WO1998035865A1 - Process for damping drive train vibrations - Google Patents

Abstract

The invention relates to a process for damping critical wheel or drive train vibrations requiring countermeasures during an ABS-controlled brake manoeuver. The speed characteristic of the wheels being driven is analyzed and upon recognition of critical wheel vibrations is switched over to a special control for a set period of time. The intervention of the special control prevents a reduction of brake pressure, keeps pressure constant or at best allows delayed pressure build-up. In the case of vibrations with a frequency which is typical for wheel vibrations, the number of successive vibrations or semi-vibrations of each individual wheel is counted. When a pre-set number is reached, vibration recognition is indicated (BY_DRIVE_REC=1) if at that time the vehicle acceleration is above a set limit value and if there has not yet been vibration recognition on the other wheel being driven.

Description

Process for damping powertrain vibrations

The invention relates to a method for damping wheel vibrations or drive train vibrations that are called during a controlled braking maneuver, in particular during an ABS-controlled braking operation.

An anti-lock control system is already known from WO 90/06250, which contains switching means for detecting wheel and axle vibrations and influencing means for initiating measures for damping such vibrations. The turning behavior of the wheels is measured with wheel sensors. According to this document, it is evaluated as a criterion for vibration detection that the cycle times are approximately the same in the presence of a vibration.

Furthermore, GB 2 289 097 A describes an anti-lock braking system in which the rotational speed at the differential is determined from the speeds of the driven wheels and by filtering this signal it is determined whether this rotational speed is an oscillation component which lies in the frequency range of the drive train vibrations. is superimposed. If two conditions are met, namely if the oscillation frequency is in the range between 5 and 12 Hz and if the filtered signal exceeds a threshold value, there are drive train vibrations. A correction of the brake pressure modulation damping the vibrations is carried out. The object of the invention is to effectively dampen wheel vibrations or drive train vibrations which impair driving comfort and control comfort and also, if the vibrations build up, which can endanger driving safety.

It has been shown that this object is achieved by the method described in claim 1, the special feature of which is that when critical vibrations are detected on a drive wheel selected according to predetermined criteria, the brake pressure control of this wheel for a specific period of time is based on a special control which Vibration damping causes, is switched.

According to an advantageous embodiment of the invention it is provided that after the onset of the special control a brake pressure reduction on this wheel is prevented and a control-related brake pressure build-up is at most delayed and / or only permitted with a flat, flattened gradient. It can also be expedient to keep the brake pressure at least approximately constant during the special control.

The special regulation is only ended when the brake slip of the wheel reaches a predetermined, high limit value in the range between 40% and 60%, e.g. of 50%.

It is further provided according to the invention to critically assess wheel vibrations that are in a predetermined frequency range of, for example, 5 Hz and 23 Hz that are typical for drive train vibrations, that occur when the vehicle acceleration is above a limit value and that persist beyond a predetermined period of time or number of vibrations . Vibration damping is primarily required in the low coefficient of friction range, which is why as a limit value for vehicle acceleration that is exceeded it must, expediently, be given a value between -0.6 g and - 0.3 g, for example -0.5 g.

You should react very quickly to wheel vibrations or drive train vibrations, but an unjustified intervention should be avoided. Therefore, according to one exemplary embodiment, a minimum number of 5 consecutive half vibrations is evaluated as a criterion for switching over to the special control or for initiating damping measures.

Further details of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying figures.

Show it:

1 is a flowchart illustrating the vibration detection,

2a shows a typical wheel speed curve during an ABS-controlled braking maneuver in the diagram,

Fig. 2b in the same representation as Fig. 2a, the wheel speed curve when drive train vibrations occur

3 shows diagrams to illustrate the course of the wheel speeds and the brake pressures during an ABS-controlled braking process when drive train vibrations occur and the triggering of damping measures.

