GB2079464A - Electrically testing power assisted steering - Google Patents

Abstract

Apparatus for testing power- assisted steering gear in a motor vehicle has a pressure transducer (8) connectible in the hydraulic circuit of the steering gear, an angular displacement transmitter (21) for mounting directly on the steering wheel hub of the vehicle, and a steering spindle torque transducer (1) attachable to the rim of the steering wheel. These sensors (1, 8, 21) are connected to an electronic processing unit including an analogue-to- digital converter (6) for providing a digital pressure readout on a pressure indicator (7), and a differential amplifier (13) and comparator (14) for controlling the display of the steering wheel angular displacement reading produced by an up/down counter (22) in response to a difference signal representing the difference between a previously sensed pressure level stored by a sample-and- hold circuit (12) and an instantaneous pressure level obtained directly from the pressure transducer. <IMAGE>

Description

SPECIFICATION Apparatus for testing the power-assisted steering gear of a motor vehicle The invention relates to an apparatus for testing, mainly as part of the regular service schedule, the hydraulic steering gear and a power-assisted steering system of a motor vehicle.

In respect of the reliability and running condition of a motor vehicle, one of the most important units is the steering gear. Its parameters and their testing are laid down in various standards and specifications.

Periodically, it is necessary to measure the listed parameters and to carry out adjustments. Devices are known for measuring each parameter of power steering gear separately, including devices for measuring the force exerted on the steering wheel by the driver of the vehicle.

In the apparatus described in the GFR Patent Specification DE 1573 957 a test steering wheel is fixed onto the steering wheel of the motor vehicle and the driver turns this testing steering wheel. A dynamometer incorporated in the steering wheel is used to measure the force applied to the wheel and a reading is recorded by a chart recorder. Handling of the apparatus requires experience in this field of measurement, and it is not suitable for fast diagnosic tests in a motor vehicle service station. Its handling under service conditions is difficult.

In the steering testing apparatus described in the GRF Patent Specification No. 25 01 521 a test steering wheel is mounted on the steering spindle of the motor vehicle in place of the standard steering wheel. Electric or electronic measuring elements are arranged in the test steering wheel, and an electric unit indicates the measured torque values. Although the measuring accuracy is adequate and the indication is reliable, the steering wheel of the vehicle has to be dismounted, and the mounted test steering wheel is not necessarily in the same position as the original steering wheel, i.e. its position in relation to the driver may be different.

Measuring the force exerted on the steering wheel by the driver, i.e. the torque, is necessary mainly when testing the steering properties of the motor vehicle naturally to be carried out while the vehicle is travelling.

The testing apparatus described in Hungarian Patent Specification No. HU 163420 is suitable for testing hydraulic power-assisted steering gear when dismounted from the motor vehicle. It records graphically the torque output of the worm shaft as a function ofthetorque applied at the steeering wheel.

Reading and evaluation of the measurement data involves subjective errors, and comparisons and calculations have to be performed by the person conducting the measuring. At the same time the measurements and tests generally apply only to a power-assisted steering wheel, and are not capable of testing a complex power-assisted steering system.

It is an object of the invention to provide checking and testing apparatus suitable for carrying out diagnostic tests relatively rapidly and with relatively little experience in making steering gear measurements.

According to this invention apparatus for testing power-assisted steering gear in a motor vehicle comprises: an incremental angle data transmitter having a rotatable part for connection to a vehicle steering spindle and a stationary part for mounting on a fixed surface on the vehicle; a pressure transducer for sensing hydraulic pressure in the power-assisted steering gear; and an electronic processing unit including a differential amplifier having one input coupled to the pressure transducer via a sample-and-hold circuit and a second input coupled to the transducer by a link by-passing the sample-and-hold circuit, the output of the differential amplifier being coupled to a comparator for producing an output pulse when the difference between two pressure signal levels or the two inputs of the differential amplifier exceeds a preselected reference level, the processing unit further including a pulse counter connected to the angle data transmitter and arranged to feed an angle data signal to an angular displacement storage means, which means is responsive to the comparator output pulse to store an angular displacement value.The apparatus enables the testing of several characteristics of the steering gear with one piece of equipment, and in its preferred form permits the automatic indication of relative hydraulic pressure values after having fixed a reference value. The numerical data may be indicated in digital form. The sensing units of the apparatus may be easily connected to steering gear in situ in a motor vehicle without substantial disassembly of the functional units of the power-assisted steering gear.

