Front-rear torque distribution control device for four wheel drive vehicle

Abstract

To maintain the traveling performance of a four wheel drive vehicle as good as possible by increasing the degree of freedom in selecting the torque distribution ratio of front and rear wheels.SOLUTION: A front-rear torque distribution control device for a four-wheel drive vehicle in which rotor shafts of front and rear drive motors are rotatably supported by rolling bearings, and a resonance range which is a predetermined bandwidth including a resonance point determined by rigidity of the rolling bearings of a drive system including the rolling bearings changes according to torque of the rotor shafts, the front-rear torque distribution control device comprising: The controller includes a drive torque setting unit (step S5) configured to set a drive torque of the front wheel drive motor and a drive torque of the rear wheel drive motor at a predetermined speed to a torque having a resonance range in a frequency band outside a frequency band at the predetermined speed and satisfying a torque required for the four wheel drive hybrid vehicle to travel.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a device for controlling a four-wheel drive vehicle that can run by driving each of the two front wheels and the two rear wheels, and in particular to a device for controlling the distribution of the total drive torque required for a four-wheel drive vehicle equipped with a drive motor for the front wheels and a drive motor for the rear wheels to the front wheels and rear wheels. [Background technology]

[0002] An example of a device for controlling driving force in a four-wheel drive vehicle is described in Patent Document 1. The device described in Patent Document 1 is intended to suppress vibrations associated with driving the vehicle, and is configured so that when resonance occurs in the vibration system extending from the front-side drive unit to the front wheels, the drive force used to drive the front wheels by the front-wheel drive unit is reduced, and the resulting lack of drive force is compensated for by increasing the drive force of the rear-wheel drive unit. Conversely, when resonance occurs on the rear wheel side, the drive force of the rear-wheel drive unit is reduced, and the drive force of the front-wheel drive unit is increased. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-041003 Summary of the Invention [Problem to be solved by the invention]

[0004] As described in Patent Document 1, the magnitude of the vibration forcing force generated in a power transmission system, including a drive shaft, corresponds to the output torque of the drive unit, which is the source of the driving force. Therefore, the device described in Patent Document 1 reduces the forcing force by reducing the driving force output by the drive unit when resonance is detected or predicted. In other words, while the device described in Patent Document 1 can reduce the forcing force, it cannot avoid resonance itself, which may restrict the driving of a four-wheel drive vehicle. For example, if the driving force of one of the front and rear wheels is reduced and the driving force of the other wheel is increased to compensate for the reduced driving force, the distribution ratio of the total driving torque required by the vehicle to the front and rear wheels may significantly deviate from the distribution ratio desired for the current driving conditions, potentially impairing driving stability, driving performance, or off-road capability.

[0005] The present invention has been made in light of the above-mentioned technical problems, and aims to provide a front / rear torque distribution control device that increases the degree of freedom in selecting the front / rear wheel torque distribution ratio and can maintain the driving performance of a four-wheel drive vehicle as good as possible. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a front / rear torque distribution control device for a four-wheel drive vehicle in which the rotor shafts of a drive motor for the front wheels and a drive motor for the rear wheels are rotatably supported by rolling bearings, and a resonance range, which is a predetermined bandwidth including a resonance point determined by the rigidity of the rolling bearings in a drive system including the rolling bearings, changes according to the torque of the rotor shafts, the device comprising: a controller that controls the drive torque provided by the drive motor for the front wheels and the drive torque provided by the drive motor for the rear wheels out of the drive torque required for the four-wheel drive vehicle to travel; and the controller is characterized by comprising a drive torque setting unit that sets the drive torque provided by the drive motor for the front wheels and the drive motor for the rear wheels at a predetermined vehicle speed to a torque that has a resonance range in a frequency band outside the frequency band at the predetermined vehicle speed and that satisfies the torque required for the vehicle to travel. [Effects of the Invention]

