CN116888002A

CN116888002A - Method and device for operating a drive train

Info

Publication number: CN116888002A
Application number: CN202180093842.4A
Authority: CN
Inventors: P·奥博罗夫斯基; F·施伦普
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-12-16
Filing date: 2021-12-07
Publication date: 2023-10-13
Also published as: DE102020215982A1; EP4263269A1; WO2022128601A1

Abstract

The invention relates to a method for operating a drive train of a motor vehicle (1), wherein the drive train has a first axle (3) with a first drive (5) and at least one wheel (7) operatively connected to the first drive (5); and having an axle (2) with a second drive (4) and at least one wheel (6) operatively connected to the second drive (4), wherein the first drive (5) has an electric motor (8), and wherein in a range-extending operating state, the electric motor (8) is normally operated in an idle mode, and the required drive torque is provided by the second drive (4). It is provided that, during the range-extending operating state, a predetermined fraction of the required drive torque is provided by the electric machine (8) in the special case of at least one wheel-specific traction limit of at least one wheel (7) of the second axle (2) being currently exceeded or being expected to be exceeded.

Description

Method and device for operating a drive train

Technical Field

The invention relates to a method for operating a drive train of a motor vehicle, wherein the drive train has: a first axle with a first drive and at least one wheel operatively connected to the first drive; and a second axle having a second drive and at least one wheel operatively connected thereto, wherein the first drive has an electric motor, and wherein, in a range-extending operating state of the drive train, the electric motor normally operates in an idle mode and the second drive provides the required drive torque.

The invention further relates to a device for operating a drive train as described above.

Background

Methods and devices of the type mentioned at the outset are known in the prior art. As the degree of electrification of motor vehicles increases, so too does the types of motor vehicles that employ individual drives for each axle. Drive trains are therefore known, which use an internal combustion engine for driving, for example, at the front wheel axle and an electric motor at the rear wheel axle. All-electric motor vehicles are also known in which only an electric motor is used on both the first axle and the second axle. Due to the limited capacity of the accumulator supplying the electric machine or machines with electric energy, an operating mode is used by which the range of the motor vehicle with the drive train is maximized. For example, a range-extending operating state is known in which the required drive torque is applied by the motor of one axle, while the motor of the other axle is switched off or deactivated and is therefore operated in idle mode. It has been found that the overall efficiency of the drive train is thereby improved and that the range of the motor vehicle can thus be increased.

Disclosure of Invention

The method according to the invention with the features of claim 1 has the following advantages: in the range extension operating state, the driving stability is improved by a simple method. According to the invention, this is achieved by: in special cases, i.e. unlike the normal cases mentioned above, the preset fraction of the required drive torque is provided by the electric motor when at least one wheel-specific traction limit of at least one wheel of the second axle is exceeded or is about to be exceeded. In the range-extending operating state, the electric machine, which is normally closed or is operated in the idle mode, is therefore used in special cases to supply the required drive torque together, and thus the second drive is supported in special cases in such a way that, in particular, the traction limit of the wheels is not exceeded. Thus, when the wheel associated with the second drive is unable to carry out the required drive torque, the electric machine is actuated for carrying out a predetermined fraction of the required drive torque. In general, the driver is thereby still provided with the required drive torque in its entirety, at least in the usual case. In this special case, the range is only slightly reduced compared to the normal case. However, this additional loss is acceptable for further ensured driving stability and better traction of the motor vehicle.

According to a preferred variant of the invention, the electric machine is operated in torque-neutral mode in idle mode. This means that the motor is driven or actuated in such a way that it applies neither a positive nor a negative torque to the drive or to the wheels of the drive. For this purpose, the motor is, if necessary, subjected to a low operating voltage, so that at least the drag losses of the motor are overcome. If the motor has a coupling or is equipped with a coupling, the motor is maneuvered in idle mode in order to disengage the motor from the rim, so that the motor can be operated without current and preferably in order to optimize efficiency further as a whole.

Furthermore, it is preferably provided that the motor is driven in idle mode. As a result, the electric machine remains connected to at least one wheel associated with it and is thereby driven by the wheel during the travel of the motor vehicle and is thereby pulled. In this case, if the motor is designed as a permanently excited synchronous motor, drag losses act on the wheels connected to the motor.

Furthermore, it is preferably provided that the electric machine is mechanically decoupled from at least one wheel of the first axle in the idle mode. As already explained above, a coupling is provided for this purpose, which is connected in particular intermediately between the motor and the wheels of the first axle.

