DE10349211A1 - Brake assistant for motor vehicles - Google Patents

Abstract

Brake assistant for motor vehicles, comprising a control device (28) for controlling the braking forces, a brake force sensor (26) and an evaluation device (24) for detecting an emergency braking request of the driver and for preparing or initiating emergency braking, characterized in that the evaluation device (24) signals an environment sensor (12) receives and evaluates.

Description

The The invention relates to a brake assistant for motor vehicles, with a Control device for controlling the braking force, a brake force sensor and an evaluation device for detecting a Notbremswunsches the driver and to prepare or initiate emergency braking.

brake Assist serve the driver of a motor vehicle at the initiation and implementation of braking to support. Motor vehicles are today usually with an ABS system (Antiblockkiersystem) equipped, which is used in a braking operation, when blocking the wheels automatically to modulate the brake pressure, so that optimum adhesion of Tires on the roadway are maintained and the vehicle is also during a Full braking remains steerable. Even with vehicles with such a. Anti-lock braking system, however, in the event of emergency braking from different establish often not the smallest possible Stopping distance reached. One of these reasons is that the brake shoes at unacknowledged Brake a certain distance to the brake disc or the brake drum have, so that a Some time passes before the brake shoes develop their braking effect. this leads to to an extension the stopping route. Another reason is that most Even when emergency braking, motorists intuitively feel inclined to do so To press the brake pedal too timidly, because they are not enough have adjusted to the presence of an anti-lock braking system and therefore fear that it when too vigorous operation The brake comes to a jamming of the wheels and they take control of that Lose vehicle or because of lack of training the technique of optimal full braking is not yet sufficient control. Correct would be instead of carrying out a so-called "brake hit" during emergency braking, d. h., To press the brake pedal abruptly until it stops, until The anti-lock braking system comes into operation. In case of faulty braking behavior of the driver, the brake pressure builds up slower than it is possible and desirable would. Further frequent Accident causes are misjudged distances and relative speeds.

A known measure to shorten the Stopping path it is so-called prefill function, in which a lower Pressure is fed into the brake system, so that the brake shoes already Apply to the brake disc or brake drum without this already a noticeable delay effect Has. Then, when the emergency braking is triggered, the desired braking effect occurs immediately.

Farther are known hydraulic brake assistants, where, when based the extent and / or the speed of the brake pedal operation an emergency brake request of Driver is automatically detected for optimal full braking necessary brake pressure is fed to the brake system to the to compensate for missing "brake hit".

at These known systems, the emergency braking request of the driver alone from the pedal operation derived.

on the other hand are known as ACC systems (Adaptive Cruise Control), the For example, when driving on the highway automatic adjustment of Speed of your own vehicle to the speed of one allow the vehicle ahead. It is using an environment sensor, for example, with the help a built in front of the vehicle radar sensor the traffic environment detected. With the help of the radar sensor the distances and relative speeds become driving vehicles and thus the conditions for one automatic distance control created. It is already proposed additional anti-collision or collision mitigation function to be implemented based on the data of the radar sensor detects an impending risk of collision and then automatically initiate emergency braking. It turns out however, an accurate evaluation of the traffic environment in practice as difficult.

Advantages of invention

By the invention having the features specified in claim 1 is a Brake Assist created a faster and more reliable Detection of an emergency braking request of the driver allows.

For this purpose, the invention provides that the evaluation device receives and evaluates signals of an environment sensor. Unlike the collision avoidance function described above, the environment sensor system is not used here to trigger the Notbremsvoraang automatically, but rather the environment sensor is used to support the evaluation device in the previously made solely due to the pedal operation recognition of the emergency braking request, while the actual emergency braking initiated by the driver himself becomes. In this way, situations in which emergency braking is anticipated can be detected early and accurately, so that the time losses at the initiation of emergency braking mini be miert. On the other hand, the risk of unnecessary false triggering is avoided and reduces the likelihood that initiated by the driver partial braking, which serves only for "soft" adaptation to the speed of the vehicle ahead, is misinterpreted as an emergency braking request and leads to an overreaction of the braking system.

advantageous Refinements and developments of the invention will become apparent the dependent claims.

The Environment sensors can z. B., as in known ACC systems an angle-resolving Radar system are formed. Alternatively or additionally, lidar sensors and / or monocular or binocular camera systems with associated image processing electronics be used as environment sensors. Radar systems offer the advantage that she not just a distance measurement, but also a direct measurement allow the relative speeds.

As a general rule The environment sensors should be able to measure the distances and also the cross offsets of to measure objects located in front of one's own vehicle. In these Objects will be primarily vehicles in front of you acting, not only on their own lane, but also to those on secondary tracks. In some circumstances, for example when driving at low speed, can even standing objects can be included in the evaluation.

