DE102014210776A1 - Method for determining a diagnostic parameter for a vehicle diagnosis of a motor vehicle - Google Patents

Abstract

The invention relates to a method for determining a diagnostic parameter for a vehicle diagnosis of a motor vehicle (2), comprising the steps of: determining a nominal drive power (Psoll) of a drive (4) of the motor vehicle (2), determining an actual drive power of a drive ( 4) of the motor vehicle (2) influencing state variables, determining the actual drive power (Pist) of the drive (4) of the motor vehicle (2) from the state variables, comparing the actual drive power (Pist) with the desired drive power (Psoll), providing a result (E) of the comparison of the actual drive power (Pist) with the desired drive power (Psoll), and evaluation of the result (E) for determining the diagnostic parameter.

Description

The present invention relates to a method for determining a diagnostic parameter for a vehicle diagnosis of a motor vehicle and a computing unit for its implementation.

State of the art

A shift in the power level of a motor vehicle, i. a deviation between desired power and actual power can be compensated by a driver of the motor vehicle. For the drivability of the motor vehicle, therefore, a detection of the actual engine power of the motor vehicle is not required. Therefore, the actual engine performance in the vehicle diagnosis is also not taken into account, which limits the validity of the vehicle diagnosis.

There is therefore a need to increase the validity of the vehicle diagnosis.

Disclosure of the invention

According to the invention, a method for determining a diagnostic parameter for a vehicle diagnosis of a motor vehicle having the features of patent claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

In the context of the invention operating data are determined and evaluated, which allow conclusions about the absolute performance of the motor vehicle. This allows determining an actual drive power of the drive of the motor vehicle and comparing the determined actual drive power with a desired drive power of the drive of the motor vehicle in the presence of a specific driving situation. This makes it possible, based on a diagnostic parameter, e.g. To detect a performance deviation, such as a loss of power, the motor vehicle by evaluating the result and also identify the cause of this by evaluating the specific driving situation. This improves the vehicle diagnosis. It should be noted that each of the provisions mentioned here can be carried out in particular mathematically and / or metrologically.

According to one embodiment, a driving resistance and a vehicle speed of the motor vehicle are determined for determining the actual drive power. This allows a particularly simple determination of the actual drive power from the already detected vehicle speed and the driving resistance of the motor vehicle. For example, the actual drive power can be calculated as the product of driving resistance and vehicle speed.

According to one embodiment, the driving resistance is in turn determined from an air resistance, a rolling resistance, a gradient resistance and / or an acceleration resistance.

Preferably, the air resistance is determined from a vehicle speed, a wind speed, a wind direction, an air pressure, an outside temperature, a body shape of the motor vehicle and / or a distance from a preceding vehicle.

Preferably, the rolling resistance is determined from a vehicle weight and a rolling resistance coefficient of vehicle tires of the motor vehicle.

Preferably, the grade resistance is determined from the vehicle weight and a vehicle pitch angle.

Preferably, the acceleration resistance is determined from the vehicle weight and a moment of inertia of rotating parts.

Preferably, the vehicle weight is determined taking into account a trailer load.

Overall, therefore, one or more of the following state variables are determined to determine the driving resistance: air resistance, rolling resistance, gradient resistance, acceleration resistance, vehicle speed, wind speed, wind direction, air pressure, outside temperature, body shape of the motor vehicle, distance from a preceding vehicle, vehicle weight, rolling resistance coefficients of vehicle tires of the motor vehicle , Vehicle tilt angle, moment of inertia of rotating parts, trailer load. The evaluation of individual or all of these state variables allows a very accurate determination of the driving resistance in different operating states of the motor vehicle. A mathematical vehicle model of the motor vehicle is used, to which one or more of the above-mentioned state variables are supplied as input variables in order to determine the current driving resistance of the vehicle in a specific driving situation.

