Method for matching torque requirements of multiple drive units of a motor vehicle

Abstract

Method (200) for matching torque requirements of several drive units (105, 110) of a motor vehicle (100), comprising the following steps: - Requesting (202) a first torque from a first drive unit (105) and a second torque from at least one second drive unit (110) to drive the motor vehicle; - Determining (225) that a first deviation between requested and delivered torque of the first drive unit (105) is less than a second deviation of the second drive unit (110); - Adapting (230) the requested torque from the second drive unit (105) to the torque of the first drive unit (110); - wherein the first and the second deviations are determined from, and thus on the basis of, average deviations of a plurality of identical drive units (105, 110), determined analytically or empirically, characterized in thatthat- the first drive unit (105) comprises an internal combustion engine and the second drive unit (110) comprises an electric motor,- the first and second deviations at different load points and the influence of a boundary condition (420) on the respective deviation are known, wherein the boundary condition (420) for the internal combustion engine and the electric motor comprises a temperature of the respective drive unit (105, 110) and an ambient temperature, wherein the boundary condition (420) for the internal combustion engine further comprises an air pressure, wherein the boundary condition (420) for the electric motor further comprises an operating voltage, and- the respective deviation is determined on the basis of an applicable load point, which is determined by a requested torque (410) and a speed (415) of the respective drive unit, and on the basis of the applicable boundary condition, such thatthat, based on the torque (410) and the rotational speed (415), the respective deviation between requested and delivered torque is determined via a characteristic map (405), and that the influence of the respective boundary condition (420) on the respective deviation between requested and delivered torque is taken into account via a characteristic curve (425), wherein the respective characteristic curve (425) assigns a factor to the respective boundary condition (420), which is multiplied by a multiplier (430) or by an adder term with the deviation between requested and delivered torque determined via the characteristic map (405).

Description

The invention relates to a method for balancing drive units in a motor vehicle that can be moved by means of several drive units. A hybrid vehicle is equipped with several drive units, preferably combining an internal combustion engine and an electric motor. An electric motor can contribute positive or negative torque to propel the vehicle. For example, a hybrid vehicle might have an internal combustion engine and an electric motor, both of which drive the vehicle's wheels. In another example, each front and rear axle of the vehicle can be assigned its own electric motor, resulting in a total of three drive units. In particular, one electric motor can also be used to decelerate the vehicle, converting its kinetic energy into electrical energy. This energy can be stored for later use in powering the vehicle. Such a system is called a recuperator. A control unit for a motor vehicle with multiple drive units typically requests a predetermined torque from one or more of the drive units to fulfill a requested power output. The power output can be controlled, in particular, by a driver input, which expresses the desired degree of acceleration or deceleration, for example, via an accelerator pedal. In another embodiment, a driver assistance system, such as automatic cruise control, can also request a predetermined power or torque at the drive units of the motor vehicle. The control unit then translates this request into a specific torque demand from the drive units. However, there is usually a difference between the target torque requested by a drive unit and the actual torque it delivers. These discrepancies can accumulate when multiple drive units are controlled to deliver positive or negative torque. DE 10 2008 009 430 A1 discloses a method for operating a hybrid drive system with an internal combustion engine and an electric drive. An adaptation value is used to compensate for a difference between a requested target torque and a delivered actual torque. DE 103 33 931 A1 discloses a method for controlling an electromechanically power-split hybrid drive of a motor vehicle with an internal combustion engine and two electric machines coupled by a transmission. DE 10 2010 012 153 A1 discloses a method for operating a vehicle according to the preamble of claim 1 with two electric motor individual wheel drive systems for one axle of the vehicle. The target torque to be provided at the axle is distributed equally between the two wheels of the axle. Component and manufacturing tolerances are taken into account in this distribution. The two target torques are corrected by means of a calculated balancing factor. The balancing factor is calculated on the basis of a measured yaw rate or a detected yaw moment. The object of the present invention is to provide a method for improved balancing of the torque requirements of several drive units of a motor vehicle. The invention achieves this object by means of a method with the features of the independent claim. The dependent claim describes a preferred embodiment. A method according to the invention for matching the torque requirements of several drive units of a motor vehicle comprises the following steps: Requesting a first torque from a first drive unit and a second torque from a second drive unit to propel the motor vehicle, wherein one of the drive units comprises an internal combustion engine and another of the drive units comprises an electric motor. Determining that a first deviation between the requested and delivered torque of the first drive unit is less than a second deviation of the second drive unit. Adapting the following torque requirements from the second drive unit to the first drive unit.The first and second deviations are determined from, and thus on the basis of, average, analytically or empirically determined deviations of a large number of identical drive units, such that the first and second deviations at different load points and an influence of a boundary condition on the respective deviation are known, whereby the respective deviation is determined on the basis of a valid load point and on the basis of a valid boundary condition. According to the invention, the controllability of the motor vehicle, which may be determined, for example, based on the shift quality of a transmission with gear ratios, drivability, or other parameters, can be improved. It can prevent differences between requested and supplied torque from accumulating at the individual drive units. It can also prevent the control systems of the individual drive units from working against each other. By adapting the drive unit exhibiting the larger control deviation to the one with the smaller or smallest control deviation, the overall control error can be minimized. This simplifies the control of the drive units. Adaptation can involve steps such as changing the requirement for the first torque by a predetermined amount, changing the requirement for the second torque to maintain a constant vehicle speed, determining the difference between these changes, and adjusting subsequent torque requirements to the second drive unit by this determined difference. The deviation of the first drive unit can thus be considered zero, and the second drive unit can be adapted to the first. This process can be performed quickly and with minimal effort while the vehicle is moving at a predetermined speed. The torques and their changes can be positive or negative. According to claim 1, the deviations at various load points are known, and the respective deviation is determined based on a valid load point. This allows the first drive unit to be adapted to the second, or vice versa, depending on the operating mode of the vehicle. For more than two drive units, a corresponding procedure is performed, whereby all drive units are adapted to the one with the smallest deviation. According to claim 1, the load point is determined by a requested torque and a rotational speed of the drive unit. This allows the most important load parameters of the drive units to be taken into account. According to claim 1, the influence of a boundary condition on the respective deviation is further known, and the deviation is determined on the basis of an applicable boundary condition. This allows the deviation to be determined even more precisely. According to claim 1, the boundary condition for the internal combustion engine and the electric motor comprises an engine temperature and an ambient temperature. For the internal combustion engine, the boundary condition further comprises an atmospheric pressure. For the electric motor, the boundary condition further comprises an operating voltage. Other boundary conditions are possible. The invention will now be described in more detail with reference to the accompanying figures, in which: Fig. 1 shows a motor vehicle with several drive units; Fig. 2 shows a flowchart of a method for balancing torque requirements of the drive units in Fig. 1; Fig. 3 shows a flowchart of a method for balancing torque requirements in the motor vehicle of Fig. 1; and Fig. 4 shows a schematic determination of a deviation between a requested and a delivered torque of one of the drive units in the motor vehicle of Fig. 1. Fig. 1 shows a motor vehicle 100 with a first drive unit 105 and a second drive unit 110. In other embodiments, more than two drive units may be provided. The first drive unit 105 comprises an internal combustion engine, and the second drive unit 110 comprises an electric motor. An electrical energy storage device 115 is preferably provided for exchanging electrical energy with the second, electric drive unit 110. The electric drive unit 110 can provide both positive and negative torque for propelling the motor vehicle 100. Several of the drive units 105, 110 can act simultaneously on the movement of the motor vehicle 100. A control unit 120 is provided for controlling the drive units 105 and 110. The control unit 120 requests a target torque from each of the drive units 105 and 110. The request from the control unit 120 can be based, for example, on the position of an accelerator pedal 125, operated by the driver of the vehicle 100. In another embodiment, the torque requirements of the drive units 105 and 110 can also be determined based on a different signal, for example, a predetermined target speed and / or the actual speed of the vehicle 100. The control unit 120 is connected to a memory 130 in which information about deviations between the requested and provided torque for the drive units 105 and 110 is stored. The control unit 120 is configured to align (adapt) the drive units 105 and 110 with each other in order to model or minimize deviations between the requested target torque and the provided actual torque. For example, if the second drive unit 110 is to deliver a torque of 50 Nm and it is known that the delivered torque is approximately 55 Nm when 50 Nm is requested, the control unit 120 can take the deviation of 5 Nm into account and request a reduced torque of 45 Nm, so that the second drive unit 110 delivers the originally desired torque of 50 Nm. The first drive unit 105 can be adjusted to the second 110, or vice versa. The control unit 120 is configured to first determine, based on the information stored in memory 130, which of the drive units 105, 110 has the smaller deviation. The other drive unit(s) 105, 110 are then adjusted to the one with the smallest deviation. Fig. 2 shows a flowchart of a method 200 for matching torque requirements of the drive units 105, 110 in Fig. 1. The method 200 is particularly designed for implementation on the control unit 120. Torques are requested from the drive units 105 and 110 to move or accelerate the vehicle 100, so that the vehicle 100 is in motion. Each torque can be positive, negative, or zero. In step 205, a load point is determined for each of the drive units 105 and 110. The load point is defined based on a requested torque and a rotational speed. In further embodiments, additional parameters can be used to describe the load point. In step 210, boundary conditions are determined that influence the respective deviation between the requested and delivered torque of the drive units 105, 110. A boundary condition includes the temperature of the respective drive unit 105, 110 and an ambient temperature. For the internal combustion engine, the boundary condition also includes at least an air pressure, and optionally an air temperature or humidity. For the electric motor, the boundary condition also includes an operating voltage. In subsequent steps 215 and 220, deviations between the requested and delivered torque are determined for the drive units 105 and 110, respectively. This determination is carried out based on the determined load points and further taking into account the specified boundary conditions. This determination is explained in more detail below with reference to Fig. 4. In step 225, the drive unit 105, 110 with the smallest deviation between requested and provided torque is determined. In a subsequent step 230, the following torque requirements for all other drive units 105, 110 are adapted based on the drive unit 105, 110 with the smallest deviation. The adaptation process is then described in more detail with reference to Fig. 3. Fig. 3 shows a flowchart of a method 300 for adjusting torque requirements in the motor vehicle 100 of Fig. 1. In a first step 305, it is optionally determined that the motor vehicle 100 moves at a constant speed. This speed can be within a predetermined range, for example between 20 and 50 km / h. In step 310, the requirement for the first torque at the first drive unit 105 is changed by a predetermined amount. The change can be positive or negative. The requested torque can also be 0 before or after the change. In step 315, the requirement for the second torque from the second drive unit 110 is changed, preferably simultaneously with step 310, in order to keep the speed of the vehicle 100 constant. This change is preferably carried out in the form of a control system. In step 320, the difference in the changes to the requested torques of the drive units 105 and 110 is determined. Subsequently, requests for a second torque to the second drive unit 110 are adjusted for the difference determined in step 320. Instead of the procedure of 300, another approach can also be used to match the torque requirements of the drive units 105, 110 in the motor vehicle 100. Fig. 4 shows a schematic determination 400 of a deviation between a requested and a delivered torque of one of the drive units 105, 110 in the motor vehicle 100 of Fig. 1. The determination 400 is particularly designed for the implementation of one of the steps 215 or 220 from Fig. 2. The expected deviation between a requested and a provided torque for one of the drive units 105, 110 is determined using a characteristic map 405 based on one or more parameters that define a load point of the drive unit 105, 110. The load point is defined by a requested torque 410 and a rotational speed 415 of the drive unit 105, 110. Furthermore, a boundary condition 420 is determined, which potentially influences the deviation of the torque of the drive unit 105, 110. This influence is recorded in a characteristic curve 425. The characteristic curve 425 assigns a factor to a value of the boundary condition 420, which is multiplied by the previously determined value for the deviation in a multiplier 430. If the boundary condition 420 has no influence on the deviation, a factor of 1 is assigned. Similarly, further boundary conditions 420 can be successively applied using further characteristic curves 425 and further multipliers 430 to correct the previously determined deviation. Once all boundary conditions 420 have been taken into account, the determined deviation is provided via an interface 435. Instead of the multipliers 430, addition terms or other terms for linear operation can also be used. In a further embodiment, the characteristic map 405 is multidimensional, with one dimension provided for each parameter of the load point and for each boundary condition 420. This allows even nonlinear or otherwise difficult-to-modulate influences of the boundary conditions 420 on the specific deviation to be modeled.

