Active suspension and procedures for operating an active suspension

Abstract

An active suspension system (10) for a motor vehicle is provided, wherein a pump (20) is provided for pressurizing an actuator cylinder (18) provided in a wheel suspension (12), wherein the pump (20) is electrically driven by pulse width modulation, wherein for the operation of the pump (20) in a first driving situation with low driving dynamics a first frequency (30) of the pulse width modulation and in a second driving situation with high driving dynamics a second frequency (32) of the pulse width modulation higher than the first frequency (30) can be switched. By adapting the frequency of the pulse width modulation to the dynamics of the driving situation, switching losses can be reduced in low-frequency driving situations, thus enabling energy-efficient operation of the active suspension system (10).

Description

[0001] The invention relates to an active chassis and a method for operating such a chassis, with the aid of which the pitching, rolling and / or lifting movements of a motor vehicle can be actively compensated.

[0002] From US 7 416 189 B1 it is known to electrically drive a pump for pressurising an actuating cylinder provided in a wheel suspension by means of pulse width modulation, wherein the duty cycle of the pulse width modulation is adapted to different situations and purposes.

[0003] From US 2017 / 0 320 368 A1 it is known to electrically drive a pump for pressurizing an actuating cylinder provided in a wheel suspension by means of pulse width modulation, whereby the pump is stopped below a defined limit speed of the motor vehicle.

[0004] From DE 10 2006 032 893 A1 it is known to modulate an electric motor for a chassis control system of a motor vehicle, which can be driven electrically by pulse width modulation, at different frequencies, which lead to different output voltages and power losses of the electric motor.

[0005] From DE 10 2015 214 839 A1 it is known to modulate a control frequency of an electrically commutated electric motor of a motor vehicle, wherein the control frequency and the modulation frequency can be changed in order to optimize the efficiency of the electric motor.

[0006] From US 2017 / 0 129 428 A1 it is known to operate an electric motor that can be driven electrically by pulse width modulation for operating a fan of an air conditioning system in a motor vehicle at two different frequencies in order to reduce switching losses at the lower frequency.

[0007] From DE 10 2006 040 660 A1 it is known to superimpose a pump of a brake system that is electrically driven by means of pulse width modulation with another low-frequency modulation frequency in order to optimize the load on the vehicle electrical system and avoid noise emissions.

[0008] There is a constant need to operate an active chassis as energy-efficiently as possible.

[0009] The object of the invention is to demonstrate measures that enable energy-efficient operation of an active chassis.

[0010] The object is achieved according to the invention by an active chassis having the features of claim 1 and a method having the features of claim 10. Preferred embodiments of the invention are specified in the subclaims and the following description, which can each individually or in combination represent an aspect of the invention, the scope of protection being determined by the claims.

[0011] One aspect of the invention relates to an active chassis for a motor vehicle, wherein a pump is provided for pressurizing an actuating cylinder provided in a wheel suspension, wherein the pump is electrically driven via pulse width modulation, wherein for the operation of the pump in a first driving situation with low driving dynamics, a first frequency of the pulse width modulation and in a second driving situation with high driving dynamics, a second frequency of the pulse width modulation higher than the first frequency can be switched.

[0012] This takes advantage of the knowledge that in the second driving situation, high-frequency vibrations occur in the wheel suspension due to the high driving dynamics, which require a correspondingly rapid response of the actuating cylinder with a higher or lower pressure provided by the pump. The high second frequency allows the resolution of the pulse width modulation to be increased to such an extent that a correspondingly high-frequency pressure curve can be set in the actuating cylinder. In the first driving situation, however, due to the low driving dynamics compared to the second driving situation, low-frequency vibrations occur in the wheel suspension for which a high resolution of the pulse width modulation is not necessary. Instead, it is sufficient to apply the lower first frequency of the pulse width modulation to the pump.This results in the pump being energized and de-energized for a longer period of pulse width modulation at the lower first frequency than at the higher second frequency. As a result, the pump switches between operation and de-operation less frequently within a given time interval at the lower first frequency, thus avoiding switching losses and improving efficiency. By adapting the frequency of the pulse width modulation to the dynamics of the driving situation, switching losses can be reduced in low-frequency driving situations, enabling energy-efficient operation of the active chassis.

