Hydraulic circuit with selectively actuatable float control

Abstract

A hydraulic system having the combination of a source of pressurized fluid, a linear hydraulic motor, a main control valve to selectively direct hydraulic fluid to the motor, and a lock valve disposed between the control valve and motor is provided with an auxiliary valve to by-pass the main control valve to disable the lock valve to provide a float condition for the motor.

Description

BACKGROUND OF THE INVENTION

The present invention relates to hydraulic circuits and pertains particularly to a circuit having a lock valve selectively actuatable to provide a floating condition for a hydraulic jack.

It is common practice to utilize an earthmoving vehicle for ancillary operations by attaching an auxiliary implement thereto. For example, motor graders are frequently employed for snow removal by attaching a snow plow to the forward end thereof. In many cases, the auxiliary implement, such as the snow plow, operates more efficiently if it is free to ride or float on the surface so it can follow the surface contour. However, many of the hydraulic control systems of such vehicles employ a lock valve which would prevent free floating of the blade. Thus, one of the difficulties encountered in using a vehicle for ancillary operations is that of providing an attachment type control circuit which provides a float position without employing a sophisticated and expensive control valve, and which is compatible with the basic hydraulic circuit of the vehicle.

SUMMARY OF THE INVENTION

It is the primary object of the present invention to provide a control system that overcomes the above problems of the prior art.

In accordance with the present invention a hydraulic control system for controlling hydraulic jacks for positioning an implement or the like and including a lock valve for maintaining the implement in a fixed position is provided with an auxiliary valve to by-pass the main control valve to disable the lock valve to provide a float condition for the implement.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic layout of a circuit in accordance with the present invention; and

FIG. 2 is a schematic of a modification of an auxiliary valve for the circuit of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring more particularly to FIG. 1 of the drawing, a hydraulic circuit in accordance with the present invention generally comprises a source of pressurized fluid including a pump 11 which draws fluid from a sump or reservoir 12. The pump supplies pressurized fluid by way of a supply conduit 13 to a main control valve 14 with fluid exhausted from the control valve being returned to the reservoir through a return line or conduit 15. A relief valve 16 interconnects the supply conduit 13 and the return conduit 15 to relieve excessive pressure in the hydraulic circuit.

The control valve 14 is of the type that has three positions attainable by actuation of a control lever 17 to one of the three positions indicated by the letters R, N, and L. The control valve is operative in selecting one of the R or L positions to direct fluid via supply lines 21 and 22 to either the head or rod end of a double acting hydraulic motor or jack 23. When the control valve is in the neutral position, both of a pair of control conduits 18 and 19 are in communication with the return conduit 15 to reservoir 12. The conduits 18 and 19 communicate fluid from the control valve 14 to a pilot operable lock valve 20, where the fluid is communicated by way of motor supply lines 21 and 22 to jack 23. The hydraulic jack 23 is controlled by the lock valve through conduits 21 and 22.

The lock valve 20 includes a valve body 24 having a bore 25 extending longitudinally therethrough. A first pair of axially spaced radial ports 26 and 27 are formed in the body and communicate the conduits 18 and 19, respectively, with the bore 25. A second pair of axially spaced radial ports 28 and 29 are formed in the body and communicate the conduits 21 and 22, respectively, with the bore. The valve body has a third radial port 30 formed therein intermediate the ports 26 and 27.

A pair of identical check valve assemblies 31 and 32 are individually disposed in opposite ends of the bore and secured in place by a respective one of a pair of plugs 33 and 34 individually threadably secured in the open end of the bore. Check valve assembly 31 normally blocks port 28 from port 26 while check valve assembly 32 normally blocks port 29 from port 27. Each check valve assembly includes a ball 35 and 36 resiliently urged against a seat 37 and 38 by a compression spring 39 and 40.

A pair of opposed axially aligned actuator pistons 41 and 42 are reciprocally mounted in the bore 25 of the valve body 24 between the check valve assemblies 31 and 32. Suitable spacing means such as protuberances 43 and 44 are adapted for abutting engagement with each other and form a chamber 45 between the pistons. Each piston includes a plunger 46 and 47 which extends outwardly from the outer end of each piston for engagement with the balls 35 and 36 of the respective check valve assembly.

