GB2192240A

GB2192240A - An axial piston machine with a revolving cylinder drum

Info

Publication number: GB2192240A
Application number: GB08715466A
Authority: GB
Inventors: Walter Heyl
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 1986-07-02
Filing date: 1987-07-01
Publication date: 1988-01-06
Also published as: DE3622220A1; GB8715466D0; FR2601080A1

Abstract

The axial piston machine has a number of cylinder bores (6 to 14) running into associated orifices (15 to 23) which are not evenly spaced around the cylinder drum (1). Radial planes, which contain the axis of rotation (25) of the cylinder drum (1) and which also contain the axis of the respective cylinder bore and associated orifice, form angles between them. In the series of angles so formed, adjoining angles are unequal. In a preferred embodiment, all of the angles do not need to be different from one another but may be such that (a) adjoining angles ( beta 1 and B2) are unequal; (b) said adjoining angles add up to the value beta ; (c) there is an uneven number of angles in the series, the last angle in said series having the value beta 3 which is equal to beta /2. <IMAGE>

Description

SPECIFICATION An axial piston machine with a revolving cylinder drum This invention concerns an axial piston machine with a rotary cylinder drum in which cylinder bores are disposed at least roughly parallel to the axis of the cylinder drum, wherein a piston braced against a piston guide face is displaceable in each cylinder and each cylinder bore debouches directly or indirectly through connecting channels into a respective orifice in an end face of the cylinder drum, and wherein a rotary spool control valve face with two roughly semi-circular channels on the radius corresponding to the orifices of the cylinder bores lies opposite this end face in the axial piston machine.In the machines known until the present date, the cylinder bores and the corresponding orifices in the cylinder drum end face are uniformly distributed (namely, they have the same spacing from one another) with the result that the angle between the centres of any two neighbouring cylinder bores and orifices or corresponding edges of orifices is the same as the angle between the centres of any other two neighbouring cylinder bores and orifices or corresponding edges of orifices. This arrangement became an obvious requirement both on manufacturing grounds and for reasons of the strength of the wall between the cylinder drums and for reasons of the fundamental arrangement. ("Fordermenge, Drehmoment und Leistung von Guldner Hydrostabil-Einheiten" in "Linde Berichte aus Technik und Wissenschaft", Volume 9, 1960, page 40).

Any axial piston machine- working under pressure produces noises. One important cause of these radiated noises is the sudden change in pressure in the cylinders when switching over from the highpressure side to the low-pressure side and vice versa, and the volume of the noises is determined by the rate at which the pressure rises in the cylinder. This rate of pressure rise is again dependent on the operating parameters of speed of rotation and pressure and on the oil temperature and the design of the edges of the orifices at the cylinder drum end face and the end parts of the semi-circular channels in the rotary spool control valve face.The fixing of optimum operating parameters, together with optimum design of the edges causing the changeover at the cylinder bore orifices and the channels in the rotary valve plate face, produce an optimum sound spectrum (noise level) in relation to frequency. A graph of this sound spectrum shows frequency-related (harmonic) peak levels, particularly with even-numbered multiples of the fundamental frequency fk=N.Zk in which fk is the fundamental frequency and n the speed of rotation and zk the number of cylinders. With the normal speeds of rotation employed nowadays, this radiated sound takes the form of high-pitched sirenlike notes.

The principal object of the present invention is to make the radiated sound more pleasant to the human ear than it has been until now.

This object is achieved in an axial piston machine made in accordance with the present invention by ensuring that the angles, measured from the axis of rotation of the cylinder drum, between the planes which extend through said axis of rotation and each of which extends through the centre or a corresponding edge of at least three neighbouring cylinder orifices (i.e: cylinder bores and cylinder orifices or just the cylinder orifices) are unequal.If the angles between the cylinder orifices alone are unequal and if the spacings between the cylinder bores are the same, the orifices of individual cylinders are offset in relation to the axis of the associated cylinder bores so that the dead centre position is displaced slightly in relation to the centre of the land between the two roughly semi-circular channels in the cylinder drum end face in line with the offset.

These unequal spacings of at least the cylinder orifices, and possibly also of the cylinder orifices and cylinder bores, around said axis of rotation have the effect of lowering the peak sound levels. Here, the angles between the various pairs of neighbouring orifices in the cylinder drum are distributed in an a periodical sequence which is such that a distinct frequency is only radiated for a length of time below the perception threshold of the human ear and then jumps to a different frequency.

