GB2263139A

GB2263139A - Vacuum pump with pendulum action.

Info

Publication number: GB2263139A
Application number: GB9226351A
Authority: GB
Inventors: Stephen Richard Earle
Original assignee: Wabco Automotive UK Ltd
Current assignee: Wabco Automotive UK Ltd
Priority date: 1991-12-18
Filing date: 1992-12-17
Publication date: 1993-07-14
Anticipated expiration: 2012-12-17
Also published as: GB9126801D0; GB2263139B; GB9226351D0

Abstract

A piston type vacuum pump has a connecting rod 21 fixed to the piston so that the piston rocks in its cylinder bore 12 during reciprocation. Articulation of the piston 14 is accommodated by a seal 15 having a depending sealing lip 17. The lip 17 may act as an outlet valve. The seal 15 may have an outwardly extending support ring (19, Fig. 3) to relieve the sealing lip of piston reaction loads; this both centralizes the piston in the bore and permits the seal to be designed for effective sealing rather than piston support and sealing. <IMAGE>

Description

VACUUM PUMP This invention relates to vacuum pumps and particularly to electrically driven pumps having a piston driven by a crank pin and connecting rod.

Hitherto vacuum pumps have often comprised a piston reciprocal in a bore and having automatic inlet and exhaust valves, the piston may be driven axially by a pushrod and cam, or by a crank pin and connecting rod.

The latter arrangement is suitable where the pump is to be driven by an electric motor, but the arrangement is rather expensive because the connecting rod must be provided with journal bearings at the big and little ends.

According to a first aspect of the present invention there is provided a vacuum pump comprising a body, a bore in the body, a piston reciprocal in the bore, a connecting rod attached to said piston and for connection to rotary drive means, and the piston having a peripheral elastomeric seal in contact with said bore, said piston and connecting rod being fixed against relative arcuate movement.

In such an arrangement the piston rocks in the bore as the big end of the connecting rod rotates about a journal on the rotary drive means; in essence, the piston and connecting rod have a fixed little end, the seal permitting arcuate piston movement whilst maintaining a seal against the wall of said bore. Such a pump has the advantage that the little end is eliminated thus, reducing manufacturing cost and eliminating the need to provide lubrication to the little end bearing.

The piston and connecting rod are preferably formed as a single plastics moulding of for example nylon.

In a preferred embodiment the seal has a continuous substantially radial support portion and a depending limb adjacent the outer end thereof, said limb extending towards the big end of said connecting rod. Preferably the free end of said limb is in sealing contact with the wall of said bore.

In a preferred embodiment said limb extends beyond the underside of said piston. This permits a considerable degree of articulation.

The piston may include a peripheral groove in which said seal is located, the seal land adjacent the top of said piston being of greater diameter than the opposite seal land. The seal may include an outwardly extending circumferential support portion in contact with the wall of said bore and radially aligned with said groove.

The support portion, which preferably has an arcuate form, serves to centralize the piston in the bore and to support the seal during articulation, thereby separating the supporting and sealing functions of the seal. The seal lip can thus be designed to accommodate rocking of the piston and to provide an effective seal, reaction to the piston being provided by the support portion.

The vacuum pump may include the usual inlet and outlet valves which open automatically in response to differential pressures acting thereon. In a preferred embodiment said valves are concentric.

According to another aspect of the invention the outlet valve of the vacuum pump is formed solely by the depending limb of the seal, pressure within the pumping chamber causing said seal to move away from the wall of said bore.

Such a pump has the advantage that the outlet valve is eliminated, the seal serving to seal the piston to the wall of the bore on the suction stroke and to act as a one way valve on the exhaust stroke.

Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example with reference to the accompanying drawings in which: Fig. 1 is an illustrative section through a vacuum pump according to the invention; Fig. 2 illustrates the piston of the pump at its maximum inclination to the axis of the pump bore.

Fig. 3 is an enlarged section through a portion of a piston seal for the pump of Fig. 1; and Fig. 4 is an illustrative section through an alternative vacuum pump according to the invention.

With reference to Figs. 1-3 of the drawings a vacuum pump 10 comprises a body 11 defining a bore 12 closed at one end by a cylinder head 13. Within the bore 12 is a piston 14 reciprocal between the positions shown respectively in dotted and solid outline. The piston carries a continuous seal 15 having a radially extending portion 16 and a depending limb 17 better seen in the enlarged view of Fig.

3 which illustrates the juxtaposition of seal and bore 12.

The depending limb 17 is in sealing contact with the bore 12 at its free end 18. The seal 15 also has a continuous protrusion 19 adjacent the upper side thereof and which guides and supports the seal and piston during reciprocation, as will be further described below.

The piston 14 is solidly connected to a connecting rod 21 or may be moulded as a unit therewith, the connecting rod thus has no little end and relative movement of the piston is not possible. The seal 15 articulates as described below.

The big end of the connecting rod is connected in the usual way to a crank pin mounted on a disc and driven by an electric motor 22.

The cylinder head 13 includes a valve body 23 having a plurality of inlet ports 24 arranged in a circle concentrically within a plurality of outlet ports 25. The inlet ports are closed by a disc valve 26 secured in a central aperture of the valve member as illustrated. The peripheral edge of the disc valve seals against the valve member thus preventing free flow through the ports 24. A similar disc valve 28 closes the outlet ports 25 and is secured between the valve body and the cylinder head as illustrated.

