Clutch and Brake Control Circuit for a Vehicle

This invention relates generally to a fluid control circuit for a vehicle and more particularly to such a fluid circuit which controls the disengagement of a drive mechanism and the engagement of a brake mechanism of the vehicle.

Construction and earthmoving vehicles, such as track-type tractors, are normally steered by interrupting the power to the drive wheel or sprocket on one side or the other of the tractor. The steering can be assisted by applying a brake to the disconnected drive components. Conventionally, the interruption of the power and the application of the brake is sequentially accomplished by a single foot operated pedal control. A first pedal controls steering to the right and a separate second pedal controls steering to the left. Most track-type tractors included a third foot operated pedal for applying brakes to both left and right drive components without disconnecting the power to the drive components. Some prior systems utilized mechanical controls to operate the steering and brake functions while others used a combination of mechanical and hydraulic control systems.

One type of steering clutch and brake control system is disclosed in U.S. Pat. No. 3,815,697, issued to J. W. Bridwell et al. on June 11, 1974. In this patent, left and right foot pedals actuates hydraulic valves to signal hydraulic motors to disengage the steering clutches, and the same pedals sequentially bear upon the valve housings to mechanically engage the corresponding steering brake. A third center mounted pedal can be independently actuated to simultaneously engage the brakes on both drive components.

Another type of steering clutch and brake control system is disclosed in U.S. Pat. No. 3,899,058, issued to D. Pasquini on Aug. 12, 1975. In this patent, a pair of hydraulic booster valves cooperate with a flow control valve for controlling fluid flow to the steering components of the vehicle. The booster valves and the flow control valve are arranged within the system for combined sequential control of the clutching and braking functions of each track of the vehicle by selective operation of a control lever associated with each booster valve. The system permits an independent braking function by simultaneous operation of the control levers to apply the brake mechanisms on both drive components. The clutches which engage the drive components remain engaged during the independent braking function of both brakes.

Each of the above-noted steering clutch and brake control systems would appear to operate satisfactorily in controlling the steering and braking functions of a vehicle. However, each system contains structural components which could be eliminated in order to simplify the system.

The present invention is directed to overcoming one or more of the problems as set forth above.

In one aspect of the present invention, a fluid control circuit for controlling the disengagement of a drive mechanism and the engagement of a brake mechanism for a vehicle includes a source of pressurized fluid, first and second control valves, first and second means for actuating the first and second control valves, first and second drive disengaging mechanisms, and first and second brake mechanisms. The fluid circuit further includes a plurality of fluid lines connecting the fluid source to the control valves, connecting the first control valve to the second control valve, and connecting the drive disengaging mechanisms to the control valves. The fluid circuit also includes a first activating means for actuating the first drive disengaging mechanism and a second activating means for activating the second drive disengaging mechanism. The first activating means includes pressurized fluid routed to the first drive disengaging mechanism through the second control valve and subsequently through the first control valve, and the second activating means includes pressurized fluid routed to the second drive disconnecting mechanism through the first control valve and subsequently through the second control valve.

In another aspect of the present invention, the drive disconnecting devices include first and second fluid actuated cylinders and each of the control valves has first and second fluid control positions. The pressurized fluid is blocked to the first and second cylinders when the control valves are in the second control positions concurrently.

Track-type tractors have generally been steered using a combination of steering clutches and steering brakes. Gradual steering is accomplished by disconnecting the power drive on one side of the vehicle by disengaging the respective steering clutch. The steering can be increased by applying a steering brake to the disconnected drive component. Conventionally, a right foot operated pedal controls disengagement of the right steering clutch and subsequent application of the right steering brake. In a similar manner a left foot operated pedal controls disengagement of the left steering clutch and subsequent application of the left steering brake. A separate foot operated pedal, normally positioned between the right and left steering clutch pedals, may apply both left and right brakes without disengaging the steering clutches. In small track-type machines, the three foot operated pedals create a crowded operator's station and complicate the operation of the machine. The subject invention provides a steering clutch and brake control having only two foot operated pedals which operate two fluid control valves. The control valves disconnect the steering clutches and actuate the steering brakes sequentially when one or the other of the pedals is activated. When both pedals are activated concurrently, both brakes are actuated while the steering clutches remain engaged. The third pedal is eliminated which provides easier machine control and a less crowded operator's station.

FIG. 1 is a schematic illustration of a steering clutch and brake control circuit of the present invention, with the first and second clutches shown engaged and the first and second brakes shown disengaged;

FIG. 2 is a schematic illustration of a control circuit, similar to FIG. 1 with a first clutch shown disengaged and the corresponding first brake shown engaged;

FIG. 3 is a schematic illustration of a control circuit, similar to FIG. 1, with a second clutch shown disengaged and the corresponding second brake shown engaged; and

FIG. 4 is a schematic illustration of a control circuit, similar to FIG. 1, with the first and second clutches shown engaged and the first and second brakes shown engaged.

Referring to the drawings, a fluid control circuit 10 for controlling the disengagement of first and second drive mechanism 12,14 and the engagement of first and second brake mechanisms 16,18 for a vehicle includes a source of pressurized fluid 20, first and second fluid control valves 22,24, first and second means 26,28 for actuating respectively the first and second control valves 22,24, first and second drive mechanisms 12,14 first and second drive disengaging mechanism 30,32, and first and second brake mechanisms 16,18. The fluid control circuit 10 further includes first and second fluid lines 34,36 which connect the fluid source 20 respectively to the first and second control valves 22,24, third and fourth fluid lines 38,40 which connect the first control valve 22 to the second control valve 24, and fifth and sixth fluid lines 42,44 which connect the first and second drive disengaging mechanism 30,32 respectively to the first and second control valves 22,24.

