GB2154799A

GB2154799A - Liquid level indicator

Info

Publication number: GB2154799A
Application number: GB08503251A
Authority: GB
Inventors: Eric Martin Lilley; David John Parker
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1984-02-18
Filing date: 1985-02-08
Publication date: 1985-09-11
Also published as: GB8404355D0; GB8503251D0; GB2154799B

Abstract

A liquid level indicator for a reservoir of a vehicle hydraulic master cylinder includes a float- operated electrical switch mechanism (8) protected by a cap (14) of plastics material having a resilient dome (18) which may be depressed manually to effect testing of a circuit in which the switch is incorporated. The switch mechanism (8) is housed within a compartment (18A) partially defined by the dome (18). The cap is provided with a vent passage (20, 21, 22) which provides communication between the exterior and the interior of the indicator body otherwise than through the compartment (18A). <IMAGE>

Description

SPECIFICATION Liquid level indicator This invention relates to a liquid level indicator, useful for monitoring the level of liquid in a container, such as a supply reservoir of an hydraulic pressure master cylinder for a vehicle clutch or brake actuating system, such indicator including a float-operated electrical switch mechanism operable, when the liquid falls below a predetermined level, to complete an electrical indicator circuit, to which it may be connected in use, and manually operable means for actuating the switch mechanism in order to effect testing of the circuit.

A problem arising in liquid level indicators of the aforesaid general kind, particularly when used in vehicle master cylinder reservoirs, is that it is necessary to provide communication between the interior of the reservoir and atmosphere to permit the liquid level to vary, for example to compensate for friction lining wear, unhindered by pressure differences which would otherwise occur. This requirement, in conventional arrangements, has exposed the switch mechanism to water vapour and other corrosive influences present in the inflow of air.

The cover member is desirably of plastics material having means for securing it in position over the switch mechanism to be actuated manually from the exterior by depression of said resilient portion in order to effect testing of the switch mechanism.

According to the present invention, a liquid level indicator comprises a housing containing a float-operated electrical switch mechanism disposed within a compartment which is sealed against ingress of injurious material from the exterior, a hollow body portion separate from said compartment and being in communication, in use, with a container for the liquid of which the level is to be sensed, the indicator being provided with a vent passage arranged so that it affords direct communication between the exterior and said hollow body portion otherwise than through said compartment.

In one convenient arrangement, the vent passage is defined, at least partially, by a cover member serving to protect the switch mechanism and preferably sealing around said compartment against ingress from the exterior of injurious material. The cover member may conveniently embody a resilient portion extending over the switch mechanism such that the latter may be manually operated from the exterior for circuit testing purposes by depression of the resilient portion.

Conveniently, the cover member is held in position by interengaging complementary formations respectively on the cover and on another part of the indicator, said formations being typically, such that said interengagement may be effected, by snap action between them. In a particularly convenient arrangement, the underside of the cover is provided with a projecting rib defining a closed formation which, when the cover is in position, engages a surface surrounding the switch mechanism to provide a continuous seal resisting ingress of injurious material to said mechanism from the exterior.

The cover member is desirably of plastics material which is not subject, to any significant extent, to degradation by mineral oils, such as engine oils and greases, generally to be found in vehicle maintenance workshops, thereby providing a measure of protection against gradual reduction in the integrity of the cap in use from this cause. This is in contrast to some conventional indicators in which such degradation of the cover results in ingress of dirt and moisture to the switch mechanism, leading to unreliable operation and even jamming of the mechanism, and possible contamination of the reservoir contents.

The invention will now be described, by way of example, with reference to the single accompanying drawing which is a view, in cross section, of one form of the liquid level indicator of the invention suitable for use with the reservoir of a vehicle hydraulic master cylinder.

The liquid level indicator shown in the drawings includes a cap 1 which is internally screw-threaded for screwing engagement with a corresponding screw thread on a neck (not shown) surrounding an opening of an hydraulic fluid reservoir of a vehicle brake or clutch system, the reservoir containing liquid indicated at A. The cap 1 acts to clamp in position on the reservoir a housing of the level indicator, indicated generally at 2, a seal 3 being provided and clamped between a shoulder 4 of the housing and the upper end of the reservoir. The housing has a hollow extension 5 which contains a float 6 connected by a stem 7 to a switch mechanism indicated generally at 8 and including fixed contacts, one of which is illustrated at 9 and a bridging contact 10 carried by an enlarged portion 11 of the stem.Said enlarged portion 11 slides freely within a bore 1 2 of the housing 2 formed in a downwardly projecting hollow boss 2A of the housing. The hollow extension 5 is provided with at least one opening 1 3 to permit ingress of liquid into the extension when the level indicator is in its normal position of use on the reservoir. As will be well understood in the art, the level of the float 6 will be dependent upon the level of liquid A present in the reservoir and the contact 10 will normally be held out of engagement with the fixed contacts 9, only engaging these contacts to provide a warning indication when the level of liquid in the reservoir falls below a predetermined level.The contacts 9 are in electrical communication with respective terminals of which one is illustrated at 1 or, permitting the level indicator to be connected in the electrical circuit of a suitable audible or visual indicator.

