Control system for front and rear wheel drive vehicle

Abstract

To provide a control device capable of improving lubricity at a low temperature in a vehicle capable of driving front wheels and rear wheels by individual motors without impairing power performance or acceleration performance.SOLUTION: The controller 9 includes a low-temperature determining unit 9a that determines whether the temperature is equal to or lower than a predetermined reference temperature, a distribution-ratio setting unit 9b that obtains, based on the detected temperature, a driving-force distribution ratio that is a ratio of the driving force between the front-wheel side and the rear-wheel side, and a current control unit 9c that controls, when it is determined that the temperature is equal to or lower than the reference temperature, an excitation current of the motor in each of the drive units such that each of the drive units outputs a torque corresponding to the driving-force distribution ratio.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a device for controlling a front and rear wheel drive vehicle having drive units provided for the front and rear wheels, respectively. [Background technology]

[0002] Vehicle drive systems are composed of numerous components with frictional contact, such as gears, rotating shafts, and bearings, making lubrication essential. It is well known that oil is used to lubricate mechanical components. Various methods are used, including upwelling lubrication, in which oil is scooped up by the rotation of gears and supplied to required locations, and forced lubrication, in which oil is supplied to required locations using an oil pump. However, oil is supplied to locations where an oil film should be formed, such as tooth surfaces and rolling surfaces of bearings, by oil flow. On the other hand, mechanical devices, such as vehicles, that are placed in natural environments may be cooled to ambient temperatures during winter, in which case the viscosity of the oil increases, making it difficult for the oil to flow to lubricated locations. Furthermore, high oil viscosity can increase stirring resistance and potentially increase power loss.

[0003] Patent Documents 1 and 2 describe devices designed to avoid such temperature-related problems. The device described in Patent Document 1 includes a motor as a driving force source, a reduction gear that increases the motor's output torque, a differential gear that distributes the driving torque output from the reduction gear to the left and right wheels, a housing that accommodates the motor, reduction gear, and differential gear, oil contained in the housing for lubrication, a temperature sensor that detects the motor temperature, and a control unit that controls the motor. The control unit limits the motor output based on the temperature detected by the temperature sensor. Therefore, when low temperatures could result in an insufficient supply of oil to lubricated areas or an insufficient oil film, the motor output is reduced, which reduces the load on frictional contact areas and prevents problems such as seizure.

[0004] Furthermore, the device described in Patent Document 2 is configured to increase the amount of heat generated by Joule loss and iron loss in the motor or motor-generator when the temperature of the lubricating fluid, such as oil, is low, and use that heat to warm the lubricating fluid. Therefore, the device described in Patent Document 2 is said to be able to reduce the viscous resistance of the lubricating fluid and thereby reduce power loss. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent International Publication No. 2020 / 213709 [Patent Document 2] Japanese Patent Publication No. 2022-174328 Summary of the Invention [Problem to be solved by the invention]

[0006] The device described in Patent Document 1 limits motor output when there is a possibility of insufficient oil lubrication, resulting in a decrease in the vehicle's overall driving force. This can result in a vehicle with poor acceleration or power performance. Furthermore, the device described in Patent Document 2 increases the motor current to raise the temperature of the lubricating fluid, which can increase the motor's output torque. While this can prevent situations such as a decrease or insufficiency in driving force, there is a possibility that the driving torque may increase unintentionally by the driver, or that changes in driving torque may cause unintended changes in vehicle behavior.

