Control device for a hydrostatic transmission

Claim 2

A control device for a transmission having a variable displacement pump driven by a prime mover having a power curve and a hydraulic motor comprising: first means sensing the load applied on the prime mover; second means for sensing the speed of the prime mover including pump means driven by the prime moveR for developing a hydraulic pressure proportional to the speed of the prime mover, and compensating means for correcting for change in hydraulic pressure from the pump means in response to speed changes of the prime mover to follow a pressure-speed curve which is substantially similar to the power curve of the prime mover up to a maximum horsepower of the prime mover; a servo device having a housing containing a cylinder, a servo piston disposed in the cylinder and a pilot spool for controlling the application of fluid pressure to the servo piston; linkage means connecting the servo piston with the hydrostatic transmission to vary the ratio of the transmission in response to movement of the servo piston; and means for combining the output of the first and second sensing means for applying a control signal to the pilot spool whereby the ratio of the hydrostatic transmission is varied in response to changes in both the load and speed of the prime mover.

Claim 3

A control device according to claim 1, which further includes a manually operated direction control device for receiving the output of the servo piston and producing the desired output for driving the hydrostatic transmission in both a forward and reverse direction.

Claim 4

A control device according to claim 1, wherein the first sensing means senses changes in the vacuum at the intake manifold of the prime mover to sense the changes of load thereon.

Claim 5

A control device according to claim 3, wherein said first means comprises a conduit extending from the intake manifold of the prime mover to a first pressure chamber, said conduit having a valve connected to a valve actuating means for opening and closing the valve to regulate flow in the conduit, said actuating means including a spring for urging the valve closed and a piston acted on by the pressure from the pump means to open the valve, a diaphragm separating the first pressure chamber from a second pressure chamber which is vented to the atmosphere and a restricted orifice interconnecting said first and second chambers, and wherein said means for combining includes a member connected to said diaphragm and having a piston disposed in a pressure chamber which receives the pressure from the pump means to act on the piston and to move the member in one direction and a spring resisting movement of the member in said one direction so that the member is moved by the pressure differential in the first and second chambers and by the piston in the one direction against the force of the spring.

Claim 6

A control device according to claim 4, wherein the compensating means of the second sensing means includes a cam and follower, said follower being connected to the pilot spool and the cam being connected to the member of the means for combining the output of the first and second sensing means so that movement of the follower on the cam causes shifting of the pilot spool with compensation for correcting the changes in the hydraulic pressure from the pump means to follow a pressure speed curve which is substantially similar to the power curve of the prime mover.

Claim 7

A control device according to claim 5, wherein the member is interconnected to the cam by a linkage including a lever bar, said lever bar having a pivotal connection at another point to the throttle linkage of the prime mover so that the bar is pivoted in response to changes in the throttle setting.

Claim 8

A control device according to claim 4, wherein said compensating means of the second sensing means is disposed adjacent to the output of the pump means and includes pressure release means for bleeding-off a variable portion of the pressure from the output of the pump means through an orifice with the effective size of the orifice varying in response to changes in the output of the pump means whereby the output pressure of the pump means is corrected to provide a modified pressure for acting on the piston of the valve actuating means and the piston of said member.

Claim 9

A control device according to claim 7, wherein the bleed means includes a cup-shaped piston received in a cylinder, said cup-shaped piston having at least one bleed orifice having an effective orifice opening depending on the displacement of the cup-shaped piston in the cylinder, means biasing the cup-shaped piston to close the bleed orifice and means applying the output pressure to the cup-shaped piston to displace it against said biasing means.

Claim 10

A control device according to claim 7, which includes a lever bar pivotally mounted on a fixed support at a first point, the pilot spool and the member each being pivotally connected to the lever bar at points spaced from said one point and said bar providing a pivot point for a throttle linkage for the prime mover at a point spaced from said other points, so that movement of the bar by the member causes changes in the throttle setting of the prime mover.

Claim 11

A control device according to claim 7, which includes a lever bar having a first portion connected to a second portion by a pivotal connection, said member and pilot spool having pivot connections with the first portion at separate points thereon, said second portion being a pivotal link in a linkage between a manually actuated throttle and a throttle valve so that during initial setting of the manually actuated throttle, the second portion pivots with respect to the first portion and as the prime mover assumes the speed for its throttle setting, the first portion pivots to a straight line relationship with the second portion as the member shifts the pilot spool.

Claim 12

A control device for a transmission having a variable displacement pump driven by a prime mover having a power curve, said transmission including a hydraulic motor, comprising: first means for sensing the load on the prime mover and providing a signal; second means for sensing the speed of the prime mover including pump means driven by the prime mover to provide a hydraulic pressure and means for bleeding the pressure of the output of the pump means in varying amounts depending on the speed of the prime mover to provide a modified pressure as a signal, said modified pressure having a curve for speed versus pressure resemblying the power curve of the prime mover up to a point of maximum power; means combining the signal of the first means and the modified pressure to form a combined signal for the two sensing means; a servo device having a housing containing a cylinder, a servo piston disposed in the cylinder and a pilot spool for controlling the application of the fluid pressure to the servo piston; linkage means connecting the servo piston with the transmission to vary the ratio of the transmission in response to the movement of the servo piston; and linkage means interconnecting the pilot spool to the means for combining so that the pilot spool is moved in response to the combined signal.

