Motors: expansible chamber type – Torque responsive motive fluid control
Reexamination Certificate
1998-12-31
2001-02-27
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Torque responsive motive fluid control
C060S468000
Reexamination Certificate
active
06192782
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to torque control means to control or limit the torque exerted by a positive displacement hydraulic motor, more particularly a positive displacement hydraulic motor that operates to rotate a tool or anchor into the ground.
BACKGROUND OF THE INVENTION
Heretofore, as shown particularly in U.S. Pat. No. 5,433,119 dated Jul. 18, 1995, a positive displacement hydraulic motor is utilized to screw a pile in the ground. It is desirable to have an indication of the torque applied to the screw pile or anchor as the level of torque required to turn the new pile is indicative of the strength of the soil and may be used to estimate the capacity of the soil. Low installation torque indicates a weak soil and low pile capacity, whereas a high installation torque indicates a relatively strong soil and greater pile capacity. Where the required installation torque can be accurately measured, the approximate holding capacity of a new pile can be reliably predicted.
A torque indicator system is illustrated in U.S. Pat. No. 5,433,119 for measuring the torque output of a positive displacement hydraulic motor that operates to screw a foundation pile into the ground. The pressure drop across the hydraulic motor is indicated on the gauge for a visual display of the torque output. However, there is no control over the amount of torque provided by the motor. It is desired to protect the motor from an unusually high output torque and also to limit the torque applied by the motor against the screw for rotating the anchor pile as damage could result. Thus, it is desired that the torque output of the hydraulic motor be controlled and limited to a predetermined amount.
It is an object of the present invention to provide a fluid pressure control system to limit the output torque of a positive placement hydraulic motor to a selected amount for rotating a member in the ground.
SUMMARY OF THE INVENTION
The present invention is directed particularly to a fluid pressure control system for limiting the output torque of a positive displacement hydraulic motor for rotating a member, such as a screw anchor, in the ground. The hydraulic motor has an inlet for the supply of high pressure fluid and an outlet for the exhaust of low pressure fluid. A differential pressure gauge is provided for a differential fluid pressure sensing means in fluid communication with the motor through a high pressure line and a low pressure line. The gauge measures the pressure drop or torque output of the motor.
A plurality of electro-hydraulic pressure switches are in fluid communication with the differential pressure line to the gauge and each switch is set at a predetermined differential pressure at which it is desired to limit the output torque for the hydraulic motor.
A hydraulic pump supplies fluid from a reservoir through a supply line to the motor and fluid is returned from the motor to the reservoir through a return line to the fluid supply. A bypass line connects the supply line and the return line and a normally closed solenoid actuated control valve is positioned in the bypass line and is responsive to a selected pressure switch for actuation at a predetermined fluid pressure differential at which the selected valve is set. Each of the pressure switches is set for a different predetermined pressure differential and a switch selected for the predetermined pressure differential is turned on. Upon the predetermined pressure differential being reached at which the switch is set, the solenoid operated control valve is actuated to permit fluid to bypass the motor thereby limiting the torque output to the motor. It is apparent that any desired number of switches may be provided for setting at various predetermined differential pressures equivalent to the pressure drop across hydraulic motor. As a result, the torque output of the hydraulic motor is limited and does not reach an undesirable high level so that injury or damage results to the motor or to the screw anchor being screwed or rotated into the ground.
Other features, and advantages of the invention will be more apparent from the following specification and drawings.
REFERENCES:
patent: 4552041 (1985-11-01), Coyle, Sr.
patent: 5433119 (1995-07-01), Rogers
Bushman Browning
Lazo Thomas E.
Look Edward K.
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