GB2114681A

GB2114681A - Reciprocating vacuum pump

Info

Publication number: GB2114681A
Application number: GB08303057A
Authority: GB
Inventors: John S Thistleton
Original assignee: Clayton Dewandre Co Ltd
Current assignee: Wabco Automotive UK Ltd
Priority date: 1982-02-05
Filing date: 1983-02-04
Publication date: 1983-08-24
Also published as: GB8303057D0; GB2114681B

Abstract

A reciprocating vacuum pump in which a lubricant flow path 37 is provided to communicate via one or more inlets in the cylinder wall with the clearance between the piston 16 and the cylinder wall throughout the piston stroke. The piston is sealed by lubricant drawn into the clearance as the piston works in the cylinder. In a double acting pump at least one of the exhaust valves 51 communicates with a reservoir 30 for the lubricant so as to recycle to the reservoir lubricant entering the working volume associated with that exhaust valve. Preferably the lubricant reservoir incorporates an overflow device 34 maintaining a constant head of lubricant above the one or more inlets 37 to the cylinder. <IMAGE>

Description

SPECIFICATION Reciprocating vacuum pump This invention relates to a reciprocating vacuum pump.

Many such pumps are known but faced with changing technical requirements and escalating material and labour costs efforts are constantly being made to improve the ease and economy of manufacture with at least no adverse effect on performance and efficiency. Normally, the piston is sealed by a PTFE seal which is expensive and, more significantly tends to generate heat which can in turn lead to greater friction in the pump.

In accordance with the present invention we propose a reciprocating vacuum pump comprising a piston working in a cylinder and a lubricant flowpath communicating via one or more inlets in the cylinder wall, with the clearance between the piston and the cylinder wall throughout the piston stroke, the piston being sealed by lubricant drawn into the clearance as the piston works in the cylinder. The lubricant, preferably, oil, is drawn into the clearance by virtue of the suction generated in the cylinder but this may be assisted, for example, by capillary action and/or by the head of oil available.

The one or more oil inlets in the cylinder wall communicate with the clearance, preferably throughout the piston stroke, these inlets being connected to a reservoir which may be supplied with oil from an engine with which the pump is associated. By controlling the head of oil in the reservoir, for example by means of a simple overflow, a consistent supply of oil can be ensured. It is preferred that the oil inlet or inlets to the cylinder be disposed at a level slightly below the maximum head of oil in the reservoir.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is a cross-section of a double-acting piston vacuum pump.

The pump housing 10 defines a cylinder 12 which is closed at one end by a pressed cover 14 and in which works a piston 1 6 having a piston rod 18 slidable and sealingly mounted in a bore 20 communicating between the cylinder 12 and a hollow extension 22. Springs 24 biasing the piston toward the position shown are disposed around the piston rod 1 8 and act between a retaining disc 26 carried by the rod 18, and the housing 10.

At its free end, the extension 22 has a flange 28 by which the pump can be mounted upon a vertical surface of the engine such that the piston is driven by a cam lobe (not shown) acting directly or via an intermediate link upon the piston rod 1 8.

Line X-X indicates the horizontal when the pump is mounted in position ready for use.

Leading from the bottom of the hollow extension is a drilling 30 which is closed at the other end by a plug 32 or the like to provide a reservoir for engine lubricant draining, under gravity into the housing. The level of oil in the reservoir is determined by an overflow or weir in the form of a drilling 34 communicating via a flexible pipe, with the engine sump (not shown).

For the bottom of the reservoir 30, another drilling 36 leads to the cylinder 12 and opens into the cylinder via an inlet orifice 37 at a level slightly below the maximum level (i.e. overflow level) of oil in the reservoir, and approximately midway along the cylinder.

The orifice 37 is positioned such that throughout the piston stroke it is always covered by the piston, including the effect of tolerances - which alter the piston position in the bore axially.

Beside the cylinder 12 is a chamber 38 having an inlet port 40 in communication with a vacuum reservoir (not shown). This chamber 38 communicates via a spring loaded disc valve 39 and a lateral drilling 42, with the cylinder 12, on one side 43 of the piston 1 6. The inlet port 40 also communicates with the space on the other side 45 of the piston via a drilling 44, and a second inlet chamber 46 containing another spring loaded disc valve 47.

The cover 14 is formed with a recess 48 establishing a connection between the cylinder space 43 and a first outlet or discharge chamber 49 via a spring loaded disc valve 51. Drilling 34 opens into the chamber 49 providing a flowpath for discharging air to the engine sump.

Another discharge flowpath is provided from the cylinder space 45 via a spring loaded disc valve 53 in a second outlet chamber 50, drillirig 30, and overflow drilling 34.

In operation, therefore the pump is double acting. As the piston moves back and forth within the cylinder 12, valves 39, and 47 admit air from the vacuum reservoir which is then expelled through the valves 53 and 51 and the ensuing discharge flowpaths.

The piston 1 6 is hollow and therefore light in weight, and is cheap to manufacture. It comprises a cup-like pressing 54 which is secured for example by brazing, to the piston rod 1 8 and closed by a sealing cover 55 having an interference fit therein. The cover 55 is pressed into the pressing 54 to accurately set the length of the piston, which dimension affects the clearance volume, and thus, the efficiency of the pump. After insertion of the cover 55 the piston is ground to the desired outside diameter, inserted in the cylinder and the cover 1 4 subsequently crimped in position.

Around the circumference of the piston 16, approximately in the middle of the working piston "skirt" is formed a groove 52 which serves to distribute oil around the piston, this oil being drawn into the clearance between the piston and the cylinder wall, through the orifice 37 by virtue of the suction generated during movement of the piston 1 6. The oil serves both to seal and to lubricate the piston. A consistent supply is ensured by the overflow drilling 34 which maintains and limits the head of oil stored in the reservoir with varying rates of gravity oil feed and which also retains sufficient oil to seal the orifice 37 when the oil feed is reduced to zero for short periods.

Since the second outlet discharge chamber 50 communicates with the drilling 30 above the oil reservoir, oil admitted to the piston space 45 is returned to the reservoir and recycled. It will be understood that this may be extended also to recycle oil from the space 43 but in the illustrated embodiment oil from this space is discharged via valve 51, to the engine sump.

Claims

1. A reciprocating vacuum pump comprising a piston working in a cylinder and a lubricant flowpath communicating via one or more inlets in the cylinder wall, with the clearance between the piston and the cylinder wall throughout the piston stroke, the piston being sealed by lubricant drawn into the clearance as the piston works in the cylinder.

2. A pump according to claim 1 and comprising a peripherai groove around the piston.

3. A pump according to claim 1 or claim 2 and which is double acting having inlet and exhaust valves associated with each of the working volumes on opposite sides of the piston, wherein at least one of the exhaust valves is in communication with a lubricant reservoir for recycling to the reservoir lubricant entering the working volume.

4. A pump according to claim 3 which is mounted on an engine, wherein the pump is fed with lubricant from the engine and wherein the other exhaust valve is connected for discharge into the engine sump.

5. A pump according to any one of the preceding claims wherein the lubricant flowpath is supplied from a reservoir incorporating an overflow device maintaining a constant head of lubricant above the one or more inlets to the cylinder.

6. A reciprocating vacuum pump constructed and arrange substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.