GB2156435A

GB2156435A - Pressure medium accumulator

Info

Publication number: GB2156435A
Application number: GB08507501A
Authority: GB
Inventors: Heinz Leiber
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1984-03-30
Filing date: 1985-03-22
Publication date: 1985-10-09
Also published as: GB2156435B; GB8507501D0; JPS60220202A

Abstract

A pressure medium accumulator (2) comprises a cylinder (3) which has an accumulator connection port (14) at one end (9) thereof, a separating piston (5) which is displaceable in the cylinder (3) and which separates a pressure medium accumulator chamber (22) from a gas chamber (21), and an internally disposed valve (6). The valve (6) comprises a valve seat (24) a valve element (25) which is movable in the longitudinal direction of the separating piston (5) and which is substantially conical, and a valve closure spring (29). The valve element (25) is pressed against the valve seat (24) by the separating piston (5) by way of the valve closure spring (29) when the separating piston (5) has moved downwardly to a predetermined extent upon emptying of the pressure medium accumulator (2). The valve closure spring (29) enables the valve element (25) to be lifted from the valve seat (24) for the purpose of re-charging tie pressure medium accumulator (2). The valve (6) protects the pressure medium accumulator (2) against loss of gas from the gas chamber (21). <IMAGE>

Description

SPECIFICATION Pressure medium accumulator The invention relates to a pressure medium accumulator. Printed specification EP 0 033 571 Al discloses a pressure medium accumulator comprising a cylinder having an accumulator connection port at one end thereof, a separating piston which is displaceable in the cylinder and isolates a pressure medium acuumulator chamber, connected to the accumulator connection port and located in the cylinder, from a gas chamber containing a gas cushion. A valve is disposed between the pressure medium accumulator chamber and the accumulator port and closes the accumulator connection port in the outlet direction when the contents of the pressure medium accumulator chamber have decreased to a predetermined minimum quantity, which can occur by, for example, switching off an accumulator charging pump and increasing the consumption of pressure medium.A specific quantity of pressure medium thereby remains in the accumulator chamber and reduces the loss of gas along seals of the separating piston. If the pressure in the accumulator connection port increases by, for example, switching on the accumulator charging pump, this valve opens in the first instance in the manner of a one-way valve, and the pressure medium accumulator chamber is thereby subjected to increased pressure, so that the separating piston is raised. The rising separating piston fully opens the valve. The valve has a hollow cylindrical valve seat and a rubber-elastic valve element in the form of a sealing sleeve which is insertable into the said valve seat by means of a stem and which slides along the valve seat and whose sealing lip is directed towards the separating piston.This valve has the disadvantage that its rubber-elastic sealing sleeve becomes worn with frequent insertion and removal and ceases to effect a proper seal, so that pressure medium leaks out of the pressure medium chamber through the closed valve after the accumulator charging pump has been switched off.

This has the disadvantage that gas from the gas cushion finally leaks through between the cylinder and the separating piston. Losses of gas reduce the quantity of the energy which can be stored.

According to the present invention there is provided a pressure medium accumulator comprising a cylinder having an accumulator connection port at or adjacent one end thereof, a separating piston which is displaceable in the cylinder and isolates a pressure medium accumulator chamber, which is located in the cylinder and which is connected to an accumulator connection port, from a gas chamber which is surrounded by the cylinder, and a puppet valve for preventing complete emptying of the pressure medium chamber, said valve comprising a valve element which is displaceable by the separating piston and a valve seat which is disposed at the accumulator connection port end of the cylinder and which forms an axial stop for the valve element, the movable valve element, which abuts against the valve seat when the separating piston is in a predetermined position, being raisable from the valve seat in the opening direction, without displacement of the separating piston, by pressure medium acting upon the movable valve element via the valve seat.

The pressure medium accumulator of the present invention has the advantage that valve wear which would cause leakage is avoided. The valve, of very simple construction, thereby remains fluidtight during the required lifetime of the pressure medium accumulator and maintains its ability to store pressure energy. As a result of the use of this valve, the pressure medium accumulator can be rapidly filled.

In one embodiment of the invention the valve element is movable relative to the separating piston against the force of a valve closure spring which abuts against the separating piston.

In one embodiment of the invention the valve element is secured to a valve stem and is liftable from the valve seat by way of the said stem by means of the separating piston.

Preferably the diameter of the valve seat is from 10% to 20% of the diameter of the separating piston.

Preferably the valve element is of substantially conical construction.

The present invention will be further described by way of example, with reference to the accompanying drawing which is a longitudinal section of a pressure medium accumulator according to the invention.

The pressure medium accumulator 2 comprises a cylinder 3, an accumulator connection piece 4, a separating piston 5 and a valve 6. The cylinder 3 has an end wall 8 at one end 7. The accumulator connection piece 4 is fitted into the opposite end 9 of the cylinder 3. The outer circumference of the accumulator connection piece 4 is cylindrical and incorporates an annular groove 10. A sealing ring 11 is inserted into the annular groove 10 and hermetically seals the cylinder 3 relative to the accumulator connection piece 4. An annular groove 12 is also formed in the end 9. The annular groove 12 accommodates a wire ring 13 against which the accumulator connection piece 4 abuts as soon as pressure prevails in the cylinder 3. A bore 14 extends along the longitudinal axis of the accumulator connection piece 4 and opens into the cylinder 3 to form an accumulator connection port.A widened portion 15 adjoins the bore 14 and is formed in the accumulator connection piece 4 outwardly of the bore 14. A mounting surface 16 protruding beyond the end 9 is adjacent to the widened portion 15. A sealing ring 17 is fitted in the widened portion 15. Screwthreaded bores 18 extend from the mounting surface 16.