A pair of solenoid control valves 48 and 49 are in communication with the port 30 and chamber 45 of the valve body through a conduit 50. The valve 48 is normally open and in communication with reservoir 12 through a return conduit 51. The solenoid valve 49 is normally closed and communicates with the fluid supply conduit 13 through a branch or by-pass conduit 52. A suitable conductor 53 electically connects the solenoid valves to a normally open toggle switch 54 which is connected to a suitable electrical source such as a battery 55.

In an alternate embodiment as shown in FIG. 2, the solenoid operated valves 48 and 49 of FIG. 1 may be replaced with a single 2-position, 3-way solenoid control valve 56 which normally communicates the conduit 50 with the return conduit 51. Closing the toggle switch 54 energizes the solenoid control valve causing it to shift to a position to communicate the branch conduit 52 with the conduit 50. This communicates pressurized fluid to chamber 45 which forces pistons 41 and 42 to unseat ball check valves 35 and 36 to thereby disable the lock valve 20.

OPERATION

During normal vehicular operation, the toggle switch 54 is open so that the chamber 45 is vented to the reservoir 12 through the conduit 50, the normally open solenoid valve 48, and the return conduit 51. With chamber 45 vented, the lock valve 20 functions as a conventional lock valve whereby fluid from both ends of the hydrostatic jack 23 is blocked by the respective check valve assemblies 31 and 32 of the lock valve. When the control valve 14 is shifted to direct pressurized fluid through conduit 18 to the lock valve, the ball 35 of the check valve assembly 31 is unseated by the pressurized fluid which is then transmitted to the hydraulic jack through conduit 21. Simultaneously, the pressurized fluid entering the lock valve through the conduit 18 acts upon the actuator piston 41 shifting it and the actuator piston 42 to the right. The plunger 47 of the piston 42 engages and unseats the ball 36 of the check valve assembly 32 permitting fluid exhausted from the hydraulic jack through the conduit 22 to be exhausted through conduit 19, the control valve 14 and the return conduit 15 to the reservoir 12. Conversely, pressurized fluid directed through conduit 19 passes through the lock valve in a similar manner and to the head end of the hydraulic jack through conduit 22. The fluid exhausted through conduit 21 passes through the lock valve 20, conduit 18, control valve 14, and return conduit 15 to the reservoir.

To obtain a float position of the hydraulic jack 23, the toggle switch 54 is closed to direct electrical energy to the solenoid control valves 48 and 49. Simultaneously, the valve 48 is shifted to a closed position blocking communication therethrough while valve 49 is shifted to an open position to direct pressurized fluid from the pump 11 through conduits 13, 52 and 50 into the chamber 45 of the lock valve 20. The pressurized fluid in chamber 45 urges the actuator pistons 41 and 42 in opposite directions to unseat the balls 35 and 36 of both check valve assemblies 31 and 32. This communicates both the head end and the rod end of the hydraulic jack 23 with the reservoir 12 through the various conduits and provides the float condition.

Claims

What is claimed is:

1. In a hydraulic system for selectively positioning a work member in selected fixed positions the combination comprising:

a linear double-acting hydraulic motor connected to a work member, a source of fluid pressure including a sump and a pump for supplying fluid for operating said motor, a three position directional control valve in a valve housing and having a neutral position, and raise and lower positions for selectively directing fluid from said source to either end of said motor for operation of said motor for positioning said work member, a single control lever for operating said control valve, lock valve means including first and second passage means communicating said fluid respectively with alternate ends of said motor, check valve means disposed in each said passage means to normally block flow of said fluid from said motor and including pressure-responsive piston and plunger means in each said passage means for unseating said check valve means to provide communication between both ends of said motor and sump by way of said directional control valve, said check valve means disposed between said control valve means and said hydraulic motor for normally locking said motor in a selected position;

solenoid operated auxiliary valve means separate spaced from and independent of said directional control valve and valve housing disposed between said source of fluid pressure and said lock valve means for bypassing said directional control valve for directing fluid solely to each said piston and plunger means solely for unseating each said check valve means for communicating both ends of said motor with said sump by way of said directional control valve for enabling free floating movement of said hydraulic motor when said main control valve is in a neutral position between said raise and said lower positions.

2. The hydraulic system of claim 1 wherein said solenoid operated auxiliary valve means comprises a pair of solenoid operated two-position valves.

3. The hydraulic system of claim 2 including control means for said solenoid operated auxiliary valve means comprising a source of electrical power and switch means for selectively activating said solenoids.