GB2310256A

GB2310256A - Noise reduction of radial piston pumps

Info

Publication number: GB2310256A
Application number: GB9701671A
Authority: GB
Inventors: Michael Reichenmiller
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1996-02-16
Filing date: 1997-01-28
Publication date: 1997-08-20
Anticipated expiration: 2017-01-28
Also published as: GB9701671D0; FR2745041B1; FR2745041A1; DE19605781A1; DE19605781B4; GB2310256B

Description

RADIAL PISTON PUMP 2310256 The present invention relates to a radial

piston pump having a plurality of pistons, which are moved back and forth in cylinder bores in a pump body and driven by an eccentric disposed on a drive shaft mounted on front and rear bearings. The pressure chambers of the pistons are connected by associated outlet valves to a common collecting chamber leading to an outlet.

A radial piston pump of this general type is known from DE 3827726. However, this pump is excessively noisy while in operation. The main cause of this noise is the bearings, the outlet valves and the pistons. The bearing noises, for example, because of the unilateral overhung belt load and the unfavourable application of force inside the bearing clearance represent a particular noise source. The outlet valves produce hammer blows on their seats which are difficult to absorb and finally the pistons also play a part in causing noise, which increases above all when their piston pressure chamber is partially filled.

It is an object of the invention to reduce noise levels so that the pump may be used in vehicles which have a high comfort requirement requiring low noise emissions.

According to the invention, there is provided a radial piston pump comprising a pump body with a plurality of - 2 cylinder bores in which pistons are driven by an eccentric disposed on a drive shaft supported in a front and rear bearing, each piston having a pressure chamber connected by an outlet valve to a common collecting chamber in the form of an annular absorbing device which surrounds the front bearing of the drive shaft, the belt pulley being pot-shaped and enclosing the outlet valves and the pistons.

With the pump of the present invention in which the collecting chamber is in the form of an annular absorbing device which surrounds the front bearing of the drive shaft in such a way that, given an appropriate oil pressure. the bearing clearance may be virtually eliminated. bearing clearance becomes "narrower" and the pump operates more quietly in said range. According to a further feature, the pot- shaped belt pulley is fitted over and around the outlet valves and the pistons so these usual noise sources operate within a soundabsorbing bell. According to a preferred feature of the invention, the belt plane lies approximately in the piston plane so that a uniform and advantageous apportioning of the bearing forces over short lengths is achieved. The bearing forces are uniformly directed without an indifferent load upon the rear shaft bearing. The rear shaft end is prevented from wobbling. Said measure additionally contributes towards smooth operation Thus, in the event of a high belt load the 3 - of the bearings.

The sound-absorbing measures may be further intensified by coating the inside of the pot-shaped belt pulley with a sound-absorbing layer. Preferably, the pulley has a hub with bores therein and its inner end faces have guide blades thereon so a directed air flow is achieved inside the pot-shaped belt pulley. It is therefore possible to achieve improved removal of air from the "hot" housing parts with the outlet valves and the pistons.

Finally, according to a further feature of the invention, a power control valve is provided which may be assembled with the radial piston pump and interrupts the connection between an oil supply tank and the pump. The power control valve controls the pump on the inlet side in that it decreases the intake cross section and reduces the power input when no further oil is required so noise levels can be further reduced.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section through a radial 25 piston pump; Figure 2 is a section along the line II-II in Figure 1 but omitting belt pulley, housing and screw plugs; and Figure 3 is a partial section of the power control valve 4 - used in the radial piston pump shown in Figures 1 and 2.

is The radial piston pump of Figure 1 comprises a pump body 1 in which, for example, six pistons 2 are arranged. Springs 3 hold the pistons 2 against eccentric 4. Screw plugs 5 close of f the pressure chambers 6 and serve as abutments f or the springs 3. The eccentric 4 rotates with a drive shaft 7 which is supported in a front bearing 8 and a rear bearing 10. Associated with each piston 2 is a corresponding outlet valve 11 having a ball 12 as its closure element. The valves 11 are screwed in the manner of cartridges into bores provided in the pump body 1. Pressure channels 13 lead from the pressure chambers 6 of the pistons to the outlet valves 11. According to a feature of the invention, a collecting chamber in the form of an annular absorbing chamber 14 is formed adjacent the outlet side of the outlet valves 11. In use, the outlet valves 11 are under pressure in the annular absorbing chamber 14 so their balls 12 normally rest sealingly against their seats. The annular absorbing chamber 14 will be described in more detail shortly. The pistons 2 have inlet openings 15 which, during the intake stroke, dip into an oil-filled eccentric chamber 16 which is connected to a tank inlet (not shown). A cover 17 is connected to the pump body 1 and is provided with a consumer connection 18, which lies in the same place as the tank inlet. By virtue of their alternating stroke movements, the pistons 2 via the - 5 pressure channels 13 force oil successively towards the respective outlet valves 11 opening into the annular absorbing chamber 14.

A pot-shaped belt pulley 20 is attached to the drive shaft 7 and surrounds the radial piston pump to enclose the outlet valves 11 and the plane 2A containing the pistons 2. As a result, any noise generated by the radial piston pump is extensively contained within the pulley 20. Where necessary, an inside surface 21 of the bell-shaped belt pulley 20 may be coated with a soundabsorbing layer (e.g. sprayed-on plastic material). An inner reinforcing member 21A which can be provided with guide blades 22 can also be mounted on the pulley 20 and additional bores 24 may be provided in hub 23. A tangential inflow of cooling air, which sweeps past the pump body 1, is used for heat removal. The part of the pump body 1 containing the annular absorbing chamber 14 surrounds and abuts the front bearing 8 so that, in the event of higher pressure, a portion 25 of the pump body 1 is forced against said bearing thereby reducing any clearance arising in the front bearing 8 as a result of the belt load. The effect achieved is therefore a reduction in running noises.

It is advantageous, according to Figure 3, to combine the radial piston pump with an electrically operable power control valve 26 which controls the power dependent on consumer demand. The power control valve 26 has a piston 27 which controls the flow through control bore 28 to the PUMP. For improved noise reduction, the valve is designed in such a way that the control piston 27 blocks the control bore 28 in its de-energized state but leakage oil flow is maintained for lubrication purposes.

7

Claims

1. A radial piston pump comprising a pump body with a plurality of cylinder bores therein in which pistons are driven by an eccentric disposed on a drive shaft supported in a f ront and rear bearing, each piston having a pressure chamber connected by an outlet valve to a common collecting chamber which surrounds the front bearing of the drive shaft, the belt pulley being potshaped and enclosing the outlet valves and the pistons.

2. A pump according to claim 1 wherein the belt plane lies approximately in the same plane as that containing the pistons.

3. A pump according to claim 1 or claim 2 wherein the belt pulley has guide blades on its inside surface and a hub provided with bores.

4. A pump according to any preceding claim wherein the inside of the potshaped belt pulley is coated with a sound-absorbing layer.

5. A pump according to any preceding claim further comprising a power control valve which in its deenergized state, separates the pump from an oil supply tank except for a small lubricating oil flow.

6. A radial piston pump substantially as herein described with reference to the accompanying drawings.