Motors: expansible chamber type – Plural relatively movable or rigidly interconnected working... – With means to control the working fluid to one working...
Patent
1979-08-30
1982-07-27
Hershkovitz, Abraham
Motors: expansible chamber type
Plural relatively movable or rigidly interconnected working...
With means to control the working fluid to one working...
60413, 60416, 91420, 91445, 91531, F15B 1116
Patent
active
043411495
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a fluid control system for a work implement of a motor grader and the like, the system being selectively operable to establish the work implement in a fixed position for a fine grading operating mode, and/or for insuring a full implement shock absorbing capacity in the system for a rough grading operating mode.
2. Background Art
Earth working and moving machines often have operating implements, such as grader blades, which are controlled by fluid control circuits selectively activated at the option of an operator of the machine. In motor graders for example, the work implement consists of a blade which is used in basically two different operating modes, one for rough grading and the other for fine grading. In the fine grading mode, the blade or implement is maintained in a fixed position, whereas in the rough grading mode, the system preferably includes means to absorb the shocks which result from the implement or blade encountering hard immovable objects such as rocks which might be embedded in the soil.
The grader blade for earth working or grading machines is normally maintained in the fixed position fine grading mode for relatively long periods of time to produce a level road surface. To accomplish and maintain accurate blade positioning, the control system for the grader blade normally includes lock valves in the fluid circuit for the blade lift jacks which control blade elevation. Such lock valves are normally positioned between a control valve and the corresponding lift jack, and serve to block fluid flow from the jack when the control valve is in a neutral or working position. With fluid flow from the lift jacks blocked, the blade is held in a fixed position and is unable to drift.
During rough grading operations, a motor grader can travel at relatively high speeds, and the implement or blade can frequently encounter immovable objects such as rocks etc. Thus the lock valves which were used in the fixed position operating mode must be deactivated or the blade will be prevented from moving at impact and damage to both the blade or related components may result. When the lock valves are deactivated, it is desirable to activate a shock absorbing system to absorb large forces experienced by the grader blade from contact with immovable objects.
The combination of a lock valve-shock absorbing system for earth working machines is shown and described in detail in U.S. Pat. No. 3,872,670 issued Mar. 25, 1975, to Joseph E. Dezelan et al. This patent discloses lock valves of the type referred to which include a pair of ball type check valves provided with pilot pressure actuated pistons for selectively moving the check valves away from a seated position against a spring bias. Another somewhat similar lock valve structure is disclosed in U.S. Pat. No. 3,857,404 issued Dec. 31, 1974 to Howard L. Johnson.
As shown in the Johnson patent, a lock valve may include a one-way choke means which cooperates with a metering means to control fluid flow from the hydraulic blade lift jacks. This combination effectively controls blade movement but does create a back pressure in the fluid line from the lift jack to the lock valve. Also, it has been found that in systems which include lock valves in combination with shock absorbing accumulators, it is possible, when the lock valve closes, to trap high pressure in the head ends of the blade lift jack cylinders. Since these head ends are connected to a shock absorbing accumulator when the grader blade is locked, for rough grading, this trapped high pressure greatly reduces the effective volume of oil in the accumulator and thus correspondingly decreases the ability of the accumulator to effectively cushion shock.
DISCLOSURE OF THE INVENTION
The present invention is directed to an improved fluid control system for controlling the work implement of an earth moving machine which provides effective shock absorbtion when the work implement is in a locked position. Such fluid control system will normally constitute a hydrauli
REFERENCES:
patent: 2506008 (1950-05-01), Arps
patent: 2765622 (1956-10-01), Hill
patent: 3857404 (1974-12-01), Johnson
patent: 3872670 (1975-03-01), Deselan
patent: 3908687 (1975-09-01), Wood
patent: 3974742 (1976-08-01), Johnson
patent: 4033236 (1977-07-01), Johnson
patent: 4192338 (1980-03-01), Gerulis
Caterpillar Tractor Co.
Hershkovitz Abraham
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