1, which shows the individual steps and the basic decision-making process in a simplified form reproduces, illustrates the inventive method. To detect wheel vibrations or drive train vibrations, it is first determined in a program step 1 or filter 1 whether the oscillation frequency f lies in a frequency range typical for drive vibrations. A frequency range from ftiin = 5 Hz to f _Max = 23 Hz has proven to be expedient. If the vibrations are in this range ("yes") and a certain minimum duration of vibration or a certain minimum number of vibrations is determined, the next step in the flow chart follows in the direction of a damping measure. In the example shown, a counter 2 is provided which is incremented by the value "1" for each half-wave of the oscillation, in particular each "peak" (see FIG. 3) of the drive train oscillation, and which reacts (step 3) when the count value " 4 "is exceeded. When the counter reading "4" is exceeded, a detection signal is shown in the flow chart according to FIG

BY_DRIVE_REC = 1 set, so to speak a preliminary stage of a vibration detection. This is done in program step 4.

The next step in step 5 is to determine whether the vehicle acceleration is above a predetermined minimum value of e.g. -0.5 g, i.e.

VehAcc> -0.5g,

and whether the second condition

BY_ DRIVE (other wheel) = 0?

is satisfied. A relatively high vehicle acceleration (> - 0.5g) or, in other words, less than -0.5g Deceleration includes a statement about the current road condition or coefficient of friction; with high vehicle deceleration, which is only possible under favorable road conditions for physical reasons, the damping measure according to the invention should not be carried out.

The second condition

BY_DRIVE (other bike) = 0

or the decision dependent on this condition has the consequence that the damping measure is only ever applied to one of the two driven wheels - only vehicles with a driven axle are considered here. This makes it possible to implement relatively "drastic" damping measures in which e.g. a very high brake slip is accepted for a short time. In one embodiment of the damping measure method according to the invention, after switching to the special control, the pressure reduction on the controlled wheel only begins when a relative slip of 50% is exceeded.

If the conditions checked in decision step 5 are met ("yes"), as symbolized in program step 6, vibration detection, i.e. the detection of drive train vibrations signals. Applies to the drive wheel in question

BY_DRIVE - 1.

For this wheel, the special control is triggered for a predetermined period of time, which effectively dampens the drive train vibrations. The standard brake pressure control of the wheel is modified for a certain period of time; this is explained in more detail below with reference to FIG. 3. 1 is thus in the flow chart

BY_DRIVE_REC

the actual vibration detection signal or detection bit; "BY_ DRIVE", on the other hand, can be interpreted as a control signal or control bit. BY_DRIVE is only set (ie BY_) RIVE = 1) if, as already described, the calculated vehicle deceleration is less than -0.5 g and if the control bit (BY_DRIVE) for the other drive wheel is not or not yet is set, ie

BY_DRIVE other wheel = 0.

The BY_DRIVE control signal is therefore only set when braking on roads with a low to medium coefficient of friction and only for one of the two drive wheels. As soon as the vehicle deceleration is greater than the predetermined limit value, in the present example greater than -0.5 g, when the vibrations have subsided or the frequency range> f _Mιn ; <f _Max have left, so that "BY_DRIVE_REC" changes from 1 to 0, the vibration detection ends and thus the damping measure triggered by the vibration detection on the wheel in question.

"BY_DRIVE" is used, for example, as a control bit for switching or modifying the pressure modulation on the drive wheels.

Resetting the counter when the frequency is outside the predetermined critical range, the status of the detection signal (BY_DRIVE_REC = 0) when the counter reading is too low and the failure to fulfill the AND condition 5 are shown in FIG. 1 by program steps 7, 8 and 9 symbolizes. Driving tests have shown that the disturbing drive train vibrations can be effectively and quickly suppressed by the described vibration detection and by the damping measures according to the invention. With a detection bandwidth of 5 Hz to 23 Hz and a reaction after five half oscillations (counter reading> 4 according to program step 3 in FIG. 1), the drive train vibrations are recognized in practice after about 250 ms. Due to the above-mentioned drastic damping measures, approximately 700 to 800 ms elapse in practice from the time the vibration begins until the vibrations fade away.

