DE102021123100A1 - Method for avoiding rear wheel lift of a single-track vehicle during deceleration and braking system for a single-track vehicle - Google Patents

Abstract

The invention relates to a method for avoiding the rear wheel lifting of a single-track vehicle (10) during deceleration processes. In the method, a front wheel brake (20) and a rear wheel brake (30) are controlled in order to decelerate the vehicle, a negative longitudinal force potential of the rear wheel tire (32) is continuously determined, and as soon as the magnitude of the negative longitudinal force potential falls below a predetermined limit value, it is the braking effect of the front wheel brake (20) is reduced and/or as soon as the magnitude of the negative longitudinal force potential decreases and assumes values just above the specified limit value, the build-up of the braking effect of the front wheel brake (20) is slowed down. The invention also relates to a braking system for a single-track vehicle.

Description

The invention relates to a method for preventing the rear wheel lifting of a single-track vehicle during deceleration processes. The invention also relates to a braking system for a single-track vehicle. The term single-track vehicles is understood to mean, in particular, motorcycles with single or double front or rear wheel guidance.

Stable and controlled deceleration processes are crucial for the safety of single-track vehicles. This applies above all in dangerous situations in which emergency braking is necessary. During the deceleration process of single-track vehicles, wheel loads change due to inertia, which is called dynamic wheel load distribution. Due to the short wheelbase and the high center of gravity, this is particularly pronounced in single-track vehicles when decelerating, in which the front wheel brake applies a significant proportion of the vehicle's deceleration. Thus, when decelerating, the wheel loads are redistributed, with the rear tire being relieved while the front tire is loaded to the same extent and the single-track vehicle lowers in the front area due to the yielding suspension. In extreme cases, the rear wheel can be relieved to such an extent that it loses contact with the ground. The single-track vehicle drives exclusively on the front wheel tyre. In this situation, if deceleration is continued by the front wheel brake, it may cause the single-track vehicle to roll over.

It is therefore essential to prevent the rear wheel from lifting off. Rear wheel lift detections are an important part of motorcycle brake control systems. These prevent the rear wheel from lifting beyond a level defined as acceptable. If the rear wheel lifts up (excessively) is detected, the braking force on the front tire is reduced to prevent the vehicle from rolling over.

According to the current state of the art, lifting of the rear wheel is detected based on the behavior of the rear wheel speed when the braking pressure of the rear wheel brake changes. With this type of rear wheel lift detection, it is assumed that a strong deceleration is applied to both the front and rear wheels. The rear wheel brake can be actuated by the driver in order to apply a corresponding braking deceleration at the rear wheel, or in which the motorcycle brake control system independently builds up braking pressure at the rear wheel brake if a severe deceleration at the front wheel is detected. During the entire braking process, the motorcycle brake control system alternately allows high braking pressure on the rear wheel, which leads to overbraking of the rear wheel tire and thus to slip, and then reduces the braking pressure in the rear wheel brake again. If the rear wheel is in contact with the ground, the slip on the rear wheel decreases when the brake pressure on the rear wheel brake is reduced and the rear wheel speed increases.

If the rear wheel loses contact with the ground during the deceleration process, the high level of slip on the rear wheel is maintained or even increased even if the brake pressure on the rear wheel brake is reduced. As a result, the rear wheel speed remains constant or drops. Thus, the motorcycle brake control system can recognize the lifted rear wheel as a condition in which there is a high rear wheel slip with a low braking pressure at the rear wheel brake. If this condition is detected, the motorcycle brake control system reduces the brake pressure prevailing at the front wheel brake until the rear wheel starts moving again, which is detected as a condition in which the rear wheel has (sufficient) contact with the ground again.

The disadvantage of this type of rear-wheel lift-off detection is that the sampling rate at which the motorcycle brake control system repeats the cycle of over-braking and reducing the brake pressure is relatively low, typically at 2 to 3 Hz, due to the technically limited brake pressure dynamics and the physically limited wheel dynamics. This can lead to a lifted rear wheel being detected with a delay of 500 ms in unfavorable cases, which can result in potentially high rear wheel lift.

