DETERMINING WHEEL AND / OR AXLE TORQUE SPECIFICATIONS IN A MOTOR VEHICLE

Description

[0001] The invention relates to the determination of torque specifications in a motor vehicle.

[0002] A so-called torque structure or torque control is often used to control the engine of motor vehicles. This involves calculating a torque target step by step based on an accelerator pedal signal characteristic of the accelerator pedal position or a driver assistance system influencing the vehicle's longitudinal movement, as well as other torque requirements. From the torque target, the engine control system then determines the engine parameters for controlling the engine actuators. Examples of a torque structure are described in the publications EP 1 277 940 A2 and EP 1 078 804 A2.

[0003] In common torque structures, the torque specification is typically calculated as the clutch torque for the transmission input, as described, for example, in document EP 1 277 940 A2. In two-axle vehicles, in which, for example, an internal combustion engine with a transmission on one axle and an electric motor on the other axle each serve as the drive, the approach of calculating torque specifications as clutch torque (transmission input torque) is hardly feasible or only with a significant conversion effort. This is because the clutch torque, as the transmission input level, is usually present on one axle at a different torque level than that of the other axle and thus cannot be transferred directly to the other axle. Equalizing the two torque levels can only be achieved with increased computational effort.

[0004] FR 2 901 762 A1 describes a device comprising a means for detecting the driving situation and a calculation means for calculating, based on the means for detecting the driving situation, a longitudinal force or a torque to drive at least one wheel of a train of the vehicle. The calculation means comprises a means for establishing a grip potential, a means for testing the vehicle's ground contact conditions, and a means for controlling the longitudinal force as a function of the grip potential and the result of the test of the vehicle's ground contact conditions.

[0005] EP 1 162 103 A2 describes a control unit that controls the torque of a front-wheel drive motor and a rear-wheel drive motor, the rotational speed of a generator, and the torque of a motor. The control unit calculates a target driving force of a vehicle based on an accelerator pedal operation amount and a vehicle speed, and divides this target driving force into a target driving force for the front wheels and a target driving force for the rear wheels. The power required to drive the generator is calculated based on the target driving force of the vehicle, and the target rotational speed of the generator is calculated based on this power and the vehicle speed.

[0006] WO 2010 / 031678 A1 describes a method for adjusting a motor drive system in a motor vehicle with at least two drive units whose drive torques can be adjusted separately. To determine a torque distribution that optimizes fuel consumption, the sum of the individual consumptions of the drive units is determined for a plurality of differently distributed drive torques, and the optimum fuel consumption is determined from the sum of the individual consumptions.

[0007] WO 2010 / 079024 A1 describes a method for operating a vehicle in which each of the two mechanically uncoupled axles of the vehicle is driven by at least one drive unit, thereby transmitting a torque to the wheels of the respective axle. To optimally utilize the different friction coefficients of the wheels that occur under different ground conditions, the rotational speeds of the wheels of both drive axles are determined and averaged. A difference is calculated from the averaged rotational speeds of both axles. Based on this difference, the torque of at least one axle is influenced in such a way that differences in the averaged rotational speeds of the wheels are counteracted.

[0008] It is therefore an object of the invention to provide a torque structure for determining one or more engine torque specifications for one or more drive motors used in the motor vehicle, which allows a simple calculation of the engine torques, in particular when using several drive motors.

[0009] The problem is solved by the features of the independent patent claims.

[0010] A first aspect of the invention relates to a method for determining at least one engine torque specification in a motor vehicle having two axles, two wheels per axle and a plurality of drive motors.

[0011] The method comprises determining a total torque specification as a function of an accelerator pedal signal characteristic of the position of the accelerator pedal or a signal from a system influencing the vehicle's longitudinal movement (in particular a driver assistance system).

[0012] The method comprises determining, for each axle, a respective axle-specific torque specification, wherein the total torque specification is distributed between the two axles depending on at least one torque distribution specification. The method comprises determining, for each wheel of at least one first axle, preferably both axles, a respective wheel-specific wheel-specific torque specification, depending on the determined axle torque specification of the respective axle.The method comprises determining an engine torque specification for the respective drive motor as a function of the determined wheel torque specification for each wheel of the first axle and as a function of either the determined wheel torque specification for each wheel of the second axle if the respective wheel-related wheel torque specifications are determined for both axles, or the axle torque specification related to the second axle if the respective wheel-related wheel torque specifications are determined only for the first axle. For each wheel of at least the first axle, preferably both axles, the respective wheel torque specification related to the respective wheel is limited upwards and downwards as a function of information from one or more vehicle dynamics control systems.The axle torque specification related to the second axle is limited upwards and downwards depending on the information from one or more vehicle dynamics control systems if the respective wheel-related wheel torque specifications are determined only for the first axle.

