WO1994021502A1

WO1994021502A1 - Testing of anti-lock braking systems

Info

Publication number: WO1994021502A1
Application number: PCT/NZ1994/000021
Authority: WO
Inventors: Warren Barry Penlington; Kevin Howie
Original assignee: VEHICLE ASSEMBLERS NEW ZEALAND Ltd
Current assignee: VEHICLE ASSEMBLERS NEW ZEALAND Ltd
Priority date: 1993-03-17
Filing date: 1994-03-16
Publication date: 1994-09-29
Anticipated expiration: 1995-09-17
Also published as: TW225003B; AU6386994A

Abstract

An apparatus and a method for testing an anti-lock braking system provides for the initial disconnection of the vehicle wiring connected to the wheel speed sensors. A wheel speed simulator then provides a signal simulating the rotation of the vehicle wheels. The wheel circuits are then sequentially tested by applying brake pressure to the wheel circuit and inserting into the wheel circuit a resistor simulating a locked wheel. The brake pressure decay and rise can then be checked against the required value.

Description

METHOD AND ..- ^PARATUS FOR THE TESTING OF ANTI-LOCK

BRAKING SYSTEMS

The present invention relates to improvements in and relating to braking systems for vehicles.

More particularly, the present invention relates to method and apparatus for the testing of anti-lock braking (ABS) systems.

ABS systems are becoming increasingly popular and in the future could be expected to be fitted to a wide range of relatively lower priced vehicles.

ABS systems act so as to prevent the brakes of a vehicle from locking. This is done by the use of a micro¬ processor which by means of sensors provided for each wheel will detect when a wheel is about to lock. The triggering of the micro-processor will then result in the brakes being released and applied several times very rapidly enabling maximum braking power to be achieved without wheel locking occurring and without loss of steering control.

It is of course extremely important to test the correct operation of the .ABS system of the vehicle both prior to its release from a manufacturing plant and after sale as part of a regular vehicle check. _ABS testing systems available to the present time have been extremely expensive and suitable only for high volume testing such as at a large manufacturing plant and are accordingly unsuitable for low volume testing such as at a small manufacturing plant or for example at a repair garage or at a vehicle testing station.

It is thus an object of the present invention to provide a method and apparatus for the testing of .ABS braking systems.

Further objects of this invention will become apparent from the following description.

SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided a method of testing an anti-lock braking system comprising;

(i) disconnecting the vehicle wiring connected to the wheel speed sensors; (ii) providing a wheel speed simulator means to provide a signal simulating the rotation of the vehicle wheels; (iii) sequentially testing each wheel circuit by applying brake pressure to the wheel circuit and inserting into the wheel circuit a circuit means to simulate a locked wheel; (iv) determining when the brake pressure has decayed to a required level and removing said circuit means to allow said brake pressure to increase to a required level;

(v) checking the decay and increase times against required values.

According to a further aspect of the present invention a method as above described in the immediately preceding paragraph repeats the simulation of a locked wheel, and the release of same, for a plurality of cycles.

According to a further aspect of the present invention there is provided a method as defined in either of the two immediately preceding paragraphs and substantially as herein described.

According to a still further aspect of the present invention there is provided an apparatus for testing an anti-lock braking system and which carries out the method as defined in any of the immediately preceding paragraphs.

According to a still further aspect of the present invention there is provided an apparatus for testing an anti-lock braking system comprising: (i) wheel speed simulating means to provide a signal simulating the rotation of the respective wheels of the vehicle;

(ii) circuit means to simulate the locking of the respective wheels of the vehicle;

(iii) signal processing means connectable with said wheel speed simulating means and said circuit means and controllable to sequentially test the respective wheels by the simulation of the respective locking of the wheels after brake pressure has been applied and to detect the subsequent decay and increase in brake pressure as the circuit means is switched in and out of the respective wheel circuit.

