Hydrostatic auxiliary wheel motor assist drive system for vehicles

Claim 2

In a drive system for a vehicle including a primary driver, a prime mover, an assist driver, a primary drive train for transmitting power from said prime mover to said primary driver, and an assist drive train for transmitting power from said prime mover to said assist driver, said assist drive train including a prime mover-driven hydraulic pump means, a hydraulic assist motor means driven by said hydraulic pump means, hydraulic fluid passage means interconnecting said assist motor means and said pump means, and drive means interconnecting said assist motor means and said assist driver, manually operable control means in said hydraulic passage means for selectively energizing said assist drive train by connecting flow from said pump means to said assist motor means, said assist drive train providing when engaged a greater speed reduction to said assist driver than said primary drive train provides to said primary driver in at least the normal low operating speed range of said primary drive train so that said assist driver is normally undriven by said assist motor means and said primary driver provides all of the tractive effort required to move said vehicle at a desired speed in the absence of power slippage in said primary drive train and so that said assist driver supplies tractive effort to supplement the tractive effort of said primary driver when there is power slippage in said primary drive train, said hydraulic passage means including an assist motor control circuit for ensuring an adequate supply of pressure fluid to the inlet side of said assist motor means to prevent cavitation when said assist drive train is energized.

Claim 3

A drive system according to claim 1 wherein said control circuit includes means operable when said assist drive train is engaged to limit the pressure demand of said assist motor means so that said demand does not exceed the available pressure fluid supply.

Claim 4

A drive system according to claim 2 wherein said drive means includes a clutch and said hydraulic control circuit includes clutch-operating means sensitive to differential pressure across said assist motor means, said clutch-operating means being operable to engage said clutch at differential pressures above a predetermined minimum said pressure and being operable to at least partially disengage said clutch at said minimum differential pressure to prevent said assist driver from back-driving said assist motor means.

Claim 5

A drive system according to claim 1 wherein said drive means interconnecting said assist motor means and said assist driver includes clutch means sensitive to differential pressure across said assist motor means, said clutch means being operable at a predetermined low said differential pressure to at least partially disengage said assist driver from said assist motor means and thereby prevent cavitation in said assist motor means.

Claim 6

A drive system according to claim 1 wherein said hydraulic control circuit has a shorting circuit portion operable under conditions wherein said assist driver tends to back-drive said assist motor means to recirculate pressure fluid from the outlet side to the inlet side of said motor means to provide for adequate filling of said motor means under said conditions.

Claim 7

A drive system according to claim 5 including means operable during energization of said shorting circuit to elevate the fluid pressure within said control circuit and thereby ensure an adequate fluid pressure at said motor inlet to prevent cavitation.

Claim 8

A drive system according to claim 6 including means selectively operable to vary the elevated pressures within said control circuit when said shorting circuit is energized.

Claim 9

A drive system according to claim 5 wherein said shorting circuit includes shorting valve means operable in response to a reduced pressure in said control circuit to energize said shorting circuit.

Claim 10

A drive system according to claim 6 wherein said pressure-elevating means includes a pilot circuit operable to elevate the pressure in said control circuit.

Claim 11

A drive system according to claim 8 wherein said shorting valve means operates to energize a pilot circuit to increase the fluid pressure in said control circuit when said shorting valve means energizes said shorting circuit.

Claim 12

An auxiliary hydraulic drive system for a vehicle having a primary drive system including engine-driven ground-engaging primary drive wheel means and other ground-engaging assist wheel means, said auxiliary drive system comprising: hydraulic pump means driven by said engine, hydraulic wheel motor means for driving said assist wheel means, said wheel motor means being supplied with pressure fluid by said pump means, auxiliary power transmission means interconnecting said pump means, wheel motor means and assist wheel means and under normal operating conditions adapted to drive said assist wheel means at a lower speed than said primary drive system is adapted to drive said primary wheel means in the absence of power slippage in said primary system so that said auxiliary system is operable to sense power slippage in said primary drive system and effective to drive said assist wheel means only when there is slippage in said primary drive system, and hydraulic control circuit means in said auxiliary drive system responsive to said slippage sensings and operable to protect said wheel motor means against cavitation in the absence of power slippage in said primary drive system sufficient to produce tractive effort at said assist wheel means.

