DE102010032436A1 - Drive system for motor vehicle, has controlling device that is coupled with road gradient sensor for determining slope value that represents road gradient - Google Patents

Abstract

The drive system has a controlling device (25) that is coupled with a road gradient sensor (27) for determining slope value that represents road gradient. The controlling device is formed in such a manner that a back roll safety device moment is controlled in dependence of the determined slope value. An electric machine (17) is controlled for producing the computed back roll safety device moment. An independent claim is also included for a method for supporting uphill driving by a motor vehicle.

Description

The The present invention relates to a drive system for a motor vehicle with hill start assistance, an electric machine for driving the motor vehicle and a Control device for driving the electric machine comprises.

electrical Driven cars are gaining in severity due to stricter ones Emissions legislation and limited supplies of fossil fuels increasing importance. There are both vehicles with purely electric Drive as well as so-called hybrid vehicles, which both an electric machine as well as an internal combustion engine. The electric machine can work in different ways with a powertrain of the associated Motor vehicle coupled or be coupled. In principle, too an arrangement of a plurality of electric machines for driving the motor vehicle be provided.

to increase of ride comfort are conventional, powered by an internal combustion engine motor vehicles devices and methods have been developed by means of which rolling back of the motor vehicle when holding at a roadway slope avoided can be. Such hill-start assistance systems will become available also as "Hill Holder" or "Hill Assist" systems designated. Known devices of this type are based, for example in motor vehicles with manual transmission on a brake intervention, d. H. upon detection of a vehicle standstill on a slope is the service or parking brake by means of a control device automatically operated, and that until the driver operates the accelerator pedal. Thereby will roll back effectively prevented, but the driver needs to start that at least nevertheless estimate the necessary engine torque independently and the accelerator pedal accordingly actuate. Furthermore, it is generally not possible with the mentioned concepts Gradients to provide a creep function, d. H. one Slow self-propelled forward movement of the vehicle without pressing the Accelerator pedal. Such creeping forward on gradients is namely when the rollback protection is activated through the automatically operated Brake prevented. As a creep in the plane spent Creep usually not enough to keep the vehicle on a slope that would Vehicle even when solved Brakes do not creep despite activated creep, but roll back. Alternatively it is possible a creep function by means of the slip in a torque converter to represent in the drive train. However, this solution is only without Significant extra effort possible if anyway such a torque converter is provided, so typically in motor vehicles with internal combustion engine and automatic transmission.

It is an object of the invention, in a motor vehicle with partial or completely electric drive in an efficient and cost-effective way to provide hill start assistance and in particular to allow a creep function on slopes.

According to the invention Control device with a road gradient sensor for determining a representing the road gradient Pitch value coupled, wherein the control device is designed to is, in dependence calculate a rollback torque from the determined slope value and the electric machine for generating at least the calculated Hill holding Moments head for. This ensures that the driving electric machine introduces a torque into the drive train that is at least sufficient at the acting due to the road gradient on the motor vehicle Downgrade force to compensate. The vehicle does not roll therefore back, but in a sense it becomes held by the electric machine. Starting on slopes will thereby effectively supported. An intervention in the brake system, which with the above Disadvantages is therefore not necessary. Furthermore is a system according to the invention to hill start assistance easy and inexpensive to realize.

further developments of the invention are in the dependent claims, the description and the accompanying drawings.

The Control device may be configured to the Rückrollsicherungsmoment according to a non-linear Context in dependence from the determined slope value. Through a non-linear context between grade value and rollback torque Driving behavior on slopes can be particularly accurate be adjusted. Furthermore, this can cause an impairment the stopping and driving behavior are avoided, which otherwise for example due to measurement inaccuracies.

Especially the control device can be designed to function as a function of from the determined slope value or one with the slope value related auxiliary quantity is a non-linear scaling factor to calculate and the determined slope value or the auxiliary size with the Multiply the scale factor to calculate the rollback torque. By such a scaling factor, the slope value be converted in a simple and fast way.

The mentioned auxiliary size may be in particular, be a base moment which is calculated directly or indirectly by multiplying the vehicle weight by the sine of the pitch angle and the radius of the wheel. This base torque is multiplied by the scaling factor and optionally by other scaling and / or correction factors, which are eg. B. can depend on the vehicle speed or the operation of the brake pedal to obtain the Rückrollsicherungsmoment. By modifying the base moment calculated from the physical conditions by means of scaling and / or correction factors, the mode of operation of the hill-assist system and thus the driving behavior of the vehicle on slopes can be adapted in detail.

Of the For example, this scaling factor can be used as a look-up table (so-called look-up table) be deposited in the controller.

