WO2001015950A1

WO2001015950A1 - Method for monitoring rotational-speed sensors in a vehicle fitted with an anti-lock braking system

Info

Publication number: WO2001015950A1
Application number: PCT/EP2000/008411
Authority: WO
Inventors: Ivica Batistic; Mathias Niepelt; Stephan Groitzsch
Original assignee: Continental Teves Ag & Co. Ohg
Priority date: 1999-08-31
Filing date: 2000-08-29
Publication date: 2001-03-08

Abstract

The invention relates to a method for monitoring the operational efficiency of sensors which measure the rotational speed, or variables derived therefrom, of the wheels of a vehicle, in particular, of a vehicle fitted with an anti-lock braking system. According to said method, a deficiency or suspected deficiency in at least one of several sensors is determined, if the signal from the sensor(s) is absent for a given period, or indicates a significant decrease in the measured wheel speed, or variables derived therefrom, in relation to the signals of at least two other sensors, preferably of all other sensors and if the signals of said other sensor(s) or of all other sensors indicate stable rotational behaviour for a given period and in particular, no locking tendency in the wheels which are assigned to the other sensors.

Description

METHOD FOR MONITORING SPEED SENSORS IN A VEHICLE WITH AN BLOCK-PROTECTED BRAKE SYSTEM

The invention relates to a method for monitoring the functional humidity of sensors measuring the speed or values derived therefrom of the wheels of a vehicle, in particular for a vehicle with an anti-lock brake system.

Vehicle brake systems with electronic control require functioning sensors to measure the

Vehicle wheel rotation speeds. With the sensors, the turning behavior of the individual wheels is determined and the vehicle braking systems are regulated according to the turning behavior. For example, a

Anti-lock braking system (ABS) the brake pressure in each

Modulated wheel brakes to prevent the wheels from locking.

A sensor can become defective due to various causes. In particular, a short circuit in the sensor, an interruption of the supply lines to the sensor or a faulty signal processing of the sensor signal before feeding into the computer of the electronic brake control system are conceivable. Other errors include a sensor missing after a visit to the workshop or a missing ring gear or a distance between the sensor and the ring gear that changes over time.

Signal failures from sensors cannot always be recognized in a short time. If the sensor does not have an electrically detectable defect, one has to rely on an error detection via plausibility considerations. These usually monitor the speed of the baby; each Wheel or compare the measured wheel speeds with each other. In order to avoid unjustified error detection, relatively long detection times are usually required.

The invention has for its object to provide a method for monitoring the functional humidity of sensors measuring the rotational behavior of the wheels of a vehicle, which can be implemented in a technically simple manner and works quickly and reliably.

The object on which the invention is based is achieved in that a malfunction or a suspected malfunction of at least one of a plurality of sensors is determined if the signal of the at least one sensor fails for a predetermined period of time or if the measured wheel speed drops sharply or is derived therefrom Large compared to the signals of at least two other sensors, preferably all other sensors, and if the signals of the at least two other sensors, preferably all other sensors, indicate a stable turning behavior for a predetermined period and in particular no blocking tendency of the wheels assigned to the other sensors.

The method according to the invention enables detection times of a malfunction or a suspicion of malfunction of about 1 second to be realized compared to relatively long detection times for a fault or failure of a sensor of typically approx. 30 seconds, in particular a sudden drop or elimination of the Signals (signal abort) even at a relatively low vehicle speed of one

Rotational behavior change can be distinguished, which is caused by a decelerating force on the wheel. With the aid of the method according to the invention, a suspected inoperability of at least one of several sensors (suspected sensor errors) can already be determined. The method according to the invention is therefore particularly intended to be implemented in a relatively short time, advantageously by specifying a suitable, relatively short period (in which the signals from the at least two other sensors, preferably all other sensors, a stable rotational behavior and in particular no blocking tendency of the others Show sensors assigned to Rader), to ascertain suspicion of an inoperability before an inoperability of the sensor (sensor error), for example also according to the known methods according to the prior art, is recognized (correctly). After the determination according to the invention of a suspicion that the at least one of a plurality of sensors is inoperable, malfunctions of the system can be prevented by appropriate measures by a “faulty” signal from the at least one sensor. Critical driving situations due to the “faulty” signal can thus be greatly reduced.

An advantage of the method according to the invention is based in particular on the fact that not only the signal from the wheel with the defective sensor is used for error detection, but also the signals from the other sensors are considered and that the failure of a sensor signal over a relatively short period of time already occurs the determination of a sensor fault suspicion makes it possible if the other sensor signals and possibly the control intervention of an electronic brake control on the affected wheel indicate that there is little or no decelerating force on the affected wheel. According to the invention, it is provided that a time period in a range between 0.5 to 3 seconds, preferably approximately 1 second, is specified. It has been found that this period of time already ensures a reliable determination of a suspected sensor error.

In one embodiment of the invention, the wheel speed measured by the at least one sensor or values derived therefrom drop sharply if a brake slip determined from the measured wheel speed or values derived therefrom is greater than a predetermined brake slip limit value, preferably 4 km / h to 6 km / h, in particular about 5 km / h.

According to the invention, there is a sharp drop in the wheel speed measured by the at least one sensor or variables derived therefrom when a wheel acceleration determined from the measured wheel speed or variables derived therefrom has a predetermined value

Wheel loading limit value, preferably -0.05 g to -1.2 g, in particular approx. -Lg, falls below. Falling below the wheel acceleration here means that the negative wheel acceleration, that is to say the wheel deceleration, assumes a greater negative value than the predetermined limit value, which can be in a range from -0.05 to -1.5 g. With a predetermined limit value of -0.05 g, for example, (negative) wheel accelerations of -0.06 g, -0.07 g, -0.08 g, etc. fall below this predetermined limit value.

According to the invention it is provided that there is a sharp drop in the wheel speed measured by the at least one sensor or in quantities derived therefrom if one derived from the measured wheel speed Wheel circumferential speed is at least about 20% lower than a calculated or estimated vehicle reference speed.

In an embodiment of the invention, a turning behavior determined by the other sensors is assumed to be stable if a brake slip indicated by the other sensors is less than a predetermined brake slip limit value, preferably 4 km / h to 6 km / h, in particular approximately 5 km /H.

According to the invention, a turning behavior determined by the other sensors is assumed to be stable if a wheel acceleration indicated by the other sensors exceeds a predetermined wheel acceleration limit value, preferably -0.05 g to -1.2 g, in particular approximately -1 g. Exceeding the wheel acceleration here, analogously to falling below a wheel acceleration, means that the negative wheel acceleration, that is to say the wheel deceleration, assumes a smaller negative value than the predetermined limit value. If a limit value of -0.05 g is specified, negative wheel accelerations of -0.04 g, -0.03 g, -0.02 g, etc., for example, exceed this specified limit value and the value 0 and all positive values for the wheel acceleration.

It is also provided that a turning behavior determined by the other sensors is assumed to be stable if there is no brake slip of the wheels assigned to the other sensors which are on a

Use of the vehicle brake or the parking brake and / or an engine towing operation indicates.

The object is further achieved by a method for monitoring the function humidity or the speed thereof Derived variables of the wheels of a vehicle measuring sensors, solved for a vehicle with an anti-lock braking system (ABS), which is characterized in that a suspected malfunction or a malfunction of at least one of a plurality of sensors is then determined when the signal of the at least one sensor fails for a predetermined period of time or indicates a sharp drop in the measured wheel speed or variables derived therefrom compared to the signals of at least two other sensors, preferably all other sensors, and if the braking pressure on the wheels which are assigned to these two other sensors is not actively indicated by the anti-lock braking system is regulated, which means if there is no ABS regulation phase.

The term “anti-lock braking system” is also to be understood here as corresponding electronic anti-lock protection systems which are part of a higher-level control system, such as traction control system (ASR) or electronic driving stability control (ESP).

In one embodiment of the invention, the brake pressure on the assigned wheels is considered to be actively regulated by the anti-lock braking system when brake pressure is reduced or maintained on the wheel brake of the assigned wheel, but is preferably reduced. Due to the additional condition of the type of control intervention, for example pressure reduction on a wheel, an error can be suspected on a sensor of this wheel, which despite a reduction in the brake pressure does not provide a signal for a certain time in accordance with an ABS control, if a Motor towing or use of the handbrake can be excluded. With the help of the additional condition of the type of control intervention (pressure reduction or pressure build-up in an anti-lock brake system), the time until a Malfunction or a suspicion of malfunction of the at least one of several sensors is reduced.