The fluid control circuit 10 also includes a first means 46 for activating the first drive disengaging mechanism 30, and a second means 48 for activating the second drive disengaging mechanism 32. The first activating means 46 includes pressurized fluid routed to the first drive disengaging mechanism 30 sequentially through the second control valve 24 and then through the first control valve 22. The second activating means 48 includes pressurized fluid routed to the second drive disengaging mechanism 32 sequentially through the first control valve 22 and then through the second control valve 24.

The source of pressurized fluid 20 includes a single fluid pump 50 and a fluid reservoir 52. The fluid pump 50 is adapted to supply pressurized fluid to other vehicle circuits through the fluid line 53. The first control valve 22 has first and second control positions 54,56 and the second control valve 24 has first and second control positions 58,60. The first and second actuating means 26,28 include respectively first and second valve actuating foot operated pedals 62,64 connected respectively to the first and second fluid control valves 22,24. The first and second foot pedals 62,64 are also connected respectively to the first and second brake mechanisms 16,18. First and second lost motion devices 63,65 associated respectively with the first and second brake mechanisms 16,18 provide that each of the control valves 22,24 can be moved a pre-determined distance from the first positions 54,58 toward the second positions 56,60 respectively before the brake mechanisms are activated. The first and second drive disengaging mechanisms 30,32 include first and second fluid actuated cylinder 66,68 and pistons 70,72 respectively. The cylinder 66 is connected to the fluid reservoir 52 through the line 42, the first control valve 22, and a first drain line 74 when the first control valve 22 is in the second control position. The cylinder 68 is connected to the fluid reservoir 52 through the line 44, the second control valve 24, and a second drain line 76 when the second control valve 24 is in the second control position. When either of the control valves 22,24 is in the second control positions 56,60, the respective drive disengaging mechanism 30,32 is de-activated and the respective drive mechanism 12,14 is engaged. First and second springs 78,80 return the pistons 70,72 to a de-activated position when the cylinders 66,68 are connected to the reservoir 52.

With reference to the drawings, the subject clutch and brake control circuit is particularly useful with track-type vehicles, but can be advantageously utilized with any type of vehicle which uses steering clutches and steering brakes.

With particular reference to FIG. 1, the control circuit 10 illustrates the first and second drive mechanism 12,14, engaged since the first and second drive disengaging mechanism 30,32 are de-activated. The drive mechanisms 12,14 are preferably steering clutch devices which are engaged by spring force and disengaged by the fluid operated mechanism 30,32. With the first and second control valves 22,24 in the first control positions 54,58 respectively, pressurized fluid from the pump 50 is supplied through the line 34, across the first control valve 22, into the line 38, and to the second control valve 24 where it is blocked. In a similar manner, pressurized fluid is supplied through the line 36, across the second control valve 24, into the line 40, and to the first control valve 22 where it is blocked. In the first control positions 54,58 of the control valves 22,24, the pressurized fluid cannot reach the first and second cylinders 66,68 to disengage the drive mechanism 12,14. With the control valves 22,24 in the first positions 54,58, the first and second brake mechanisms 16,18 are disengaged.

With reference to FIG. 2, the first control valve 22 is shown shifted to the second control position 56. Fluid from the pump 50 flows into the line 36, across the second control valve 24, into the line 40, through the first control valve 22, into the line 42, and into the first cylinder 66. The fluid in the cylinder 66 moves the piston 70 which disengages the first drive mechanism 12. The control valve 22 is moved from the first position 54 to the second position 56 by applying the first foot pedal 62, while the second foot pedal 62 has also activated the first brake mechanism 16. The fluid flowing into the line 34 is blocked at the first control valve 22.

With reference to FIG. 3, the second control valve 24 is shown to the second control position 60 by applying the second foot pedal 64, while the first foot pedal 62 remains inactive. Fluid from the pump 50 flows into the line 34, across the second control valve 24, into the line 44, and into the second cylinder 68. The fluid in the cylinder 68 moves the second piston 72 which disengages the second drive mechanism 14. During movement of the second control valve 24, the second foot pedal has also activated the second brake mechanism 18. The fluid flowing into the line 36 is blocked at the second control valve 24.

With reference to FIG. 4, both the first and second control valves 22,24 have been shifted to the second positions 56,60 by application of both the first and second foot pedals 62,64. Fluid from the pump 50 flows into the first and second fluid lines 34,36 and to the first and second fluid control valves 22,24 respectively. At the control valves 22,24, the first and second fluid lines 34,36 are blocked and the pressurized fluid cannot reach the cylinders 66,68. The first cylinders 66 is vented to the reservoir 52 through the fifth fluid line 42, through the first control valve 22, through the fourth fluid line 40, across the second control valve 24, and through the second drain line 76. In a similar manner, the second cylinder 68 is vented to the reservoir 52 through the sixth fluid line 44, through the second control valve 24, through the third fluid line 38, across the first control valve 22, and through the first drain line 74. The first and second drive disengaging mechanism 30,32 respectively to their de-activated positions. Application of both the first and second foot pedals 62,64 concurrently has activated both the first and second brake mechanism 16,18. The first and second drive mechanism 12,14, and the first and second brake mechanisms 16,18 will remain engaged until the first or second foot pedals 62,64 is released.

Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims.