METHOD AND DEVICE FOR DETERMINING AN ENGINE REFERENCE TORQUE OF A MOTOR VEHICLE

Description

[0001] The invention relates to a method and a device for determining the engine reference torque of a motor vehicle used in a control unit, as well as a control unit of a braking system of a motor vehicle with such a device and / or with hardware and / or software modules for carrying out the steps of such a method.

[0002] Conventional commercial vehicles are often equipped with anti-lock braking systems (ABS) or electronic braking systems (EBS) that use a value for the engine reference torque (or maximum engine torque) for internal calculations, such as for engine drag torque control (SMR). This engine reference torque value is often transmitted by the vehicle's engine control unit or transmission control unit via the vehicle's CAN bus.

[0003] However, with certain CAN bus types, specific vehicle types, or under fault conditions, the ABS or EBS systems do not receive information about the engine reference torque from the vehicle's CAN bus. This can be due to specifications from the vehicle manufacturer, for example.

[0004] Furthermore, in hybrid vehicles - i.e. vehicles with a hybrid drive which usually includes an electric motor in addition to an internal combustion engine - the information on the engine reference torque of the internal combustion engine is not sufficient as a relevant engine reference torque, since the additional drive would be disregarded.

[0005] The invention is therefore based on the objective of determining the motor reference torque independently of any information about the motor reference torque that may be transmitted via a CAN bus.

[0006] German patent DE 102013008839A1 relates to a method for determining the mass m of a motor vehicle, in particular a commercial vehicle, based on the principle of mechanical power. To determine the vehicle mass as accurately as possible in a simple manner while driving, the vehicle's speed v and its drive power PA are determined. The mass m of the vehicle can then be calculated from the speed v and the drive power PA. The invention further relates to a device for carrying out such a method and to a motor vehicle with such a device.

[0007] WO2015004639A2 discloses an electronic control unit for motor vehicles which is programmed to estimate in real time either a vehicle mass or a road inclination or both.

[0008] German patent DE19728867A1 describes a method that includes measuring first and second acceleration values, representing the vehicle's accelerations at the first and second time points. At least two driving parameters are measured, representing the driving force and / or driving torque at these times. Based on at least these acceleration and driving parameters, at least two rolling resistances or estimated masses are determined. Mass determination depends at least on a comparison between the determined first and second rolling resistances or mass estimates.

[0009] German patent DE112011104629T5 describes a power transmission control device for a hybrid vehicle, comprising an internal combustion engine and a motor (MG) as power sources, and a manual transmission and a friction clutch. The engine torque is generally set to the lower of the engine torque end reference value of an engine torque reference value determined based on throttle opening and an engine torque limit value determined based on clutch return stroke. As a result, a driving mode can be obtained that more appropriately or better corresponds to the driver's intentions.

[0010] The invention solves this problem with the features of a method according to claim 1, as well as with a device according to claim 14 and a control unit of a braking system of a motor vehicle according to claim 15.

[0011] The inventive method for determining the engine reference torque (maximum engine torque) of the motor vehicle used in a motor vehicle control unit provides that the engine reference torque is determined by estimation. For this purpose, a value for the mass of the motor vehicle is determined. In addition, a motor vehicle speed value is determined at two different times during acceleration of the motor vehicle. In this sense, acceleration means only positive acceleration, i.e., no deceleration, meaning that the vehicle is traveling faster at the later time than at the earlier time.

[0012] Vehicle speed values ​​can be determined, for example, from the vehicle's wheel speeds. This is advantageous because modern braking systems, such as ABS and EBS systems, have wheel speed sensors installed on all or at least several wheels, which provide wheel speed data from which the vehicle speed can be determined with minimal effort and therefore cost-effectively.

[0013] The current engine power is calculated from the vehicle's mass and the two vehicle speed values. Preferably, the calculation is based on the equation of motion for a moving vehicle.

[0014] Based on the calculated engine power, a value for the engine reference torque is estimated using power and torque curves stored as a function of engine speed in the control unit or another module of the vehicle. The estimation of the engine reference torque can, but does not necessarily have to, take the engine speed into account, since the engine torque can be directly derived from the engine power.

[0015] If a current engine power cannot be clearly assigned to a current engine torque - e.g. because two different engine torques could be possible for a certain engine power - the previous or preceding course of the engine power can be taken into account, which allows a clear assignment of engine power to engine torque.

[0016] The determination of the motor reference torque (motor maximum torque) according to the invention allows a determination of a value for the motor reference torque independent of the CAN bus, taking into account the actual performance characteristics of the drive of a motor vehicle.

[0017] The determination of the motor reference torque according to the invention is therefore also suitable for special vehicle CAN types or under fault conditions where, conventionally, no or no correct information on the motor reference torque can be obtained via the vehicle's CAN bus.

[0018] A particular advantage of the invention is that the motor reference torque can be determined with only a small number of input variables. No further information from the motor or gearbox is required.

[0019] Overall, the invention advantageously enables the provision of a high-performance motor drag torque control without requiring a signal via the CAN bus containing information about the motor reference torque.

[0020] An inventive device for determining the engine reference torque used in a control unit of a motor vehicle comprises a computer which calculates the engine power of the motor vehicle from a value for the mass of the motor vehicle and from vehicle speed values ​​obtained at two different times during an acceleration of the vehicle.

[0021] The device also includes an estimator that estimates a value for the engine reference torque based on the calculated engine power and torque curves stored as a function of the engine speed in the control unit or another module.

[0022] Preferably, the device comprises (further) hardware and / or software modules for carrying out the steps of the method according to the invention and its further developments explained below.

[0023] The control unit according to the invention for a braking system of a motor vehicle comprises a device for determining the motor reference torque of the aforementioned type and / or hardware and / or software modules for carrying out the steps of the method according to the invention and its further developments explained below.

[0024] According to a further development of the invention, the two points in time are chosen to be so close together that the acceleration values ​​of the motor vehicle at these points in time do not differ significantly from each other. This makes it possible to base the model on uniformly accelerated motion. Furthermore, the influence of other driving resistances can be kept to a minimum in this way.

[0025] A further development of the invention provides that the mass of the motor vehicle is determined from the air spring pressures measured on the vehicle. The air spring pressures depend on the vehicle's load and thus, overall, on the vehicle's mass. The air spring pressures can therefore provide information about the vehicle's mass. Using the air spring pressures to determine the vehicle's mass is advantageous because it avoids the need to weigh the vehicle and its load. Weighing is disadvantageous because it involves considerable effort, especially since the mass obtained by weighing would also have to be communicated to the vehicle and its control units. This effort can be avoided thanks to this further development of the invention.

[0026] According to a further development of the invention, the motor power is calculated as follows: P = m 2 ⋅ v t 2 2 − v t 1 2 t 2 − t 1 where P is the engine power, m is the determined value of the vehicle's mass, v(t1) is the vehicle speed determined at time t1, and v(t2) is the vehicle speed determined at time t2. The simplified basic energy equations are used for this calculation of engine power. ΔE = m 2 ⋅ v t 2 2 − v t 1 2 and P = ΔE Δt = ΔE t 2 − t 1 The formula is used where E denotes the kinetic energy of the vehicle and thus ΔE / Δt represents the change in the vehicle's kinetic energy over time. The vehicle is traveling faster at time t2 than at time t1, since these times fall within an acceleration phase of the vehicle.

[0027] A further development of the invention provides that one or more of the following correction factors are taken into account when calculating the engine power: Correction factor corr a,rot, which represents an acceleration of rotating masses of the motor vehicle, e.g. the wheels and / or rotating masses in the engine and drivetrain; correction factor corr R, which represents a rolling resistance of the wheels of the motor vehicle; correction factor corr L, which represents an air resistance of the motor vehicle; correction factor corr St, which represents a gradient resistance of a gradient of the road used by the motor vehicle; correction factor corr div, which represents further frictional resistances.

[0028] Taking these correction factors into account means that the calculated engine power only considers the energy for translational acceleration on a flat surface. This eliminates other driving resistances that would contribute to an inaccurate determination of the engine reference torque.

