drive system

Abstract

A drive system for controlling torque output to a first shaft and a second shaft is provided with: a first speed sensor configured to measure the rotational speed of the first shaft; a second speed sensor configured to measure the rotational speed of the second shaft; a first output device coupled to the first shaft; a second output device coupled to the second shaft; and an electronic control unit electrically connected to the first and second speed sensors and the first and second output devices, and containing a memory unit that stores one or more values ​​of differential torque ratios, wherein the electronic control unit is configured to retrieve a target torque value, determine a difference in the rotational speed of the first shaft relative to the second shaft,a character is determined from the specified difference in rotational speed and the target torque value, one of the values ​​is retrieved from the storage unit, a first distribution ratio in which the torque is to be distributed to the first shaft and a second distribution ratio in which the torque is to be distributed to the second shaft are calculated from the retrieved value and the determined character, and a control is carried out to cause the first output device to output a torque obtained by multiplying the calculated first distribution ratio by the target torque value, and to cause the second output device to output a torque obtained by multiplying the calculated second distribution ratio by the target torque value.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a drive system used in a vehicle having a plurality of power sources for controlling the torque output to the shafts associated with the power sources, respectively. STATE OF THE ART

[0002] In a conventional vehicle, torque generated by a power or drive source is distributed among several drive wheels. A differential, for example, is used for distribution.

[0003] A differential without a limiting force cannot transfer torque to the other shaft if one of the shafts is rotating freely. Therefore, differentials are often equipped with a mechanism to limit or temporarily stop the limiting force. A mechanism that limits the limiting force using a frictional means is often called a limited-slip differential (LSD), and in particular, such a mechanism that can dynamically change the limiting force depending on the input torque is called a torque-sensing limited-slip differential (LSD). A limited-slip differential (LSD) with a mechanical device for controlling the limiting force can be called a mechanical limited-slip differential, and a limited-slip differential (LSD) with an electronic control unit can be called an electronic limited-slip differential.

[0004] Patent Literatures 1 and 2 disclose the related prior art. Citation listPatent literature PTL 1: International PCT Publication WO 2010 / 078937 A1 PTL 2: International PCT Publication WO 2020 / 129400 A1 SUMMARY OF THE INVENTION

[0005] In an electric vehicle, the power source is relatively compact compared to a vehicle with an internal combustion engine, so each drive wheel can be equipped with an independent power or drive source. Since torque control can be performed for each drive wheel, understeer and oversteer can be easily prevented with appropriate torque control, or special driving behaviors that are hardly possible in a conventional vehicle, such as torque vectoring, can be realized. However, a driver who is well-versed in driving a conventional vehicle, if they encounter behavior that contradicts their intention, would have difficulty experiencing a comfortable drive and might prefer behavior achieved by a drive system with a conventional limited-slip differential.

[0006] The system disclosed below, although directed to a drive system for a vehicle having a plurality of drive sources, realizes a similar behavior to a drive system with a conventional limited-slip differential.

[0007] According to one aspect, a drive system used to control the torque output to a first shaft and a second shaft, respectively, is provided with: a first speed sensor configured to measure a speed of the first shaft; a second speed sensor configured to measure a speed of the second shaft; a first output device drivingly coupled to the first shaft; a second output device drivingly coupled to the second shaft; and an electronic control unit electrically connected to the first and second speed sensors and the first and second output devices and including a storage unit storing one or more values ​​of differential torque ratios, wherein the electronic control unit is configured to retrieve a desired torque value, determine a difference in the speed of the first shaft relative to the second shaft,determines a sign from the determined difference in the rotational speed and the target torque value, retrieves one of the values ​​from the storage unit, calculates a first distribution ratio in which the torque is to be distributed to the first shaft and a second distribution ratio in which the torque is to be distributed to the second shaft from the retrieved value and the determined sign, and performs control to cause the first output device to output a torque obtained by multiplying the calculated first distribution ratio by the torque target value and to cause the second output device to output a torque obtained by multiplying the calculated second distribution ratio by the torque target value. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing an example of a vehicle to which a drive system according to the present embodiment is applied, in which the right and left rear axles are driven independently by respective power sources. Fig. Figure 2 is a schematic drawing showing an example where the front axle is also driven by a motor. Fig. Figure 3 is a schematic drawing showing an example where the drive system controls both power sources at the front and rear. Fig. 4 is a schematic diagram showing an example in which a drive system controls both a front and a rear front power source, and in which the front power source is an internal combustion engine. Fig. Figure 5 is a schematic drawing showing an example where all axles are driven independently by respective power sources. Fig. 6 is a sectional view of a transmission according to an embodiment used for a case where one motor drives both axles. Fig. 7 is a diagram schematically showing the torque to be generated at the inner and outer wheels when the vehicle turns, showing a running state in which the vehicle is driven forward. Fig. 8 is a diagram schematically showing the torque to be generated at the inner and outer wheels when the vehicle turns, showing a roll or push state in which the vehicle rolls freely forward. Fig. Figure 9 is a diagram schematically showing the arithmetic operations of an electronic control unit. Fig. Figure 10 is a graph showing an example of a function used to convert an input variable. Fig. 11 is a flowchart of the arithmetic operations and controls performed by the electronic control unit. DESCRIPTION OF THE EMBODIMENTS