Furthermore, it is preferably provided that in special cases the proportion of the required drive torque which is or should be provided subsequently by the electric motor is preset independently of the wheel-specific traction limit. Such an embodiment of the invention therefore provides that in special cases the torque proportion of the electric machine is determined independently of the traction limit which is actually present. It is particularly preferred if the required drive torque is divided equally between the first drive and the second drive, so that the proportion of the electric motor corresponds to 50% or half of the required drive torque. This provides a simple embodiment, so that the driving stability is further ensured.

According to a further embodiment of the invention, it is preferably provided that, in special cases, the fraction of the required drive torque which is provided by the electric motor is determined as a function of the wheel-specific traction limits of the wheels of the drive train which can be driven by the first drive and the second drive. Thus, according to this embodiment, the traction limits are taken into account, and the required drive torque is allocated or divided for the drive device as a function of these traction limits. In this way, it is achieved, for example, that the traction limits of the wheels of the second drive are not exceeded, but that the traction limits of the wheels of the first drive are not exceeded by the torque fraction now provided by the electric motor. The torque proportion provided by the electric motor is limited or limited, in particular, as a function of the traction limits associated with the wheels of the first drive, in order to avoid that the wheels of the first drive exceed wheel-specific traction limits. The total drive torque of the motor vehicle is thereby reduced if necessary, so that it no longer corresponds to the required drive torque.

It is furthermore preferred that the maximum torque that can be applied to the driving path from the respective wheel is ascertained from the wheel-specific traction limit of at least the second drive, and in particular cases the fraction of the required drive torque that is provided by the electric motor is preset as a function of the difference between the required drive torque and the sum of the maximum torques that can be applied of at least the second drive. This achieves that the first drive takes over and applies a torque which can no longer be applied by the second drive, so that the motor vehicle as a whole is provided with the required drive torque.

In determining the share of the required drive torque, the traction limits of all wheels of the first drive and of the second drive are preferably taken into account. As already explained above, it is thereby also achieved that the torque contribution of the electric machine is preferably reduced when the traction limit of the wheel connected to the electric machine is exceeded or is about to be exceeded.

The wheel-specific traction limit is preferably ascertained by means of a sensor, in particular by means of a wheel-specific sensor of the driving stability assurance device of the motor vehicle. Conventional ESP (esp=electronic stability program) devices, ABS (abs=antilock brake system) devices or ASR (asr=anti-skid control) devices in motor vehicles use wheel-specific sensors in order to recognize whether slip or static friction losses and the resulting traction are or are likely to occur. For this purpose, for example, a rotational speed sensor is used. Alternatively or additionally, at least one acceleration sensor is used, which is read by a controller, in particular a central controller. Thereby, axle loads on the front and rear wheel axles are calculated by means of the model. The axle load is proportional to the traction limit, whereby the traction limit is detected in a simple manner. Unlike the wheel speed sensors used in ESP systems, the traction limit is more easily detected here, since the accuracy of the measurement is not as important as in ESP systems. Furthermore, at least one environmental factor concerning the surroundings of the motor vehicle is preferably taken into account, for example, the driving road characteristics, the weather conditions and/or the ambient temperature of the motor vehicle are monitored and incorporated into the determination of the traction limit. In this case, the redistribution of the drive torque required for traction reasons is preferably provided in addition to the driving stability control device and its intervention, so that it is not an alternative to an ESP system, an ABS system or an ASR system. The traction limit is calculated in particular with a simple model or is obtained by the ESP controller of the motor vehicle.

The device according to the invention having the features of claim 10 is characterized in that it has a specially designed controller which is designed to carry out the method according to the invention in the case of a defined use. The advantages already mentioned are thus obtained.

Drawings

Further advantages and preferred features and combinations of features emerge from the description above and the claims. The invention is explained in detail below with the aid of the drawing. Wherein:

fig. 1 shows a motor vehicle in a simplified plan view;

fig. 2 shows a flow chart for illustrating an advantageous method for operating a drive train of the motor vehicle from fig. 1.

Detailed Description

Fig. 1 shows a simplified plan view of a motor vehicle 1, which in the present case is designed as an electric vehicle. For this purpose, the motor vehicle 1 has two axles 2 and 3 which can be driven and each have a drive 4, 5 and each have at least two wheels 6 or 7 which are connected to the respective drive. The wheels 6, 7 are either directly coupled to the respective drive 4, 5 or are connected with a transmission and/or a coupling. The second axle 3 is in this embodiment a rear axle of the motor vehicle 1, the drive unit 5 of which second axle has an electric motor 8 as drive unit. In this exemplary embodiment, the drive 4 likewise has an electric motor 9 as a drive motor.

