GB2249588A

GB2249588A - External axis rotary piston blower

Info

Publication number: GB2249588A
Application number: GB9121740A
Authority: GB
Inventors: Wolfgang Sohler; Rainer Linsenmeyer
Original assignee: Wankel GmbH
Current assignee: Wankel GmbH
Priority date: 1990-10-30
Filing date: 1991-10-14
Publication date: 1992-05-13
Anticipated expiration: 2011-10-14
Also published as: DE4034465A1; GB9121740D0; GB2249588B; JPH04265487A; FR2668549A1

Abstract

An external-axis rotary piston blower is provided with two mutually intersecting cylindrical peripheral running surfaces (6) and pistons (7, 8) with running surfaces that are concentric with their axes and which engage their peripheral running surface and axially concentric cylindrical surfaces of smaller radius running against the respective opposing piston. The pistons (7, 8) are radially split in the middle and the two axially end-to-end portions (9, 10, 11, 12) so formed are displaced with respect to one another by 25 DEG to 45 DEG to reduce the overall intake and delivery noise, the displacement being clockwise in one piston and in the opposite sense in the opposing piston. <IMAGE>

Description

2249538 1 EXTERNAL AXIS ROTARY PISTON BLOWER This invention relates to an

external-axis rotary piston blower of the kind comprising a housing enclosing a cavity defined by two intersecting hollow cylinders forming peripheral running surfaces and side walls extending perpendicular to them, the housing having in the region of the intersections of the cylindrical surfaces mutually opposed inlet and delivery ports for the working medium, and being axially traversed by two shafts mounted in the side walls, with each shaft carrying a two-vane piston, the pistons being interengaging and rotating at the same speed in opposite directions, the vanes of each piston being defined by cylindrical surface portions concentric with the axis of its shaft, the surface portions running on the one hand on the peripheral running surfaces and on the other hand on cylindrical surfaces of smaller radius concentric with the axis of the opposing piston, transition surfaces being provided between these cylindrical surfaces, comprising two interengaging surfaces bent back outwards to form a rolling curve.

Such blowers serve to deliver gaseous media with a large throughput and minimal pressure rise, preferably as superchargers for internal combustion engines. They are described in detail in DE A 35 19 170.

Whilst blowers of this type show better performance than other types of blower, they suffer from a noise penalty which is regarded as a drawback in their use as a supercharger for vehicle engines. The noise is generated in the intake and especially in the delivery port by the sudden impact-like discharge on the opening and closing of the pressure chambers by the 2 trailing edge of the piston vane as well as by the reverse flow of compressed gas in the space formed by the retreating vane of the counter- piston. For _ the reduction or damping of the noise generated hitherto only expensive sound insulations or buffer spaces have been considered, for which there is generally insufficient space in vehicle engines.

Patent Specification A B 261 792 describes a piston with offset axial portions, which comprises several portions angularly displaced in steps to form a screw compressor with an intake opening at one axial end of the housing and a delivery opening at the other. The individual discs are mutually sealed off from one another by their offset in such a way that their charge is transferred respectively from the chamber on the pressure side on the preceding disc into that of the following disc, the discs being progressively smaller and accordingly the chamber volumes being progressively reduced. Similar proposals are contained in DE A 25 34 22 and OS B 3 844 695 and 40 33 708. In none of these cases does the offsetting of the parts of the piston serve f or damping the noise but solely for achieving a screw compressor effect. The reference in A B 261 792 to a continuous flow of the emerging gas., and a gentle manner of operation, refers simply to the characteristics of the screw compressor. Indeed the compressor disclosed in A B 261 792 suffers from an increased level of noise generation on account of its delivery flow being under increased pressure.

The aim of the present invention is to reduce the maximum noise generated in blowers of the kind set forth, using simple means and without taking up extra space.

1 3 According to the present invention anexternal axis rotary piston blower is set forth in which each piston is split by a radial plane into two parts of similar construction. The two parts of one piston being angularly offset by an angle between 250 and 450 about the axis of rotation of its shaft, and the two parts of the other piston being angularly offset in the opposite sense by the same angle about the axis of rotation of its shaft.