[0013] The torque structure is therefore calculated based on the wheel torques of the individual wheels, or based on the axle torques of both axles, or based on one axle torque and two wheel torques. Thus, wheel-specific wheel torque specifications, or at least axle-specific axle torque specifications, are determined for all wheels.

[0014] According to the method, a motor torque specification is calculated for each of the one or more drive motors based on one or more wheel torque specifications and / or axle torque specifications. After calculating the wheel torques or axle torques, the calculation is then converted to the motor level.

[0015] The calculation of wheel torque specifications for individual wheels or axle torque specifications for individual axles allows the implementation of an initially generic torque structure, whereby the torque structure is initially independent of the specific drive concept used, and the wheel torque specifications and axle torque specifications are only later mapped to the motors used in the drive concept. This takes into account the increasing complexity of the drive concepts used with multiple motors (e.g., an internal combustion engine and two or three electric motors). For example, the motor vehicle can comprise an internal combustion engine and an electric motor as drive motors, with the internal combustion engine and the electric motor driving different axles or wheels of the motor vehicle.

[0016] The torque structure based on wheel torques or axle torques offers the advantage of being completely independent of any drive concept, the number, and type of drive units. This allows the functional basis for any drive concept to be created from the perspective of the torque structure, and the interface to vehicle dynamics control systems or energy-related operating strategies can be set up accordingly.

[0017] The method according to the invention enables engine intervention by vehicle dynamics control systems (e.g., DSC - Dynamic Stability Control, ASR - Traction Control, or ABS - Anti-lock Braking System) with respect to the respective individual wheel (when calculating the respective wheel torque specification) or at least with respect to the respective axle in the torque structure. Preferably, at least one wheel torque specification or one axle torque specification can be determined for this purpose depending on the information from one or more vehicle dynamics control systems. For example, the wheel torque or axle torque can be limited upwards or downwards depending on such information.

[0018] The method allows for any torque distribution to the wheels (when calculating the corresponding wheel torques) or axles (when calculating the corresponding axle torques). A negative torque for energy recuperation can also be specified for a single axle (or for both wheels of that axle) when using at least one electric motor to drive that axle, while a positive drive torque is specified for the other axle.

[0019] The motor vehicle preferably comprises at least one electric motor for driving one of the axles, which can also be operated as a generator for charging an electrical energy source. In this case, one or more axle torque specifications are preferably determined as a function of a charging power specification, which indicates a desired charging power for the electric motor or for the axle driven by the electric motor.

[0020] To determine one or more engine torque specifications, several wheel torque specifications for wheels on the same axle can be combined. Based on the combination of wheel torque specifications, the engine torque specification for the first drive motor and the engine torque specification for the second drive motor can be determined in a motor vehicle with two drive motors driving the same axle.

[0021] A second aspect of the invention is directed to a device for determining at least one engine torque specification in a motor vehicle with two axles, two wheels per axle, and multiple drive motors. The device can, in particular, be part of an engine control unit. The device comprises means for determining a total torque specification as a function of an accelerator pedal signal characteristic of the position of the accelerator pedal or a signal from a system influencing the vehicle's longitudinal movement. The device comprises means for determining, for each axle, an axle torque specification related to the respective axle, wherein the total torque specification is distributed between the two axles as a function of at least one torque distribution specification.The device comprises means for determining, for each wheel of at least one first axle, preferably both axles, a wheel torque specification related to the respective wheel as a function of the determined axle torque specification of the respective axle.

