Vehicle drive force control method and vehicle drive force control device

Abstract

Provided is a vehicle drive force control method that comprises measuring a frictional coefficient and a slip rate on a vehicle travel road surface in a prescribed measurement period, generating a µ-S characteristic map that represents a relationship between the frictional coefficient and the slip rate on the travel road surface on the basis of a combination of the frictional coefficient and the slip rate obtained in each measurement period, determining whether the travel road surface is a muddy road surface on the basis of the generated µ-S characteristic map, identifying an appropriate slip rate zone on the µ-S characteristic map in which the slip rate is lower than the slip rate during maximum friction and the road surface transmission torque is equal to or greater than a prescribed value when the travel road surface is determined to be a muddy road surface, and adjusting the drive force so that the slip rate is included in the appropriate slip rate zone.

Description

Vehicle driving force control method and vehicle driving force control device

[0001] The present invention relates to a vehicle driving force control method and a vehicle driving force control device for performing slip control to adjust the output torque of a driving source according to the slip ratio of the vehicle.

[0002] Conventionally, anti-skid control devices have been known to prevent wheels from locking and slipping when braking a vehicle. These anti-skid control devices set a target slip ratio at which the coefficient of friction (road surface μ) is maximized, and control each actuator (drive source or brake) to determine torque so that the slip ratio during travel matches the target slip ratio.

[0003] However, the relationship between the friction coefficient and the slip ratio (μ-S characteristics) varies depending on the road surface on which the vehicle is traveling. Therefore, even if the slip ratio that maximizes the friction coefficient is set as the target slip ratio, it may not be possible to achieve the desired vehicle driving characteristics.

[0004] In response to this, JP3479210B proposes a control in which the slip ratio is calculated while the vehicle is traveling on a rough road, and when it is determined that the vehicle is traveling on an unpaved road (gravel road or dirt road) based on the calculated slip ratio, the amount of operation of the actuator (brake) is increased compared to when the vehicle is traveling on a paved road.

[0005] On the other hand, the inventors have noticed that the above-mentioned existing slip control cannot achieve the desired driving characteristics (good acceleration feeling and suppression of tire stacking) on ​​special driving surfaces (particularly muddy road surfaces) that exhibit more distinctive μ-S characteristics than unpaved roads such as gravel roads or dirt roads.

[0006] Therefore, an object of the present invention is to realize slip control that can achieve both a good acceleration feeling and prevention of stuckness on muddy road surfaces.

[0007] According to one aspect of the present invention, there is provided a vehicle driving force control method for controlling the driving force output by a driving source mounted on a vehicle based on the slip ratio of the vehicle. This vehicle driving force control method measures the friction coefficient and slip ratio of the road surface on which the vehicle is traveling at a predetermined measurement period, generates a μ-S characteristic map representing the relationship between the friction coefficient and slip ratio of the road surface based on the combination of the friction coefficient and slip ratio obtained at each measurement period, determines whether the road surface is a muddy road surface based on the generated μ-S characteristic map, and if it is determined that the road surface is a muddy road surface, identifies an appropriate slip ratio zone on the μ-S characteristic map that is lower than the slip ratio at maximum friction and where the road-transmitted torque is equal to or greater than a predetermined value, and adjusts the driving force so that the slip ratio falls within the appropriate slip ratio zone.

[0008] According to one aspect of the present invention, it is possible to realize slip control that can achieve both a good acceleration feeling and prevention of stuck on a muddy road surface.

[0009] FIG. 1 is a block diagram illustrating a vehicle configuration to which a vehicle driving force control method according to an embodiment of the present invention is applied. FIG. 2 is a block diagram illustrating the function of a motor controller. FIG. 3 is a block diagram illustrating the function of a correction torque calculation unit. FIG. 4 is a flowchart illustrating processing in the correction torque calculation unit. FIG. 5 is a diagram illustrating an example of a μ-S characteristic map generated during driving and a prepared μ-S characteristic for a muddy road surface. FIG. 6 is a diagram illustrating a comparison between the μ-S characteristic map and the μ-S characteristics for various road surfaces. FIG. 7 is a diagram illustrating changes over time in wheel speed on a muddy road surface and various other road surfaces. FIG. 8 is a diagram illustrating an example of a method for setting an appropriate slip ratio zone. FIG. 9 is a timing chart illustrating the effects of this embodiment. FIG. 10 is a timing chart illustrating the effects of this embodiment.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] FIG. 1 is a block diagram illustrating the configuration of a vehicle 100 according to this embodiment. In this embodiment, the vehicle 100 is an electric vehicle. An electric vehicle is a vehicle equipped with an electric motor (hereinafter simply referred to as a "motor") as a drive source and driven by generating drive force resulting from torque generated by the motor on one or more wheels. Therefore, electric vehicles include not only so-called electric automobiles but also hybrid vehicles that use both a motor and an engine as a drive source. A four-wheel drive vehicle is a vehicle that uses four wheels as drive wheels. Four-wheel drive vehicles include vehicles that always use four wheels as drive wheels, as well as vehicles that can switch between two-wheel drive (front-wheel drive or rear-wheel drive) and four-wheel drive. Four-wheel drive vehicles can also control some of their four wheels as drive wheels in conjunction with one another, or control all four wheels as independently driven drive wheels.

[0012] 1, the vehicle 100 is an electric four-wheel drive vehicle. The vehicle 100 includes a front drive system fds, a rear drive system rds, a battery 1, and a motor controller 2 (controller).

