Method for determining the drive train sensitivity of a drive train of a motor vehicle

Abstract

A method for determines the drive train sensitivity of a drive train of a motor vehicle. A vehicle body is placed in longitudinal oscillations in the direction of travel and a parameter for the drive train sensitivity is determined as a function of the determined longitudinal accelerations of the vehicle body and the resultant angular accelerations of a transmission input shaft of a transmission of the motor vehicle.

Claims

1. A method for determining a drive train sensitivity of a drive train of a motor vehicle, wherein a vehicle body is placed in longitudinal oscillations in a direction of travel and, depending on longitudinal accelerations of the vehicle body and angular accelerations of a transmission input shaft of a transmission of the motor vehicle, a parameter for the drive train sensitivity is determined, wherein the drive train sensitivity denotes transmission behavior between a torque modulation of a slipping friction clutch and an acceleration amplitude of the motor vehicle that the driver can feel, wherein a linear oscillator with at least one eccentric mass is connected to the vehicle body to generate the longitudinal oscillations.

2. The method according to claim 1, wherein the parameter is used to determine an estimate of a susceptibility to judder of a friction clutch arranged between an internal combustion engine and the transmission.

3. The method according to claim 1, wherein the parameter is determined from the frequency dependence of the frequency of the longitudinal oscillations.

4. The method according to claim 1, wherein the parameter is determined depending on the at least one eccentric mass.

5. The method according to claim 1, wherein detected angular acceleration signals of the angular acceleration are treated by means of at least one order sorting filter.

6. The method according to claim 1, wherein the parameter is determined depending on a selected gear in the transmission.

7. The method according to claim 1, wherein the parameter is validated by means of a predetermined coherence.

8. The method according to claim 1, wherein a frequency sweep of the longitudinal oscillations is carried out over a predetermined number of identical oscillation periods.

9. The method according to claim 1, wherein the longitudinal oscillations are predetermined with force excitation that is constant over the frequency.

10. A method of determining a drive train sensitivity of a motor vehicle, the method comprising: connecting a linear oscillator with at least one eccentric mass to a body of the motor vehicle to generate oscillations in a longitudinal direction; placing the vehicle in motion in the longitudinal direction; varying a frequency of the linear oscillator over a range of frequencies; and measuring angular accelerations of a transmission input shaft.

11. The method of claim 10 further comprising treating the angular acceleration measurements using an order sorting filter.

12. The method of claim 10 further comprising repeating the varying of the frequency and the measuring of the angular acceleration with a transmission in a different gear state.

13. The method of claim 10 further comprising attaching a different eccentric mass to the linear oscillator and repeating the varying of the frequency and the measuring of the angular acceleration.

14. The method of claim 10 wherein the range of frequencies includes 3 Hz and 30 Hz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The method is explained in more detail with reference to the exemplary embodiment shown in FIGS. 1 to 7. In the figures:

(2) FIG. 1 shows a schematic illustration of a motor vehicle for carrying out the method,

(3) FIG. 2 shows a schematic illustration of an exemplary embodiment of a linear oscillator,

(4) FIG. 3 shows characteristic excitation curves for different oscillating masses,

(5) FIG. 4 shows a diagram of drive train sensitivities and associated coherences for a given oscillating mass,

(6) FIG. 5 shows a diagram of drive train sensitivities with different oscillating masses and gears engaged in the transmission,

(7) FIG. 6 shows a diagram of the coherences of determined drive train sensitivities with different oscillating masses and

(8) FIG. 7 shows a diagram of an improved excitation for determining the transfer function.

DETAILED DESCRIPTION

(9) FIG. 1 shows a schematic representation of the motor vehicle 1 for determining the drive train sensitivity of the drive train 2 here a front transverse installation with the driven wheels 3. When the motor vehicle 1 is driving on the roadway 4 in the direction of travel, the vehicle body 5 is excited to longitudinal oscillations along the direction of travel by means of the linear oscillator 6. The longitudinal oscillations are detected by means of the acceleration sensor 7 and correlated with the angular accelerations determined from the speed sensor 8 of the transmission input shaft of the drive train 2. From this, the drive train sensitivity and a susceptibility to judder of a friction clutch arranged in the drive train 2 are determined.