[0022] The device comprises means for determining an engine torque specification for the respective drive motor as a function of the determined wheel torque specification for each wheel of the first axle and as a function of either the determined wheel torque specification for each wheel of the second axle, if the respective wheel-related wheel torque specifications are determined for both axles, or the axle torque specification related to the second axle, if the respective wheel-related wheel torque specifications are determined only for the first axle. For each wheel of at least the first axle, preferably both axles, the respective wheel torque specification related to the respective wheel is limited upwards and downwards as a function of information from one or more vehicle dynamics control systems.The axle torque specification related to the second axle is limited upwards and downwards depending on the information from one or more vehicle dynamics control systems if the respective wheel-related wheel torque specifications are determined only for the first axle.

[0023] The above statements regarding the method according to the invention according to the first aspect of the invention also apply correspondingly to the device according to the invention according to the second aspect of the invention.

[0024] The invention is described below with reference to several exemplary embodiments and with reference to the accompanying drawings. In these drawings: Fig. 1 shows a first exemplary embodiment for determining engine torque specifications in a motor vehicle with an internal combustion engine and three electric drive motors; and Fig. 2 shows a second exemplary embodiment for determining engine torque specifications in a motor vehicle with an internal combustion engine and two electric drive motors.

[0025] Fig. 1 shows a first example of a torque structure according to the invention, wherein the motor vehicle comprises both an internal combustion engine VM and an electric motor EM3 for driving the rear axle. An electric motor EM1 and EM2, respectively, are provided to drive the left and right wheels of the front axle. The electric motors EM1 and EM2 are preferably wheel hub motors.

[0026] In addition to the actual calculation path for calculating the torque specifications, there is also a modeling block 30, in which, among other things, actual values ​​and control limits are calculated, as well as a block 31 for implementing the operating strategy. In modeling block 30, both the currently set torques and the potentials for a minimum and maximum of the individual actuating units are calculated. These potentials can be used to ensure that the required torques are within the control range of the drive units.

[0027] Depending on the accelerator pedal position indicated by signal 32, a driver command torque M_driver is calculated in an accelerator pedal interpreter 1, particularly taking the vehicle speed into account. The driver command torque M_driver can, for example, be a total wheel torque for all four wheels.

[0028] Furthermore, an optional interface 2 to a driver assistance system influencing the vehicle's longitudinal movement (for example cruise control or adaptive cruise control) is provided, which provides a torque specification M_FAS of the driver assistance system.

[0029] In stage 3, either the driver's desired torque M_Driver or the torque M_FAS of the driver assistance system is selected. Interfaces from the modeling 30 of the overall vehicle and the operating strategy 31 enable the required total wheel torque or its dynamic curve to be influenced depending on various influencing factors, such as environmental conditions, operating states of the drive units, and / or drivetrain configurations.

[0030] The resulting output torque MDR_GES of stage 3 is then distributed in axle distribution stage 4 depending on a torque distribution specification 5 (e.g. 40% front axle and 60% rear axle) to the front axle and the rear axle; in Fig. 1 The resulting axle torque of the front axle is designated M_VA and the resulting axle torque of the rear axle is designated M_HA.

[0031] Furthermore, it can be provided that the two electric machines EM1 and EM2 of the front axle can be operated as generators to charge an electrical energy source, while the vehicle is driven via the rear axle. Fig. 1 The input variable P_LAD shown describes a charging power specification for the two electric motors. The axle torque specifications M_VA and M_HA are adjusted depending on the charging power specification P_LAD.

[0032] In the Fig. 1 In stages 6 and 7 shown, wheel torque specifications for the two wheels of the front axle and wheel torque specifications for the two wheels of the rear axle are calculated from the axle torque specification M_VA of the front axle and the axle torque specification M_HA of the rear axle. Due to the different actuation speeds of the required torques on the two axles, there is an optional option to temporarily compensate for the difference between the required and ultimately actuated torque of the dynamically slower axle on the faster axle.

[0033] Stages 8-11 are used to limit the wheel torques to specified individual wheel-related maximum torque values ​​Md_max,rad per wheel and individual wheel-related minimum torque values ​​Md_min,rad per wheel, which are supplied by one or more driving dynamics control systems (e.g. DSC - Dynamic Stability Control, ASR - Traction Control or ABS - Anti-lock Braking System).

[0034] A further limitation to the dynamically quickly adjustable unit limits is implemented in the optional stages 12-15. The outputs of stages 12-15 result in the individual wheel-specific wheel torque specifications M_VL, M_VR, M_HL, M_HR of the front left wheel, the front right wheel, the rear left wheel, and the rear right wheel, respectively.

