FR2695998A1 - Wheel alignment system for measuring alignment angles of wheels - Google Patents

Abstract

The wheel alignment system has a system function control unit for providing system operating instructions and for receiving alignment angle data. An angle sensor is mounted on at least two of the vehicle support wheels for providing angle measurement signals indicative of the angle between the planes of the support wheels and a reference direction. The angle sensor also has fast response signal amplitude sampler for providing instantaneous toe angle measurement signal detection. Data update frequency is increased and angle sensing accuracy is improved.A sensor system interface control unit receives and reprocesses the angle measurement signals and external system control inputs and provides bi-directional data flow between the angle sensor and the system function control unit. A graphics array control and display unit receives and displays measureed alignment angle data.

Description

 The present invention relates to an assembly for measuring the characteristic angles of the wheels which support a vehicle on a running surface, which comprises a device for controlling the operation of the assembly intended to transmit instructions for controlling the assembly and to receive characteristic angle data, and angle detection devices mounted on at least two vehicle support wheels and intended to give measurement signals representative of the angle of the planes of the wheels and of a reference direction, the angle detection devices further comprising a parallelism detection device for ensuring almost instantaneous detection of the angle measurement signal, so that the frequency of data updating is high and the accuracy on detection angle is very high, and a sensor and interface controller is used to receive signals of angle measurement and of the external control signals of the assembly and to form a bidirectional data current between the angle detection device and the device operating control device. In addition, the assembly includes a graphical control and display device intended to receive and display the measured data of characteristic angles.

 A parallelism signal detection assembly is for detecting the parallelism of a pair of wheels supporting a vehicle intended to move on a support surface, and overall, a plurality of light beams having a predetermined carrier frequency are projected at known successive moments and with known angles towards the plane of one of the pairs of wheels, and a light beam receiver is mounted in known position and on the path of several paths of light beams and forms a signal angle representative of the reception of some of the light beams. The set includes a high pass filter connected so that it receives the angle signal and having a bandwidth significantly greater than the noise frequencies due to ambient light and containing the carrier frequency so that it gives a high pass signal corresponding to the angle signal, and a device for detecting the high pass signal and mem orization of the signal representative of its amplitude.

In addition, a control device intended to receive and erase the memorized signal representative of the amplitude before the detection of the next light beam by the light beam receiver.

 A method is for adjusting the rolling direction of a pair of wheels by a predetermined angle, in which the wheels are connected by a rigid axle supported by two distant spring assemblies which are fixed to the axle by passing joints in holes in a pair of yokes. The method includes measuring the wheel rolling direction angle, calculating an adjustment angle between the measured wheel rolling direction and the predetermined wheel rolling direction, measuring the distance between the spring assemblies which are spaced, and the calculation of a dimension of the elongation and a direction of the holes in the yoke as the product of the distance by the sine of the angle of adjustment.

 In another aspect of the invention, a method simultaneously adjusts the camber and caster of a wheel on a vehicle, to a specified value, in which the wheel is supported, so that it can pivot on the vehicle, by a member having a particular geometric configuration and which is fixed to the chassis of the vehicle at front and rear fixing points which are adjustable, measuring instruments giving measurements of caster and camber of the wheel.The method comprises the steps of initial adjustment the position of one of the adjustable front and rear fixing points, detecting the effect of the initial adjustment on the camber and caster measurement, predicting the effect of an additional adjustment to the other of the adjustable front and rear fixing points by using the effect taken from the detection step, and of calculating the adjustments in each of the adjustable front and rear fixing points for obtaining n of specified caster and wheel camber values for any particular geometrical configuration of the member supporting the wheel so that it can pivot.

 The invention also relates to a method for adjusting the characteristic angles of two independent suspension wheels arranged laterally on a vehicle, the wheels having instruments for measuring characteristic angles which cooperate with them for the measurement of characteristic angles of the pair of wheels, the wheels being supported by a support structure and being connected by a rigid member placed between them.The method comprises steps for measuring the camber characteristics and the inclination of the steering axle for each of the two wheels, of comparing the characteristic angles measured for each wheel of the pair so that a lateral offset of the rigid member is indicated, and of adjusting the lateral position of the rigid member in the direction which displaces the measurements of inclination d the steering and camber axis of the two wheels towards the specified values when there is an indication of the offset of the rigid member.

 Furthermore, a method is intended for adjusting the inclination of the steering axis, the angle included and the camber of a wheel suspended from a vehicle which supports it, the vehicle being intended to move on a support surface, while the wheel is lifted above the support surface, characteristic angle measuring instruments are coupled to the wheel so that they give characteristic angle signals, the brakes being applied and the measuring characteristic angles being locked so that they prevent rotation relative to the wheel in known parts of the operation, the method comprising steps of steering the wheels straight ahead, and memorizing the camber measurement signal when the vehicle is supported on the support surface.Moreover, the method comprises steps of raising the vehicle above the support surface, of measuring the camber signal when e the vehicle is raised, calculating the difference between the camber signals when the vehicle is lowered and raised, steering the wheel by a known angle to the left, memorizing the left turn output signal from characteristic angle of inclination of the steering axis, direction of the wheel of a known angle to the right, memorizing the right turn output signal of characteristic angle of the steering axis, calculation of the direction axis tilt angle from the left and right turn signals to calculate a modified direction axis tilt angle signal using the difference between the camber signals obtained in the lowered position in the raised position, memorizing the modified steering axis tilt angle output signal, and adjusting the camber and steering axis tilt output signals to the state raised using the memorized modified signal of Steering axis tilt output and stored camber measurement output signal obtained when the wheel has been lowered.

 In another aspect, the invention relates to a display for a set of characteristic angle measurement, intended to indicate the characteristic angles of the wheels of a vehicle, and which comprises a graphical control device, and a device intended to give a display. variable from all angles, and connected to the graphic control device, so that all the variations of angles relating to the characteristic angles during an adjustment are displayed.

Other characteristics and advantages of the invention will be better understood on reading the description which will follow of exemplary embodiments, made with reference to the appended drawings in which
Figure 1 is a block diagram of an assembly according to the invention;
Figure 1A is another block diagram showing more details than the diagram of Figure 1;
Figure 2 is a perspective view showing the relative mounting positions of the camber clinometers and tilt of the steering axis
Figure 3 is a block diagram of a parallelism measuring circuit according to the invention;
Figure 4 is a graph illustrating the detection of the signal produced by the device of Figure 3
Figure 5 is a schematic front elevational view showing a cradle displacement
Figure 6 is a plan view of a pair of vehicle support wheels connected by a rigid axle
Figure 6A is a plan view of a spring-loaded yoke
Figure 7 is a diagram of a symmetrical wheel support member
Figure 7A is a graph corresponding to the support member of Figure 7
Figure 8 is a diagram of a diffeient wheel support member
Figure 8A is a graph corresponding to the support member of Figure 8
Figure 9 is a diagram of another wheel support member
Figure 9A is a graph corresponding to the support member of Figure 9
FIG. 10 is a diagram of a device for displaying measurements of the characteristic angles of the wheels;
FIG. 11 is another diagram of a device for displaying measurements of the characteristic angles of the wheels
FIG. 12 is another diagram of a device for displaying measurements of the characteristic angles of the wheels; and
FIG. 13 is another diagram of a device for displaying measurements of the characteristic angles of the wheels.

 The assembly for measuring the characteristic angles of the wheels described in this specification makes it possible to measure the characteristic angles of the four wheels used for supporting a vehicle on a surface. The importance of obtaining suitable characteristic wheel angles is well known and is not described in this specification. A set of characteristic wheel angle measurement which can advantageously benefit from the improvements of the present invention is described in United States Patent No. 4,761,749. As this document indicates, a set of measurement of the characteristic wheel angles allows the alignment of the wheels of a four-wheeled vehicle and includes alignment heads to be mounted on each of the four wheels so that characteristic wheel angle data can be obtained between the wheel on which is mounted the head and a console of the assembly which is intended to receive and prepare the data and to memorize and / or display the data, if necessary. The sensors for measuring the quantities relative to the characteristic angles for each head mounted on a wheel include clinometers 11 and 12 mounted in orthogonal planes 13 and 14 as shown in FIG. 2. The plane 13 is a vertical plane available dried laterally with respect to the wheels supporting the vehicle and the plane 14 is a vertical plane disposed longitudinally with respect to the support wheels. FIG. 2 represents these relationships, with in addition the representation of a third orthogonal plane 16. The plane 13 is known by the name of camber plane, inclination of direction axis and angle included, while the plan 14 is known as the hunting plan, since the aforementioned measures are planned in these plans. The plane 16 is known as the plane of parallelism in which the measurements of parallelism of the four wheels are carried out.

 Figure 1 shows two rectangles 17 and 18 which designate heads. These rectangles indicate the individual heads mounted on the wheels and carrying the instruments for measuring the characteristic angles, such as the camber clinometer 11 and the steering axis tilt clinometer 12. The heads mounted on the wheels also include a parallelism measuring device described in US Pat. No. 4,180,326. In FIG. 1, the heads 17 and 18 can be connected by cables 19 for connection or by transmission 21 of infrared or high frequency data to a section 22 for controlling the interface of sensors of the measuring assembly shown. A keyboard 23, a sensor 24 for controlling the optical system and a speaker 26 are also connected to the interface control section. A command 27 of the assembly is also shown. The interface command 22 is the intermediary between the digital and analog input signals of the assembly, the data series communication devices. and the digital or output control signals of the assembly, circulating between the control 27 of the assembly, and the elements 17, 18, 23, 24 and 26. The control 27 of the assembly comprises a direct access memory , a read only memory, a keyboard control member, a microprocessor and associated logical interfaces, in a computer architecture.

 It should be noted that a universal job computer, as incorporated in the command 27, is not intended to perform high speed data acquisition and processing. One to four serial data entry channels are common and allow the reading, storage and calling of data in a multiplexed manner. It is a relatively slow process. The sensor interface command 22 receives the data from the sensors of the assembly and pre-processes the data to present them to a display device of the assembly so that the immediate display of the data can be obtained.

This relieves the control 27 of all the difficult work of converting and processing the raw data coming from the sensors and leaves it with more elaborate tasks such as the calculation of the values of the characteristic angles, the calibration, the implementation of an expert system, etc. Thus, the interface control 22 fulfills a well-defined function having high-speed performance between the control 27 and the associated sensors for measuring angles and the controls incorporated into the assembly.

As can be noted in FIG. 1A, the interface control 22 contains an electrically erasable programmable read-only memory 80 (EEPROM) and a programmable read-only memory 81 (PROM) intended for use by the host computer only. A two-way direct access memory 82 (RAM) is used so that it allows communication between an interface microprocessor 83 and the control 27 of the same. The "Hitachi" component
HD 6475328 gives a capacity to the interface microprocessor. The interface card comprises, in addition to the direct access memory, an EEPROM memory 84 intended to receive programs which can be downloaded to it and calibration factors, and a PROM memory 85 intended to contain the main control program .

 An octal 86 universal asynchronous transceiver (UART) provides eight communication channels that are programmable. These channels are used for communication with remote sensors, for example those of heads 17 and 18 or any peripheral equipment associated with the assembly. Data can be transmitted and received through these channels. A digital-analog converter 87 is connected to an audio frequency amplifier 88 by a digital volume control member 89 which is an electrically erasable potentiometer. A wide range of sounds can be produced by the microprocessor 83, and in addition, external received audio frequency signals can be processed for transmission of audio frequency output signals.

 The interface controller 22 receives analog or digital output signals from the sensors and transmits digital output control signals. Software can be downloaded via the two-way RAM memory 82 to the EEPROM memory 84 which facilitates upgrades on site without changing the integrated circuit components of the assembly. A remote control receiver section 90 is used for receiving digital output signals from the optical sensor 26 or other digital signals transmitted to the assembly.

 FIG. 1 also shows a command 28 of high density disk RAM (CD) memory which is connected to the command 27. This command 28 is connected to a high density disk unit 29 which ensures the mechanical reading of the disc. An audio frequency output signal from a CD disc is transmitted to the sensor interface controller 22 which transmits the audio signals to the speakers 26 accordingly.

 A video graphic display TM (VGA) control 31 is connected to control 27 and is directed by the control of the assembly so that it gives displays on a monitor 32. An input-output control, hard disk and floppy disk is also incorporated into the command 27. The command 33 ensures the control of a hard disk unit 34 and a diskette unit 36, giving other signals to the assembly. The command 34 also controls a printer 37 and an input-output communication channel 38.

 While the clinometers 11 and 12 give a vertical reference for certain measurements of characteristic angles, the measurement of the parallelism is carried out in the plane 16 of FIG. 2 and reference is made to FIG. 3 of the drawings for the description of the improvements made to the measurement of parallelism according to the invention. As described in the aforementioned patents, a structure is intended to project several light beams having a predetermined carrier frequency at a series of known instants and with a known angular orientation relative to the plane of a wheel on which such a projector is mounted. A receiver 39 of a light beam is shown in FIG. 3 and it receives the light beams which are in its field of vision. The carrier frequency of the light beams is approximately 16,000 Hz and the received beam is identified by its own time of issue. Consequently, the angle of the projected beam coming from the plane of the wheel on which the headlight is mounted is known. Consequently, the angle of the plane of the wheel on which the headlamp is mounted is known with respect to a reference direction when the light beam signals are analyzed for the determination of those which fall most directly among the different beams.

 The receiver 39 receives three to five light beams projected at any time. As indicated in the lower part of FIG. 4, the light beam represented by the carrier frequency at 16,000 Hz from time t1 does not constitute the most direct primary or incident beam. Although the light beam which appears at time t4 is closer to the direct incidence on the receiver 39, it is the beam which appears at time t8 which constitutes the primary beam reaching the receiver 39. This appears in the form of the greater amplitude of the received signal which is evident in the representations of the substantially rectangular waves in the upper part of FIG. 4, from time t9 to time t10, for the signal V3.

 The signal received by the receiver 39 and which contains the carrier at 16,000 Hz is connected to a high-pass filter 41 which suppresses the noise of light at low frequency.

The received signal, including the frequency of 16,000 Hz, is much higher than the bend of the filter response and well inside the bandwidth. The filtered signal containing the beam signal received at 16,000 Hz is connected to a variable amplifier which determines the primary light beam or which comes most directly. The variable amplifier includes an electrically adjustable potentiometer 42 whose input is controlled by a microprocessor 43 of the circuit for detecting and controlling the parallelism signal. The potentiometer 42 is connected to the input of a broadband amplifier 44 whose gain it adjusts. The gain is fixed for the first scan of the signals created by the received light beams. Each signal is digitized and stored, as described below. The highest stored signal in the first scan is selected. If the amplifier gain does not place the highest received signal in the range of about 2 to 4.5 V, the microprocessor calculates a new gain of l 'amplifier and adjusts potentiometer 42 so that the gain of the amplifier' is adjusted to a value such that the largest amplified output signal is included in the window. The remaining signals which are received are then amplified with the new fixed value and give lower values as indicated in the lower part of FIG. 4, depending on the angle of incidence on the sensor 39. The potentiometer 42 to electrical control is of the X9CMME type from Xicor, Milpitas,
This characteristic allows the parallelism circuit to manage the reception of the transverse and following light beams by optimizing the gain for each of the transverse and following measurements, allowing the obtaining of the measurement signals which can be interpreted most easily. .

 A detector circuit 46 provides single-wave rectification of the filtered and amplified signal at 16,000 Hz from the receiver 39 so that only half of the signal in the lower part of FIG. 4 remains. The rectified signal is stored in a capacitor C of FIG. 3 as indicated by the amplitudes V1, V2, V3 and V4 in FIG. 4. It is noted that the high-pass filter 41 has an amplified signal at the detector 46, this signal being sampled in amplitude by the holding capacitor C, in less than three cycles of the carrier frequency. The period of one cycle is 62.5 ijs. Thus, the maximum amplitude of the signal resulting from the signal of the received light beam is detected at the level of the capacitor C in less than 200 to 250 Ps. Consequently, the stored signals V1, V2, V3 and V4 in the upper half of the figure 4 almost look like rectangular waves. The practically rectangular wave which exists from time t9 to time t10 in FIG. 4 comes from the light beam which most directly falls on the receiver 39 and, consequently, with the signals coming from the beams received at neighboring times (signals V1, V2, V4), it is representative of the angle of the plane of the wheel on which the light projector is mounted with respect to a predetermined reference direction.

 The circuit of Figure 3 has a transistor Q connected across the charge storage capacitor C.

When the microprocessor puts the transistor in the conducting state, the load is immediately dissipated by the capacitor. In this way, the capacitor can keep a new signal created by the next received light beam.

The operation of the circuit in FIG. 3 will now be described with reference to the diagram in FIG. 4. A first light beam is received by the receiver 39 at time t0 (FIG. 4) and the transistor Q is set to the non-conducting state at time tl by the microprocessor 43. The capacitor C is charged by the signal at 16,000 Hz, at an amplitude V1 in about three cycles and a practically rectangular wave begins at time tl. The voltage V1 is digitized by an analog-digital converter 47 and transferred to the microprocessor 43. At time t2, the transistor conducts under the control of the microprocessor 43, and the rectangular wave V1 ends (upper part of FIG. 4). first light beam is interrupted at approximately time t3 (lower part of FIG. 4). At time t4, the next light beam is transmitted and, at time t5, the microprocessor 43 places the clipping transistor Q in the non-conducting state. The signal resulting from the reception of the next light beam begins to be stored on the capacitor C at time t6 and reaches the maximum value of the amplitude V2 in a few cycles of the carrier frequency and is stored on the capacitor C in the form of a practically rectangular wave. The signal
V2 is connected to the converter 47 in digitized form and it is transmitted to the microprocessor 43 to be memorized and used according to the program of the assembly for measuring the characteristic angles. At time t7, when the microprocessor 43 causes the setting to the state conductor of transistor Q, capacitor C is discharged.

 The second received light beam is interrupted soon after and the third light beam which can be received is transmitted at time t8. The transistor Q is removed from the conductive state by the microprocessor 43 and the capacitor C begins to charge at time t9. The voltage V3 is obtained in the same way as the voltages V1 and V2.

The sampled amplitude of the voltage is transmitted to the converter 47 which gives a digital value to the microprocessor 43, corresponding to the amplitude V3. This operation is performed for each signal due to the reception of one of the light beams. As a result, signal levels can be updated frequently by the microprocessor which increases the likelihood of an accurate measurement by the assembly.

 The high-pass filter 41 improves the response time of the parallelism detection circuit so that an accurate measurement of the amplitude of the signal produced by the received beam is detected in less than 250 µs. Previously, the parallelism detection assembly contained a bandpass filter and required approximately 2,500 ps to detect the signal produced by a received light beam. As a result, the frequency of updating the data was limited. It is now possible to update the data of the set more often and consequently to carry out a more regular and more precise detection. The smoother, sharper signal detected allows conversion to a ten-bit number, whereas previously an eight-bit number was obtained. This gives an increase in precision by a factor of 4 (from 256 to 1024).

 Sometimes the structure placed on a vehicle between two wheels with independent suspensions can shift laterally causing a misalignment at the wheels. It is useful to detect the moment when such an offset has occurred and to consider the repositioning of the offset member before the adjustment of the wheel angles, so that the adjustments are greatly reduced and make it easier to obtaining the specified values of the angles. For example, as shown in FIG. 5, a pair of front wheels 51 and 52 with independent suspensions are shown in broken lines as being fixed to lower support members 53 and 54 projecting inwardly from the wheels. The actual fixation is removed so that the representation remains clear. A rigid member is fixed between the internal ends. lower members 53 and 54, in the form of a cradle 56 for engine support in this case. The lower support members and the cradle are shown shifted to the right in Figure 5 in broken lines, so that the camber of the left wheel of the figure is positive and that of the right wheel is negative.

As shown, the inclination 57 of the steering axis of the left wheel in the figure is negative and the inclination 58 of the right wheel is positive. The upper fixing point which determines the inclination of the steering axis on each side of the vehicle is stable and is fixed to the chassis 59 of the vehicle. It should be noted that it would be difficult to align the wheels in this condition to obtain the specified camber and tilt of the steering axis. The condition shown in Figure 5 generally occurs as a result of an impact to the vehicle and must be corrected before the wheel adjustment test to obtain specified values of the characteristic angles. , bolts or suitable fasteners are loose and a lever is used for the lateral movement of the cradle 56 to the left in Figure 5 so that it takes its normal neutral position shown in solid lines. As a result, the wheels 51 and 52 have a neutral camber position, and adjustment for the specified camber is easier relative to this position. Furthermore, the inclinations 57 and 58 correspond to a more normal position indicated in solid lines from which inclination adjustments of the steering axis or of the included angle can be easily made. If the camber is different from side to side, if the steering axis tilt readings are different from one side of the vehicle to the other, and if the differences have opposite signs and roughly the same amplitude, an offset of the cradle is indicated, and it is advisable to adjust the lateral position of the cradle before trying additional adjustments of the characteristic angles of the wheels. Thus, the camber and tilt values of the steering axis can be inspected for any pair of wheels with independent suspensions, for the determination that it is necessary to adjust the lateral position of a rigid connecting member. placed between the wheels.