In a preferred embodiment becomes one of the data provided by the environment sensor Notbremswahrscheinlichkeit calculated, and to control the Brake pressure serving control device is dependent configured by this emergency braking probability. The configuration can z. B. be that at high emergency brake probability a prefill function is triggered, to the distance between the brake shoes and the brake disc or To reduce the brake drum, preferably to zero. This prefill feature can be triggered at the first, even the slightest operation of the brake pedal or, if necessary, anticipatory, before the driver at all the brake pedal is pressed.

Complementary or additionally In the configuration, the triggering threshold for a "brake stroke" of the hydraulic Brake assistants in dependence be reduced by the emergency braking probability. For example the brake strike is triggered, if the extent of the brake pedal operation a certain. Threshold exceeds or if the speed at which the brake pedal is actuated exceeds a certain threshold or if given an appropriate combination of these two conditions is. The higher the probability of emergency braking is lower, the lower the respective ones Thresholds selected, so that the Brake hit earlier is initiated.

to Calculation of the emergency braking probability will be the first Conflict potential of each located object assessed. This is z. B. based on the distance and relative velocity data, the so-called Avoidance acceleration calculated. Under the (negative) avoidance acceleration understands one the braking delay, which, when the object is on the driving trajectory of your own vehicle befände, would be necessary to avoid a collision. The greater the braking delay calculated in this way, the bigger the conflict potential of the object in question.

Farther is for each object is calculated based on the location data of the lateral offset. In a straight road, this transverse offset is due to the lateral Storage of the object given by the imaginary grades, in the direction of travel passes through the middle of your own vehicle. In a curved lane is the curvature the expected driving trajectory of the own vehicle. Method for price prediction, with which this curvature are determined and known in existing ACC systems already used.

Based of the transverse offset, the located objects are then in follower objects and secondary track objects. Follow-on objects are objects (preceding vehicles), which are on the lane of their own Vehicle are located. Secondary track objects are objects on secondary tracks or possibly also on the roadside. For follow-on objects is the potential for conflict from the avoidance acceleration defined above dependent. A high avoidance acceleration results z. In cases, in which the follow-up object in turn initiates emergency braking or bouncing on an obstacle or where that is on the trajectory of the own vehicle suddenly appears behind a curve and get into the detection range of the environment sensor. For the calculation the emergency braking probability is also on the secondary lane objects shut off, as these also an emergency brake request of the driver can cause. Indeed It can be assumed that the Drivers more often will respond to follow-on objects as secondary-track objects. at Side track objects is also the probability of emergency braking generally higher bigger her Potential for conflict and the lower their transverse offset.

According to a development, Be calculation of the Notbremswahrscheinlichkeit additional criteria are used, for example, the lateral extent of the secondary lane objects, which can be estimated at least roughly using the environment sensors, for example with the aid of an angle-resolving radar system, as well as the measured transverse movements of the secondary lane objects. With a decrease in the transverse offset of a secondary track object, the emergency braking probability will increase the more depending on the situation, the greater the potential for conflict of this object.

on the other hand are also conceivable criteria that lead to a decrease in the emergency braking probability. If For example, a following object a negative relative speed has, d. h., When the own vehicle on the preceding vehicle ascends, it is to be expected that the driver your own vehicle will make a moderate partial braking, to adapt its speed to that of the vehicle in front, and the sooner the shorter the distance of the following object is. Likewise, if the distance traveled by the following object is not too great to expect that the Driver of the vehicle makes a partial braking, if that the vehicle ahead slows down, especially if the speed is reduced of the preceding vehicle is greater as the delay achievable by the action of the engine brake own vehicle. If in these situations the driver depresses the brake pedal actuated, so it is to be expected that he no emergency braking but only an adaptation of the speed wants to make by a partial braking, and the emergency braking probability is correspondingly low. In particular, in this situation should be the thresholds for increased the brake so that it does not trigger an unwanted emergency braking. In contrast, the prefill function can be activated in these situations, unless conflicting Secondary track objects are present.

Also the number of secondary track objects has an influence on the emergency braking probability. If z. B. only one einlenens secondary track object is present, so can one strong braking reaction of the driver only an emergency stop as plausible appear. In contrast, if yet another secondary track object with low conflict potential is present, so is both an emergency and a partial braking to adapt the speed to the speed of this Sub-track object plausible.

In a particularly preferred embodiment are therefore for the prefill function and for the triggering threshold for the Brake stop two independent emergency braking probabilities calculated.

drawing

One embodiment The invention is illustrated in the drawings and in the following Description closer explained.

