WO2015007368A1

WO2015007368A1 - Measuring device for measuring a friction co-efficient on a drive wheel

Info

Publication number: WO2015007368A1
Application number: PCT/EP2014/001802
Authority: WO
Inventors: Olena IVANOVA
Original assignee: Daimler Ag
Priority date: 2013-07-18
Filing date: 2014-07-01
Publication date: 2015-01-22
Also published as: EP2864165A1; DE102013011998A1

Abstract

The invention relates to a measuring device (1) for measuring the carriageway friction (μ ₁, μ ₂, μ ₃) on a vehicle wheel driven by an electric motor (2), said measuring device (1) comprising a sensing element (3, 4, 5) for sensing a measured value on the vehicle wheel of the electric motor vehicle and an evaluation circuit (6, 7, 8) for evaluating the measured value. To simplify the construction, the sensing element (3, 4, 5) detects an alternating voltage portion (9, 10, 11) of the total voltage (12) decreasing over the electric motor (2) and the evaluation circuit (6, 7, 8) derives the carriageway friction (μ ₁, μ ₂, μ ₃) from the alternating voltage portion (9, 10, 11) that has been detected.

Description

Measuring device for measuring a friction coefficient on a drive wheel

The invention relates to a measuring device for measuring a road friction of a vehicle wheel according to the preamble of claim 1. The invention further relates to a suitably equipped electric motor according to the preamble of claim 9.

In drive technology, a drive with at least one electric motor as

Electric drive designates. Generic electric drives are typically controlled by a regulation. If the engine power is large, conventional electronic power actuators are switched between the controller and the electric motor. These are considered here as part of the electric drive.

Often, the control of the electric drive in the form of a speed, torque, position, speed or more variable control is executed. For practical operation are the skilled person also separate components for the inputs and

Shut down the drive and necessary backup and

Monitoring devices, also known as an energy source in the form of a network connection, a generator in the form of a fuel cell or a rechargeable battery or double-layer capacitor, for example in the form of so-called ultra or supercaps.

Vehicles that have such an electric drive and are not tied to rails are known in the automotive industry as electric motor vehicles. The terms used for different types of electric vehicles in the art are extensive, but at the present time little systematic and ambiguous. In the present context, the term "electric motor vehicle" is therefore to be used in its comprehensive sense, which is called hybrid electric motor vehicles, which have an additional,

non-electric drive system - such as an internal combustion engine - without having direct mechanical connection to the drive train expressly includes. The problem in this context is to ensure the highest possible driving safety. Thus, in conventional electric vehicles, the contact between the vehicle and the roadway only by several approximately palm-sized areas, the

Radaufstandsflächen, mediated. The force generation in these contact surfaces is thus of particular interest for the driving dynamics.

To increase driving safety, DE 10 2009 022 592 A1 therefore proposes a method for determining the road friction coefficient during operation of a motor vehicle, which also appears to be fundamentally suitable for use in electric motor vehicles. In order to determine the road friction coefficient during the operation of a motor vehicle, the tire return torques of the wheels of an axle are measured or determined from measured variables in accordance with this approach. Furthermore, the lateral forces and / or the lateral acceleration are determined on these wheels. Tire return torques and

Side forces or lateral acceleration serve as input variables of a calculation model stored in the vehicle, which supplies the road friction coefficient as output variable.

A disadvantage of this approach, however, lies in the constructive complexity of the

Implementation of the proposed method required device. Their implementation requires a specially configured sensors for detecting the force acting on the tie rods of a suitably equipped motor vehicle forces, which then form the basis of a model-based calculation of the resulting

Forming tire return torques.

The invention therefore has the task of a structurally simplified

To provide a measuring device for measuring the road friction coefficient.

This task is performed by the feature combinations of independent

Claims solved.

A basic idea of the invention is therefore to be specific

Configuration of the frequently installed in generic electric motor vehicles

To take advantage of electric motors.