[0029] Depending on the vehicle type and therefore its intended use and / or the driving situation, either none, only one, only a selection or all of the correction factors are used. When selecting the correction factors, all possible combinations are considered, i.e., of the five correction factors mentioned above, in particular: 1. with 2., 1. with 3., 1. with 4., 1. with 5., 2. with 3., 2. with 4., 2. with 5., 3. with 4., 3. with 5., 4. with 5., 1. with 2. with 3., 1. with 2. with 4., 1. with 2. with 5., 1. with 3. with 4., 1. with 3. with 5., 1. with 4. with 5., 2. with 3. with 4., 2. with 3. with 5., 2. with 4. with 5., 3. with 4. with 5., 1. with 2. with 3. with 4., 1. with 2nd with 3rd with 5th, 1st with 2nd with 4th with 5th, 1st with 3rd with 4th with 5th, 2nd with 3rd with 4th with 5th correction factor, etc.

[0030] According to a further development of the invention, one or more of the correction factors are determined as a function of speed. Typically, the air resistance of a motor vehicle is speed-dependent; it can be assumed that air resistance increases quadratically with speed.

[0031] Furthermore, the correction factor corr a,rot, which represents an acceleration of rotating masses of the motor vehicle, e.g. the wheels and / or rotating masses in the engine and drivetrain, is speed-dependent; it can be assumed that the kinetic energy stored in rotating masses increases with the rotational speed of the rotating masses.

[0032] Other phenomena can affect the other correction factors.

[0033] When taking correction factors into account, a preliminary engine power is first calculated without considering correction factors; then the value of the preliminary engine power is multiplied by the correction factor(s) to be taken into account, resulting in the calculated engine power.

[0034] By taking these correction factors into account, a higher accuracy is achieved in estimating the motor reference torque.

[0035] A further development of the invention provides for the repeated estimation of the engine reference torque, taking into account state models of the motor vehicle and / or using recursive or iterative estimation algorithms, e.g., using a Kalman filter. This also achieves higher accuracy in estimating the engine reference torque.

[0036] According to a further development of the invention, the times at which vehicle speed values ​​are determined are examined for their suitability, and if a time is found to be unsuitable, the corresponding vehicle speed value is discarded or filtered out. This procedure is advantageous because unsuitable speed values ​​thus do not distort the estimation of the engine reference torque.

[0037] A further development of the invention provides that, when examining the suitability of the timing, signals from a braking system of the motor vehicle, e.g., from a control unit of an anti-lock braking system or an electronic braking system, are taken into account, which may indicate unsuitable vehicle behavior. In this way, unfavorable driving conditions can be excluded for estimating the engine reference torque.

[0038] According to a further development of the invention, these signals include a brake actuation signal to signal brake actuation and / or an ABS activation signal to signal activation of an anti-lock braking system. Thus, information available in brake systems can be used to improve the estimation of the engine reference torque.

[0039] A further development of the invention provides that a gradient resistance is calculated using a tilt sensor, and depending on the calculated gradient resistance, the correction factor corr St, which represents the gradient resistance of a gradient of the road surface used by the motor vehicle, is calculated, and / or if a gradient is detected based on an incline angle generated by the tilt sensor outside a predetermined range, a simultaneously determined motor vehicle speed value is excluded or declared unsuitable. In this way, measurements on uneven surfaces can be discarded and do not distort the estimate of the engine reference torque.

[0040] According to a further development of the invention, the engine power is continuously recalculated, and a maximum engine power value, Pmax, is determined by replacing an existing Pmax value with a larger calculated value, provided the larger calculated value has previously been deemed reliable. In this way, after a certain observation period, the vehicle or one of its control units obtains the maximum engine power solely from measurements and calculations during driving. The maximum engine power therefore does not need to be programmed into the corresponding control units. This is particularly advantageous when the engine power is unknown during the manufacture of such control units, as it is not yet clear in which vehicle such a control unit will be installed.

[0041] A further development of the invention provides that measured engine speed information or engine speed information derived from information about an engaged gear and a wheel speed is used, and the engine reference torque is determined from the engine speed information and the engine power.

[0042] According to a further training, the motor reference torque is continuously estimated and a maximum value of the motor reference torque is determined by replacing an existing value for the maximum value with a larger estimated value of the motor reference torque, provided that the larger estimated value has been assessed as reliable.