This means that the interval of time between two changes in pressure in two neighbouring cylinder bores is different from the interval of time between the next two pressure changes and, because so many other pressure changes occure before the same interval of time between two pressure changes recurs, the human ear does not perceive any continuous frequency; that is to say, the human ear only perceives a confused back-ground noise and distinct notes can no longer be detected. Although this does not change the noise level, it does change the character of the noise.

One embodiment of an axial piston machine according to the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 snows a cylinder drum of an axial piston machine in accordance with the invention viewed along (in the direction of) the axis of rotation- and looking at the end face on the rotary spool control valve side; and Figure 2 shows a view of the same cylinder drum also viewed along the axis of rotation of the cylinder drum but looking at the side from which the pistons emerge.

Referring to the drawings, a cylinder drum 1 has a rotary valve plate face 2. and a central bore 3 (Figure 1) which widens into a bore 5 (Figure 2) towards the end face 4 from which the pistons (not shown) emerge. The cylinder drum 1 is provided with nine cylinder bores which are numbered from 6 to 14, and there are nine orifices which are numbered from 15 to 23; the cylinder bore 6 is associated with an orifice 15, the cylinder bore 7 is associated with an orifice 16, and so on until one reaches the cylinder bore 14 which is associated with an orifice 23.

The centre line plane 26 (Figure 1) extends through the axis of rotation 25 of the cylinder drum and also through the axis of the cylinder bore 6 and of the orifice 15 and, similarly, the median plane 27 extends through the axis of rotation 25 and also through the axis of the cylinder bore 7 and of the orifice 16. The same applies to ail of the remaining median planes 28 to 34, each of which extends through the axis 25 and through the axis of the respective cylinder bore/orifice.

The median planes 26 and 27 form between them an angle pl and the median planes 28 and 28 form between them an angle ss2. The angles ss1 and 42 are unequal.

The sum of the angles ss1 and ss2 equals the angle ss. The median planes 28 and 29, the median planes 30 and 31 and the median planes 32 and 33 each form between them an angle pl, whereas the median planes 29 and 30, the median planes 31 and 32 and the median planes 33 and 34 each form between them an angle ss2. This means that the median planes 26 and 34 form an angle ss3. Thus, we have a total of three different spacings, i.e.

fil, ss2 and ss3, and preferably ss3 = ss/2. This arrangement ensures that different sound frequencies are produced.

It is not necessary for all of the angles between the several pairs of median planes to be unequal to one another; it is sufficient if the adjoining angles are unequal, the same angle only recurring as the next but one in the series and,where possible, a third size of angle also being included.

Reference was made above to the fact that, utilising the present invention, the human ear is only able to perceive a confused background noise, distinct notes no longer being detectable; this was stated to change the character of the noise as distinct from the noise level. This effect of the arrangement in an axial piston machine made in accordance with the invention is explained by the following brief analysis.Given uniform distribution, the spacing of the bores in the cylinder drum is obtained by the formula tzyi = 3600/Zk When resolved according to the number of cylinders, this gives Zk = 360"/t, When this value is introduced into the formula for the fundamental frequency, the result is fk = 360.n/tzy, From this it can be seen that the frequency fk can be changed by varying the spacing.

The principle of altering sound by unequal spacing is already known and applied in the spacing of fan blades in axial or radial blowers but the principle has never been applied in axial piston machines. In the case of axial piston machines, the unequal spacing of the bores has also been found to produce the effect that the restoring or centrifugal forces vary as regards their magnitude and direction and the vibration characteristics vary when the frequency is uneven, and all of these things can be handled better as a result of adoption of said principle.

Claims

1. An axial piston machine with a rotary cylinder drum in which cylinder bores are disposed, a piston braced against a piston guide face being displaceable in each cylinder and each cylinder bore debouching into a respective orifice in the end face of the cylinder drum, wherein, of the several angles formed between the several planes each of which extends through the axis of rotation of the cylinder drum and through the centre or other identifiable location of a respective one of said orifices, the adjoining angles are unequal.

2. An axial piston machine as claimed in Claim 1, wherein, of the series of adjoining angles whose sum is equal to 360 , there is an uneven number of angles, and wherein each pair of adjoining unequal angles makes an angle whose value is twice that of the last angle of said series.

3. An axial piston machine constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

4. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawings.