Drive system

Abstract

This driving system controls torques to be outputted to a first shaft and a second shaft and is provided with an electronic control apparatus which comprises: a first speed sensor configured to measure the rotation speed of the first shaft; a second speed sensor configured to measure the rotation 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 a storage device that is electrically connected to the first and second speed sensors and to the first and second output devices and that stores at least one bias ratio value. The electronic control apparatus is configured to: acquire a target torque value; determine the difference in rotation speed of the first shaft with respect to the second shaft; determine a sign on the basis of the determined difference in rotation speed and the target torque value; read one value from the storage device; calculate a first distribution ratio to be distributed to the first shaft and a second distribution ratio to be distributed to the second shaft on the basis of the read value and the determined sign; and control the first output device and the second output device so as to output torques obtained by multiplying the calculated first and second distribution ratios by the target torque value.

Description

[Technical Field]

[0001] The following disclosure relates to a drive system that is used in a vehicle equipped with multiple power sources and controls the torque output to shafts corresponding to each of the power sources. [Background technology]

[0002] In conventional vehicles, torque generated by a single power source is distributed to multiple drive wheels, for example, by a differential.

[0003] Without a differential limit, when one shaft spins freely, it cannot output torque to the other shaft. Therefore, differentials often have a mechanism to limit or temporarily stop the differential. A mechanism that limits the differential, for example, by friction, is often called a limited slip differential (LSD), and a mechanism in which the differential limiting force changes dynamically depending on the input torque is called a torque-sensitive LSD. A mechanism in which the limiting force is controlled by a mechanical mechanism is called a mechanical LSD, and a mechanism that uses an electronic control device is called an electronically controlled LSD.

[0004] Patent Documents 1 and 2 disclose related techniques. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Patent Application Publication WO2010 / 078937A1 [Patent Document 2] International Patent Application Publication WO2020 / 129400A1 Summary of the Invention

[0006] Unlike gasoline engines, electric vehicles have relatively small power sources, allowing for a power source to be placed at each drive wheel. Because torque can be controlled individually for each drive wheel, torque control makes it easier to prevent understeer and oversteer, and also makes it possible to achieve behaviors that are difficult to achieve with conventional vehicles, such as torque vectoring. However, for drivers who are particularly skilled at driving conventional vehicles, the occurrence of unintended behavior does not necessarily translate into ease of driving, and they may even find the behavior of a conventional powertrain using an LSD more preferable.

[0007] The system disclosed below is a vehicle drive system with multiple power sources, yet achieves behavior similar to a power system that uses an LSD.

[0008] According to one aspect, a drive system for controlling torques output to a first shaft and a second shaft, respectively, includes 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 device electrically connected to the first and second speed sensors and the first and second output devices, the electronic control device storing one or more differential torque ratio values, wherein the electronic control device stores one or more differential torque ratio values, and the target torque is calculated based on the calculated differential torque ratios. and an electronic control device configured to control the first output device and the second output device to respectively output torques obtained by multiplying the calculated first and second distribution ratios by the target torque value, obtaining a torque value from the storage device, determining a rotational speed difference of the first shaft with respect to the second shaft, determining a sign from the determined rotational speed difference and the target torque value, reading a value from the storage device, calculating a first distribution ratio to be distributed to the first shaft and a second distribution ratio to be distributed to the second shaft from the read value and the determined sign. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 1 is a diagram showing a schematic diagram of an example of a vehicle to which a drive system according to this embodiment is applied, in which the right and left rear axles are driven by respective power sources. [Figure 2] FIG. 2 is a schematic diagram showing an example in which the front axle is driven by a motor. [Figure 3] FIG. 3 is a schematic diagram showing an example in which the drive system controls the front power source and the rear power source. [Figure 4] FIG. 4 is a schematic diagram showing an example in which the drive system controls a front power source and a rear power source, and the front power source is an engine. [Figure 5] FIG. 5 is a schematic diagram showing an example in which all axles are driven by their own power sources. [Figure 6] FIG. 6 is a cross-sectional view of an example of a gear arrangement used when one motor drives both axles. [Figure 7] FIG. 7 is a diagram showing the torques that should be generated on the inner and outer wheels when the vehicle turns a curve, and shows the driving state in which the vehicle is driven forward. [Figure 8] FIG. 8 is a diagram showing the torques that should be generated on the inside and outside wheels when a vehicle turns a curve, and shows a coasting state in which the vehicle moves forward by inertia. [Figure 9] FIG. 9 is a diagram that schematically shows the calculations performed by the electronic control unit. [Figure 10] FIG. 10 is a graph showing an example of a function used for input conversion. [Figure 11] FIG. 11 is a flowchart of the calculations and controls executed in the electronic control unit. DETAILED DESCRIPTION OF THE INVENTION

[0010] Some exemplary embodiments are described below with reference to the accompanying drawings.