[0013] The front drive system fds receives power from the battery 1 and drives the front wheels 9f under the control of the motor controller 2. The front drive system fds includes a front inverter 3f, a front drive motor 4f, a front reduction gear 5f, a front rotation sensor 6f, a front drive shaft 8f, and front wheels 9f. The subscript f indicates a front-side configuration. The front wheels 9f are a pair of wheels that are relatively forward of the vehicle 100, out of the four wheels equipped on the vehicle 100. The forward direction of the vehicle 100 is a predetermined direction that is formally determined depending on the orientation of the driver's seat, etc. The front drive system fds causes the front wheels 9f to function as drive wheels 9 that generate driving force for the vehicle 100.

[0014] The rear drive system rds receives power from a battery 1 and drives rear wheels 9r under the control of a motor controller 2. The rear drive system rds is symmetrical to the front drive system fds and includes a rear inverter 3r, a rear drive motor 4r, a rear reduction gear 5r, a rear rotation sensor 6r, a rear drive shaft 8r, and rear wheels 9r. The subscript r indicates a rear-side configuration. The rear wheels 9r are a pair of wheels that are relatively rearward of the vehicle 100 out of the four wheels equipped on the vehicle 100. The rearward direction of the vehicle 100 refers to the direction opposite to the forward direction of the vehicle 100. With the rear drive system rds, the rear wheels 9r function as drive wheels 9 that generate driving force for the vehicle 100.

[0015] The battery 1 is connected to the motor 4 via an inverter 3 and supplies drive power to the motor 4 by discharging. The battery 1 can also be charged by receiving regenerative power from the motor 4. In the front drive system fds, the battery 1 is connected to the front drive motor 4f via a front inverter 3f. Similarly, in the rear drive system rds, the battery 1 is connected to the rear drive motor 4r via a rear inverter 3r.

[0016] The motor controller 2 is a control device for the vehicle 100 and is a computer comprising a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), an input / output interface (I / O interface), etc. The motor controller 2 generates control signals for controlling the front drive motor 4f and the rear drive motor 4r based on vehicle variables of the vehicle 100. The vehicle variables are information indicating the operating state or control state of the entire vehicle 100 or of each part constituting the vehicle 100, and can be obtained by detection, measurement, calculation, etc. The vehicle variables include, for example, the accelerator opening APO, longitudinal and lateral G, vehicle speed V, gradient value, steering angle, and wheel speed, as well as the rotational speeds NMf and NMr of the motors 4f and 4r, and three-phase AC current, as described below. The motor controller 2 uses these vehicle variables to control the front drive motor 4f and the rear drive motor 4r, respectively.

[0017] The front inverter 3f and the rear inverter 3r convert the DC current supplied from the battery 1 into AC current by turning on / off switching elements in response to drive signals generated by the motor controller 2, and adjust the current supplied to the front drive motor 4f and the rear drive motor 4r, respectively. In addition, the inverters 3f and 3r inversely convert the AC current generated by the front drive motor 4f and the rear drive motor 4r due to regenerative braking force back into DC current, and adjust the current supplied to the battery 1.

[0018] The front drive motor 4f and the rear drive motor 4r are, for example, three-phase AC motors that generate drive force (torque) using AC current supplied from the inverter 3. The drive force generated by the front drive motor 4f is transmitted to the front wheels 9f via the front reduction gear 5f and the front drive shaft 8f. Similarly, the drive force generated by the rear drive motor 4r is transmitted to the rear wheels 9r via the rear reduction gear 5r and the rear drive shaft 8r. When the front drive motor 4f and the rear drive motor 4r rotate in conjunction with the front wheels 9f and the rear wheels 9r, respectively, they generate regenerative braking force and recover the kinetic energy of the vehicle 100 as electrical energy. The front drive motor 4f constitutes a drive source (front drive source) that drives the front wheels 9f. Similarly, the rear drive motor 4r constitutes a drive source (rear drive source) that drives the rear wheels 9r independently of the front wheels 9f.

[0019] The front reduction gear 5f and the rear reduction gear 5r are each made up of, for example, multiple gears. Each of these reduction gears 5f, 5r reduces the rotational speed NM of the motor 4 connected to it and transmits the reduced rotational speed to the drive shaft 8, thereby generating a driving torque or braking torque proportional to the reduction ratio.

[0020] The vehicle 100 is equipped with sensors such as an accelerator opening sensor 15a, a vehicle speed sensor 15b, and a wheel speed sensor 15c. The accelerator opening sensor 15a detects the accelerator opening APO, which is the amount of accelerator operation. The vehicle speed sensor 15b detects the vehicle speed V of the vehicle 100. The wheel speed sensor 15c detects the wheel speed of each drive wheel 9. The detection values ​​detected by the various sensors are input to the motor controller 2.

[0021] In the vehicle 100, the required torque T is determined according to the accelerator opening APO. ｒｅ is distributed to the front wheels 9f and the rear wheels 9r. In particular, by determining the front / rear distribution ratio γ in advance or in accordance with the running state, the final command value of either the front torque Tf or the rear torque Tr is determined, and the other is also determined.

[0022] In particular, the motor controller 2 calculates a final command value for either the front torque Tf or the rear torque Tr using the vehicle speed V and the wheel speed rw as inputs, and calculates the other in accordance with the front / rear torque distribution ratio γ. Furthermore, the motor controller 2 controls the driving force of the vehicle 100 by operating the front inverter 3f and the rear inverter 3r, respectively, based on the final command values ​​for the front torque Tf and the rear torque Tr calculated in this manner.

[0023] The processing performed by the motor controller 2 will be described in more detail below. In particular, slip control applied to at least one of the front drive system fds and the rear drive system rds will be described. For simplicity, the letters "f" and "r" representing the front and rear drive systems will be omitted.

