WO1989005243A1

WO1989005243A1 - Process for adjusting wheel suspensions

Info

Publication number: WO1989005243A1
Application number: PCT/DE1988/000656
Authority: WO
Inventors: Erich Rubel; Ute Gerlach
Original assignee: Robert Bosch Gmbh
Priority date: 1987-12-02
Filing date: 1988-10-26
Publication date: 1989-06-15
Also published as: DE3740792A1

Abstract

This invention concerns a process and a device for regulating the wheel suspension of a motor vehicle (1) with a wheel suspension comprising springs and means for adjusting the spring. To improve driving confort and/or safety, the road surface (FO) in front of the vehicle or in front of the vehicle wheel is monitored. When unevennesses of the surface are encountered, a signal depending on the size of the unevennesses is produced and influences the spring.

Description

Chassis control procedure

State of the art

The invention relates to a method for chassis control according to the preamble of the main claim. It is already known to statically adjust the suspension properties of a chassis, for example by changing the damping factors of shock absorbers. H. only at the beginning of a journey to change to improve driving comfort and / or driving safety. In this way, it is not possible to adapt the vehicle to constantly changing road conditions.

Advantages of the invention

The method according to the invention with the characterizing features of the main claim offers the advantage that the current road condition can be taken into account during driving operation and that the behavior of the undercarriage can be adapted immediately to the road conditions that occur in the sense of improving driving comfort and driving safety.

Advantageous developments and improvements of the method specified in the main claim are possible through the measures listed in the subclaims. In further subclaims Means specified for performing the method according to the invention.

drawing

The method and the devices for carrying out the method are explained in more detail with reference to the drawing and in the description below. FIG. 1 shows the front part of a vehicle with an ultrasound transducer arranged thereon to explain the measuring principle on which the method is based, FIG. 2 shows the block diagram of a device for carrying out the method according to the invention, FIG. 3 shows the circuit diagram of an exemplary embodiment of the device, and FIG ; 5 shows a diagram for explaining the radiation characteristic of the ultrasonic funnel, FIG. 6 shows a time diagram of the evaluation circuit, FIG. 7 shows the relationship between the number of pulses and the output voltage of the DA converter contained in the ultrasound device, FIG. 8 shows the relationship between speed and Number of pulses, FIG. 9 is a block diagram of the evaluation circuit, FIG. 10 is a circuit diagram of the evaluation circuit, FIG. 11 shows the ultrasound signal and the spring arm deflection of a vehicle wheel as a function of time in a diagram; FIGS. 12 to 15 in diagrams the ultrasound signal and the stamp speed of a stamp simulating the road as a function of time.

Description of the invention

In order to improve comfort and driving safety, the suspension of a vehicle 1 should be adjusted in accordance with the road conditions encountered in the driving operation. For this purpose, the road surface FO is monitored in order to detect bumps in the road before the tires run over it. The temporal change in the distance a (see FIG. 1) between the vehicle floor and the road surface can serve as a measure of the unevenness of the road. This rate of change

v = da / dt (1)

is measured with the correct sign using an ultrasonic sensor 2, which works according to the Doppler effect.

In practical operation, each of these sensors 2 must be attached to the front of the vehicle in the track of each front wheel so that the condition of the road can be detected separately for each of the two pairs of wheels.

The acoustic Doppler effect that occurs with all sound waves, including ultrasound, means a frequency shift between the transmission and reception frequencies when the transmitter and receiver move relative to each other. Only the radial speed component in the direction of connection between transmitter and receiver is decisive, tangential speed components do not cause any frequency shift.

A distinction must be made between two cases:

a) Station at rest, moving receiver

If the receiver moves towards the stationary transmitter at the relative speed v, the receiver registers the changed frequency instead of the transmission frequency f ₀

f = f ₀ (1 + v / c). (2)

C is the speed of sound in the medium in question, v is positive if the movement is in the direction of the transmitter. b) Moving transmitter, stationary receiver

If, on the other hand, the transmitter moves with the relative speed v towards the stationary receiver, the frequency becomes

received, ie there is the same frequency shift as when the transmitter is stationary and the receiver is moving.