[0035] Starting from stage 16, the wheel torque specifications (i.e. M_VL, M_VR, M_HL, M_HR) are transformed into engine torque specifications (see M_EM1, M_EM2, M_VM, M_EM3) for the individual motors EM1, EM2, VM and EM3. In stage 16, the wheel torque specifications M_VL and M_VR are translated directly into transmission input-side engine torque specifications MJEM1 and M_EM2 for the electric motors EM1 and EM2 by multiplying them by the transmission ratio. Furthermore, in stage 16, the wheel torque specifications M_HL and M_HR for the rear axle wheels are combined by addition. Furthermore, the combination of both wheel torque specifications is transformed into a transmission input torque M_GW for the shared transmission of the combustion engine VM and the electric machine EM3 by multiplying them by the transmission ratio.

[0036] In the torque distribution stage 17, the transmission input torque M_GW is divided into an engine torque specification M_VM for the combustion engine VM and an engine torque specification M_EM3 for the electric machine EM3 depending on a control signal 18.

[0037] The engine torque specification M_VM of the combustion engine VM results in engine parameters 19 (e.g. ignition timing, injection timing, injection quantity, etc.) for the operation of the combustion engine VM.

[0038] The engine torque specifications M_EM1, M_EM2, M_VM and M_EM3 can also be limited to maximum and minimum torque values ​​20 specified by the unit 30.

[0039] Instead of a drive concept with a combustion engine VM and an electric motor EM3 to drive the rear axle, and with two electric motors EM1 and EM2 to drive the front axle, an alternative drive concept can use the combustion engine VM and the electric motor EM3 to drive the front axle, and the electric motors EM1 and EM2 to drive the rear axle. The above statements apply accordingly to this case, with the front and rear axles being interchanged.

[0040] Fig. 2 shows a second example of a torque structure according to the invention, wherein the motor vehicle comprises both an internal combustion engine VM and an electric machine EM3 for driving the rear axle. In contrast to Fig. 1 a single electric machine EM1 is provided.

[0041] The above statements on Fig. 1 largely also apply to Fig. 2 In contrast to the moment structure in Fig. 1 are in Fig. 2 through stage 16, the wheel torque specifications M_VL and M_VR of the wheels of the front axle are combined and transformed into a transmission input-side engine torque specification M_EM1 for the electric machine EM1, taking the transmission ratio into account.

[0042] Instead of a drive concept with a combustion engine (VM) and an electric motor (EM3) to drive the rear axle, and a single electric motor (EM1) to drive the front axle, an alternative drive concept can use the combustion engine (VM) and the electric motor (EM3) to drive the front axle, and the electric motor (EM1) to drive the rear axle. The above statements apply accordingly to this case, with the front and rear axles being interchanged.

[0043] The Fig. 2The torque structure shown can be further simplified by using only one internal combustion engine to drive the rear axle instead of one internal combustion engine VM and one electric motor EM3. In this case, distribution stage 17 is omitted. Of course, the front and rear axles can also be swapped in this case, with the front axle being driven by the internal combustion engine VM and the rear axle by the electric motor EM1.

Claims

1. Method for determining at least one motor torque specification (M_EM1, M_EM2, M_VM, M_EM3) for each of several drive motors (EM1, EM2, EM3, VM) in a motor vehicle having two axles and two wheels per axle, comprising the steps of: - determining a total torque specification (MDR_GES) depending on an accelerator pedal signal (32) characteristic of the position of the accelerator pedal or on a signal (M_FAS) of a system influencing the longitudinal movement of the vehicle; - determining for each axle a respective axle torque specification (M_VA, M_HA) based on the respective axle, wherein the total torque specification (MDR_GES) is distributed to the two axles depending on at least one torque distribution indication (5); - determining for each wheel of at least a first axle, preferably both axles, a respective wheel torque specification (M_VL, M_VR, M_HL, M_HR) based on the respective wheel depending on the determined axle torque specification (M_VA, M_HA) of the respective axle; and - determining a motor torque specification (M_EM1, M_EM2, M_VM, M_EM3) for the respective drive motor (EM1, EM2, VM, EM3) depending on the determined wheel torque specification (M_VL, M_VR, M_HL, M_HR) for each wheel of the first axle and depending on either the determined wheel torque specification (M_VL, M_VR, M_HL, M_HR) for each wheel of the second axle if the respective wheel-based wheel torque specifications (M_VL, M_VR, M_HL, M_HR) are determined for both axles or the axle torque specification (M_VA, M_HA) based on the second axle if the respective wheel-based wheel torque specifications (M_VL, M_VR, M_HL, M_HR) are determined only for the first axle; characterized in that - for each wheel of at least the first axle, preferably both axles, the respective wheel torque specification (M_VL, M_VR, M_HL, M_HR) based on the respective wheel is upwardly and downwardly limited depending on information from one or more vehicle movement dynamics control systems (Md_max, rad; Md_min,rad), and - the axle torque specification based on the second axle is upwardly and downwardly limited depending on the information from the one or more vehicle movement dynamics control systems (Md_max,rad; Md_min,rad) if the respective wheel-based wheel torque specifications (M_VL, M_VR, M_HL, M_HR) are determined only for the first axle.