[0024] 2 is a functional block diagram of the motor controller 2. As shown in the figure, the motor controller 2 calculates a final command value (final command torque T ＊＊ ) is required.

[0025] In particular, the motor controller 2 includes a basic command torque calculation unit 21, a correction torque calculation unit 22, and an adder 23.

[0026] The basic command torque calculation unit 21 calculates the vehicle speed V and the required torque T ｒｅ is input, and the basic torque command value T ＊ Here, the required torque T ｒｅ is a parameter indicating the driving force required for the vehicle 100. ｒｅis determined in accordance with, for example, the operation amount of the accelerator pedal (accelerator opening APO) mounted on the vehicle 100, or a command driving force received from a predetermined upper controller such as an automatic driving controller. ＊ is the required torque T ｒｅ Furthermore, it may be set to an appropriate value by referring to parameters that indicate the driving conditions, such as lateral G and road gradient.

[0027] The correction torque calculation unit 22 calculates the vehicle speed V, the wheel speed rw, and the final command torque T ＊＊ The feedback value is input, and the correction torque T ｓｌｐ The correction torque T ｓｌｐ The details of the calculation will be described later.

[0028] The adder 23 calculates the basic torque command value T ＊ , the correction torque T calculated by the correction torque calculation unit 22 ｓｌｐ The final command torque T ＊＊ Calculate the following.

[0029] The following describes the details of the correction torque calculation unit 22. In the following description, when it is clearly desired to distinguish that various control parameters are acquired at each measurement period k (k=1, 2, . . .), the subscript "(k)" is added to the reference numerals.

[0030] FIG. 3 is a functional block diagram of the correction torque calculation unit 22, and FIG. 4 is a flowchart illustrating the processing in the correction torque calculation unit 22.

[0031] The correction torque calculation unit 22 includes a wheel angular acceleration calculation unit 221 , a friction coefficient measurement unit 222 , a slip ratio measurement unit 223 , a μ-S characteristic map generation unit 224 , a road surface determination unit 225 , and a correction torque calculation unit 226 .

[0032] The wheel angular acceleration calculation unit 221 calculates the wheel speed rw detected by the wheel speed sensor 15c at every predetermined measurement period k. （ｋ） The wheel speed rw （ｋ） The time differential value of the wheel angular acceleration rω （ｋ） (S101).

[0033] The friction coefficient measurement unit 222 measures the vehicle weight W and the drive train inertia I ｐ , final command torque T ＊＊ The feedback value of the previous final command torque T ＊＊ （ｋ－１） "), and the wheel angular acceleration rω （ｋ） Based on this, the road surface μ （ｋ） In this embodiment, the road surface μ is a parameter that indicates the friction coefficient of the contact area between the road surface and the drive wheels 9. More specifically, the friction coefficient measurement unit 222 calculates the road surface μ based on the following equations 1 and 2: （ｋ） Calculate the following.

[0034]

[0035] In addition, "T" in Equation 1 ｔｒ（ｋ） " represents the value of the torque transmitted from the motor 4 to the road surface via the drive wheels 9. In the following, for the sake of simplicity, this will be referred to simply as "road surface transmission torque T ｔｒ（ｋ） " is also called.

[0036] The slip ratio measurement unit 223 measures the vehicle speed V detected by the vehicle speed sensor 15b at every predetermined measurement period k. （ｋ） and wheel speed rw （ｋ） Based on this, the slip rate S for each measurement period k is calculated. （ｋ） In this embodiment, the slip ratio S is a parameter that represents the degree of slippage of the drive wheels 9 relative to the road surface. More specifically, the slip ratio measurement unit 223 calculates the slip ratio S based on the following equation 3: （ｋ） Calculate the following.

[0037]

[0038] As can be seen from Equation 3, the slip ratio S （ｋ） is the wheel speed rw （ｋ） Vehicle speed V （ｋ） The deviation amount relative to the vehicle speed V （ｋ） In the following, for convenience, the slip ratio S calculated by the formula (3) is （ｋ） When specific numerical values ​​are given, the values ​​are expressed as percentages (%).

[0039] The μ-S characteristic map generating unit 224 calculates the road surface μ （ｋ） and slip ratio S （ｋ） The combination of each measurement point (μ （ｋ） , S （ｋ） ) and the μ-S characteristic map M μＳ is generated (S104).

[0040] The road surface determination unit 225 uses the generated μ-S characteristic map M μＳ It is determined whether the road surface on which the vehicle 100 is currently traveling is a muddy road surface based on the above information. Note that a muddy road surface in this embodiment refers to a road surface made of soil containing moisture due to rain or melting snow.

[0041] More specifically, first, as a first determination, the road surface determination unit 225 uses the generated μ-S characteristic map M μＳ It is determined whether or not the μ-S characteristic of a predetermined muddy road surface is met (S105).

[0042] FIG. 5 shows the μ-S characteristic map M μＳ 5 is a diagram showing an example of a μ-S characteristic map M μＳ , and the road surface μ and slip ratio S at each measurement point (μ （ｋ） , S （ｋ） ) is shown as a set of open plots. The μ-S characteristics on a muddy road are shown by a dashed line.