Claim 13

An auxiliary hydraulic drive system for a vehicle having a primary drive system including engine-driven ground-engaging primary drive wheel means and other ground-engaging assist wheel means, said auxiliary drive system comprising: hydraulic pump means driven by said engine, hydraulic wheel motor means for driving said assist wheel means, said wheel motor means being supplied with pressure fluid by said pump means, auxiliary power transmission means interconnecting said pump means, wheel motor means and assist wheel means and under normal operating conditions adapted to drive said assist wheel means at a lower speed than said primary drive system is adapted to drive said primary wheel means in the absence of power slippage in said primary system so that said auxiliary system is operable to sense power slippage in said primary drive system and effective to drive said assist wheel means only when there is slippage in said primary drive system, and hydraulic control circuit means in said auxiliary drive system responsive to said slippage sensings and operable to protect said wheel motor means against cavitation in the absence of power slippage in said primary drive system sufficient to produce tractive effort at said assist wheel means.

Claim 14

A system according to claim 11 wherein said control circuit means includes means for controlling the demAnd pressure of said wheel motor means and clutch means between said wheel motor means and said assist wheel means, said control circuit being operable when energized to control the extent of engagement of said clutch means in a manner such that said demand pressure of said motor means does not exceed the capacity of said pump means to meet said demand pressure.

Claim 15

A system according to claim 11 wherein said hydraulic control circuit includes power control valve means in said control circuit, said control circuit including bypass passage means bypassing said power control valve means from said pump means to said wheel motor means, pilot hydraulic circuit means for applying a control pressure to said power control valve means, and shorting valve means operable to connect said bypass passage means and said pilot circuit means under predetermined pressure conditions in said control circuit in a manner so as to maintain minimum predetermined inlet pressures at said wheel motor means under various operating modes of said wheel motor means.

Claim 16

A system according to claim 11 wherein said control circuit includes power control valve means, manually operable master control valve means for selectively energizing said control circuit, said master control valve means and control circuit including means for selectively directing a flow of pressure fluid either to a forward or a reverse motor port of said wheel motor means independently of the directional mode of said primary drive system.

Claim 17

A system according to claim 11 including: fluid pressure-operated clutch means for transmitting torque from said wheel motor means to said assist wheel means, clutch modulator means in said control circuit for sensing differential pressure across said wheel motor means, said modulator means being operable at differential pressures above a low predetermined said differential pressure to admit fluid to said clutch means at a pressure sufficient to effect full clutch engagement and being operable below said low predetermined pressure to effect at least partial clutch disengagement sufficient to prevent cavitation at said wheel motor means.

Claim 18

A system according to claim 15 wherein said clutch means includes friction clutch means and said modulator means is operable at or below said low predetermined differential pressure to admit fluid to said clutch means at a pressure sufficient to effect no more than partial clutch engagement so that said wheel motor means is driven at a speed dictated by the available supply of pressure fluid and independent of the speed of said assist wheel means.

Claim 19

An auxiliary drive system according to claim 11 wherein said hydraulic control circuit includes pressure-sensitive control valve means sensitive to discharge pressure at said wheel motor means and operable with said circuit energized to meter flow back to said pump means so as to maintain a predetermined discharge pressure at said motor means in a manner such that inlet pressure at said motor means at any time is a function of said discharge pressure and the differential pressure across said motor means.

Claim 20

An auxiliary drive system according to claim 17 wherein said control circuit includes means for restricting flow from the discharge side of said motor means back to said pump and recirculating flow from the discharge side to the inlet side of said motor means within said control circuit when the discharge pressure of said motor means exceeds the inlet pressure thereof.

Claim 21

An auxiliary drive system according to claim 11 including: manual selector means for controlling the flow of pressure fluid between said pump and motor means and for alternatively (1) interrupting said flow, (2) directing said flow to a side of said motor means to tend to cause forward vehicle movement, and (3) reversing said flow to an opposite side of said motor means to tend to effect reverse vehicle movement, said selector means being operable with said control circuit to direct fLuid flow to said wheel motor means in a retarding directional mode opposing the directional mode of said primary drive system so that said auxiliary drive system has a retarding effect on vehicle movement.

Claim 22

An auxiliary drive system according to claim 19 including fluid pressure-responsive control valve means in said control circuit operable during fluid flow in said retarding mode to recirculate flow from the outlet side to the inlet side of said motor means so as to tend to increase the inlet pressure at said motor means.

