Hydraulic systems for small loader

• US 20030089002A1
• Filed: 02/25/2002
• Published: 05/15/2003
• Est. Priority Date: 11/15/2001
• Status: Active Grant

• Current Assignee: Clark Equipment Company (Doosan Enerbility Company Limited)
• Original Assignee: Clark Equipment Company (Doosan Enerbility Company Limited)
• Inventors: Bares, Mark F., Page, James H.
• Granted Patent: US 6,662,556 B2
• Time in Patent Office: Days
• US Class Current: 37/348
• CPC Class Codes: E02F 9/2239 using two or more pumps with cross-assistance
• CPC Class Codes: E02F 9/225 Control of steering, e.g. for hydraulic motors driving the vehicle tracks steering in general B62D
• CPC Class Codes: E02F 9/2292 Systems with two or more pumps

Abstract

A small self-propelled loader has hydraulic drive motors and at least one work cylinder, and has a hydraulic system that efficiently utilizes the available horse power from an internal combustion engine on the loader. The engine drives a tandem pump and the flows from two sections of the tandem pump pass through a first diverter valve that permits using the flow from each of the pump sections to drive a respective one of the drive motors. The return or drain flow from valves controlling the drive motors is connected to a second diverter valve to selectively direct the drain flow from the drive motors for operating remote work cylinders. Alternately, the first diverter valve directs the output from one pump section to the work cylinders, so that when the loader is standing still or moving very slowly, the work cylinder has adequate flow, and flow from the other pump section is split to power the drive motors. The motors and work cylinders are connected to separate relief valves so that a higher working pressure is available for the drive motors.

Claims

1. A hydraulic system for a power machine having a frame, a drive motor for propelling the machine, power at least one work cylinder operated under hydraulic pressure, a pump assembly, a motor control valve connected to said pump assembly to receive flow from said pump assembly and operable to drive the motors, the motor control valve having a center flow through position, and at least a forward drive position for the motor, a common drain line from the motor control valve to carry the flow from the motor control valve in the center flow through position and connected to receive return flow from the motor, and a diverter valve connected to selectively divert the flow from the common drain line to a cylinder control valve for controlling the work cylinder.

2. The hydraulic system of claim 1, wherein said diverter valve has a position to connect the flow carried by the common drain line from the motor control valve to a second drain line.

3. The hydraulic system of claim 2, wherein said pump assembly comprises two individual pump sections each providing a flow, the diverter valve comprising a first diverter valve, and a second diverter valve for receiving flow from both of said pump sections of the pump assembly and movable to a flow control position to direct at least a portion of the flow from the pump assembly to a separate line leading to the second diverter valve, the first diverter valve being connected to the second drain line when the second diverter valve is connected to the flow control position.

4. The hydraulic system of claim 1, wherein the drive motor comprises a first drive motor for drive elements on a first side of the frame, a second drive motor for drive elements on a second side of the frame, the motor control valve comprising a first motor control valve, a second motor control valve each valve controlling the respective motors, the said second diverter valve has a second position to direct the flow from one of the pump sections through a flow control valve, the flow control valve dividing the flow from the one pump section to provide substantially equal flow to each of the first and second motor control valves, and the second pump section then being connected to the cylinder control valve controlling the least one work cylinder.

5. The hydraulic system of claim 4, wherein said first and second motor control valves have first relief valves connected thereto to control the maximum pressure of fluid provided to the drive motors, the cylinder control valve for controlling the at least one cylinder having a second separate relief valve, the first and second relief valves being fluidly independent of each other with the diverter valve in the second position.

6. A hydraulic system for a self propelled machine having a frame, a hydraulic pump assembly having separate pump sections providing separate flows, first and second hydraulic drive motors, first and second motor control valves connected to operate the first and second hydraulic drive motors, respectively, a power source on the frame for powering the pump assembly of the hydraulic system, a diverter valve having a first position for receiving the individual flows from each of the pump sections and directing individual flow from the pump sections to one of the first and second motor control valves, respectively, a flow divider, said first diverter valve being shiftable to a second position to direct the fluid flow from a first of the pump sections to a flow divider, the flow divider providing divided flow to both the first and second motor control valves, and the diverter valve providing flow from a second pump section directly to a work valve on the machine for operating at least one work cylinder.