[0043] As shown in the figure, in the muddy road surface μ-S characteristics, the road surface μ is the slip ratio S at which the road surface μ is maximum (hereinafter referred to as the "slip ratio S at maximum friction"). Ｍａ」 Furthermore, the muddy road surface μ-S characteristic has a tendency to change from increasing to decreasing at the boundary of the slip ratio S Ｍａ A certain slip ratio S (hereinafter referred to as the "inflection slip point S") that is relatively close to this value is ｉｐ The road surface μ tends to decrease sharply (the decrease becomes sharper) at the inflection slip point S ｉｐ Although the slip ratio S at maximum friction is not limited to a specific value, it is generally about 20%. Ｍａ and the inflection slip point S ｉｐ The difference is generally between 0 and a few percent.

[0044] The inventors have determined that the muddy road surface μ-S characteristic is at the inflection slip point S ｉｐ The reason for this is speculated to be as follows: A muddy road surface is made up of two layers (upper and lower) with different properties. In particular, the upper layer is made up of mud that contains a certain amount of moisture and therefore has a relatively high rolling resistance. On the other hand, the lower layer is made up of mud that contains a certain amount of moisture but is harder than the upper layer and has a relatively low rolling resistance.

[0045] In addition, in areas where the slip ratio S is relatively small on a muddy road surface, the amount of sinking of the drive wheels 9 is relatively small, so the μ-S characteristic in low slip ratio sections is more dominated by the influence of the upper layer, which has high running resistance. For this reason, in low slip ratio sections, the μ-S characteristic on a muddy road surface shows a profile similar to that of high μ roads such as unpaved roads and roads with fresh snow. On the other hand, in high slip ratio sections, the amount of sinking of the drive wheels 9 becomes relatively large, and the influence of the lower layer, which has low running resistance, is more strongly evident in the μ-S characteristic. For this reason, in high slip ratio sections, the μ-S characteristic on a muddy road surface shows a profile similar to that of low μ roads such as icy roads. Therefore, near the boundary between the low slip ratio section and the high slip ratio section, the characteristics of the change in road surface μ in relation to the change in slip ratio S change abruptly, and the inflection slip point S ｉｐ It is thought that this will occur.

[0046] Therefore, the road surface determination unit 225 determines the road surface at each measurement point (μ （ｋ） , S （ｋ） The μ-S characteristic of the road surface determined by the following equation is the characteristic inflection slip point S ｉｐ The μ-S characteristic map M μＳ and estimate the conformity of the μ-S characteristics on muddy roads.

[0047] More specifically, the road surface determination unit 225 determines the road surface at each measurement point (μ （ｋ） , S （ｋ） ) at which the decrease in road surface μ between the previous and next measurement periods changes by more than a predetermined threshold decrease. （ｋ） , S （ｋ） ) slip ratio S at the inflection slip point S ｉｐThe threshold decrease amount is determined in advance as an appropriate value taking into consideration the reference muddy road surface μ-S characteristics. On the other hand, the measurement point (μ （ｋ） , S （ｋ） ) does not exist, the inflection slip point S ｉｐ is determined to not exist.

[0048] Then, the road surface determination unit 225 determines the inflection slip point S ｉｐ When the μ-S characteristic map M μＳ On the other hand, the road surface determination unit 225 determines that the inflection slip point S ｉｐ When there is no μ-S characteristic map M μＳ is determined not to match the μ-S characteristics of a muddy road surface.

[0049] As mentioned above, the inflection slip point S ｉｐ The generated μ-S characteristic map M μＳ By determining whether or not the μ-S characteristic of the muddy road surface matches the μ-S characteristic of the muddy road surface, it is possible to estimate with a certain degree of accuracy the scene in which the vehicle 100 is traveling on the muddy road surface.

[0050] On the other hand, even when the vehicle is traveling on a road surface other than a muddy road surface, the μ-S characteristic map M μＳ Inflection slip point S ｉｐ It is conceivable that there may be a situation where it is determined that the

[0051] FIG. 6 is a diagram showing an example of μ-S characteristics on a muddy road surface and various road surfaces other than a muddy road surface. Of the various road surfaces shown in FIG. 6, the μ-S characteristics of an unpaved road and a fresh snow road show a tendency for road surface μ to always increase with an increase in slip ratio S. Furthermore, the μ-S characteristics of a dry asphalt road and an icy road show a tendency for road surface μ to always increase with an increase in slip ratio S, similar to the muddy road surface μ-S characteristics. Ｍａ However, the μ-S characteristics of the dry asphalt road and the frozen road show that the slip ratio S at maximum friction is Ｍａ Even in the above high slip ratio section, no sudden decrease in road surface μ is observed (inflection slip point S ｉｐ does not exist).

[0052] Therefore, basically, the μ-S characteristic map M μＳ Inflection slip point S ｉｐ By checking whether or not there is a muddy road surface, it is possible to determine with a certain degree of accuracy whether the road surface is a muddy road surface or a different road surface.

[0053] On the other hand, it is also assumed that the road surface on which the vehicle 100 is traveling may change. For example, as shown in FIG. 6, in a scene where the road surface on which the vehicle 100 is traveling changes from a fresh snowy road to an icy road, the rate of decrease in road surface μ relative to the increment in slip ratio S before and after the change in road surface becomes larger than a certain value. For this reason, the values ​​of each measurement point (μ （ｋ） , S （ｋ） ) is referred to, the inflection slip point S ｉｐ Therefore, in this embodiment, from the viewpoint of estimating the scene of traveling on a muddy road surface with higher accuracy, the μ-S characteristic map M μＳ In addition to the first determination for confirming the agreement between the road surface μ-S characteristic and the muddy road surface μ-S characteristic, a second determination, which will be described later, is performed.

[0054] Returning to FIG. 4, if the determination result in S105 is affirmative, the road surface determination unit 225 executes a second determination (S106).