According to one embodiment the controller is adapted to the scaling factor to set the value to about 0 (zero) if the slope value or the auxiliary size less is as a first threshold, and / or the controller is designed to set the scaling factor to about 1 (one) to set if the grade value or the auxiliary size is larger as a second threshold. By setting the scaling factor to the value 0 if the slope value is a predetermined threshold falls below the output of a Rückrollsicherungsmoments low slopes prevented. Ie. driving in the plane and on low gradients remains due to the hill-start assist function unaffected. In this way can be particularly effective an undesirable impairment the stopping and driving behavior are avoided, which otherwise due to measurement inaccuracies of the road gradient sensor or could result from pitching movements of the vehicle. By Set the scale factor to 1 if the slope value is one predetermined threshold value is exceeded z. B. the calculated base torque unmodified at high gradients as Rückrollsicherungsmoment output.

According to one embodiment is the addiction of the non-linear scale factor from the determined slope value or the auxiliary size given a steady and monotonically increasing function. The function may have a variable pitch and in particular an S-shaped course have, z. B. On the one hand, a substantial or complete suppression of Hill-Assist function at low slopes and on the other hand one essentially unmodified output of due to physical considerations Calculated base torque to achieve pronounced slopes. The function can have a continuously variable slope or the non-linear relationship may be due to a step function be shown.

Of the The road gradient sensor may detect an acceleration sensor the longitudinal inclination of the motor vehicle. Such acceleration sensors are available in the form of microelectromechanical components, which is a signal dependent on its orientation relative to gravity output (eg ADXL103 from Analog Devices). They are both uniaxial as well as biaxial static acceleration sensors in use. Advantageously, z. B. an already provided in the vehicle anyway Acceleration sensor - z. B. an anti-theft device or a driver assistance system assigned sensor - used are the angle of inclination of the vehicle in the longitudinal direction for a calculation the Rückrollsicherungsmoments to investigate.

The Control means may be adapted to the slope value only after expiration of a predetermined period of time from a determined To determine vehicle standstill. For this purpose, the counting up of a Time variable (timer) can be started as soon as a standstill of the Vehicle is detected. Only after the time variable one reaches the predetermined final value, the specified by the sensor Slope value read out. The by the final value of the time variable predetermined waiting time is chosen such that after their expiration Nick movements of the vehicle have largely subsided. A vehicle standstill For example, it can always be determined when the vehicle speed has dropped to zero. This can be done in particular by means of wheel speed sensors be recognized, which in many vehicles anyway, z. B. for driver assistance systems like ABS or ESP are provided.

The control device may further be coupled to a brake pedal actuation sensor for determining a brake pedal actuation value representing a brake pedal actuation, wherein the control device is configured to calculate the restoring torque also in dependence on the ascertained brake pedal actuation value. In particular, the Rückrollsicherungsmoment can be reduced or set to zero in a brake application. Ie. it will be issued with sufficient operation of the service or parking brake no Rückrollsicherungsmoment, since such a braked vehicle is not necessary. Thus, the electric power consumption can be lowered. However, a Rückrollsicherungsmoment can be issued even before the brake is fully released to safely prevent rewinding. Also considering the brake pedal Activity can be easily accomplished by multiplying the slope value (or auxiliary value related to the slope value) by a suitable scaling factor.

alternative or additionally the control device may be equipped with a vehicle speed sensor for determining a vehicle speed representing Speed value coupled, the control device is designed to the Rückrollsicherungsmoment also in dependence from the determined speed value. Advantageous can for this purpose z. B. used anyway existing wheel speed sensors become. The speed-dependent calculation the Rückrollsicherungsmoments can in turn be multiplied by the slope value (or a auxiliary value associated with the slope value, e.g. B. a base moment) with a suitable scaling factor become. In particular, the Rückrollsicherungsmoment decreases steadily from a predetermined speed threshold not by an abrupt withdrawal of the roll-back protection torque An unpleasant jerking of the vehicle occurs.

The Control device can also be configured by addition the Rückrollsicherungsmoments and at least one additional torque, in particular a creep torque, to calculate a total moment and the electric machine to produce of the calculated total torque. The total moment can So they are composed of several different individual functions. By adding a creep torque to the Rückrollsicherungsmoment can For example, even on a slope creep of the vehicle allows become. Preferably, the creeping torque is selected such that the maximum crawl speed on a slope is less than in the plane. This increases the ride comfort, since the driver a fast creep to strong Gradients as unnatural would be felt.

The The invention further relates to a method for supporting the Berganfahren in a motor vehicle, which is an electric machine for driving the motor vehicle.

