Rotary expansible chamber devices – With mechanical sealing – Axially movable end wall or end wall portion
Reexamination Certificate
2000-04-19
2001-09-25
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
With mechanical sealing
Axially movable end wall or end wall portion
C418S170000, C137S112000, C137S111000
Reexamination Certificate
active
06293777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a hydraulic positive displacement machine, especially a gear wheel machine, having a housing in which conveying elements, especially gear wheels, are supported by which hydraulic medium is taken in through an intake or suction opening and expelled under pressure via an outlet or pressure opening, and wherein the end faces of the gear wheels are sealed by at least one pressure plate. The hydraulic positive displacement machine further comprises a control device by which the pressure for loading the pressure plate into a sealing position can be adjusted. The invention also relates to such a control valve for controlling the hydraulic positive displacement machine.
2. Description of the Related Art
Gear wheel machines, for example, gear pumps, are used primarily in mobile hydraulics because they have a comparatively simple construction and allow relatively high pressures while being of minimal weight. A further advantage of gear wheel machines is that they can be employed in comparatively large rpm, temperature, and viscosity ranges.
In European patent document 0 445 529 B1 a gear pump is disclosed in which two gear wheels are rotatably supported in a housing. The displacement chambers are delimited by the meshing tooth flanks, the inner wall of the housing, and an axial plate or pressure plate. The latter is loaded on its backside by a hydraulic medium so that it contacts sealingly the end faces of the gear wheels. The pressure acting on the backside of the pressure plate can be adjusted by a control device in which a metering orifice embodied as a directional control valve and a three-port directional pressure regulator (pressure scale) cooperate. It is loaded in the sense of increasing the pressure at the backside by the pressure downstream of the metering orifice as well as a pressure spring and in the sense of a reduction of the pressure at the backside by the pressure upstream of the metering orifice. The pressure regulator (pressure scale) connects for this purpose a control connector connected to a pressure chamber on the backside of the pressure plate with the pressure outlet of the pump or with the tank, so that the sealing gap between the pressure plate and the end faces of the gear wheels is reduced or enlarged. For an enlarged sealing gap the hydraulic medium can flow directly from the high pressure side to the low pressure side so that the volumetric efficiency of the gear wheel machine can be reduced and, for example, the conveying volume or capacity of the gear pump can be adjusted as a function of the gap width. This means that by influencing the hydraulic medium pressure acting on the pressure plate an exact conveying flow regulation can be performed.
A problem of this configuration is that the pump housing must be comparatively complex since space for the directional control valve to the consumer and the pressure regulator (pressure scale) must be provided. Moreover, a separate pressure limitation valve must be provided in order to limit the maximum pressure.
In U.S. pat. No. 4, 014,630 a pump arrangement is disclosed in which a sealing plate is forced by a spring into the contact positioned on the conveying elements. The spring chamber is connected by a throttle bore to the displacement chamber of the pump arrangement so that the pressure plate is also hydraulically prestressed into its sealing position. The pressure acting on the pressure plate can again be adjusted by a control device via which the hydraulic medium can be returned to a tank. A disadvantage of this construction is that at all times hydraulic medium is removed through the throttle bore from the displacement chambers so that the volumetric efficiency is reduced. Moreover, the throughbore of the pressure plate can easily become clogged so that, correspondingly, a servicing of the pump arrangement is required.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a hydraulic positive displacement machine, especially a hydraulic gearwheel machine, in which with minimal device-technological expenditure a sufficiently precise conveying flow regulation is possible. A further object is to provide a control valve which is suitable for such positive displacement machines.
In accordance with the present invention, this is achieved in that the control device has a control valve with a metering orifice bore that is provided in a piston and connects an inlet connector and an outlet connector, wherein the piston, on the one hand, is loaded by the pressure of the hydraulic medium upstream of the metering orifice bore and, on the other hand, by the pressure downstream of the metering orifice bore as well as the force of a pressure spring, and that via the piston, depending on the pressure differential, a control connector hydraulically connected to the pressure plate can be connected to a pressure connector (inlet connector and outlet connector) for the purpose of increasing the pressure and to a return connector for the purpose of decreasing the pressure.
In accordance with the present invention, the object in regard to the control valve is further achieved in that the control valve has a sleeve with an axial bore for receiving a piston, wherein a radial connector and a control connector in the form of radial bores open into the axial bore, wherein the axial bore, on the one hand, opens into the inlet connector and, on the other hand, into the outlet connector, wherein the piston is penetrated by a metering orifice bore connecting the inlet and outlet connectors and has control edges by which the connection of the control connector to the pressure connector (inlet connector and outlet connector) and the radial connector can be controlled for opening and closing.
The inventive positive displacement machine is preferably embodied as a gear wheel machine wherein the sealing of the displacement chamber at the end faces is realized by a pressure plate whose back side is loaded by a control pressure via a control valve. The control valve has a piston by which the volume flow to the consumer can be controlled and by which a control connector, hydraulically connected to the pressure plate, can be connected to a pressure connector or a return connector so that the pressure on the back side of the pressure plate can be increased or decreased. The piston is a hollow piston wherein the throughbore acts as a metering orifice so that one end face of the piston is loaded by the pressure downstream of the metering orifice and the other end face of the piston is loaded by the pressure upstream of the metering orifice.
This control valve is characterized by an extremely compact configuration so that the housing of the displacement machine can be of a very simple design.
In an especially preferred embodiment, the controlling action for opening and closing the control connector and the return connector of the control valve can be realized by two control edges of the piston positioned axially spaced to one another so that the piston with increasing volume flow can be brought into a control position in which by means of the control edges the control connector can be connected to the pressure connector or the return connector.
The piston is advantageously provided with a further control edge by which a flow cross-section upstream of the metering orifice bore can be connected to the return connector upon a sufficiently large movement of the piston away from the control position so that the pressure plate is relieved and a fast adaptation to conveying volume changes is possible.
The technological expenditure for manufacturing the piston is especially simple when the metering orifice is formed by a portion of the throughbore of the piston.
For damping the volume flow fluctuations or pressure fluctuations, one end portion of the piston can be designed to provide a damping gap with a circumferential wall of the axial bore receiving the piston, wherein pressure medium can pass through the damping gap when the piston moves axia
Denion Thomas
Huckett Gudrun E.
Hydraulik-Ring GmbH
Trieu Theresa
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