[0055] Specifically, the road surface determination unit 225 determines whether the current wheel angular acceleration rω is equal to or less than a predetermined threshold angular acceleration A.

[0056] The threshold angular acceleration A is determined in advance as an appropriate value that takes into consideration the difference between the time-varying increase trend of the wheel speed rw when traveling on a muddy road surface and the time-varying increase trend of the wheel speed rw when traveling on other road surfaces. In particular, it is preferable to determine the threshold angular acceleration A by taking into consideration the difference between the time-varying increase trend of the wheel speed rw on a muddy road surface and on other road surfaces that exhibit μ-S characteristic profiles that are at least partially similar to the muddy road surface.

[0057] 7 is a diagram showing the time-dependent change in wheel speed rw on a muddy road surface and other road surfaces. In particular, FIG. 7 shows the time-dependent change in wheel speed rw when the same motor torque T is applied in driving scenes on each road surface.

[0058] Muddy road surfaces exhibit higher running resistance than fresh snow, frozen, and unpaved roads. Therefore, on muddy road surfaces, the rate of increase per hour of the wheel speed rw is relatively small compared to fresh snow, frozen, and unpaved roads. Therefore, by referring to the wheel angular acceleration rω, which indicates the rate of increase, it is possible to more reliably distinguish between running on a muddy road surface and running on a fresh snow, frozen, or unpaved road. In particular, even when the running road surface changes from a fresh snow or unpaved road to an icy road, the μ-S characteristic map M μＳ Even if the driving scene is similar to the μ-S characteristics of a muddy road surface, by referring to the rate of increase in the wheel speed rw through the wheel angular acceleration rω, it is possible to more accurately distinguish the driving scene from the muddy road surface.

[0059] Returning to FIG. 4, if the determination result in S106 is affirmative, the road surface determination unit 225 calculates the μ-S characteristic map M μＳ Each measurement point (μ （ｋ） , S （ｋ） It is determined whether the total number of data items in the μ-S characteristic map M is equal to or greater than a predetermined number (S107). μＳ This is carried out with the aim of verifying the reliability of the

[0060] If the results of the determinations in S105 to S107 are all positive, the road surface determination unit 225 determines that the vehicle 100 is traveling on a muddy road surface (S108). ｓｌｐ is the first correction torque T ｓｌｐ１ Here, the first correction torque T ｓｌｐ１ is the slip ratio S within a predetermined appropriate slip ratio range ΔS ｏｐｔ The basic torque command value T is used to adjust the motor torque T so that it is included in ＊ is defined as a correction value for

[0061] FIG. 8 shows the appropriate slip ratio section ΔS ｏｐｔ 8 is a diagram illustrating an example of a method for setting the μ-S characteristic map M μＳ At each measurement point (μ （ｋ） , S （ｋ） ) is shown as a fitting curve by a solid line.

[0062] As shown in the figure, in this embodiment, the slip ratio S Ｍａ The range of slip ratio S that is lower than the predetermined value is called the appropriate slip ratio range ΔS. ｏｐｔ In particular, the appropriate slip ratio section ΔS ｏｐｔ is the road surface transmission torque T determined by Equation 1 ｔｒ The appropriate slip ratio range ΔS is defined as the range of the slip ratio S in which the slip ratio ΔS is equal to or greater than a certain value. ｏｐｔ Although there is no specific numerical range for the slip ratio S at maximum friction, for example, Ｍａ or inflection slip point S ｉｐ It is preferable to define the appropriate slip ratio range ΔS as a range with a lower limit of 10% lower than the appropriate slip ratio range ΔS and an upper limit of 5% lower than the appropriate slip ratio range ΔS. ｏｐｔ The slip ratio S at maximum friction Ｍａ or inflection slip point S ｉｐ It is preferable to set the slip ratio S to a range that is 0.05 to 1 (5 to 10%) lower than the range.

[0063] Then, the first correction torque T ｓｌｐ１ is the slip ratio S in the appropriate slip ratio section ΔS ｏｐｔ The basic torque command value T ＊ Therefore, the first correction torque T ｓｌｐ１ By calculating the road surface transmission torque T ｔｒ To ensure that the road surface transmission torque T ｔｒ More specifically, the driving force of the vehicle 100 is adjusted so that the slip ratio S is within the appropriate slip ratio section ΔS ｏｐｔIf the slip ratio S is less than the target slip ratio, the motor torque T is corrected in the increasing direction so that the slip ratio S increases toward the target slip ratio (first correction torque T ｓｌｐ１ On the other hand, when the slip ratio S is within the appropriate slip ratio range ΔS ｏｐｔ If the slip ratio S exceeds the target slip ratio, the motor torque T is corrected in the decreasing direction so that the slip ratio S decreases toward the target slip ratio (first correction torque T ｓｌｐ１ will be negative).

[0064] The first correction torque T ｓｌｐ１ The effects of defining the above will be explained in detail.

[0065] First, as described above, the muddy road surface has a maximum friction slip ratio S Ｍａ Inflection slip point S close to ｉｐ Therefore, as in the case of general slip control, the slip ratio S Ｍａ is the target slip ratio, the actual slip ratio S during travel is likely to enter a region where the road surface μ decreases rapidly, which is expected to lead to tire stuck (spinning). Therefore, on muddy roads, it is possible to apply the driving force control of Reference Example 1 or Reference Example 2 described below instead of the general slip control described above.

[0066] FIG. 9 shows the change over time in the vehicle speed V and the operating point on the μ-S characteristic when the driving force controls according to the first and second reference examples are executed in a driving scene on a muddy road surface.