If not all state variables are known, the unknown state variables themselves can be determined as diagnostic parameters if setpoint and actual drive lines are equated. Several unknown state variables can be particularly suitably determined by comparing the actual state Determine drive power with the target drive power at different operating points with different influence of the unknown state variable on the actual drive power. The desired drive power can be calculated in particular from the operating data of the engine control, such as injection quantity, injection time, ignition point, air mass, etc. This is familiar to the expert. A deviation between actual drive line and desired drive power now either means that a state variable used for the calculation of the actual drive power has a wrong value and itself must be determined more accurately as a diagnostic parameter, or that actually a deviation between the desired drive power and actual drive Drive power is determined as a diagnostic parameter. Which of the two options is available can be decided on the basis of the plausibility and expected value considerations explained below.

According to a further embodiment, a vehicle weight of the motor vehicle is determined as a parameter of state as a diagnostic parameter. Thus, exceeding the maximum permissible weight of the motor vehicle can be detected and stored. This information can be used as part of a vehicle diagnosis to ward off claims against the vehicle manufacturer, which are based on damage to the motor vehicle due to exceeding the maximum permissible weight of the motor vehicle. Furthermore, it is possible to monitor whether the motor vehicle is properly used when it is rented or lent.

According to a further embodiment, a plurality of actual drive powers are determined and stored over time, and the desired drive power is determined from the stored actual drive powers. In particular, expected values can be calculated from the stored values according to suitable provisos, from which it is possible to determine a current setpoint drive power. The appropriate specifications include, in particular, suitable mediations, e.g. to calculate situation, operating point and / or location dependent averages.

According to a further embodiment, it is determined as a diagnosis parameter whether an increased power requirement of the motor vehicle exists, in particular by comparing the current actual drive power with a desired drive power determined from stored actual drive powers. The presence of an increased power requirement can be stored as an error entry in a fault memory and / or the driver of the motor vehicle visually and / or visually communicated. Alternatively or additionally, this may be communicated to a workshop or service center, e.g. wireless. By means of a specific evaluation, it can be determined whether the cause for the increased power requirement of the drive of the motor vehicle is an increased rolling resistance due to a too low tire pressure or an increased resistance of ancillary components of the motor vehicle, such as e.g. an air conditioner with a clogged filter, is. The assignment is made in particular via known dependencies of the influences. For example, e.g. The influence of the air or rolling resistance when the vehicle is not available, where the ancillaries are dominant. In the air conditioner, for example, the judgment by power comparison is possible before and after turning on or off. The most important influencing factors for the actual drive power are speed, acceleration, inclination, speed, condition of the auxiliary units (activated / not activated / if necessary also direct power requirement, as with the alternator).

According to a further embodiment, it is determined as a diagnostic parameter whether there is a drive power of the motor vehicle, i. whether the actual drive power is smaller than the target drive line. For this purpose, operating data of the engine control of the motor vehicle can be evaluated, so that deviations in certain operating states of the drive can be detected. This facilitates the vehicle diagnosis for malfunctioning, such as malfunctioning. a reduced compression of an internal combustion engine of the drive.

According to a further embodiment, it is determined as a diagnosis parameter whether there is a drive power of the motor vehicle, i. whether the actual drive power is greater than the desired drive line. Thus, in addition to power losses, power surpluses can also be detected, e.g. based on inadmissible measures to increase the performance of the drive of the motor vehicle (tuning).

An arithmetic unit according to the invention, e.g. a control device of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying 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 indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

1 shows a schematic representation of a motor vehicle with a power determination unit.

2 shows a schematic representation of the structure of the power determination unit in 1 ,

Embodiment (s) of the invention

The 1 shows a schematic representation of a motor vehicle 2 , In the present embodiment, the motor vehicle 2 trained as a passenger car. Notwithstanding the present embodiment, the motor vehicle 2 be designed as a commercial vehicle.