The valve body 23 has an upstanding wall 29 defining an inlet chamber 31 into which opens an inlet pipe 32. An annular outlet chamber 33, defined between the cylinder head and valve body, opens through a series of radial transfer ports 34 into an annular exhaust passage 35; a circular silencer 36 is contained within the exhaust passage 35 as shown.

The upper side of the piston 14 is shaped so as to closely fit the adjacent surface of the valve body and inlet disc valve, thereby to minimise the unpumped volume and increase volumetric efficiency.

In operation the inlet pipe 32 is connected, usually by a hose, to a reservoir. The reservoir may for example be the vacuum chamber of a brake servo.

The electric motor is activated in response to a demand signal generated for example by a sensor in the reservoir. Reciprocation of the piston 14 causes air to be sucked automatically through the inlet ports 24 and expelled through the outlet ports 25 thereby exhausting the reservoir to level at which the demand is satisfied and the motor can be de-activated.

As a consequence of the lack of relative movement between the piston 14 and connected rod 21, the piston rocks in the bore 12 as it reciprocates. The seal limb 17 accommodates such rocking and the protruding portion 19 acts as a bumper to guide and support the piston in the bore.

The rocking angle is a function of the piston stroke and the length of the connecting rod but is typically in the range 8-150. The protruding portion 19 is not intended to provide a seal against the wall of the bore 12. Maximum inclination of the piston 14 in the described embodiment is illustrated in Fig. 2.

The portion 19 ensures that reaction loads on the piston are not taken by the seal limb 17, which limb can thus be designed solely to provide an effective seal at maximum piston inclination.

In an alternative embodiment the outlet path through the valve body and cylinder head is eliminated, pressure in the cylinder causing the depending limb 17 to lift away from the wall of the bore 12 and allow gas to escape through an aperture (not shown) in the body 11. Such a construction has the advantage of eliminating the cylinder head 13, outlet ports 25 and disc spring 28, the valve body being adapted to fix directly to the open end of the cylinder.

Fig. 4 illustrates an alternative embodiment viewed at right angles to the embodiment of Fig. 1; corresponding parts are given the same reference numerals. The outlet is by way of outlet pipe 41, and the crankpin carries a part circular balance weight 42. In this embodiment the protrusion 43 of the seal is in contact with the cylinder wall 12 only at that side of the piston 14 which requires support - the arrangement nevertheless relieves the depending seal lip 44 of the need to resist the majority of the reaction load and allows the lip to be designed to provide an effective seal.

The pumps illustrated in Figs. 1 and 3 show the piston running in a bore defined by the pump body; it would be possible to allow the piston to reciprocate in a liner of the bore thus allowing optimization of bore material and pump body material. The bore could for example be of a low friction PTFE filled polymer, and the pump body of a glass filled polymer for external rigidity and strength.

Claims

CLAIMS:

1. A vacuum pump comprising a body (11), a bore (12) in the body, a piston (14) reciprocal in the bore, and a connecting rod (21) attached to the piston and for connection to rotary drive means, the piston (14) having a peripheral elastomeric seal (15) in contact with said bore, and the piston t14) and connecting rod (21) being fixed against relative arcuate movement.

2. A pump according to claim 1 wherein the piston (14) and connecting rod (21) comprise a single plastics moulding.

3. A pump according to claim 1 or claim 2 wherein said seal (15) has a continuous substantially radially extending support portion (19) and a continuous depending limb (17) extending radially outwardly and toward the big end of said connecting rod (21).

4. A pump according to claim 3 wherein the free end (18) of said limb (17) is in sealing contact with said bore (12).

5. A pump according to claim 3 or claim 4 wherein said limb (17) extends beyond the underside of said piston (14).

6. A pump according to any of claim 3-5 wherein said piston includes a groove to locate said seal (15), the piston land 'adjacent the top of said piston (14) being of greater diameter than the opposite piston land.

7. A pump according to claim 6 wherein said support portion is radially aligned with said groove.

8. A pump according to any of claims 3-7 wherein said depending limb (17) and bore (12) define an outlet valve of said pump

9. A pump substantially as described herein with reference to the accompanying drawings.

9. A pump according to any of claims 3-8 wherein said support portion (19) contacts said bore (12) at maximum inclination of said piston (14).

10. A pump substantially as described herein with reference to the accompanying drawings.

CLAIMS: 1. A vacuum pump comprising a body (11), a bore (12) in the body, a piston (14) reciprocal in the bore, and a connecting rod (21) attached to the piston and for connection to rotary drive means, the piston (14) having a peripheral elastomeric seal (15) in contact with said bore, and the piston (14) and connecting rod (21) being fixed against relative arcuate movement, said seal (15) having a continuous substantially radially extending support portion (19) to resist reaction loads from said bore, and a continuous depending limb (17) extending radially outwardly and toward the big end of said connecting rod (21) to seal said piston in the bore.

3. A pump according to claim 1 or claim 2 wherein the free end (18) of said limb (17) is in sealing contact with said bore (12).

4. A pump according to any preceding claim wherein said limb (17) extends beyond the underside of said piston (14).

5. A pump according to any preceding claim wherein said piston includes a groove to locate said seal (15), the piston land adjacent the top of said piston (14) being of greater diameter than the opposite piston land.

6. A pump according to claim 5 wherein said support portion is radially aligned with said groove.

7. A pump according to any preceding claim wherein said depending limb (17) and bore (12) define an outlet valve of said pump.

8. A pump according to any preceding claim wherein said support portion (19) contacts said bore (12) at maximum inclination of said piston (14).