Power plants – Pressure fluid source and motor – Having means controlling or attenuating shock vibration,...
Reexamination Certificate
2002-09-25
2004-03-16
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Having means controlling or attenuating shock vibration,...
C091S433000
Reexamination Certificate
active
06705079
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hydraulically powered equipment, such as off-road construction and agricultural vehicles, and more particularly to apparatus for reducing bounce when a hydraulically driven member on the equipment is stopped suddenly.
2. Description of the Related Art
With reference to
FIG. 1
, a backhoe
10
is a common type of earth moving equipment that has a bucket
12
attached to the end of an arm
14
which in turn is coupled by a boom
15
to the frame of a tractor
18
. A joint
16
enables the bucket, arm, and boom assembly
17
to pivot left and right with respect to the rear end of the tractor. A hydraulic cylinder
19
is attached on one side of the tractor
18
to the boom
15
and provides the drive force for the pivoting motion. For larger backhoes, a pair of hydraulic cylinders are attached on opposite sides of the tractor
18
to pivot the boom. Hydraulic fluid is supplied to the cylinder
19
through valves that are manipulated by the backhoe operator. This movement of the boom
15
is referred to as “swing” or “slew”.
As the boom swings, pressurized fluid is introduced into one chamber of the cylinder
19
, referred to as the “driving chamber”, and fluid is exhausted from the other cylinder chamber, referred to as the “exhausting chamber”. When the operator suddenly stops the boom swing, inertia causes the motion of the backhoe assembly
17
to continue in the direction of the swing. The amount of inertia is a function of the mass of the backhoe assembly
17
and any material carried in the bucket
12
. This continued movement after the control valves have been shut compresses the hydraulic fluid in the previous exhausting chamber of the cylinder
19
and may produce a void, or cavitation, in the previous driving cylinder chamber. Anti cavitation valves typically are provided in the hydraulic system to overcome this latter problem.
Eventually the backhoe assembly
17
stops and starts moving in the opposite swing direction due to the relatively high pressure created in the previous exhausting chamber. This subsequent movement produces a reversal of the pressure conditions, wherein the previous driving chamber of the boom swing cylinder
19
becomes pressurized. As a result, the backhoe assembly
17
swing oscillates until inherent dampening provided by other forces eventually brings the assembly to a stop. This phenomenon is known either as “swing bounce” or “swing wag” and increases the time required to properly position the boom
15
, thereby adversely affecting equipment productivity.
Various approaches have been utilized to minimize the swing bounce. For example, U.S. Pat. No. 4,757,685 employs a separate relief valve for each hydraulic line connected to the swing cylinder, which valves vent fluid to a tank line when excessive pressure occurs in that cylinder. Additional fluid is supplied from the supply line through makeup valves to minimize voids in the cylinder as the swing stops.
U.S. Pat. No. 5,025,626 describes a cushioned swing circuit which also has relief and make-up valves connected to the hydraulic lines for the boom swing cylinder. This circuit also incorporates a cushion valve which in an open position provides a fluid path between the cylinder hydraulic lines. That path includes a flow restriction orifice. The cushion valve is resiliently biased into the shut position by a spring and a mechanism opens the cushion valve for a predetermined time period when the pressure differential between the cylinder chambers exceeds a given threshold.
Both of the previous circuits required a number of relatively complex valves. Therefore, it is desirable to provide a more simplified mechanism for reducing swing bounce.
SUMMARY OF THE INVENTION
A hydraulic system includes a control valve assembly, which selectively couples a pump and a tank to a hydraulic actuator that drives a member on a machine. The system has a device which produces a command designating desired movement of the load. A sensor detects pressure in the hydraulic actuator.
A method is provided to reduce bounce of the member when it stops. A command is received from the device designating that movement of the member in a given direction is to stop. The signal from the sensor is employed to determine the rate at which the pressure in the hydraulic actuator changes. When the rate of change of the pressure is less than a defined threshold after receiving the command, pressure in the hydraulic actuator is relieved. For example the pressure is relieved by opening a control valve that is connected to the hydraulic actuator.
In one application, the present bounce reduction method is used on a machine in which the member is driven by a cylinder that has first and second chambers. It is a well-known practice that this type of installation includes first and second pressure relief valves that are respectively connected to the first and second cylinder chambers. Thus upon receiving the command, pressure in the second chamber is relieved by opening an associated control valve. Then a determination is made whether the first pressure relief valve is open due to excessive pressure in the first chamber. If the first pressure relief valve is found to be open, the bounce reduction method waits for that valve to close, and thereafter opens another control valve that relieves pressure remaining in the first chamber. Otherwise if the first pressure relief valve is found to be closed, the rate of pressure change in the first chamber is determined, and pressure in the first chamber is relieved by opening the other control valve when the rate of pressure change is less than a defined threshold.
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patent: 4194365 (1980-03-01), Stoufflet et al.
patent: 4520625 (1985-06-01), Sato et al.
patent: 4586332 (1986-05-01), Schexnayder et al.
patent: 4628690 (1986-12-01), Arai et al.
patent: 4757685 (1988-07-01), Burckhartzmeyer
patent: 5025626 (1991-06-01), Crosser et al.
patent: 5622226 (1997-04-01), Hausman et al.
patent: 5832730 (1998-11-01), Mizui
patent: 5857333 (1999-01-01), Schmidt et al.
patent: 5897287 (1999-04-01), Berger et al.
patent: 6328173 (2001-12-01), Wimmer
patent: 6328275 (2001-12-01), Yang et al.
patent: 6532738 (2003-03-01), Sharkness et al.
patent: 6634172 (2003-10-01), Schoonmaker et al.
Pfaff Joseph L.
Stephenson Dwight B.
Tabor Keith A.
Haas George E.
Husco International Inc.
Leslie Michael
Quarles & Brady LLP
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