According to the invention, the method only functions when the calculated or estimated vehicle reference speed exceeds a predetermined speed limit value, preferably 4 to 10 km / h, in particular approximately 6 km / h.

According to the invention, it is provided that after the determination of a malfunction or a suspicion of malfunction of at least one of a plurality of sensors, an error signal is generated and / or the signal of the at least one sensor for electronic control of a braking system of the vehicle is not taken into account for at least as long until the inoperability or the suspected inoperability of the sensor is no longer determined.

According to the invention, after determining a suspicion of a malfunction or a

Inoperability of at least one of a plurality of sensors, at least the malfunctioning system part, in particular the ABS control channel, of the at least one of a plurality of sensors, is switched off at least until the suspicion of inoperability or inoperability of the sensor is no longer detected.

A combination of the following conditions has proven to be particularly advantageous for reliable error detection:

No signal or brake slip on the at least one wheel has been sensed for more than one second. All other wheels deliver a wheel signal which corresponds to a wheel circumferential speed greater than 6 km / h or indicates that these other wheels are not in the brake slip.

The wheel acceleration on no other wheel is less than -0.1 g.

If all of the above conditions are met, an error is suspected on the sensor that does not provide a signal. A (further) pressure drop in the brake pressure on the affected wheel caused by the error or failure of the sensor is prevented. Sub-functions of the brake system that require the wheel signal recognized as faulty are at least temporarily shut down.

The invention will now be explained in more detail by way of example using figures (FIGS. 1 to 5).

1 schematically shows in a flowchart individual query steps of an embodiment of the method according to the invention for a wheel.

2 graphically shows the failure of the signal one

Sensor shown at constant vehicle speed.

3 shows the signals from the sensors in an accelerated vehicle.

4 shows the signals from the sensors of a vehicle which has a constant vehicle speed. Fig. 5 graphically shows the case where the vehicle speed is reduced.

In Fig. 1, the query steps for determining a suspected sensor error on a specific wheel, here referred to as "wheel 1", of a vehicle with four wheels (wheel 1 to wheel 4) are shown schematically in a flow chart. From a starting point of the query steps ( Step 1) is checked in a second step (Step 2) whether the sensor delivers a sensor signal on the wheel 1 under consideration. If no signal is detected, a step 3 is checked in a step 3 whether on all other wheels (wheels 2 to 4) If a sensor signal is detected on all other wheels, the next step is to check whether the other three wheels are in a stable state, because if the other wheels are stable and show no blocking tendency, then according to the invention, one is suspected Errors are not given, for example, in a subsequent step (step 4), a query is made as to whether the ABS is engaged on wheels 2 to 4. With this query it is checked whether the other three wheels are in a stable condition. If the other wheels are stable and show no blocking tendency, intervention by the ABS in the brake control, in particular a pressure reduction phase or pressure maintaining phase, is not necessary to stabilize one or more of these wheels. Then there is no intervention by the ABS and the query proceeds to the next step 5. The query in step 5 additionally checks whether the wheel acceleration of the other wheels (bikes 2 to 4) is greater than or equal to a predetermined limit value, greater in this example is equal to -0.1 g. With this step, as with the query before (step 4), it is checked whether the other wheels show stable behavior. For certain applications it is provided that step 5 is omitted and after step 4 the query of the Step 6 follows. In this case, only the criterion of ABS-pickup (step 4) is used to assess the wheel stability of the wheels 2 to 4. For reasons of the detection reliability of a suspected sensor error and to rule out an unjustified suspected error, the further criterion for assessing the wheel stability is preferred , the query according to step 5 is checked. As a further criterion or as the sole criterion for assessing the wheel stability, the can also be used for other applications

Wheel circumferential speed can be used. Following step 5, if the condition of a wheel acceleration greater than -0.1 g is fulfilled, this means that if there are no decelerating forces acting on the wheel, a wheel acceleration of less than -0.1 g, for example -0.2 g, - 0.3 g, -0.4 g or a higher negative wheel acceleration, the query proceeds to step 6. In step 6 it is checked whether the vehicle is moving. This means whether the vehicle speed is greater than a predetermined vehicle speed limit, for example greater than 6 km / h. It is also provided that step 6 is omitted. In principle, this is possible since the query in step 3 has already checked whether sensor signals are present at all. If the vehicle speed is greater than the vehicle speed limit, for example greater than 6 km / h, a subsequent query (step 7) asks whether these conditions (steps 2 to 6) have been valid for at least one second. If this condition of step 6 is also met, then a suspected malfunction of the sensor, a suspected sensor error, is determined on the wheel concerned (step 8). The query advances to the next wheel (step 9) and the queries return to the beginning 1 (step 10) and start again with the first query of step 2. It then becomes the query steps mentioned above for the next wheel, for example wheel 2, also carried out, a comparison with the three other wheels, in this case wheels 1, 3 and 4, being carried out accordingly.

