure valve means are selectively subjectable to pilot pressures from opposite sides of said closed circuit; valve positioning means adapted to be operatively connected with said control means for presetting said low pressure valve means into positions corresponding to said positions of said control means; said low pressure valve means being normally closed to pilot pressure between opposite sides of said circuit, when power flow is from the pump to the motor, but being operatively responsive, when the power flow is from the motor to the pump, to an increase of pilot pressure for short-circuiting a portion of the fluid flow therein between opposite sides of said closed circuit and incident thereto opening a corresponding one of said high pressure pilot-operated valves to effect a short-circuiting of the remainder of the fluid flow in said closed circuit between opposite sides thereof whereby the flow of power through said unit is disrupted; anti-coast valve means disposed in said first fluid passage means and responsive to pressure developed when the power flow is from the motor to the pump to block flow to said high pressure pilot valve means whereby the dynamic braking may continue to be utilized; and dampening means associated with said anti-coast valve means for controlling its rate of movement.

Claim 8

In a hydrostatic transmission having a pump and motor hydraulically interconnected to form a closed circuit for transmitting power therethrough, a reservoir source of fluid, at least one of said pump and motor having a variable displacement, and speed and direction of movement control means connected to said one of said pump and motor and movable at a given rate in opposite directions from a neutral center position for controlling displacement to selectively produce forward and reverse direction of drive of the motor when the power flow is from the pump to the motor, the combination therewith, comprising: a pair of high pressure pilot-operated relief valves communicatively connected across opposite sides of said circuit and normally closed to fluid flow between opposite sides of said circuit, but each of which is operable responsive to development of a pressure differential thereacross for short-circuiting fluid flow between opposite sides of said circuit; one of said high pressure relief valves receiving drive pressure from the pump with the transmission displaced for drive in a reverse direction, when the power flow is from the pump to the motor, and receiving motor pressure from the motor with the transmission displaced for drive in a forward direction, when the power flow is from the motor to the pump; a manually controllable poppet valve means normally blocking communication between said high pressure relief valves and said reservoir but manually movable to permit such communication; anti-coast valve means interposed between and normally permitting fluid communication between said poppet valve means and said high pressure relief valves; a pair of low pressure relief valves normally blocking communication between said high pressure relief valves and said anti-coast valve; valve positioning means associated with said conTrol means for opening the low pressure relief valve associated with said one high pressure relief valve for subjecting said anti-coast valve to the pressure received by said one high pressure relief valve; said anti-coast valve being movable responsive to receiving drive and motoring pressure to block communication with said poppet valve means; and dampening means for controlling the movement of said anti-coast valve so that its rate of movement is no greater than said given rate.

Claim 9

In a hydrostatic transmission having a pump and motor hydraulically interconnected to form a closed circuit for transmitting power therethrough, a reservoir source of fluid, at least one of said pump and motor having a variable displacement, and speed and direction of movement control means connected to said one of said pump and motor and movable at a given rate in opposite directions from a neutral center position for controlling displacement to selectively produce forward and reverse direction of drive of the motor when the power flow is from the pump to the motor, the combination therewith, comprising: a pair of high pressure pilot-operated relief valves communicatively connected across opposite sides of said circuit and normally closed to fluid flow between opposite sides of said circuit, but each of which is operable responsive to development of a pressure differential thereacross for short-circuiting fluid flow between opposite sides of said circuit; one of said high pressure relief valves receiving drive pressure from the pump with the transmission displaced for drive in a reverse direction, when the power flow is from the pump to the motor, and receiving motor pressure from the motor with the transmission displaced for drive in a forward direction, when the power flow is from the motor to the pump; a manually controllable poppet valve means normally blocking communication between said high pressure relief valves and said reservoir but manually movable to permit such communication; anti-coast valve means interposed between and normally permitting fluid communication between said poppet valve means and said high pressure relief valves; a pair of low pressure relief valves normally blocking communication between said high pressure relief valves and said anti-coast valve; valve positioning means associated with said conTrol means for opening the low pressure relief valve associated with said one high pressure relief valve for subjecting said anti-coast valve to the pressure received by said one high pressure relief valve; said anti-coast valve being movable responsive to receiving drive and motoring pressure to block communication with said poppet valve means; and dampening means for controlling the movement of said anti-coast valve so that its rate of movement is no greater than said given rate.

Claim 10

The combination according to claim 5 wherein said dampening means comprises: a guide pin; said anti-coast valve having a bore mating with and slidable on the guide pin and defining therewith a clearance; said clearance metering the flow of hydraulic fluid into and out of said bore to thereby control the rate of movement of said anti-coast valve.

Claim 11

A control system for a transmission having variable displacement pump and motor units and a hydraulic interconnection between same for transmitting power between said units, an improved control servo means comprising: a. control means for variably controlling the power transfer from said pump unit to said motor unit in forward or reverse directions; b. means associated with said hydraulic interconnection for limiting power transmission from said motor unit to said pump unit so as to permit dynamic braking of the transmission while minimizing overspeed conditions; c. feathering control means associated with said transmission for interrupting power transmission from said pump to said motor, and d. dashpot means associated with said feathering control valve for normally precluding interruption of power transmission from said motor to said pump, but permitting such power transmission when said servos are moving from forward to reverse or reverse to forward drive.

Claim 12

A control system for a transmission having variable displacement pump and motor units and a hydraulic interconnection between same for transmitting power between said units, an improved control servo means comprising: a. control means for variably controlling the power transfer from said pump unit to said motor unit in forward or reverse directions; b. means associated with said hydraulic interconnection for limiting power transmission from said motor unit to said pump unit so as to permit dynamic braking of the transmission while minimizing overspeed conditions; c. feathering control means associated with said transmission for interrupting power transmission from said pump to said motor, and d. dashpot means associated with said feathering control valve for normally precluding interruption of power transmission from said motor to said pump, but permitting such power transmission when said servos are moving from forward to reverse or reverse to forward drive.

Claim 13

A control system for a transmission having a pump unit and a motor unit and a hydraulic interconnection between same for transmitting power between said units, an improved control means comprising: a. means associated with said hydraulic interconnection for limiting power transmission from said motor unit to said pump unit so as to permit dynamic braking of the transmission, b. feathering control valve means associated with said transmission for interrupting transmission of power between said pump and said motor, and c. time delayed anti-coast means operatively associated with said feathering control valve means for overriding same so as to preclude only interruption of power transmission from said motor to said pump.

Claim 14

A control system for a transmission having a pump unit and a motor unit and a hydraulic interconnection between same for transmitting power between said units, an improved control means comprising: a. means associated with said hydraulic interconnection for limiting power transmission from said motor unit to said pump unit so as to permit dynamic braking of the transmission, b. feathering control valve means associated with said transmission for interrupting transmission of power between said pump and said motor, and c. time delayed anti-coast means operatively associated with said feathering control valve means for overriding same so as to preclude only interruption of power transmission from said motor to said pump.