According to a further aspect of the present invention there is provided an apparatus for testing an anti-lock brake system as defined in the paragraph immediately above wherein said circuit means comprises an impedance means connectable in and out of a respective circuit for a wheel to simulate the locking and release of said wheel.

According to a still further aspect of the present invention there is provided an apparatus as defined in either of the two .immediately preceding paragraphs and

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subs" tia^* as herein described with reference to the accompanying drawings.

Further aspects of this invention, which should be considered in all its novel aspects, will become apparent from the following description given by way of example of possible embodiments thereof and in which reference is made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows very diagrammatically an anti-lock brake system testing apparatus according to one possible embodaiment of the invention;

Figure 2 shows a flow chart identifying the steps in testing the front and rear A.B.S. circuits of a vehicle and according to one possible embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS In ABS systems, the ABS CPU, by an international standard relating to such systems, will be looking at the third slowest wheel of a vehicle and using that to detect the onset of locking so that the circuit will take the appropriate action when locking is detected. A typical car will either have three or four channels for the ABS system, the two rear wheels either having a common channel or their own channel. In the former instance, if the sensor on either rear wheel indicates that locking is about to occur, then both the rear wheels will be released from braking pressure. In testing ABS systems, the high volume testing units available to the present time require actual running and locking of the respective wheels so that the reaction of the ABS system to such locking occurring can be determined. Where such testing units are not available then manufacturing plants or garages have had to rely on road testing vehicles, which is clearly unsatisfactory.

Referring to the accompanying drawings and firstly to Figure 1, a testing system is illustrated very diagrammatically and shows by way of example a brake testing unit such as a CRYPTON FKI690 (Trade Mark) unit connected into the relevant circuits of a vehicle to be tested. A programmable logic controller (P.L.C), acting as an interface unit, is shown connected with a wheel speed simulator and through left and right wheel sensor testers to the vehicle circuitry itself.

The wheel speed simulator is illustrated very diagrammatically as consisting of a motor driving a pulley through a belt drive so as to rotate the tone wheels and provide signals commensurate with the normal signals which would be received by the ABS control unit if the vehicle wheels were in fact rotating. In the simulator circuit for each wheel is shown a switch which can switch an impedance, into each wheel circuit shown as a resistor, which in the example shown s illustrated as being 2.2KOhm.

The switching circuit should incorporate the use of a make before break relay or appropriate semiconductor switching circuit, so that the vehicle control unit cannot see the switching into the circuit of the resistor, as if it did it would act as if there was a broken circuit. The appropriate resistor or other suitable circuit means switched into the circuit of a particular wheel, will replace the simulated signal of the wheel rotating. This will then simulate that wheel being locked and the reaction of the circuit will be able to be accordingly tested.

The embodiment shown in Figure 1 is illustrated with test rollers on which the vehicle's wheels can be positioned and rotated so that the wheel speed sensors on each wheel can be tested. This is suitably done initially for each of the vehicle wheels as indicated on the flow chart of Figure 2 of the accompanying drawings.

Referring to Figure 2 it is seen that Step 8 consists of a wiring loom test which will generally check that there are no crossed wiring looms. This will generally be done by starting one of the test rollers when the processor will be looking for an input from the corresponding input from the brake sensor monitor.

Step 9 is indicated as the front sensor voltage and frequency test, provided by a test roller being started and the processor checking that each sensor is sending the correct voltage and frequency. If the voltage to frequency ratio is other than within a predetermined range then this will indicate that the sensor is too close or too distant from the tone wheel.

Step 11, in the test for a Ford Telstar vehicle (Trade Mark) may suitably require the operator to apply a brake force of 1.8 kilo newtons (2.0 kilo newtons being suitable for a Ford Falcon (Trade Mark) ) and once this brake force has been reached by a gentle application of the brake, the processor will commence its testing of the brake force decay and build for each front wheel.