[0007] In the four-wheel drive vehicle of the present invention, the rotor shafts of the front and rear drive motors are supported by rolling bearings, and the drive system, which is composed of the rotor shafts and rolling bearings, has a resonance range that changes depending on the torque of the rotor shaft. When the front and rear drive motors are operated to output drive torque, the drive torque is output, the resonance range being in a frequency band outside the frequency band of the drive system at a predetermined vehicle speed. This makes it possible to avoid or suppress resonance in the vibration system that accompanies the output of drive torque from the front and rear drive motors. Furthermore, as long as the drive torque has a resonance range outside the frequency band of the drive system at the predetermined vehicle speed, the drive torque can be either large or small. This allows for a wide range of options for the drive torque of the front wheels and the drive torque of the rear wheels. In other words, the degree of freedom in selecting the drive torque is high, so the ratio of drive torque between the front and rear wheels (front / rear torque distribution ratio required for vehicle travel) can be brought closer to the distribution ratio required for the vehicle, thereby maintaining or improving the vehicle's driving performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an example of a four-wheel drive vehicle according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a part of a drive system in which drive torque is output from motors in front and rear drive units to a differential mechanism. [Figure 3] FIG. 10 is a diagram showing measurement results of vibration levels for a plurality of driving torques. [Figure 4] FIG. 4 is a vibration characteristic diagram that schematically shows resonance ranges for three drive torques in a front-wheel drive unit and resonance ranges for three drive torques in a rear-wheel drive unit. [Figure 5] This is a map that defines the range of drive torque that can be set or selected (preferably set or selected) for the front and rear drive units for each vibration frequency band (vehicle speed range). [Figure 6]3 is a flowchart illustrating an example of control executed in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of how the present invention can be implemented, and is not intended to limit the present invention.

[0010] The vehicle in the embodiment of the present invention is a four-wheel drive vehicle, an example of which is shown schematically in Figure 1. The four-wheel drive vehicle (hereinafter sometimes simply referred to as the vehicle) 1 shown here comprises a front-wheel drive unit 3 that drives the two front wheels (front wheels) 2, and a rear-wheel drive unit 5 that drives the two rear wheels (rear wheels) 4. These drive units 3, 5 are mainly composed of a drive motor (hereinafter simply referred to as the motor), which is an electric motor, and a differential mechanism that enables differential rotation of the left and right wheels. Note that a limited slip differential mechanism may be built in as necessary.

[0011] FIG. 2 shows a portion of a drive system that outputs drive torque from the motor in each of the drive units 3 and 5 to a differential mechanism. The motor 6 shown here is, for example, a permanent magnet synchronous motor, and both ends of a rotor shaft 62 integral with the rotor 61 are supported by rolling bearings (hereinafter simply referred to as bearings) 63, such as ball bearings. In the example shown in FIG. 2, the rotor shaft 62 is a hollow shaft, and an output shaft 64 is inserted into one end of the rotor shaft 62 and spline-fitted. The output shaft 64 is disposed coaxially with the rotor shaft 62, and both ends are rotatably supported by bearings 65. A drive gear 66 is integrally formed at the middle of the output shaft 64. A differential mechanism (not shown) is disposed parallel to the output shaft 64, and a ring gear 67 of the differential mechanism meshes with the drive gear 66. The differential mechanism transmits drive torque to left and right wheels (front wheels 2 and rear wheels 4).

[0012] The drive gear 66 and the ring gear 67 are helical gears, and therefore, as torque is transmitted between them, a thrust load corresponding to the torque is generated. Furthermore, as the teeth repeatedly mesh with each other, the thrust load repeatedly changes, which acts as a vibratory force (or a forcing force) and causes vibration. To withstand such thrust loads, a preload is applied in the axial direction to the bearing 63 of the rotor shaft 62, increasing its rigidity.

[0013] A controller 7 is provided to control the output torque of the motor 6 in each of the drive units 3, 5. The controller 7 is an electronic control device mainly composed of a microcomputer, and is configured to perform calculations using input data and pre-stored data and output the results of the calculations as control command signals to the front and rear drive units 3, 5. The input data includes, for example, the accelerator opening representing the required drive amount of the vehicle 1, and the wheel speeds representing the rotational speeds or rotational frequencies of the front wheels 2 and rear wheels 4. The pre-stored data includes a map that calculates the drive torque required for the vehicle 1 based on the vehicle speed calculated from the wheel speed and the accelerator opening, a map that defines the front / rear torque distribution ratio based on the vehicle speed and the accelerator opening, and a map that defines the front / rear torque distribution based on the resonance range for each drive torque in the front and rear drive units 3, 5.

[0014] Here, we will explain the resonance of the drive system including the rotor 61, rotor shaft 62, and bearing 63. The resonance frequency fn of this drive system is given by fn=1 / 2π √(k / m) where k is the rigidity of bearing 63 and m is the mass of rotor 61 and rotor shaft 62. The rigidity of bearing 63 increases in accordance with the load applied in the axial direction, so as the axial load increases, the rigidity of bearing 63 also increases. In the drive system shown in FIG. 2, the axial load increases in accordance with the torque between drive gear 66, which is a helical gear, and ring gear 67, i.e., the drive torque that drives vehicle 1. Therefore, the resonance frequency shifts to a higher frequency as the drive torque increases.