[0008] Exemplary embodiments are described below with reference to the accompanying drawings.

[0009] Referring to Fig. 1, a drive system according to the present embodiment is applicable or usable, for example, in a vehicle 1 in which the right and left rear wheels are each driven by independently equipped output devices 7. The drive system controls the torque output to the right and left axles, respectively. The front wheels can in this case either be undriven or they can be driven by a power source 3 with an internal combustion engine or a hybrid system comprising an internal combustion engine and an electric motor. Combined with the drive or power source 3 is a transmission system with a transmission 5 for transmitting torque to the front axles. Alternatively, the drive system can be used for a vehicle in which the front axles are driven by independently equipped output devices 7 instead of the rear axles. Further alternatively, as in Fig. 2, the front axles can be driven by an electric drive system 9 with an electric motor.

[0010] The drive system can be used to control torques delivered to the right and left axles respectively, but instead also to control torques delivered to the front and rear axles by controlling front and rear drive sources when the front axles and rear axles are each equipped with independent drive sources. Fig. Figure 3 shows an example of such a vehicle 1 in which electric drive systems 9 drive both the front and rear axles. Alternatively, the present embodiment is applicable to a vehicle in which either the front axles or the rear axles are driven by a power source 3 comprising an internal combustion engine, or an internal combustion engine and an electric motor.

[0011] According to another alternative, as in Fig. 5, the drive system according to the present embodiment can also be used for torque control of the right and left front axles and the right and left rear axles, that is, all axles.

[0012] With reference to one of the Fig. 1 to 5, each electronic control unit (ECU) is equipped with a memory unit that stores commands and data, and a microcontroller that can read these commands and execute them. The number of electronic control units (ECUs) in a typical vehicle can be several dozen or more, but the Fig. Figures 1 to 5 show only 6 ECUs each. These ECUs 13-17 read the states of the respective vehicle elements and are connected to each other via a bus line or bus 19. The ECUs 13-17 communicate with each other or exchange information, for example, via a so-called controller area network (CAN). The information contains not only the read states but also requests or queries to other ECUs, and the respective ECUs use this information to control the corresponding elements of the vehicle.

[0013] The ECU 13 is electrically connected to, for example, a console, a steering system, an accelerator pedal, a brake pedal, etc., and reads and controls the driver's inputs. It should be understood that information acquisition and control are not limited to a single ECU; rather, multiple ECUs can perform this task for multiple elements. The vehicle 1 is further equipped with a plurality of speed sensors 11 for measuring the speeds of the respective axles, and the ECU 15 is electrically connected to these sensors, for example, to read their output values ​​and calculate the speeds. The ECU 17 is electrically connected to, for example, the power source 3, the transmission 5, the output devices 7, and / or the electric drive system 9, and controls these processes.