The sensing units emit electrical measuring signals which are processed by the electronic unit containing logic circuits permitting several operation modes, the tests corresponding to each operation mode being carried out with a specified input signal value combination. In this way, the diagnostic tests can be carried out comparatively rapidly and substantially without the subjective operator errors often associated with known measuring equipment.

In the preferred embodiment the elements sensing the angular displacement of the steering spindle and the torque exerted on the steering wheel can be particularly quickly and easily fixed.

The invention will now be described by way of example with reference to the drawings, in which: Figure lisa block diagram of measuring apparatus in accordance with the invention; Figure 2 is a longitudinal section of a steering spindle torquemeter mounted on the steering wheel of a motor vehicle; and Figure 3 is a longitudinal section of a steering spindle angular displacement transmitter mounted on the steering wheel.

Referring to Figure 1, a torque measuring transducer 1 attached to the motor vehicle steering spindle is connected to a torque level sensing and processing unit 2, which drives, via its output 2d, a digital torque indicator 3. Another output 2a of the unit 2 is connected through the short-time delay unit 4to a timing and torque level selector switch 28. A further output 2b is connected to the selector switch 28 through a long-time delay unit 5. The timing and torque level selector switch 28 is provided for adjusting e.g. the signal level of the dynamometer fixed on the steering wheel which can thereby be corrected according to the effective radius of the wheel, and it also enables a delay to be introduced while hydraulic pressure in the steering system stabilises. The output 28c of the selector switch 28 is coupled to the control input 6a of an anlogue-todigital converter 6.The purpose of the analogue-todigital converter 6 is to digitise an analogue pressure signal produced by a pressure sensor 8 and to drive a digital pressure indicator 7. An output 8b of the pressure sensor 8 is coupled via a signal conditioning unit 9 and a low-pass filter 10 to the signal input of the analogue-to-digital converter 6.

The output of a second processing unit 11 including a signal processing unit and low-pass filter is connected directly to the input 13b of a pressure signal differential amplifier 13 and indirectly through a sample-and-hold circuit 12 to the input 13a.

Alternatively the input of the sampie-and-hold circuit 12 and the input 13b of the differential amplifier 13 may be connected in parallel with the data connection to the analogue-to-digital converter 6 at the output of the low-pass filter 10. Output 13c of the differential amplifier 13 is connected to a selector switch 20 which in its first position connects the output 13e of the differential amplifier 13 to the input 14a of the comparator 14. In its second position it connects input 14a to the third output 2c of the torque signal processing unit 2. In its third position it connects the input 1 4a to a steering wheel movement sensing signal transmitter 29.The comparator 14 has a reference input 14b connected to a comparison level adjusting device 17a via a measuring limit selector switch 17, by means of which the required measuring pressure levels can be adjusted relative to the normal pressure level of the hydraulic pump of the power-assisted steering gear. Under test, a first output 1 4c of the comparator and pulse transmitter 14 is connected to the first input 15a of an OR-gate 15, while its second output 14d is connected to the second input 26b of the null circuit 26. A first input 26a of the null circuit 26 is connected to a null switch 16 and an output of the sample-and-hold circuit 12.

A switch 19 for producing a continuous display indication provides a logic input to the second input 15b of the OR-gate 15. The output 15c of the OR-gate 15 is coupled to a steering spindle angular displacement store 18 and its control input. The data input 1 8a of the store 18 receives signals from the output 22b of an up/down counter 22 which in turn receives at its input 22a from the output of a direction sensitive angular data transmitter 21. The angular data transmitter 21 is fixed to the steering spindle of the power-assisted steering gearto be tested, orto the steering wheel. Output 27c of the null circuit 27 is connected to the control input 22a of an up/down counter 22. A steering spindle angular displacement indicator (not shown in Figure 1) is connected to the output of the steering spindle angular displacement store 18.