[0007] The present invention has been made with an eye on the above-mentioned technical problems, and aims to provide a control device that can improve lubrication at low temperatures in a vehicle in which the front and rear wheels can be driven by separate motors without impairing power performance or acceleration performance. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a control device for a front-wheel drive vehicle having a drive unit for the front wheels that includes a motor and is lubricated by oil, and a drive unit for the rear wheels that includes a motor and is lubricated by oil, and has a controller that controls each of the motors, the controller having a low temperature determination unit that determines whether the temperature is below a predetermined reference temperature, a distribution rate setting unit that determines, based on the detected temperature, a driving force distribution rate that is the ratio of driving force between the front wheel side and the rear wheel side that satisfies the driving force required for the front-wheel drive vehicle, and a current control unit that controls the motor current in each of the drive units so that, when it is determined that the temperature is below the reference temperature, each of the drive units outputs torque according to the driving force distribution rate. [Effects of the Invention]

[0009] According to the present invention, when low temperature can increase oil viscosity, the driving force distribution ratio between the front and rear wheels is set based on the low temperature, increasing the current to one of the front and rear motors and decreasing the current to the other motor. Therefore, the torque (i.e., load) output by one of the front and rear drive systems is reduced, so that even if the high oil viscosity causes insufficient lubrication in that one drive system, excessive friction or wear can be avoided or suppressed. Furthermore, in the other drive system, the motor current increases and its temperature rises quickly, reducing the oil viscosity and increasing its fluidity, enabling early and sufficient lubrication, thereby avoiding or suppressing excessive friction or wear. In this case, the overall driving force required for a front-wheel-drive vehicle is maintained, preventing a decrease in driving force or a deterioration in acceleration. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram schematically illustrating an example of a front-wheel drive vehicle according to an embodiment. [Figure 2]FIG. 2 is a skeleton diagram for explaining an example of the drive device. [Figure 3] FIG. 2 is a block diagram showing the functional configuration of a controller. [Figure 4] 10 is a flowchart showing an example of control for determining whether to perform oil temperature increase control. [Figure 5] 3 is a flowchart illustrating temperature rise control in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] The vehicle in the embodiment of the present invention is a front-wheel drive vehicle in which the front wheels and rear wheels can be driven independently by corresponding drive units, and is particularly an electric vehicle (BEV, PHEV) equipped with a motor or motor-generator (hereinafter collectively referred to as a motor) as a drive power source. An example is shown in Figure 1. The vehicle 1 shown here is a four-wheel drive vehicle or an all-wheel drive vehicle that runs by driving the front wheels 2 and the rear wheels 3, and is equipped with a front-wheel drive unit 4 that drives the front wheels 2 and a rear-wheel drive unit 5 that drives the rear wheels 3.

[0013] These drive units 4, 5 are equipped with motors 6, 7, respectively, as sources of drive power. These drive units 4, 5 are configured so that the left and right wheels can rotate differentially; one example is a configuration equipped with a differential mechanism, and another example is a configuration in which the left and right wheels are driven by motors individually provided for each wheel. An example of the former drive unit 4, 5 equipped with a differential mechanism is shown in the skeleton diagram of Figure 2. The example shown here is a device called an e-Axle, in which a motor M, a reduction mechanism R, and a differential mechanism D are housed inside a casing C and lubricated and cooled by a lubricant (oil) O sealed inside.

[0014] The motor M is, for example, a permanent magnet synchronous motor, and is controlled by a power control unit (PCU) P, which is mainly composed of electronic devices such as an inverter and a computer. The reduction mechanism R is a known mechanism including a drive gear connected to the rotor shaft of the motor M, a counter driven gear provided on a counter shaft and meshing with the drive gear and having a larger diameter than the drive gear, and a counter drive gear provided on the counter shaft. The differential mechanism D is a known mechanism including, for example, a pair of left and right side gears arranged opposite each other with a pinion gear in between, and the pinion gears are held so as to rotate and revolve by a differential case equipped with a ring gear. The ring gear meshes with the counter drive gear, and the driving torque transmitted from the motor M is output from the side gears to the left and right wheels 2, 3.

[0015] The front and rear drive units 4, 5 are controlled to satisfy the required drive force, which is expressed by the depression amount (or accelerator opening) of the accelerator pedal 8. In this control, the drive force to be shared by each drive unit 4, 5 out of the required drive force is calculated based on the vehicle speed, wheel speed, or the ground load and slip ratio of the wheels 2, 3. The ratio of the drive force shared by each drive unit 4, 5 is the drive force distribution rate.