It demonstrate:

1 a sketch of a traffic situation to explain the operation of the brake assistant according to the invention; and

2 a block diagram of the Brake Assist.

In 1 is in outline the front end of a vehicle 10 shown with an environment sensor 12 in the form of an angle-resolving radar sensor and with a brake assist 14 equipped. On the of the vehicle 10 busy lane 16 is located ahead of a slower preceding vehicle 18 that of the brake assistant 14 is classified as a follow object.

On the right side lane is another very slow vehicle 20 that is classified as a secondary track object. The speeds of the vehicles 10 . 18 and 20 are symbolized by velocity vectors V10, V18 and V20. The transverse offset of the vehicle 18 opposite the vehicle 10 is with y18 and corresponding to the transverse offset of the vehicle 20 denoted by y20.

With the help of the angle-resolving radar sensor of the vehicle 10 become the distances and relative speeds of the vehicles 18 and 20 (each in the direction of travel) measured. Due to the angular resolution of the radar sensor, it is also possible to determine the azimuth angles of the vehicles 18 and 20 to measure and from this together with the respective vehicle distances to calculate the transverse offsets y18 and y20. A slight inclination of the velocity vector V20 should symbolize that the vehicle 20 a little to the left, so on the lane 16 too moved, as if to make a lane change. The measured lateral offset y20 therefore decreases with time in terms of magnitude.

As the vehicle 18 at a great distance to the vehicle 10 and also the relative speed of this vehicle 18 (Difference between the speed V10 and V18 vents) is relatively low, a low braking deceleration of the vehicle is sufficient 10 to the speed of this vehicle to that of the preceding vehicle 18 adapt. This braking delay is significantly less than the maximum braking deceleration of the vehicle 10 , should be in here However, the assumed example may be greater than the maximum deceleration of the vehicle 10 that would be achievable solely due to the effect of the engine brake, without operating the brake pedal. The potential for conflict of the vehicle 18 That is, the probability that this vehicle an emergency braking request of the driver of the vehicle 10 is virtually zero under these conditions. On the contrary, it can be expected that the driver of the vehicle 10 Immediately moderate moderate braking will make its speed to that of the vehicle 18 adapt. Considering the vehicle alone 18 , is therefore for the driver of the vehicle 10 the emergency braking probability is zero.

For the vehicle 20 on the other hand, the (negative) relative speed is high and the distance is small, so that even with a full braking of the vehicle 10 A collision would be unavoidable if the vehicle 20 on the lane 16 or change to this lane. The potential for conflict of the vehicle 20 is therefore high. Taking into account the vehicle 20 Therefore, there is a certain probability that the driver of the vehicle 10 will trigger an emergency stop. This probability is further increased by the transverse offset y20 of the vehicle 20 decreases. The evaluation of the environment sensor data 12 speaks therefore altogether that the brake assistant 14 preventively should go into a state of increased braking readiness.

In 2 are the essential elements of the brake assistant 14 shown in a block diagram. The environment sensor 12 is an evaluation device 22 associated with the location data of the radar sensor, the distances di, the relative velocities vi and the transverse offsets yi all located objects i (in the example of the vehicles 18 and 20 ) and to an evaluation facility 24 of the brake assistant 14 transmitted. A brake force sensor 26 measures the pedal travel W of the brake pedal and its time derivative W ', ie the speed with which the brake pedal is actuated, and also transmits these quantities to the evaluation device 24 , The pedal travel W is also (preferably mechanically or hydraulically) to a control device 28 transmitted the hydraulic brake pressure in the braking system of the vehicle 10 controls. In the case of "normal" braking processes, that is to say not in the case of emergency brake predecessors, the brake pressure is thus set in accordance with the pedal travel W and optionally modulated as part of an ABS function. An alternative to measuring the pedal travel is to measure the pressure and pressure gradient in the master cylinder.

In the control device 28 In addition, a prefill function is implemented with which one of the rating facility 24 received command "prefill" the hydraulic pressure in the brake system is increased so that the brake shoes are made against the brake discs or brake drums, but without exerting a significant braking delay. Furthermore, the control device has 28 the functionality of a hydraulic brake assistant, on another command "HBA" from the evaluation device 24 abruptly increased the brake pressure in the system to build up the maximum brake pressure as quickly as possible in the event of emergency braking.

The evaluation facility 24 generates the commands "prefill" and "HBA" depending on the signals that they receive from the evaluation device 22 and the pedal sensor 26 receives. Based on the signals di, vi and yi calculates the evaluation device 24 the conflict potential of each located object.

