GB2283466A

GB2283466A - Suspension damper test method and apparatus

Info

Publication number: GB2283466A
Application number: GB9322905A
Authority: GB
Inventors: John David Turner; Martyn Hill; Angus Charles Robert Tavner
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1993-11-06
Filing date: 1993-11-06
Publication date: 1995-05-10
Anticipated expiration: 2013-11-06
Also published as: GB9322905D0; GB2283466B

Abstract

A method and apparatus are provided for detecting failure of switchable suspension dampers on a wheeled vehicle such as a motor car to switch between hard and soft settings. Each wheel of the car is damped by one of the switchable dampers and the vehicle is subject to a test at each of its wheels. The test consists of depressing the vehicle by a preset amount and then releasing the vehicle to derive data by way of a linear transducer such as a potentiometer 10 indicating if the damper is set hard or soft. The data is processed by a data processor 17 to determine if the two dampers of a pair of wheels (front pair or rear pair) meet the criteria for both hard and soft settings and how many tests are failed by the dampers of a pair of wheels. Where the dampers of a pair fail two tests in one damper setting and the criteria for the other damper setting are not met by both dampers, the damper which comes closest to the criteria for the other damper setting is selected as a failed damper. <IMAGE>

Description

SUSPENSION DAMPER TEST METHOD AND APPARATUS The present invention relates to a method and apparatus for testing to detect failure of switchable suspension dampers on a wheeled vehicle to switch between hard and soft settings. In such a vehicle to be tested the vehicle has front and rear pairs of wheels, each wheel being damped by one of the switchable dampers.

In a known adaptive suspension system of a motor vehicle, each wheel is damped by a damper having hard and soft settings that are selected by an electrically controlled solenoid valve in the damper. The switching of the solenoids is controlled automatically by an electronic control system incorporating an accelerometer to measure vertical acceleration of the vehicle body and which also receives information concerning parameters of vehicle behaviour such as braking, acceleration, steering angle, and rate of steering adjustment caused by the driver of the vehicle. There is also a facility for manual override which keeps the dampers in the hard setting.

In the event of a malfunction of the adaptive suspension, it is important to be able to test whether the dampers are switching correctly between the hard and soft settings. Since the dampers are of a welded construction, it is impractical to gain access to the interior of the dampers to verify the switching action. Furthermore, it is important to be able to make a test of the vehicle suspension without recourse to dismantling the suspension. It is also important to use a method which is simple and inexpensive to apply throughout a network of vehicle retail distributors.

It has already been proposed in German patent application DE 3826196 Al to test a vehicle suspension system to determine the wear and possible failure of the dampers in the suspension system by subjecting the vehicle to a downward displacement followed by release of the vehicle. Measuring apparatus registers the damping rate of the dampers by reference to the amplitude of the oscillations of the vehicle. However the prior proposal does not discriminate between a pair of dampers of which one fails to switch between hard and soft settings while the other is switching correctly. Such a situation is liable to register a failure of both dampers because a failure to switch by one damper of a pair will affect the damping action at the wheel of the other damper of the pair.

According to the present invention there is now provided a method of detecting failure of switchable suspension dampers on a wheeled vehicle to switch between hard and soft settings, the vehicle having front and rear pairs of wheels, each wheel being damped by one of the switchable dampers, the method including the steps of subjecting the vehicle to a test at each wheel for both hard and soft settings, the test including the downward displacement of the vehicle by at least a predetermined amount and subsequent release of the vehicle, deriving by means of a displacement transducer and data collection means data indicating whether the damper meets predetermined criteria for both hard and soft settings, processing the data from the two dampers at the hard and soft settings for each pair of wheels, the data for one pair of wheels being processed separately from the other pair of wheels, to determine how many tests are failed by the dampers of each pair, and where the dampers of a pair fail two tests in one damper setting and the criteria for the other damper setting are not met by both dampers, selecting as a failed damper the one which comes closest to the criteria for the said other damper setting.