7. The hydraulic system of claim 6, wherein said first and second motor control valves each have a first position wherein the flow passes through the valves to a common drain, a second position wherein said the motor controlled by the respective valve is operated in a forward direction, and a third position wherein the motor controlled by the respective valve is operated in a reverse direction, a return flow from the motors passing to the common drain in each of the second and third positions of the motor control valves, a second diverter valve connected to the common drain and moveable to positions to selectively connect the common drain to a second drain line with the first diverter valve in its second position, and to connect the common drain line to the work valve, with the first diverter valve in its first position.

8. The hydraulic system of claim 7, wherein said first and second diverter valves are connected together, so that when said first diverter valve is moved to its second position, the second diverter valve substantially simultaneously directs flow from the common drain to the second drain line.

9. The hydraulic system of claim 7, and an adjustable flow restrictor between the first diverter valve and the flow divider to limit the flow of hydraulic fluid directed to the first and second motor control valves and thus to the motors, the flow restrictor being connected to add portions of flow therethrough to the flow from the second pump section and to the work valve.

10. A loader having a frame and drive motors on opposite sides of the frame, the drive motors being individually selectably drivable, and the loader having at least one work cylinder operated under hydraulic pressure, a pump assembly, first and second valves connected to said pump assembly to receive substantially equal flow from said pump assembly, said first and second valves being operably connected to control rotation of the drive motors, the first and second valves each having a center flow through position, and at least a forward drive position for each of the motors, respectively, a common drain line from both of the first and second valves to carry the flow from the first and second valves in the center through flow positions and the common drain line being connected to receive return from both of the drive motors, a diverter valve connected to selectively divert the flow from the common drain line to a third control valve for controlling the work cylinder.

11. The loader of claim 10, wherein said diverter valve has a position to connect the common drain line from the first and second valves to a second drain line.

12. The loader of claim 10, wherein said pump assembly comprises two individual pump sections each providing a flow, the diverter valve receiving flow from both of said separate pump sections and selectively directing flow from each of the pump sections into a respective individual line to the first and second valves for controlling the drive motors and in an alternate position directing flow from one pump section to the at least one work cylinder and flow from the other pump section to a flow control valve connected to the motors and dividing the flow from the other pump section between the first and second valves.

13. The loader of claim 12, wherein the flow control valve divides the flow from the other pump section to provide substantially equal flow to each of the first and second valves.

14. The loader of claim 10, wherein each of said first and second valves have a relief valve connected thereto to control the maximum pressure of fluid provided at the first drain line and the valve for controlling the at least one work cylinder having a separate relief valve set for opening at a lower pressure than the relief pressure of the first and second valves.

15. The loader of claim 13, wherein said flow control valve has a flow restrictor connected thereto to divert a portion of the flow from the other pump section to the valve for controlling the at least one work cylinder.

16. The loader of claim 10, wherein the first and second valves are movable to a reverse position to reverse the respective drive motor, and a separate flow restrictor connected to a drain line of each drive motor that limits flow through the drive motors when the respective drive motors are operated in reverse.

17. The loader of claim 14, wherein there are a plurality of work cylinders, and each of the work cylinders has an individual work valve, the relief valve for the one work cylinder being common to all of the valves for the plurality of work cylinders

18. The loader of claim 11, wherein said first and second diverter valves are simultaneously operated, so that when the second diverter valve is moved to direct flow from one of the pump sections through the flow control valve, the first diverter valve connects the common drain line from the first and second valves to the second drain line.

19. The loader of claim 15, wherein said flow restrictor in said flow control valve is manually adjustable.

20. The loader of claim 10, wherein said pump assembly is connected to an internal combustion engine on the frame.