2. Method according to Claim 1, wherein - the motor vehicle, for driving one of the axles, comprises at least one electric machine (EM1, EM2, EM3), which can also be operated as a generator for charging an electrical energy source, and - one or more axle torque specifications (M_VA, M_HA) are determined depending on a charging power indication (P_LAD), which indicates a desired charging power for the electric machine or for the axle which can be driven by the electric machine.

3. Method according to Claim 1 or 2, wherein several wheel torque specifications (M_HL, M_HR) for wheels of the same axle are combined with another for determining one or more motor torque specifications (M_VM, M_EM3).

4. Method according to Claim 3, wherein - the motor vehicle comprises at least one first drive motor (VM) and one second drive motor (EM3) for driving the same axle, and - the motor torque specification (M_VM) for the first drive motor (VM) and the motor torque specification (M_EM3) for the second drive motor (M_EM3) are determined depending on the combination of the several wheel torque specifications (M_HL, M_HR).

5. Method according to one of the preceding claims, wherein - the motor vehicle comprises, as drive motors, an internal combustion engine (VM) and an electric machine (EM1, EM2), and - the internal combustion engine and the electric machine drive different axles or wheels of the motor vehicle.

6. Device for determining at least one motor torque specification (M_EM1, M_EM2, M_VM, M_EM3) for each of several drive motors (EM1, EM2, EM3, VM) in a motor vehicle having two axles and two wheels per axle, comprising: - means for determining a total torque specification (MDR_GES) depending on an accelerator pedal signal (32) characteristic of the position of the accelerator pedal or on a signal (M_FAS) of a system influencing the longitudinal movement of the vehicle; - means for determining for each axle a respective axle torque specification (M_VA, M_HA) based on the respective axle, wherein the total torque specification (MDR_GES) is distributed to the two axles depending on at least one torque distribution indication (5); - means for determining for each wheel of at least a first axle, preferably both axles, a respective wheel torque specification (M_VL, M_VR, M_HL, M_HR) based on the respective wheel depending on the determined axle torque specification (M_VA, M_HA) of the respective axle; and - means for determining a motor torque specification (M_EM1, M_EM2, M_VM, M_EM3) for the respective drive motor (EM1, EM2, VM, EM3) depending on the determined wheel torque specification (M_VL, M_VR, M_HL, M_HR) for each wheel of the first axle and depending on either the determined wheel torque specification (M_VL, M_VR, M_HL, M_HR) for each wheel of the second axle if the respective wheel-based wheel torque specifications (M_ VL, M_VR, M_HL, M_HR) are determined for both axles or the axle torque specification (M_VA, M_HA) based on the second axle if the respective wheel-based wheel torque specifications (M_VL, M_VR, M_HL, M_HR) are determined only for the first axle; characterized in that - for each wheel of at least the first axle, preferably both axles, the respective wheel torque specification (M_VL, M_VR, M_HL, M_HR) based on the respective wheel is upwardly and downwardly limited depending on information from one or more vehicle movement dynamics control systems (Md_max,rad; Md_min,rad), and - the axle torque specification based on the second axle is upwardly and downwardly limited depending on the information from the one or more vehicle movement dynamics control systems (Md_max,rad; Md_min,rad) if the respective wheel-based wheel torque specifications (M_VL, M_VR, M_HL, M_HR) are determined only for the first axle.