Control system for four-wheel drive vehicles

Abstract

The present invention provides a control device for a four-wheel drive vehicle that can suppress the discomfort experienced by the driver while also suppressing the decline in drivability during manual driving. [Solution] The four-wheel drive vehicle 10 includes a front motor MGf that drives a pair of front wheels 14 and a rear motor MGr that drives a pair of rear wheels 44. When the rear motor temperature THmgr is above the determination temperature THmgr_jdg during four-wheel drive driving using the front motor MGf and rear motor MGr as power sources for driving, the electronic control device 90 of the four-wheel drive vehicle 10 determines that (a) it is neither during a predetermined acceleration or a predetermined turn based on a request from the driver, the distribution ratio X is switched using an overheat distribution ratio map in which the distribution ratio X of the driving force Fw to the pair of front wheels 14 and the pair of rear wheels 44 is increased as the vehicle speed V increases, and (b) it is determined that it is neither during a predetermined acceleration or a predetermined turn, the distribution ratio X is maintained.

Description

Technical Field

[0001] The present invention relates to a control device for a four-wheel drive vehicle including a front motor that drives a pair of front wheels and a rear motor that drives a pair of rear wheels.

Background Art

[0002] A control device for a four-wheel drive vehicle including an engine or an engine and a front motor that drive a pair of front wheels and a rear motor that drives a pair of rear wheels is known. For example, the control device for a four-wheel drive vehicle described in Patent Document 1 is such a device. In Patent Document 1, during automatic driving, the arrival temperature of the rear motor is predicted from an action plan based on the input content to the navigation system, and the distribution ratio of the driving force to the pair of rear wheels is controlled in advance so that the temperature of the rear motor does not exceed the upper limit value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, during manual driving in which a driver (= operator) manually operates rather than during automatic driving, there is no action plan, so the arrival temperature of the rear motor cannot be predicted. Therefore, the distribution ratio of the driving force to the pair of rear wheels cannot be controlled in advance so that the temperature of the rear motor does not exceed the upper limit value. Further, during manual driving, it is desired to improve the drivability that can realize the power performance of four-wheel drive required by the driver as much as possible. Under such circumstances, when the rear motor overheats during manual driving, suddenly changing the distribution ratio of the driving force to the pair of rear wheels may make the driver feel uncomfortable.

[0005] This invention was made against the above circumstances, and its objective is to provide a control device for a four-wheel drive vehicle that can suppress the discomfort experienced by the driver while suppressing the decline in drivability during manual driving. [Means for solving the problem]

[0006] The gist of the present invention is a control device for a four-wheel drive vehicle equipped with a front motor that drives a pair of front wheels and a rear motor that drives a pair of rear wheels, wherein when the temperature of the rear motor is above a predetermined determination temperature during four-wheel drive driving using the front motor and the rear motor as power sources for driving, (a) if it is determined that it is neither during a predetermined acceleration or a predetermined turn based on a request from the driver, the distribution ratio is switched using a map in which the distribution ratio of the driving force to the pair of front wheels and the pair of rear wheels increases as the vehicle speed increases, and (b) if it is determined that it is neither during the predetermined acceleration or the predetermined turn, the change in the distribution ratio is made smaller than when using the map. [Effects of the Invention]