An oil temperature transmitter 23 senses the oil temperature in the hydraulic system of the powerassisted steering gear. This transmitter 23 is con- s nected to a measuring bridge and comparator unit 24, which drives an oil temperature indicator unit 25 indicating the actual temperature or a number of different temperature ranges. A pressure changeover switch unit (not shown) is connected to control inputs of the pressure transducer 8 and signal conditioning unit 9.

Referring now to Figure 2 a dynamometer unit 1 is shown fixed to a steering wheel by means of a clamping yoke 4. The dynamometer arbor 6, arranged tangentrally to the steering wheel rim 3, is screwed to the shanks 5 of the clamping yoke 4. The dynamometer 1 has a housing 15 formed as a handle, one end of which is movably guided on the cylindrical surface 11 of the dynamometer arbor 6.

Its other end is guided by the spring cup 31 sliding on the pilot pin 23 of the dynamometer arbor 6. A second spring cup 20 guided on the pilot pin 23 has an end plate 19 urged against a shoulder 18 of the dynamometer arbor 6 by a coil spring 28. The dynamometer spring 28 is supported by supporting surface 21 of a second spring cup 20. The end plate 19 of the spring cup 20 is supported at the same time by a shoulder 37 in the inner wall 36 ofthe dynamometer housing 15 in its normal stationary position. The other end of the dynamometer spring 28 is similarly supported by the supporting surface 29 of the spring cup 30 guided on pilot pin 23, while the opposite end plate 32 of the spring cup 30 is in contact with the internal surface 34 of a lock nut 31 screwed onto the housing 15.A movable stop ring 25 is arranged on the pilot pin 23 between the spring cups 21 and 30, the end surfaces 24 and 26 of which form contact surfaces for the stop collar 22 of the spring cup 20 and the stop collar 21 of spring cup 20.

The length of the stop ring 25 determines the minimum, compressed length of the spring 28. A second stop ring 33 is arranged on the pilot pin 23 of the dynamometer arbor 6 between the shank 5 of the clamping yoke 4 and the spring cup 30, the length of which stop ring is determined so that there is no play in the normal stationary position of the housing 15 between the stop ring end surface 35 and the end surface 32 of the spring cup 30.

The dynamometer housing 15 is prevented from rotating on the dynamometer arbor 6 by a pin 39 fixed in a hole 40 in the dynamometer housing 15 and received in a groove 38, in the arbor 6.

During operation, the dynamometer housing 1Y moves axially on the dynamometer arbor 6, its displacement from the normal stationary position' representing the torque applied at the steering wheel. The displacement is measured by an electrical measuring element pair 13, in the form of a thrust resistor the stationary part of which is fixed in a recess 7 in the dynamometer arbor 6. A connecting cable 10 for the stationary part has an outlet through a terminal 8 fixed in the recess 7. A slide 16 fixed to and moving with the dynamometer housing 15 had a contact base 17 which contacts the potentiometer 14.

The slide 16 is connected to a cable 4 which passes through the terminal 8.

The displacement sensing element 13 produces an output voltage proportional to the dynamometer displacement and proportional to the applied torque.

Measurement of the angular displacement of the steering wheel is performed by a measuring unit 2, shown in Figure 3. The unit is fixed with a clamp 80 designed for rapid attachment in the cylindrical recess 45 of the steering wheel hub 43, which hub is fastened by bolts 44to the steering spindle 42. The outer mantle surface of a clamping ring 49, which ensures the locating and fixing of the clamp 80, bears against the inner surface 50 of the recess 45 of the steering wheel hub 43. A pressure plate 52 is movably fitted on the cylindrical surface 54 of a carrier shaft 53 which has a thread 56 mounting a clamping nut 57 and handle 58. The clamping nut 57 serves to compress the flexible clamping ring 49 between the pressure plate 52 and a cup 46, firmly fixed to the cylindrical surface 54 of the shaft 53.