When used as an ultrasonic sensor, the transmitter and receiver are mounted next to each other, perpendicular to the road, on the vehicle front (see FIG. 1). The rate of change is considered

v = da / dt (1)

the distance a between the vehicle floor (and thus the transmitter and receiver) and the road surface. A system moved with the vehicle is chosen as the reference system so that the transmitter and receiver appear to be at rest.

The (stationary) transmitter attached to the vehicle sends the frequency f ₀ perpendicular to the road. The frequency thus becomes from the road surface that moves perpendicular to the vehicle floor with the relative speed v

f _r = f ₀ (1 + v / c) (4)

receive. The road surface reflects this frequency and acts as such as a moving transmitter, as it were, while the receiver on the vehicle is at rest. So now the frequency

receive.

For very low speeds v approximately applies

In addition, the vehicle moves at the vehicle speed v parallel to the road. However, as a tangential velocity, it does not cause any frequency shift. However, the rate of change v = da / dt depends on the driving speed v _Fahr = ds / dt:

s is the distance covered by the vehicle. This must be taken into account when processing the determined speed v later. At a speed v in the range between - v _max and

+ v _max the received frequency fluctuates between

f _emin = f ₀ (1 - 2 v _max / c) (7)

and

f _emax = f ₀ (1 + 2 v _min / c) (8)

In order to evaluate the speed information contained in this frequency, the difference frequency f _d between the reception frequency f _e and a fixed superposition frequency f _{ü must be} formed:

= ∣ f _ü - f _e ∣ (9)

Of course, this difference frequency can only be positive. If the transmission frequency f _{0 is} used as the superimposition frequency, no information is obtained about the direction of the movement, ie the sign of v, because positive and negative speeds provide the same positive difference frequency.

It is therefore more sensible to use a frequency that is more than the maximum possible frequency shift as the superposition frequency

∣ f ₀ - f _e | _{max =} 2 f ₀ v _max / c (10)

differs from the transmission frequency f ₀ . Here f _u> f ₀ is selected, it would be equally f _u <f ₀ have been possible. The difference frequency is now calculated

f _d = f _ü - f _e

= f _ü - f ₀ (1 + 2 v / c) (11)

It fluctuates around the offset value

f _do = f _ü - f ₀ (12)

around between the frequencies

f _dmin = f _ü - f _emax

= f _ü - f ₀ (1 + 2 v _max / c)

= f _do - 2 v _max / c (13)

and

f _dmax = f _ü - f _emin

= f _do + 2 v _max / c (14)

It makes sense to then halve the difference frequency in order to create an exactly the same pulse-pause ratio.

This results in the gate frequency

f _g = 1/2 f _d

= 1/2 [f _ü - f ₀ (1 + 2 v / c)], (15) which is then fed to a counter.

The further evaluation of the differential frequency f _d takes place in a counter by means of a comparison signal, the fixed frequency f _{v of which is} substantially greater than the gate frequency f _g . For this purpose, the pulses of the comparison signal are counted during half a period of the gate signal (corresponding to a period of the difference signal). The number of pulses is a measure of the size of the differential frequency and thus also of the speed v.

So three different frequencies are required: the transmission frequency f ₀ , the beat frequency f _ü and the comparison frequency f _v .

If one generates these three frequencies from a single oscillator by multiplication and division, one achieves that the number of impulses is independent of the oscillator frequency:

Oscillator frequency f ₀

Beat frequency f _ü = N1 / N2 f ₀ (16)

Comparison frequency f _v = N1 / N3 f ₀ (17).

The factor N3 is freely selectable, it essentially determines the resolution of the measured speed.

The measuring time on the counter (half the period of the gate signal) is then

This results in the number of pulses

regardless of the transmission frequency.

There are further advantages from this that the oscillator can be of simple construction and that no high demands are placed on the frequency stability, that the temperature drift of the oscillator has no influence, and that no adjustment is required if, for. B. a new ultrasonic transducer is installed.

As a result, a significantly higher accuracy of the measurement result can also be achieved.