[0067] First, as a reference example 1, the basic torque command value T ＊ This is the final command torque T ＊＊ When the control of Reference Example 1 is applied to a driving scene on a muddy road, no correction (limitation) is applied to the motor torque T even if the slip ratio S increases. Therefore, as the accelerator opening APO increases, the slip ratio S increases, and the road surface μ enters a section where it rapidly decreases (see maps C and D), causing the tire to become stuck.

[0068] On the other hand, as a reference example 2, slip control is assumed in which the target slip ratio is set to a relatively low range (for example, 10 to 15%). When the slip control of the reference example 2 is applied to a driving scene on a muddy road surface, the maximum friction slip ratio S Ｍａ Compared to general slip control that sets the target slip ratio at , the slip ratio S is maintained in a region of relatively low road surface μ (see maps E to H). This makes it possible to avoid entering a region of sudden decrease in road surface μ, which is a cause of the above-mentioned stuck condition. However, it is not possible to use regions of high road surface μ, and the amount of restriction on motor torque T becomes excessive, resulting in a decrease in the acceleration feeling of the vehicle 100.

[0069] FIG. 10 shows the change over time in the vehicle speed V and the operating point on the μ-S characteristic when the driving force control according to this embodiment (slip control of the example) is executed in a driving scene on a muddy road surface.

[0070] As shown in the figure, in the slip control of the embodiment, in a driving scene on a muddy road surface, the slip ratio S is within the appropriate slip ratio section ΔS ｏｐ (See maps J to L in particular) and adjusts the road surface μ to the maximum value (road surface transmission torque T ｔｒ Therefore, the motor torque T can be adjusted to maintain the inflection slip point S ｉｐ The subsequent slip ratio section where the road surface μ suddenly decreases is avoided to prevent the vehicle from getting stuck, while the amount of restriction on the motor torque T is kept as low as possible to maintain the acceleration feeling of the vehicle 100.

[0071] 4, if any of the determination results in S105 to S107 is negative, the road surface determination unit 225 determines that the vehicle 100 is traveling on a road surface other than a muddy road surface (S110). ｓｌｐ is the second correction torque T ｓｌｐ２ Here, the second correction torque T ｓｌｐ２ is the slip ratio S when the friction is maximum. Ｍａ The basic torque command value T is used to adjust the motor torque T so that it approaches ＊ is defined as a correction value for

[0072] Therefore, in the driving force control method according to this embodiment, when it is determined that the vehicle is traveling on a road surface other than a muddy road surface that requires slip control, the motor torque T is adjusted to the slip ratio S that maximizes the road surface μ. In other words, even when it is determined that the vehicle is traveling on a road surface other than a muddy road surface (particularly a dry asphalt road or an icy road as shown in FIG. 6), it is possible to achieve driving force control that can achieve both a good acceleration feel and prevention of stuckness.

[0073] The main effects of this embodiment will be described below.

[0074] In this embodiment, a vehicle driving force control method is provided that controls the driving force (motor torque T) output by the driving source (motor 4) mounted on the vehicle 100 based on the slip ratio S of the vehicle 100.

[0075] In this vehicle driving force control method, the coefficient of friction (road surface μ （ｋ） ) and slip ratio S （ｋ） Measure the road surface μ obtained at each measurement period k （ｋ） and slip ratio S （ｋ） Combination of measurement points (μ （ｋ） , S （ｋ） )) based on the μ-S characteristic map M which shows the relationship between the road surface μ and the slip ratio S of the traveling road surface. μＳ The generated μ-S characteristic map M μＳ Based on this, it is determined whether the road surface is a muddy road surface.

[0076] When it is determined that the road surface is muddy, the μ-S characteristic map M μＳ The slip ratio S at maximum friction is Ｍａ and the road surface transmission torque T ｔｒ is equal to or greater than a predetermined value. ｏｐｔ The slip ratio S is determined to be within the appropriate slip ratio range ΔS ｏｐｔ The driving force (first correction torque T ｓｌｐ１ ) to adjust the

[0077] This allows for the realization of specific control logic for appropriately estimating whether the road surface being traveled on is a muddy road surface, and then performing slip control to prevent the tires from getting stuck while maintaining the acceleration feel of the vehicle 100 on the muddy road surface.

[0078] In particular, the determination of whether the road surface is muddy or not is based on the μ-S characteristic map M μＳ The inflection slip point S is where the decrease in road surface μ relative to the slip ratio S exceeds a certain value. ｉｐ exists, and a second step (S106) of determining whether the wheel angular acceleration rω of the vehicle 100 is equal to or less than a predetermined threshold angular acceleration A. If the determination results in both the first step and the second step are positive, the traveling road surface is determined to be a muddy road surface, and otherwise the traveling road surface is determined to be not a muddy road surface.

[0079] This allows for a more specific control logic to be implemented to more reliably estimate whether the road surface is muddy. In particular, the first determination is made based on the μ-S characteristic map M μＳ However, the characteristic inflection slip point S in the μ-S characteristics of the muddy road surface ｉｐ Furthermore, in the second determination, by focusing on whether the increasing rate of the wheel speed rw is low, which is characteristic of a muddy road surface, it is possible to more accurately estimate the driving scene on a muddy road surface. In particular, if the μ-S characteristic map M μＳ Inflection slip point S ｉｐ Even if the first determination is affirmative due to the appearance of rω, the driving scene on a muddy road surface can be determined with higher accuracy by also performing the second determination that references the wheel angular acceleration rω.

[0080] In addition, the appropriate slip ratio section ΔS ｏｐｔ The slip ratio S at maximum friction Ｍａ The lower limit is set to a value 10% lower than the reference value, and the upper limit is set to a value 5% lower than the reference value.