 FIG. 6 represents a pair of vehicle support wheels 61 and 62 connected by a rigid axle 63. This axle is suspended from the chassis by springs 64 and 66 which are fixed to the chassis at their two ends. The axle 63 is fixed to the springs 64 and 68 by elastic yokes 67 which surround the rigid axle and are fixed to the plates 68 themselves fixed to the springs 64 and 66. The central geometric axis 65 of the vehicle is defined by l axis passing through the midpoints of a pair of front wheels and a pair of rear wheels. If the planes of the wheels 61 and 62 are not parallel to the central axis 65, the whole of the axle 63 and the wheels must be displaced by the angle a, as shown in FIG. 6.

 So that a mechanic can offset the axle without repeating several operations, the assembly can provide the necessary amount of adjustment of the yokes. In this way, the mechanic can lengthen the mounting holes by the proper amount and can offset the axles and the rolling direction of the wheels so that they are properly aligned with the central axis of the vehicle in a single operation.

 The adjustment of the wheels 61 and 62 of FIG. 6 can be carried out by the assembly described in this specification by measuring the total parallelism of the wheels 61 and 62 and by determining the bisector of the total parallelism in order to obtain the rolling direction of the wheels which forms the angle a with the geometric central axis 65 of the vehicle. The distance W between the springs 64 and 66 is known or is measured. The calculation L = Wsina is then executed, L being the length of the holes 69 in FIG. 6A. The determination of the dimension L and the elongation of the holes of one of the yokes 68 of this dimension allow the wheels 61, 62 fixed to the rigid axle to be displaced by an angle such that the direction of rolling of the wheels is then aligned on the geometric axis 65. It should be noted that the dimension L of elongation of the holes 69 can be adjusted to half on one side and half on the other side, so that the same correction of the wheel track can be obtained.

The dimension L is shown in FIG. 6A in one direction for the hole 69 in a direction of rotation and in the other direction for the hole 69 in the opposite direction of rotation of the rolling direction of the wheels 61 and 62. It appears as well as the elongation necessary for the correction of the condition of Figure 6 must be made in the yoke 68 on the left side, the hole 69 being elongated backwards as indicated by Lr in Figure 6A. In
r variant, the state of Figure 6 can be corrected by lengthening the holes 69 of half Lr in the left yoke and half Lf (forward) in the right yoke.

 The set of characteristic angles described above can be used for adjusting the camber, the inclination of the steering axis and / or the included angle (angle formed by the inclination of the axis of steering and camber), while the vehicle is raised and when the display represents values corresponding to the values that should exist if the wheels were placed on a support surface. We usually lifted the vehicle, measured the inclination of the steering axis by turning the steering wheel and calculated, then we lowered the vehicle, we checked the camber variation read from the raised position to the lowered position, and we corrected the tilt of the steering axis with the change in camber reading. As this memo proposes, the measurements of the steering axis tilt, included angle and camber can be obtained by wheel direction guidelines straight ahead and conservation of the camber reading from the camber clinometer (item 11 in Figure 2). Locking the brakes and locking the rotating heads on the wheels and lifting the vehicle above the support surface are then a common process. At this time, the variation in camber reading is observed and kept as the camber difference. The inclination of the steering axis is measured with the wheels raised by rotation of a known left angle of direction, by reading the clinometer. steering axis tilt (item 12 in Figure 2), with steering in a known right turn, and by another reading of the steering axis tilt clinometer. The tilt of the steering axis is calculated from the left and right readings, in a manner known to those skilled in the art. Next, a modified steering axis tilt and a modified included angle value are calculated with the camber difference value retained after the vehicle has been lifted. The modified value of inclination of the steering axis and included angle is memorized. The wheels are steered straight ahead and the camber reading (already known from the reading before lifting the vehicle) is extracted. At this time, the camber and steering axis tilt readings exist as if the vehicle was placed on a support surface. The readings are studied for the determination of a possible adjustment of the cradle, as described previously with reference to FIG. 5. If an adjustment of the cradle seems necessary and if the operator wants to adjust the cradle, the operation is carried out as described with reference to FIG. 5. At this time, the direction axis inclination, the values of the included angle and the camber are displayed as if the vehicle were placed on a support surface and the values are adjusted to the raised state by using the readings in the "set" state.