In addition, in motorcycle brake control systems that do not have an actuator for an automatic brake pressure build-up on the rear wheel brake, the driver must actuate the rear wheel brake strongly enough to cause the rear wheel to slip and thus cause the rear wheel to overbrake. If the rear wheel brake is not applied strongly enough by the driver or if the rear wheel brake is not applied at all, it cannot be determined whether the rear wheel is lifting off. Furthermore, it is possible that even if a rear wheel lift is detected, the rear wheel will be offset in unfavorable driving situations and thus an undesired instability.

Solutions are also known in which the previously described rear wheel lifting detection is combined with a deceleration limiter is used. A maximum deceleration is defined here, which is just below the critical deceleration at which the rear wheel of the vehicle lifts off. If this maximum deceleration is exceeded during a deceleration process, either the brake pressure build-up on the front wheel is greatly slowed down so that the rear wheel is only slowly relieved or lifted off, or the brake pressure on the front wheel is reduced so that the rear wheel does not lift off and ground contact is maintained. A disadvantage of this method is that the critical deceleration at which the rear wheel of the single-track vehicle lifts off depends largely on the load, the existing downhill or uphill gradient. A conservative choice of the maximum deceleration is therefore necessary in order to cover as many driving conditions as possible. This in turn has the consequence that in many driving conditions the motorcycle brake control system intervenes well below the critical deceleration actually prevailing at that moment and the full deceleration performance is not achieved.

The object of the invention is to detect lifting of the rear wheel as quickly as possible without the driver having to actuate the rear wheel brake. In addition, when decelerating, the maximum available deceleration power should be utilized in the braking process.

1. a) es werden eine Vorderradbremse und eine Hinterradbremse angesteuert, um das Fahrzeug zu verzögern,
2. b) es wird kontinuierlich ein negatives Längskraftpotential des Hinterradreifens bestimmt,
3. c) sobald der Betrag des negativen Längskraftpotentials unter einen vorgegebenen Grenzwert sinkt, wird die Bremswirkung der Vorderradbremse verringert und/oder sobald der Betrag des negativen Längskraftpotential abnimmt und Werte knapp oberhalb des vorgegebenen Grenzwerts annimmt, wird der Aufbau der Bremswirkung der Vorderradbremse verlangsamt.

The task of avoiding the rear wheel lift of a single-track vehicle during deceleration is solved by a method with the following steps:

1. a) a front wheel brake and a rear wheel brake are activated in order to decelerate the vehicle,
2. b) a negative longitudinal force potential of the rear wheel tire is continuously determined,
3. c) as soon as the magnitude of the negative longitudinal force potential falls below a specified limit value, the braking effect of the front wheel brake is reduced and/or as soon as the magnitude of the negative longitudinal force potential decreases and assumes values just above the specified limit value, the build-up of the braking effect of the front wheel brake is slowed down.

The invention is based on the basic idea of recognizing a lifting or a critical relief of the rear wheel tire based on the longitudinal force potential available on the rear wheel tire, which is dependent on the contact force prevailing on the rear wheel. The negative longitudinal force potential means the maximum transmissible longitudinal force of the rear wheel tire during the deceleration process under the prevailing conditions. If the magnitude of the negative longitudinal force potential on the rear wheel is low or if no available negative longitudinal force potential can be detected on the rear wheel tire, it can be concluded that the contact force on the rear wheel tire is low and the rear wheel is about to lift off or that there is no contact force on the rear wheel tire is available and there is no ground contact. The negative longitudinal force potential on the rear wheel tire is determined continuously, which is why a lift of the rear wheel tire can be detected immediately. This allows the motorcycle brake control system to react quickly and adjust the braking effect of the front brake.

Advantageously, as soon as the longitudinal force potential rises again and is above the limit value, the braking effect of the front wheel brake is increased or an increase in the braking effect of the front wheel brake is permitted again. Thus, with available negative longitudinal force potential on the rear tire, the single-track vehicle can again be decelerated more strongly. Depending on how great the braking effect requested by the driver via the front and rear wheel brakes is, either a greater deceleration is applied via the front wheel or only the limitation of the maximum possible deceleration at the front wheel is partially or completely withdrawn. This ensures that in subsequent deceleration processes, the entire deceleration power is initially available at the front wheel brake.

The rear wheel brake activated in step a) for decelerating the vehicle is preferably an electric machine. It is conceivable that a conventional friction brake is additionally arranged on the rear wheel. The electric machine not only applies deceleration power to the rear wheel tyre, but also determines the negative longitudinal force potential of the rear wheel tyre.

The continuous determination of the longitudinal force potential of the rear wheel tire in step b) can preferably be carried out by a PID slip control, which determines the longitudinal force potential of the rear wheel tire based on the actual slip acting on the rear wheel tire. This adaptive control enables implementation without expensive sensors or complex algorithms that estimate the available coefficient of friction on the road in order to draw conclusions about the longitudinal force potential. In this way, a cost-effective development can be realized.

The given limit value in step c) can be based on an estimated coefficient of friction between the rear tire and the road and a minimum allowable Significant contact force on the rear tire can be calculated. In this way, a sensible limit value can be set so that the rear wheel is completely prevented from lifting off and there is no critical driving situation, since the rear wheel does not lose contact with the ground. This contributes to the fact that the vehicle can be braked in a controlled and stable manner despite heavy deceleration processes and increases safety.

Preferably, the braking effect of the front wheel brake can be reduced in step c) by reducing the brake pressure, so that the contact force on the rear wheel tire is increased and/or the deceleration of the build-up of the braking effect of the front wheel brake takes place by slowing down the build-up of brake pressure. With regard to the resulting advantages, reference is made to the above explanations for adjusting the braking effect of the front wheel brake.

The braking effect of the front wheel brake in step c) can be reduced if the predetermined limit value is exceeded by canceling all measures that limit the brake pressure and/or slow down the brake pressure build-up. This ensures that after the tire longitudinal force potential has reached a non-critical value, the full deceleration performance is available again.

The object mentioned at the outset is also achieved by a braking system for a single-track vehicle, with a front wheel brake, a rear wheel brake, which has an electric machine, and a vehicle-integrated controller, the vehicle-integrated controller being set up to continuously monitor the rear tire on the basis of data determined to determine acting negative longitudinal force potential, and wherein the vehicle-integrated controller controls the maximum permissible braking effect of the front wheel brake as a function of the negative longitudinal force potential determined on the rear tire. The resulting advantages can be found in the above statements. The definition given above with regard to the negative longitudinal force potential on the rear tire also applies here.

The vehicle-integrated controller advantageously has a PID slip controller. This allows the longitudinal force potential of the rear tire to be continuously determined.

The electric machine can also form the drive of the single-track vehicle. Thus, the electric machine not only serves to decelerate the single-track vehicle, but also to accelerate it.

• - 1 eine schematische Zeichnung eines einspurigen Fahrzeugs mit einem erfindungsgemäßen Bremssystem;
• - 2 zeigt ein Diagramm mit einer grafischen Darstellung der vereinfachten Abhängigkeit des negativen Längskraftpotentials eines Reifens von der Aufstandskraft bei unterschiedlichen Reibwerten; und
• - 3 ein Blockschaltbild einer fahrzeugintegrierten Steuerung mit einem PID-Schlupfregler.

The invention is described below with reference to an embodiment which is illustrated in the accompanying drawings. In these show:

• - 1 a schematic drawing of a single-track vehicle with a braking system according to the invention;
• - 2 shows a diagram with a graphical representation of the simplified dependency of the negative longitudinal force potential of a tire on the contact force with different coefficients of friction; and
• - 3 a block diagram of a vehicle-integrated controller with a PID slip controller.

1 FIG. 1 shows a single-track vehicle 10 having a front wheel brake 20, which is used to decelerate the front wheel tire 22, and a rear wheel brake 30, which is used to decelerate the rear wheel tire 32. FIG. The rear wheel brake 30 includes an electric machine 40. The braking effect of the front wheel brake 20 is controlled by a vehicle-integrated controller 50.