[0015] This state is shown in FIG. 3. FIG. 3 shows the measurement results of the vibration level (dB) for each of a plurality of driving torques. In FIG. 3, the horizontal axis represents the frequency (Hz), which corresponds to the vehicle speed. The driving torques increase in the order of T1 to T5 (T1 < T2 < T3 < T4 < T5), and for each driving torque, a so-called peak appears where the vibration level increases rapidly. The frequency at which the vibration level peaks is the resonance frequency (resonance point), and the resonance frequency is displaced toward the high-frequency side as the driving torque increases. For the driving torque indicated by symbol T5 in FIG. 3, no peak of the vibration level appears, but the resonance point for this driving torque T5 is at a frequency higher than the frequency range shown in FIG. 3. Also, as shown in FIG. 3, on both sides of the peak of the vibration level, the vibration level changes gradually according to the frequency. Therefore, it is considered that the vibration level does not decrease rapidly just because the frequency is slightly deviated from the resonance point. In the embodiment of the present invention, a predetermined frequency range determined in design including the resonance frequency (resonance point) is defined as the "resonance region".

[0016] Since the rigidity of the bearing 63 in the front-wheel drive unit 3 and the rear-wheel drive unit 5 shown in FIG. 1 is not necessarily the same, the resonance regions for each driving torque in the front-wheel drive unit 3 and the rear-wheel drive unit 5 are shifted to the high-frequency side or the low-frequency side. FIG. 4 schematically shows the vibration characteristic lines of the resonance regions for each of the three driving torques A, B (>A), C (>B) in the front-wheel drive unit 3 and the resonance regions for each of the three driving torques D, E (>D), F (>E) in the rear-wheel drive unit 5. In FIG. 4, symbols I, II, and III indicate the frequency bands (vehicle speed ranges). In the first frequency band I, no resonance region appears regardless of which torque the driving torque of the front-wheel drive unit 3 is set to, but in the rear-wheel drive unit 5, a resonance region appears with the driving torque D. Similarly, hereinafter, in the frequency band II, a resonance region with the driving torque A appears in the front-wheel drive unit 3, and a resonance region with the driving torque E appears in the rear-wheel drive unit 5. Also, in the frequency band III, a resonance region with the driving torque C appears in the front-wheel drive unit 3, and a resonance region with the driving torque F appears in the rear-wheel drive unit 5.

[0017] Therefore, in a vehicle 1 having the vibration characteristics shown in Figure 4, in frequency band (vehicle speed range) I, the drive torque of the front-wheel drive unit 3 can be set to any of the above drive torques A, B, and C, but it is preferable to set the drive torque of the rear-wheel drive unit 5 to drive torques E and F other than the first drive torque D. Similarly, in frequency band (vehicle speed range) II, it is preferable to set the drive torque of the front-wheel drive unit 3 to drive torques B and C other than the first drive torque A, and for the rear-wheel drive unit 5 to drive torques D and F other than the second drive torque E. Furthermore, in frequency band (vehicle speed range) III, it is preferable to set the drive torque of the front-wheel drive unit 3 to drive torques A and C other than the second drive torque B, and for the rear-wheel drive unit 5 to drive torques D and E other than the third drive torque F.

[0018] As described above, the settable or selectable drive torque for avoiding resonance can be determined for each frequency band (vehicle speed range). FIG. 5 shows an example of a map that defines the settable or selectable (preferably settable or selectable) drive torque range for each frequency band (vehicle speed range) for the front-wheel drive unit 3 and the rear-wheel drive unit 5. In FIG. 5, the horizontal axis represents rear-wheel torque (drive torque of the rear-wheel drive unit 5) and the vertical axis represents front-wheel torque (drive torque of the front-wheel drive unit 3), with the hatched area indicating the settable or selectable (preferably settable or selectable) drive torque range. FIG. 5(a) is a map for the first frequency band (vehicle speed range) I described above, and FIG. 5(b) is a map for the second frequency band (vehicle speed range) II described above.

[0019] The controller 7 in the embodiment of the present invention stores, in advance, for example, the map shown in Fig. 5, and sets the drive torques of the front and rear drive units 3, 5 based on this map. An example of this control will be described with reference to the flowchart shown in Fig. 6.

[0020] The series of routines shown in Figure 6 are repeatedly executed by the controller 7 at predetermined short intervals when the vehicle 1 is traveling in a so-called four-wheel drive state. First, in step S1, the resonance frequencies of the front wheel drive unit 3 and the rear wheel drive unit 5 are found from the current motor torque. The calculation formula is as described above. Next, in step S2, it is determined whether the found resonance frequency is within the frequency band corresponding to the current vehicle speed or the intended vehicle speed. The functional means in the controller 7 that makes this determination in step S2 can be called a resonance determination unit.

