METHOD AND APPARATUS FOR TESTING SHOCK ABSORBERS AND/OR SUSPENSION SYSTEMS IN MOTOR VEHICLES

Abstract: A method and apparatus for testing a shock absorber and/or suspension system of a motor vehicle uses means (6A, 6B) to raise a wheel (15) and vehicle bodywork (16) to a predetermined height for free dropping so as to cause relative vertical motion between the wheel (15) and the bodywork (16), electronic sensing means (2), such as a laser scanner, to sense a characteristic of the wheel/bodywork relative motion e.g. the speed differential, indicating means (1) for noting the sensed characteristic, and comparison means (3) for example in the form of computer apparatus, for comparing the sensed characteristic with a corresponding characteristic obtained for the vehicle when it has new or as new shock absorbers and suspension system whereby the condition of the shock absorber and suspension system can be checked.

Description: "METHOD AND APPARATUS FOR TESTING SHOCK ABSORBERS AND/OR SUSPENSION SYSTEMS IN MOTOR VEHICLES" DESCRIPTION: The present invention relates to a method and apparatus for testing shock absorbers and/or suspension systems in motor vehicles, especially in motor cars and light commercial vehicles. For safety reasons, it is necessary for the suspension systems of motor vehicles to be in acceptable order, and this applies particularly to the condition of the shock absorbers or dampers in the suspension system. Shock absorbers fitted to motor cars and light-vans usually have a life expectancy of around 35 000 miles (21 875 KM). At present, without removing the shock absorber from the vehicle and testing it on a special testing machine it can be difficult to assess the condition of the shock absorber. Of course, if the item is leaking or has an obvious mechanical defect then the need for replacement will be very apparent, but otherwise the assessment of the shock absorbers' condition can be a rather arbitrary affair. It is the principal object of the present invention to enable the condition of motor vehicle shock absorbers to be accurately assessed without the need for removal of the shock absorbers from the vehicle. According to one aspect of the present invention a method of testing a shock absorber and/or suspension system while in situ in a motor vehicle comprises causing relative vertical motion between a wheel and the bodywork or chassis of a motor vehicle under test, electronically assessing the speed differential or other parameter of the relative motion, noting the assessed characterised, and comparing the assessed characteristic with the corresponding characteristic obtained for the motor vehicle having a new or as new shock absorbers and suspension system whereby the condition of the shock absorber and/ or suspension system of the tested vehicle is established. Preferably, said relative motion is achieved by lifting one of the motor vehicle wheels from a ground engaging Posi- lion then releasing said one wheel to fall under spring/gravity force whereby the wheel is arrested by the ground and subsequent motion of the bodywork noted. The assessment is preferably done utilising computer apparatus enabling the assessed characteristic to be displayed on a monitor screen and/or set out on a computer print out, the computer apparatus preferably including memory storage means for the corresponding characteristics of a range of vehicles having new or as new shock absorbers and suspension systems to facilitate comparison with the assessed characteristic. Preferably the relative motion is assessed by an electronic scanning operation of an indicator element on the wheel and an associated indicator element on the bodywork. According to another aspect of the present invention apparatus for use in testing a shock absorber and/or suspension system of a motor vehicle comprises means for causing relative vertical motion between a wheel and the bodywork or chassis of a motor vehicle, electronic sensing means for sensing as a sensed characteristic, the speed differential or other parameter of said relative motion including means for noting the sensed characteristic, and comparison means for comparing said sensed characteristic with a corresponding characteristic obtained for the motor vehicle when it has new or as new shock absorbers and suspension system whereby the condition of the shock absorber andfor suspension system of the tested vehicle is established. Preferably said relative motion creating means comprises means for raising the wheel together with the bodywork by a predetermined amount from a ground engaging position then releasing the wheel at the raised position. Preferably the electronic sensing means comprises an electronic scanner, such as a laser scanner, scanning indicator elements mounted on the wheel and the vehicle bodywork respec tivelyssensed indications from these elements preferably being fed to computer apparatus for the provision of said sensed characteristic. The computer apparatus preferably includes a monitor screen and/or a print out for display of the sensed characteristic Preferably further, the computer apparatus includes memory storage means for the corresponding characteristics of a suitable range of motor vehicles having new or as new shock absorbers and suspension system to facilitate comparison with the sensed characteristic. An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig. 1 shows a schematic view of apparatus for testing the shock absorbers and/or the suspension system of a motor vehicle, according to the present invention; Fig. 2 shows the laser scanner of the apparatus of Fig. 1 to a larger scale; Fig. 3 shows the rotary prismatic beam generator of the scanner; Fig. 4 is a graph of the scanning action with regard to a pair of indicating elements on the vehicle wheel and bodywork respectively; Fig. 5 shows a typical curve produced by the apparatus of Fig. 1 for a test carried out on a vehicle, and Figs 6A - 6D represent stages in the test