Piezo transducers designed as flexible oscillators are used both as transmitters and receivers. These transducers, for example, have a pronounced natural frequency in the range between 30 kHz and 35 kHz. The oscillator oscillates at this resonance frequency and the bandpass filter (see FIG. 3) is tuned to this center frequency. The same exponential funnel explained later with reference to FIG. 4 was used as the sound funnel in front of the transmitter and receiver. Because the beam can be focused in this way, the beam can be directed onto the measuring surface and disturbing influences from the surroundings are kept to a minimum.

However, excessive beam bundling must be avoided because the ultrasound beam is diffracted by air currents (wind) and temperature differences. Diffraction is more pronounced the sharper the beam is focused.

Figure 2 shows the block diagram of a device for performing the method according to the invention. The device comprises an oscillator 10 which generates a transmission signal of frequency f _0. Oscillator 10 is a piezoelectric transducer designed as a flexural oscillator which generates a transmission frequency f ₀ in the range between 30 kHz and 35 kHz. The transmission signal with the frequency f ₀ is supplied on the one hand to a transmission antenna 11 for radiation onto the road surface and on the other hand to a phase lock loop stage 12. Subsequent divider multiplier stages 13, 14 generate the superimposition frequency f _u and the comparison frequency f _v from the frequency f _{0 of} the transmission signal. The device further comprises a receiving part 15 for receiving a signal of the frequency f _e , which results from the signal emitted by the oscillator 10 by reflection on the road surface. The receiving part 15 comprises a receiving antenna 16 and, as a receiver 17, a piezo transducer configured as a bending oscillator of the same type already used in the oscillator 10. The receiving frequency f _e is fed to a mixing stage 20 after amplification in a selective amplifier 18, 19. In this mixing stage 20, the reception frequency f _{e is} mixed with the fixed beat frequency f _ü , so that the Differential frequency f _d results. This difference frequency f _d becomes

Generation of a gate frequency fed to a further divider stage 21, which divides the difference frequency f _d appropriately by two. The gate frequency f _g and the fixed comparison frequency f _v are fed to an evaluation circuit 22 which will be explained later with reference to FIG. 9. This evaluation circuit 22 influences the suspension means 23 of the chassis of the vehicle 1 by means of an output signal U _A.

FIG. 3 shows in the form of a circuit diagram an exemplary embodiment of the device shown as a block diagram in FIG. 2 without the components 22 and 23.

FIG. 4 shows, in side view and partially in longitudinal section, on an image scale of approximately 2: 1, an ultrasonic funnel used both as a transmitting antenna 11 and as a receiving antenna 16, which consists of a first, essentially cylindrical section 41 and a second section 42 , which is substantially frustoconical. The cylindrical first section 41 sits on the base of the frustoconical second section 42. The sections 41 and 42 are penetrated by a bore 43 which extends in the axial direction and widens in a funnel shape towards the radiation or irradiation opening 43a. The ultrasonic funnel 40 enables the emitted ultrasonic waves to be focused so that they can be directed specifically onto the measuring surface. The radiation characteristic of the ultrasonic funnel 40 is shown in the diagram in FIG. On the receiver side, the focusing characteristic of the ultrasonic funnel 40 ensures that as little interference as possible is recorded in addition to the frequency f _e of interest. However, excessive beam bundling should be avoided, as driving due to air Currents and temperature differences can cause diffraction effects that can impair the coupling between the transmitting antenna and the receiving antenna.

The evaluation circuit designated 22 in the block diagram of FIG. 2 will now be described with reference to FIG. 6, FIG. 9 and FIG. 10. Figure 6 shows a timing diagram of the evaluation circuit, while Figure 9 shows the evaluation circuit as a block diagram and Figure 10 shows the evaluation circuit as a circuit diagram. The evaluation circuit according to FIG. 9 comprises an EX-OR gate 90, the input terminal of which is supplied with the gate frequency f _g . The output connection of the EX-OR gate 90 is connected on the one hand to the input connection of a monostable multivibrator 91, and on the other hand to the stop connection of a binary counter 92. The comparison frequency f _{v is} supplied to the input terminal of the binary counter 92. The output terminal of the binary counter 92 is connected to a buffer 93. The output terminal of this buffer 93 is in turn connected to the input terminal of a digital-to-analog converter 94, at the output terminal of which the output signal U is available. To explain the function of the evaluation circuit 22, FIG. 6 and FIG. 10 are now considered in addition.