Afemale thread 60 of a second shaft 81 carrying the electric angular displacement transmitter 74 (21 in Figure 2) fits the thread 56 of the shaft 53, and the threaded elements are screwed into each other until they contact. A ball bearing 63 on the journal 66 is in contact with a shoulder 61 on the carrier shaft 53, and has an outer race which fits into the recess 64 of a stationary substained hub 70. The ball bearing 63 is located on the journal 66 with a circlip 65 and in the stationary hub 70 with a circlip 62. A stationary part 72 of the angular displacement transmitters 74 is arranged in a recess 71 of the stationary hub 70. The coupling 68 joins dog 69 of the rotary part 73 of the angular displacement transmitter 74through dog 67 to the carrier shaft 59.The stationary hub 94 has a restraining arm 78, which is rigid in the plane of the longitudinal section of the carrier shaft 59 and jointed in the cross sectional plane. The restraining arm 78 has a clamping element formed as a suction-grip disc 79 which can be fixed to the driver's cabin, suitably onto the windscreen.

The testing apparatus is suitable for performing the following tests on hydraulic power-assisted steering gear and on the steering mechanism of a motor vehicle: - maxiinally drivable pressure by the powerassisted steering gear - mechanical play of the steering mechanism - hydraulic steering limit - hydraulic play -determination of play in the steering rods - checking the operation temperature range of hydraulic oil in the hydraulic system of the powerassisted steering gear.

The apparatus functions as follows: The torque transducer 1 and the dynamometer units are fixed with clamping screw 68 (Figure 2) onto the steering wheel 3 of the motor vehicle and power-assisted steering gear, and the steering spindle angular displacement measuring unit 2 (Figure 3) is fixed to the steering wheel hub 43 of the steering wheel. The suction-grip disc 79 (Figure 3) of the restraining arm 78 is fixed onto the windscreen of the vehicle's cabin.

During measurement, the operator turns steering wheel rim using the dynamometer housing 15 (Figure 2) as a handle. As a result of the turning force, the dynamometer spring 28 of the dynamometer unit 1 is compressed, the dynamometer housing 15 moves on the dynamometer arbor 6 to produce a displacement signal at the output of the displacement sensing element 13. In this embodiment, the output signal is proportional to the turning force, since the dynamometer spring 28 has a linear rate characteristic, and the resistor 14 also has a linear resistance characteristic.

The magnitude of the turning angle of the steering wheel 3 is measured with the angular displacement transmitter 21 in that the rotary part 73 (Figure 3) turns with the steering wheel 3 and relative to the stationary part 72 and the stationary hub 94, the coupling 99 transferring the rotation of the steering wheel 3 via carrier shaft 81.

The angular displacement transmitter 21 emits an anlogue electric signal on its output 21 a (Figure 1).

To measure maximum drivable pressure on the power-assisted steering gear, the steering spindle of the motorvehicle is manually turned through the handle of the steering spindle torque measuring transmitter 1 fixed to the steering wheel, while the steered wheels of the motor vehicle, or the steering rods actuating the wheels are prevented from moving. The torque signal transmitted by the steering spindle torque measuring transmitter 1 passes to the input 2e of the torque level sensing and processing unit 2 (Figure 1). In the torque level sensing and processing unit 2 the analogue signal passes through a receiving amplifier and rectifier, as well as through a multiplier stage adjustable according to the diameter of the steering wheel 3. The signal at output 2d is fed to the continuously indicating digital torque indicator 3.An output signal produced at output 2c is passed to the comparator circuit 14 set to a fixed torque level of preselected value. For this measurement, the timing and torque level selector switch 6a connects the control input of the analogueto-digital converter 6 via the long-time delay to the unit 2 for controlling the commencement of the count of the analogue-to-digital converter 6. A sudden change of the comparator output signal connected to the output 2b of the torque level sensing and processing unit 2 - which occurs when the steering spindle torque increases to a given value, starts an internal timing circuit of the longtime delay unit 5. If no change occurs on the output 2b within the set time, then at the expiry of that time a measurement starting pulse is fed through the timing and torque level selector switch 28 to the control input of the analogue-to-digital converter 6.

