EP0252105A1

EP0252105A1 - Axial piston machine.

Info

Publication number: EP0252105A1
Application number: EP87900123A
Authority: EP
Inventors: Gerhard Lutz; Ulrich Breining
Original assignee: Oerlikon Boehringer GmbH
Current assignee: Hydrokraft GmbH
Priority date: 1985-12-19
Filing date: 1986-12-12
Publication date: 1988-01-13
Anticipated expiration: 2006-12-12
Also published as: DE3545137A1; EP0252105B1; DE3678287D1; WO1987003926A1; DE3545137C2

Abstract

Un piston est utilisé dans des machines à piston axial, en particulier des machines à piston axial à faible course du type à disque incliné avec un alésage dans l'axe de symétrie du piston. Afin d'obtenir un piston ayant un volume mort et une masse aussi réduits que possible et qui soit facile à fabriquer, le piston présente dans le sens axial uniquement dans une première zone tournée du côté de l'extrémité libre du cylindre, c'est-à-dire du joint à rotule du piston, dans une deuxième zone à son autre extrémité un contour extérieur qui correspond à la section transversale du cylindre. La zone intermédiaire, située entre les deux extrémités, présente une section transversale sensiblement plus réduite.A piston is used in axial piston machines, in particular short stroke axial piston machines of the inclined disc type with a bore in the axis of symmetry of the piston. In order to obtain a piston having a dead volume and a mass as small as possible and which is easy to manufacture, the piston has in the axial direction only in a first zone turned towards the free end of the cylinder, it is ie of the ball joint of the piston, in a second zone at its other end an outer contour which corresponds to the cross section of the cylinder. The intermediate zone, located between the two ends, has a substantially smaller cross section.

Description

PISTON PISTON AXIAIEOLBEUMASCHINE

The invention relates to a piston according to the preamble of claim 1.

These pistons are to be used in axial piston machines which, in general, serve to convert pressure energy into rotational energy or vice versa, that is to say can be used either as pumps or hydraulic motors.

The principle of an axial piston machine is that the pistons can move axially back and forth in cylinders, and the size of the displacement space delimited by the piston in the cylinder can be changed as a result. When used as a pump, the hydraulic medium is conveyed by changing this volume; when used as a motor, this volume is changed cyclically by the inflow of hydraulic medium and, as a result, causes the engine to rotate. The cylinders with the pistons axially displaceable therein are arranged in a circle and parallel to one another in a rotatably mounted piston drum. One end of each of the pistons protrudes into the cylinder space, while the other end is usually spherical and lies in a suitably designed, pan-shaped bearing. The pistons are supported by a pan-shaped bearing on a level slide, which is part of the cradle. This disc can be inclined relative to the axis of rotation of the piston drum, so that from a

Swashplate is spoken. As a result, with each revolution of the piston drum, the piston is pushed into the cylinder for half a revolution and pulled out again for the next half revolution, and the more so, the more obliquely the swash plate is set relative to the axis of rotation of the piston drum. Since the pan-shaped bearings do not run on a circle but an ellipse when the swashplate is tilted, these bearings must be on the

Not only can the swash plate circulate, but also be radially displaceable.

In order to prevent the pan-shaped sliding shoes from lifting off the swashplate, a hold-down device is provided, from which the following forces have to be overcome:

- Force from the pressure difference between the housing and cylinder

Frictional forces

Accelerating forces of the piston masses.

I make ^m usual speed range of more than 1,000 rpm latter from the largest share. This is also clear from the relationship to the calculation of the maximum acceleration into which the angular velocity, and thus the rotational speed, is squared:

amax = D0 _n / 2 • tan / _* - ^{1 "}

D _n = pitch circle diameter of the pistons in the piston drum y = swivel angle of the swash plate ü = angular velocity.

Since the parameters responsible for determining the piston acceleration are generally not without

Disadvantages can be changed, the stress on the hold-down can only be reduced by reducing the piston mass. A large piston barrel, however, not only stresses the hold-down device, but also affects the balance of the piston drum: The centrifugal forces of the rotating pistons, under the influence of the piston stroke, cause a moment on the piston drum by one

Axis that is perpendicular to the axis of rotation of the piston drum and at the same time parallel to the pivot axis of the cradle on which the swash plate is arranged. This undesirable torque of the piston drum can only be compensated for by corresponding additional pressing forces in the axial direction of the piston drum.