The pulses of the comparison signal f _{v are} counted during a half period of the gate signal f _g . The number of pulses determined is converted into an analog voltage value U _A. However, in another exemplary embodiment of the invention, the pulses present as digital information can be taken over directly by a computer for further processing.

On each edge of the gate rectangular signal f _g (FIG. 6b), a short rectangular pulse is first generated by the EX-OR gate 90 (EXOR signal FIG. 6c). Its falling edge triggers a mono stable flip-flop 91, which then also emits a short square pulse (monoflop signal Figure 6d). The duration of the two pulses is determined by the external RC circuit (see Figure 10).

As long as no EXOR signal is present, the pulses of the comparison signal f _v (FIG. 6a) are counted up by the binary counter 92 (FIG. 9). As soon as the EXOR signal jumps to H, the counter 92 is stopped. At the same time, the counting result achieved so far, the number of pulses n _I , is transferred to the buffer memory 93, which acts as a holding element. Then the binary counter 92 is reset by the monoflop signal and it can be counted again.

The total duration t _e + t _{m of} the two rectangular pulses

EX-OR gate 90 and the monostable multivibrator 91 is appropriately dimensioned such that:

t _e + t _m <T _v = 1 / f _v , (20)

This ensures that only a maximum of one pulse of the comparison signal f _{v is} omitted during counting. For N3 ≥ 2 this can be achieved with the circuit proposed here. For N3 = 1, however, this condition can no longer be met; then the duration of the EX-OR pulse t _e should be as short as possible.

The result pending at the output of the buffer memory 93 is converted into an analog one by a digital-to-analog converter 94

Voltage value U _A , implemented. The signal U _A then affects the

Suspension means 23 in the sense of improving driving comfort and / or driving safety. The time until the next measured value update depends on the frequency of the gate signal f _g and thus on the measured value. It is on average

and thus depends on the chosen oscillator frequency f ₀ .

The output voltage of digital-to-analog converter 94 was measured at some predetermined fixed pulse numbers. The relationship determined is shown in FIG. 7.

Out

results for the dependence of the speed on the measured number of impulses

The relationship calculated in this way is plotted in FIG. 8.

A test run was made for N3 = 5 and an 8-bit digital-to-analog converter 94 in the evaluation circuit according to FIG. 9, FIG 10 used. The device was attached under the bumper of the test vehicle in the track of the right front wheel in such a way that the funnels of the ultrasonic transducers were directed approximately perpendicularly downwards onto the surface of the road. FIG. 11 shows the ultrasound signal in the upper curve and the spring deflection of the shock absorber on the right front wheel measured for comparison when driving at a constant speed of 80 km / h in the lower curve.

Substantially better results were achieved with N3 = 1 and a 10-bit DA converter in the evaluation circuit according to FIG. 9, FIG. 10.

Further measured values (FIGS. 12 to 15) were obtained on a test bench. The vehicle was driven to the test stand in such a way that the device was fixed above a stamp that was arranged to move up and down and simulate the surface of the road. The stamp was moved sinusoidally up and down at an average measuring distance of approx. 30 cm. Stamp deflection and the output signal of the DA converter were recorded as a function of time in the measurement diagram.

Using the relationship between the output voltage of the DA converter and the number of pulses (Figure 7) was able to

the corrected double signal can be calculated. The corrected Doppler signal (lower curve) and the punch speed (upper curve) are shown for different vibration frequencies of the punch in FIGS. 12 to 15. For better differentiation, the two signals in the diagrams are slightly shifted from each other in the vertical direction. From the diagrams it can be clearly seen that the corrected Doppler signal obtained by reflection on the stamp surface reproduces the stamp movement very precisely, so that unevenness in the road surface can be determined in this way and used to influence the spring means 23.

It was mentioned above that a sensor 2 is attached to the front of the vehicle in the track of each front wheel in order to be able to separately detect the road condition for each of the two wheel pairs. It is also possible to assign a separate sensor to each wheel of the undercarriage.

