Selectively Actuatable Shock Absorbing System For An Implement Control Circuit

Abstract

Hydraulic control system for holding a work implement in a fixed position, said system including selectively operative shock absorbing means for negating any large force experienced by the implement on contact with an immovable object.

Description

BACKGROUND OF THE INVENTION

Many earth working machines employ hydraulic jacks for controlling work implements. The jacks are usually actuated by spool-type control valves which have a tendency to leak causing the jacks to drift. Although slight drifting is not detrimental to the operation of most earth working machines, it can be a problem in a grading machine where the operator must accurately hold the grader blade in a fixed position for relatively long periods of time to produce a level road surface. In order to achieve such blade accuracy lock valves are commonly included in the hydraulic circuitry for the blade lift jacks. Such lock valves are positioned between the control valve and the jacks and function to block fluid flow from the jacks when the control valve is in the neutral position. With the fluid flow blocked, the jacks are prevented from drifting and the grader blade is held in a fixed position.

This rigid blade positioning is highly desirable if the motor grader is being used for final finish grading and the machine is traveling at relatively slow speeds. During rough grading work, however, the motor grader travels at relatively high speeds and the grader blade frequently encounters hard immovable objects, such as large rocks and the like which are embedded in the soil. Because of the lock valve, however, the blade is prevented from moving and impact with such objects frequently causes damage, both to the blade and related components. Therefore, while it is desirable for the blade to be rigidly held during finish grading operations, it is equally desirable that the blade be permitted to move upon impact during rough grading operations.

Examples of prior art related to the present invention include U.S. Pat. No. 3,543,647, issued Dec. 1, 1970 to Hall et al. and U.S. Pat. No. 3,587,399, issued June 28, 1971 to Parquet et al. These patents generally disclose hydraulic systems having lock valves provided with pilot pressure actuated pistons for unseating spring biased check valves. U.S. Pat. No. 3,213,762, issued Oct. 26, 1965 to DuBuf is of interest in showing a check valve assembly for hydraulic systems having high inertia.

While the above patent art does disclose pilot operated check valve assemblies, none of the patents cited show such an assembly including shock absorbing means.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide means for overcoming the above deficiencies of the prior art.

Another object of the present invention is to provide a hydraulic control system for holding a work implement in a fixed position.

A further object of the present invention is to provide shock absorbing means for use in a hydraulic control circuit for negating large forces experienced by the work implement on contact with immovable objects.

Still another object of the present invention is to provide selectively actuatable shock absorbing means including fluid accumulator means for connecting the accumulator means with the implement lift jacks.

A still further object of the present invention is to provide lock valve means having pilot pressure actuated pistons for unseating the valve checks.

In accordance with the present invention there is provided a hydraulic implement control circuit in operative combination with selectively responsive shock absorbing means. The shock absorbing system functions to negate any large force experienced by the implement upon contact with an immovable object.

BRIEF DESCRIPTION OF THE DRAWINGS

Other and further objects, features and advantages of the present invention will be apparent in the following description taken in conjunction with the accompanying drawings:

FIG. 1 is a schematic diagram of a hydraulic control system embodying the present invention.

FIG. 2 is a schematic illustration of an alternate embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is illustrated a hydraulic control system embodying the principals of the present invention. The system includes shock absorbing means, generally indicated by the numeral 10, in combination with a hydraulic control circuit 11 for a pair of lift jacks 12 and 13 which may be employed for controlling a motor grader blade or the like. The system includes a pump 15 which draws fluid from a tank 16 to provide fluid pressure to a pair of control valves 18 via conduits 20 and 21. The control valves 18 may be of any suitable well known construction. Fluid exhausted from the control valves 18 is returned to the tank 16 by conduits 22 and 23. A relief valve 24 is interconnected between the output of the pump 15 and the tank 16 to relieve excessive pressure in the hydraulic system.

As the hydraulic circuits for each of the control valves 18 are identical, the same numbers are used to identify similar components thereof. The control valves 18 direct fluid pressure to and from a pair of lock valves 26 via conduits 28 and 29. The lock valves may be of any suitable construction known in the art. The lock valves 26 permit fluid flow to and from the rod and heads ends of the lift jacks 12 and 13 via conduits 32 and 33 respectively.

The shock absorbing system 10 includes a pair of fluid accumulators 48 and 49 and a lock valve 34 including control means to selectively connect the accumulators to the jacks 12 and 13. The lock valve 34 includes a valve housing 36 provided with an elongated cylindrical bore 38. A first pair of laterally spaced ports 40 and 41 connect opposite ends of the bore 38 with the head ends of the lift jacks 12 and 13 via conduits 42 and 43 respectively. A second pair of ports 44 and 45, disposed intermediate the first ports 40 and 41, connect the bore 38 with shock absorbing means such as a pair of gas charged fluid accumulators 48 and 49 via conduits 50 and 51 respectively.