[0007] According to the control device for a four-wheel drive vehicle of the present invention, when the temperature of the rear motor is above a predetermined determination temperature during four-wheel drive driving using the front motor and the rear motor as power sources for driving, (a) if it is determined that neither a predetermined acceleration nor a predetermined turn based on a request from the driver is occurring, the distribution ratio is switched using a map in which the distribution ratio of the driving force to the pair of front wheels and the pair of rear wheels is increased as the vehicle speed increases, and (b) if it is determined that either a predetermined acceleration or a predetermined turn is occurring, the change in the distribution ratio is made smaller than when using the map. The higher the vehicle speed, the easier it is for the rear motor to be cooled by the airflow while driving. Therefore, even if the distribution ratio of the driving force to the pair of rear wheels is increased as the vehicle speed increases, the temperature of the rear motor is less likely to rise. When the temperature of the rear motor is above a predetermined determination temperature during four-wheel drive driving, and it is determined that neither a predetermined acceleration nor a predetermined turn based on a request from the driver is occurring, the distribution ratio is switched using a map in which the distribution to the pair of rear wheels is increased as the vehicle speed increases. This reduces the reduction in drivability by relaxing the rear motor's driving force limit during manual driving. On the other hand, if the rear motor temperature is above a predetermined threshold temperature during four-wheel drive driving, and it is determined that either a predetermined acceleration or predetermined cornering is occurring based on a request from the driver, the change in the distribution ratio is made smaller than when using the aforementioned map. This suppresses the change in the distribution ratio during predetermined acceleration and predetermined cornering based on a request from the driver during manual driving, thereby suppressing changes in drivability and reducing the discomfort the driver may feel. Therefore, the discomfort the driver may feel is suppressed while reducing the reduction in drivability during manual driving. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of a four-wheel drive vehicle equipped with an electronic control device according to an embodiment of the present invention. [Figure 2] Figure 1 is an example of a flowchart illustrating the key aspects of the control operation of the electronic control unit shown. [Figure 3] This is an example of a heat distribution ratio map that takes into account the cooling performance due to airflow while driving. [Figure 4] This figure shows an example of a time chart when the control operation shown in the flowchart in Figure 2 is executed. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Unless otherwise specified, the drawings in the embodiments have been simplified or modified as appropriate, and the dimensional ratios and shapes of each part are not necessarily depicted accurately. [Examples]

[0010] Figure 1 is a schematic diagram of a four-wheel drive vehicle 10 (hereinafter simply referred to as "vehicle 10") equipped with an electronic control device 90 according to an embodiment of the present invention.

[0011] Vehicle 10 is equipped with a front motor MGf and a rear motor MGr, which are power sources for driving. The front motor MGf is a motor that drives a pair of front wheels 14. The rear motor MGr is a motor that drives a pair of rear wheels 44. The front motor MGf is connected to the pair of front wheels 14 via a front differential gear 16 and a pair of front drive shafts 18, which are a well-known configuration. The rear motor MGr is connected to the pair of rear wheels 44 via a rear differential gear 46 and a pair of rear drive shafts 48, which are a well-known configuration. Vehicle 10 also includes an inverter 50f for controlling the MGf, an inverter 50r for controlling the MGr, a battery 52, and an electronic control unit 90.

[0012] For example, the front motor MGf and the rear motor MGr are synchronous motors. The front motor MGf and the rear motor MGr are rotationally driven by power stored in the battery 52 via the MGf control inverter 50f and the MGr control inverter 50r, respectively. The MGf control inverter 50f and the MGr control inverter 50r are power supply circuits that convert DC to AC and AC to DC, respectively, under the control of the electronic control device 90.

[0013] The electronic control unit 90 is composed of a so-called microcomputer, for example, equipped with a CPU, RAM, ROM, input / output interface, etc. The CPU performs various controls on the vehicle 10 by performing signal processing according to a program pre-stored in the ROM, for example. The electronic control unit 90 corresponds to the "control device" in this invention.

[0014] The electronic control unit 90 receives various signals based on values ​​detected by various sensors (for example, vehicle speed sensor 70, accelerator pedal position sensor 72, steering angle sensor 74, acceleration sensor 80, rotational speed sensor 82, rotational speed sensor 84, temperature sensor 86, temperature sensor 88, etc.). These signals include various signals such as vehicle speed V [km / h], accelerator pedal position θacc [%] which represents the amount of accelerator operation by the driver, indicating the magnitude of the driver's acceleration operation, steering angle φste [deg] of the steering wheel 60 provided on the vehicle 10, longitudinal acceleration Ax [m / sec²] and lateral acceleration Ay [m / s²] of the vehicle 10, front wheel rotation speed Nmgf [rpm], rear wheel rotation speed Nmgr [rpm], front motor temperature THmgf [℃] which is the temperature of the front motor MGf, and rear motor temperature THmgr [℃] which is the temperature of the rear motor MGr.