Such an electric motor may for example be a wheel near electric motor. Wheel near electric motors can be arranged on a chassis component or, although less frequently, on a body part. Preferably, wheels are close to electric motors a wishbone arranged, wherein the electric motor at one end fixed to the

Wishbone connected or movable can be arranged on this. At the free, wheel-side end of the electric motor, a shaft transmits the moment of the electric motor to a drive wheel.

Alternatively, the wheel near the electric motor can each have a shaft at both ends which transmit the torque of the electric motor to the opposite wheels of a vehicle axle.

Furthermore, such an electric motor can also be a wheel hub motor. This is directly integrated in a vehicle wheel of the electric motor vehicle and at the same time carries its associated wheel hub. A part of the electric motor can therefore transmit the torque generated by this, waiving a classic drive train directly to the revolving around it with the vehicle. Since the driving of the

Electric vehicle from the tire to the wheel rims transmitted vibrations thus not from gearbox, cardan shaft, differential gear, drive shaft or other

Components of a conventional drive train are attenuated, they act directly on the vehicle wheel adjacent to the electric motor and induce in this a high-frequency alternating current, which can manifest itself in a measurable alternating component of the voltage dropping between the poles of the electric motor.

According to the invention, precisely such an AC voltage component of the total voltage thus resulting at the electric motor by means of a suitable

Sensor tapped at the terminals of the engine and a

supplied electronic evaluation circuit. This circuit can now conclude from the amplitude of the AC voltage on the characteristic friction coefficient. In other words, the evaluation circuit determines at least the road friction based on at least that of the

Transducer detected AC voltage component, wherein the transducer detects the AC voltage component of the voltage applied to the electric motor total voltage.

The transducer can be based on a between a

Voltage input and a voltage output arranged high-pass filter circuit can be realized, due to their configuration of only

AC voltage components above a predetermined cutoff frequency happens can be. While relevant for determining the coefficient of friction

AC components thus rest almost unattenuated voltage output, lower voltage frequencies are significantly attenuated and ignored.

Such a high-pass filter circuit can be realized in a straightforward manner by means of an ohmic resistance and a capacitor of known electrical capacity connected in series with the coveted one

AC voltage component between the voltage output serving as bilateral terminals of the capacitor can be removed. The described combination of two elementary electrotechnical components creates an im

Substantially linear, time-invariant system, which allows the developer, in view of his simple transformation equations, to flexibly design the system behavior by means of familiar configuration parameters at comparatively low unit costs.

For example, the cut-off frequency of the high-pass filter circuit based on such an RC element can be structurally varied within a wide range by suitable dimensioning of the capacitor. From this point of view, it is advisable to choose a capacity that allows the filter to pass especially AC components in the frequency range above 25 Hertz, since voltage components of corresponding frequencies are to be fed to the evaluation as an indication of increased road friction of the vehicle wheel.

Even a plurality of different frequency ranges can be covered by means of a measuring device according to the invention if their measuring transducer comprises a plurality of parallel-connected high-pass filter circuits of the type described. To enter at a comparatively small number of parallel filters

To take into account the largest possible frequency spectrum, the capacities of the individual high passes should be chosen so that each has a different cutoff frequency.

For the evaluation of the output at the voltage output AC voltage component offers itself as an analog comparator, which is probably the simplest

Circuit alternative digitizing the sensor supplied by the sensor Analog signal allowed by detecting the exceeding of a predetermined reference voltage. By suitable concatenation of a plurality of such comparators can be even gradations of the voltage amplitude

play.

However, as an alternative to the use of a comparator may be considered the use of a Schottky diode, which allows a safe rectification of the AC voltage component even at high voltage frequencies. A correspondingly designed evaluation circuit thus enables the construction of a measuring device which can be integrated into fast TTL logic circuits by means of powerful MOSFETs.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

In each case show schematically:

Fig. 1 shows the simplified circuit diagram of a measuring device according to the invention and

Fig. 2 is a line diagram of the functional relationship between a

Voltage amplitude at the voltage output of the measuring device according to Figure 1 and the vibration of a wheel on different road surfaces.