Further according to the present invention there is provided apparatus for detecting, in accordance with the method of the invention described in the preceding paragraph, the failure of switchable dampers on a wheeled vehicle to switch between hard and soft settings, the apparatus comprising displacement transducer means to detect displacement of the vehicle during the test at each wheel of the vehicle, data collection means to collect digital data indicative of whether the damper at each wheel meets the criteria for both hard and soft settings of the dampers, and digital processing means programmed to indicate in a first step how many tests are failed by the dampers of each pair of wheels, and, in a case where the dampers of a pair fail two tests in one damper setting and the criteria for the other setting are not met by both dampers, in a subsequent step, to signal the selection as a failed damper the one which comes closest to the criteria for the said other damper setting.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows in simple diagrammatic form a test apparatus according to the present invention, Figure 2 shows the output from a displacement transducer used in the apparatus of Figure 1 and, Figure 3 shows the flow diagram of a digital processor used in the apparatus of Figure 1.

In Figure 1 there is shown a test apparatus including a displacement transducer in the form of a linear potentiometer 10 which is connectable at the upper end 11 to the bodywork of a motor vehicle to be tested. The lower end 12 of the potentiometer is connectable to the centre of a wheel of the vehicle. A power supply 13 is connected to supply a d.c. voltage to the potentiometer along a power input line 14 and an output voltage is supplied by the potentiometer along an output line 15 to an analog to digital converter 16. The output voltage from the potentiometer 10 is proportional to the displacement of the upper end 11 from the lower end 12 and the converter 16 converts the displacement indicated by the potentiometer 10 into a corresponding digital value for entry into a digital processor 17.Display means 18 are connected to the digital processor to display to an operator of the apparatus the results of the test on a vehicle.

In known adaptive vehicle suspension systems there is provided a damper for each of the four wheels of the vehicle which is switchable between a hard setting and a soft setting. The switch between the hard and the soft settings is made by an electrically controlled solenoid valve in the damper. The apparatus of Figure 1 is used to test at each wheel of a vehicle having such an adaptive suspension system by connecting the potentiometer 10 at its upper end 11 to the wheel arch of the vehicle and the lower end to the centre hub of the wheel. The vehicle is tested at each wheel for both hard and soft settings of the dampers.

The test at each wheel consists of displacing the body of the vehicle downwardly by at least a preset amount followed by the sudden release of the vehicle. The resulting output curve from the potentiometer for both hard and soft settings of the damper is shown in Figure 2. As will be seen in Figure 2, the initial downward displacement from the rest position of the vehicle suspension is followed by a return beyond the rest position as the vehicle overshoots and subsequently returns to the rest position. The portion of the curve identified as "a" represents a test with the dampers set to the soft setting. The portion of the curve identified as b represents a test with the dampers set to the hard setting.

In an actual test on a motor vehicle, it was found that the initial depression of the vehicle had to exceed 12 mm to distinguish between hard and soft settings. Practical experience suggested that the initial depression should be between 18 and 30 mm on the vehicle under test.

Distinguishing between hard and soft settings is achieved by comparing the distance of the overshoot with the distance of the initial depression. If the ratio of the overshoot to the initial depression is greater than 0.2, the damper under test is set to the soft setting. If the ratio is less than 0.1, the damper under test is set to the hard setting.

The test procedure consists of taking the potentiometer measurement at each front wheel for both hard and soft settings of the dampers to derive four test results for the front of the vehicle. The four tests of the front wheel dampers are then repeated for the rear wheel dampers. The output from the potentiometer is applied through the analog to digital converter to derive a digital representation of the potentiometer test results at the four wheels. The data collected is registered in the processor 17 which is programmed to process the data for the front wheels and subsequently process the rear wheel data as is shown in the flow diagram of Figure 3. It will be readily apparent that two potentiometers could be used simultaneously to derive the data for the front wheels and then the data for the back wheels.It will also be apparent that the potentiometer or potentiometers could be replaced by any suitable alternative displacement transducer.

As will be seen from Figure 3, the first four test results from the front wheel dampers are processed to determine how many test failures were experienced. The criteria for the test results is that a soft setting should provide an overshoot ratio of more than 0.2 and a hard setting should produce an overshoot ratio of less than 0.l.In the case where only one failure has occurred, the processor indicates to the display device which damper has failed to switch. In the case where more than two tests were failed, the processor indicates to the display device that both dampers have failed to switch. Finally, where two tests were failed, the processor will most likely face a set of circumstances where one of the dampers has failed to switch and this failure has an effect on the response of the other damper of the pair.