Claims

Method (200) for matching torque requirements of several drive units (105, 110) of a motor vehicle (100), comprising the following steps: - Requesting (202) a first torque from a first drive unit (105) and a second torque from at least one second drive unit (110) to drive the motor vehicle; - Determining (225) that a first deviation between requested and delivered torque of the first drive unit (105) is less than a second deviation of the second drive unit (110); - Adapting (230) the requested torque from the second drive unit (105) to the torque of the first drive unit (110); - wherein the first and the second deviations are determined from, and thus on the basis of, average deviations of a plurality of identical drive units (105, 110), determined analytically or empirically, characterized in thatthat- the first drive unit (105) comprises an internal combustion engine and the second drive unit (110) comprises an electric motor,- the first and second deviations at different load points and the influence of a boundary condition (420) on the respective deviation are known, wherein the boundary condition (420) for the internal combustion engine and the electric motor comprises a temperature of the respective drive unit (105, 110) and an ambient temperature, wherein the boundary condition (420) for the internal combustion engine further comprises an air pressure, wherein the boundary condition (420) for the electric motor further comprises an operating voltage, and- the respective deviation is determined on the basis of an applicable load point, which is determined by a requested torque (410) and a speed (415) of the respective drive unit, and on the basis of the applicable boundary condition, such thatthat, based on the torque (410) and the rotational speed (415), the respective deviation between requested and delivered torque is determined via a characteristic map (405), and that the influence of the respective boundary condition (420) on the respective deviation between requested and delivered torque is taken into account via a characteristic curve (425), wherein the respective characteristic curve (425) assigns a factor to the respective boundary condition (420), which is multiplied by a multiplier (430) or by an adder term with the deviation between requested and delivered torque determined via the characteristic map (405). Method (200) according to claim 1, wherein the adaptation (230) comprises the following steps (300): - Changing (310) the requirement for the first torque by a predetermined amount; - Changing (315) the requirement for the second torque in order to keep the speed of the motor vehicle (100) constant as a result of adjusting the rotational speeds of the drive unit(s); - Determining (320) a difference between the changes in the requirements, and - Adjusting (325) the following torque requirements to the second drive unit (110) by the determined difference.

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