In addition to the query steps shown in FIG. 1, it is provided that the suspicion of an error in the sensor in question is withdrawn if a fault in one sensor (for example on wheel 1) has been detected, but if the query is subsequently run again Sensor signal on the wheel in question (wheel 1) is determined (step 2) and the wheel in question is stable again (steps 4, 5).

The following illustrations (FIGS. 2 to 5) show examples of a failure of the sensor on a wheel 4 for different driving situations of a vehicle with 4 wheels, with the suspicion of failure of one sensor on wheel 4, for example, with the aid of previously shown embodiment of the invention can be determined.

Fig. 2 shows a schematic representation of the course of the signals from four wheel speed sensors of a vehicle against time (t). The vehicle is moving at a constant vehicle speed. Therefore, the sensors of the wheels 1 to 3 provide signals for a constant

Wheel circumferential speed (VI to V3). The sensor of the wheel 4 shows a signal abort at the time tl, ie the wheel circumferential speed V4 suddenly drops to zero at tl. By comparing the signals according to the invention, that means in particular comparing the signal of the one (failed) sensor on wheel 4 with the signals of the three other sensors of wheels 1 to 3, the sensor on wheel 4 fails from a point in time tx . for example approx. 1 sec. after the time t1, a suspected sensor error is determined.

3 and 5 show situations in which the signal from the sensor at wheel 4 also drops or drops off sharply at time t1, while all other speed sensors of wheels 1 to 3 have a uniform wheel turning behavior (see VI to V3). Show.

3 increases

Wheel circumferential speed (VI to V3) with time; the vehicle accelerates. According to the idea on which this invention is based, such a signal drop of a single sensor due to decelerating forces on the wheel is unlikely when all other sensors indicate that the vehicle is accelerating smoothly or, as shown in FIG. 2, has a constant, constant speed. Through the method according to the invention, a suspicion of a sensor failure on wheel 4 from tx, e.g. approx. 1 second after tl, so it can be determined reliably.

According to FIG. 5, a reduction in the speed of the fan vehicle due to the decrease in the sensed wheel circumferential speeds VI to V3 on the sensors of the wheels 1 to 3 is indicated. The vehicle decelerates with a relatively small wheel deceleration (relatively small decrease in the circumferential wheel speeds VI to V3). If the determined wheel acceleration is greater than approx. -0.1 g and there is no ABS intervention on the wheels 1 to 3, the signal abort at the sensor of the wheel 4 at time t1 can also trigger a suspected sensor error in this situation. Because it can be excluded according to the invention that 4 retarding forces act on the wheel in question, which could cause such a signal drop. The Detection time for a suspected failure or error of the affected sensor (V4) is therefore also relatively short in this case, for example approx. 1 second after tl.

According to FIG. 4, the sensor signal of the sensor on wheel 3 drops to a certain value at time t2 after the signal on the sensor at wheel 4 at time t1. After a short time, the sensed wheel circumferential speed V3 increases again and finally at time t3 the sensors of the wheels 1 to 3 again deliver an approximately identical signal. In this situation, a suspicion of the failure of the sensor on wheel 4 cannot be determined until time t3, since the drop in sensor signal V3 indicates that other forces could also cause a delay in the sensed wheel circumferential speeds. But from time tx, e.g. Approx. 1 second after t3, analogous to the situation shown in FIG. 2, the signal difference between the sensors of wheels 1 to 3 and the sensor on wheel 4 can be used to reliably ascertain a suspected error on the sensor of wheel 4. The method according to the invention thus ensures that a suspected error of a sensor is detected relatively early and relatively reliably, even for a wide variety of driving situations, before a sensor failure can be recognized as being safe due to other plausibility considerations.