The lock valve 34 further includes a pair of identical spring biased ball check valve assemblies 52 and 53 mounted in the valve bore 38. Check valve assembly 52 is interposed ports 40 and 44 to normally block fluid flow from the head end of the jack 12 to the accumulator 48 via conduits 42 and 50. Check valve assembly 53 is interposed ports 41 and 45 to normally block fluid flow from the jack 13 to the accumulator 49 via conduits 43 and 51.

A pair of pistons 56 and 57 are slidably disposed in the bore 38 between the check valve assemblies 52 and 53. The pistons have opposing radial faces provided with abutting protuberances 58 which serve to separate the pistons and provide a variable fluid chamber 59 therebetween. The outer ends of the pistons 56 and 57 are provided with axial plungers 60 and 61 which engage and unseat the check valves 52 and 53 when the chamber 59 is pressurized sufficiently to overcome the fluid pressure and spring forces acting to seat the valves.

A conduit 64 communicates fluid pressure between the chamber 59 and a solenoid operated, two position valve 66. Pressurized fluid is communicated to the valve 66 from the pump 15 through conduit 68 and returned to the tank through conduit 69. The solenoid operated valve 66 is selectively actuated through normal closure by the operator of a manually operated switch 70 which communicates electrical current from a battery 72 to the valve solenoid through a lead 74.

In operation, closure of the switch 70 shifts the solenoid operated valve 66 to communicate fluid pressure from the pump 15 to the chamber 59 via conduits 68 and 64. When the chamber 59 is sufficiently pressurized, the pistons 56 and 57 are moved outwardly and the axial plungers 60 and 61 engage and unseat the ball checks of valve assemblies 52 and 53 respectively. The unseating of the valve assemblies 52 and 53 permits communication of ports 40 and 41 with ports 44 and 45 respectively so that the head end of jack 12 is in communication with accumulator 48 via conduits 50 and 42 and the head end of jack 13 is in communication with accumulator 49 via conduits 51 and 43. Consequently, if a large external force F is experienced on the rod end of one or both of the jacks 12 and 13, such as occurs when a grader blade connected to the jacks hits an object, the energy from the impact is absorbed by one or both of the accumulators 48 and 49, and the jacks 12 and 13 are permitted to retract. After such an impact, the energy stored in the accumulators 48 and 49 returns the jacks 12 and 13 to their former positions.

When the switch 70 is open, fluid pressure from the pump 15 is blocked by the valve 66 and the chamber 59 is open to the tank 16 via conduits 64 and 69. Under these conditions the spring biased check valves 52 and 53 will be seated and escape of fluid from the jacks 12 and 13 will be prevented. Thus, with the switch 70 open, the hydraulic system functions in a conventional manner and may be employed for final finish grading operations.

FIG. 2 illustrates an alternate embodiment of the present invention, wherein identical elements are identified by the same numerals and equivalent elements by the number primed. This embodiment differs from FIG. 1 primarily in that the lock valve has been replaced by a pair of solenoid operated selector valves 75 and 76 which are actuated through closure of a switch 77 which communicates electrical current from a battery 78 to the valve solenoids through a lead 79.

Thus, there is provided a hydraulic control system for positioning a work implement, having means to selectively bring shock absorbing means into the circuit.

Claims

What is claimed is:

1. A hydraulic system for selectively holding an implement or the like in a fixed position and for selectively providing shock absorbing means for the implement comprising:

a hydraulic motor;

a source of fluid pressure;

first control valve means comprising lock valve means disposed in a motor control circuit between said source of fluid pressure and said hydraulic motor for selectively directing said fluid to and from said motor; and

shock absorbing means comprising fluid accumulator means and control means including second control valve means independent of said first control valve means including pilot operated lock valve means disposed between said fluid accumulator means and said hydraulic motor and operated by a pilot control circuit independent of said motor control circuit and including a two-position selector valve for selectively communicating said fluid accumulator means with said motor.

2. The hydraulic system of claim 1 wherein said fluid accumulator means comprises a gas charged accumulator.

3. The hydraulic system of claim 1 wherein said lock valve means of said selector valve means comprises:

passage means connecting said fluid accumulator means with said motor;

check valve means disposed in said passage means to normally isolate said fluid accumulator means from said motor;

means for unseating said check valve means to provide communication between said accumulator means and said motor.

4. The hydraulic system of claim 1 wherein said means for unseating said check valve means comprises:

a pressure responsive piston; and

said second valve means is operatively connected for directing fluid from said source to said piston.

5. The hydraulic system of claim 4 including a source of electrical power and manually operable switch means for selectively activating said solenoids.

6. The hydraulic system of claim 1 including a second hydraulic motor;

a second accumulator for connection to said second motor,

said pilot-operated lock valve means includes a second lock valve disposed between said second hydraulic motor and said second accumulator for controlling communication between said second motor and said second accumulator; and

said second control valve means includes a pair of solenoid-operated two-position valves.