Expansible chamber devices – Rotating cylinder – Plural cylinders
Patent
1996-07-24
1998-03-24
Thorpe, Timothy
Expansible chamber devices
Rotating cylinder
Plural cylinders
91499, 417269, F01B 1304, F04B 120
Patent
active
057300437
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic axial piston motor having a rotatable cylinder drum, in which several work pistons, each provided at one end with a slider shoe, are arranged in work cylinders so as to be axially movable, having a control plate, a swash plate against which the slider shoes bear, a pressure plate which holds the slider shoes against the swash plate, and a pressure-applying unit, which acts on the pressure plate and comprises a hydraulic piston-cylinder arrangement.
In operation, the work cylinders are supplied with hydraulic fluid under pressure, under the influence of which the work pistons are pushed out of the work cylinders. The work pistons lie via the intermediary of their slider shoes against the swash plate. Because the swash plate takes up a pre-determined or adjustable angle with respect to the direction of the axis of the cylinder drum, an effective force resulting from the slant is consequently produced, which with its lever arm acts in the form of a rotary torque on the cylinder drum and turns this. To reduce friction, a small part of the hydraulic fluid introduced into the work cylinders is often passed right through the piston to the sliding face of the slider shoes, in order there to build up a lubricating film or to effect pressure relief, for example as a result of hydrostatic lubrication. In order, inter alia, not to let the resulting losses due to leakage become too great, and also for other reasons, for example, the control behaviour of the motor or to counteract centrifugal forces, it is important to keep the slider shoes in contact with the swash plate at all times. The pressure plate, which is pressurized by the pressure-applying unit with a pressure force, is used for that purpose. This pressure force must not, on the one hand, be large enough to increase the friction losses between slider shoes and swash plate unnecessarily, but on the other hand it must be large enough to counteract the tendency of the slider shoes to lift away at least partially from the swash plate at higher speeds.
Since such an adjustment of the pressure force solely by means of a spring is virtually impossible, DE 39 01 064 A1 discloses in addition a hydraulic piston-cylinder arrangement which can be supplied with pressures of different levels in dependence on the speed of the motor. At low speeds, it is possible to ensure that the contact pressure of the slider shoes against the swash plate is also low, which leads to correspondingly low friction losses. At higher speeds, the pressure is correspondingly increased, so that the slider shoes are unable to lift away from the swash plate.
The axial piston machine according to DE 39 01 064 A1 has as its pressure-applying unit a concave bearing for the pressure plate which is mounted so as to be axially displaceable on a shaft carrying the cylinder drum. Pressure is exerted on the bearing by an annular piston by way of bolts, the annular piston being arranged in a ring-shaped cylinder in the cylinder drum within a circle formed by the work cylinders and surrounding the shaft. Upon an increase in pressure in the cylinder, the piston is loaded in a direction towards the bearing. A corresponding pressure force is therefore exerted by way of the bearing on the pressure plate. In the ring-shaped cylinder there is furthermore arranged a compression spring which ensures that the bearing is biassed. The annular piston has, however, a relatively small face on which pressure can act so that either the desired increase in contact pressure cannot be achieved or the hydraulic fluid has to be supplied at relatively large pressures. This is not quite without problems because the high pressures still have to be changed in dependence on the operational behaviour of the motor.
SUMMARY OF THE INVENTION
The invention is therefore based on the problem of providing an axial piston motor in which a sufficiently large contact pressure can be produced using simple means.
The problem is solved in an axial piston motor of the kind mentione
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Jepsen Hardy Peter
Kristensen Egon
Danfoss A/S
Korytnyk Peter G.
Thorpe Timothy
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