Claims
- 1. Hydraulic control valve means of the type having an inlet to receive pressure fluid from a source, source fluid receiving means in communication with the inlet, and a function control valve element movable to and from an operative position at which it establishes communication between said fluid receiving means and a work port, characterized by:
- means providing a bypass passageway connected with said inlet and through which pressure fluid from the source can bypass said fluid receiving means to thereby prevent pressurization thereof,
- a bypass control valve element intersecting said passageway and which must be moved from a bypass open position, at which it causes source fluid to bypass said receiving means, to an operative bypass closing position before source fluid can flow to said fluid receiving means to effect pressurization thereof,
- and first biasing means acting on said bypass control valve element to normally yieldingly hold the same in its bypass open position at which the function control valve element is ineffective.
- 2. The hydraulic control valve means of claim 1 further characterized by:
- means for effecting successive actuation of said valve elements to their operative positions, including
- means for assuring movement of the bypass control valve element toward its bypass closing position in advance of movement of the function control valve element to its operative position.
- 3. The hydraulic control valve means of claim 1 further characterized by:
- means for effecting independent actuation of said valve element to their operative positions.
- 4. The hydraulic control valve means of claim 1 further characterized by:
- second biasing means acting on said function control valve element to normally yieldingly hold the same in its inoperative position,
- said valve elements being moved to their operative positions by means of a common pressurized pilot fluid acting on both of said valve elements with said pilot fluid overcoming said first biasing means prior to overcoming said second biasing means so that said bypass control valve moves to its operative or closed position prior to said function control valve moving to its operative position.
- 5. The hydraulic control valve means of claim 1 further characterized by:
- second biasing means acting on said function control valve element to normally yieldingly hold the same in its inoperative position,
- said valve elements being moved to their operative positions by means of a common pressurized pilot fluid acting on both of said valve elements, and
- means for independently providing actuating pilot fluid to each of said valve elements.
- 6. The hydraulic control valve means of claim 1 further characterized by:
- said bypass control valve element comprising an axially slidable spool having circumferential groove means therein to provide part of said bypass passageway,
- and said groove means defining lands having opposing faces of equal area that provide the sole spool surfaces that are exposed to pressure fluid from the source in said bypass open position of the spool.
BACKGROUND OF THE INVENTION
This is a continuation-in-part of application Ser. No. 06/503,910 filed June 13, 1983 and now abandoned.
The present invention relates to hydraulic control valves for earthmoving and construction equipment, and more particularly to a hydraulic control valve with independent pump and function control spools.
A typical control valve includes a single independently operable control spool slidably received therein within a bore for moving from a neutral position to each of a pair of operating positions. The control spool functions to control both the pump flow as well as the directional flow of hydraulic fluid to and from a hydraulic actuator or load.
Various types of hydraulic control valves are known and commonly used in earthmoving and construction vehicles. See for example U.S. Pat. Nos. 3,729,026 and 3,881,512, both of which are assigned to the assignee of the present application, as well as U.S. Pat. Nos. 4,154,262 and 3,209,781. In these types of control valves, a spool connects either of a pair of service or work ports with a bridge-like feeder passage and the other work port with one of a pair of exhaust ports. The spools are generally three position spools which are designed to block the work ports in their neutral positions. In one operating position, the spool directs oil from the pump to one port and oil from the other work port returns to tank. In the other operating position, the oil flow is reversed.
In order to accomplish the fine regulation of flow and pressure required, control spools include a plurality of axially spaced circumferential grooves that define a series of lands. The position of the grooves and lands within the bore thus controls the flow of hydraulic fluid. As a result, the spool-to-bore fit is very critical in order to minimize leakage. Thus, the spools are honed to a select fit within the bore with the maximum spool-to-bore lap possible. However, in more complex spool designs it becomes difficult to maintain a sufficient spool-to-bore lap and thus fluid leakage becomes more difficult to control. In addition, the more complex the spool the more difficult it becomes to modify the valve function.
A hydraulic control valve includes separate pump pressure and function control spools. The spools may be actuated independently and sequentially to provide raising, holding and power down functions for earthmoving and construction equipment.
In one form, the valve includes a pump pressure control spool and a function control spool. The two spools separate the functions normally performed by a single spool in conventional control valves so that the function control spool directs the flow of fluid to and from a hydraulic actuator and the pump pressure control spool controls pump flow. This provides for precise regulation of the flow and pressure of hydraulic fluid in the circuit.
The positions of the pump pressure and function control spools can be controlled by pilot operated spring centering mechanisms. By changing the spring forces and varying the relationship between the spring forces on the two spools, their relative movements can be changed depending on the desired function, circuitry or type of control desired. For example, the spring force acting on the pump pressure control spool can be less than that acting on the function control spool so that the pump pressure control spool can be moved to its stroked position first, pump pressure can be elevated to a "precharge" level prior to moving the function control spool to an operating position. This "precharge" pump pressure eliminates voids by providing sufficient pressure in the circuit when the function control spool is operated. In contrast, if the function control spool is moved to an operating position first while maintaining the pump pressure control spool in its neutral position, undesirable flow from a work port to tank can be initiated first.
The provision of a pair of spools instead of a single spool also eliminates the bridge-like feeder passage which communicates near the opposite ends of a conventional function control spool. This provides a valve housing which is easier and less expensive to manufacture. Separate pump pressure and function control spools also provide maximum spool-to-bore lap for minimum fluid leakage since the complex design of a single function control spool may be divided into two spools.
Additional function control spools may also be added to the valve structure to provide multiple function control. When more than one function control spool is utilized, the valve functions like a standard parallel valve with the individual spools connected to the input or feed line of the control valve by a common passage so that the spool with the lowest pressure requirement will become operational first. Thus, when a plurality of function control spools are utilized in the present valve, the valve functions can be modified by merely changing the operational sequencing of the spools and not the spool design itself.
US Referenced Citations (3)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 897547 |
Apr 1972 |
CAX |
Continuation in Parts (1)
|
Number |
Date |
Country |
| Parent |
503910 |
Jun 1983 |
|
Patent Grant
4570672