The smallest possible piston mass would thus relieve important parts of the axial piston machine by reducing the inertia.

For this reason, hollow drilling of the pistons has been used, for example. The closed piston end protrudes from the cylinder and the drilled piston crown into the cylinder. As a result, however, the previous displacement, the so-called stroke volume, is increased by the volume of the bore, the so-called dead volume, which does not take part in the production, but because of its compressibility, a higher pressure pulsation with all negative effects. for example, increased noise emission and lower efficiency.

In order to avoid this disadvantage, pistons for axial piston machines are known in which the piston crown is drilled out as shown above, but then, in order to avoid the dead volume, was closed and sealed again by a cover Reducing the

Friction required through hole from the piston crown to the opposite end of the piston or the relief pressure fields are attached. Another known solution, in which the pistons were drilled centrally but in a ring, so that material for introducing said through-bore was present in the axis of symmetry of the piston

Disadvantage that the manufacture of such pistons was very complex and, especially in smaller quantities, uneconomical, since both special tools were necessary for boring and, for example, the complex friction welding had to be used for the subsequent closing with an annular cover.

The object of the invention is therefore to create pistons with a through bore from the piston crown to the opposite piston end and with the smallest possible dead volume, which have the lowest possible mass and are easy to manufacture.

The solution to this problem is set out in the characterizing part of claims ^{1 1.} and 2. Appropriate designs result from the subclaims.

Such a weakened, central region of a piston can, if simple manufacture is in the foreground, be formed with a constant cross-section, especially if the bending forces acting on it are not very different over the axial length of the central region, in which case, of course, the Cross-section must be dimensioned according to the greatest bending load occurring.

If, on the other hand, the mass reduction is to be further optimized while accepting a somewhat more complex manufacture of the piston, the piston cross section in the axial course of the central region is changed in accordance with the bending loads occurring at every point, so that there is a constant deflection over the piston course. A further reduction in the mass of the piston is made possible by turning the two edge regions, in which the piston rests against the cylinder wall, from the central region, which has the advantage that the remaining lateral surfaces on the cylinder wall, which have a load-bearing capacity Lubricating film and a sufficient sealing length must not be reduced.

Of course, the two basic solutions, reducing the outer cross section in the central piston area and concentrically arranged longitudinal bores closed on the piston head, can also be combined accordingly if required. Different embodiments of the invention are shown in the drawings and are described in more detail below: It shows:

1 shows a cross section through an axial piston machine with pistons according to the invention,

2 shows a partially cut piston with constant. Reduced piston in the middle area,

Fig. 3 is a partially cut piston with different cross-section in the central area, and

FIG. 4 shows a piston similar to FIG. 3 with the end regions turned behind.

Fig. 5 shows a partially cut piston with concentrically arranged longitudinal bores in plan and elevation.

.

In Fig. 1, an axial piston machine is shown, which is located in a cup-shaped housing 2, which is closed with a cover 1. The. both parts are screwed together via the tie rod 5 with the aid of the nuts 21. , Slides in the pump operation, via the shaft ^• 19 driven axial piston machine essentially consists of coaxially about the shaft 19 rotatably disposed piston drum 12 on the plate one side on the Verteiler¬ 14 and protrude into the on the other side of the piston 13 The end of the pistons 13 protruding from the piston drum 12 is spherical and is mounted in the sliding shoes 16 provided with a corresponding inner contour. The sliding shoes 16 are slidably supported on the fixed swash plate 17 in order to be able to maintain the elliptical orbit around the shaft 19 due to the inclined position of the swash plate 17 relative to the shaft 19. By the dimension of those occurring with each revolution of the shaft 19

Longitudinal displacement of the pistons 13 in the piston drum 12, and thus to be able to adjust the stroke volume during pump operation, the swash plate 17, against which the sliding shoes 16 are pressed with the aid of a hold-down device 15, is arranged on a cradle 18, which with its semi-cylindrical outer contour is pivotable in a corresponding recess in the bearing body 10.

