Unloading means for flow-pressure compensated valve

• US 4,355,510 A
• Filed: 09/12/1980
• Issued: 10/26/1982
• Est. Priority Date: 09/12/1980
• Status: Expired due to Term

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Americas Company (Caterpillar Incorporated)
• Inventors: Ruseff, Walter Z.
• Primary Examiner(s): Croyle, Carlton R.
• Assistant Examiner(s): LOOK, EDWARD K
• Application Number:
  US06/261,117
• Time in Patent Office: 774 Days
• Field of Search: 60/445-452, 60/486, 417/212, 417/216-222
• US Class Current: 60/452
• CPC Class Codes: F04B 1/08 regulated by delivery pressure

Abstract

A "load-plus" valve (34) is oftentimes utilized in the servo-system (20) for a variable displacement pump (11) to maintain pump discharge pressure (P_D) above a minimum pressure level and above a load pressure signal (P_L) generated in a fluid actuator (13). Valves of this type normally include a margin spring (39) for biasing a modulating spool (36) against the opposing force of pump discharge pressure (P_D) to maintain a constant margin over the load pressure signal (P_L) throughout the working range of the system. When the load pressure signal (P_L) exceeds a maximum pressure level, it is normally vented to tank (12), or continuously bled to tank across an orifice, resulting in horsepower losses. The control package employed in systems of this type are also somewhat bulky. The improved fluid circuit (10) of this invention employs an unloading arrangement (50/50a) in association with the above type of "load-plus" valve (34) which functions to inactivate the margin spring (39) to reduce the above margin between the pump discharge pressure (P_D) and load pressure signal (P_L) to zero in response to the load pressure signal (P_L) exceeding a maximum pressure level.

Claims

1. In a fluid circuit (10) having a fluid actuator (13), a variable displacement pump (11) including a control member (24) movable between first and second displacement positions, first biasing means (26) for urging said control member (24) towards its first displacement position, second biasing means (27) for urging said control member (24) towards its second displacement position in opposition to said first biasing means (26) and in response to a variable control pressure (P_C), first means (35) for varying said control pressure (P_C) in response to variations in the discharge pressure (P_D) of said pump (11), second means (37) for controlling said first means (35) to modulate said control pressure (P_C) in response to variations in a load pressure signal (P_L) received from said fluid actuator (13), and third biasing means (38) for applying a margin force to said first means (35) to maintain a pressure differential between said pump discharge pressure (P_D) and said load pressure signal (P_L) during a predetermined range of said load pressure signal (P_L), the improvement comprising:

unloading means (50/50a) for unloading the margin force applied to said first means (35) in response to said load pressure signal (P_L) exceeding a maximum pressure level and for inactivating said third biasing means (38) to at least substantially equalize said pump discharge pressure (P_D) and said load pressure signal (P_L) in response to said unloading.

2. The fluid circuit (10) of claim 1 wherein said unloading means (50/50a) includes a piston (53/53a).

3. The fluid circuit (10) of claim 2 wherein said unloading means (50/50a) further includes spring means (51/51a) for normally biasing said third biasing means (38) and applying said margin force to said first means (35) and for being compressed by said piston (53/53a) in response to said load pressure signal (P_L) exceeding said maximum pressure level.

4. The fluid circuit (10) of claim 3 further including a retainer (52) disposed between said third biasing means (38) and said spring means (51) and wherein said retainer (52) is attached to said piston (53).

5. The fluid circuit (10) of claim 4 further including stop means (57) for limiting movement of said retainer (52) toward said third biasing means (38).

6. The fluid circuit (10) of claim 3 wherein said piston (53a) is disposed between said third biasing means (38) and said spring means (51a) and further including an orifice (58) defined through said piston (53a), a chamber (56a) defined at one side of said piston (53a), a drain passage (55a) in fluid communication with said chamber (56a), and shuttle valve means (59) for opening said drain passage (55a) in response to said load pressure signal (P_L) exceeding said maximum pressure level.

7. A fluid circuit (10) comprising

a source of pressurized fluid, including a variable displacement pump (11) having a control member (24) movable between first and second displacement positions,

a fluid actuator (13),

a directional control valve (14) interconnected between said pump (11) and said actuator (13),

first biasing means (26) for urging said control member (24) towards its first displacement position,

second biasing means (27) for urging said control member (24) towards its second displacement position in opposition to said first biasing means (26) and in response to a variable control pressure (P_C) in a control chamber (33) thereof,

a "load-plus" valve (34) including modulating valve means (36) for modulating communication of pressurized fluid from said pump (11) to said control chamber (33), and

third biasing means (38) for applying a force to said modulating spool means (36) and maintaining a pressure differential between pump discharge pressure (P_D) and said load pressure signal (P_L) during a predetermined range of said load pressure signal (P_L), and

unloading means (50/50a) for unloading the force applied to said modulating valve means (36) in response to said load pressure signal (P_L) exceeding a maximum pressure level and for inactivating said third biasing means (38) to at least substantially equalize said pump discharge pressure (P_D) and said load pressure signal (P_L) in response to said unloading.

8. The fluid circuit (10) of claim 7 wherein said unloading means (50/50a) includes a piston (53/53a).

9. The fluid circuit (10) of claim 8 wherein said unloading means (50/50a) further includes spring means (51/51a) for normally biasing said third biasing means (38) and applying said margin force to said modulating valve means (36) and for being compressed by said piston (53/53a) in response to said load pressure signal (P_L) exceeding said maximum pressure level.

10. The fluid circuit (10) of claim 9 further including a retainer (52) disposed between said third biasing means (38) and said spring means (51) and wherein said retainer (52) is attached to said piston (53).

11. The fluid circuit (10) of claim 10 further including stop means (57) for limiting movement of said retainer (52) toward said third biasing means (38).

12. The fluid circuit (10) of claim 9 wherein said piston (53a) is disposed between said third biasing means (38) and said spring means (51a) and further including an orifice (58) defined through said piston (53a), a chamber (56a) defined at one side of said piston (53a), a drain passage (55a) in fluid communication with said chamber (53a), and shuttle valve means (59) for opening said drain passage (55a) in response to said load pressure signal (P_L) exceeding said maximum pressure level.