The car 2 has a drive 4 and one to the drive 4 assigned motor control 6 on. The drive 4 has in the present embodiment, an internal combustion engine. Notwithstanding the present embodiment, the drive 4 also be a combination of an internal combustion engine and an electric motor or only an electric motor.

The car 2 also has a speedometer in the present embodiment 8th for measuring a vehicle speed V, a navigation device 10 for providing route data, a temperature sensor 12 for measuring an outside temperature T, a pressure sensor 14 for measuring an ambient air pressure P, a communication interface 16 for reading in weather data D, a trailer hitch 18 with a trailer sensor 20 for detecting a coupled trailer load, a power determination unit 22 and a distance radar 24 for measuring a distance Ab to a preceding vehicle (not shown).

The 2 shows that the power determination unit 22 Data transmission via data lines with the motor control 6 the speedometer 8th , the navigation device 10 , the temperature sensor 12 , the pressure sensor 14 , the communication interface 16 , the trailer sensor 20 , and the distance radar 24 connected is. In this case, the data lines can form a bus system, such as a CAN bus, to reduce the wiring effort.

In operation is by the engine control 6 a target drive power Psoll of the drive 4 to the power determination unit 22 transfer. With the speedometer 8th the vehicle speed V is detected with the navigation device 10 is based on stored route profiles a vehicle inclination angle N in the direction of travel of the motor vehicle 2 determined, with the temperature sensor 12 the outside temperature T is measured with the pressure sensor 14 the air pressure P is measured, with the communication interface 16 For example, the weather data D, such as wind force and direction data, are read in by the trailer sensor 20 If a trailer load is coupled, a signal A is generated, and with the distance radar 24 the distance Ab to a preceding vehicle is measured.

The power determination unit 22 is in the present embodiment as part of a control device (not shown) of the motor vehicle 2 educated. The power determination unit 22 has an input interface 26 , an evaluation unit 28 , a comparison unit 30 and an output interface 32 on. The power determination unit 22 , the input interface 26 , the evaluation unit 28 , the comparison unit 30 and the output interface 32 may include hardware and / or software components.

The input interface 26 is designed to the target drive power Psoll of the drive 4 to read the vehicle speed V, the vehicle tilt angle N, the outside temperature T, the air pressure P, the weather data D, a trailer towed load signal A and the distance Ab, and the vehicle speed V, the vehicle tilt angle N, the outside temperature T, the air pressure P, the weather data D, the signal A and the distance Ab to the evaluation unit 32 forward while the target drive power Psoll of the drive 4 in the present embodiment, directly to the comparison unit 30 is forwarded.

The evaluation unit 28 is adapted to the vehicle speed V, the vehicle inclination angle N, the outside temperature T, the air pressure P, the data D, the signal A, the vehicle weight M and the distance Ab is an actual drive power Pist of the drive 4 to be calculated.

It is assumed that the engine power, ie the actual drive power Pist of the drive 4 , by the product of driving resistance W (= force) of the motor vehicle 2 and given its vehicle speed V is: Pist = W · V (performance model)

The driving resistance W denotes the sum of the resistances that the motor vehicle 2 with the help of a driving force to drive at a constant speed on a horizontal plane.

The driving resistance W is in the present embodiment by means of a mathematical vehicle model of the motor vehicle 2 determined by the following formulas:
The running resistance W is composed of the air resistance CW, the rolling resistance RW, the pitch resistance SW and the acceleration resistance BW: W = CW + RW + SW + BW

The air resistance CW depends on the vehicle speed V, the wind speed Vwind and wind direction WR, the air pressure P, the outside temperature T and the body shape K (c _W value) of the motor vehicle 2 from: CW = f (V, Vwind, WR, P, T, K)

The dependence of the air resistance CW on the variables mentioned can, for example, be determined empirically and stored in a characteristic field or calculated from a model with specified parameters.

The rolling resistance RW depends on the vehicle weight M and the rolling resistance coefficient RK of the vehicle tires of the motor vehicle 2 from: RW = f (M, RK)

The dependence of the rolling resistance RW on the variables mentioned can be determined empirically, for example, and stored in a characteristic map or calculated from a model.