[0011] For example, referring to FIG. 1 , the drive system according to this embodiment can be applied to a vehicle 1 in which the right and left rear axles are each driven by a separate output device 7. The drive system controls the torque output to each of the right and left axles. In this case, the front axle may be a non-drive axle, or may be driven by a power source 3 such as an engine or a hybrid system equipped with both an engine and an electric motor. The power source 3 is combined with a gear system including a transmission 5 that transmits torque to the front axle. Alternatively, the drive system can be applied to a vehicle in which the front axle, instead of the rear axle, is driven by a separate output device 7. Alternatively, as shown in FIG. 2 , the front axle may be driven by an electric system 9 equipped with an electric motor.

[0012] Alternatively, instead of controlling the torque output to the right and left axles, the front and rear axles may each be equipped with a power source, and the drive system may be used to adjust the torque output to the front and rear axles by controlling the front and rear power sources. Figure 3 shows an example of such a vehicle 1, in which both the front and rear axles are driven by an electric system 9. Alternatively, this embodiment can also be applied to a vehicle in which one of the front and rear axles is driven by a power source 3 equipped with an engine or both an engine and an electric motor.

[0013] Alternatively, as illustrated in FIG. 5, the drive system according to this embodiment can be used to control the torque of the right front axle and the left axle in addition to the right rear axle and the left rear axle, that is, all axles.

[0014] Referring to any of Figures 1 to 5, each ECU includes a storage device that stores commands and data, and a microcontroller that can read these commands from the storage device and execute them. A typical vehicle includes dozens of ECUs, but Figures 1 to 5 show only six of them. These ECUs 13 to 17 read the status of each part of the vehicle using various sensors and are connected to each other via a bus 19. The ECUs 13 to 17 communicate and share information, for example, via a so-called controlled area network (CAN). This information includes not only the read status but also requests to other ECUs, and each ECU uses this information to control each part of the vehicle.

[0015] The ECU 13 is electrically connected to, for example, the console, steering, accelerator pedal, brake pedal, etc., and receives inputs from the driver through these and controls them. Of course, instead of using a single ECU, independent ECUs may be responsible for information acquisition and control. The vehicle 1 also has multiple speed sensors 11 that measure the rotational speed of each axle, and the ECU 15, for example, is electrically connected to these sensors and receives their outputs to calculate the rotational speed. The ECU 17, for example, is electrically connected to the power source 3, transmission 5, output device 7, and / or electric system 9 and controls their operation.

[0016] 6, the electric system 9 includes, for example, an electric motor 23, a reduction gear set 25 that reduces the rotation generated by the electric motor 23 before transmitting it, and a differential 27 that distributes torque to both axles. The output device 7 has a similar configuration and includes an electric motor and a reduction gear set, but does not include the differential 27, and the reduction gear set directly meshes with the gear portion of the output shaft. Here, the reduction gear set 25 is not essential, but is advantageous for increasing the output of the electric motor 23. The entire electric system 9 or the entire output device 7 can be housed in a single casing 21, or one or more of these elements may be separate.

[0017] The electric motor 23 is, for example, a known inverter-driven motor, and when power is input to the coil, it generates torque around the shaft according to the input, causing the rotor shaft 31 to rotate. The rotor shaft 31 can be a hollow shaft, and can be arranged coaxially with the differential 27, with one axle extending through the hollow 31H. Such a coaxial arrangement is advantageous for reducing the overall dimensions of the electric system 9. Of course, the electric motor 23 and both axles may have different axes. Gear teeth are formed near the end of the rotor shaft 31, and rotation is output to the reduction gear set 25 via this gear portion 31G.

[0018] The reduction gear set 25 includes, for example, a gear shaft 35 having gear portions 33 and 35G. The gear portion 33 meshes with the gear portion 31G of the rotor shaft 31, and the gear portion 35G meshes with the gear portion 37 of the differential 27. The gear portion 33 can have a larger diameter than the gear portion 35G, so that the reduction gear set 25 can output a rotation that has been reduced in speed (i.e., increased in power).

[0019] The differential 27 includes a casing 41 having a gear portion 37 on its outer circumferential surface and supporting a differential gear set therein. The differential gear set includes a pair of side gears 43R and 43L, each of which has an engaging means such as a spline on its inner surface and is coupled to the right and left rear axles, respectively. In other words, the differential 27 receives torque via the gear portion 37 and distributes the torque to the right and left rear axles via the side gears 43R and 43L.