2a illustrates the speed curve of a wheel during a normal controlled braking operation. If one differentiates the control process and the control reaction, as indicated in FIG. 2a, into successive phases Ph2, Ph4, Ph3, the pressure reduction takes place in the phase Ph2, the pressure build-up in the phase Ph3 and essentially a pressure maintenance in the phase Ph4, if necessary an early build-up of pressure instead.

Occur during the ABS-controlled braking maneuver

Drive train vibrations, this leads to the course of the wheel speed shown in Fig. 2b. Without damping measures, there is a rapid change between pressure reduction and pressure build-up phases, the control frequency becomes high. This results in the previously mentioned loss of comfort and disturbing noises, increased wear and also safety-critical control processes.

3 is a section of an ABS-controlled braking maneuver showing the speed curve

Vi, v _{2 of} the two drive wheels of a vehicle in a braking phase stressed by drive train vibrations give. In addition, the detection and control signals

BY_DRIVE_REC 1.2

(i.e. on wheel "1", wheel "2") and

BY_DRIVE 1.2

shown. The continuous characteristic curves apply to drive wheel 1, the dashed lines apply to drive wheel 2.

The speed curve of the two wheels and the brake pressure pl, p2 are shown in the associated wheel brakes.

The drive wheels with the wheel speeds v _x , v ₂ start to oscillate at the time t ₀ after the anti-lock control has been activated. The oscillation frequency f (cf. FIG. 1) lies in the range typical for drive train vibrations and in the frequency range specified by the filter 1. The oscillation half-waves are counted by counter 2. The counter reading reached at the time t _x the value "5", that exceeds at that time t _x the limit value "4", and thereby triggers a detection signal BY_DRIVE_REC 1 (see top curve in Fig. 3). At this point in time tj the vehicle acceleration is above -0.5 g (this is not shown in FIG. 3); in addition, the signal BY_DRIVE 2, that is to say the control bit of the “other” wheel, has not yet been set at the time t _x , so that a detection or control signal is now provided for this drive wheel 1

BY DRIVE 1 = 1 given and a damping measure is triggered on this wheel. As can be seen from the course of the brake pressure pl on the drive wheel 1, the brake pressure is kept constant after ti, although with "normal" brake pressure control the strong deceleration or the increasing slip on the wheel 1 should result in a decrease in pressure.

The slip on the drive wheel 1 finally reaches a certain limit value at the time t ₃ , for example a relative slip value of 50%, so that a control-related reduction in the brake pressure pl now takes place independently of the vibration detection signals. This decrease in pressure then, as can be seen from the speed curve Vi, very soon results in a recovery of the wheel 1 and an approximation of the wheel speed v _x to the vehicle speed (not shown).

The second drive wheel with the speed v ₂ also _starts to oscillate from about the time t ₀ . However, this is not "recognized" in the example shown and does not lead to damping measures on wheel 2, because first, namely at time t _x , vibration detection takes place on wheel 1. This is illustrated by the small time difference between t _x and t ₂ , which affects a corresponding delay in the BY_DRIVE_REC 2 signal compared to the BY_DRIVE_REC 1 signal. By restricting the damping measures to a specific drive wheel, it becomes possible to provide a radical, "drastic" damping measure which leads to the driveline vibrations subsiding in a very short time. A comparison of the brake pressure curve pl on the wheel 1, which is subject to the special regulation, with the pressure p2 on the drive wheel 2, which is regulated normally, illustrates the differences. By keeping the brake pressure constant in the period from t _x to t ₃ and accepting a very high brake slip the effective damping achieved. The reduction of the brake pressure p2 on the wheel 2, on the other hand, begins as a result of the wheel profile v ₂ before the time t ₂ .

The detection signals following t ₄ do not lead to any further damping measures in the example of a braking process shown in FIG. 3, because obviously the brake pressure has already largely been reduced or the controlled braking process has largely ended. The amplitudes of the superimposed vibrations after t ₄ are relatively low.