Claim 23

An auxiliary drive system according to claim 11 including: manual selector valve means for directing flow to said hydraulic control circuit and said motor means in a forward or reverse directional mode independently of the directional mode of said primary drive system, control valve means in said control circuit sensitive to discharge pressure at said motor means and operable at discharge pressures below a predetermined minimum control circuit charge pressure to recirculate fluid flow from the outlet side of said motor means back to the inlet side thereof while restricting return flow from said circuit to said pump means to ensure adequate cavitation-preventing fluid flow through said motor means, said control valve means being operable at motor discharge pressures above said predetermined minimum pressure to meter fluid flow from the outlet side of said motor means back to said pump means, thereby tending to maintain said predetermined control circuit charge pressure, said control circuit including charge pressure-regulating means operable to elevate the level of said predetermined charge pressure when said selector valve means directs fluid flow to said circuit and motor means in a directional mode opposite the directional mode of said primary drive system so that during flow in said opposite directional mode said flow will have a retarding effect on vehicle movement while protecting said motor means against cavitation.

Claim 24

An auxiliary drive system according to claim 21 wherein said charge pressure-regulating means is operable to elevate said charge pressure level whenever said assist wheel means back-drives said wheel motor means.

Claim 25

A drive system according to claim 21 including manually operable variable control means selectively operable to elevate the discharge pressure of said motor means upon operation of said auxiliary drive system in a retarding mode.

Claim 26

An auxiliary drive system for a vehicle having a primary drive system including an engine and primary power transmission means for driving primary drive wheel means, said auxiliary drive system comprising: traction assist wheel means, hydraulic wheel motor means and auxiliary power transmission means carried by said assist wheel means for driving the same, pump means driven by said engine and supplying pressure fluid for driving said assist wheel means, wheel motor fluid control circuit means connected to forward and reverse sides of said motor means, supply and return passage means connecting forward and reverse sides of said motor control circuit means to said pump means for supplying said motor circuit means with pressure fluid and returning said fluid to said pump means, manually operated master control valve means (1) movable to a first position for directing flow from said pump means through said supply and return passage means in one direction to said forward side of said motor circuit means, (2) movable to a second position for directing flow in an opposite direction to said reverse side of said motor circuit means and (3) movable to a third position to block flow through said supply passage means to said motor circuit means while permitting return flow through said return passage means to said pump means, said motor control circuit means comprising: forward power control valve means sensitive to fluid pressure in said motor circuit means and operable under fluid pressures beloW a predetermined motor circuit charge pressure to restrict flow to the forward side of said motor means and operable under motor circuit pressures above said predetermined pressure to permit full flow through the forward side of said motor circuit means to the forward side of said motor means when said master control valve is in said first position, forward bypass passage means for bypassing flow into said motor circuit means past said forward power control valve means to energize said motor circuit means when said master valve means is in said first position and said motor circuit pressure is below said predetermined charge pressure, reverse power control valve means sensitive to fluid pressure in said motor circuit means and operable under motor discharge pressures below said predetermined charge pressure to block return flow through said reverse valve means from the reverse side of said motor control circuit means to said pump means and operable in response to discharge pressures above said predetermined pressure to meter flow from the reverse side of said motor circuit means to said pump means when said master control valve means is in said first position, reverse bypass passage means for bypassing flow into the reverse side of said motor circuit means past said reverse power control valve means when said master valve means is in said second position, and shorting valve means operable when either one of said forward and reverse power control valve means is blocking flow out of said motor circuit means to permit recirculating flow within said motor control circuit so as to provide a positive pressure at the inlet side of said motor means.