 If the included angle is fixed, in the most common case, the included angle is displayed as fixed and the tilt of the steering axis and camber are displayed as variable values. A variable value on a display is a value that changes on the display when the value is adjusted. A fixed or frozen value is a value that does not change on the display of the characteristic angles when the adjustment is made. If the included angle is adjustable, the display shows the tilt of the steering axis as fixed and the included angle and camber as variable values.

Then the adjustments are made. The steering axis inclination, included angle and camber values are memorized after adjustment. The vehicle is then lowered so that it is in contact with the support surface and the variation in the camber value is observed from the raised position to the lowered position. If there is a change between the lifted and lowered values as a result of lowering the vehicle onto the support surface, the change should be taken into account for the correction of the steering axis tilt readings and camber since this is the last information available. If a quantity deviates from the specifications following such a correction, it is possible to repeat the measurement adjustment subroutine in the raised state with the values in the lowered state or to adjust the quantities of characteristic angles while the vehicle is in the lowered state.

 We now refer to Figure 7; a suspension member 71 which is shown carries a wheel on a steering joint 72a and a spindle 72b, shown in phantom. A wheel is mounted on the spindle 72b and the upper part of the steering axis in FIG. 7 is indicated by the point P. A front end F and a rear end R of the support member 71 are shown. The member 71 is called an "A" arm and has a symmetrical configuration as shown in FIG. 7. A change of adjustment at point F by insertion or removal of shims between the vehicle and the member 71 at point F causes a displacement of the point P in the direction Ft. Likewise, the addition and extraction of shims at the point R causes a displacement of the point P in the direction Rt. FIG. 7A represents a graph of the variation of the camber as a function of the variation of the hunting representing the displacements Ft and Rt for exclusive adjustments in F and R respectively. We know that these displacements are offset by approximately 90 ". If we want to obtain a change in camber and a change in flush represented by the point on the graph in FIG. 7A called SEC", it is known that the adjustment can be realized on Ftl and Rtl to obtain the desired camber and the desired hunting.

 Similarly, the arm at A 73 in FIG. 8 having the point P on the steering axis of a supported wheel moves the point P in the direction Ft when adjusting shims inwards at the point F and in the direction Rt when adjusting shims inward at point R. The directions inward IN, outward EX and forward AV are shown in Figure 8 as in the case of Figures 7 and 9. The graph in Figure 8A shows the corresponding adjustments and affects the camber variation and the effect on the hunting variation described with reference to Figure 7A.

Similarly, for a camber and hunting variation represented by the point "SPEC" in the graph of FIG. 8A, adjustments must be made at the points
F and R of the arm at A 73 to perform the variation Ft2 and
Rt2 as shown in Figure 8A.

 In FIG. 9, an A 74 arm of another configuration is shown. The configuration of the arm 74 allows movement in the directions Ft and Rt for adjustment at the points F and R respectively. Obtaining a camber and hunting variation represented by the point "SPEC" on the graph in FIG. 9A requires the adjustment of the point F inwards so that it moves the point P by the distance Ft3 and the displacement of the point R inwards so that it carries out the displacement of the point P of the distance Rt3.