According to the invention is a representing the road gradient Slope value determined, a Rückrollsicherungsmoment dependent on calculated from the determined slope value and the electric machine controlled to generate at least the calculated Rückrollsicherungsmoments.

at the method according to the invention in particular depending from the determined slope value or one with the slope value related auxiliary quantity is a non-linear scaling factor calculated, wherein the determined slope value or the auxiliary size with the scaling factor is multiplied to the Rückrollsicherungsmoment to calculate.

Of the Scaling factor can be set to about 0 (zero), if the slope value or the auxiliary quantity is less than a first threshold value, and / or the scaling factor can be set to about 1 (one) when the slope value or the auxiliary magnitude is greater than a second threshold.

Of the Slope value can only after expiration of a predetermined period of time be determined from a determined vehicle standstill to distortions to exclude the measurement result due to pitching movements.

The The invention will be described below by way of example with reference to the accompanying drawings described.

1 shows a schematic view of a drive train of a motor vehicle.

2 FIG. 13 is a diagram illustrating an example dependency of a first scale factor on a slope value. FIG.

3 FIG. 13 is a diagram illustrating an example dependency of a second scale factor on a brake pedal actuation value. FIG.

4 FIG. 15 is a diagram illustrating an exemplary dependency of a third scale factor on a vehicle speed value. FIG.

5 FIG. 12 is a graph illustrating an exemplary dependency of a creep torque on a vehicle speed value. FIG.

6 FIG. 10 is a graph illustrating an example dependency of a calculated rollback torque from a vehicle speed value. FIG.

7 FIG. 15 is a diagram illustrating an exemplary dependency of a calculated total torque on a vehicle speed value. FIG.

1 schematically shows the drive train 11 a motor vehicle, which is a front axle 13 , a rear axle 15 and an electric machine 17 includes. The electric machine 17 is supplied by a battery assembly, not shown, with electrical energy. An exit 19 the electric machine 17 is with a front axle differential 21 coupled to the wheels 22 the front axle 13 drive. In addition to the electric machine 17 can also use an internal combustion engine in the powertrain 11 be integrated in what 1 but not shown. Basically, could also be the rear axle 15 through the electric machine 17 be driven or it could be provided a transfer case to both the front axle 13 as well as the rear axle 15 through the electric machine 17 drive.

A control device 25 is with the electric machine 17 coupled and controls this in response to a driver's request and various driving condition parameters according to one in the drive train 11 to be initiated target torque. The control device 25 is in particular with an acceleration sensor configured as a tilt sensor 27 , a brake pedal actuation sensor 29 and wheel speed sensors 31 coupled to receive from these input signals. The control device 25 evaluates the input signals, calculated based on a total moment M _Ges and controls the electric machine 17 such that it generates the calculated total moment M _Ges . With regard to the determination of the total torque M _Ges is the control device 25 designed to provide a so-called hill-assist function, as will be explained in more detail below.

Once the wheel speed sensors 31 indicate that the vehicle is stationary and the brake pedal actuation sensor 29 indicates that the brake pedal is not actuated, the controller starts 25 with the incrementing of a time variable. As soon as the time variable has reached a predetermined end value, the control device determines 25 by means of the acceleration sensor 27 the instantaneous longitudinal inclination of the vehicle relative to the horizontal in the form of a slope value a. For example, the slope value a indicates the gravitational acceleration multiplied by the sine of the inclination angle of the vehicle and therefore represents the inclination angle of the longitudinal axis of the motor vehicle relative to the horizontal. The slope value a is then multiplied by the known mass m of the vehicle and the dynamic wheel radius R to obtain a base moment M _B which is just large enough to compensate for the pitch-dependent weight component: M _B = a.m.R

The base torque M _B calculated in this way is multiplied by three scaling factors K1, K2, K3 in order to obtain a roll-back securing torque M _R : M _R = M _B * K 1 * K 2 * K 3

The three scaling factors K1, K2, K3 and optionally further scaling and / or correction factors can be determined empirically and in a non-volatile memory of the control device 25 be filed. The first scaling factor K1 depends in a non-linear manner on the slope value a. An exemplary dependency is through the in 2 given function with S-shaped course given. How out 2 The first scaling factor K1 has the value 0 below a first gradient _threshold value a _{S1 and} the value 1 above a second gradient _threshold value a _S2 . This means that at road inclinations which deviate only slightly from the horizontal plane, no rollback securing torque M _{R is} output at all. an undesirable rise of control actions due to measurement inaccuracies of the acceleration sensor 27 or due to pitching motion of the vehicle. On the other hand, above the second gradient threshold value a _S2 , no slope value-dependent modification of the calculated base torque M _B takes place.