This is achieved by the switching in of the 2.2 KOhm resistor into the sensor circuit for the respective wheel so as to simulate the presence of a locked wheel. This will result in the .ABS system immediately decaying the brake pressure to allow that wheel to rotate. When the brake pressure has decayed to a required level, which is preferably preset and adjustable, the resistor will be switched out of the circuit and the brake pressure will be allowed to build again.

Preferably the test will continue with the sequential switching in and switching out of the resistor so that a number of brake force decays and builds will be detected. The testing unit will be looking for a build and decay which would not take any longer than a prescribed time such as 4 seconds so that over a five sequence test a total test t.ime of 20 seconds would in that case be allowable.

Any failure of the system that may be detected may be caused by various reasons such as the need for the brake system to be bled, the existence of a sticking caliper or possibly a faulty ABS processor.

Assuming the front wheels pass the required tests then the testing will proceed to the testing of the rear wiring loom (step 24) and the testing of the rear sensors (step 26). The tone wheel simulator will then be switched on (step 29) and brake pressure applied before the resistor is switched into the circuit to simulate a wheel being locked. The decay and build of brake pressure will then be detected over a required number of sequences, five again being indicated in Figure 2. For a vehicle having a three channel circuit. so that a common line is connected to both the rear wheels, the test will then need to be repeated for the rear wheel which was not identified as being the first to respond. That first responding sensor is ignored as the second acting sensor is tested.

It is seen therefore that by providing both a wheel speed and wheel locking stimulation, the ABS system of a vehicle can be speedily and effectively tested without requiring the expense and complexity of a high volume ABS testing unit and avoiding the unsatisfactory nature of road testing.

Where in the aforegoing description reference has been made to specific components or integers having known equivalents, such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to particular embodiments thereof, it is to be understood that modifications and improvements may be made thereto without departing from the appended claims.

Claims

CLAIMS :

1. A method of testing an anti-lock braking system comprising:-

(i) disconnecting the vehicle wiring connected to the wheel speed sensors;

(ii) providing a wheel speed simulator means to provide a signal simulating the rotation of the vehicle wheels;

(iii) sequentially testing each wheel circuit by applying brake pressure to the wheel circuit and inserting into the wheel circuit a circuit means to simulate a locked wheel;

(iv) determining when the brake pressure has decayed to a required level and removing said circuit means to allow said brake pressure to increase to a required level;

(v) checking the decay and increase times against required values.

2. A method of testing an anti-lock braking system as claimed in Claim 1 wherein the simulation of a locked wheel and the release of same is repeated through a plurality of cycles for each wheel circuit.

3. A method of testing an anti-lock braking system as cla^jajned in Claim 2 wherein said step of inserting into the wheel a circuit means comprises the operation of a switch which inserts into the wheel circuit a resistor.

4. A method of testing an anti-lock braking system as claimed in Claim 3 wherein the step of switching in a resistor includes the step of using a make before break switching circuit.

5. An apparatus for testing an anti-lock braking system comprising:-

(i) wheel speed simulating means to provide a signal simulating the rotation of the respective wheels of the vehicle;

6. An apparatus for testing an anti-lock braking system as claimed in Claim 5 wherein said circuit means comprises a resistor which can be switched into each wheel circuit to simulate the locking of a respective wheel of the vehicle.

7. An apparatus for testing an anti-lock braking system as claimed in Claim 6, wherein said circuit

SUBSTITUTE SHEET means further comprises a make before break switching means, whereby said signal processing means does not detect that a switching has been effected.

8. An apparatus for testing an anti-lock braking system wherein said circuit means includes means for repeating the simulation of a locked wheel and the release of same for a plurality of cycles.

9. A method of testing an anti-lock braking system substantially as herein described with reference to the accompanying drawings.

10. An apparatus for testing an anti-lock braking system substantially as herein described with reference to the accompanying drawings.

11. A vehicle having an anti-lock braking system which has been tested by the method and/or apparatus of any one of the preceding claims.

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