The grade resistance SW (downhill force) depends on the vehicle weight M and the vehicle pitch angle N: SW = f (M, N)

The functional relationship between grade resistance SW and vehicle pitch angle N follows a sine.

The acceleration resistance BW depends on the vehicle weight M and the moment of inertia of the rotating parts. Here, the variable relationship between rotational speeds and vehicle speed V by taking into account the selected gear G can be included. BW = (M, V, G)

The dependence of the acceleration resistance BW on the variables mentioned can, for example, be determined empirically and stored in a characteristic field.

Some of these state variables, such as the outside temperature T or the air pressure P, are measured, and other state variables are roughly known, such as the rolling resistance coefficients RK of the vehicle tires of the motor vehicle 2 ,

Further state variables are adapted. Thus, e.g. the influence of the body shape K on the air resistance CW at high vehicle speeds V and the influence of the vehicle weight M on the vehicle speed V at large vehicle tilt angles N particularly large.

Are the specific actual drive powers Pist of the drive 4 Conclusions can also be drawn from the comparison of current values with earlier values. In particular, mean values can be formed from the stored values depending on the situation, operating point and / or location. When the motor vehicle is in a driving situation 2 Eg is located on a section of track with a large slope, for the maintenance of a constant vehicle speed V, a specific location-dependent actual drive power Pist_0 is necessary. However, if in this specific driving situation the vehicle weight M is above an allowable upper limit due to vehicle loads, maintaining the constant vehicle speed V requires a particularly high actual drive power Pist_1. If, apart from the vehicle weight M, all other values and / or state variables in the specific driving situation are the same, then the difference between the location-dependent actual drive power Pist_0 and the current actual drive power Pist_1 is due to the vehicle weight M increased by the vehicle loadings. Thus, from a comparison of the location-dependent actual drive power Pist_0 with the current actual drive power drive power Pist_1 in such a concrete driving situation, the vehicle weight M of the motor vehicle 2 be determined.

With the trailer sensor 20 can be detected coupled trailer load and thus the increase of the vehicle weight M by the trailer load are taken into account.

The accuracy with which the actual drive power Pist is determined can be increased if the power requirements of ancillary components, such as an electric generator, an air conditioner or from the operating point of the drive 4 independently adjustable pumps, with is taken into account. For this purpose, for example, a control unit (not shown) of the motor vehicle 2 record whether auxiliary units are in operation and what current power requirements they have due to their current operating status.

Furthermore, for example, in the determination of the air resistance CW with the distance radar 24 detected distance Ab detected to a preceding vehicle and thus a slipstream effect are taken into account. For this purpose, it is possible, for example, to resort to a stored table in which wind shadow effect values for different detected distances Ab are stored, with which the wind shadow effect is taken into account in the determination of the air resistance CW. In addition, the wind speed Vwind and wind direction WR from the weather data D can be taken into account.

The navigation device 10 determined on the basis of stored route profiles the vehicle inclination angle N. Furthermore, the motor vehicle 2 alternatively and / or additionally have inclination angle sensors (not shown) for detecting the vehicle inclination angle N. The inclination may also be determined from the change in altitude, whether obtained by barometric measurement or by data from a satellite navigation system.

It is thus by evaluating the movements of the motor vehicle 2 the applied power, the actual drive power Pist, determined, which then with the target drive power Psoll, supplied by the engine control 6 , is compared. For preparation, these data are averaged and stored. The averaging takes into account how different parameters change. For example, parameters that change the characteristics of the drive change 4 describe, only slowly, so with a large time constant, but at a vehicle hold, the vehicle weight M of the motor vehicle 2 change abruptly. In this case, it can be observed whether the previously assumed value is still correct or whether the value has to be adapted anew. With the averaging the stochastic noise can be filtered out. Both arithmetic and exponential moving averages can be used and the learning speed of the filters can be adjusted.

