Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Patent
1995-04-06
1996-05-28
Ryznic, John E.
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
91499, F04B 120, F01B 300
Patent
active
055200885
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an axial piston machine having a cylinder body that is rotatable relative to a wobble plate and in which several pistons are arranged so as to be axially displaceable, the pistons being supported on a sliding-contact face of the wobble plate by means of slider shoes articulated at the free ends of the pistons, wherein a pressure element holding the slider shoes on the sliding-contact face is provided.
Axial piston machines of that kind can be used as pumps or as motors. One area of use is the drive of vehicles, in which the axial piston machine forms part of the drive system. In such vehicles it has been found that the blocking action of such an machine, that is, the "motor braking action" is inadequate in many cases. Consequently, such a vehicle starts to move by itself when standing on a sloping surface although the axial piston machine is in its neutral position, that is, should actually block the drive.
This phenomenon can be attributed to internal leaks in the drive system; a large part of these internal leaks occurs in the axial piston machine.
The problem of internal leaks in axial piston machines is well known. DE 37 25 979 C2, for example, which discloses an axial piston machine of the kind mentioned in the introduction, describes an attempt to prevent canting by matching the slider shoe bearing surface to the corresponding counter-surface of the wobble plate. DE 28 04 912 C2 provides a retaining ring which holds the slider shoes down at the radially outer end of the wobble plate on the sliding-contact face of the wobble plate. U.S. Pat. No. 3,382,793 discloses an attempt to guarantee contact by means of a holding-down plate.
All the known solutions do improve internal sealing of the axial piston machine, but essentially they only prevent the slider shoes from canting relative to the sliding-contact face. They fail in particular in the axial piston machine during the transition from the pressure stroke to the suction stroke (in the case of the pump) or during the transition from the working stroke to the supply stroke (in the case of the motor) or vice versa. During such a transition, the force relationships are indeterminate, that it, neither the forces acting from the slider shoe side nor the forces acting from the wobble plate side on the contact area between the slider shoe and the sliding-contact face are substantial enough to guarantee a reliable seat of the slider shoes on the sliding-contact face. Since a part of the slider shoes is always located in a such a region, as before there are unsealed points here which lead to internal leaks.
The invention is therefore based on the problem of reducing the internal leakage in an axial piston machine.
In an axial piston machine of the kind mentioned in the introduction, this problem is solved in that a spring element is provided between each slider shoe and the pressure element.
The force acting on the slider shoe, which causes the slider shoe to bear on the sliding-contact face, is therefore no longer produced directly by the pressure element, but by way of a spring element which is inserted with a certain prestress between the pressure element and the slider shoe. This spring element is prestressed sufficiently so that it itself exerts the necessary force on the slider shoe even at the maximum possible spacing between the slider shoe and the pressure element, so that the slider shoe rests reliably on the sliding-contact face. Hydraulic fluid is therefore largely prevented from escaping between the slider shoe and the sliding-contact face so that internal leakage can be kept to a minimum. The only hydraulic fluid to escape is that required for lubrication of the contact face between the slider shoe and the sliding face, and this is only an extremely small amount. Since the slider shoe is held permanently under pressure on the sliding-contact face, there is no interruption in the lubrication, as could occur previously when the slider shoe lifted off the sliding-contact face. Wear is accordingly quite considerably reduced.
REFERENCES:
patent: 2925046 (1960-02-01), Budzich
patent: 3246577 (1966-04-01), Macintosh
patent: 4111103 (1978-09-01), Mauch
patent: 4602554 (1986-07-01), Wagenseil et al.
patent: 4620475 (1986-11-01), Watts
patent: 4637293 (1987-01-01), Yamaguchi et al.
patent: 4771676 (1988-09-01), Matsumoto et al.
Danfoss A/S
Ryznic John E.
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