[0014] Referring to Fig. 6, the electric drive system 9 is equipped, for example, with an electric motor 23, a reduction gear 25 for transmitting the rotary motion generated by the electric motor 23 while reducing the speed, and a differential 27 for distributing torque to both axles. The output device 7 has a similar configuration with an electric motor and a reduction gear, but without a differential 27, and the reduction gear is directly meshed with a gear portion of the output shaft. In this case, the reduction gear 25 is not essential but is advantageous for multiplying the power output by the electric motor 23. The entire unit of the electric drive system 9 or the output device 7 can be housed or accommodated in a single housing 21, although one or more elements can also be separate from it.

[0015] The electric motor 23 is, for example, a well-known inverter-controlled motor and, when electrical energy is supplied to its coil, generates a torque about an axis corresponding to the supply to rotate a rotor shaft 31. The rotor shaft 31 can be a hollow shaft and arranged coaxially with the differential 27 so that one of the axes can pass through the hollow space 31H. The coaxial arrangement is advantageous for reducing the overall size of the electric drive system 9. It is understood that the electric motor 23 and these axes can also have no common axis instead. The rotor shaft 31 is provided with a toothing at its end and transmits the rotary motion to the reduction gear 25 via this gear section 31G.

[0016] The reduction gear set 25 is provided, for example, with a gear shaft 35 having gear portions 33, 35G. The gear portion 33 meshes with the gear portion 31G of the rotor shaft 31, and the gear portion 35G meshes with a gear portion 37 of the differential 27. The gear portion 33 may have a larger diameter than the gear portion 35G, so that the reduction gear 25 can output or transmit the rotational movement at a reduced speed (i.e., with increased power).

[0017] The differential 27 is provided with the gear portion 37, e.g., on its outer periphery, and a housing 41 that supports a differential gear set inside. The differential gear set is provided with a pair of side gears 43R, 43L, each provided with engagement means, such as splines, and thereby coupled to the right rear axle and the left rear axle. More specifically, the differential 27 distributes the torque received via the gear portion 37 to the right rear axle and the left rear axle, respectively, via the side gears 43R, 43L.

[0018] Although not essential in the present embodiment, the housing 41 may be composed of an outer housing 41A and a coaxial and relatively rotatable inner housing 41B. When an actuator is actuated to engage the inner housing 41B with the outer housing 41A, these housings rotate together, transmitting torque to the differential gear set. In the disengaged state, torque is not transmitted.

[0019] With reference to the Fig. 7 to 10, torque control modes in the drive system according to the present embodiment will be described below. While the following description refers to an example of torque distribution to the right and left axles, the description can of course also apply to cases of torque distribution to the front and rear axles.

[0020] If the power source generates a driving force in the forward direction and the vehicle moves forward (DRIVE), and the driver turns the steering wheel, for example, to the left, as in Fig. 7, the vehicle follows a path such as that shown by the arrow DT. The left rear wheel then rotates at a lower speed than the right, inside wheel. In a conventional drive system with a limited-slip differential (LSD), the torque acting on the left rear wheel is T L greater than the torque T acting on the right rear wheel R . Using an appropriate simulation, a torque distribution ratio can be calculated from a hypothetical locking rate in a hypothetical limited-slip differential (LSD).

[0021] With particular reference to Fig. 9, if a ratio of the torque T L to torque T Ris defined as the torque balance ratio TBR, a hypothetical locking rate F LSD required to achieve a TBR target value is represented by a formula (TBR-1) / (TBR+1). A torque distribution ratio LH Ratio the torque distribution to the left rear wheel is 1 / 2(1+f LSD ) and a torque distribution ratio RH Ratio on the right rear wheel is 1 / 2(1-f LSD ). By multiplying these ratios with the torque setpoint T FrRg one obtains values ​​for the torques that must be delivered to the left and right rear wheels, respectively, and the sum of these values ​​naturally corresponds to the torque target value T FrRg .

[0022] It is understood that the torque distribution ratios are reversed when the vehicle turns or drives to the right, so that the torque distribution ratio LH Ratio to the left rear wheel 1 / 2(1-f LSD) and a torque distribution ratio RH Ratio to the right rear wheel 1 / 2(1+F LSD ) amounts.