The separating piston 5 has a peripheral groove 19 into which a sealing ring 20 is fitted. The sealing ring 20 seals a gas chamber 21, located above the separating piston 5, relative to a pressure medium accumulator chamber 22 located below the separating piston 5. The accumulator connection piece 4 has an end face 23 which is remote from the fastening surface 16 and which forms an axial stop for the separating piston 5.

The valve 6 comprises a valve seat 24 which is located at the transition from the accumulator connection port 14 to the end face 23, and a substantially conical valve element 25 to which a valve element stem 26 is connected. A spring abutment plate 27 is adjoining, and secured to, the valve element stem 26. The spring abutment plate 27 is displaceable against the force of a valve closure spring 29 within a cylindrical recess 28 disposed coaxially in the separating piston 5. In the illustrated embodiment, the separating piston 5 has an annular surface 5a which is directed towards the end face 23 of the accumulator connection piece 4.

The valve element 25 projects from the separating piston 5 and beyond the annular surface 5a.

After the pressure medium accumulator 2 has been assembled, the gas chamber 21 is filled with a gas, such as nitrogen, through an opening (not illustrated) in the end wall 8. This gas forms, in a known manner, a gas cushion which causes the separating piston 5 to move towards the end face 23. The valve closure spring 29 is constructed such that, when the separating piston 5 has been moved to within a predetermined distance from the end face 23, the valve element 25 is pressed against the valve seat 24 with a predetermined force by way of the spring abutment plate 27 and the valve element stem 26. The convolutions of the valve closure spring 29 are then at minimum distances apart.When a hydraulic system (not illustrated), which may be, for example, a vehicle brake system, is put into operation, its accumulator charging pump develops a pressure which lifts the valve element 25 from the valve seat 24 against the action of the valve closure spring 29. Pressure medium thereby flows into the pressure medium chamber 22 and urges the separating piston 5 towards the end wall 8 against the gas cushion.

When the separating piston 5 has been displaced over a short distance, lugs 30 on the piston 5 engage below the spring abutment plate 27 and finally displace the valve element 25 away from the valve seat 24, so that the filling of the pressure accumulator is accelerated. When pressure medium flows out through the accumulator connection port 14 after the accumulator charging pump has been switched off, the gas cushion displaces the separating piston 5 towards the end face 23. The valve element 25 thereby finally comes into contact with the valve seat 24 and seals the latter. By way of example, the valve seat 24 and the valve element 25 are made from a metallic material or a material which has a wear resistance comparable with metallic material. The valve 6 thus has a long working life during which it reliably seals the pressure medium chamber 22.Furthermore, the fluid-tightness of the valve is enhanced if the diameter of the valve seat 24 is in the order of magnitude of from 10% to 20% of the diameter of the separating piston 5. It is thereby possible to maintain permanently a relatively large pressure difference between the pressure medium chamber 22 and the accumulator connection port 14. The leakage of pressure medium through the valve 6 and into the accumulator connection port 14 is avoided. This has the advantage that the minimum quantity of liquid pressure medium within the pressure medium chamber 22 is subjected to a pressure which is substantially equal to the pressure in the gas chamber. The gas thereby remains enclosed in the gas chamber 21, and the ability of the pressure medium accumulator 2 to store pressure is maintained.

It is also pointed out that, although the illustrated valve element is substantially conical, it may be of partspherical configuration adjacent to the valve seat 24. By way of example, the valve seat 24 may be of bell- like configuration, hence ensuring a reliable sealing action in conjunction with the conical valve element 25. Finally a ball may be fitted as a valve element.

These constructions also ensure the tightness in the event of misalignment between the valve seat 24 and the recess 28 or the lugs 30 as a result of inaccuracies in the manufacture of individual parts.

The advantage of the valve 6 resides in the fact that its valve element 25 is applied to the valve seat 24, which acts as a stop for the valve element 25, and is pressed thereagainst by means of the valve closure spring 29. This results in the required fluid-tightness. In contrast to this, the sealing sleeve in the known valve is pushed into the cylindrical bore like a cork in the neck of a bottle, which finally leads to leaks as a result of wear.

Claims

1. A pressure medium accumulator comprising a cylinder having an accumulator connection port at or adjacent one end thereof, a separating piston which is displaceable in the cylinder and isolates a pressure medium accumulator chamber, which is located in the cylinder and which is connected to an accumulator connection port, from a gas chamber which is surrounded by the cylinder, and a puppet valve for preventing complete emptying of the pressure medium chamber, said valve comprising a valve element which is displaceable by the separating piston and a valve seat which is disposed at the accumulator connection port end of the cylinder and which forms an axial stop for the valve element, the movable valve element, which abuts against the valve seat when the separating piston is in a predetermined poistion, being raisable from the valve seat in the opening direction, without displacement of the separating piston, by pressure medium acting upon the movable valve element via the valve seat.

2. A pressure medium accumulator as claimed in claim 1, in which the valve element is movable relative to the separating piston aainst the force of a valve closure spring which abuts against the separating piston.

3. A pressure medium accumulator as claimed in claim 1 or 2, in which the valve element is secured to a valve stem and is raisable from the valve seat by way of the said stem by means of the separating piston.

4. A pressure medium accumulator as claimed in any of claims 1 to 3, in which the diameter of the valve seat is from 10% to 20% of the diameter of the separating piston.

5. A pressure medium accumulator as claimed in claim 4, in which the valve element is of substantially conical construction.

6. A pressure medium accumulator, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.