Claims

Expectations

1. A method for chassis control of a motor vehicle with a suspension comprising suspension means, and with means for influencing the suspension means, characterized in that the road surface in front of the vehicle or in front of the wheels of the vehicle is monitored and that when bumps occur on the extent of the bumps dependent Signals are generated and the suspension means are influenced in the sense of improving driving comfort and / or driving safety.

2. The method according to claim 1, characterized in that the temporal change (da / dt) of the distance (h) between the vehicle floor and road surface (0) is evaluated to determine uneven road surfaces.

3. The method according to any one of claims 1 and 2, characterized in that to determine the change over time (v = da / dt) of the distance (a) between the vehicle floor and road surface (0), the speed-dependent frequency change of a radiated from the vehicle and from the road surface reflected signals of the frequency (f ₀ ) is evaluated.

4. The method according to any one of claims 1 to 3, characterized in that the signal reflected from the road surface to form a differential frequency (f _d ) is superimposed with a signal whose frequency (f _ü ) is more than the maximum possible frequency shift ( Doppler effect) on the frequency (f ₀ ) of the

Broadcast signals differentiates.

5. The method according to any one of claims 1 to 4, characterized in that the differential frequency (f _d ), optionally by division, is converted into a gate frequency (f _g = 1/2 f _d ) and fed to a counter in which the gate frequency (f _g ) is compared with a comparison signal, the frequency (f _v ) of which is constant and substantially greater than the gate frequency (f _d ).

6. The method according to any one of claims 1 to 5, characterized in that the frequencies (f ₀ , f _ü , f _v ) are derived from a single oscillator.

7. The method according to any one of claims 1 to 6, characterized in that an ultrasonic signal is emitted from the vehicle.

8. The method according to any one of claims 1 to 7, characterized in that the frequency (f ₀ ) of the ultrasound signal emitted by the vehicle between 30 kHz and 35 kHz, in particular at about

33 kHz.

9. The method according to any one of claims 1 to 8, characterized in that the following relationships between the frequencies (f ₀ , f _ü and f _v ) are maintained

N1 = 32, N2 = 30 and N3 = 1.

10. Device for carrying out the method according to one of claims 1 to 9, characterized by an oscillator (10) for generating the oscillator frequency (f ₀ ) and a transmitting antenna (11) for radiation of the oscillator frequency (f ₀ ) on the road surface, divider or multiplication stages (13, 14) for generating a superposition frequency (f _ü ) or a comparison frequency (f _v ) from the oscillator frequency (f ₀ ). a receiving part (15) comprising a receiving antenna (16) and a receiver (17) and a selective amplifier (18, 19) for receiving and amplifying the signal of frequency (f _e ) reflected from the road surface, a mixing stage (20) for Forming a difference frequency (f _d ) between the reception frequency (f _e ) and the fixed superposition frequency (f _ü ), a division stage (21) to form a

Gate frequency (f _g ) from the difference frequency (f _d ), an evaluation circuit (22) which, to form an output signal (U _A ) influencing the suspension means (23), the gate frequency (f _g ) and the comparison frequency (f _v ) are forwarded.

11. The device according to claim 10, characterized in that the evaluation circuit (22) comprises an EX-OR gate (90), the input terminal of which is fed the gate frequency (f _g ), the output terminal on the one hand with a monostable multivibrator (91) and on the other hand is connected to the lock input of a binary counter (92), at the input connection of which the comparison frequency (f _v ) is conducted and whose erase input is connected to the output connection of the monostable multivibrator (91), that the binary counter (92) has a buffer (93) and this in turn is followed by a digital-to-analog converter (24), and the output voltage (U _A ) for influencing the spring means (23) is derived from its output connection.

12. Device according to one of claims 10 and 11, characterized in that both the oscillator (10) and the receiver (17) each comprise a piezoelectric transducer designed as a bending oscillator.

13. Device according to one of claims 10 to 12, characterized in that the device has a transmitting antenna (11) and a receiving antenna (16) which are designed as "ultrasonic funnels", d. H. which have a central axial, substantially rotationally symmetrical recess, which has the shape of an exponential funnel.

14. Device according to one of claims 10 to 13, that each track of the vehicle is assigned a device, wherein at least oscillator (10) and receiving part (15), including the associated transmit and receive antennas (11, 16) in the vehicle front before Front wheel are arranged.