The vehicle-integrated controller 50 is set up to recognize and reduce or even completely prevent lifting of the rear wheel tire 32 during deceleration processes. For this purpose, the controller 50 continuously determines the negative longitudinal force potential available at the rear wheel tire 32 on the basis of vehicle data during deceleration processes and controls the braking effect of the front wheel brake 20 depending on this.

The negative longitudinal force potential of the rear wheel tire 32 is defined in simplified form from the product of the contact force prevailing on the rear wheel tire 32 and the coefficient of friction prevailing between the rear wheel tire 32 and the road surface: $$f_{L\ddot{a}nGsk\mathrm{right}aftpOtential,HR}=f_{A\mathrm{and}fstan\mathrm{i.e}sk\mathrm{right}aft,HR}\ast {\mu }_{RS}$$

Put simply, the negative longitudinal force potential of the rear wheel tire 32 is directly proportional to the contact force of the rear wheel tire 32. As a result, the available longitudinal force potential of the rear wheel tire 32 can be used to draw conclusions about the contact force prevailing at the rear wheel tire 32. The more the load shifts to the front wheel tire 22 during a deceleration process due to the dynamic wheel load distribution, the lower the contact force prevailing on the rear wheel tire 32 becomes, and the negative longitudinal force potential also decreases as a result.

In order to completely prevent the rear wheel tire 32 from being lifted off, a limit value is specified, below which the amount of the negative Longitudinal force potential of the rear tire 32 must not be, otherwise the contact force is too low and the rear tire 32 is about to lose ground contact. If the limit value is not reached, the vehicle-integrated controller 50 reduces the braking effect of the front wheel brake 20, specifically at least by slowing down the build-up of brake pressure, but mostly by reducing the brake pressure. Once the vehicle 10 reaches a steady state with sufficient ground-up force on the rear tire 32, the controller 50 overrides any actions that limit brake pressure or slow brake pressure build-up. It is conceivable that the measures are lifted continuously, since a sudden lifting could cause unstable vehicle behavior.

2 shows a diagram that illustrates how the limit for the negative longitudinal force potential is set. The x-axis of the chart in 2 shows the negative longitudinal force potential on the rear wheel tire 32. The vertical force acting on the rear wheel tire 32 is shown on the y-axis. The two straight lines through the origin 60 and 62 show the dependency of the negative longitudinal force potential on the contact force with different coefficients of friction. A minimum coefficient of friction is set for the straight line through the origin 60, which is not fallen below in reality. For the straight line 62 through the origin, a coefficient of friction is set that is not exceeded by commercially available tires for single-track vehicles, even under optimal conditions. Based on this, a value range can be defined in which the contact force must be at a certain negative longitudinal force potential. If, for example, the effective contact force is to be estimated with a defined negative longitudinal force potential 64 because the coefficient of friction between the tires and the road is unknown, it can be determined that the effective contact force lies within the value range that consists of the maximum possible contact force 66 with the minimum coefficient of friction and the minimum possible contact force 68 is limited at maximum coefficient of friction. Shortly before the rear wheel tire 32 is lifted off, the negative longitudinal force potential also falls with the contact force, which is why the absolute inaccuracy in the calculation of the possible value range of the contact force also becomes very small. This is due to the fact that the minimum and maximum possible contact forces 68 and 66 are closer together as the negative longitudinal force potential becomes smaller. In order to prevent the rear wheel tire 32 from being lifted off with certainty and to design the controller 50 conservatively, the straight line 62 at the origin, at which the maximum coefficient of friction is used to calculate the contact force, can be used to determine the limit value.

The 3 schematically shows a block diagram of the vehicle-integrated controller 50 with a PID slip controller 70.

The PID slip controller 70 is used to determine the negative longitudinal force potential of the rear wheel tire 32 with input signals.

This determination is made using, among other things, the slip present at the rear wheel tire 32 , which is present to the PID slip controller 70 in the form of the input signal 72 .

