Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reexamination Certificate
1999-07-22
2001-10-02
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
C073S861710
Reexamination Certificate
active
06295810
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydrostatic drive system with an adjustable pump in the delivery flow and at least one consuming device connected to the pump. More specifically associated with each consuming device are actuation means that specify the direction of movement and the speed of movement, and a control valve to control the direction of movement and the speed of movement, and wherein the delivery flow of the pump can be adjusted to the hydraulic fluid flow required by the actuated consuming devices.
2. Background Information
Similar hydrostatic drive systems for the control of a plurality of consuming devices are load-sensing drive systems in which the delivery flow of the pump can be adjusted to the hydraulic flow required by the consuming devices. In these systems, when the consuming device is actuated by the control valve, the load pressure of the consuming device is measured, transmitted to a pump regulator that controls the delivery volume of the pump and compared to the delivery pressure of the pump.
The speed of the consuming device is controlled by a control valve that, when actuation means are actuated, is deflected to correspond to the specified speed and direction of movement. The opening width of the control valve thereby forms a measurement throttle that determines the speed of movement of the consuming device. By measuring the load pressure of the consuming device and comparing it with the delivery pressure supplied by the pump at a pump regulator that controls the delivery volume of the pump, the pump thereby delivers a flow that corresponds to the hydraulic flow required by the consuming device. Thereby a delivery pressure is achieved that is higher than the load pressure of the consuming device by a defined control pressure that equals the spring bias on the pump regulator.
In the event of a simultaneous actuation of a plurality of consuming devices, the highest load pressure of the actuated consuming devices is transmitted to the pump regulator, as a result of which a delivery pressure is set that is above the highest load pressure by the control pressure.
For operation of the consuming devices independently of the load, associated with each control valve there is a pressure balance that forms an additional throttle point and keeps the pressure differential at the measurement throttle formed by the opening width of the control valve constant. The pressure balances that are associated with the control valves thereby prevent the consuming devices with the lower load pressures from being operated at an excessive speed of movement. The consuming devices are thereby operated independently of the load at the respective speed of movement set at the control valve.
With such a control valve, however, for the control of the consuming devices at the control valve and at the pressure balance associated with the control valve, there must be a pressure difference. The level of this pressure difference thereby determines the level of the control pressure set at the pump regulator. Because the delivery pressure supplied by the pump equals the sum of the load pressure and the control pressure, the level of the control pressure results in pressure losses and thus in energy losses in the hydrostatic drive system.
In addition, with such a control consisting of a pressure balance and control valve, only the hydraulic flow to the respective consuming device can be controlled. In the event of a change in the load direction of the load being applied to the consuming device, for example in the event of a change from a positive load to a negative load, there is an increase in the speed of movement of the consuming device. To prevent such an increase in the speed of movement in the event of a change in the direction of the load, corresponding valve means, for example braking valves, must be provided on the discharge side of the consuming device, which makes the construction more complicated and expensive.
DE 37 16 200 C2 describes a control and regulation device for a hydrostatic drive system with a pump and a plurality of consuming devices, in which the speed of movement of each consuming device is compared with a specified speed of movement in an electronic control, and the delivery of the pump is adjusted so that the set speed of movement of the consuming devices can be achieved with low energy losses. The measurement of the actual speed of movement is thereby measured by position or speed-of-rotation sensors on the consuming devices, or by flow meters, in particular rotating impeller wheels, by which the delivery flow of a consuming device can be measured. Position or speed-of-rotation sensors are expensive and complicated, however, and must also be located in the immediate vicinity of the consuming device. When such a drive system is used in a machine such as an excavator, for example, however, the consuming devices are exposed to environmental factors such as dirt, moisture, etc. The sensors must also be protected against these environmental influences. The electrical connections between the sensors that are located on the consuming devices and the electronic control must also be protected against mechanical damage. This environmental protection is both complicated and expensive. When flow meters are used, of course, the consuming devices can be operated independently of the load, but if the direction of the load being exerted on the consuming device changes, for example from a positive to a negative load, the consuming device cannot be operated independently of the load.
The object of the invention is therefore to make available a hydrostatic drive system of the type described above that makes it possible to operate the consuming devices independently of the load, and to operate the consuming devices independently of the direction of the load with low energy losses, thereby requiring little construction effort and expense.
SUMMARY OF THE INVENTION
The invention teaches that associated with each consuming device is a delivery flow sensor that measures the hydraulic flow out of the consuming device to a reservoir, and/or a delivery flow sensor that measures the hydraulic flow into the consuming device from a delivery line of the pump. The delivery flow sensor is connected with an electronic control. The electronic control is connected with the actuation means, the control valve device and a delivery flow adjustment device of the pump. The electronic control controls the control valve device and/or the delivery flow adjustment device as a function of the direction of movement and speed of movement specified by the actuation means as well as the hydraulic flow into and/or out of the consuming device a s measured by the delivery flow sensor.
When a consuming device is actuated, the hydraulic flow into and/or out of the consuming device is determined by the electronic control and is compared with the speed setpoint set on the actuation means. The delivery flow of the pump is calculated by the electronic control on the basis of the speed of movement set on the actuation means, and the delivery flow setting device of the pump is actuated accordingly. The control valve device is actuated such that no pressure decrease occurs at that point. As a result of the measurement of the speed of movement of the consuming device on the basis of the incoming and/or outgoing hydraulic flow and a control of the delivery flow setting device of the pump or of the control valve device, the consuming device can be actuated independently of the load at the speed of movement specified at the actuation means. The operation of the consuming device independently of the direction of the load is also possible as a result of the control of the control valve device as a function of the hydraulic flow discharged from the consuming device.
When a plurality of consuming devices is actuated simultaneously, on the basis of the speeds of movement of the actuated consuming devices set at the actuation means, a delivery flow is calculated and the delivery flow s
Deininger Horst
Langen Alfred
Linde Aktiengesellschaft
Ryznic John E.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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