The comparison unit 30 compares the actual drive power Pist with the target drive power Psoll and delivers as output a result E.

To determine the result E, in a first step, via the input interface 26 the target drive power Psoll of the drive 4 , the vehicle speed V, the vehicle pitch angle N, the outside temperature T, the air pressure P, the weather data D, the trailer connected load signal A, and the distance Ab.

In a further step is then by the evaluation 28 determines the running resistance W, which is composed of the air resistance CW, the rolling resistance RW, the pitch resistance SW and the acceleration resistance BW.

In a further step is also the evaluation unit 28 then using the vehicle speed V then determines the actual drive power Pist.

In a further step is by the comparison unit 30 the actual drive power Pist is compared with the target drive power Psoll, and the result E of this comparison is output.

By evaluating the result E in a further step, a diagnostic parameter of the motor vehicle 2 be determined.

The performance model includes vehicle and environmental variables (general state variables), such as vehicle weight M, wind speed, body shape (c _W value), rolling resistance coefficients or a resistance of the air conditioning system, with different contexts. In principle, all of the n sizes mentioned can be calculated by measuring n linearly independent combinations (eg, air conditioning on / off (or two speeds), high, medium, and low vehicle speeds, acceleration / no acceleration).

If, for example, the determined actual drive power at high speed is greater than the desired drive power determined from stored actual drive powers, it is possible, for example, to conclude that the cause is an improved c _W value or an engine over-output. An improvement of the c _W value can, however, be excluded in principle for vehicles. Although a c _W value can be increased compared to the standard state, for example, by roof rack, etc., but not reduced.

If, for example, the determined actual drive power on gradients is greater than the desired drive power determined from stored actual drive powers, a reduced vehicle weight or an engine output can be taken as the cause. However, a reduced vehicle weight can basically be excluded for vehicles. The vehicle weight may indeed be increased compared to the curb weight, but not reduced.

Thus, certain causes can already be excluded from plausibility considerations. In the above case, when occurring simultaneously at high speed and uphill gradients, engine overrun is the only possible cause for both cases.

The engine power, in turn, will change very little over a long time whereas, e.g. the weight between two trips is considered variable. For evaluation, therefore, the combinations of the measurements at different states are weighted, and from this both the out-of-state state variables (for example vehicle weight, cw value) and the more / reduced engine power are determined.

The already described above determination of the vehicle weight M of the motor vehicle 2 allows exceeding the maximum permissible weight of the motor vehicle 2 capture. This information may be used in the context of a vehicle diagnosis to make claims against the vehicle manufacturer based on damage to the motor vehicle 2 due to exceeding the maximum authorized weight of the motor vehicle 2 are based, ward off. Furthermore, it is possible to monitor whether the motor vehicle 2 was properly used in the case of a rental or a rental.

Furthermore, it can be determined by comparison of the actual drive power with the determined from stored actual drive performance target drive line, whether an increased power requirement of the motor vehicle 2 is present. The result E can be the driver of the motor vehicle 2 visually and / or visually communicated or the result E is transmitted to a workshop or service point, eg wirelessly using the output interface 32 the power determination unit 22 and the communication sections 18 of the motor vehicle 2 , Cause of the increased power requirement of the drive 4 For example, an increased rolling resistance due to insufficient tire pressure or increased resistance of ancillary components of the motor vehicle 2 , such as an air conditioner with a clogged filter, be. The cause can, for example, be determined by checking the power difference between the actual drive power and the desired drive line determined from stored actual drive powers for known dependencies of state variables. If, for example, the power difference has a speed-independent quadratic relationship with the speed, this can be used to deduce an increased c _W value. The performance of the air conditioning system may be determined as the difference in total power between the on and off state when the other power demand during the determination is constant and / or low. The differentiation takes place, for example, in that the power requirement before switching on is compared with the power requirement directly after switching on, or when switching off directly at the shutdown command, when the air conditioner is still running, with the state a few seconds later, when the air conditioning compressor is disconnected.