The input signal 72 for the slip present at the rear wheel tire 32 results from the signals 74 and 76, which contain the vehicle speed or the circumferential wheel speed of the rear wheel tire 32 as a measured variable. The two speeds can be measured by sensors. The slip on the rear wheel tire 32 is determined from the signals 74 and 76 using the slip calculation 78 .

In addition, the controller 50 includes a setpoint slip controller 80 which provides the PID slip controller 70 with the setpoint slip in the form of a signal 82 as an input variable.

The negative longitudinal force potential is determined using the I component of the rear wheel tire braking torque of the PID slip controller 70, and the desired wheel slip is determined using the negative longitudinal force potential.

Before the negative longitudinal force potential is determined using the I component of the rear wheel tire braking torque, the I component is filtered by a low-pass filter 84 .

The PID slip controller 70 supplies the negative longitudinal force potential of the rear wheel tire 32 as an output variable, the amount of which is compared with the predetermined limit value in the limit value check 86 . If the value is not reached, the limit control 86 outputs a signal which reduces the brake pressure in the front wheel brake 20 or slows down the brake pressure build-up.

It is also conceivable that the PID slip controller 70, depending on the determined negative longitudinal force potential of the rear wheel tire 32, also specifies a rear wheel tire braking torque as an output variable, which the PID slip controller 70 feeds back to the rear wheel brake 30 in order to achieve the maximum possible braking effect by the Exploit available negative longitudinal force potential of the rear wheel tire 32 during the deceleration process.

Claims (10)

Method for avoiding rear wheel lift of a single-track vehicle (10) during deceleration operations, comprising the following steps: a) a front wheel brake (20) and a rear wheel brake (30) are activated in order to decelerate the vehicle (10), b) a negative longitudinal force potential of the rear wheel tire (32) is continuously determined, c) as soon as the magnitude of the negative longitudinal force potential falls below a specified limit value, the braking effect of the front wheel brake (20) is reduced and/or as soon as the magnitude of the negative longitudinal force potential decreases and assumes values just above the specified limit value, the braking effect of the front wheel brake (20) is built up 20) slows down. procedure after claim 1 , characterized in that as soon as the longitudinal force potential rises again (and is above the limit value), the braking effect of the front wheel brake (20) is increased or an increase in the braking effect of the front wheel brake (20) is permitted again. procedure after claim 1 or 2 , characterized in that the rear wheel brake (30) controlled in step a) for decelerating the vehicle (10) is an electric machine (40). procedure after claim 1 or 2 , characterized in that the continuous determination of the longitudinal force potential of the rear wheel tire (32) in step b) is carried out by a PID slip control, which determines the longitudinal force potential of the rear wheel tire (32) based on the actual slip acting on the rear wheel tire (32). Method according to one of the preceding claims, characterized in that the specified limit value in step c) is calculated using an estimated coefficient of friction between the rear wheel tire (32) and the road and a minimum permissible contact force on the rear wheel tire (32). Method according to one of the preceding claims, characterized in that the braking effect of the front wheel brake (20) is reduced in step c) by reducing the brake pressure, so that the contact force on the rear wheel tire (32) is increased and/or that the slowing down of the build-up of the Braking effect of the front brake (20) takes place by slowing down the brake pressure build-up. Method according to one of the preceding claims, characterized in that the braking effect of the front wheel brake (20) is reduced in step c) if the predetermined limit value is exceeded by canceling all measures which limit the brake pressure and/or slow down the build-up of brake pressure. Braking system for a single-track vehicle (10), with a front wheel brake (20), a rear wheel brake, which has an electric machine (40), and a vehicle-integrated controller (50), wherein the vehicle-integrated controller (50) is set up on the basis of determined data to continuously determine the negative longitudinal force potential acting on the rear wheel tire (32), and wherein the vehicle-integrated controller (50) controls the maximum permissible braking effect of the front wheel brake (20) as a function of the negative longitudinal force potential determined on the rear wheel tire (32). braking system after claim 8 , characterized in that the vehicle-integrated controller (50) has a PID slip controller (70). braking system after claim 8 or 9 , characterized in that the electric machine (40) also forms the drive of the single-track vehicle (10).

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