Figure 1 illustrates the structure of a measuring device 1 according to an exemplary embodiment of the invention for measuring a road friction. According to DIN 1319 In the present context, as a measuring device, the entirety of all measuring devices and additional devices for detecting the frictional forces is used here

understood, which occur at the contact surface of the vehicle wheel of a (not shown) electric motor vehicle to the road surface during operation of the electric motor vehicle.

In order to set the described frictional force in relation to the contact force between the vehicle wheel and its base, serves in the following the

dimensionless friction coefficient, which outside the tribology also called

Denotes friction coefficient or coefficient of friction and is usually symbolized by the symbol μ.

The measuring device 1 of Figure 1 is connected according to the invention with an electric motor 2, in particular with a wheel hub or wheel near electric motor of the electric motor vehicle. Although realizable as an inner or outer rotor in a variety of conceivable configurations, such a motor 2 forms with him

associated vehicle wheel via interacting surfaces of both components a common oscillating system, so even a slight vibration of the

Vehicle wheel detectable electrical alternating currents within the electric motor 2 is able to induce. In the case of a substantially designed as a DC motor electric motor 2, this phenomenon manifests itself in the form of a superposition of falling between the electrical poles of the motor 2 DC voltage by periodic voltage fluctuations, which as a result to a skilled in the art

Total voltage 12 referred totals voltage leads.

A measured value sensor 3, 4, 5 connected to the electric motor 2 via a voltage input 13, 14 serves in the given embodiment to isolate three alternating voltage components 9, 10, 11 contained in the total voltage 12

different frequency ranges, which by means of an electronic

Evaluation circuit 6, 7, 8 let close to the currently present coefficient of friction μ. For this purpose, the transducer 3, 4, 5 comprises a parallel connection of three electrical filters, which the total voltage 12 depending on the voltage frequency f of the AC voltage components 9, 10, 11 in their

Change voltage amplitude. The filters used are so-called high-pass filter circuits 15, 16; 17, 18; 19, 20, also known as high passes or depth locks, let the AC components 9, 10, 11 of a frequency / above their respective cutoff frequency pass almost unattenuated and attenuate lower frequencies.

The high-pass filter circuits 15, 16; 17, 18; 19, 20 of the issue in question

Embodiment put as so-called high passages first order in each case of an ohmic resistance 15, 17, 19 and a respective resistor 15, 17, 19 connected in series electrical capacitance 16, 18, 20 in the form of a capacitor together. At low frequency f, the constructional reactance of the capacitor blocks the flow of current through the high-pass filter circuits 15, 16; 17, 18; 19, 20.

The cut-off frequencies of the high-pass filter circuits 15, 16; 17, 18; 19, 20 are selected by dimensioning the respective capacitances 16, 18, 20 such that the alternating voltage component 9 dropping at the first voltage output 21, 22 has a voltage frequency f between 20 and 25 hertz, the alternating voltage component 10 dropping at the second voltage output 23, 24 Voltage frequency f between 28 and 30 hertz and at the third voltage output 25, 26 falling

AC voltage component 11 has a voltage frequency / ^"between 35 and 40 Hertz. The voltage frequencies said f are chosen as an example and can practice due also differ by up to five Hertz. The voltage frequencies f are not limited to low voltage frequencies f. Likewise, the

Use of voltage frequencies f greater than 40 hertz be expedient.

The said AC voltage components 9, 10, 11 are on the

Voltage outputs 21, 22; 23, 24; 25, 26 of one of the high-pass filter circuits 15, 16; 17, 18; 19, 20 associated evaluation circuit 6, 7, 8 supplied, which is based here on a Schottky diode.

