GB2023718A - Improvements in or relating to a rotary fluid displacement machine - Google Patents

Abstract

To reduce noise in a displacement machine, e.g. a radial or axial piston or gear pump or motor, in which two separate arcuate valve openings 25, 27, connected respectively to the inlet and the outlet of the machine, are alternately swept, in use, by, and have a common interface with, valve orifices each connected to a respective working chamber of the machine, a passage 31, 32 is connected to one of the arcuate openings 27 and opens into the interface upstream of that opening and is swept, in use, by the valve orifices, and an adjustable throttle 33 is provided in that passage to control fluid flow between the passage and the said one opening. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a rotary fluid displacement machine This invention relates to a rotary fluid displacement machine (for use as a motor or pump) particularly a radial piston pump, in which two part annular grooves in a control surface, namely-when the machine is used as a pump-a suction groove connected to the suction connection and a pressure groove connected to the pressure connection, are alternately swept by the valve orifices connected to the compression chambers and at least the pressure groove is preceded by an additional aperture which communicates with the pressure groove by way of a throttle path and is likewise swept by the valve orifices.

In known pumps of this kind, the pressure groove is preceded by a flat throttle groove of triangular cross-section which diverges towards the pressure groove in width as well as depth to result in a wedge-shaped additional aperture. This throttle groove permits pressure equalisation between the compression chamber and the pressure groove before the valve orifice connected to the compression chamber comes into direct communication with the pressure groove. This enables one to reduce impacts in the pumped liquid and noise arising out of pressure pulses.

Noise damping is strongly dependent on the manner in which the pump is operated. In general, one can say that the noise is louder, the higher is the required pressure and the higher is the rotary speed. For a pump with given operating data, if it has been possible to obtain a very low noise level by appropriately dimensioning the throttle groove, the pump is not suitable for other operating conditions because in that case loud noise occurs again.

Even in the case of a series of like pumps intended to operate under the same operating conditions, different noise levels arise as a result of tolerances in the construction of the throttle groove.

A rotary piston pump is also known in which not only the pressure groove is preceded by a wedge-shaped additional aperture but the suction groove is also followed by a wedge-shaped additional aperture. The apices of both throttle grooves are brought so close to each other that in the central position of the valve orifice the associated compression chamber is simultaneously connected to the pressure groove by way of the one throttle groove and to the suction groove by way of the other throttle groove. Instead of the wedge-shaped additional apertures formed by the throttle grooves, it is also possible to provide circular additional apertures which are disposed in the vicinity of the apex of the wedge and are formed by the mouth of a bore perpendicular to the control surface, which bore communicates with the pressure or suction groove by way of a transverse passage.

Such a substitution does not substantially alter the function of the throttle path in relation to the nosie damping.

It is the problem of the invention to modify a rotary fluid displacement machine of the aforementioned kind so that the desired low noise level can be ensured independently of the subsequent operating condition.

This problem is solved according to the invention in that the additional aperture is formed by the mouth of a conduit and an adjustable throttle is provided in this conduit.

The use of a conduit instead of a throttle groove makes it possible to employ an adjustable throttle. With the aid of this adjustable throttle, the throttling resistance of the throttle path can be adapted to the operating conditions under which the pump has to work. This setting can be effected after installation. For variable operation, it is best to do the setting at a high speed and high pressure because in that case there will also be adequate damping at other values. In addition, there are simplifications in production; no particular regard must be had to the tolerances of the throttle path and one and the same pump type can be employed for very different operating conditions.

From a constructional point of view, it is favourable if the conduit comprises a first bore substantially perpendicular to the control surface and a second bore at an angle thereto and the adjustable throttle comprises a screw in a tapped hole coaxial with the first bore.

This construction is particularly easy to bring about.

In one embodiment, it is ensured that the front of the screw carries a pin which has a somewhat smaller diameter than the first bore and engages in said first bore to form an annular throttle gap and that the second bore communicates with the first bore. By turning the screw, the length of the annular throttle gap and thus the throttling resistance can be changed. In another construction, the front of the screw carries a pin which is substantially the same diameter as the internal diameter of the tapped hole and the second bore communicates with the tapped hole. In this case the grooves of the tapped hole which are covered by the pin and which are disposed between the first and second bore serve as a throttle passage which can be very finely adjusted.

To secure against rotation, the screw may have an elastic plug. In addition, the tapped hole can be covered on the outside by a closure. This prevents unintentional or unauthorised intentional adjustment of the throttling resistance.

It is particularly favourable if the mouth of the conduit is offset from the neutral line of the pump towards the pressure groove and is spaced from the suction groove substantially equal to the width of the valve orifice. In this construction, each compression chamber is already separated from the suction groove by a small angle before reaching the maximum volume but is connected to the pressure groove by way of the throttle path so that filling of the remainder already takes place from the pressure side. Subsequently, some pressure fluid is delivered to the pressure groove again by way of the throttle path.

