Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Reexamination Certificate
1999-07-22
2001-07-10
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
C060S466000, C073S861710
Reexamination Certificate
active
06256986
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydrostatic drive system with a pump and at least one consuming device that is connected to the pump and can be actuated by a control valve. In particular, the control valve can be actuated as a function of an actuator that specifies a desired speed of movement and a direction of movement of the consumer, and the control valve, in the neutral position, makes possible an unpressurized circulation of the pump.
2. Background Information
Similar hydrostatic drive systems in which a pump, for example a pump with a constant delivery volume, is provided for the pressurization of a plurality of consuming devices, and when the consuming devices are not actuated, the pump is operated in an unpressurized circulation, are used in machines, for example in fork-lift trucks, to actuate the hydraulic work system.
The prior art discloses systems in which the control valves are directional control valves that throttle the flow in intermediate positions and have an open neutral position. Therefore, the control valves are also designated open-center control valves that can be actuated by a human operator as a function of the deflection of the actuator. When the directional control valve is deflected, the directional control valve throttles the unrestricted circulation of the pump and connects the delivery line of the pump with the hydraulic line that leads to the consuming device. A pressure is thereby built up in the delivery line, as a result of which the consuming device is set in motion. A desired speed of movement of the consuming device is specified by the opening width of the directional control valve as a function of the deflection of the actuator. The delivery current of the pump not required by the actuated consuming device flows via the unrestricted circulation of the directional control valves to the reservoir. When a plurality of consuming devices that have different load pressures are actuated simultaneously, however, operating conditions can occur in which an excessive hydraulic flow is delivered to the consuming device that has the lower load pressure. To prevent an increase in the speed of movement of the consuming device that has the lower load pressure, the corresponding directional control valve must be modulated into a switched position that throttles the admission to the consuming device. As a result, however, there is an increased amount of effort required on the part of the operator who is operating the drive system, because when the operator has to actuate a plurality of consuming devices simultaneously, he must readjust the speed of movement of the consuming devices by a corresponding deflection of the actuator.
The object of this invention is to make available a hydrostatic drive system of the type described above that easily and economically makes it possible to operate the consuming devices independently of the load.
SUMMARY OF THE INVENTION
The invention teaches that the control valve can be actuated electrically, and there is a device (i.e., sensor) that indicates the actual speed of the consuming device, whereby the control valve, the device that indicates the actual speed of movement and the actuator are effectively connected to an electronic control that controls the control valve as a function of the direction and speed of movement specified by the deflection of the actuator, as well as the speed of movement of the consuming device as measured by the sensor that measures the actual speed of movement.
When the actuator is actuated, a desired direction of movement and a desired speed of movement of the consuming device are specified, and the control valve that actuates the consuming device is actuated. It is possible to actuate the control valve by the speed-of-movement sensor such that the actual speed of movement equals the desired speed of movement specified by the actuator. If an additional consuming device with a higher load pressure is actuated, the speed-of-movement sensor detects an increase in the actual speed of the consuming device that is pressurized by the lower load pressure. The electronic control actuates the consuming device that has the lower load pressure by the control valve so that its actual speed of movement is retained. The consuming devices are therefore operated independently of the load at the desired speed of movement specified at the actuator.
In one embodiment of the invention, the speed-of-movement sensor is a delivery flow sensor. Using a delivery current sensor that measures the hydraulic flow, it becomes possible for the electronic control to easily measure the actual speed of movement of the consuming device. It is also possible to measure the actual speed of movement by speed sensors located on the consumer, e.g. displacement sensors or sensors that measure angular rotation.
In one embodiment of the invention in which the consuming device is a double-acting consuming device, the delivery flow sensor is located in a hydraulic line that leads from the consuming device to the reservoir. In this case, the delivery flow sensor is located in the discharge line of the consuming device, and thus measures the hydraulic flow from the consuming device to the reservoir. As a result of the measurement of the hydraulic flow being discharged by the consuming device, it is also possible, when there is a change in the direction of the load exerted on the consuming device, for example from a positive load to a negative load, to measure an increase in the actual speed of movement of the consuming device and to actuate the control valve such that the consuming device is operated at a constant actual speed of movement, even in the event of a change in the direction of the load. With a delivery flow sensor located in the discharge line of the consuming device, both in the event of the simultaneous actuation of a plurality of consumers with load pressures at different levels and in the event of the reversal of the direction of the load on the consuming device, an elevated discharge-side hydraulic flow and an increase in the actual speed of movement of the consuming device can be measured in a simple manner. The delivery flow sensor can thereby be located upstream or downstream of the control valve.
The delivery flow sensor may be located in a return line that leads from the control valve to the reservoir. With a double-acting consuming device, in which the control valve is connected to a delivery line of the pump, a return line and two hydraulic lines that lead to the consuming device, the flow of hydraulic fluid out of the consuming device can be measured by only one delivery flow sensor. The delivery flow sensor may be located in the return line downstream of the control valve, regardless of the direction of movement of the consuming device. This results in reduced effort, time and cost of construction.
It is appropriate, when the control valve is actuated toward the neutral position, if the admission cross section of a pump delivery line to a hydraulic line in communication with the consuming device can be reduced by the control valve before the discharge cross section of a hydraulic line in communication with the consuming device to the reservoir. If, when the control valve is deflected, the delivery flow sensor located in the return line detects an excessive actual speed of movement, this situation may be the result of the actuation of an additional consuming device at a higher load pressure, or by a reversal of the load direction on the consuming device. In the event of an excessive actual speed of movement, the electronic control actuates the control valve toward the neutral position. First the admission cross section formed by the control valve is reduced and thus throttled. Under operating conditions in which an additional consuming device is actuated at a higher load pressure, it becomes possible to counteract an increase in the speed of movement of the consuming device. If, when the admission cross section is throttled, the speed of movement of the consuming
Deininger Horst
Langen Alfred
Linde Aktiengesellschaft
Ryznic John E.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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