The piston 13 used in the axial piston machine of FIG. 1 is shown in more detail in FIG. 2. The piston 13 has an outer contour in the front area 3 and rear area 4, which corresponds to the inner contour of the cylinder and slides along it. In the central region 6, however, the cross-section of the piston 13 is significantly smaller, namely over the entire axial length of the central region. Before that

the front region 3 is of the ball-shaped head 7 of the piston 13, which is rotatably mounted in a recess of the sliding shoe ent speaking ^'16th

In order to keep the two parts displaceable relative to one another despite the high pressure of the sliding shoe 16 on the swash plate 17, pockets 8 are formed on the underside of the sliding shoe, which serve as relief pressure fields when the pressure is applied accordingly. The necessary pressure supply takes place via the bore 9 in the slide shoe 16 and the further bore 11 in the piston 13 from the compression chamber. inside the cylinder. Since the bore 11 advantageously lies in the longitudinal axis of the piston 13, its function is restricted by the cross-sectional constriction in the. middle region 6 of the piston 13 is not affected.

Another embodiment of the piston 13 according to the invention is shown in FIG. 3. In contrast to the piston of FIG. 2, the central region 6 of the piston has. 13 does not have a constant cross-section, but the cross-section of the piston increases towards the front end, corresponding to the increasing bending load, which results in a uniform deflection in the longitudinal direction over the central region 6 of the piston 13.

The in Fig. Piston 13 shown 3 can in mass savings are still being optimized on the piston that der.'vordere region 3 and ^"the rear portion 4 of the piston are behind 13 rotates from the middle section 6, without the remaining lateral surfaces, with which the piston 13 abuts the cylinder wall to further reduce, as shown in Fig. 4. The use of such pistons is particularly advantageous in the case of short-stroke axial piston machines, since in this case only relatively small bending forces act on the pistons due to the overall short overall length of the pistons 13, and the axial length of the front region 3 of the piston 13 is all the less can be selected, the smaller the stroke of the piston, if a complete disengagement of the lateral surface of the front area 3 with the cylinder wall is to be avoided.

5, on the other hand, a piston is shown, the mass of which was reduced without accepting a dead volume in that bores 22 were made concentrically about the longitudinal axis of the piston in the piston head, so that enough material remained in the center of the piston to introduce the bore 11 therein . So that the cavities of the bores 22 do not act as a dead volume during operation of the axial piston machine, they are closed and sealed on the piston head by covers 23, which are fastened, for example, by brazing in the piston. The embodiments shown in FIGS. 2 to 4 and 5 can of course also be combined in a new embodiment in the case of appropriately dimensioned pistons, in which case the concentrically arranged hollow bores which are closed again on the cylinder base either only in the front region 4 of the piston are arranged, or are so close to the center of the piston that they can extend through the narrower, central region 6 of the piston.

Claims

-A0-10

1. ^" Pistons for axial piston machines, in particular

^ - Short-stroke axial piston machines of the swash plate type with through hole arranged in the axis of symmetry of the piston, characterized in that the piston in the axial direction only in a first area 0, which faces the free cylinder end, that is to say the ball joint of the piston, and in a second area on the other Kolbehende has an outer contour corresponding to the cylinder cross-section and has a substantially smaller cross-section in the middle region in between.

2. Pistons for axial piston machines, in particular short-lived axial piston machines of the swash plate type with a through-hole arranged in the axis of symmetry of the piston, that is, the piston several symmetrically around the piston center in

Has longitudinal piston holes that are closed towards the piston head with lids.

5

_Third , Piston according to claim 1 or 2, characterized in that the central piston region has a constant cross section over its axial length.

4. Piston according to claim 1 or 2, characterized in _{that the} central piston region has a different thickness in its course, the strength of which changes analogously to the bending stress changing with the axial extension, in order to achieve a uniform deflection in the central piston region .

5. Piston according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t, d a ß the length of the first, the free cylinder end, ie the ball joint of the piston facing piston area is greater. als., dar- -π-a-xiπale.Jϊub the axial piston machine.

6. Piston according to one of claims 1 to 5, characterized in that the front region (3) and the rear region (4) of the piston (13) are not solid, but are hollowed out in an annular manner from the central region (6) without to reduce the lateral surfaces of the front area (3) and rear area (4).