Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Patent
1996-10-07
1999-02-09
Denion, Thomas E.
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
74 60, 91499, F01B 300
Patent
active
058680616
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydraulic axial piston machine having axially movable pistons, which at one end bear by means of slider shoes against a slanting plate, and having a pressure plate for holding the slider shoes in contact with the slanting plate.
The pressure plate holds the slider shoes in engagement with the slanting plate. Here, it is desirable for the alignment of the slider shoe running face with the slanting plate to be as parallel as possible, so that wear and tear on the slider shoes is not lop-sided and at the same time hydraulic deloading can be effected by fluid fed in between the slider shoe running face and the slanting plate.
The problem involved here, however, is that in operation the pressure plate and the slider shoes are exposed to considerable forces, which in many cases try to lift the slider shoe running face away from the slanting plate. These forces include, inter alia the centrifugal force acting on the slider shoes and the acceleration force caused by the acceleration of the piston, as well as forces caused in pump operation by suction pressures. The contact force exerted by the pressure plate has to act against these forces. In many cases this force originates in the centre of the pressure plate, for example, through a ball-and-socket joint. Since the pressure plate is not infinitely rigid, the above-mentioned forces subject it to a distortion, so that the pressure plate becomes slightly concave, that is to say, the distance to the slanting plate from its middle is smaller than from its radially outer edge. This in turn leads to the point of engagement between slider shoe and pressure plate being shifted inwards, that is, towards the midpoint of the pressure plate. Combined with the above-mentioned forces acting on the slider shoes, this shift in the point of engagement results in the slider shoes tilting and lifting away at one side from the slanting plate. In that case, on the one hand the wear and tear on the slider shoes is undesirably lop-sided, as mentioned above, and on the other hand the pressure relief acting on the slider shoes no longer functions, so that additional wear occurs there.
The problem is known per se. In DE 37 25 979 C2, an attempt to overcome this problem is made by using a slanting plate of a smaller diameter, so that the slider shoe running face projects radially outwards a little way beyond the slanting plate.
U.S. Pat. No. 3,382,814 discloses a different axial piston machine, in which the pressure plate is in the form of a spring, which is biassed so that a predetermined minimum contact force acts on the slider shoe irrespective of the load.
The problem underlying the invention is to ensure that the slider shoes lie on the slanting plate.
This problem is solved in a hydraulic axial piston machine of the kind mentioned at the outset in that the pressure plate acts only on a part of the slider shoes lying, in the radial direction of the slanting plate, outside a predetermined region.
This construction enables the pressure plate to act only or at least mainly on the region of the slider shoes that tries to lift away from the slanting plate as a result of the said forces. The point of engagement of the slanting plate on the slider shoes is therefore shifted radially further outwards. Although in that case a part of each slider shoe is not acted on by the pressure plate, namely, that part of the slider shoe which is located within the predetermined region, the slider shoes are normally so rigid that it is sufficient to hold them firm at the point at which their tendency to lift away from the slanting plate is greatest. Because the point of engagement is shifted further outwards, forces much greater than before are now required to lift the slider shoes.
In a preferred construction, the predetermined region has an at least approximately circular form. This facilitates manufacture of the machine quite considerably. In addition, the control behaviour can be better predicted and thus better determined.
Advantageously, a radially outer boundary of the reg
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Hansen Ove Thorb.o slashed.l
Martensen Lars
Danfoss A/S
Denion Thomas E.
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