The switch mechanism 8 is covered by a separate cap 14, typically of resilient plastics material, and having a peripheral surrounding flange 1 5 in which is formed a groove 1 6 into which may be received, by snap engagement, a complementary dove tail flange 1 7 of the housing 2, the cap thereby being retained in position over the switch mechanism 8. A central portion of the cap directly above the switch mechanism 8 is in the form of a resilient dome 18, of which the lower peripheral extremity terminates in a peripheral projecting rib 1 9 which, when the cap is in its normal position of use as shown, is firmly engaged with an opposed surface 2B of the housing 2 to form an effective seal around the switch mechanism to exclude ingress of injurious materials such as water vapour and grit.

The body 2 and dome 1 8 effectively define a compartment 1 8A housing the switch mechanism.

Manual testing of the electrical indicator circuit of which the switch mechanism forms part, may be effected by depressing the resilient dome 1 8 into contact with the stem part 11, enabling the contacts 9 and 10 to be engaged manually for testing purposes. The use of plastics material for the cap renders the cap largely impervious to the effects of mineral oil and grease to which the dome portion in particular is very likely to be exposed when depressed, for example, by a mechanics contaminated hands in a workshop. The cap 1 4 is also particularly advantageous in providing the sealing rib 1 9 which makes a significant contribution towards minimising the ingress of contaminants to the contacts of the switch mechanism.In this embodiment, the dome 1 8 affords greater resistance to depression than the remainder of the cap affords to lifting away from the body about the flange connection 15, 17.

In order to permit the liquid level in the reservoir to vary unhindered by pressure differences, provision is made for venting the reservoir to atmosphere. By contrast with some conventional arrangements, this is accomplished, in accordance with the invention, by providing a vent passage which communicates with the reservoir interior without passing through the chamber 1 8A containing the switch mechanism thereby minimising exposure of the switch contacts to the inflowing air which may contain corrosive material, such as water vapour.

The vent passage, in the embodiment described, includes a small hole 20 in the flange 1 7 of the housing which establishes communication between the exterior and a space 21 between the cap and body which is sealed from the contacts 9, 10 by the rib 1 9 of the cap 14. Said space communicates in turn with a passage 22 in the body leading to the interior of the indicator housing 2. It will be seen that incoming air is thus directed into the housing 2 and thence, via the extension 5, to the reservoir without passing over the contacts 9 and 10 of the switch mechanism 8. This significantly reduces the exposure of the contacts to the corrosive influence of water vapour and other contaminants carried by the air and longer reliable operation of the switch can be expected.

It is possible to provide a vent passage in alternative locations to that shown in the drawing. For example, a hole may be provided through the cap 14 outside the sealing area defined by the rib 19, or alternatively through the side wall of the indicator body 2 so as to communicate either with the hole or the body interior, the essential requirement being that the inflow of air should not pass over the contacts before entering the interior of the housing.

Claims

1. A liquid level indicator comprising a housing containing a float-operated electrical switch mechanism disposed within a compartment which is sealed against ingress of injurious material from the exterior, a hollow body portion separate from said compartment and being in communication, in use, with a container for the liquid of which the level is to be sensed, the indicator being provided with a vent passage arranged so that it affords direct communication between the exterior and said hollow body portion otherwise than through said compartment.

2. An indicator according to Claim 1 wherein the vent passage is defined, at least partially, by a cover member serving to protect the switch mechanism.

3. An indicator according to Claim 2 wherein the cover member seals around said compartment against ingress from the exterior of injurious material.

4. An indicator according to Claim 2 or Claim 3 wherein the cover member embodies a resilient portion extending over the switch mechanism such that the latter may be manually operated from the exterior for circuit test ing purposes by depression of the resilient portion.

5. An indicator according to any one of Claims 2 to 4 wherein the cover member is held in position by interengaging complementary formations respectively on the cover and on another part of the indicator.

6. An indicator according to Claim 5 wherein said formations are such that said interengagement is effected by snap-action between them.

7. An indicator according to any one of Claims 3 to 6 wherein the underside of the cover is provided with a projecting rib defining a closed formation which, when the cover is in position, engages a surface surrounding the switch mechanism to provide a continuous seal resisting ingress of injurious material to said mechanism from the exterior.

8. An indicator according to Claim 7 wherein said vent passage extends exteriorily of said rib.

9. An indicator according to any one of Claims 2 to 8 wherein the under-surface of the cover is shaped to define part of said vent passage which communicates with another part of the passage formed through a wall of said housing.

10. An indicator according to Claim 9 wherein said passage part defined by the cover communicates with a further passage part extending generally radially through the housing, said another passage part extending generally axially.

11. A liquid level indicator substantially as hereinbefore described with reference to the accompanying drawing.