(10) FIG. 2 shows a schematic illustration of the linear oscillator 6 of FIG. 1. The two interlocked eccentric discs 9, 10 are arranged such that they can be rotated about the axes of rotation d1, d2 and are rotationally driven, for example, by at least one DC motor. The eccentric discs 9, 10 have eccentric masses 11, 12 arranged eccentrically to the axes of rotation d1, d2, so that when the rotary drive is used, this results in a linear force in the direction of the arrow 13, which corresponds to the direction of travel of the motor vehicle 1 in FIG. 1. The two counter-rotating eccentric masses 11, 12 are used as force excitation, wherein the maximum force is set by different eccentric masses and a speed limitation.

(11) FIG. 3 shows the diagram 14 with the characteristic curves 15, 16, 17, 18, 19, 20, 21, which show the force of the excitation of the drive train via the frequency with different masses of the linear oscillator. The horizontal line 22 shows the desired excitation, and the horizontal line 23 shows the maximum desired excitation. The masses are between 0.073 kg of the characteristic curve 21 and 1.27 kg of the characteristic curve 15. An acceleration amplitude on the motor vehicle of 0.3 m/s2 is perceived by most drivers and is defined here as the minimum acceleration amplitude. Usual vehicle masses from 1500 kg to 3000 kg therefore require a force excitation from 500 N to 1000 N. The transfer function in the motor vehicle is preferably determined for a frequency range from 3 Hz to 30 Hz.

(12) A massive increase in force excitation can lead to falsifications of the transfer function due to non-linear stiffness. To enable a uniform, slow speed ramp and thus a quasi-static evaluation of the frequencies, two DC motors can be adapted as drives to the two axes of rotation d1, d2 (FIG. 2). A slow increase in speed or a slow decrease in speed is advantageous so that the natural frequencies can develop in sufficient time.

(13) FIG. 4 shows the diagram 24 with partial diagrams I and II. The partial diagram I shows the sensitivity of the drive train to the frequency of the linear oscillator for a given mass of 0.45 kg. The curve 25 shows a real measurement without an order sorting filter, the curve 26 shows a real measurement using an order sorting filter and the curve 27 shows a simulation result. It can be seen that unadjusted eigenmodes and interference components falsify the measurements and that order sorting filters are preferably used in the measurement of the angular accelerations of the transmission input shaft.

(14) The partial diagram II uses the curves 28, 29 to show the coherence of the curves 25, 26 over the frequency. The coherence is to be understood as a measure of the degree of linear dependency of the input to the output signal and is defined in the value range from zero to one. A coherence of one means that there is a complete linear dependency between input and output signals. Coherence is therefore a suitable measure for assessing whether the measured signals are suitable for identifying the system behavior of a linear time-invariant system with the aid of linear system theory. For practical use, a coherence of >0.75 is sufficient to be able to determine a reliable transfer function from the measured signals. The reasons for a coherence deviating from one are generally:

(15) non-linear system behavior,

(16) influence on the output signal by other signals that do not correlate with the input signal,

(17) uncorrelated noise of the input/output signal,

(18) leak effects due to insufficient frequency resolution.

(19) The curve 29 therefore shows the clearly improved coherence of a signal curve of the angular acceleration with application of order sorting filters compared to the signal behavior shown in the curve 28 without an order sorting filter.

(20) FIG. 5 shows the diagram 30 with partial diagrams I, II, III. The partial diagram I shows the sensitivity of a drive train when the first gear is engaged. The curve 31 is based on a mass of 1.2 kg, the curve 32 on a mass of 0.45 kg and the curve 33 on a mass of 0.3 kg. For comparison, the curve 34 shows a simulation of the drive train.