[0016] In an embodiment of the present invention, a controller 9 is provided that sets the driving force distribution ratio based on temperature. The controller 9 is mainly configured with a microcomputer equipped with a processing element (CPU), memory elements (RAM, ROM), and various interfaces (I / F), and is configured to perform calculations according to a preset program using input data and pre-stored data, and to output the results of the calculations as control command signals. In particular, the controller 9 is configured to set the driving force distribution ratio based on temperature, and therefore a detected temperature from a temperature sensor 10 is input to the controller 9. The temperature detected by the temperature sensor 10 may be the outside air temperature, the coolant temperature of the drive units 4 and 5, or the temperature of the oil O.

[0017] The functions of the controller 9 for determining the driving force distribution ratio based on temperature are shown in a block diagram in Figure 3. Figure 3 shows the functional configuration of the controller 9, which includes a low-temperature determination unit 9a. The low-temperature determination unit 9a determines whether the temperature detected by the temperature sensor 10 is equal to or lower than a predetermined reference temperature. The reference temperature is the temperature at which the viscosity of the oil O is expected to increase to such an extent that it will not flow onto gears, bearings, etc., and is a temperature that is determined in advance by experiments, simulations, etc. and stored in the controller 9.

[0018] If the temperature is low, control is performed to increase the temperature of the oil O. Motors 6 and 7 are used as heat sources for this purpose, and the controller 9 is configured to set the driving force distribution ratio between the front and rear drive units 4 and 5 in order to increase the heat generation amount of either of the motors 6 and 7. That is, the controller 9 is provided with a distribution ratio setting unit 9b. Here, the driving force distribution ratio refers to the proportion of the driving force provided by the drive units 4 and 5, or the driving force that should be output by the drive units 4 and 5, of the overall driving force of the vehicle 1 calculated based on factors such as the accelerator pedal position and vehicle speed. The driving force distribution ratio is basically set based on the driving conditions of the vehicle 1, such as vehicle speed, required driving force, road gradient, and tire slip ratio. However, in this embodiment of the present invention, the distribution ratio is set or changed based on temperature in addition to these factors. This will be described in detail later.

[0019] Furthermore, the controller 9 includes a current control unit 9c. The current control unit 9c controls the current of the motors 6, 7 in each of the drive units 4, 5 so that the motors 6, 7 output a drive torque determined by the set distribution ratio. In this case, the overall required drive force of the vehicle 1, which is calculated based on the accelerator opening, vehicle speed, etc., is set to "100%," and the current is controlled so that the motors 6, 7 output a drive torque multiplied by the drive force distribution ratio (%). Therefore, the overall drive force of the vehicle 1 is maintained without any particular change before and after the change in the drive force distribution ratio.

[0020] Next, the control executed in this embodiment of the present invention will be described. FIG. 4 shows a control flowchart for determining whether to execute temperature increase control. First, in step S1, it is determined whether "Ready ON" is set. This determination is made to determine whether a ready switch (not shown) provided on the vehicle 1 is on and whether the motors 6, 7 can be energized and started immediately. If the result of the determination in step S1 is "Yes," the process proceeds to step S2, where it is determined whether the temperature is low. As described above, this determination is made to determine whether the temperature detected by the temperature sensor 10 is equal to or lower than a predetermined reference temperature. If the result of the determination in step S2 is "Yes" because the temperature is low, the process proceeds to step S3, where ATF temperature increase control is executed, and then the routine shown in FIG. 4 is temporarily terminated.

[0021] If the determination result in step S1 is "NO" or if the determination result in step S2 is "NO", the process proceeds to step S4, where the ATF temperature increase control is not performed, and then the routine shown in FIG. 4 is temporarily terminated.