[0015] The electronic control unit 90 outputs various control signals (such as the MGf control signal Smgf for driving the front motor MGf, the MGr control signal Smgr for driving the rear motor MGr, etc.) to each device installed in the vehicle 10 (for example, the MGf control inverter 50f, the MGr control inverter 50r, etc.).

[0016] In vehicle 10, a four-wheel drive driving mode can be selected. The four-wheel drive driving mode is a driving mode that realizes four-wheel drive driving by using both the front motor MGf and the rear motor MGr as power sources for driving.

[0017] Figure 2 is an example of a flowchart illustrating the main parts of the control operation of the electronic control unit 90 shown in Figure 1. The flowchart in Figure 2 is repeatedly executed when the rear motor temperature THmgr is below the limit temperature THmgr_lmt during four-wheel drive driving. The "limit temperature THmgr_lmt" is the upper limit temperature at which the rear motor MGr can be driven and controlled normally, and is, for example, the upper limit temperature at which the impact on the durability of the rear motor MGr is within an acceptable range. If the rear motor temperature THmgr is above the limit temperature THmgr_lmt, regardless of the flowchart in Figure 2, the rear motor MGr is immediately de-driven for cooling, and the vehicle 10 is switched from four-wheel drive mode to front-wheel drive mode. The front-wheel drive mode is a driving mode that realizes front-wheel drive driving using only the front motor MGf as the power source.

[0018] First, in step S10 (hereinafter, "step" is omitted), it is determined whether the rear motor temperature THmgr is equal to or higher than the determination temperature THmgr_jdg. The determination temperature THmgr_jdg is a predetermined determination temperature that is experimentally or designedly determined in advance as being less than the limit temperature THmgr_lmt [°C] and having room to suppress the rise of the rear motor temperature THmgr by cooling with the running wind. The determination temperature THmgr_jdg corresponds to the "predetermined determination temperature" in the present invention. When the rear wheel driving force Fwr [N] output from the rear motor MGr is large, the driving current is large, so the rear motor temperature THmgr tends to rise. However, since the rear motor temperature THmgr is determined by heat generation due to the driving current and cooling due to heat dissipation, the rear motor temperature THmgr does not immediately rise just because the driving current increases, nor does the rear motor temperature THmgr immediately drop just because the driving current decreases. That is, there is a time lag between the change in the rear wheel driving force Fwr and the change in the rear motor temperature THmgr. The same applies to the front motor MGf. If the determination in S10 is NO, in S20, a non-overheating time-sharing ratio Xi that emphasizes 4WD performance is calculated, and the sharing ratio X is controlled to the non-overheating time-sharing ratio Xi.

[0019] Hereinafter, the non-overheating time-sharing ratio Xi will be described.

[0020] In the four-wheel drive running mode, the driving force Fw [N] of all the driving wheels of the vehicle 10 is controlled to be the required driving force Fwdem [N]. The required driving force Fwdem is calculated by applying the actual accelerator opening θacc and vehicle speed V to the relationship between the accelerator opening θacc and vehicle speed V, and the required driving force Fwdem, which is experimentally or designedly obtained and stored in advance. The required driving force Fwdem is the target value of the driving force Fw. The non-overheating time-sharing ratio Xi is set to the same value as, for example, the well-known dynamic load sharing ratio d. The dynamic load sharing ratio d is the ratio (= Wdr / W) of the dynamic rear axle load Wdr [kg] to the vehicle weight W in the running state of the vehicle 10.

[0021] If the determination in S10 is YES, in S30, it is determined whether it is during a predetermined acceleration or a predetermined turn based on a request from the driver. For example, based on the fact that the required driving force Fwdem is greater than the actual driving force Fw and the acceleration Ax in the longitudinal direction is a positive value, it is determined that it is during a predetermined acceleration. For example, based on the absolute value of the steering angle φste being greater than or equal to the determination angle φste_jdg, it is determined that it is during a predetermined turn. The determination angle φste_jdg is a predetermined determination value determined experimentally or by design such that when the distribution ratio X changes and the driver feels a discomfort that exceeds the allowable range. If the determination in S30 is NO, in S40, the overheat time distribution ratio Xh considering the cooling performance by the traveling wind is calculated, and the distribution ratio X is controlled to the overheat time distribution ratio Xh. Preferably, the overheat time distribution ratio Xh is smaller than the non-overheat time distribution ratio Xi.