[0043] A particular advantage of the invention is that no information about the clutch status of the vehicle needs to be available, since maximum acceleration values ​​are generally only achieved when the clutch is engaged.

[0044] The invention can be applied both in conventional vehicles, in particular vehicles with internal combustion engines, and in parallel hybrid vehicles, where the input speeds of the transmission are typically in the operating range of a diesel engine.

[0045] Further developments of the invention are described in the claims, the description, and the drawings. The aforementioned advantages of features and combinations of features are examples and can be achieved alternatively or cumulatively, without necessarily requiring that the advantages be obtained in specific embodiments of the invention. Further features can be seen in the drawings. It is understood that numerous modifications and adaptations are possible without thereby exceeding the scope of protection defined by the patent claims.

[0046] The drawing shows: Fig. 1 shows an embodiment of a device according to the invention for determining the engine reference torque of a motor vehicle engine, Fig. 2 shows an embodiment of a method according to the invention for determining the engine reference torque with a device according to Fig. 1 , Fig. 3 an embodiment of an arrangement of the in Fig. 1 The device shown is located outside a control unit that uses the engine reference torque, and Fig. 4 shows an embodiment of an alternative arrangement of the device shown. Fig. 1 The device shown is located within a control unit that uses the engine reference torque.

[0047] Fig. 1 Figure 1 shows an embodiment of a device 10 according to the invention for determining the engine reference torque of the engine of a motor vehicle.

[0048] The term "engine" in a motor vehicle refers to the engine system, which in its simplest form comprises only an internal combustion engine. However, in more sophisticated engine systems, such as hybrid vehicles, it encompasses all the drive components, for example, an internal combustion engine and one or more electric motors, which serve to propel the vehicle. Depending on the operating mode, a hybrid vehicle is driven either solely by the electric motor(s), solely by the internal combustion engine, or simultaneously by both the internal combustion engine and the electric motor(s). The engine reference torque refers to the maximum torque of all drive components combined.

[0049] Device 10 is part of the motor vehicle, in particular part of one of its system components.

[0050] The facility 10 includes a computer 12 and an estimator 14.

[0051] Computer 12 receives various quantities and parameters, in particular a value for the mass m of the vehicle and two vehicle speed values ​​v(t1) and v(t2) obtained at different times t1 and t2. The vehicle speed values ​​v(t1) and v(t2) can, for example, be determined from wheel speeds obtained from wheel speed sensors. Such wheel speed sensors are regularly installed in vehicles equipped with an anti-lock braking system (ABS) or an electronic braking system (EBS). The vehicle speed values ​​v(t1) and v(t2) can also be transmitted directly to device 10 from the control unit of an ABS or EBS.

[0052] The mass m of a motor vehicle can be determined, for example, from air spring pressures measured on the vehicle. For this purpose, a pressure is measured in the air spring system and the mass m of the motor vehicle is calculated from the measured pressure.

[0053] Determining the mass m of the motor vehicle is particularly useful for commercial vehicles, since the load of a commercial vehicle is significantly variable and therefore a loaded commercial vehicle can reach a mass several times greater than the same commercial vehicle without a load.

[0054] The computer 12 first calculates an engine power P from the values ​​of the mass m and the vehicle speed values ​​v(t1), v(t2) using the equation P = m 2 ⋅ v t 2 2 − v t 1 2 t 2 − t 1 . Preferably, the engine power calculated in this way is considered only as a preliminary value P', which is corrected by one or more of the correction factors by multiplying the preliminary value P' by one or more of the correction factors.

[0055] The correction factors include the following quantities: a correction factor corr a,rot, which represents an acceleration of rotating masses of the motor vehicle, a correction factor corr R, which represents a rolling resistance of the wheels of the motor vehicle, a correction factor corr L, which represents an air resistance of the motor vehicle, a correction factor corr St, which represents a gradient resistance of a gradient of the road used by the motor vehicle, a correction factor corr div, which represents further frictional resistances.

[0056] The value for engine power P output by computer 12 is therefore obtained by multiplying the preliminary value P' by the correction factor corr a,rot , the correction factor corr R , the correction factor corr L , the correction factor corr St and / or the correction factor corr div .

[0057] The computer 12 can receive further quantities and parameters such as the inclination or gradient α of the vehicle, which can be measured using an inclination sensor.

[0058] Furthermore, the computer 12 can obtain the speed of the motor n M determined by measurement or - if available - the speeds of other motors, especially in hybrid vehicles.

[0059] Furthermore, the computer 12 can obtain the rotational speed of a wheel n M or the rotational speeds of several wheels, as determined by measurement. The computer 12 can also obtain information about the selected gear G. From the information about the selected gear G and the determined wheel rotational speed n M, the computer 12 can derive the engine speed.

[0060] Computer 12 also receives information about any interventions affecting the wheel brakes or engine speed from an anti-lock braking system (ABS), an electronic braking system (EBS), an electronic stability program (ESP), an traction control system (ASR), and / or an engine drag torque control system (MSR). From this information, it is determined whether the vehicle speed values ​​v(t1) and v(t2) used for estimating the engine reference torque are suitable or unsuitable. These vehicle speed values ​​v(t1) and v(t2) are typically unsuitable if they were determined during an intervention by one of these systems. If the vehicle speed values ​​v(t1) and v(t2) are found to be unsuitable, either the power calculation is not performed at all, or any power value P obtained is discarded.

[0061] Computer 12 transmits suitable power values ​​P to estimator 14. Based on the calculated engine power P and power and torque curves 16, which are stored as a function of the engine speed n M, estimator 14 estimates a value for the engine reference torque MRM. This value is further processed by device 10, possibly taking into account state models of the vehicle and / or recursive and interactive estimation algorithms, e.g., using a Kalman filter.

[0062] Finally, device 10 provides a value for the engine reference torque (MRM) to one or more control units of the motor vehicle, such as an engine drag torque control unit, an ABS control unit, or an EBS control unit.

[0063] Fig. 2 Figure 20 shows an exemplary procedure for determining the motor reference torque MRM.

[0064] After starting the procedure 20, 24 procedure parameters are initialized in an initialization step.

[0065] In investigation step 26, a value m of the mass of the motor vehicle is determined, as described above, e.g. based on pressures in the air suspension system.

[0066] In a further investigation step 28, a vehicle speed value v(t1), v(t2) is determined at two different times t1 and t2 during an acceleration of the motor vehicle.

[0067] In test step 30, it is checked whether the acceleration of the motor vehicle was approximately the same at both points in time, in order to ensure that the motor vehicle's acceleration was approximately uniform. If this is not the case, the procedure branches off via branch 32 back to investigation step 28.

[0068] Provided the vehicle exhibits an approximately uniformly accelerated motion, a further test step 34 verifies whether the times t1 and t2, as well as the vehicle speed values ​​v(t1) and v(t2), are suitable. This involves checking whether the times were sufficiently close to each other to allow for a sufficiently high degree of accuracy in assuming uniformly accelerated motion. Furthermore, as explained above, it is checked whether any interventions by driver assistance systems, such as an anti-lock braking system (ABS), an electronic braking system (EBS), an electronic stability program (ESP), an traction control system (ASR), and / or an engine drag torque control system (MSR), occurred at times t1 and t2, in order to potentially declare the vehicle speed values ​​v(t1) and v(t2) unsuitable.

[0069] Furthermore, if an inclination is detected based on a gradient angle generated by an inclination sensor outside a predetermined range, a simultaneously determined vehicle speed value is excluded or declared unsuitable.

[0070] If the values ​​used, in particular motor vehicle speed values, are found to be unsuitable, the procedure branches off via branch 36 back to investigation step 28.

[0071] In calculation step 38, a preliminary value for the engine power P' is calculated from the mass m of the motor vehicle as well as the motor vehicle speed values ​​v(t1), v(t2) and the time difference t2 - t1 between the two times t1 and t2.

[0072] In a subsequent correction step 40, the preliminary value for the engine power P' is corrected by multiplication with one or more of the above correction factors.