3 therefore shows an example of an effective measure for vibration damping as a result of the

Powertrain vibration detection, which also includes the selection or detection of one of the two wheels according to predetermined criteria and thus the preparation for the damping measures according to the invention; Since the wheel vibrations are caused by drive train vibrations, such vibrations naturally occur on both drive wheels, even if with different intensities and phases.

The selection of the detection bandwidth from 5 Hz to 23 Hz, implemented by the filter 1 according to FIG. 1, and the counting of at least five consecutive half-vibrations as a prerequisite for the vibration detection, on the one hand have a reliable reaction to vibrations and, on the other hand, a quick detection and thus Triggering countermeasures or damping measures. In practice, drive train vibrations are recognized after 250 ms at the latest and can be effectively damped in a subsequent period of 400 ms - 600 ms.

Powertrain vibrations occur particularly when braking is controlled when engaged Low friction roads on. They are particularly strong on so-called "peak ice", namely in road conditions in which the coefficient of friction is maximum only within a relatively narrow slip range and rapidly decreases outside this range.

An analysis showed that the pressure modulation that results in a controlled braking process, in the worst case, increases the tendency of the drive wheels to vibrate, by relieving pressure precisely when the wheel is in the re-acceleration phase and, conversely, when pressure is built up when that Wheel slips. In order to counteract this behavior, the described method was developed, which deals with the early detection of drive train vibrations, the determination of a drive wheel on which the damping measure is applied, and the switch to the special control that effects the vibration damping.

The countermeasures are generally intended to prevent vibration and, if vibration is detected, pressure reduction, pressure build-up and constant pressure control are controlled in such a way that a vibrating wheel is actively damped.

In order to avoid vibration excitation, an early build-up of pressure, which makes sense in the actual pressure-constant phase under certain conditions, is ruled out if pressure-reduction and build-up processes take place directly one after the other.

If the drive train nevertheless starts to vibrate or the vibrations continue, further measures will take effect. A pressure reduction stop has proven to be the most effective measure, in which the pressure level in the wheel brake cylinder of one of the two oscillating wheels is maintained until a maximum of 50% relative wheel slip is reached. This leads to a deep slip run-in of the wheel, whereby the vibration decays strongly. Vibration damping is also transmitted via the differential to the second drive wheel of the axle, for which there is no pressure stop.

If a relative wheel slip of more than 50% is reached, the wheel is given the possibility of re-acceleration by pulsed pressure reduction. This and the fact that this measure is only used for one wheel means that the engine does not stop.

Claims

Claims: 1. A method for damping wheel vibrations or drive train vibrations during a controlled braking maneuver, characterized in that when critical vibrations are detected on a drive wheel selected according to predetermined criteria, the brake pressure control of this wheel is switched to a special control for a certain period of time. 2. The method according to claim 1, characterized in that, after the onset of the special control, brake pressure reduction is prevented and a control-related brake pressure build-up is delayed and / or is only permitted with a flat gradient. 3. The method according to claim 1, characterized in that the brake pressure is at least approximately kept constant during the special control. 4. The method according to one or more of claims 1 to 3, characterized in that the special regulation is ended as soon as the brake slip of the wheel reaches a predetermined limit value, in particular a relative slip value in the order of magnitude between 40 and 60%, e.g. 50%, exceeds. 5. The method according to one or more of claims 1 to 4, characterized in that wheel vibrations which lie in a predetermined frequency range typical of drive train vibrations, which occur when the vehicle acceleration is above a limit value and which persist beyond a predetermined period of time or number of vibrations, are rated as critical. 6. The method according to claim 5, characterized in that an oscillation range between 5 Hz and 23 Hz is specified as the typical frequency range. 7. The method according to claim 5, characterized in that a vehicle acceleration which is greater than -0.6 g to -0.3 g, in particular greater than -0.5 g, is specified as the limit value. 8. The method according to one or more of claims 5 to 7, characterized in that only wheel vibrations that persist beyond a predetermined minimum number of successive vibrations or semi-vibrations are assessed as critical. 9. The method according to claim 8, characterized in that the minimum number 4 to 8, e.g. 5, successive semi-oscillations can be specified