of the shock ab absorbers and suspension system of a motor vehicle. Referring to the drawings, especially Fig. 1, testing apparatus for testing the condition of shock absorbers and suspension systems in motor vehicles (especially motor cars and light vans) comprises an interface unit 1, indicating elements (sensors) bl, W1/b2, W2, a pair of laser beam generators 2, a computer 3 including a monitor screen 4 and a printer 5, and lifter devices 6A, 6B each adapted to raise a respective wheel5 of a pair of opposed wheels (i.e. front or back) of the vehicle. Each indicating element W1, W2 is adapted for fitting on a respective vehicle wheel at a set position, preferably the wheel centre, while the corresponding elements bl, b2 are fitted at a set position on the vehicle bodyworkl6for example on the wheel arch above the relevant wheel element W1, W2. The indicating elements bl, Wl/b2, W2 are connected to the interface unit 1 by leads 7, whereby signal pulses are fed to the unit 1 from the indicating elements, and it is the principal object of the unit 1 to determine these signal pulses so as to produce a com puted output signal representing the motion relationship between a vehicle wheel and the vehicle bodywork. The output signal is fed to the computer 3 via lead 8. The unit 1 additionally inc ludescontrols U1, U2 for raising the devices 6A, 6B and also controls dl d2 to enable the devices 6A, 6B to be lowered, the control arrangement enabling precise positioning and movement of the devices 6A, 6B. Leads 9 connects the controls U1, U2, D1, D2 to the devices 6A, 6B. Each laser beam generator 2 provides a vertically oscillating laser beam L as is shown in Fig. 2, which L impinges on the relevant indicators W, b, during the beams' oscillations. The generator 2 is set to give an oscillating beam of precise period and to this end the generator 2 can include for example a rotary polygonal element 10 (Fig. 3) which converts a primary beam P into the desired oscillating laser beam L. By way of example the element 10 could have eight sides and a suitable rotational speed, such as for example 750 RPM (for 100 oscillations per second) or greater. The unit l, the laser generators 2, and the computer 3 are connected to a suitable electric power source, e.g. the mains supply, by leads 11. Further, a data storage memory 12 is provided for the computer 3 which memory 12 includes pre-recorded data of selected characteristics as will be discussed later of shock absorbers and suspension systems of a range of motor vehicles in the new or as new condition. In the testing procedure it is an object to acheive a relative motion effect between the wheels and the bodywork which approximately simulates the motion when wheels encounter potholes during normal driving as this is the situation which presents greatest demands on the shock absorbers. Thus to test shock absorbers and/or the suspension system of the vehicle, the vehicle is positioned with a pair of its opposed roadwheels e.g. the front wheels (Fig. 6A) over the lifting devices 6A, 6B. The lifting devices 6A, 6B are actuated by the controls on the unit 1, specifically control items U1/U2 to raise the opposed wheels (and the bodywork) by a specified amount h above the initial surface level G: the situation is now as in Fig. 6A with the bodywork indicating element b located at distance S above the corresponding indicating element w at the wheel. With the laser beam generators 2 providing oscillating laser beams L scanning the elements w, b of the opposed vehicles wheels and with the unit 1 operatively coupled to the computer 3, the next stage in the test is to remove the devices 6A, 6B from supportive engagement with the wheels and this is preferably achieved by means of power actuation (down and sideways as shown in Figs. 6A and 6B) so that the wheels are permitted to fall without obstruction onto the surface G. In the dropping action, the wheels will move away relatively from the bodywork by virtue of suspension spring action so that when the wheels engage the surface G as in Fig. 6B the spacing S2 between the elements b, w is greater than S1. The bodywork which continues to fall after Fig. 6B will compress the suspension spring under damper action until the "bottom" position shown in Fig. 6C is reached where S3 is now less than S1. Oscillation of the bodywork will then follow until the steady state condition as shown in Fig. 6D is obtained when S4 substantially equals S1. Fig. 4 shows the operation of the scan by each oscillating beam L. Thus each time the beam L passes a wheel indicator w(1/2) a signal pulse is generated i.e. pulses Wa, Wb and similarly signal pulses Ba, Bb are produced by the bodywork indicators. The various signal pulses Wa B are fed to the interface unit 1 where they are determined to assess the verti ca motion and speed of the bodywork relative to the associated wheel: this is a factor represented by the changing period between successive wheel/body pulses Waba, Wbbb etc. An output signal representing the instantaneous relative speed or motion value is fed to the computer 3 from the unit 1 via lead 8 and the computer 3 functions to present overall characteristic of bodywork motion (relative to the wheel). This characteristic can be displayed on the monitor screen 4 and/or printed on printer 5. Fig. 5 represents a typical graph of the relative motion (against time) as would be displayed on the screen 4 or printed out on printer 5. Thus, the first inversion I in Fig. 5 represents the situation in Fig. 6B where the indicator spacing (S2) is greatest. Inversion II represents the Fig. 6C position, the degree of overshoot D indicating the compression created in the suspension spring by the dropping bodywork. The graph also indicates the bodywork oscillation after II until the steady state condition at III (equivalent to the Fig. 6D situation) is reached. Any weak spot of the shock absorber is shown as a blip or extended movement on the waveform, while