Claim 27

An auxiliary drive system for a vehicle having a primary drive system including an engine and primary power transmission means for driving primary drive wheel means, said auxiliary drive system comprising: traction assist wheel means, hydraulic wheel motor means and auxiliary power transmission means carried by said assist wheel means for driving the same, pump means driven by said engine and supplying pressure fluid for driving said assist wheel means, wheel motor fluid control circuit means connected to forward and reverse sides of said motor means, supply and return passage means connecting forward and reverse sides of said motor control circuit means to said pump means for supplying said motor circuit means with pressure fluid and returning said fluid to said pump means, manually operated master control valve means (1) movable to a first position for directing flow from said pump means through said supply and return passage means in one direction to said forward side of said motor circuit means, (2) movable to a second position for directing flow in an opposite direction to said reverse side of said motor circuit means and (3) movable to a third position to block flow through said supply passage means to said motor circuit means while permitting return flow through said return passage means to said pump means, said motor control circuit means comprising: forward power control valve means sensitive to fluid pressure in said motor circuit means and operable under fluid pressures beloW a predetermined motor circuit charge pressure to restrict flow to the forward side of said motor means and operable under motor circuit pressures above said predetermined pressure to permit full flow through the forward side of said motor circuit means to the forward side of said motor means when said master control valve is in said first position, forward bypass passage means for bypassing flow into said motor circuit means past said forward power control valve means to energize said motor circuit means when said master valve means is in said first position and said motor circuit pressure is below said predetermined charge pressure, reverse power control valve means sensitive to fluid pressure in said motor circuit means and operable under motor discharge pressures below said predetermined charge pressure to block return flow through said reverse valve means from the reverse side of said motor control circuit means to said pump means and operable in response to discharge pressures above said predetermined pressure to meter flow from the reverse side of said motor circuit means to said pump means when said master control valve means is in said first position, reverse bypass passage means for bypassing flow into the reverse side of said motor circuit means past said reverse power control valve means when said master valve means is in said second position, and shorting valve means operable when either one of said forward and reverse power control valve means is blocking flow out of said motor circuit means to permit recirculating flow within said motor control circuit so as to provide a positive pressure at the inlet side of said motor means.

Claim 28

A system according to claim 24 including pilot fluid circuit means, said pilot circuit means being energized through said shorting valve means when at least one of said forward and reverse power control valve means is in a flow-blocking position and being operable when energized to apply a pilot pressure to said forward and reverse power control valve means tending to resist movement of said power control valve means toward their flow-metering positions and thereby elevate the charge pressure in said control circuit.

Claim 29

In a drive system for a vehicle including a primary driver, a normally undriven assist driver, an engine, a primary drive train for transmitting power from said engine to said primary driver, and an assist drive train for transmitting power from said engine to said assist driver, said assist drive train including an engine-driven hydraulic pump means, a hydraulic assist motor means adapted to be driven by said pump means, a hydraulic fluid circuit for circulating flow between said pump means and said motor means, and drive means interconnecting said assist motor means and said assist driver, manually operable directional control valve means in said circuit for selectively connecting said pump means to said assist motor means in either a forward or a reverse mode of operation of said motor means independent of the directional mode of said primary drive train, and selectively de-energizing said assist drive train, said hydraulic circuit including an assist motor control circuit toward said assist motor means from said directional control valve means with said control circuit including said assist motor means and a power control valve means responsive to fluid pressure in said control circuit at the inlet side of said motor means for controlling the flow of pressure fluid from said pump means into said control circuit and responsive to fluid pressure in said control circuit at the outlet side of said assist motor means for controlling the return flow of pressure fluid from said control circuit to said pump means to ensure adequate fluid pressurization of said control circuit in all operational modes of said assist motor means to prevent cavitating said motor means.

Claim 30

In a drive system for a vehicle including a primary driver, a normally undriven assist driver, an engine, a primary drive train for transmitting power from said engine to said primary driver, and an assist drive train for transmitting power from said engine to said assist driver, said assist drive train including an engine-driven hydraulic pump means, a hydraulic assist motor means adapted to be driven by said pump means, a hydraulic fluid circuit for circulating flow between said pump means and said motor means, and drive means interconnecting said assist motor means and said assist driver, manually operable directional control valve means in said circuit for selectively connecting said pump means to said assist motor means in either a forward or a reverse mode of operation of said motor means independent of the directional mode of said primary drive train, and selectively de-energizing said assist drive train, said hydraulic circuit including an assist motor control circuit toward said assist motor means from said directional control valve means with said control circuit including said assist motor means and a power control valve means responsive to fluid pressure in said control circuit at the inlet side of said motor means for controlling the flow of pressure fluid from said pump means into said control circuit and responsive to fluid pressure in said control circuit at the outlet side of said assist motor means for controlling the return flow of pressure fluid from said control circuit to said pump means to ensure adequate fluid pressurization of said control circuit in all operational modes of said assist motor means to prevent cavitating said motor means.

Claim 31

A system according to claim 23 wherein said wheel motor means drives said assist wheel means throuGh a fluid-operated clutch means, said clutch means including a multiple disc friction clutch pack biased to a disengaged condition, a clutch shaft slidable axially through said wheel motor means but rotatable by said motor means to transmit output torque from said motor means, said clutch shaft being operably connected to said clutch pack, a clutch piston at the opposite end of said shaft operable under a predetermined clutch fluid pressure to shift said clutch shaft axially toward said clutch pack to effect clutch engagement.