Claim 13

A control device for a transmission having a variable displacement pump driven by a prime mover having a power curve, said transmission including a hydraulic motor, comprising: first means for sensing the load on the prime mover and providing a signal; second means for sensing the speed of the prime mover including pump means driven by the prime mover to provide a hydraulic pressure and means for bleeding the pressure of the output of the pump means in varying amounts depending on the speed of the prime mover to provide a modified pressure as a signal, said modified pressure having a curve for speed versus pressure resemblying the power curve of the prime mover up to a point of maximum power; means combining the signal of the first means and the modified pressure to form a combined signal for the two sensing means; a servo device having a housing containing a cylinder, a servo piston disposed in the cylinder and a pilot spool for controlling the application of the fluid pressure to the servo piston; linkage means connecting the servo piston with the transmission to vary the ratio of the transmission in response to the movement of the servo piston; and linkage means interconnecting the pilot spool to the means for combining so that the pilot spool is moved in response to the combined signal.

Claim 14

A control device according to claim 11, which further includes manually actuated direction control means interposed between the output of the servo piston and the hydrostatic transmission to vary the output signal in response to selected forward and reverse drive of the vehicle.

Claim 15

A control device according to claim 11, wherein the means for combining the signals from the first and second sensing means includes a member shifted in response to the combined signal and wherein the linkage interconnecting the pilot spool and the means includes a bar pivotally connected to a fixed support, said bar having pivotal connections to the pilot spool and the member at spaced points from the fixed support and also providing a pivot point in a linkage between the manually actuated throttle and the throttle of the prime mover so that movement of the bar in response to the combined signal causes changes in the throttle setting of the prime mover.

Claim 16

A control device according to claim 11, wherein the means for combining the signal has a member movable in response to the combined signal, wherein the linkage interconnecting the means for combining to the pilot spool includes a lever bar having a first portion pivotally connected to a second portion with means biasing the two portions into a straight line arrangement, said pilot spool being pivotally connected to the first portion at a first point and said member being connected at a second point to the first portion by a pivotal connection spaced from the first point, a manually actuated throttle being pivotally connected to the second portion at a third point and a linkage system extending to the throttle of the prime mover pivotally connected at a fourth point on the second portion spaced from the third point so that said second portion acts as a link in a linkage therebetween, whereby during initial acceleration the second portion pivots relative to the first portion until the sensed modified pressure increases at which time the first portion moves relative to the second portion to cause movement of the pilot spool and when the first portion is in line with the second portion, further movement due to the combined signal causes variations in the output of the servo piston and changes in the throttle setting of the prime mover.

Claim 17

A control device according to claim 14, wherein the first and second portion of the bars are provided with a last motion connection therebetween to limit the pivotal movement therebetween.

Claim 18

A control device according to claim 14, wherein said first sensing means senses changes in the vacuum at the intake manifold of the prime mover and includes a conduit extending from the intake manifold of the prime mover to a first pressure chamber, said conduit having a valve connected to a valve actuating means for opening and closing the valve to regulate flow in the conduit, said actuating means including a spring for urging the valve closed and a piston acted on by the modified pressure to open the valve, a diaphragm separating the first pressure chamber from a second pressure chamber which second pressure chamber is vented to the atmosphere, and a restricted orifice interconnecting the first and second chambers, wherein said member of the means for combining is provided with a piston for receiving modified pressure and is connected to the diaphragm and wherein said means for combining further includes a spring for opposing movement of said member in one direction so that application of the modified pressure and the pressure differential between the first and second chambers causes movement against said spring in said one direction.

Claim 19

A control device according to claim 16, wherein the spring of the valve actuating means is bottomed between the piston of the valve actuating means and an adjustment device to enable changing of the compression on the spring to vary the spring loading on the valve member.

Claim 20

A control device according to claim 17, wherein the adjustment means includes a plunger bottomed on the spring of the actuating means and engaging a rotatable cam, said cam being rotated by linkage attached to the manually actuated throttle so that the spring pressure is increased as the throttle is returned to the idle position to ensure positive closing of the valve when the prime mover is in an idle condition.

Claim 21

A control device according to claim 16, which further includes temperature responsive means for compensating the fluid pressure from the pump means in response to the increase in temperature of the hydraulic fluid.

Claim 22

A control device according to claim 16, wherein the linkage means between the servo piston and the transmission includes means for changing the direction of displacement of the servo piston to enable change in the ratio of transmission for both a forward and reverse direction.