wear of suspension parts will be indicated by waveform distortion at waveform limits i.e. at I, II etc. The testing apparatus can function to provide an instantaneous but separate motion characteristic for each of the opposed wheels (i.e. with respect to sensors w, b and w2 b2). Also, aimilar test will be carried on the other wheel pair i.e. the rear wheels. A significant feature of the present invention lies in the prior carrying out of equivalent tests on vehicles (i.e. "new" vehicles) having their shock absorbers and suspension systems in correct order. The characteristics (e.g. graphs) obtained from these prior tests are stored in the computer memory 12, so that data can be readily drawn from the memory 12 to enable a comparison of the tested characteristic of a particular vehicle model with the correct characteristic for that model. This comparison should make it readily evident where a shock absorber requires replacement, or where the suspension system requires attention. The memory 12 can be readily up-dated to include the necessary data on additional motor vehicle models. The following benefits accrue to the customer and to the garage from the above tester according to the present invention: The Customer - Will not have to rely only on the word or advice of the mechanic or fitter (whom apart from the mileage has no "accurate" indication of wear). As the customer is shown the car on test and the results afterwards, he has a clear indication of any need for replacement. The Garage - Will have much needed credibility created by the accuracy associated with lasers and the veracity of computers. He will have a much better rela tionship with his customer if he only replaces parts which are not only worn but are seen to be worn. Modifications are of course possible. For example, the sensing of wheel motion could be achieved by some other sensing apparatus than the laser generator 2 and indicating elements W, b as shown in Fig. 2. Also, different means could be used for raising the wheels and bodywork, and these may be applied on the bodywork rather than on a wheel or wheels.

Claims: CLAIMS l. A method of testing a shock absorber and/or suspension system while in sitfl in a motor vehicle, characterised in that the method comprises causing relative vertical motion between a wheel and the bodywork or chassis of a motor vehicle under test, electronically assessing the speed differential or other parameter of the relative motion, noting the assessed characteristic, and comparing the assessed characteristic with the corresponding characteristic obtained for the motor vehicle having new or as new shock absorbers and suspension system whereby the condition of the shock absorber and/or suspension system of the tested vehicle is established. 2. A method according to claim l, characterised in that said relative motion is achieved by lifting one of the motor vehicle wheels from a ground engaging position then releasing said one wheel to fall under spring/gravity force whereby the wheel is arrested by the ground and subsequent motion of the bodywork noted. 3. A method according to claim 1 or 2, characterised in that the assessment is achieved utilising computer apparatus enabling the assessed characteristic to be displayed on a monitor screen and/or set out on a computer print out. 4. A method according to claim 3, characterised in that computer apparatus includes memory storage means for the corresponding characteristics of a range of vehicles having new or as new shock absorbers and suspension systems to facilitate comparison with the assessed characteristic. 5. A method according to any one of the preceding claims, characterised in that the relative motion is assessed by an electronic scanning operation of an indicator element on the wheel and an associated indicator element on the bodywork. 6. Apparatus for use in testing a shock absorber and/or suspension system of a motor vehicle characterised by comprising means (6A, 6B) for causing relative vertical motion between a wheel (15) and the bodywork (16) or chassis of a motor vehicle, electronic sensing means (2) for sensing as a sensed characteristic, the speed differential or other parameter of said relative motion including means (1) for noting the sensed characteristic, and comparison means (4/5) for comparing said sensed characteristic with a corresponding characteristic obtained for the motor vehicle when it has new or as new shock absorbers and suspension system whereby the condition of the shock absorber and/or suspension system of the tested vehicles established. 7. Apparatus according to claim 6, characterised in that said relative motion creating means comprises means (6A) for raising the wheel (15) together with the bodywork (16) by a predetermined amount from a ground engaging position (G-G) then releasing the wheel at the raised position. 8. Apparatus according to claim 6 or 7, characterised in that the electronic sensing means comprises an electronic scanner (2) such as a laser scanner, scanning indicator elements (owl/2, by/2) mounted on the wheel 15 and the vehicle bodywork (16) respectively. 9. Apparatus according to claim 8, characterised in that sensed indications from these elements (wl/2, bl/2) are fed to computer apparatus (3) for the provision of said sensed characteristic. 10. Apparatus according to claim 9, characterised in that the computer apparatus (3) includes a monitor screen (4) and/or a print out (5) for display of the sensed characteristic. 11. Apparatus according to claim 9 or 10, characterised in that the computer apparatus (3) includes memory storage means (12) for the corresponding characteristics of a suitable range of motor vehicles having new or as new shock absorbers and suspension system to facilitate comparison with the sensed characteristic.

Inventors: BUCHANAN NIGEL, BUCHANAN, NIGEL
Applicants: LIQUID LEVERS LTD, LIQUID LEVERS LIMITED
Application year: 1989
Main classification: G01M17
IPC codes: G01M17