[0013] In pulse width modulation, a duty cycle is varied at a constant frequency. The duty cycle is defined as the ratio of a pulse duration to the period duration. If a higher power is to be transmitted using pulse width modulation, the pulse duration is increased at the same frequency, which also increases the duty cycle and the equivalent of the pulse width modulation. If a lower power is to be transmitted using pulse width modulation, the pulse duration is reduced at the same frequency, which also reduces the duty cycle and the equivalent of the pulse width modulation. By alternating between the low first frequency and the high second frequency of the pulse width modulation, a change is made between a long period duration at the low first frequency and a short period duration at the high second frequency.By adjusting the pulse duration according to the ratio of the first frequency to the second frequency, the duty cycle or a specified duty cycle range can be maintained. Pulse width modulation, in particular, provides a signal that is as close as possible to a square wave.

[0014] The actuating cylinder can, in particular, provide variable damping and preferably form a damped mass-spring system with a spring element of the wheel suspension. The active chassis preferably has a separate wheel suspension for each wheel, each with an actuating cylinder and, in particular, a pump that can be operated according to the invention.

[0015] In particular, the pump can pump a hydraulic medium into the actuating cylinder and / or discharge it from the actuating cylinder to hydraulically provide the actuating force applied by the actuating cylinder. The pump can be electrically driven by an electric machine operating in motor mode, whereby the electrical power transmitted to the pump can be varied by pulse width modulation.

[0016] The active chassis can in particular provide level control and / or roll stabilization for the motor vehicle, in particular by influencing a spring and / or damping in the respective wheel suspension with the aid of the actuating cylinder.

[0017] In particular, the pulse width modulation, preferably when switching between the first frequency and the second frequency, has a substantially identical duty cycle range at the first frequency and the second frequency. At the time when switching between the first frequency and the second frequency is used for the switched PWM frequency for operating the pump, the identical duty cycle is used. After switching between the first and second frequencies, the duty cycle can be varied to change the PWM equivalence. This enables a motor driving the pump to be operated more energy-efficiently.

[0018] Preferably, an electric motor, adjustable within a limited control range, is electrically connected to the pump. The motor can be configured to adapt its output power to a required power within the limited control range, for example, by varying the duty cycle of the pulse width modulation accordingly. The motor can have a motor controller configured for this purpose. This allows the pump to induce pressures in the actuating cylinder, which can lead to improved driving stability.

[0019] Particularly preferably, it is provided that a control signal generated within the control range contains the first frequency of the pulse width modulation and the second frequency of the pulse width modulation. This makes it possible to represent a time-varying control signal with greater accuracy in a dynamic driving situation and with fewer switching losses in a less dynamic driving situation, in which less significant changes in the control signal are to be expected. A considered time range of the control signal can be composed of sub-sections of varying accuracy when switching between the first and second frequencies. The frequency of the pulse width modulation can in particular only be changed by circumstances external to the engine, in particular sensor data relating to the driving dynamics of the current driving situation.Switching between different pulse width modulation frequencies can, in turn, force the motor control system of the motor to adjust the duty cycle to the changed pulse width modulation frequency in order to be able to provide the required power as accurately as possible even at the new pulse width modulation frequency.

[0020] In particular, it is intended that the motor varies a pulse width modulation duty cycle to provide a required power, in particular exclusively. By varying the pulse width modulation duty cycle, the equivalent value of the pulse width modulation and thus the supplied electrical power can be adjusted, in particular if switching between different pulse width modulation frequencies has previously occurred. Varying the pulse width modulation frequency within the motor control system for the purpose of providing the required power is not intended. Within a closed-loop control of the motor control system, the pulse width modulation frequency is at most a disturbance variable, but not a manipulated or controlled variable.