 The foregoing description indicates that, since the responses to the adjustment are offset by 90 "as shown in FIGS. 7 to 9A, the response to the adjustment of a wheel support member such as an arm at A of a first adjustment member (F or R) can be used to predict the effect of the adjustment on the other adjustment member (R or F). or the other adjustment member allows the response of the suspension to be measured and the assembly described calculates a response expected for the other adjustment member. These expected responses are then used for guiding an operator in the flush and camber adjustment operation despite the fact that the adjustment members have interdependent effects on the hunting and camber angles to be corrected. For example, as shown in FIG. 7A, an operator knows that an adjustment (i.e. a cam or shim size adjustment) must be r performed in F to obtain an offset of the suspension of Ftl and another adjustment must be made in R to obtain the offset of the suspension Rtl. Consequently, the method described requires the constant measurement of the flush and the camber, and the displacement of one of the adjustment members with control of the results by the assembly described in the present specification. characteristics thus foresees the effects of the other adjustment member and calculates the necessary displacements of each adjustment member (that is to say the dimension of the shims) which allow the suspension to be adjusted to the specified value. In a further example, in the case of the support member 74 in FIG. 9, an inward adjustment at point F of Ft3 and an inward adjustment at point R of Rt3 are necessary to obtain the desired point SEC ". The operator is then guided during the appropriate adjustments by the display device of the assembly so that it can obtain the value" SPEC "of hunting and camber at the first attempt at separate adjustments, one for F and one for R. The sensor output signals are checked during adjustment and compared to the expected values of the output signals, if the signals have the predicted values or correspond to them with acceptable tolerances , the operation can continue. If the comparison indicates that an error is likely, the operator is warned and guided to compensate for this error. The technique described can be used with suspensions having adjustable lower arms as well. as wheel support members although the adjustment may give responses of opposite polarities.

 Reference is now made to FIGS. 10 to 13 of the drawings which represent various displays for a set of characteristic angle measurements according to the invention. In FIG. 10, the measuring members 75 are arranged on the display device and are referenced by the suitable variable such as hunting, camber, parallelism, inclination SAI, angle included IA, etc., each display device having a needle 76 and a strongly colored line 77 indicating the acceptable range for adjustment on the measuring member. As shown in FIG. 10, all quantities, including transverse flush, transverse camber, full parallelism and recoil are shown for the front wheels of the vehicle and all values are shown as variable values or values that change when adjusting the quantity, as well as with the value of any interdependent quantity . Figure 11 gives the same information as the display in Figure 10, but the information is presented in alphanumeric form. In Figure 12, the display is such that the information given is the same as in Figures 10 and 11, but the information is shown as light bars 78 which can be aligned and text. In all devices display of Figures 10, 11 and 12, the values of the characteristic angles are variable values.

 In the representation of FIG. 13 of the drawings, the quantities representing the angles, for the front and rear steering wheels of a vehicle, are indicated with the format of the measuring device (elements 75, 76 and 77) of FIG. 10 , and caster, camber, parallelism, inclination of steering axis or angle included, transverse caster, transverse camber and full parallelism are indicated for the front and rear wheel pairs. The recoil is displayed for the front wheels and the thrust angle is indicated for the rear wheels in figure 13. All the values indicated on the display device of figure 13 are variable values which can change during the adjustment of the alignment characteristic itself or of any interdependent characteristic.

 In a particular embodiment, the pivotable support member of the wheel has a lower ball joint, and the method includes changing the assignment of adjustment polarities from the assignment of polarities when the member has a joint upper ball joint.

 Of course, various modifications can be made by those skilled in the art to the assemblies and methods which have just been described only by way of nonlimiting examples without departing from the scope of the invention.

Claims (5)

 1. Display for a set of characteristic angle measurement, intended to indicate the characteristic angles of the wheels of a vehicle, characterized in that it comprises:  a graphic control device (31), and  a device (32) intended to give a variable display of all the angles, and connected to the device (31) for graphic control, so that all the variations of angles relating to the characteristic angles during an adjustment are displayed.  2. Display device according to claim 1, characterized in that the device (32) intended to give a variable display comprises a device intended to give signs displayed on an indicator member.  3. Display device according to claim I, characterized in that the device (32) intended to give a variable display comprises a device intended to give signs in alphanumeric form.  4. Display device according to claim 1, characterized in that the device (32) intended to give a variable display comprises a device having adjustment bars and text.  5. Display device according to claim 1, characterized in that the device (32) intended to give a variable display comprises a device intended to display the front parallelism of the individual wheels, the rear parallelism of the individual wheels, the front camber of the individual wheels, front caster of individual wheels, rear camber of individual wheels, rear caster of individual wheels, total parallelism of individual front wheels, total parallelism of individual rear wheels, recoil of front wheels and angle of rear wheel thrust.