DE102006051261A1 - Method for determining braking force differences in braking control system of motor vehicle, requires examining wheel speeds via wheel revs sensors for discrete wheels - Google Patents

Abstract

Method for determining braking force differences in which the braking system comprises at least two pressurizing agent actuated braking circuits. During the braking process in which at least one slip control system is not active, wheel speeds (Vcr0 (t), (Vcr1 (t)) on the basis of wheel revs sensors of discrete wheels or for wheels of each braking circuit are examined over one time period, and the wheel speeds are assigned to braking circuits in a comparative numerical relationship to form a revs difference value (Delta Vcr (t)). An independent claim is given for an electronic motor-vehicle braking system.

Description

The The invention relates to a method according to the preamble of claim 1, its use according to claim 12 and an electronic motor vehicle brake system according to claim 13th

electronic Automotive brake systems with the functions ABS, ESP and the like are known per se. In conjunction with additional sensors (distance sensor, Wheel pressure sensor) can be additionally with these systems Longitudinal control functions such as adaptive distance control (ACC).

The Accuracy of the above-mentioned longitudinal control functions hang Among other things, very sensitive to the proper functioning of the brake system from. This concludes in addition to the electronic components, the hydraulic components, but also the mechanical components (calipers, brake discs, etc.) with one. An object of the invention is an analysis of the hydraulic-mechanical Perform part of the braking system, to detect errors or above addition, the function of the above-mentioned to improve complex control functions.

These The object is achieved by the method defined in claim 1.

The method according to the invention is preferably carried out in an electronic brake control system for determining brake force differences. According to the method of the invention, during a braking operation in which at least one slip control system is not active, wheel speeds (v _Cr0 (t), v _Cr1 (t)) are considered based on wheel speed sensors for wheels of each brake circuit over a period of time. The wheel speeds or filtered wheel speeds derived therefrom are then brought into a comparative numerical relationship, in particular associated with the brake circuits, to form a speed differential quantity (Δv _Cr (t)). The numerical relationship preferably consists in the formation of the difference of the wheel _{speed variables} v _Cr0 (t), v _Cr1 (t). Alternatively, however, it is also possible, and therefore preferred, to relate the two variables to one another in a quotient.

today Brake systems usually comprise at least two pressure-medium-operated brake circuits. If the above method used to determine brake circuit differences will be preferred from the wheel speeds of each Circles averages formed. These averages are then in the said numerical relationship.

With The above method may be smallest Differences in the brakes, preferably the brake circuits found be, with a particular advantage of the above method signal formed its extensive independence from the vehicle steering angle is. The above method according to the invention is also suitable to improve the accuracy in determining the wheel pressure.

Next the detection of brake force differences of the brake circuits can be also carry out a single wheel comparison with the method according to the invention. at This method is preferably evaluated statistically, as often a pair of wheels one over a fixed threshold speed difference having. Indicates the frequency the difference transgressions towards one or more non-normal wheels, this will be a suitable measure met.

The Brake control system in which the method according to the invention accomplished can, in addition to the functions ABS, even more for electronic Brake systems usual Functions, such as electronic brake force distribution (EBV), driving stability system (ESP) etc., include. The ABS function and the other functions are hereinafter referred to as slip control systems.

The execution the method according to the invention in a brake control unit is therefore particularly advantageous because only there the high-resolution raw signals the ABS wheel speed sensors are present. Outside the brake control unit are these raw signals are usually not available.

The determination according to the invention the wheel speeds or the final evaluation of these speed signals takes place only if at least one slip control system while is not active. Preferably, the processing is carried out according to the invention only if no electronic brake distribution (EBV) is active. Furthermore, it is preferred that the determination according to the invention or evaluation is performed only if one is not any control functions affected conventional uncontrolled braking is present. Particular preference is given to the criteria known per se for the Determination of straight-ahead driving also checked and further processing only made if there is essentially a straight ahead.

Preferably, the speed difference quantity (Δv _Cr (t)) is subjected to numerical filtering in which short-term signal fluctuations are reduced. The numerical filters which can be used for numerical filtering are algorithms which are known per se, such algorithms preferably being used for Are used, which only take a relatively small amount of computing time. Corresponding algorythmic filter methods are used, for example, in systems known per se for wheel-speed-based tire pressure loss determination. The use of the said filter with a low computing time allows a diagnosis of the brake system already during a braking operation.

To a further preferred embodiment of the method does not become a pressure sensor signal for the determination of the wheel cylinder pressure considered. It may still be appropriate, the inventive method within a braking system where signals from wheel pressure sensors to disposal to use, for example, to make a review of Raddrucksensoren.

The The above method is used in an electronically controlled fluid-operated brake system carried out, this is preferably in each case a pump for conveying hydraulic fluid having. Furthermore, the brake system preferably has a common Motor for controlling the pumps. The delivery rate of the pumps is through suitable switching of hydraulic valves and an adjustable Pump speed, however, for each circle can be dosed separately.