[0020] Although not essential in this embodiment, the casing 41 may be composed of an outer casing 41A and an inner casing 41B that is coaxial with the outer casing 41A and can rotate relatively thereto. When the actuator 29 is driven to engage the inner casing 41B with the outer casing 41A, the two rotate together and transmit torque to the differential gear set. When they are disengaged, torque is not transmitted.

[0021] 7 to 10, the torque control mode in the drive system according to this embodiment will be described. In the following description, torque distribution to the left and right axles will be exemplified, but it goes without saying that the following description also applies to torque distribution to the front and rear axles.

[0022] When the vehicle is moving forward (drive) with the power source exerting driving force in the forward direction, if the driver turns the steering wheel, for example, to the left, the vehicle will follow the path shown by the arrow DT, as shown in Figure 7. At this time, the left rear wheel rotates at a slower speed than the right inner wheel. In a conventional powertrain using an LSD, the torque T distributed to the left rear wheel is L is the torque T distributed to the right rear wheel R When simulating this, the torque distribution rate is calculated as the virtual lock rate f LSD It can be calculated based on the following.

[0023] Referring mainly to Figure 9, torque T R Torque T L If the ratio of these factors is defined as the differential torque ratio TBR, then the virtual locking ratio f required to achieve the target TBR is LSD is expressed by the formula (TBR-1) / (TBR+1). Therefore, the torque distribution ratio to the left rear wheel LH Ratio is 1 / 2(1+f LSD ) and the torque distribution ratio to the right rear wheel RH Ratio is 1 / 2(1-f LSD ) and the target torque value T FrRg The values obtained by multiplying these by are the torques to be output to the left and right rear wheels, respectively, and the sum of these is the target torque value T FrRg Matches.

[0024] As can be easily understood, when the vehicle turns to the right, the torque distribution ratio is reversed, and the torque distribution ratio to the left rear wheel is LH Ratio is 1 / 2(1-f LSD ) and the torque distribution ratio to the right rear wheel RH Ratio is 1 / 2(1+f LSD )

[0025] Whether the vehicle is turning right or left can be determined by the steering direction, or by the difference in rotational speed between the right and left axles ΔN RL It can also be determined by the sign of ΔN RL When turning left, ΔN RL >0, and when moving straight, ΔN RL =0, and when turning right, ΔN RL <0, and when these are converted into signed binary values and reflected in the value of k (k=1, 0, -1), the torque distribution ratio to the left rear wheel F LSD is 1 / 2(1+k·f LSD ) (in the right column of Figure 9). That is, LH Ratio =1 / 2(1+k f LSD ) and RH Ratio =1 / 2(1-k f LSD )

[0026] On the other hand, as shown in Figure 8, when the vehicle is coasting, the engine brake or regenerative brake is usually activated, and the torque T L ,T R The direction of the torque is reversed (the sign is reversed), and the magnitude is also reversed. Whether the vehicle is in drive mode or coast mode depends on the target torque value T FrRg The sign reversal due to drive / coast can be determined by the torque distribution ratio F LSD The rotational speed difference ΔN RL and the target torque value T FrRg The product of and can be converted into a signed binary value and reflected in the value of k (k=1, 0, -1) (upper center of Figure 9).

[0027] Also, different differential torque ratios TBR can be used depending on whether the vehicle is in drive or coast mode. Drive ,TBR Coast In other words, referring to the bottom left of FIG. 9, the target torque value T FrRg When is a positive value, the forward TBR Drive is used as the TBR, and when it is negative, it is used as the reverse TBR. Coastcan be adopted as the TBR. Forward TBR Drive and reverse TBR Coast For example, the forward TBR can be set to a different optimal value. Drive = 2.7 and reverse TBR Coast =2.3, but of course it is not limited to these.

[0028] By the way, ΔN RL and T FrRg When is close to 0, even a slight disturbance can cause the sign to change. This can lead to a sudden change in the value of k, which can cause the behavior of the drive system to become unstable. RL and T FrRg One or both of the values may be filtered, such as by a low-pass filter, to remove noise. Alternatively, or in addition, the values may be transformed by a suitable function to smooth out sudden changes in sign. Figure 10 shows an example of such a function, the so-called hyperbolic tangent function.

[0029] The ECU 17 can obtain the values necessary for the above judgments and calculations at any time through CAN communication via the bus 19. The calculated distribution ratio LH Ratio , R.H. Ratio The value of the target torque value T FrRg The ECU 17 controls the left and right output devices 7 so as to output the torque obtained by multiplying the torque by .times. ...

[0030] In the above explanation, the torque output to both drive shafts is controlled, and the sum of the torques is set to the target torque value T FrRg Each motor is controlled to match the rotational speed of the drive wheels. When torque is distributed by a differential, if there is no slip on the drive wheels, the average peripheral speed of both drive wheels should match the vehicle speed. If only the output torque is controlled and the rotational speed of each motor deviates from this constraint, the vehicle may behave in an unexpected manner by the driver. Therefore, in addition to controlling the torque of each motor, the rotational speed of each motor may also be controlled.

