Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Reexamination Certificate
1999-02-17
2001-01-16
Thorpe, Timothy S. (Department: 3746)
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
C091S506000, C092S012200
Reexamination Certificate
active
06174139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an axial piston machine according to the preamble of claim
1
including a cylinder block having cylinder bores provided therein for the displaceable guidance of pistons so as to execute a lifting movement against an inclined or wobble plate. A pivoting device is adapted to change the inclination of the inclined or wobble plate by pivoting ht latter about a pivot axis.
2. Discussion of the Prior Art
An axial piston machine of this type is known for example, from DE 34 28 591 A1. In this axial piston machine, a plurality of cylinder bores, in which pistons are displaceably guided, are formed in known manner in a rotating cylinder block. The pistons are supported via slippers against a non-rotating inclined plate. The inclination of the inclined plate, which determines the displacement volume of the axial piston machine, is adjustable by means of a hydraulic adjusting piston, in that the inclined plate is pivotable through a given angle range about a pivot axis. When the inclined plate is pivoted back from the lift position in the direction of the zero lift position, the adjusting pressure acting upon the hydraulic adjusting piston is increased and the inclined plate pivots back until it reaches the zero lift position by abutting against an abutment surface. However, the movement of the inclined plate is relatively uncontrolled, so that the inclined plate strikes hard against the abutment surface upon reaching the zero lift position. This is undesirable, since it increases wear to the abutment and the inclined plate and also results in a mechanical impact loading of the entire axial piston machine.
Disclosed in DE 44 40 452 A1 is an axial piston machine with an inclined plate construction, in which two separate hydraulic cylinders are provided for the variation in the inclination of the inclined plate. In this respect, one of the hydraulic cylinders is used for pivoting the inclined plate outwards and the second hydraulic cylinder is used for pivoting the inclined plate back. Whilst the inclined plate is guided in a controlled manner during the entire movement sequence in this solution, the second hydraulic cylinder requires a comparatively large structural outlay, which results in relatively high manufacturing costs. Furthermore, a separate hydraulic control of both hydraulic cylinders is required.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to further develop an axial piston machine having an inclined or wobble plate construction in such a manner that the movement sequence during the pivoting of the inclined or wobble plate is not effected abruptly but continuously.
The invention is based upon the knowledge that the pivoting back of the inclined or wobble plate can be controlled by providing a damping element acting upon the inclined or wobble plate. The damping piston is displaceably arranged in a damping cylinder, which is connected via a throttle element and a non-return valve arranged parallel to the throttle element to a pressure fluid reservoir. In this respect, the non-return valve allows for an unthrottled supply of the pressure fluid from the pressure fluid reservoir into the damping cylinder and prevents an unthrottled outflow of the pressure fluid from the damping cylinder bypassing the throttle element.
According to the invention, a restoring spring can act upon the damping piston in such a manner that the damping piston draws further pressure fluid out of the pressure fluid reservoir via the non-return valve and optionally via the throttle valve as soon as the damping piston is freely movable in the direction of an increase in volume of the damping cylinder. In this manner, it is ensured that the damping cylinder is instantaneously refilled with pressure fluid and therefore that the pivoting movement of the inclined or wobble plate occurs directly. According to an inventive aspect, the pressure medium reservoir can be a leakage fluid collecting chamber surrounding the damping element, the leakage fluid collecting chamber usually being formed by the housing interior of the axial piston machine.
According to a further feature, the inclined or wobble plate can have a first pivot position with a larger angle of inclination and a second pivot position with a smaller angle of inclination and can be pivoted back and forth between these two pivot positions. According to invention, the axial piston machine can also be designed with an inclined plate construction, it being possible to arrange the damping element in the inclined plate or in a stationary counter element opposing the inclined plate according to FIG.
9
. In this respect, the restoring spring holds the damping piston in abutment against the inclined plate or against the stationary counter element.
According to the invention, the inclined plate can also comprise a first and a second abutment surface on its side facing away from the pistons, the abutment surfaces each forming an abutment for the first and second pivot position of the inclined plate.
According to another feature, it is particularly advantageous to offset the point of application, at which the damping piston acts upon the inclined plate, relative to the cylinder block axis in such a manner that the resulting force, which is composed of the force exerted by the damping piston upon the inclined plate, the force exerted by the pivoting device upon the inclined plate during the pivoting procedure and the force exerted by the pistons upon the inclined plate, acts at a center of gravity of the forces which is located on the cylinder block axis. In this manner, non-symmetrical bearing forces are prevented and a levering-out of the bearing is avoided.
REFERENCES:
patent: 2299235 (1942-10-01), Snader et al.
patent: 3156159 (1964-11-01), Cadiou
patent: 3784328 (1974-01-01), Pedersen
patent: 4690036 (1987-09-01), Kosaka et al.
patent: 4896506 (1990-01-01), Shivvers et al.
patent: 5794515 (1998-08-01), Bethke
patent: 2347542 (1973-06-01), None
patent: 3428591 A1 (1986-02-01), None
patent: 4440452 A1 (1995-09-01), None
patent: 63-075366 (1988-04-01), None
patent: 63-306287 (1988-12-01), None
patent: 4-350370 (1992-12-01), None
Brueninghaus Hydromatik GmbH
Scully Scott Murphy & Presser
Thorpe Timothy S.
Tyler Cheryl J.
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