The second scaling factor K2 depends on the brake pedal actuation value b, which is from the brake pedal actuation sensor 29 is issued. An exemplary dependency is in 3 shown. Below a predetermined actuation threshold _S b the second scaling factor K2 is a constant 1, while _S linearly to 0 drops above the operating threshold value b. When the brake pedal is fully depressed, the second scaling factor K2 is therefore 0, ie, in this case as well, the electric machine 17 no rollback protection performed. When the brake pedal is released gradually, the second scaling factor K2 and therefore the rollback securing torque M _R increase steadily so that the rollback safety device is active even before the brake is completely released.

The third scaling factor K3 is dependent on the instantaneous vehicle speed v, which is based on the wheel speed sensors 31 is determined. An exemplary dependency is in 4 shown. The speed-dependent progression of the third scaling factor K3 is similar to the brake-pedal-actuation-dependent progression of the second scaling factor K2, ie the third scaling factor K3 is constant 1 below a speed threshold v _S , while it decreases linearly to 0 above the speed threshold v _S. In this way, the effect of the Rückrollsicherungsmoments M _{R is} limited to the process of starting, ie it will be avoided unwanted accelerations and consequently increased speeds after the start-up.

The course of the individual scaling factors K1, K2, K3 defining functions and in particular the position of the threshold values a _S1 , a _S2 , b _S , v _S can be adapted in any way to the respective vehicle properties or a selected driving program.

After the calculation of the Rückrollsicherungsmoments M _R performs the controller 25 to fulfill a Kriechreglerfunktion optionally an addition of the Rückrollsicherungsmoments M _R and a creep torque M _K through to get the total moment M _Ges : M _Ges = M _R + M _K

The creep torque M _K serves to provide a low propulsion when the accelerator pedal is unactuated and may in particular depend on the vehicle speed v. An exemplary course is in 5 shown. at 33 the creep speed v _{KE is} reached, with which the vehicle creeps constantly in the plane after completion of the creep acceleration.

The electric machine 17 is finally from the controller 25 controlled such that the total moment M _Ges in the drive train 11 is initiated.

The interaction of creep control and hill start assistance can be determined by 5 with further reference to 6 and 7 be illustrated.

In 6 the course of the Rückrollsicherungsmoments M _{R is shown} as a function of the vehicle speed v. This progression results from the scaling with the third scaling factor K3 (FIG. 4 ). If now the controller 25 the rollback securing torque M _R ( 6 ) and the creep moment M _K ( 5 ), the result is the in 7 shown driving speed dependent course of the total torque M _Ges . Above the vehicle speed, from which the creep torque M _{K is} steadily reduced, results in a relatively sharply decreasing total moment M _Ges . Since constant pitch creep must overcome both pitch resistance and rolling resistance, it becomes a stable point 35 just above the rollback torque M _R. The Rückrollsicherungsmoment M _R compensated at this point, the slope resistance, while over the Rückrollsicherungsmoment M _R beyond moment serves to overcome the rolling resistance.

It is thus achieved that the vehicle behaves exactly as in the plane up to the speed at which the roll-back securing torque M _{R is} reduced continuously. In particular, the creep process begins with the same acceleration as in the plane. Once the Rückrollsicherungsmoment M _{R is} steadily reduced, is sufficient - at least at larger roadway slopes - the total moment M _Ges with increasing speed v not soon enough for further acceleration. The vehicle then crawls uphill at a constant velocity v _Ka which is lower than the creep velocity v _KE in the plane. This driving behavior is advantageous in that a faster creep at high Fahrstesteiungen can be perceived by the driver as unpleasant.

All in all allows the invention provides an effective starting assistance on inclines, without this to intervene in the brake system. Especially advantageous is the combination of creep control and rollback avoidance on a slope, so that even on slopes comfortable maneuvering without pressing the Accelerator pedal is possible.