[0031] Furthermore, the rotational speed of both drive wheels may be controlled to limit the difference in rotational speed, or both drive wheels may be controlled to rotate at the same speed under certain conditions. These methods more closely simulate the behavior of an LSD and are advantageous for preventing wheel spin, for example.

[0032] The rotation speed control may be performed constantly or only under specific conditions. In the former case, it is possible to control the rotation speed so that it remains within a range by setting appropriate upper and lower limits for the rotation speed that satisfies the constraints imposed by the vehicle speed. In the latter case, it is possible to set appropriate conditions and limit the rotation speed only when the conditions are satisfied, or to switch to rotation speed control instead of torque control.

[0033] The vehicle speed may be calculated from the average value of the outputs of the speed sensors 11 on the left and right drive axles, or may be calculated using the average value of the outputs of the speed sensors 11 on all axles. Alternatively, other appropriate values, such as the integrated value of the outputs of the acceleration sensors, may be referenced. These values can also be acquired by the ECU 17 at any time through CAN communication via the bus 19.

[0034] Since the above-described calculations are routine, they can be performed by an independent calculation circuit without relying on the ECU 17. That is, under the control of the ECU 17, an external calculation circuit may execute the above-described calculations.

[0035] The control procedure by the ECU 17 will be described with reference to Figure 11. First, the ECU 17 acquires numerical values such as the target torque and the rotational speed of each axle using CAN communication or the like. From these numerical values, the ECU 17 calculates the target torque, determines the direction the vehicle is turning, and determines whether to drive or coast. Next, the ECU 17 determines the sign from the numerical values such as the rotational speed difference and reflects it in the value of k. Next, the ECU 17 determines TBR by selecting it from a pre-stored data table or according to set conditions. Using these, the ECU 17 calculates a virtual lock ratio, and then calculates the torque distribution ratio to both shafts from the calculated virtual lock ratio. The ECU 17 adjusts the power applied to the motor so that the torque obtained by multiplying the calculated torque distribution ratio by the target torque value is output to the output device of each shaft. These procedures are constantly repeated.

[0036] According to the above-described embodiment, even in a vehicle in which a power source is provided for each drive wheel, the torque of each drive wheel can be controlled so that the vehicle behaves similarly to a conventional vehicle. It is possible to provide a driving experience that is natural even to drivers who are accustomed to driving conventional vehicles. Furthermore, since the parameters to be adjusted correspond to the parameters of conventional vehicles, it is convenient to utilize knowledge gained in the design of conventional vehicles. In other words, this embodiment is also advantageous in terms of ease of vehicle design.

[0037] Although several embodiments have been described, modifications or variations of the embodiments can be made based on the above disclosure.

Claims

1. A drive system that controls torque output to a first shaft and a second shaft, respectively, comprising: a first speed sensor configured to measure a rotational speed of the first shaft; a second speed sensor configured to measure the 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; an electronic control device electrically connected to the first and second speed sensors and the first and second output devices, and including a storage device that stores one or more differential torque ratio values, the electronic control device being configured to: acquire a target torque value; determine a rotational speed difference of the first shaft with respect to the second shaft; determine a sign from the determined rotational speed difference and the target torque value; read a value from the storage device; calculate a first distribution ratio to be distributed to the first shaft and a second distribution ratio to be distributed to the second shaft from the read value and the determined sign; and control the first output device and the second output device to output torques obtained by multiplying the calculated first and second distribution ratios by the target torque value, respectively; A drive system with

2. 2. The drive system of claim 1, wherein the first output device comprises a first electric motor electrically connected to the electronic control device and a reduction gear set that reduces the rotation generated by the first electric motor and transmits the reduced rotation to the first shaft, and the second output device comprises a second electric motor electrically connected to the electronic control device and a reduction gear set that reduces the rotation generated by the second electric motor and transmits the reduced rotation to the second shaft.

3. 2. The drive system of claim 1, wherein the electronic control device is configured to calculate the first distribution ratio based on the formula 1 / 2{1+k(TBR-1 / TBR+1)} and the second distribution ratio based on the formula 1 / 2{1-k(TBR-1 / TBR+1)}, where TBR is the read value and k is the determined sign.

4. 2. The drive system of claim 1, wherein the storage device stores two or more differential torque ratio values, and the electronic control device is configured to select and read one of the stored values depending on the sign of the target torque value.

5. 2. The drive system of claim 1, wherein the electronic control device is configured to adopt the sign of a result obtained by multiplying the determined rotational speed difference by the target torque value as the determined sign.

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