The controller 10 controls the motors 8, 9 in accordance with the required driving torque to drive the motor vehicle 1 and applies the required driving torque to the running road through the wheels 6, 7. For this purpose, the control unit 10 is connected to a device 11, which ascertains the required drive torque and transmits it to the control unit 10. The device 11 is, for example, an accelerator pedal of the motor vehicle 1, a driving computer of an automated or autonomous driving system of the motor vehicle 1, or another regulating means by means of which a driver or user of the motor vehicle 1 can request or preset a driving torque.

The control unit 10 is furthermore connected to a control unit 12 of a driving stability system of the motor vehicle 1, in particular an ESP system. Each wheel 6, 7 of the motor vehicle 1 is assigned a rotational speed sensor 13 of the driving stability system and is connected to the controller 12. The driving stability system or control unit 12 is designed to detect a slip or impending slip of the wheels 6, 7 during continuous operation. The traction limits of the individual wheels 6, 7 are thus ascertained, in particular by the controller 10. In this context, the term "traction limit" is understood to mean the maximum torque that can be applied to the driving path by the respective wheel under the current and/or expected driving situation. When its traction limit is exceeded, the wheels begin to slip. For example, when the motor vehicle 1 passes from a dry driving path to a wet driving path, the respective traction limit can be varied according to the varying environmental conditions and road conditions, independently of the torque actually applied to the respective wheel 6, 7. If the traction limit or the maximum torque that can be applied is exceeded, the wheel in question loses its static friction with respect to the driving path, so that it slips and therefore no longer transmits additional torque and no longer transmits lateral guidance forces to the motor vehicle, or only a reduced amount.

In order to maximize the range of the electric vehicle, the controller 10, in the range-extended operating state, actuates the motors 8, 9 in such a way that normally only the motor 9 of the axle 2 is actuated for applying torque to the driving path by means of the wheels 6 for driving the motor vehicle 1, while the motor 8 of the axle 3 is operated in an energy-saving manner in the idle mode.

The electric machine 8 is therefore operated in a torque-neutral manner, for example in the range of the range-extending operating state, so that even if it is operated as a motor, it is operated with such a low torque that the friction forces in particular in the electric machine 8 itself or in the axle 3 are overcome overall, and in particular no negative or positive drive torque is transmitted to the driving path via the wheels 7.

According to an alternative embodiment, the motor 8 is towed in idle mode, so that the mechanical losses of the motor 8 and the axle 3 are generally overcome together by the torque provided by the motor 4.

According to another embodiment, there is a coupling between the motor 8 and the wheel 7, which is opened in the idle mode, so that the wheel 7 is mechanically decoupled from the drive 5.

Fig. 2 shows a flow chart by means of which an advantageous method for operating the motor vehicle 1 is described below, by means of which traction losses at the wheels 6, 7 are advantageously avoided.

The method starts in step S1 when a user or device 10 requests a driving torque. In the next step S2, it is checked whether the vehicle is in the range extension operation state. For example, if the capacity of the electrical energy store of the motor vehicle is below a preset limit value, the range extension operating state is preferably automatically set. Alternatively, the range extension operating state is set in accordance with a user selection of the operating mode by the motor vehicle 1. If the range extension operating state does not exist (n), the method begins from scratch. However, if the query in step S2 indicates that the range extension operating state (j) is set, it is checked in a subsequent query S3 whether the traction limit of one of the wheels 6, 7 is exceeded or is about to be exceeded.

As previously mentioned, the wheel specific traction limits are provided, inter alia, by the controller 12 and are preferably continuously updated. In this case, the traction limit of the wheels 6 of the front wheel axle 2 is monitored in the present case and compared with the required torque. If the torque transmitted to the wheel 6 by the motor 9 is below the traction limit (n) of the wheel 6, the method continues in step S1. However, if one of the current traction limits is exceeded or is about to be exceeded (j), then in a next step S4 it is determined that there is a special case of a range extension operating state. In this particular case, the requirement for using only the drive device 4 for generating drive torque is at least temporarily canceled in order to prevent traction losses on the wheels 6 of the axle 2. For this purpose, in step S5, the proportion of the requested torque that should be provided by the motor 5 of the axle 3 is ascertained. The total required drive torque is thus divided over the two axles 2, 3 and the torque provided by the motor 5 is subtracted from the torque to be provided by the drive 4, whereby the drive torque is reduced on the wheels 6 of the axles 2 and the corresponding traction limits of the wheels 6 are thereby complied with or not exceeded. Therefore, the torque provided at the wheels 6 is below the maximum torque that can be applied, thereby reliably preventing traction loss.