[0022] Hereinafter, the overheat time distribution ratio Xh will be described.

[0023] FIG. 3 is an example of an overheat time distribution ratio map considering the cooling performance by the traveling wind. The overheat time distribution ratio map corresponds to the "map" in the present invention. The overheat time distribution ratio map is a predetermined relationship having a switching line (shown by a dashed line in FIG. 3) for determining the change of the overheat time distribution ratio Xh on a two-dimensional coordinate with, for example, the vehicle speed V and the rear motor temperature THmgr as variables. In the overheat time distribution ratio map, it is determined such that the overheat time distribution ratio Xh increases as the vehicle speed V increases. Also, in the overheat time distribution ratio map, it is determined such that the overheat time distribution ratio Xh decreases as the rear motor temperature THmgr increases. Thereby, as the rear motor temperature THmgr rises, the ratio of the rear wheel driving force Fwr is decreased, and as the vehicle speed V increases, the ratio of the rear wheel driving force Fwr is increased. In the overheat time distribution ratio Xh shown in FIG. 3, the ratio Xh0 is smaller than the ratio Xh1, the ratio Xh1 is smaller than the ratio Xh2, and the ratio Xh2 is smaller than the ratio Xh3. The vehicle speed values V0 to V3, the time points t0 to t3, and the ratios Xh0 to Xh3 shown in FIG. 3 are consistent with those used in the description of the time chart of FIG. 4 described later.

[0024] Return to Figure 2. If the determination in S30 is YES, in S50 the distribution ratio X is maintained at its current value. After the execution of S50, in S60 it is determined whether the predetermined acceleration or predetermined turning is continuing. If the determination in S60 is YES, S50 is executed again. As a result, if in S10 the rear motor temperature THmgr is determined to be equal to or greater than the determination temperature THmgr_jdg and in S30 it is determined that either the predetermined acceleration or predetermined turning is occurring, the distribution ratio X is maintained at its current value until that predetermined acceleration or predetermined turning state is resolved. This avoids abrupt changes in drivability due to changes in the distribution ratio X. After the execution of S20, after the execution of S40, and if the determination in S60 is NO, the process returns.

[0025] Figure 4 shows an example of a time chart when the control operation shown in the flowchart of Figure 2 is executed. The horizontal axis in Figure 3 represents time t [s].

[0026] Before time point t0, it is, for example, an acceleration period by an acceleration operation by a driver (= during a predetermined acceleration based on a request from the driver). After time point t0, it is, for example, an acceleration period by a downhill road (= not during a predetermined acceleration based on a request from the driver). At time point t0, the vehicle speed V is the vehicle speed value V0, and the rear motor temperature THmgr is the temperature value TH0 (< THmgr_jdg). At this time point t0, the distribution ratio X is controlled to the non-overheat time distribution ratio Xi. At time point t1 (> t0), the rear motor temperature THmgr becomes the determination temperature THmgr_jdg. At this time point t1, since the vehicle speed V is the vehicle speed value V1, based on the overheat time distribution ratio map, the distribution ratio X is changed from the non-overheat time distribution ratio Xi to the ratio Xh1 (see FIG. 3) at the overheat time distribution ratio Xh. Due to the acceleration by the downhill road, at time point t2 (> t1), the vehicle speed V becomes the vehicle speed value V₂ (> V1). At this time point t2, since the rear motor temperature THmgr is the temperature value TH₂ (> THmgr_jdg), based on the overheat time distribution ratio map, the distribution ratio X is changed from the ratio Xh1 at the overheat time distribution ratio Xh to the ratio Xh2 (> Xh1) (see FIG. 3). Due to the acceleration by the downhill road, at time point t3 (> t2), the vehicle speed V becomes the vehicle speed value V3 (> V2). At this time point t3, since the rear motor temperature THmgr is the temperature value TH3 (> THmgr_jdg), based on the overheat time distribution ratio map, the distribution ratio X is maintained at the ratio Xh2 at the overheat time distribution ratio Xh.