[0023] Whether the vehicle is turning or driving to the right or left can be determined by the direction of rotation of the steering wheel, or alternatively by a sign or signum of a speed difference ΔN RL between the right and left axes. For example, with reference to ΔN RL In the case of a left turn ΔN RL > 0, in the case of straight-ahead driving ΔN RL = 0 and for the case of a right turn ΔN RL < 0. If these values ​​are converted into signed binary numbers and then expressed in the value k (k=1, 0, -1), the ratio of the torque distribution F LSD on the left rear wheel as 1 / 2(1 + k · f LSD ) (see column or box on the right in Fig. 9). More precisely, this results in the formulas LH Ratio =1 / 2(1+k·f LSD ) and RHRatio =1 / 2(1-k·f LSD ).

[0024] In contrast, in a case where the vehicle rolls forward (COAST), as in Fig. 8, normally engine braking or regenerative braking occurs, and the directions of the torque T L , T R are reversed (the signs are inverted), and the magnitudes are also inverted. Whether it is a drive state or a coast state can be determined from the sign of the torque setpoint T FrRg To ensure that the sign reversal of drive / rollers in the torque distribution ratio F LSD reflects, a product of the speed difference ΔN RL multiplied by the torque setpoint T FrRg converted into a signed binary value and then represented in the value k (k = 1, 0, -1) (see the upper middle of Fig. 9).

[0025] In addition, it is possible to assume different torque compensation ratios TBR, depending on whether a drive state or a coast state is present. The ECU 17 can therefore accept a variety of different values ​​of TBR. Drive , TBR Coast and accept or use one of them, depending on whether it is in the drive state or coast state. More precisely, referring to the lower left side of Fig. 9, the forward direction TBR Drive be assumed as TBR if the target torque value T FrRg has a positive value, and the reverse direction TBR Coast can be assumed as TBR if the target torque value T FrRg has a negative value. Independent optimal values ​​can be used as forward direction TBR Drive or as reverse direction TBR Coast According to an example of such a set, the forward direction TBRDrive = 2.7 and the reverse direction TBR Coast = 2.3, without being limited to it.

[0026] However, if one of the values ​​of ΔN RL and T FrRg are close to 0, a small disturbance can lead to a change in the sign of these values. This can lead to a rapid change in the value k and thus to instability in the behavior of the drive system. Therefore, one or both of the values ​​ΔN RL and T FrRg filtered through a low-pass filter or similar to remove noise. Instead, or in addition, the values ​​can be converted into other values ​​using a suitable (mathematical) function, so that rapid changes in the values ​​can be smoothed out. Fig. Figure 10 shows as an example a function which is a so-called hyperbolic tangent function.

[0027] The ECU 17 can retrieve all values ​​required for the aforementioned determinations and calculations at any time via CAN communication on bus 19. The ECU 17 controls the left and right output devices 7 so that the devices output a torque resulting from the multiplication of the calculated distribution ratios LH Ratio , RH Ratio with the torque setpoint T FrRg results.

[0028] In the above description, the torque delivered to the two drive axles is regulated and the respective motors are controlled so that their sum corresponds to the torque setpoint T FrRgHowever, if torque is distributed via a differential, the average rotational speed of the two drive wheels must match the vehicle speed when the drive wheels have no slip. If only the output torque is controlled and the speeds of the respective motors deviate from this specification, the vehicle could behave in a way that the driver could not have foreseen. Therefore, in addition to controlling the torque, the speeds of the respective motors can also be controlled.

[0029] In addition, the control may include an additional speed control that limits the speed difference between the two drive wheels, or an additional control that ensures that the speeds of the drive wheels are equal under a specific condition. These controls improve the simulation of a limited-slip differential (LSD) and are beneficial, for example, for preventing wheel spin.

[0030] Speed ​​control can occur regularly or be limited under certain conditions. In the former case, for example, the control can be performed such that the speed is maintained within suitable upper and lower limits relative to a specific speed that satisfies the constraint imposed by the vehicle speed. In the latter case, a specific condition can be specified in advance, and only when the condition is met can the speed be limited, or torque control switched to speed control.

[0031] The vehicle speed can be calculated from an average of the output signals of the speed sensors 11 on the right and left drive axles, or it can be determined by using an average of the output signals of the speed sensors 11 on all wheels. Alternatively, other suitable values, such as integral values ​​determined from acceleration sensor outputs, can be used. The ECU 17 can also periodically retrieve these values ​​via CAN communication on bus 19.