To a further preferred embodiment invention, the method described above is thus extended, that is an offset or correction value for the electric pump drive is determined. This is especially true for distance control methods (ACC), because of Distance control procedure is typical that a very specific Pressure in the wheel brakes must be adjusted. Includes the brake system However, now no pressure sensors for the Radkreise, the wheel pressure on a suitable model can be determined. Such wheel pressure models are already widely known become. The value determined by the wheel pressure model for the pump control is then slightly corrected in the manner described above. In this way, for example, for each brake circuit exactly the same delivery rate be set.

The Method according to the invention is suitable, any imbalances and / or defects and / or malfunctions in a brake system to simple Way to determine. In this context, even the lowest brake force differences be determined. Furthermore the procedure offers the possibility a general measure of the general wear factor or condition in the sense of a need for maintenance (Status) of the brake system. The method can in particular used to asymmetric wear of the brakes or Tires that have an impairment the comfort or safety of the motor vehicle can, for example, a stronger one Normal braking without a control function, to recognize and appropriate countermeasures and / or initiate alerts.

According to a further preferred embodiment, the quantity Δv _Cr (t) is used to deduce a pressure difference ΔP (t) in the wheel brake circuits. The determined pressure difference .DELTA.P (t) can be used in particular to detect a leak within a brake circuit. An assignment between the pressure difference and the wheel speed difference is effected in particular by a fixed assignment rule (mathematical equation, value table), which is preferably determined individually for each vehicle type.

The Method may according to a preferred embodiment in a brake system used with wheel pressure sensors to make a comparison between Set pressure and actual pressure.

Preferably will be according to specification the determined brake pressure difference .DELTA.P (t) during braking, in particular while uncontrolled braking phases (no ABS etc.), compensating for the braking behavior the braking system intervened so that the wheel speeds each other be aligned. This can be done, for example, by increasing the Brake pressure on the wheels with too high wheel speed and / or corresponding reduction the brake pressure of the wheels take place with too low a wheel speed. In the last case However, care must be taken to ensure that no appreciable reduction the braking path brought about becomes.

The The invention also relates to the use of the above method in an adaptive distance control system. Furthermore, the method can be used in a corresponding brake control system that is instructed to a precisely metered Raddruckregelung.

Further preferred embodiments emerge from the dependent claims and the following description with exemplary embodiments.

It demonstrate

1 Wheel speed characteristics of a braking system over time,

2 the difference of the speed signals 1a )

3 . 4 Examples of deviations of the speed signal at a pressure difference between the brake circuits and

5 . 6 Examples of a differential evaluation on single wheels.

1a and 1b Figure 4 illustrates wheel speed versus time curves measured during a braking event obtained in an electronic braking system having ABS and EBV functions based on wheel speed information from wheel speed sensors. The brake system has two hydraulically separated brake circuits, wherein in the example described here the front wheels are associated with the first brake circuit (Circ_0) and the rear wheels are associated with the second brake circuit (Circ_1). The method is also applicable to systems with diagonal brake circuit distribution. It is a conventional braking without intervention of the electronic control system. Partial image a) shows two speed profiles derived from wheels of different hydraulic brake circuits, wherein the curves of the front brake circuit (Circ_0) and the rear brake circuit (Circ_1) substantially coincide. Partial image b) shows the corresponding wheel speed curve of the individual wheels Wh_0 (front left), Wh_1 (front right), Wh_2 (rear left) and Wh_3 (rear right) of a four-wheeled motor vehicle. Already in this diagram small speed deviations are recognizable. The wheel speeds in connection with the curves Circ_0 and Circ_1 are obtained by averaging the wheel speeds of the brake circuits Wh_0 and Wh_2 as well as Wh_1 and Wh_3.

In the diagram in 2 , is the difference of the speed signals 1a ) over time. Here, v _Cr0 (t) is the wheel speed curve of the first circle Circ_0 and v _Cr1 (t) is the corresponding curve of the circle Circ_1. Partial image a) represents the unfiltered (raw) signal and partial image b) a signal which is filtered in a manner known per se, which signal was obtained from the signal in partial image a). The signal in 2 B ) clearly shows that there are deviations between the wheel speeds during braking. With the help of this signal, a diagnosis of the condition of the brakes or tires is possible.

In 3 Examples of curve curves of the speed difference are shown, as they may occur during exemplary fault conditions of the brake system. Sub-images a) to c) show different driving conditions in which there is a higher brake pressure in the front brake circuit Circ_0. This driving condition may be caused, for example, by a leak in the rear brake circuit. Parts a) to c) in 4 in each case the partial images in 3 correspondingly assigned to the pressure difference, which were specified in the brake circuits during the measurement of the curves for the speed difference. It can be seen from the curves that even slight differences in pressure between the brake circuits below 5 bar lead to clearly discernible deviations of the speed difference curves in 3 to lead. The sensitivity of the difference signal depends relatively strongly on the quality of the signal filter used. Thus, in principle, there is an ideal brake pressure distribution within the brake system when the speed difference signal is close to zero.