[0027] According to this embodiment, when the rear motor temperature THmgr is above the determination temperature THmgr_jdg during four-wheel drive driving using the front motor MGf and rear motor MGr as the power source for driving, (a) if it is determined that neither a predetermined acceleration nor a predetermined turn based on a request from the driver is occurring, the distribution ratio X is switched using an overheat distribution ratio map in which the distribution ratio X of the driving force Fw to the pair of front wheels 14 and the pair of rear wheels 44 is increased as the vehicle speed V increases, and (b) if it is determined that neither a predetermined acceleration nor a predetermined turn based on a request from the driver is occurring, the distribution ratio X is maintained. The higher the vehicle speed V, the easier it is for the rear motor MGr to be cooled by the airflow while driving. Therefore, even if the distribution ratio X is increased to the pair of rear wheels 44 as the vehicle speed V increases, the rear motor temperature THmgr is less likely to rise. When the rear motor temperature THmgr is above the predetermined temperature THmgr_jdg during four-wheel drive driving, and it is determined that neither a predetermined acceleration nor a predetermined turn based on a request from the driver is occurring, the distribution ratio X is switched using an overheat distribution ratio map that increases the distribution to the pair of rear wheels 44 as the vehicle speed V increases. This reduces the driving force limitation of the rear motor MGr during manual driving, thereby suppressing a decrease in drivability. On the other hand, when the rear motor temperature THmgr is above the predetermined determination temperature THmgr_jdg during four-wheel drive driving, and it is determined that neither a predetermined acceleration nor a predetermined turn based on a request from the driver is occurring, the distribution ratio X is maintained. This suppresses changes in the distribution ratio X during predetermined acceleration and predetermined turns during manual driving, thereby suppressing changes in drivability and reducing the discomfort the driver may feel. Therefore, the discomfort the driver may feel is suppressed while the decrease in drivability during manual driving is suppressed.

[0028] The above-described examples are embodiments of the present invention, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, without departing from its spirit.

[0029] In the above-described embodiment, when the rear motor temperature THmgr is above a predetermined determination temperature THmgr_jdg during four-wheel drive driving, the distribution ratio X is maintained if it is determined that either a predetermined acceleration or predetermined cornering is occurring. However, the present invention is not limited to this embodiment. For example, if it is determined that either a predetermined acceleration or predetermined cornering is occurring, the change in the distribution ratio X may be made smaller than when using an overheat distribution ratio map. When the change in the distribution ratio X is made smaller than when using an overheat distribution ratio map, the change in the distribution ratio X is suppressed compared to when it is not, and the discomfort felt by the driver is suppressed. [Explanation of symbols]

[0030] 10: Four-wheel drive vehicle, 14: Pair of front wheels, 44: Pair of rear wheels, 90: Electronic control unit (control unit), MGf: Front motor, MGr: Rear motor, THmgr: Rear motor temperature (temperature of the rear motor), THmgr_jdg: Judgment temperature (predetermined judgment temperature), V: Vehicle speed, X: Distribution ratio

Claims

[Claim 1] A control device for a four-wheel drive vehicle, comprising a front motor that drives a pair of front wheels and a rear motor that drives a pair of rear wheels, When the temperature of the rear motor is above a predetermined threshold temperature during four-wheel drive operation using the front motor and the rear motor as power sources for driving, if it is determined that neither a predetermined acceleration nor a predetermined turn is occurring based on a request from the driver, the distribution ratio of the driving force to the pair of front wheels and the pair of rear wheels is switched using a map that increases the distribution to the pair of rear wheels as the vehicle speed increases. If it is determined that either a predetermined acceleration or a predetermined turn is occurring, the change in the distribution ratio is made smaller than when using the map. A control device for a four-wheel drive vehicle, characterized by the following features.

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