The offset of the piston portions solves the problem, as it results in a more even noise output.

An embodiment of the invention is further described by way of example with reference to the accompanying drawings, in which Fig.1 is a radial section through the axial centre of a blower in accordance with the invention and showing the pistons unsectioned; and Fig.2 shows oscilloscope diagrams of sound level measurements over one rotation of the pistons of a machine according to the invention and in particular at a) that of the individual piston halves and at b) the actual resulting curve.

Fig. 1 shows a blower with a housing 1, a peripheral wall 2 of the housing and a rear side wall 3. An intake 4 f or the gaseous medium and a delivery port 5 are provided on the lines of intersection of the two cylindrical surf aces which form the peripheral running surfaces 6 for the first and second pistons 7 and 8 respectively. The major part of the flanks of the two 4 pistons 7 and 8 overlap with the intake and delivery ports during the blowing portions of each cycle. The pistons 7 and 8 are of the same construction, and each comprises a upper portion 9 and 11 respectively and a bottom portion 10 and 12 respectively. The portions are offset with respect to one another about their common axis by 35', the upper portion 9 and 11 forming the leading portion in each case. The offset in each of the two pistons occurs in the opposite rotational sense, i.e. in the second piston 8 the lower portion 12 is offset with respect to the upper portion 11 in a clockwise direction, whereas in the first piston 7 the lower portion 10 is offset with respect to the upper portion 9 in a counterclockwise sense. The portion 9, 10, 11, 12 of the pistons are made by extrusion from aluminium and are hollow in order to achieve maximum weight reduction and they must accordingly be covered over at the step points 13, 14 between the trailing edges (visible in the drawing) and 15, 16 between the leading edges (not visible in the drawing).

The blower operates in the conventional manner.

The performance of this arrangement in operation is as follows: in Figure 2a the continuous curve indicates the sound vibrations generated by the one piston half, and the broken-line curve those generated by the other piston half, which is displaced through 351. The regions of greatest amplitude arise, thanks to this offset, in opposition to one another so that the mean value shown in Figure 2b is a substantially smoother and more even curve.

The angle through which the respective halves (9,10, 11,12) of the pistons (7,8) are offset with respect to one another can, according to the dimensions of the blower, be greater or-smaller and lie between 25" and 45'. The angular offset should however be set so that the maxima of the noise curves (corresponding to Figure 2a) for the one half (9,11) of the pistons (7,8) lie exactly opposite the minima from the other piston halves (10,12), as indicated at 17 in Figure 2a. The reference numeral 18 in Figure 2b indicates the reduced value of the sound vibrations through using the arrangement in accordance with the invention.

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Claims

1. An external-axis rotary piston blower, comprising a housing enclosing a cavity defined by two intersecting hollow cylinders forming peripheral running surfaces and side walls extending perpendicular to them, the housing having in the region of the intersections of the cylindrical surfaces mutually opposed inlet and delivery ports for the working medium, and being axially traversed by two shafts mounted in the side walls, with each shaft carrying a two-vane piston, the pistons being interengaging and rotating at the same speed in opposite directions, the vanes of each piston being defined by cylindrical surface portions concentric with the axis of its shaft, the surface portions running on the one hand on the peripheral running surfaces and on the other hand on cylindrical surfaces of smaller radius concentric with the axis of the opposing piston, transition surfaces being provided between these cylindrical surfaces, comprising two interengaging surfaces bent back outwards to form a rolling curve, each piston being split by a radial plane into two portions of similar construction, with the two portions of one piston being angularly offset by an angle between 250 and 450 about the axis of rotation of its shaft, and the two portions of the other piston being angularly offset in the opposite sense by the same angle about the axis of rotation of its shaft.

2. A rotary piston blower according to Claim 1 in which the noise maxima generated by the one half of the piston coincides in time with the occurrence of the noise minima produced by the other half of the respective piston.

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3. A rotary piston blower according to Claim 1 in which the angle of offset between the piston portions is 35.

4. An external axis rotary piston blower substantially as described herein with reference to, and as illustrated by the accompanying drawings.

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