GB2302948A

GB2302948A - Brake fluid tester

Info

Publication number: GB2302948A
Application number: GB9513372A
Authority: GB
Inventors: Michael Edward Brown
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-06-30
Filing date: 1995-06-30
Publication date: 1997-02-05
Anticipated expiration: 2015-06-30
Also published as: GB2302948B; GB9513372D0

Abstract

A capacitive brake fluid water content tester comprises elongate test 6 and reference chambers 10 in thermal communication. When the probe is dipped into the brake fluid, the uncontaminated reference fluid in the sealed chamber 10 and the brake fluid which fills the open test chamber 6 rapidly assume a common temperature, enabling the temperature of the brake fluid under test to be taken into account when comparing the electrical properties of the test and reference fluids. A ready, pass, or fail indication is given by a three colour LED (34, figure 4) or alternatively by a digital or graphical display. The tester may be powered by an internal battery (38, figure 4) or by the vehicle battery.

Description

ANALYSER FOR LIOUIDS DESCRIPTION This invention relates to an analyser for liquids, particularly for analysing the hydraulic brake fluids used in the automotive industry.

Such liquids are Hygroscopic, i.e. they are capable of absorbing water from the atmosphere. This has the effect of reducing the boiling point of the liquid enabling the liquid to evaporate more easily in heavy use within a braking system thus activated effecting the efficiency of the system.

The boiling point of the liquid has a clear relationship to the dielectric properties of the liquid at a given temperature but the dielectric properties of the liquid change with temperature to such a degree that previous devices which measure dielectric properties are inherently inaccurate because they can not take account of this phenomenon.

An object of the invention is to provide an analyser which is accurate in that it tests the dielectric properties of the liquid and also takes into account the temperature of the liquid at which the test takes place.

According to the invention there is provided an analyser for liquids comprising a probe portion and a body portion connected to the probe portion. the probe portion comprising a pair of sampling electrodes and a reference electrode arrangement, the pair of sampling electrodes being housed in an elongate chamber which is open at the free end of the probe portion and is also vented at some distance from such free end so as to allow liquid to be tested to enter the chamber when the probe portion is dipped into the liquid, and the reference electrode arrangement comprising at least one pair of reference electrodes housed in a closed elongate chamber containing a sealed quantity of the reference liquid in its uncontaminated form, the chambers being in close thermallyexchanging relationship so that when the probe portion is dipped into the liquid to be tested the liquid which has entered the open chamber and the sealed quantity of liquid rapidly assume the same temperature, and the body portion containing circuitry and carrying an indicating device to exhibit information to the user, the circuitry being connected to the electrodes and designed for comparison between the signals received from the respective pairs of electrodes and for interpreting and directing the result of this comparison to the indicating device for exhibition thereby.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a front elevation of an analyser according to the invention; Fig. 2 is an elevation of the analyser turned through 45" and partly in section; Fig. 3 is a pictorial view of the analyser; Fig. 4 is a section of the analyser on one medial plane: and Fig. 5 is a section of the analyser on the other medial plane.

In the drawings there is a compact, self-contained analyser designed for easy use with most motor vehicles. The analyser comprises a probe portion 1 and a body portion 2 connected to the probe portion 1. In this embodiment the probe portion 1 forms an assembly with and extends from the body portion 2. The probe portion 1 compnses an elongate probe member 3 having an oblong external cross-section so that it resembles a blade. The probe member 3 is integral with and extends from the mount 4 which is square in cross-section and larger in transverse dimensions than the probe member 3.

The probe portion 2 also comprises a pair of sampling electrodes 5 and a reference electrode arrangement. The pair of sampling electrodes 5 is housed in an elongate chamber 6 with an insulating spacer 7 between the individual electrodes. The chamber 6 is open at the free end 8 of the probe portion 1 and is also vented at 9 some distance from the free end 8. In this embodiment the reference electrode arrangement consists of a single pair of reference electrodes 10 housed in a closed elongate chamber 11 with an insulating spacer 12 between the individual electrodes. The chamber 11 contains a sealed quantity of the reference liquid in its uncontaminated form. The two chambers 6 and 11 are in close thermally-exchanging relationship. The electrodes 5 and 10 are sealingly mounted in a disc 13 which is itself secured on the mount 4 by screws 14 passing through openings in a sealing gasket 15.The electrodes 5 and 10 are potted in an epoxv resin 16 in the disc 13.

The body portion 2 comprises a first housing 17 having the same extended shape and dimensions as the mount 4, a second housing 18 and a knurled closure cap 19. The second housing 18 has a base 20 of the same extemal shape and dimensions as the mount 4 and the housing 17. The housing 17 is in the form of a thin-walled shell open at both ends, one end being sealed to the mount 4 by means of the gasket 15 and the other end being sealed to the base 20 bv means of an 0being 21. Assembly of the housing 17 between the mount 4 and the base 20 is achieved bv means of four elongate bolts 22, one at each of the four corners of the square cross-section the housing 17.Each bolt 22 has its externally screw-threaded end 23 threadedly received in an internally screw-threaded blind bore 24 in the base 20 and its head 25 received in a shouldered bore 26 in the mount 4. The housing 18 has an open-topped cylindrical part 27 having internal screwthreading 28. The cap 19 has a cylindrical skirt 29 with external screw-threading 30 threadedly received in the threading 28. An O-ring 31 is provided to seal the cap 19 to the housing 18.