Altogether, one therefore obtains a very gradual pressure rise and little creation of noise.

The present invention also provides a rotary fluid displacement machine in which two separate arcuate valve openings, connected respectively to the inlet and the outlet of the machine, are alternately swept, in use, by, and have a common interface with, valve orifices each connected to a respective working chamber of the machine, wherein a passage is provided which is connected to one of the arcuate openings and the mouth of which opens into the interface upstream of that opening and which is likewise swept, in use, by the valve orifices, and wherein an adjustable throttle is provided in the passage to control fluid flow between the passage and the said one opening.

The present invention further provides a rotary fluid displacement machine comprising an inlet, an outlet, and a valve having two relatively rotatable parts, one part having two separate arcuate valve openings connected respectively to the inlet and the outlet of the machine and lying on a circle, and the other part having a number of circumferentially spaced valve orifices each connected to a respective working chamber of the machine and lying on another circle coaxial with, and of equal radius to the first-mentioned circle, the orifices being co-operable in a common interface with the openings, in use, to control fluid flow between the working chambers of the machine and the inlet and the outlet, wherein a passage is provided in the said one part which is connected to one of the openings and the mouth of which opens into the interface between the openings and which is co-operable, in use, with the said orifices, and wherein an adjustable throttle is provided in the passage to control fluid flow between the passage and the said one opening.

A radial piston pump, constructed in accordance with the invention, will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a cross-section through the radial piston pump; Figure 2 is a partial plan view of a cover plate of the pump; Figure 3 is a part-section through the boundary region between the suction and pressure grooves; Figure 4 is a section through an adjustable throttle, and Figure 5 is a section through another adjustable throttle.

Referring to the accompanying drawings, Fig. 1 shows a housing or track carrier 1 having a first cover plate 2 with a sleeve bearing 3, a spacer or intermediate ring 4 and a second cover plate 5 with a ball bearing unit 6. The parts 2, 4 and 5 are held together by bolts 7. A motor-driven drive shaft 8 is mounted in the sleeve bearing 3 and in the ball bearing 6. By way of a groove and key connection 9, the shaft 8 is connected for rotation with a piston carrier 10, a valve plate 11 and a relief plate 1 2.. The piston carrier 10 is circumscribed by a track ring or carrier 14 which comprises a track surface 1 3 and the eccentricity of which is adjustable (by means not shown) in relation to the piston carrier 10.

The piston carrier 10 comprises a number of radially extending cylinders 1 5 in each of which a piston 1 6 is displaceable radially.

Each piston 1 6 is supported on the track 1 3 by a respective articulated slide shoe 1 7. A compression chamber 1 8 is formed in each cylinder 1 5. These chambers are bounded on both sides of the carrier 10 by a respective pressure ring 1 9 or 20 which, under pump pressure, presses the valve plate 11 against a control surface 21 of the cover plate 2 and the relief plate 1 2 against an abutment surface 22 of the cover plate 5.

Circumferentially equi-spaced axial valve orifices 23 arranged on a circle and each associated with a respective compression chamber 1 8 are provided in the valve plate 11. Correspondingly orifices 24 are provided in the relief plate 1 2. Each valve orifice 23 cooperates, in operation of the pump, alternately with a C-shaped suction groove 25, which is in the cover plate 2 and which is connected to an inlet (suction) connection 26 (see Fig. 3), and a C-shaped pressure groove 27, which is also in the plate 2 and which is connected to an outlet (pressure) connection 28. The grooves 25 and 27 are arcuate and lie on a circle which is coaxial with and of equal radius to the valve orifice circle.

Additional apertures 29 and 30 are provided in the plate 2 between the ends of the suction and pressure grooves. These apertures are formed by the mouth of a first bore 31 (see Fig. 3) which, together with a second oblique bore 32, forms a conduit containing an adjustable throttle 33. The latter comprises a screw 34 in a tapped hole 35 and has the construction shown in Fig. 4. The tapped hole 35 is covered at the top by a closure in the form of a screw 36.

Fig. 4 shows that the leading end of the screw 34 carries a pin 37 of which the external diameter is equal to the smallest internal diameter of the tapped hole 35, and that the second bore 32 opens into the tapped hole 35. Consequently there is pro vided between the second bore 32 and the lower end of the pin 37 a throttle passage 38 formed by a length of the groove or thread of the tapped hole 35 that has been preset by turning the screw 34. An elastic plug 39 preferably of plastics material such as polyamide is inserted in a transverse hole of the screw 34 and secures the screw in its preset position.