[0022] The ATF is the oil O mentioned above, and in step S3, the heat generated by the motors 6 and 7 is controlled to increase the temperature of the oil O using the heat from the motors 6 and 7. A specific example is shown in FIG. 5. First, in step S11, the vehicle driving force is calculated. The overall driving force of the vehicle 1 can be determined based on the accelerator opening, vehicle speed, and the like. The calculation of the driving force may be performed by the controller 9, or the vehicle driving force may be obtained from another control device (not shown) that controls the driving force of the vehicle 1.

[0023] Next, in step S12, the front and rear drive force distribution ratio is calculated. This control increases the heat generation of the motors 6, 7 in order to raise the temperature of the oil O. The distribution ratio can be set by predetermining the distribution ratio according to the temperature and reading out the distribution ratio based on the detected temperature. For example, the distribution ratio for the front wheels 2 (Fr distribution) and the distribution ratio for the rear wheels 3 (Rr distribution) can be set as follows: Fr allocation:Rr allocation = 95%:5% Fr allocation:Rr allocation = 5%:95% The allocation rate is set to, and the allocation rate is alternately switched at predetermined time intervals. Also, this allocation rate and its switching may be performed during steady running when the vehicle speed changes little, and may be controlled to a different allocation rate during acceleration or deceleration. For example, during acceleration, Fr allocation:Rr allocation = 5%:95% When decelerating, Fr allocation:Rr allocation = 95%:5% It may be possible to maintain the

[0024] Then, in step S13, a current that outputs torque according to the distribution ratio calculated in step S12 is calculated. Therefore, heat generation due to Joule loss or iron loss in either the front or rear motor 6(7) increases, causing the temperature of the oil O to rise and its viscosity to decrease. On the other hand, the torque output by the other motor 7(6) on the opposite side decreases, reducing the load on the drive unit 5(4) including that motor 7(6). Therefore, friction or wear can be suppressed even if the viscosity of the oil O is high.

[0025] The current control for increasing the temperature may be control of the excitation current (d-axis current), in which case the current value for outputting the driving force required for the vehicle 1 may be increased by multiplying the current value by a predetermined coefficient (>1). Furthermore, when the vehicle 1 is in a parking state (a so-called parking lock state), control may be performed to further increase the d-axis current that does not generate torque in the motors 6 and 7.

[0026] Since the temperature gradually increases by performing the control of step S13, the result of the determination in step S2 shown in Fig. 4 becomes "NO" during this process. In this case, the process proceeds to step S4 as described above, and the temperature increase control ends.

[0027] The present invention is not limited to the above-described embodiment, and the distribution ratio of driving force between the front and rear wheels can be set appropriately as needed other than the above-described ratio. For example, it may be changed according to the elapsed time since the start of the temperature rise control. Appropriate control may also be performed, such as changing the distribution ratio so that the deviation from the distribution ratio when temperature rise control is not executed gradually decreases as time passes or as the temperature changes. [Explanation of symbols]

[0028] 1 vehicle 2 front wheels 3 rear wheels 4 Front wheel drive unit 5 Rear wheel drive unit 6,7 Motor 8 Accelerator pedal 9 Controller 9a Low temperature judgment section 9b Allocation rate setting section 9c Current control section 10 Temperature Sensor C casing D Differential mechanism Medium motor O Oil R reduction mechanism

Claims

[Claim 1] A control device for a front-wheel drive vehicle including a drive unit for front wheels that includes a motor and is lubricated by oil, and a drive unit for rear wheels that includes a motor and is lubricated by oil, a controller for controlling each of the motors; The controller a low temperature determination unit that determines whether the temperature is equal to or lower than a predetermined reference temperature; a distribution rate setting unit that calculates a driving force distribution rate, which is a ratio of driving force between the front wheels and the rear wheels that satisfies the driving force required for the front-wheel-drive vehicle, based on the detected temperature; and a current control unit that controls a motor current in each of the drive devices so that the drive devices output torque according to the driving force distribution ratio when it is determined that the temperature is equal to or lower than the reference temperature; Equipped with A control device for a front and rear wheel drive vehicle.

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