Furthermore, it can be determined by evaluating the diagnostic parameter, whether a drive power of the drive 4 is present when the actual drive power Pist is greater than the target drive power Psoll. This may, for example, indicate impermissible changes or malfunctions, eg of the fuel metering system, and is expediently stored in a fault memory. This information can be used as part of a vehicle diagnosis.

Finally, it can be determined by evaluating the diagnosis parameter, whether a drive power of the drive 4 is present when the actual drive power Pist is greater than the target drive power Psoll. For this purpose, additional data of the engine control 6 be evaluated so that deviations in certain operating conditions can be detected. This facilitates the vehicle diagnosis in terms of malfunction, such as a reduced compression of an internal combustion engine of the drive 4 ,

Claims (15)

Method for determining a diagnosis parameter for a vehicle diagnosis of a motor vehicle ( 2 ), comprising the steps of: determining a desired drive power (Psoll) of a drive ( 4 ) of the motor vehicle ( 2 ), Determining an actual drive power of a drive ( 4 ) of the motor vehicle ( 2 ) influencing state variables, determining the actual drive power (Pist) of the drive ( 4 ) of the motor vehicle ( 2 ) from the state quantities, comparing the actual drive power (Pist) with the target drive power (Psoll), providing a result (E) of the comparison of the actual drive power (Pist) with the target drive power (Psoll), and evaluating the result (E) for determining the diagnostic parameter. Method according to Claim 1, in which the actual drive power (Pist) comprises a driving resistance (W) and a vehicle speed (V) of the motor vehicle ( 2 ) than the actual drive power (Pist) of the drive ( 4 ) of the motor vehicle ( 2 ) influencing state variables is determined. Method according to Claim 2, in which one or more of the following determine the actual drive power of the drive (W) for determining the driving resistance (W). 4 ) of the motor vehicle ( 2 Air resistance, rolling resistance, gradient resistance, acceleration resistance, vehicle speed (V), wind speed (VWind), wind direction, air pressure (P), outside temperature (T), body shape (K) of the motor vehicle, vehicle weight (M), rolling resistance coefficient of Vehicle tire of the vehicle, vehicle inclination angle (N), moment of inertia of rotating parts, trailer load (A), distance (Ab) from a preceding vehicle. Method according to one of the preceding claims, wherein as a diagnostic parameter one of the actual drive power of the drive ( 4 ) of the motor vehicle ( 2 ) influencing state variables is determined. The method of claim 4, wherein the one of the actual drive power of the drive ( 4 ) of the motor vehicle ( 2 ) influencing state variables by comparing the actual drive power (Pist) with the target drive power (Psoll) at different operating points with different influence of the state variable on the actual drive power (Pist) is determined. Method according to one of the preceding claims, in which a drive power of the motor vehicle ( 2 ) is determined. Method according to one of the preceding claims, in which a drive power of the motor vehicle ( 2 ) is determined. Method according to one of the preceding claims, wherein as diagnostic parameter an increased power requirement of the motor vehicle ( 2 ) is determined. Method according to one of the preceding claims, in which as diagnostic parameter one of the actual drive power of the drive ( 4 ) of the motor vehicle ( 2 ) influencing state variables is determined. Method according to one of the preceding claims, in which a vehicle weight (M) of the motor vehicle ( 2 ) is determined. Method according to one of the preceding claims, in which a plurality of actual drive powers (Pist) are determined and stored with time and the target drive power (Psoll) is determined from the stored actual drive powers (Pist). Method according to one of the preceding claims, wherein the desired drive power (Psoll) from operating data of the engine control of the motor vehicle ( 2 ) is determined. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims. A computer program that causes a computing unit to perform a method according to any one of claims 1 to 12 when executed on the computing unit. A machine-readable storage medium having a computer program stored thereon according to claim 14.

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