In the alternative throttle arrangement shown in Fig. 5, the leading end of the screw 1 34 carries a pin 1 37 which is somewhat smaller in diameter than the first bore 131.

Consequently an annular throttle gap 1 38 remains between the two parts into which the second bore 1 32 also opens. The length of the annular throttle gap can be altered by turning the screw 1 34.

As shown in Fig. 2, the position of the additional aperture 29 (and also of the additional aperture 30) is so selected that when a given valve orifice 23 is moved in the direction of the arrow V, it reaches the additional aperture 29 at the instant at which it leaves the suction groove 29. At that instant, the compression chamber 1 8 is not at its maximum volume; it reaches that condition when the orifice 23 has turned through an angle e to bring the centre of that orifice onto the neutral line of the pump.Consequently, postfilling of the compression chamber 1 8 from the pressure groove 27 takes place by way of the adjustable throttle 33 whilst the orifice 23 is turned through the angle . Consequently, a premature and gradual build-up of pressure occurs in the compression chamber 1 8. Connection of the valve orifice 23 to the pressure groove 27, by means of the bores 31 and 32, only occurs as the orifice 23 is turned through an angle y, flow first of all taking place from the groove 27 to the chamber 1 8 (during the angular movement ) and then from the chamber 18 to the groove 1 7. The build-up of pressure and thus the reduction of noise can be optimised by setting the adjustable throttle 33.

By supplying fluid under pressure to one of the ports 26 or 28 the machine can be used as a motor, rather than as a pump as described above, to drive the shaft 8.

The machine described and illustrated is of the radial piston type to which the invention finds special application. However, the invention is not limited to such a machine and can be used for rotary fluid displacement machines of various types, for example axial piston pumps or motors, or gear type pumps or motors (in particular, a fixed-axes gerotor type, that is to say, where the rotor and stator rotate about a respective fixed axis, the two axes being parallel) or any such machine which requires a commutator valve having two relatively rotatable valve members with co-operable valve orifices for controlling fluid flow between the working chambers of the machine and the inlet and outlet of the machine.

Claims (11)

1. A rotary fluid displacement machine in which two separate arcuate valve openings, connected respectively to the inlet and the outlet of the machine, are alternately swept, in use, by, and have a common interface with, valve orifices each connected to a respective working chamber of the machine, wherein a passage is provided which is connected to one of the arcuate openings and the mouth of which opens into the interface upstream of that opening and which is likewise swept, in use, by the valve orifices, and wherein an adjustable throttle is provided in that passage to control fluid flow between the passage and the said one opening.

2. A rotary fluid displacement machine comprising an inlet, an outlet, and a valve having two relatively rotatable parts, one part having two separate arcuate valve openings connected respectively to the inlet and the outlet of the machine and lying on a circle, and the other part having a number of circumferentially spaced valve orifices each connected to a respective working chamber of the machine and lying on another circle coaxial with, and of equal radius to the first-mentioned circle, the orifices being co-operable in a common interface with the openings, in use, to control fluid flow between the working chambers of the machine and the inlet and the outlet, wherein a passage is provided in the said one part which is connected to one of the openings and the mouth of which opens into the interface between the openings and which is co-operable, in use, with the said orifices, and wherein an adjustable throttle is provided in the passage to control fluid flow between the passage and the said one opening.

3. A machine as claimed in claim 1 or claim 2, in which the passage comprises a bore substantially perpendicular to the interface and another bore lying at an angle to the first-mentioned bore, and in which the adjustable throttle comprises a screw in a tapped hole which is coaxial with the first-mentioned bore.

4. A machine as claimed in claim 3, in which the leading end of the screw carries a pin which has a somewhat smaller diameter than the first-mentioned bore and is arranged in that bore to form an annular throttle gap, and in which the said other bore communicates with the first-mentioned bore.

5. A machine as claimed in claim 3, in which the leading end of the screw carries a pin of substantially the same diameter as the internal diameter of the tapped hole and in which the said other bore communicates with the tapped hole.

6. A machine as claimed in any one of claims 3 to 5, in which the screw has a resilient plug to secure it against rotation in the tapped hole.

7. A machine as claimed in any one of claims 3 to 6, in which that end of the tapped hole remote from the first-mentioned bore is provided with a closure member.

8. A machine as claimed in any one of claims 1 to 7, in which the mouth of the passage is offset from the neutral line of the machine towards the said one opening and is spaced from the other opening by a distance substantially equal to the width of a valve orifice.

9. A machine as claimed in any one of claims 1 to 8, in which the machine is a radial piston machine.

1 0. A machine as claimed in any one of claims 1 to 8, in which the machine is an axial piston machine.

11. A machine as claimed in any one of claims 1 to 10, in which the machine is a pump.

1 2. A reciprocating piston machine substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.