[0021] If the result of the determination in step S2 is "NO", the process proceeds to step S3, where the drive torque in the front and rear drive units 3, 5 is set to the torque obtained by conventional torque distribution control, and then the process returns. Here, conventional torque distribution control is a control that determines the torque in the front and rear drive units 3, 5 based on a map in which the torque distribution ratio is set based on the accelerator opening and vehicle speed described above. The torque distribution ratio is the proportion of the drive torque (required torque) required for the vehicle 1 to travel that is shared by the front wheel drive unit 3 or the rear wheel drive unit 5.

[0022] If the result of the determination in step S2 is "Yes" because the resonance band of either the front or rear drive unit 3, 5 is included in the frequency band corresponding to the vehicle speed, the process proceeds to step S4, where it is determined whether or not the torque distribution can be changed. Here, changing the torque distribution means changing the torque distribution determined by conventional torque distribution control, and therefore if the result of the determination in step S4 is "No," the process proceeds to step S3 above, where the drive torque in the front and rear drive units 3, 5 is set to the torque determined by conventional torque distribution control, and then the process returns. Note that if the torque distribution ratio has been set manually, for example, the result of the determination in step S4 will be "No."

[0023] On the other hand, if the result of the determination in step S4 is "Yes," the process proceeds to step S5, where the torque distribution is changed to one that does not cause resonance, and then the process returns. The change in torque distribution in step S5 is a control that sets the drive torque of the front and rear drive units 3, 5 based on the map shown in FIG. 5 described above. That is, the drive torque of one of the drive units 3, 5, whose resonance range is within the frequency band determined by the vehicle speed, is changed to a drive torque whose resonance range is outside the frequency band (torque within the hatched range in FIG. 5(a) or (b)). At the same time, the drive torque of the other drive unit 3, 5 is changed to a drive torque whose resonance range is outside the frequency band determined by the vehicle speed, and whose total drive torque of each drive unit 3, 5 matches the total drive torque required for running the vehicle 1. Therefore, the functional means in the controller 7 that performs the control in step S5 corresponds to the drive torque setting unit in this embodiment of the present invention.

[0024] In this way, when changing the front / rear torque distribution, it is sufficient that the drive torque of the front and rear drive units 3, 5 is within the hatched range in the map shown in FIG. 5(a) or 5(b), and the drive torque may be increased or decreased within that range. In other words, there are fewer restrictions on the selection or setting of the drive torque, increasing the degree of freedom in setting the drive torque. Furthermore, when there is a possibility of resonance in either drive unit 3, 5 and the drive torque is changed, the drive torque can be increased as well as decreased. Therefore, according to the embodiment of the present invention, it is possible to set a torque distribution ratio as close as possible to the torque distribution ratio set in accordance with the required drive amount of the vehicle 1, road surface conditions, etc., and as a result, it is possible to improve the driving performance of the vehicle 1, such as driving stability and rough road performance.

[0025] The present invention is not limited to the above-described embodiment, and can be modified and implemented as appropriate within the scope of the object of the present invention. [Explanation of symbols]

[0026] 1. Four-wheel drive vehicle 2 front wheels 3 Front-wheel drive unit 4 rear wheels 5 rear wheel drive unit 6 Drive motor 7 Controller 61 Rotor 62 rotor shaft 63 Rolling bearings 64 Output shaft 65 bearings 66 Drive gear 67 Ring gear

Claims

[Claim 1] A front-rear torque distribution control device for a four-wheel drive vehicle, in which rotor shafts of a drive motor for a front wheel and a drive motor for a rear wheel are rotatably supported by rolling bearings, and a resonance region, which is a predetermined bandwidth including a resonance point determined by the rigidity of the rolling bearings in a drive system including the rolling bearings, changes according to the torque of the rotor shafts, a controller for controlling the drive torque provided by the drive motor for the front wheels and the drive torque provided by the drive motor for the rear wheels out of the drive torque required for the four-wheel drive vehicle to travel; The controller a drive torque setting unit that sets the drive torque by the drive motor for the front wheels and the drive motor for the rear wheels at a predetermined vehicle speed to a torque that has a resonance region in a frequency band outside the frequency band at the predetermined vehicle speed and that satisfies the torque required for the vehicle to travel; A front and rear torque distribution control device for a four-wheel drive vehicle.

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