[0081] As a result, the appropriate slip ratio section ΔS ｏｐｔAs a result, it is possible to determine a particularly preferable specific numerical range that can prevent the vehicle from getting stuck while maintaining a sense of acceleration when driving on a muddy road surface.

[0082] In particular, in this embodiment, the road surface μ is calculated as the road surface transmission torque T ｔｒ and vehicle weight W (Equation 2). Slip ratio S is calculated from vehicle speed V and wheel speed rw (Equation 3). Road surface transmission torque T ｔｒ is the command torque to the motor 4 (final command torque T ＊＊ (feedback value of ) and the drive train inertia I ｐ It is calculated from (Equation 1).

[0083] As a result, the μ-S characteristic map M μＳ Generation of appropriate slip ratio section ΔS ｏｐｔ A more specific calculation logic is realized to obtain various parameters used for setting the parameters.

[0084] Furthermore, in this embodiment, if it is determined that the road surface is not a muddy road surface, the slip ratio S is equal to the maximum friction slip ratio S Ｍａ The driving force (second correction torque T ｓｌｐ２ ) to adjust the

[0085] As a result, even in a situation where it is determined that the vehicle is traveling on a road surface other than a muddy road surface, the motor torque T is adjusted to target the slip ratio S at which the road surface μ becomes maximum. In other words, even when it is determined that the vehicle is traveling on a road surface other than a muddy road surface, it is possible to achieve driving force control that can achieve both a good acceleration feeling and prevention of getting stuck.

[0086] If it is determined that the road surface is not a muddy one, the generated μ-S characteristic map M μＳ is the slip ratio S at maximum friction Ｍａ and the slip ratio S at maximum friction is determined. Ｍａ When the slip ratio S is greater than the maximum friction slip ratio S Ｍａ The second correction torque T ｓｌｐ２ While setting the slip rate at maximum friction S ＭａWhen the vehicle does not have the second correction torque T ｓｌｐ２ is set to 0 (basic torque command value T ＊ In other words, the μ-S characteristic map M μＳ is the slip ratio S at maximum friction Ｍａ , the motor torque T is the required driving force for the vehicle 100 (required torque T ｒｅ ) according to the basic value (basic torque command value T ＊ ) will be maintained.

[0087] As a result, on a road surface where the road surface μ tends to increase as the slip ratio S increases, the slip control can be essentially turned off, and unnecessary restrictions on the motor torque T can be suppressed.

[0088] In addition, this embodiment provides another aspect of a vehicle driving force control method that controls the driving force (motor torque T) output by the driving source (motor 4) mounted on the vehicle 100 based on the slip ratio S of the vehicle 100.

[0089] In this vehicle driving force control method, the coefficient of friction (road surface μ （ｋ） ) and slip ratio S （ｋ） Measure the road surface μ obtained at each measurement period k （ｋ） and slip ratio S （ｋ） Combination of measurement points (μ （ｋ） , S （ｋ） )) based on the μ-S characteristic map M which shows the relationship between the road surface μ and the slip ratio S of the traveling road surface. μＳ The generated μ-S characteristic map M μＳ Whether the road surface is a special road surface or not is determined based on the wheel angular acceleration rω of the vehicle 100. The special road surface is determined by the μ-S characteristic map M μＳ The inflection slip point S where the decrease in road surface μ relative to the slip ratio S exceeds a certain value. ｉｐ is present and the wheel angular acceleration rω is equal to or less than a predetermined threshold angular acceleration A.

[0090] When the road surface is determined to be a special road surface, the μ-S characteristic map M μＳ The slip ratio S at maximum friction is Ｍａ and the road surface transmission torque T ｔｒ is equal to or greater than a predetermined value. ｏｐｔ The slip ratio S is determined to be within the appropriate slip ratio range ΔS ｏｐｔ The driving force (first correction torque T ｓｌｐ１ ) to adjust the

[0091] This makes it possible to appropriately estimate whether the road surface is a special road surface where normal slip control cannot adequately provide an appropriate acceleration feeling or prevent the vehicle from getting stuck. Based on this, a specific control logic is realized for performing slip control that prevents the vehicle from getting stuck (tire spin) while maintaining the acceleration feeling of the vehicle 100 on the special road surface. In particular, this control logic makes it possible to perform appropriate slip control when the vehicle is traveling on a muddy road surface and when the vehicle is traveling on other road surfaces, without requiring a mode selection operation by the driver of the vehicle 100 or the like.

[0092] Furthermore, in this embodiment, a motor controller 2 is provided that functions as a vehicle driving force control device suitable for executing the vehicle driving force control method.

[0093] In particular, the motor controller 2 calculates the friction coefficient (road surface μ （ｋ） ) and slip ratio S （ｋ） and a measurement unit (222, 223) for measuring the road surface μ obtained at each measurement period k. （ｋ） and slip ratio S （ｋ） Combination of measurement points (μ （ｋ） , S （ｋ） )) based on the μ-S characteristic map M which shows the relationship between the road surface μ and the slip ratio S of the traveling road surface. μＳ and a generating unit (224) for generating the μ-S characteristic map M μＳ a determination unit (225) for determining whether the road surface is a muddy road surface based on the μ-S characteristic map M μＳ The slip ratio S at maximum friction is Ｍａand the road surface transmission torque T ｔｒ is equal to or greater than a predetermined value. ｏｐｔ and a determination unit (226) for determining whether the slip ratio S is within an appropriate slip ratio range ΔS. ｏｐｔ The driving force (first correction torque T ｓｌｐ１ and an adjusting portion (22, 23) for adjusting the