[0021] Preferably, a sensor system is provided for detecting the presence of low driving dynamics and high driving dynamics, wherein low driving dynamics can be detected at a driving speed and / or acceleration in the X direction and / or acceleration in the Y direction and / or acceleration in the Z direction below a respectively assigned first threshold value and high driving dynamics can be detected above a respectively assigned second threshold value. With the aid of these measurable parameters for the sensor system, the presence of low driving dynamics and the presence of high driving dynamics can be detected reliably and robustly. The X direction is understood to be a coordinate direction along a longitudinal axis of a motor vehicle when the active chassis is installed in the motor vehicle. The X direction runs essentially horizontally when the motor vehicle is parked on a flat, horizontal surface.A Y-direction is understood to be a coordinate direction along a transverse axis of a motor vehicle when the active chassis is installed in the motor vehicle. The Y-direction is essentially horizontal when the motor vehicle is parked on a flat, horizontal surface. A Z-direction is understood to be a coordinate direction along a vertical axis of a motor vehicle when the active chassis is installed in the motor vehicle. The Z-direction is essentially vertical when the motor vehicle is parked on a flat, horizontal surface. The X-direction, the Y-direction, and the Z-direction are aligned orthogonally to one another.

[0022] Particularly preferably, the respective second threshold value is higher than the first threshold value by a respective offset. This offset ensures that there is no constant switching between the detection of low driving dynamics and high driving dynamics within an excessively small transition range, thus avoiding a constant change between the first frequency and the second frequency for pulse width modulation. Unnecessary control effort and the associated energy consumption can be avoided.

[0023] In particular, the first and second thresholds each have different values ​​depending on a manually adjustable driving mode. This allows the active suspension setup to be customized and adapted to different driving styles. For example, significantly lower thresholds can be set for a racing situation in motorsports or rallying, allowing rapid acceleration out of a corner after a slow corner without any problems in the suspension setup.

[0024] Preferably, the first threshold value and the second threshold value can be corrected depending on a sensor signal relevant to driving safety. For example, depending on the driving speed and / or the lateral acceleration and / or the longitudinal acceleration of the motor vehicle and / or a set driving mode and / or the road conditions, the associated sensor signal can adjust the threshold values ​​to deviate from the originally specified values. Potentially dangerous threshold values ​​in the current driving situation can be avoided and overwritten by safer values ​​for the duration of the detected situation. Driving safety can thus be improved.

[0025] Particularly preferably, a limited number of more than two driving situations with different pulse width modulation frequencies are provided. This makes it possible to define several driving situations with different driving dynamics, for each of which a specific frequency is defined for the pulse width modulation. In this case, for each subsequent driving situation characterized by a driving dynamics, the driving situation with the lower driving dynamics corresponds to the first driving situation described above, and the immediately following driving situation with the higher driving dynamics corresponds to the second driving situation. In particular, only a significantly limited number of different driving situations is provided, in which jumps are made in increments between the different pulse width modulation frequencies, such that a continuous and / or stepless change in the pulse width modulation frequencies is avoided.The control of the active chassis remains simple and energy-efficient.

[0026] A further aspect of the invention relates to a method for operating an active chassis, which can be designed and developed as described above, in which the first frequency for the pulse width modulation is activated upon detection of the first driving situation, and the second frequency for the pulse width modulation is activated upon detection of the second driving situation. By adapting the frequency of the pulse width modulation to the dynamics of the driving situation, switching losses can be reduced in low-frequency driving situations, thus enabling energy-efficient operation of the active chassis.

[0027] The invention will now be explained by way of example with reference to the accompanying drawings using preferred embodiments. The features presented below may represent an aspect of the invention, both individually and in combination, with the scope of protection being determined by the claims. They show: Fig. 1: a schematic diagram of an active chassis and Fig. 2: a schematic comparison of two different pulse width modulations for the active chassis from Fig. 1.