[0073] In test step 42, it is checked whether the calculated and, if necessary, corrected current engine power Pneu is greater than a previously calculated and, if necessary, corrected engine power Palt. If this is the case, a branch occurs to replacement step 44, in which a previously stored maximum value Pmax is replaced by the current value for the engine power Pneu, and then estimation step 46 is performed.

[0074] However, if it is determined in test step 42 that the calculated and possibly corrected current engine power Pneu is not greater than a previously calculated and possibly corrected engine power Palt, the replacement step 44 is skipped and the estimation step 46 is continued.

[0075] In estimation step 46, the engine reference torque (MRM) is estimated. Since steps 28, 30, 34, 38, 40, 42, and 44 are performed repeatedly, the engine reference torque is also estimated repeatedly. State models of the vehicle can be used and / or recursive or iterative estimation algorithms can be incorporated, e.g., using Kalman filters. Unsuitable values ​​can be identified and filtered out.

[0076] In test step 48, it is checked whether the currently estimated motor reference torque MRMneu is greater than the previously estimated motor reference torque MRMalt. If this is the case, a branch occurs to replacement step 50, in which a previously stored motor reference torque MRMalt is replaced by the currently estimated motor reference torque MRMneu, and the process continues with determination step 28.

[0077] However, if it is determined in test step 48 that the currently estimated engine reference torque MRMneu is not greater than the previously estimated engine reference torque MRMalt, the replacement step 50 is skipped and the determination step 28 is continued.

[0078] Fig. 3 shows an arrangement of the in Fig. 1 The device 10 shown is located outside a control unit 60, which receives and uses the motor reference torque (MRM) from the device 10. Data, in particular data related to Fig. 1 The parameters explained are exchanged between the control unit 60 and the device 10.

[0079] Fig. 4 shows an alternative arrangement of the in Fig. 1 shown device 10 within such a control unit 62 which uses the motor reference torque MRM. Reference symbol list (part of the description):

[0080] 10 Setup 12 Computer 14 Estimator 16 Power and torque curves 20 Procedure flow 22 Start 24 Initialization step 26 Determination step 28 Determination step 30 Test step 32 Branching 34 Test step 36 Branching 38 Calculation step 40 Correction step 42 Test step 44 Replacement step 46 Estimation step 48 Test step 50 Replacement step 60 Control unit 61 Data connection 62 Control unit m Mass of the vehicle t1 Time t2 Time v(t1) Vehicle speed value at time t1 v(t2) Vehicle speed value at time t2 a(t1) Vehicle acceleration value at time t1 a(t2) Vehicle acceleration value at time t2 corr a,red Acceleration of rotating masses of the motor vehicle, representing correction factor corr R Rolling resistance of the wheels of the motor vehicle, representing correction factor corr L Air resistance of the motor vehicle, representing correction factor corr St Gradient resistance, representing correction factor corr div Other frictional resistances, representing correction factor α Incline / Gradient n M Engine speed n R Wheel speed GG Gear MRM Engine reference torque MRMneu Current engine reference torque MRMalt Previous engine reference torque P Engine power P'Preliminary engine power Pneu Current engine power Palt Previous engine power Pmax Maximum engine power ABS Anti-lock braking system EBS Electronic braking system ESP Vehicle dynamics control system ASR Traction control system MSR Engine drag torque control system

Claims

1. Method for determining the engine reference torque (MRM) of an engine of a motor vehicle, which engine reference torque is used in a control unit (60, 62) of the motor vehicle, characterized in that the engine reference torque (MRM) is determined by estimation (46), a value for the mass (m) of the motor vehicle being ascertained and a motor vehicle speed value (v(t1), v(t2)) being ascertained at each of two different times (t1, t2) during an acceleration of the motor vehicle, an engine power (P'; P) of the engine is calculated from these values (m, v(t1), v(t2)) and, on the basis of the calculated engine power (P'; P), a value for the engine reference torque (MRM) is estimated on the basis of power and torque curves (16) which are stored as a function of the speed (nM) of the engine.

2. Method according to claim 1, characterized in that the two times (t1, t2) are selected to be temporally close to one another such that the acceleration values (a(t1), a(t2)) of the motor vehicle at these times (t1, t2) do not differ significantly from one another.