Thus in the case of a single damper remaining in the hard setting, that damper will not give a ratio above 0.2 in the soft setting and the other damper of the pair is also unable to give a ratio above 0.2 in the soft setting. In this case the dampers will give a ratio in the range between 0.1 and 0.2. What happens is that when the vehicle is depressed on the "hard" corner, the end of the vehicle under test behaves in a harder manner than when the vehicle is depressed on the soft corner. As shown in the logic of Figure 3, if both tests that have been failed are tests for the hard setting and both dampers do not meet the soft criteria, the softest damper is stuck in the soft setting.

If both dampers do meet the soft criteria, then both are stuck in the soft setting.

Alternatively, if the two tests that were failed are the tests in the soft setting and the dampers both do not meet the hard criteria, the hardest damper has stuck in the hard setting. If both do meet the hard criteria, then they are both stuck in the hard setting as indicated in the flow diagram of Figure 3.

Finally if the two tests that are failed are for one hard setting and one soft setting, one damper is stuck in the hard setting and the other is stuck in the soft setting.

In each of the sets of circumstances depicted in the flow diagram of Figure 3, the processor gives an indication to the operator of the identity of the failed damper or dampers. The indication takes the form of a screen display but it will be apparent that the precise form of the indication is not important to the functioning of the invention provided it is easily read by the operator. The indication to the operator could be in the form of a printed osput.

Having completed the processing of the data derived from the four tests applied to the dampers at the front pair of wheels of the vehicle, the tests are conducted on the dampers of the rear pair of wheels and the data so derived is collected and processed according to the flow diagram already described in relation to the tests on the front wheel dampers. At the end of the test procedure, the operator has a ready indication on the display means of which damper has failed to switch out of the four dampers on the vehicle.

Claims

CLAINS

1. A method of detecting failure of switchable suspension dampers on a wheeled vehicle to switch between hard and soft settings, the vehicle having front and rear pairs of wheels, each wheel being damped by one of the switchable dampers, the method comprising the steps of subjecting the vehicle to a test at each wheel for both hard and soft settings, the test including the downward displacement of the vehicle by at least a predetermined amount and subsequent release of the vehicle, deriving by means of a displacement transducer and data collection means data indicating whether the damper meets predetermined criteria for both hard and soft settings, processing the data from the two dampers at the hard and soft settings for each pair of wheels, the data for one pair of wheels being processed separately from the data for the other pair of wheels, to determine how many tests are failed by the dampers of each pair, and where the dampers of a pair fail two tests in one damper setting and the criteria for the other damper setting are not met by both dampers, selecting as a failed damper the one which comes closest to the criteria for the said other damper setting.

2. A method according to claim 1 wherein the predetermined criteria for the hard and soft damper settings are measurements of the ratio of the overshoot of the vehicle after release to the length of the downward displacement of the vehicle.

3. Apparatus for detecting, in accordance with the method of claim 1, the failure of switchable dampers on a wheeled vehicle to switch between hard and soft settings, the apparatus comprising displacement transducer means to detect displacement of the vehicle during the test at each wheel of the vehicle, data collection means to collect digital data indicative of whether the damper at each wheel meets the criteria for both hard and soft settings of the dampers, and digital processing means programmed to indicate in a first step how many tests are failed by the dampers of each pair of wheels, and, in a case where the dampers of a pair fail two tests in one damper setting and the criteria for the other damper setting are not met by both dampers, in a subsequent step, to signal the selection as a failed damper the one which comes closest to the criteria for the said other damper setting.

4. Apparatus as claimed in claim 3 wherein the displacement transducer means comprise a linear potentiometer.

5. Apparatus as claimed in claim 3 or 4 wherein the predetermined criteria for the hard and soft damper settings are measurements of the ratio of the overshoot of the vehicle after release to the length of the downward displacement of the vehicle.

6. A method of detecting failure of switchable suspension dampers on a wheeled vehicle to switch between hard and soft settings, the vehicle having front and rear pairs of wheels, each wheel being damped by one of the switchable dampers, the method being substantially as hereinbefore described with reference to the accompanying drawings.

7. Apparatus for detecting, in accordance with the method of claim 1, the failure of switchable dampers on a wheeled vehicle to switch between hard and soft settings, the apparatus being substantially as hereinbefore described with reference to the accompanying drawings.