FIG. 2 illuminates a functional relationship between the voltage frequency f and the voltage amplitude Q of the alternating voltage component 9, 10, 11 on which the evaluation circuit 6, 7, 8 is based, with different coefficients of friction μ 1, μ ₂ , μ 3. The diagonal auxiliary lines of the diagram illustrate that the

Voltage amplitude Q increases approximately linearly with increasing voltage frequency f. The specific slope of the voltage amplitude ü with the

Voltage frequency f allows the evaluation circuit 6, 7, 8, the distinction between three different friction coefficients μ, μ ₂ , μ ₃ , where a higher

Amplitude gradient is considered an empirical indication of increased road friction.

Claims

claims

1. measuring device (1) for measuring a road friction (μ · ,, μ ₂ , j- ₃ ) one of

an electric motor (2) driven vehicle wheel, wherein the measuring device (1) has a transducer (3, 4, 5) for receiving a measured value on the vehicle wheel of the electric motor vehicle and

an evaluation circuit (6, 7, 8) for evaluating the measured value, characterized in that

the measuring transducer (3, 4, 5) detects an AC voltage component (9, 10, 11) of a total voltage (12) dropping across the electric motor (2); and the evaluation circuit (6, 7, 8) derives the road friction (μ ^ μ ₂ , μ ₃ ) from the detected AC voltage component (9, 10, 11).

2. Measuring device (1) according to claim 1,

characterized in that

the transducer (3, 4, 5)

a voltage input (13, 14) connected to the electric motor (2) for applying the total voltage (12),

a high-pass filter circuit (15, 16, 17, 18, 19, 20) for coupling the AC voltage component (9, 10, 11) from the total voltage (12) when the AC component (9, 10, 11) has a voltage frequency () above a predetermined cut-off frequency of the high-pass filter circuit (15, 16; 17, 18; 19, 20), as well as

a voltage output (21, 22, 23, 24, 25, 26) connected to the evaluation circuit (6, 7, 8) for outputting the AC voltage component (9, 10, 11). Measuring device (1) according to claim 2,

characterized in that

the high-pass filter circuit (15, 16, 17, 18, 19, 20) is a series connection of an ohmic resistor (15, 17, 19) with an electrical capacitance (16, 18, 20), so that the AC voltage component (9, 10, 11) at the resistor (15, 17, 19) drops when the total voltage (12) at the voltage input (13, 14) is applied.

Measuring device (1) according to claim 3,

characterized in that

the capacitance (16, 18, 20) is dimensioned such that the cut-off frequency is between 20 hertz and 25 hertz.

Measuring device (1) according to claim 4,

characterized in that

the transducer (3, 4, 5) a parallel connection of at least two

High-pass filter circuits (15, 16; 17, 18; 19, 20) whose capacitances (16, 18, 20) are dimensioned differently such that the high-pass filter circuits (15, 16; 17, 18; 19, 20) are different Have cutoff frequencies.

Measuring device (1) according to claim 5,

characterized in that

the parallel connection

a first high-pass filter circuit (15, 16) having a first capacitance (16),

- A second high-pass filter circuit (17, 18) with a second capacitor (18) and

- A third high-pass filter circuit (19, 20) with a third capacitor (20), wherein the capacitances (16, 18, 20) are dimensioned such that

the first high-pass filter circuit (15, 16) has a first cut-off frequency between 20 hertz and 25 hertz,

- The second high-pass filter circuit (17, 18) has a second cutoff frequency between 28 hertz and 30 hertz and

- The third high-pass filter circuit (19, 20) has a third cutoff frequency between 35 hertz and 40 hertz

having.

7. Measuring device (1) according to one of claims 1 to 6,

characterized in that

the evaluation circuit (6, 7, 8) comprises an analog comparator for comparing the AC voltage component with a reference voltage.

8. Measuring device according to one of claims 1 to 7,

characterized in that

the evaluation circuit (6, 7, 8) comprises a Schottky diode for rectifying the AC voltage component (9, 10, 11).

9. electric motor (2) for a vehicle wheel,

marked by

a measuring device (1) according to one of claims 1 to 8 for measuring a road friction μ ₂ , μ ₃ ) of the vehicle wheel.