Neutral control for hydraulic transmission

Claim 2

In a hydromechanical transmission having an axial piston pump and an axial piston motor hydraulically connected in driving relation to each other through a pair of valving slots in a valve plate interposed between said pump and motor, control means to vary the displacement of the pump, wherein the improvement comprises: a neutral control valve positioned in said valve plate in a bore communicating one of said valve slots with a low pressure sump, said control valve including valve means having a first position blocking flow to said low pressure sump and a second position permitting flow to be exhausted from said slot to said sump, biasing means urging said valve member to said first flow blocking position, operating means for moving said valve means to said second position, and actuating means associated with said displacement control means whereby upon positioning said control means in a neutral position said actuating means urges said operator to move said valve means to said second flow exhausting position.

Claim 3

In a hydromechanical transmission having an axial piston pump cylinder barrel and axial piston motor cylinder arranged in driving relationship to one another, a valve disc interposed between the pump and motor having a pair of through valve slots communicating said pump and motor; reciprocable pistons in the pump and motor extending outwardly of the barrels in opposite directions to drivingly engage tiltable swash plates respectively associated with the pump and motor, means securing the valve disc and swash plates to rotate synchronously with the output shaft, and an axially slidable outer control sleeve member engaging said swash plates to vary inclination of the swash plates to vary the transmission output in a preselected manner; wherein the improvement comprises: a pair of neutral control valves disposed in the valve disc within bores intersecting said valve slots, each of said valves comprising, a movable poppet member having a first position blocking flow from the valve slot to the exterior of the valve disc through said bore and a second position permitting flow from the valve slot to the exterior of the valve disc through said bore, a biasing member urging said poppet to the closed flow blocking position; and a stem on said poppet extending through said bore to the exterior of said valve disc; actuating means on said control sleeve comprising a pair of grooves in said sleeve each accepting one of said extending stems, and cam means on said sleeve engaging said stems upon positioning the sleeve to the neutral position so as to urge said poppets to an open position permitting exhausting fluid and pressure from said valve slots.

Claim 4

In a hydromechanical transmission having an axial piston pump cylinder barrel and axial piston motor cylinder arranged in driving relationship to one another, a valve disc interposed between the pump and motor having a pair of through valve slots communicating said pump and motor; reciprocable pistons in the pump and motor extending outwardly of the barrels in opposite directions to drivingly engage tiltable swash plates respectively associated with the pump and motor, means securing the valve disc and swash plates to rotate synchronously with the output shaft, and an axially slidable outer control sleeve member engaging said swash plates to vary inclination of the swash plates to vary the transmission output in a preselected manner; wherein the improvement comprises: a pair of neutral control valves disposed in the valve disc within bores intersecting said valve slots, each of said valves comprising, a movable poppet member having a first position blocking flow from the valve slot to the exterior of the valve disc through said bore and a second position permitting flow from the valve slot to the exterior of the valve disc through said bore, a biasing member urging said poppet to the closed flow blocking position; and a stem on said poppet extending through said bore to the exterior of said valve disc; actuating means on said control sleeve comprising a pair of grooves in said sleeve each accepting one of said extending stems, and cam means on said sleeve engaging said stems upon positioning the sleeve to the neutral position so as to urge said poppets to an open position permitting exhausting fluid and pressure from said valve slots.

Claim 5

The device of claim 2 further including charging means communicating each of the valve slots with a source of make-up flow and a one-way check valve in each of said neutral valves controlling flow of the charging fluid into the respective valve slot.

Claim 6

The device of claim 3 wherein said biasing member urges both said poppet and said charging check valve to their closed positions.

Claim 7

A hydromechanical transmission comprising: first and second cylinder barrels supported upon a common central shaft, said barrels having axial bores arranged therein, said bores communicating through passages with adjacent and spaced apart respective faces of said first and second barrels; a power input shaft at one end of the unit drivingly engaging the first cylinder barrel; a stationary shaft at the other end of the unit engaging the second barrel to hold same stationary; first and second tiltable swash plates at opposite ends of the unit; pistons in said bores extending oppositely from said first and second barrels to drivingly engage said first and second swash plates respectively; a valve plate between said barrel faces secured to said central shaft and having a pair of arcuate through slots adapted to carry fluid between said first and second barrel bores; means securing said first and second swash plates and said valve disc for synchronous rotation, said means also forming the rotary power output; a pair of neutral check valves in said valve disc controlling flow between the respective arcuate slot and a low pressure exhaust zone; a biasing member urging each of said check valves to a closed flow blocking position; a stem extending from each of said check valves adjacent said control member adapted to move the check valves to open positions to relieve pressure in said slots upon actuation; and a manual control member operatively engaging said swash plates for varying The displacement of the pump and motor in a predetermined manner to vary transmission output speed rotation, said control member having means associated therewith adapted to engage and depress said neutral valve stems when said control is moved to a zero output speed position thereby relieving and equalizing pressure in said arcuate slots.

Claim 8

A hydromechanical transmission comprising: first and second cylinder barrels supported upon a common central shaft, said barrels having axial bores arranged therein, said bores communicating through passages with adjacent and spaced apart respective faces of said first and second barrels; a power input shaft at one end of the unit drivingly engaging the first cylinder barrel; a stationary shaft at the other end of the unit engaging the second barrel to hold same stationary; first and second tiltable swash plates at opposite ends of the unit; pistons in said bores extending oppositely from said first and second barrels to drivingly engage said first and second swash plates respectively; a valve plate between said barrel faces secured to said central shaft and having a pair of arcuate through slots adapted to carry fluid between said first and second barrel bores; means securing said first and second swash plates and said valve disc for synchronous rotation, said means also forming the rotary power output; a pair of neutral check valves in said valve disc controlling flow between the respective arcuate slot and a low pressure exhaust zone; a biasing member urging each of said check valves to a closed flow blocking position; a stem extending from each of said check valves adjacent said control member adapted to move the check valves to open positions to relieve pressure in said slots upon actuation; and a manual control member operatively engaging said swash plates for varying The displacement of the pump and motor in a predetermined manner to vary transmission output speed rotation, said control member having means associated therewith adapted to engage and depress said neutral valve stems when said control is moved to a zero output speed position thereby relieving and equalizing pressure in said arcuate slots.

Claim 9

The device of claim 5 wherein said swash plate and valve disc securing means comprises a housing surrounding said cylinder barrels and swash plates, said swash plates tiltably secured upon the housing.

Claim 10

The device of claim 6 wherein said control member is an axially slidable external sleeve surrounding said housing having cam grooves on its interior surface, said swash plates being provided with control arms which are received in said cam grooves, whereby movement of said sleeve will vary the swash plate inclinations.

Claim 11

The device of claim 5 further including an auxiliary pump delivering low pressure fluid through communicating conduits in said stationary shaft, said central shaft and said valve disc directing fluid to each of said arcuate slots.

Claim 12

The device of claim 8 further including check valves in said valve disc permitting one-way flow of charging fluid to said arcuate slots, said biasing members also urging said check valves to closed flow blocking positions.

Claim 13

The device of claim 9 wherein said neutral check valves each comprise a poppet movably disposed within a bore in said valve disc intercepting said arcuate slot, said poppet engaging a shoulder on said valve disc in the closed position to block flow from the arcuate slot through said bore to the exterior of said valve disc.

Claim 14

The device of claim 10 wherein said stem is integrally formed on said poppet extending through said bore to the control member.

Claim 15

The device of claim 11 wherein each of said charging check valves comprises a ball sealingly engaging a second shoulder aligned and opposing said poppet shoulder, said biasing member extending between said poppet and ball and urging same in opposite directions against the respective shoulders.