An analogue pressure signal generated by the pressure sensing unit 8 connected to the highpressure conduit of the power-assisted steering gear hydraulic system, passes to the measuring input of the analogue-to-digital converter 6 through the signal conditioner 9 (which has an amplifier set by the pressure limit change-over switch for measuring a high-pressure range) and through the low-pass filter 10 for filtering the oscillations generated by the pump of the hydraulic cycle present in the measur ing signal. At the end of the conversion cycle of the analogue-to-digital converter 6, the value of the maximum drivable pressure of the power-assisted steering gear appears on the digital pressure indicator 7 in numerical form.

When measuring the hydraulic steering limits of the power-assisted steering gear, it is necessary to place stop inserts onto the wheel stops corresponding to the specified limiting angle, then the steering wheel rim 3 is turned as described before through the handle 15 of the steering spindle torque measuring transmitter 1 until contact while watching on the digital indicator 3 as the steering spindle torque increases to a specified value. When measuring the hydraulic steering limitation, the timing and torque level selector switch 6a connects the short-time delaying unit 4 to the control input 6a of the analogue-to-digital converter 6 for starting the conversion cycle. The measurement differs from measuring the maximally drivable pressure only in the value of the steering spindle torque level which triggers the analogue-to-digital converter.

Hydraulic play can be measured when the powerassisted steering pump runs at the given speed, by actuation of the null switch 16 so that the sampleand-hold circuit 12 stores a reference voltage signal in analogue form, measured by the pressure sensing unit 8 in the hydraulic cycle of the power-assisted steering gear, said reference signal corresponds to the reference pressure values fed to the sample-andhold circuit 12 input processed through the signal conditioner 9 and low-pass filter 10 set to low measuring limit with the pressure change-over switch 11. In the so-formed reference voltage signal remains unchanged on the input 13a of the pressure signal differential amplifier 13, while on its input 13b a voltage signal appears corresponding to the existing pressure value arising at start of the servoeffect occurring when the steering wheel 3 is turned.

The output signal of the pressure signal differential amplifier 13 is proportional to the difference in the voltage signals at the inputs 13a and 13b, and the said output signal is fed by switch 20 to the input 14a of the pressure comparator and pulse transmitter 14.

Fixed voltage values set by a resistance divider corresponding to pressure levels of 0.5 and 1 bar are fed to the input 14b of the comparator 14 by the measuring limit selector switch 17. When the steering wheel rim is turned in one direction, pressure signal at input 14a rises in relation to the reference value, and when it reaches the value set on the input 14b a pulse is generated at the output 14d which passes to the input 26b of the null circuit 26, and also clears the counter 22. When the steering wheel rim is turned in the opposite direction, the pressure value returns to the reference value, then rises again to reach the voltage level set on the reference output 14b of the comparator and pulse transmitter 14.At this point an entry pulse is fed through the OR-gate 15 to the steering spindle angular displacement store 18, which then takes over and records via its data input 18a the number of pulses received bythe up/down counter 22 from the incremental directionsensitive angle data transmitter fixed onto the steering wheel between the positions corresponding to the null pulse and entry pulse. The numerical value of the hydraulic steering play appears on the steering spindle angular displacement indicator (not shown) connected to the output of the steering * spindle angular displacement store 18.

Measurement of the mechanical play of the pow- er-assisted steering gear and steering mechanism,' and of the total play of the steering system and rods (linkages) is similar two the measurements described above, with the difference that the switch 20 con necks the input 14a of the comparator and pulse transmitter 14 in one case to the output 2c of the torque level sensing and processing unit, while in the other case to the output of the signal transmitter 29 sensing the movement of the steering wheel.

When the switch 19 gives "Yes" level to the input 15b of the OR-gate 15, it enables the continuous overwriting of the output 22b of the up/down counter 22 into the steering spindle angular displacement store 18, thereby providing a continuous indication of the instantaneous value of the steering angular position.

The tests give comparative measuring values the hydraulic system of the power-assisted steering gear when in the warmed up condition. This condition can be monitored by the temperature transmitter 23 which senses the temperature of the hydraulic oil, and provides a signal to the measuring bridge and comparator unit 24 to the unit 25 for indicating various temperature ranges.