From the totality of conflict potentials of all objects, the evaluation device calculates 24 a prefill emergency braking probability. If this probability is above a predetermined threshold, the command "prefill" is issued. The prefill emergency braking probability is calculated, for example, by calculating a weighted sum of the conflict potentials of all objects. The weighting factors with which the individual conflict potentials are weighted depend, for example, on the transverse offsets yi and transverse movements (time derivatives of yi) of the objects, so that the prefill emergency braking probability increases, the closer a secondary track object (for example the vehicle 20 ) own lane 16 or driving trajectory is coming. For follower objects (for example the vehicle 18 ) the weight factors can be calculated according to other criteria. In particular, an increase in the relative speed (in the sense of an approach) and the sudden emergence of a so far from the environmental sensor system do not increase weight 12 captured object. In this way, the braking system is always preparatory prepared for an emergency braking when there is a sufficiently high prefill emergency braking probability.

Furthermore, the evaluation device calculates 24 an HBA emergency braking probability that triggers the command HBA (brake stroke) when a certain threshold value is exceeded. For the calculation of this HBA emergency braking probability, the secondary lane objects are evaluated in the same way as for the prefill emergency braking probability. Follow-up objects (vehicle 18 However, here lead to a reduction of the HBA emergency braking probability or to a complete blocking of the HBA function, if it follows from the distance and relative speed data that with ei moderate braking (partial braking) is expected, because the driver of the vehicle 10 must adapt its speed to that of the preceding vehicle. Under these conditions, the prefill function is thus possibly activated, while the release of a brake shock is suppressed.

The HBA emergency braking probability does not directly lead to the output of the command HBA, but rather the command HBA is output when the pedal travel W below / or its time derivative W 'is above a respectively associated threshold value. These thresholds are determined by the evaluation facility 24 varies as a function of the HBA emergency braking probability, so that the higher the HBA emergency braking probability, the lower the threshold for the brake stroke. In this way, a rapid and efficient emergency braking with fast brake pressure build-up can be initiated at high HBA emergency braking probability, while on the other hand at low HBA emergency braking probability for the. Rider sufficient leeway for a moderate partial braking remains.

In a modified embodiment Is it possible, only one single emergency brake probability in the same Way to calculate how it is here for the HBA emergency braking probability was described and to issue the prefill command if this Notbremswahrscheinlichkeit exceeds a certain threshold.

Claims (7)

Brake assist for motor vehicles, with a control device ( 28 ) for controlling the braking force, a brake force sensor ( 26 ) and an evaluation facility ( 24 ) for the detection of an emergency braking request of the driver and for the preparation or initiation of emergency braking, characterized in that the evaluation device ( 24 ) Signals of an environment sensor system ( 12 ) receives and evaluates. Brake assistant according to claim 1, characterized in that the surroundings sensor system ( 12 ) has an angle-resolving radar sensor. Brake assist according to claim 1 or 2, characterized in that in the control device ( 28 ) a prefill function is implemented with which, on the 24 ), the brake pressure in the brake system is increased so that a dead gear between the brake shoes and the brake discs or brake drums of the brakes is reduced without a significant braking effect already occurs. Brake assist according to claim 3, characterized in that the evaluation device ( 24 ) is designed to, based on the data of the environment sensor ( 12 ), in particular based on the distances and relative speeds of located vehicles ( 18 . 20 ) to calculate an emergency braking probability and issue the command for the prefill function when the emergency braking probability exceeds a predetermined threshold. Brake assist according to one of the preceding claims, characterized in that in the control device ( 28 ) a brake-stop function is implemented by which, on the order of the evaluator ( 24 ) the brake pressure in the brake system is abruptly increased when the brake pedal sensor ( 26 ) and / or its time derivative (W ') exceeds an associated threshold, and that the evaluation device ( 24 ) is adapted to the threshold value for the pedal travel or its time derivative as a function of a based on the signals of the environment sensor ( 12 ) to vary the calculated emergency braking probability. Brake assist according to claim 4 or 5, characterized in that the evaluation device ( 24 ) is designed to be based on the signals of the environment sensor ( 12 ) between follower objects ( 18 ), based on the expected trajectory of the own vehicle ( 10 ), and secondary track objects ( 20 ), which are located away from this trajectory, and that the location data of the follower objects and he subordinate track objects enter into the calculation of the emergency braking probability in different ways. Brake assist according to Claim 6, characterized in that the emergency braking probability decreases when a follower object ( 18 ) or a secondary track object whose distance and relative speed data provide a moderate braking action for adjusting the speed of the own vehicle ( 10 ) to the speed of this object ( 18 ) can be expected.