LIST OF REFERENCE NUMBERS

11

powertrain

13

Front

15

rear axle

17

electric machine

19

output

21

Front axle differential gear

22

wheel

25

control device

27

accelerometer

29

Brake pedal sensor

31

wheel speed sensor

33

endpoint the creep acceleration

35

stable Point

mGES

total moment

m

vehicle mass

R

dynamic wheel radius

MB

base torque

MR

Hill holding moment

K1

first scaling factor

K2

second scaling factor

K3

third scaling factor

aS1

first Slope threshold

aS2

second Slope threshold

b

Brake pedal operation amount

AA

Actuation threshold

v

vehicle speed

vS

Speed threshold

UQ

creep in the plane

MCA

creep at a roadway slope

MK

creeping

Claims (16)

Drive system for a motor vehicle with a mountain starting assistance, with an electric machine ( 17 ) for driving the motor vehicle and a control device ( 25 ) for driving the electric machine ( 17 ), characterized in that the control device ( 25 ) with a road gradient sensor ( 27 ) for determining a gradient value (a) representing the roadway inclination, the control device ( 25 ) is designed to calculate a roll-back securing torque (M _R ) in dependence on the ascertained gradient value (a) and the electric machine ( 17 ) to generate at least the calculated Rückrollsicherungsmoments (M _R ) to control. Drive system according to claim 1, wherein the control device ( 25 ) is configured to calculate the roll-back protection torque (M _R ) according to a non-linear relationship as a function of the determined slope value (a). Drive system according to claim 1 or 2, wherein the control device ( 25 ) is designed to calculate a non-linear scaling factor (K1) as a function of the ascertained slope value (a) or an auxiliary variable associated with the slope value and to add the ascertained slope value (a) or the auxiliary variable with the scaling factor (K1) multiply to calculate the rollback retention torque (M _R ). Drive system according to claim 3, wherein the control device ( 25 ) is configured to set the scaling factor (K1) to approximately zero if the slope value (a) or the auxiliary variable is less than a first threshold value (a _S1 ), and / or wherein the control device ( 25 ) is adapted to set the scaling factor (K1) to approximately the value 1 if the slope value (a) or the auxiliary variable is greater than a second threshold value (a _S2 ). Drive system according to claim 3 or 4, wherein the dependence of the non-linear scale factor (K1) from the determined slope value (a) or the auxiliary size by a steady and monotonically increasing function is given. Drive system according to claim 5, wherein the function a variable slope and in particular an S-shaped course having. Drive system according to at least one of the preceding claims, wherein the road gradient sensor ( 27 ) comprises an acceleration sensor for detecting the longitudinal inclination of the motor vehicle. Drive system according to at least one of the preceding claims, wherein the control device ( 25 ) is designed to determine the slope value (a) only after a predetermined period of time from a determined vehicle standstill. Drive system according to at least one of the preceding claims, wherein the control device ( 25 ) further comprising a brake pedal actuation sensor ( 29 ) for determining a brake pedal actuation value (b) representing a brake pedal actuation, the control device ( 25 ) is designed to calculate the Rückrollsicherungsmoment (M _R ) also in dependence on the determined brake pedal actuation value (b). Drive system according to at least one of the preceding claims, wherein the control device ( 25 ) further comprising a vehicle speed sensor ( 31 ) for determining a speed value (v) representing the vehicle speed, the control device ( 25 ) is designed to calculate the Rückrollsicherungsmoment (M _R ) also in dependence on the determined speed value (v). Drive system according to at least one of the preceding claims, wherein the control device ( 25 ) is configured to calculate a total moment (M _Ges ) by adding the rollback protection torque (M _R ) and at least one additional torque, in particular a creep torque (M _K ), and the electric machine ( 17 ) to generate the calculated total torque (M _Ges ). Drive system according to claim 11, wherein the control device ( 25 ) is adapted to calculate the total torque (M _Ges ) to add the Rückrollsicherungsmoment (M _R ) and a creep (M _K ), wherein the creep (M _K ) is selected such that the creep (v _KE ) of the motor vehicle on level road is higher than the creep speed (v _Ka ) at a road gradient. Method for supporting hill-climbing in a motor vehicle, comprising an electric machine ( 17 ) for driving the motor vehicle, characterized by the steps of: determining a slope value (a) representing the roadway slope; Calculating a rollback torque (M _R ) in response to the determined slope value (a); and driving the electric machine ( 17 ) for generating at least the calculated Rückrollsicherungsmoments (M _R ). The method of claim 13, wherein a non-linear scaling factor (K1) is calculated in dependence on the ascertained slope value (a) or an auxiliary variable associated with the slope value, and the determined slope value (a) or the auxiliary quantity is multiplied by the scaling factor (K1) in order to calculate the rollback securing torque (M _R ). The method of claim 13 or 14, wherein the scaling factor (K1) is set to about zero when the slope value (a) or the auxiliary magnitude is less than a first threshold (a _S1 ), and / or the scaling factor (K1) for example, the value 1 is set if the gradient value (a) or the auxiliary variable is greater than a second threshold value (a _S2 ). Method according to at least one of claims 13 to 15, wherein the slope value (a) only after a predetermined Duration is determined from a determined vehicle standstill.

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