Claims (9)

1. Apparatusfortesting power-assisted steering gear in a motor vehicle, the apparatus comprising: an incremental angle data transmitter having a rotatable part for connection to a vehicle steering spindle and a stationary part for mounting on a fixed surface on the vehicle; a pressure transducer for sensing hydraulic pressure in the power-assisted steering gear; and an electronic processing unit including a differential amplifier having one input coupled to the pressure transducer via a sample-and-hold circuit and a second input coupled to the transducer by a link by passing the sample-and-hold circuit, the output of the differential amplifier being coupled to a comparator for producing an output pulse when the difference between two pressure signal levels or the two inputs of the differential amplifier exceeds a preselected reference level, the processing unit further including a pulse counter connected to the angle data transmitter and arranged to feed an angle data signal to an angular displacement storage means, which means is responsive to the compars- tor output pulse to store an angular displacement value.

2. Apparatus for testing power-assisted steering gear in a motor vehicle, which apparatus has a pressure transducer connectible to the highpressure circuit of the power-assisted steering gear hydraulic system, an incremental direction-sensitive angle data transmitter emitting an electrical output signal, the transmitter having a stationary part fixed to the driver's cabin and being in motion transferring connection with the steering spindle, characterized in that the pressure sensing unit is connected to a signal conditioning unit the output of which is connected through a low-pass filter firstly to a first input of a pressure signal differential amplifier and secondly via a null switch actuated sample-andhold circuit to a second input of the pressure signal differential amplifier, the output of the differential amplifier being connected to a first input of a comparator and pulse transmitter, the second input of which is connected to a comparison level adjusting device through a measuring limit selector switch, the first output of the comparator and pulse transmitter being connected via an OR-gate to a steering spindle angular displacement storage unit, and further characterised in that the output of an upl down counter is connected to a data input of the angular displacement storage unit, the output of the incremental direction-sensitive angle data transmitter is connected to the input of the up/down counter which counter has a control input connected to the output of the null circuit, the output of the steering spindle angular displacement storage unit being connected to a steering spindle angular differential indicator, and furthermore in that a pressure indica torwith digital read-out is connected through an anlogue-to-digital converter to the output of the low-pass filter.

3. Apparatus according to claim 2, characterised in that a switch is arranged between the pressure signal differential amplifier and the comparator for connecting the comparator to the third output of a torque sensing and processing unit which is coupled to a steering spindle torque measuring transmitter, and in that a second output a torque level sensing and processing unit is connected through a delay unit to the input of a timing and torque level selector switch, the output of which is connected to the control input of the said analogue-to-digital converter, a digital torque indicator being connected to a third output of the torque level sensing and processing unit.

4. Apparatus according to claim 2, characterized in that the switch arranged between the comparator and the pressure signal differential amplifier has an input terminal connected to a signal transmitter sensing the movement of the steering wheel of the motor vehicle during steering.

5. Apparatus according to claim 1, characterized in that a pressure limit switch is connected to a control input of the pressure transducer and/or the signal conditioning unit.

6. Apparatus according to claims 2 to 5, including a temperature transducer for sensing the temperature of hydraulic oil in the hydraulic system of the power-assisted steering gear, the transducer being connected through a measuring bridge and comparator unit to a unit indicating various temperature ranges.

7. Apparatus according to claim 3, characterized in that the steering spindle torque measuring transmitter comprises a dynamometer shaped as handle for fixing on the steering wheel rim of the motor vehicle, the dynamometer having a housing which is movably mounted on an arbor arranged generally tangentially on the steering wheel rim, the dynamometer having a spring connecting the housing and the arbor, the torque transmitter being mounted in the housing to sense movement of the housing relative to the arbor.

8. Apparatus according to claim 7, wherein the stationary part of the incremental angle data transmitter is fixed to a stationary hub rotatably supported on a rotatable carrier shaft which is clamped to the steering spindle and steering wheel hub while the rotary part is coupled to the carrier shaft, and wherein a restraining arm, jointed in the plane of the steering spindle and rigid in the plane perpendicular to it, is fixed to the stationary hub, the said restraining arm having means for fixing itto a stationary surface of the driver's cabin of the motor vehicle.

9. Apparatus for testing power-assisted steering gear in a motor vehicle, the apparatus being constructed and arranged, substantially as herein described and shown in the drawings.