Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reexamination Certificate
2000-03-23
2001-11-06
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
Reexamination Certificate
active
06311489
ABSTRACT:
The invention relates to a control device for a hydraulic pump, particularly for controlling a construction machine such as an excavator/loader.
A control device is known from DE 195 17 974 A1. A similar control device emerges from DE 33 45 264 A1. In the known control devices an adjustable hydraulic pump delivers into a delivery line which leads to a user. An adjustable delivery flow throttle and/or proportioning throttle with which the delivery flow for the user is pre-set is provided in the delivery line. To control the delivery flow delivered by the hydraulic pump, a delivery flow control valve is provided which is connected to the delivery line downstream of the proportioning throttle via a first control line and to the delivery line upstream of the proportioning throttle via a second control line. The pressure drop occurring at the proportioning throttle thus serves to control the delivery flow control valve which controls the adjusting pressure for an adjusting device acting on the delivery volume of the hydraulic pump. A power control valve is additionally provided, which is arranged between the first control line and a pressure medium tank. In the direction of opening the power control valve is acted upon by the control pressure in the first control line whereas in the closure direction it is acted upon by the adjusting device via a measuring spring arrangement as a function of the delivery volume of the hydraulic pump pre-set by the adjusting device. By means of a suitable selection of the measuring spring arrangement the hyperbolic characteristic of a pre-set maximum power may be at least approximately simulated. In a control range below the pre-set maximum power the control characteristic of the control device is determined by the delivery flow control valve which adjusts the delivery flow of the hydraulic pump to the value pre-set by the opening cross-section of the proportioning throttle. If the pre-set maximum power is exceeded, however, the power control valve responds and limits the pressure in the first control line so that the hydraulic pump is swivelled back and an overload is prevented.
In principle the known control devices are also suitable for controlling several users. In practice, however, the problem arises that power control is not required in all operating states. In construction machines in particular there are hydraulic users for which power control is required in order to prevent an overload of the drive motor for the hydraulic pump whereas there are other users for which a power restriction leads to an undesired shortage of power. In an excavator/loader for example, one or more items of hydraulic operating equipment and a hydraulic travel drive are driven. In the excavator operation of the excavator/loader in which the vehicle is at a fixed location, the drive power for the excavating shovels is unlimitedly available and a power restriction would lead to an undesired shortage of power. In a loader operation, however, in which the excavator/loader is continuously moved by a hydraulic travel drive, the available pump output must be distributed to the item or items of operating equipment and the travel drive. In this case a power restriction for the travel drive is required so as to prevent an overloading of the motor driving the hydraulic pump. Similar problems also arise in practice for other construction machines.
The object of the invention is therefore to provide a control device for an adjustable hydraulic pump with which the control of several users is possible in such a way that as optimum as possible a power distribution is achieved.
The invention is based on the finding that an optimum power distribution may be achieved in that only selected, power-controlled users are connected to the power control valve whereas the remaining users do not respond to the power control valve. In contrast the delivery flow control valve is connected to all users including the non-power-controlled users via a pressure change device. The highest control pressure in each case of the control pressures prevailing in the first control lines is selected and conveyed to the delivery flow control valve. According to the solution according to the invention, therefore, only those users which may actually lead to an overload of the drive motor driving the hydraulic pump have an influence on power control. For the remaining users, a shortage of power by means of an unnecessary power restriction is avoided.
In the simplest case, only a single power-controlled user may be provided, the first control line of which is connected to the power control valve via a connecting line. The connecting line opens into the first control line of this power-controlled user upstream of the first pressure change device for selecting the control pressure for the delivery flow control valve. The power-controlled user in a construction machine, e.g. an excavator/loader, may be the travel drive for example.
If a power control for several users is to be provided, the highest control pressure in each case in the first control lines of the group of power-controlled users may be selected by a second pressure change device and be conveyed to a connecting line leading to the power control valve.
A throttle to limit the flow through the power control valve may be provided in the connecting line leading to the power control valve. Alternatively or additionally this throttle may also be arranged in each first control line allocated to a power-controlled user.
The first and the second pressure change device may consist of one pressure change valve or several pressure change valves arranged behind each other in interconnected manner. Particularly advantageously the second pressure change device may be part of the first pressure change device. By means of a last pressure change valve the highest control pressure in each case of the power-controlled users is compared with the highest control pressure in each case of the non-power-controlled users and the control pressure which is the highest overall in each case is selected to control the delivery flow control valve. Additionally, a pressure control valve, which is controlled by the control pressure in the second control line, may be arranged between the delivery flow control valves of the adjusting device. The control pressure in the second control line corresponds to the pressure in the delivery line at the outlet of the hydraulic pump upstream of the proportioning throttles. When the outlet pressure of the hydraulic pump exceeds a pre-set limit, the pressure control valve responds and swivels the hydraulic pump back.
The control device according to the invention may be used to control a construction machine, particularly an excavator/loader in particularly advantageous manner. In this case at least the travel drive of the excavator/loader is a power-controlled user.
REFERENCES:
patent: 4668171 (1987-05-01), Beutler et al.
patent: 5201803 (1993-04-01), Goto et al.
patent: 5993168 (1999-11-01), Erkkilae et al.
patent: 34 10 071 A1 (1985-10-01), None
patent: 36 28 370 A1 (1988-02-01), None
patent: 195 17 974 A1 (1996-11-01), None
patent: 05-099126 (1993-04-01), None
Erkkilae Mikko
Stangl Helmut
van Bracht Detlef
Brueninghaus Hydromatik GmbH
Lopez F. Daniel
Scully Scott Murphy & Presser
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