The proportion of the drive torque to be provided or to be provided by the drive 5 of the axle 3 can be ascertained in different ways described below. According to the first embodiment, in a following step S6, the share of the drive torque provided by the electric motor 8 is preset in a manner independent of the wheel-specific traction limit. Therefore, the drive torque is divided into the axles 2, 3 in a fixed and predetermined manner. It is particularly preferred that the required drive torque is divided equally between the two axles 2, 3, so that the respective drive 4 or 5 respectively carries out or supplies 50% of the required power or the required drive torque.

According to another embodiment, in a step S7 following step S5, the fraction of the required drive torque that should be provided by the electric motor 8 is determined as a function of at least the wheel-specific traction limit of the wheels 6 of the drive device 4. By taking into account wheel-specific traction limits, the share of the drive torque for the electric motor 8 can be embodied in such a way that, for example, emphasis is placed on the implementation of special cases in an energy-saving manner, so that, for example, only the share of the drive torque cannot be taken over by the electric motor 5 on the wheels of the axle 2 in relation to the traction limit. The method provides, in particular, that the maximum torque that can be applied to the driving path by the respective wheel 6 is ascertained from the wheel-specific traction limit of at least the wheel 6, and in special cases the fraction of the required drive torque that is provided by the electric motor 8 is preset as a function of the difference between the required drive torque and the sum of the maximum torques that can be applied by the wheels 6 of at least the second drive. In particular, the proportion of the drive torque of the motor 8 corresponds to the aforementioned difference. This results in an excess torque fraction exceeding the traction limit of the wheel 6 being tapped just by the motor 8 and transferred to the wheel 7.

Particularly preferably, the traction limits of all wheels 6, 7 of the first and second drive 4, 5 are taken into account when determining the share of the required drive torque for the electric machine 8. As a result, for example, the drive torque provided by the motor 5 can also be influenced by the traction limits of the wheels 7. It is thus provided in particular that the fraction of the drive torque provided by the electric motor 5 is limited by the traction limits of the wheels 7 or the maximum torque that can be applied if the traction limits of the wheels 7 are exceeded. In this case, the proportion is preferably limited independently of the required drive torque, so that in the event that the entire required drive torque cannot be applied due to the traction limit on the wheels 6, 7, the drive torque is reduced overall in order to maintain the traction limit.

Claims

1. A method for operating a drive train of a motor vehicle (1), wherein the drive train has a first axle (3) with a first drive (5) and at least one wheel (7) operatively connected to the first drive (5); and having an axle (2) with a second drive (4) and at least one wheel (6) operatively connected to the second drive (4), wherein the first drive (5) has an electric motor (8), and wherein in a range-extending operating state, the electric motor (8) is normally operated in an idle mode and a required drive torque is provided by the second drive (4), characterized in that during the range-extending operating state, a preset fraction of the required drive torque is provided by the electric motor (8) in the special case in which at least one wheel-specific traction limit of at least one wheel (7) of the second axle (2) is currently exceeded or is expected to be exceeded.

2. Method according to claim 1, characterized in that in the idle mode the motor (8) is operated in a torque neutral manner.

3. Method according to claim 1, characterized in that in the idle mode the motor (8) is dragged.

4. Method according to claim 1, characterized in that in the idle mode the electric motor (8) is mechanically decoupled from at least one wheel (7) of the first axle (3).

5. Method according to any of the preceding claims, characterized in that in the special case the fraction of the required drive torque provided by the electric machine (8) is preset independently of the wheel-specific traction limit.

6. Method according to any of the preceding claims, characterized in that in special cases the fraction of the required drive torque provided by the electric machine (8) is determined as a function of at least the wheel-specific traction limit of the drive train of the wheel (6) drivable by the second drive means (5).

7. Method according to any of the preceding claims, characterized in that the maximum torque that can be applied by the respective wheel (6) on the road of travel is ascertained from the wheel-specific traction limit of at least the second drive (4), and in special cases the fraction of the required drive torque that is provided by the electric motor (8) is preset as a function of the difference between the required drive torque and the sum of the maximum torques that can be applied of at least the second drive (4).

8. Method according to claim 7, characterized in that the traction limits of all wheels (6, 7) of the first and second drive means (4, 5) are taken into account when determining the share of the required drive torque.

9. Method according to any of the preceding claims, characterized in that the wheel-specific traction limit is ascertained by means of a sensor, in particular by means of a wheel-specific sensor (13) of a driving stability assurance device of a motor vehicle.

10. Device for operating a drive train, characterized by a specially designed controller (10) which is designed to carry out the method having the features of any one of claims 1 to 9 when used as intended.