If the pressure difference in the brake circuits is negative, that is at a higher pressure in the rear brake circuit, that turns into 3 displayed signal um.

The above-described principle of the evaluation of speed differences for the detection of pressure deviations in the brake circuits can also be applied to an independent wheel analysis. In the diagram in 5a ) the speed difference of the fastest and the slowest wheel is plotted during a braking process. In this case, in contrast to the above method, it is important that the described evaluation is carried out only during a straight-ahead drive, since cornering influences do not cancel each other out in this particular case. In 5b ), the wheels are represented, which represent the wheel with the lowest or the highest wheel speed at a certain time. On the y-axis, the number of the wheel (from 1 to 4) is plotted together with the value 0. In this case, the curves which are assigned to wheels with the currently lowest wheel speed, drawn with greater thickness, so the curves, which are assigned to wheels having the momentarily highest wheel speed. If the wheel speed difference in sub-picture a) is above the threshold of 0.15 km / h, the plot of a line (in the example at a time of about 390 ms) that leads from zero to the wheel is started in the diagram in sub-picture b) the lower wheel speed shows. If no pair of wheels is above the said threshold, a value of zero is plotted. In the example shown, the wheel with the number 3 (rear right) shows a much higher wheel speed than the other wheels (the thin line is often in the range of the wheel number 3). The evaluation according to the example described here can also be carried out by the electronic brake system and be used, for example, to detect a defect in the brake system (leak, lining wear, etc.).

In the example according to 6 the wheel that shows the most conspicuousness was out of the data of the example in 5 away. As you can see from the diagrams, you can not see any particular frequency for the remaining wheels. From this it can be concluded that in the area of the brake circuit, which is assigned to the wheel with the number 3, probably a defect is present, which should be checked in the workshop. It is also possible that this wheel has a non-standard tire pressure, therefore, the method can in principle be used to detect a tire pressure loss.

Claims (13)

Method for determining brake force differences of the brake circuits in a motor vehicle, wherein the brake system comprises at least two pressure-medium-actuated brake circuits, characterized in that during a braking operation in which at least one slip control system is not active, wheel speeds (v _Cr0 (t), v _Cr1 (t) ) are considered based on wheel speed sensors of individual wheels or for wheels of each brake circuit over a period of time and the wheel speeds or derived filtered wheel speeds, especially associated with the brake circuits, are brought into a comparative numerical relationship to form a speed difference quantity (Δv _Cr (t)) , A method according to claim 1, characterized in that the speed difference quantity (Δv _Cr (t)) is subjected to a numerical filtering in which short-term signal fluctuations are reduced. A method according to claim 1 or 2, characterized in that from the speed difference variable (.DELTA.v _Cr (t)) is closed to a pressure difference .DELTA.P (t) in the wheel brake circuits of a pressure-medium-operated brake system. Method according to claim 3, characterized that the pressure difference ΔP (t) is used to detect a leak within a brake circuit or a mechanical defect of the brake circuit associated brake to detect. Method according to at least one of the preceding Claims, characterized in that a cornering signal is considered and the consideration of the Radgeschwindkeitsdifferenz or the pressure difference only during a driving situation takes place in which there is substantially straight ahead. Method according to at least one of the preceding Claims, characterized in that from the pressure difference .DELTA.P (t) a Offset for one or more hydraulic pumps is calculated, which at a known per se, the pump speed within the system considered is, wherein the brake system comprises one pump per brake circuit. Method according to at least one of the preceding Claims, characterized in that in this no pressure sensor signal for the determination of the wheel cylinder pressure is used. Method according to at least one of claims 1 to 6, characterized in that the wheel brake cylinder pressure is determined by means of one or more pressure sensors and from the speed difference variable (Δv _Cr (t)) a desired brake pressure difference for the corresponding wheels by means of a predetermined assignment is determined and this with a Istdruckdifferenz is compared. Method according to claim 8, characterized in that that in accordance the comparison of the actual pressure difference with the target pressure difference in non-control phases of the brake system, a brake pressure correction is performed. Method according to claim 9, characterized in that that the brake pressure correction at a speed difference of more than 0.3 km / h or with a corresponding pressure difference carried out becomes. Method according to claim 9 or 10, characterized that a cornering signal is considered and the brake pressure correction only during one Driving situation takes place, in the substantially straight ahead is present. Use of the method according to at least one of claims 1 to 11 in an adaptive distance control system or a corresponding to a precisely metered Raddruckregelung instructed brake control method or to detect a tire pressure loss. Electronic motor vehicle brake system, characterized in that in this a method according to at least one of claims 1 to 11 performed becomes.