[0028] The Fig. The active chassis 10 indicated in Figure 1 can be used in a motor vehicle, for example, for level control. The active chassis 10 has at least one wheel suspension 12 with a wheel 14, which is suspended displaceably in the Z direction via a spring 16 and an actuating cylinder 18 acting as a damper. The damping effect of the actuating cylinder 18 can be varied with the aid of a pump 20, which can pump a hydraulic fluid originating from a reservoir 22 into and out of the actuating cylinder 18. The pump 20 is driven by a motor 24 via pulse width modulation. Preferably, the motor 24 has a motor controller 26, with the aid of which a duty cycle and / or an amplitude of the pulse width modulation can be varied in order to adapt the damping hardness of the actuating cylinder to current driving situations, for example, to compensate for shocks and jolts from bumps in the road or to achieve the most level alignment of the motor vehicle when cornering.In addition, with the aid of a sensor system 28, it can be detected whether a first driving situation with low driving dynamics or a second driving situation with high driving dynamics exists and, depending on the detected driving situation, switch between different predetermined frequencies of the pulse width modulation.

[0029] As in Fig.2, in the first driving situation with low driving dynamics, a first frequency 30 can be provided for the pulse width modulation which is lower than a second frequency 32 for the pulse width modulation which is activated in the second driving situation with high driving dynamics. In the illustrated embodiment, the ratio of the second frequency 32 to the first frequency 30 is approximately 1.5, although other ratios, for example 2.0 or 2.5 or 3.0, are also possible. At the first frequency 30, a first pulse width modulation 34 results, while at the second frequency 32, a second pulse width modulation 36 results, which basically have almost identical duty cycles for the same requirements for the damper hardness of the actuating cylinder 18.Since in the first driving situation a lower resolution is sufficient for the operation of the pump 20 due to the low driving dynamics, switching losses can be reduced by the lower first frequency.

Claims

[1] Active chassis (10) for a motor vehicle, wherein a pump (20) is provided for pressurising an actuating cylinder (18) provided in a wheel suspension (12), wherein the pump (20) is electrically driven via pulse width modulation, characterized by , that for the operation of the pump (20) in a first driving situation with low driving dynamics, a first frequency (30) of the pulse width modulation and, in a second driving situation with high driving dynamics, a second frequency (32) of the pulse width modulation which is higher than the first frequency (30) can be switched over. [2] Active chassis (10) according to claim 1, wherein the pulse width modulation has substantially the same duty cycle range at the first frequency (30) and at the second frequency (32). [3] Active chassis (10) according to claim 1 or 2, wherein an electric motor (24) which can be controlled within a limited control range is electrically connected to the pump (20). [4] Active chassis (10) according to claim 3, wherein a control signal generated within the control range contains the first frequency (30) of the pulse width modulation and the second frequency (32) of the pulse width modulation. [5] Active chassis (10) according to claim 3 or 4, wherein the motor (24) varies a duty cycle of the pulse width modulation to provide a required power, in particular exclusively. [6] Active chassis (10) according to one of claims 1 to 5, wherein a sensor system (28) is provided for detecting the presence of low driving dynamics and high driving dynamics, wherein low driving dynamics can be detected at a driving speed and / or an acceleration in the X direction and / or an acceleration in the Y direction and / or an acceleration in the Z direction below a respectively assigned first threshold value and high driving dynamics can be detected above a respectively assigned second threshold value. [7] Active chassis (10) according to claim 6, wherein the respective second threshold value is higher than the first threshold value by a respective offset. [8] Active chassis (10) according to claim 6 or 7, wherein the first threshold value and the second threshold value each have different values ​​depending on a manually adjustable driving mode. [9] Active chassis (10) according to one of claims 6 to 8, wherein a limited number of more than two driving situations with different frequencies of the pulse width modulation are provided. [10] Method for operating an active chassis (10) according to one of claims 1 to 9, wherein upon detection of the first driving situation, the first frequency (30) for the pulse width modulation is switched on and upon detection of the second driving situation, the second frequency (32) for the pulse width modulation is switched on.

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