(21) The partial diagram II shows the sensitivities of the drive train with a second gear engaged with the curve 35 with a mass of 1.2 kg, with the curve 36 with a mass of 0.45 kg and the curve 37 with a simulation.

(22) The partial diagram III shows the drive train with a reverse gear engaged. The curve 38 shows the sensitivity with a mass of 1.2 kg, the curve 39 with a mass of 0.45 kg, the curve 40 with a mass of 0.3 kg and the curve 41 with a simulation.

(23) The respective deviations from the simulations of the measured sensitivities, for example at 15 Hz, are due to the excessive or non-constant force amplitudes.

(24) FIG. 6 shows the diagram 42 with the curves 43, 44, 45, 46, 47 of the coherence over the frequency with different masses. The curve 43 shows the coherence with a mass of 1.2 kg, the curve 44 with a mass of 0.45 kg, the curve 45 with a mass of 0.117 kg, the curve 46 with a mass of 0.095 kg and the curve 47 with a mass of 0.073 kg.

(25) FIG. 6 shows which force amplitudes a linear oscillator must provide to generate an evaluable reaction on the transmission input shaft. Table 1 shows assessment criteria for evaluability based on the coherence of the measured sensitivities. A reliable evaluation of a measured transfer function with a coherence of λ≥0.8 is assumed. Here, a motor vehicle with a mass of approximately 1500 kg is assumed. From a force amplitude of 210 N, the transfer function in the frequency range from 3 Hz to 30 Hz can be evaluated according to Table 1. Extrapolated to higher vehicle masses, this means that with a force amplitude of 400 N motor vehicles up to approx. 3000 kg would be sufficiently excitable by a linear oscillator.

(26) TABLE-US-00001 TABLE 1 Eccentric Frequency @ Frequency @ mass λ ≈ 0.8 Force @ λ ≈ 0.8 450 N 0.073 kg 16.3 Hz 138 N 30 Hz 0.095 kg 17.77 Hz 190 N 26 Hz 0.117 kg 14.11 Hz 166 N 23 Hz  0.45 kg 7.26 Hz 168 N 12 Hz  1.2 kg 4.97 Hz 210 N 7 Hz

(27) FIG. 7 shows the diagram 48 of the frequency over time with an optimized frequency sweep of a linear oscillator. To form a robust evaluation, the same number of measurement periods is excited for all frequencies, so that a longer time is provided at small frequencies than at higher frequencies, and a frequency curve shown in the curve 49 is produced.

(28) Furthermore, constant force excitation is proposed, which contributes to an improvement in the transfer function. The reason for this is that in the case of constant excitation, the non-linearities of stiffnesses and non-linearities of damping have less influence on the transfer function. All of the measurement improvements mentioned here are possible with a linear oscillator with constant force excitation and a freely configurable frequency response.

LIST OF REFERENCE SYMBOLS

(29) 1 Motor vehicle 2 Drive train 3 Wheel 4 Roadway 5 Vehicle body 6 Linear oscillator 7 Acceleration sensor 8 Speed sensor 9 Eccentric disc 10 Eccentric disc 11 Eccentric mass 12 Eccentric mass 13 Arrow 14 Diagram 15 Characteristic curve 16 Characteristic curve 17 Characteristic curve 18 Characteristic curve 19 Characteristic curve 20 Characteristic curve 21 Characteristic curve 22 Line 23 Line 24 Diagram 25 Curve 26 Curve 27 Curve 28 Curve 29 Curve 30 Diagram 31 Curve 32 Curve 33 Curve 34 Curve 35 Curve 36 Curve 37 Curve 38 Curve 39 Curve 40 Curve 41 Curve 42 Diagram 43 Curve 44 Curve 45 Curve 46 Curve 47 Curve 48 Diagram 49 Curve I Partial diagram II Partial diagram III Partial diagram d1 Axis of rotation d2 Axis of rotation