Within the housing 17 there is mounted a printed circuit board 32 carrying circuitry to which are connected the electrodes 5 and 10 at 33. An indication device in the form of a tri-colour light-emitting diode assembly 34 is received in a hooded mounting grommet 35 inserted into a hole 36 in the thin wall of the housing 17 near the housing 18. The diode assembly 34 is connected at 37 into the circuitry carried on the board 32. Further details of the circuitry are not shown but include capacitance circuits for comparison between the respective signals received from the reference electrodes 10 and the sampling electrodes 5.Additionally there are included a microprocessor capability and memory having a store of information and instructions for defining the correlation between electrical values and temperatures for the reference liquid, and also the correlation between electrical values and moisture contents for the liquid being tested. Furthermore circuits are included for interpreting and directing the result of the comparison, in this case selecting "pass" or "fail" signals to the diode assembly 34 for exhibition thereby. A further feature is a tilt switch which, when the analyser is substantially upright, passes an "on' signal to be exhibited by the diode assembly 34.

The ''pass", "fail" and "on" signals may be green, red and yellow respectively and the circuitry may include a feature to cause the yellow signal to flash intermittently. The circuitry is powered by a 9 volt battery 38 housed between and within the housing 18 and the cap 19, the battery 38 being connected by means (not shown) through the base 20 of the housing 18.

In use the cap of the reservoir for hydraulic brake fluid in a motor vehicle, is removed followed by any other components necessary to expose the surface of the liquid in the reservoir. The analyser is removed from a position in which it is lying, say a wooden bench, in which position, due to the tilt switch, no signal is exhibited by the diode assembly 34. The analyser is then turned into an upright position with the probe member 3 lowermost. If the battery 38 is not discharged, the diode assembly 34 exhibits a flashing yellow signal. If no flashing yellow signal is exhibited the battery 38 is disconnected and replaced by a fresh one to restore the flashing yellow signal.The probe member 3 is then dipped into the surface of the liquid for a number of seconds sufficient to permit the temperature of the liquid in the closed chamber 11 to equalise with the temperature of the small quantity of liquid from the reservoir which has entered the open chamber 6. This causes the flashing yellow signal to change either to a green signal indicating that the liquid being tested has passed the dielectric property test or to a red signal indicating failure in the test.

There are three main types of hydraulic braking liquids used in the automotive industry and it is envisaged to provide a model of analyser for each type, the body of the analyser being colour-coded for ease of identification. In a refinement, the reference electrode arrangement may comprise a plurality of, say three, pairs of reference electrodes each pair being housed in its own closed elongate chamber containing a sealed quantity of uncontaminated liquid different from the other sealed quantity or quantities of liquid. In such refinement a selector switch may be provided on the housing 17 for selecting which pair of reference electrodes is being used as a basis for comparison. In another modification, the probe portion may be connected to the body portion by means of a short flexible cable link so as to cater for less accessible reservoirs of hydraulic braking fluid. In a further modification, the circuitry may be powered from an extemal source, e.g. the battery of the motor vehicle itself.

The tri-colour lightemitting diode assembly may be replaced by a number of individual light-emitting diodes for respective exhibition of the "on", "pass" and "fail" signals. Altematively, the tri-colour light-emitting diode assembly may be replaced by a digital or graphical display readout providing the user with the same or additional information.

Claims

1. An analyser for comparing the electrical properties of liquids, comprising a probe portion and a body portion connected to the probe portion, the probe portion comprising an elongate sampling chamber which is open at the free end of the probe portion and is also vented at some distance from such free end so as to allow liquid to be tested to enter the chamber when the probe portion is dipped into the liquid, at least one closed elongate chamber containing a sealed quantity of a reference liquid having known electrical properties, the chambers being in close thermally-exchanging relationship so that when the probe portion is dipped into the liquid to be tested the liquid which has entered the sampling chamber and the sealed liquid rapidly assume a common temperature, and a plurality of electrodes so associated with the chambers as to produce respective signals therefrom, and the body portion containing circuitry and carrying an indicating device to exhibit information to the user, the circuitry being connected to the electrodes and designed for comparison between the signals and for interpreting and directing the result of this comparison to the indicating device for exhibition thereby.

2. An analyser according to claim 1, wherein each one of the chambers has its own pair of electrodes.

3. An analyser according to claim 1 or 2, wherein the probe portion forms an assembly with and extends from the body portion.

4. An analyser according to claim 1 or 2, wherein the probe portion is connected to the body portion by means of a flexible cable link.

5. An analyser according to any preceding claim, wherein there is a single closed chamber.

6. An analyser according to any one of claims 1 to 4, wherein there is a plurality of closed chambers containing reference liquids having differing known electrical properties, and a selector means is provided for selecting individual closed chambers to be used as a basis for comparison.

7. An analyser according to any preceding claim, wherein the circuitry is powered by an electrical battery removably housed in the body portion, and the indicating device is adapted to indicate the condition of the battery.

8. An analyser for comparing the electrical properties of liquids, substantially as herein described and illustrated in the accompanying drawings.