3. Method according to claim 1 or 2, characterized in that the value for the mass (m) of the motor vehicle is ascertained from air spring pressures measured on the motor vehicle.

4. Method according to any of the preceding claims, characterized in that the engine power (P) is calculated as follows: P = m 2 ⋅ v t 2 2 − v t 1 2 t 2 − t 1 P being the engine power, m being the ascertained value of the mass of the motor vehicle, v(t1) being the value of the motor vehicle speed ascertained at the time t1, and v(t2) being the value of the motor vehicle speed ascertained at the time t2.

5. Method according to any of the preceding claims, characterized in that, when calculating the engine power (P), one or more of the following correction factors are taken into account: - correction factor (corr)a,rot which represents an acceleration of rotating masses of the motor vehicle, - correction factor corrR which represents a rolling resistance of the wheels of the motor vehicle, - correction factor corrL which represents an air resistance of the motor vehicle, - correction factor corrSt which represents a gradient resistance of a gradient of the roadway used by the motor vehicle, - correction factor corrdiv which represents further frictional resistances.

6. Method according to any of the preceding claims, characterized in that the engine reference torque (MRM) is repeatedly estimated (46), taking into account state models of the motor vehicle and / or using recursive or iterative estimation algorithms, e.g. using a Kalman filter.

7. Method according to any of the preceding claims, characterized in that the times (t1, t2) are examined (34) with regard to the suitability thereof and if a time (t1, t2) is found to be unsuitable, the associated motor vehicle speed value (v(t1), v(t2)) is discarded or filtered out.

8. Method according to claim 7, characterized in that, when examining (34) the suitability of the times (t1, t2), signals from a brake system of the motor vehicle, e.g. from a control unit of an anti-lock braking system (ABS) or of an electronic braking system (EBS), are taken into account, which signals indicate an unsuitable motor vehicle behavior.

9. Method according to claim 8, characterized in that the signals comprise a brake application signal for signalizing a brake application and / or an activation signal for signalizing an activation of an anti-lock braking system (ABS).

10. Method according to any of the preceding claims, characterized in that a gradient resistance is calculated by means of an inclination sensor, and the correction factor corrSt is calculated on the basis of the gradient resistance, which correction factor represents the gradient resistance, and / or, when an inclination is detected on the basis of a gradient angle generated by the inclination sensor, which gradient angle is outside a predetermined range, a simultaneously ascertained motor vehicle speed value is excluded or declared unsuitable (34).

11. Method according to any of the preceding claims, characterized in that the engine power (P) is continuously repeatedly calculated and a maximum value (Pmax) of the engine power is ascertained by replacing an existing maximum value (Pmax) of the engine power by a larger calculated value of the engine power (Pneu), provided that the larger calculated value (Pneu) has previously been assessed as reliable.

12. Method according to any of the preceding claims, characterized in that measured engine speed information (nM) or engine speed information (nM) derived from information about an engaged gear (G) and a wheel speed (nR) is used and the engine reference torque is determined from the engine speed information (nM) and the engine power (P).

13. Method according to any of the preceding claims, characterized in that the engine reference torque (MRM) is continuously repeatedly estimated, and a maximum value (MRM) of the engine reference torque is determined by replacing an existing value (MRMalt) for the maximum value by a larger estimated value of the engine reference torque (MRMneu), provided that the larger estimated value (MRMneu) has been assessed as reliable.

14. Device for determining the engine reference torque (MRM) of an engine of a motor vehicle, which engine reference torque is used in a control unit (60; 62) of the motor vehicle, characterized by a computer (12) which calculates an engine power (P', P) of the engine from a value for the mass (m) of the motor vehicle and from motor vehicle speed values (v(t1), v(t2)) obtained during an acceleration of the motor vehicle at two different times (t1, t2), and an estimator (14) which estimates, on the basis of the calculated engine power (P', P), a value for the engine reference torque (MRM) on the basis of power and torque curves (16) which are stored as a function of the speed (nM) of the engine.

15. Control unit of a brake system of a motor vehicle, characterized by a device (10) for determining the engine reference torque (MRM) of the engine of the motor vehicle according to claim 14 and / or hardware and / or software modules for carrying out the steps of a method according to any of claims 1 to 13.