In principle, an opposing wheel turning behavior, that means a strong, abrupt increase in the wheel speed measured by the at least one sensor or variables derived therefrom, can indicate a sensor error. Consequently, such an effect can in principle be determined on the basis of the idea of the method according to the invention, the method steps previously described in correspondingly, with a reversed sign, if applicable, can be used analogously.

Claims

claims

1. Method for monitoring the functional humidity of sensors measuring the speed of rotation or variables derived therefrom of the wheels of a vehicle, in particular for a vehicle with an anti-lock brake system, characterized in that a malfunction or a suspected malfunction of at least one of several sensors is then determined , if the signal of the at least one sensor fails for a predetermined period of time or if there is a sharp drop in the measured wheel speed or variables derived therefrom compared to the signals of at least two other sensors, preferably all other sensors, and if the signals of the at least two other sensors, preferably all other sensors, a stable turning behavior for a predetermined period of time and in particular no blocking tendency of the wheels assigned to the other sensors.

2. The method according to claim 1, characterized in that a period in a range between 0.5 to 3 sec, preferably about 1 sec, is specified.

3. The method according to claim 1 or 2, characterized in that there is a sharp drop in the wheel speed measured by the at least one sensor or values derived therefrom when a brake slip determined from the measured wheel speed or values derived therefrom is greater than is a predetermined brake slip limit value, preferably 4 km / h to 6 km / h, in particular approximately 5 km / h.

4. The method according to any one of claims 1 to 3, characterized in that there is a sharp drop in the wheel speed measured by the at least one sensor or variables derived therefrom when a wheel acceleration determined from the measured wheel speed or variables derived therefrom has a predetermined wheel acceleration -Limit value, preferably -0.05 g to -1.2 g, in particular approx. -1 g.

5. The method according to any one of claims 1 to 4, characterized in that there is a sharp drop in the wheel speed measured by the at least one sensor or variables derived therefrom when a circumferential wheel speed derived from the measured wheel speed is at least approximately 20% lower as a calculated or estimated vehicle reference speed.

6. The method according to any one of claims 1 to 5, characterized in that a rotational behavior determined by the other sensors is assumed to be stable if there is no brake slip of the wheels assigned to the other sensors, which is due to the use of the vehicle brake or the parking brake or Engine towing indicates.

Method according to one of claims 1 to 6, characterized in that a rotational behavior determined by the other sensors is assumed to be stable if one by the other sensors displayed brake slip is less than a predetermined brake slip limit value, preferably 4 km / h to 6 km / h, in particular approximately 5 km / h.

8. The method according to any one of claims 1 to 7, characterized in that a rotational behavior determined by the other sensors is then assumed to be stable if a wheel acceleration indicated by the other sensors has a predetermined wheel acceleration limit value, preferably -0.05 g to - 1.2 g, in particular approx. -1 g, exceeds.

9. A method for monitoring the functionality of the rotational speed or variables derived therefrom of the wheels of a vehicle sensors for a vehicle with an anti-lock braking system (ABS), characterized in that an inoperability or a suspected inoperability of at least one of several sensors is then determined , if the signal of the at least one sensor fails for a predetermined period of time or if there is a sharp drop in the measured wheel speed or variables derived therefrom compared to the signals of at least two other sensors, preferably all other sensors, and if the braking pressure of the wheels assigned to these at least two other sensors is not actively regulated by the anti-lock braking system.

10. The method according to claim 9, characterized in that the brake pressure on the assigned wheels is then considered to be actively regulated by the anti-lock braking system when brake pressure is reduced or maintained at the wheel brake of the assigned wheel.

11. The method according to any one of claims 1 to 10, characterized in that the method only comes into operation when the calculated or estimated vehicle reference speed a predetermined one

Speed limit value, preferably 4 to 10 km / h, in particular about 6 km / h.

12. The method according to any one of claims 1 to 11, characterized in that after determining a malfunction or a suspicion of malfunction of at least one of several sensors, an error signal is generated and / or the signal of the at least one sensor for electronic control of a brake system of the vehicle is at least not taken into account until the inoperability or the suspected inoperability of the sensor is no longer determined.

13. The method according to claim 12, characterized in that after determining a malfunction or a suspicion of malfunction of at least one of several sensors, at least the malfunctioning system part, in particular the ABS control channel, of the at least one of several sensors is switched off for at least as long until the suspicion of a malfunction or malfunction of the sensor is no longer recognized.

14. The method according to any one of claims 1 to 13, characterized in that a suspected malfunction is determined.