[0032] Since the aforementioned calculations can be performed in a fixed manner, they can also be performed not by the ECU 17, but by any independent calculation circuit. More specifically, the calculations can be performed by an external calculation circuit under the control of the ECU 17.

[0033] A process for control by the ECU 17 will be described below with reference to Fig.11. The ECU 17 first uses CAN communication to retrieve various values ​​such as the target torque and the rotational speeds of the respective axles. The ECU 17 next calculates a target torque from these values ​​and determines a direction in which the vehicle is turning or traveling and whether it is in a drive state or a coast state. The ECU 17 next determines a sign from the values, such as the difference in rotational speeds, and reflects the determined sign in the value k. The ECU 17 next determines the torque balance ratio (TBR) by selecting it from a pre-stored data table or in accordance with the predetermined condition. The ECU uses these values ​​to calculate a hypothetical lock rate and to calculate a torque distribution ratio for the shafts from the calculated hypothetical lock rate.The ECU 17 controls the electrical power supplied to the motors so that the output devices of the associated shafts deliver the torques resulting from multiplying the calculated torque distribution ratio by the target torque value. This process would be repeated regularly.

[0034] According to the aforementioned embodiment, even in a vehicle in which each drive wheel is equipped with an independent power source, the torque at each drive wheel can be controlled in a manner consistent with the behavior of a conventional vehicle. This embodiment can provide a good driving experience to a driver who is familiar with a conventional vehicle. Since the parameters to be controlled are completely consistent with those of conventional vehicles, this is advantageous for the practical utilization of knowledge gained in the design of conventional vehicles, or more specifically, the present embodiment is advantageous in terms of simplicity of vehicle design.

[0035] Although certain exemplary embodiments are described above, modifications and variations of the embodiments will be apparent to those skilled in the art in light of the above teachings. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2010 / 078937 A1

[0004] WO 2020 / 129400 A1

[0004]

Claims

[1] A drive system used to control the transmission of torque to a first and a second shaft, comprising: a first speed sensor configured to measure a rotational speed of the first shaft; a second speed sensor configured to measure a rotational speed of the second shaft; a first output device drivingly coupled to the first shaft; a second output device drivingly coupled to the second shaft; and an electronic control unit electrically connected to the first and second speed sensors and the first and second output devices and including a storage unit storing one or more values ​​of differential torque ratios, the electronic control unit being configured to retrieve a target torque value, determine a difference in the rotational speed of the first shaft relative to the second shaft, determine a sign from the determined difference in rotational speed and the target torque value, retrieve one of the values ​​from the storage unit, calculate a first distribution ratio in which the torque is to be distributed to the first shaft and a second distribution ratio in which the torque is to be distributed to the second shaft from the retrieved value and the determined sign, and perform control to cause the first output device to output a torque,which is obtained by multiplying the calculated first distribution ratio by the target torque value, and causing the second output device to output a torque obtained by multiplying the calculated second distribution ratio by the target torque value. [2] The drive system according to claim 1, wherein the first output device comprises a first electric motor electrically connected to the electronic control unit and a reduction gear set configured to transmit a rotational motion generated by the first electric motor to the first shaft, thereby reducing a rotational speed, and the second output device comprises a second electric motor electrically connected to the electronic control unit and a reduction gear set configured to transmit a rotational motion generated by the second electric motor to the second shaft, thereby reducing a rotational speed. [3] The drive system according to claim 1, wherein the electronic control unit is configured to calculate the first distribution ratio based on a formula 1 / 2{1+k(TBR-1 / TBR+1)} and calculate the second distribution ratio based on a formula 1 / 2{1-k(TBR-1 / TBR+1)}, where TBR represents the retrieved value and k represents the detected character. [4] A drive system according to claim 1, wherein the storage unit stores two or more values ​​of the differential torque ratios, and the electronic control unit is configured to select and retrieve one of the stored values ​​in accordance with a sign of the target torque value. [5] The drive system according to claim 1, wherein the electronic control unit is configured to adopt, as the determined sign, a sign of a result obtained by multiplying the target torque value by the determined speed difference.

Images