[0094] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0095] In the above embodiment, the μ-S characteristic map M μＳ As a specific example of the determination (first determination) of whether the μ-S characteristic map M μＳ Inflection slip point S ｉｐ On the other hand, instead of this, the μ-S characteristic map M μＳ The conformity of the μ-S characteristics of the muddy road surface to the μ-S characteristics map M may be estimated by other methods. μＳ The matching rate between the fitting curve of each measurement point (μ, S) constituting the map and a curve representing the μ-S characteristics of a muddy road surface prepared in advance is calculated using a predetermined statistical algorithm or machine learning, and if the matching rate is equal to or greater than a certain value, the μ-S characteristics map M μＳ It is also possible to adopt a logic that determines that the μ-S characteristics of the muddy road surface are met.

[0096] In the above embodiment, an example of executing driving force control (slip control) has been described assuming that the vehicle 100 is configured as a four-wheel drive electric vehicle. However, the driving force control logic described in the above embodiment can also be applied to a two-wheel drive electric vehicle equipped with a motor 4 that drives only one of the front wheels 9f and the rear wheels 9r, with some modifications that will be obvious to those skilled in the art. Furthermore, the driving force control logic can be similarly applied to two-wheel drive vehicles or four-wheel drive vehicles equipped with an internal combustion engine as a driving source.

Claims

1. A vehicle driving force control method for controlling the driving force output by a driving power source mounted on a vehicle based on the slip ratio of the vehicle, comprising: measuring the friction coefficient and the slip ratio on the driving road surface of the vehicle at a predetermined measurement period; generating a μ-S characteristic map representing the relationship between the friction coefficient and the slip ratio on the driving road surface based on the combination of the friction coefficient and the slip ratio obtained in each measurement period; determining whether the driving road surface is a muddy road surface based on the generated μ-S characteristic map; when it is determined that the driving road surface is the muddy road surface, specifying an appropriate slip ratio range that is lower than the slip ratio at maximum friction on the μ-S characteristic map and at which the road surface transmission torque is equal to or greater than a predetermined value; adjusting the driving force so that the slip ratio is included in the appropriate slip ratio range; the determination as to whether the driving road surface is the muddy road surface includes a first step of determining whether there is an inflection slip point on the μ-S characteristic map at which the decrease width of the friction coefficient with respect to the slip ratio is equal to or greater than a certain value; and a second step of determining whether the wheel angular acceleration of the vehicle is equal to or less than a predetermined threshold angular acceleration, and determining that the driving road surface is the muddy road surface when each determination result in the first step and the second step is affirmative, and determining that the driving road surface is not the muddy road surface otherwise. Vehicle driving force control method.

2. The vehicle driving force control method according to claim 1, wherein the appropriate slip ratio range is defined as a range having a lower limit of a value 10% lower than the slip ratio at maximum friction and an upper limit of a value 5% lower than the slip ratio at maximum friction. Vehicle driving force control method.

3. The vehicle driving force control method according to claim 1, wherein the friction coefficient is calculated from the road surface transmission torque and the vehicle weight, the slip ratio is calculated from the vehicle speed and the wheel speed, and the road surface transmission torque is calculated from the command torque for the driving power source and the inertia of the vehicle's drive system. Vehicle driving force control method.

4. The vehicle driving force control method according to claim 1, wherein when it is determined that the driving road surface is not the muddy road surface, the driving force is adjusted so that the slip ratio approaches the slip ratio at maximum friction, or the driving force is maintained at a basic value corresponding to the required driving force for the vehicle. Vehicle driving force control method.

5. A vehicle driving force control method for controlling the driving force output by a driving power source mounted on the vehicle based on the slip ratio of the vehicle, comprising: Measuring the friction coefficient and the slip ratio on the driving road surface of the vehicle at a predetermined measurement period; Generating a μ-S characteristic map representing the relationship between the friction coefficient and the slip ratio on the driving road surface based on the combination of the friction coefficient and the slip ratio obtained in each measurement period; Determining whether the driving road surface is a predetermined special road surface based on the generated μ-S characteristic map and the wheel angular acceleration of the vehicle; The special road surface is a road surface having a characteristic that there is an inflection slip point at which the decrease width of the friction coefficient with respect to the slip ratio becomes a certain value or more on the μ-S characteristic map and the wheel angular acceleration becomes equal to or less than a predetermined threshold angular acceleration; When it is determined that the driving road surface is the special road surface, specifying an appropriate slip ratio range that is lower than the maximum friction slip ratio on the μ-S characteristic map and at which the road surface transmission torque is equal to or more than a predetermined value; Adjusting the driving force so that the slip ratio is included in the appropriate slip ratio range; Vehicle driving force control method.

6. A vehicle driving force control device for controlling the driving force output by a driving power source mounted on the vehicle based on the slip ratio of the vehicle, comprising: A measuring unit that measures the friction coefficient and the slip ratio on the driving road surface of the vehicle at a predetermined measurement period; A generating unit that generates a μ-S characteristic map representing the relationship between the friction coefficient and the slip ratio on the driving road surface based on the combination of the friction coefficient and the slip ratio obtained in each measurement period; A determination unit that determines whether the driving road surface is a muddy road surface based on the generated μ-S characteristic map; When it is determined that the driving road surface is the muddy road surface, specifying an appropriate slip ratio range that is lower than the maximum friction slip ratio on the μ-S characteristic map and at which the road surface transmission torque is equal to or more than a predetermined value; An adjustment unit that adjusts the driving force so that the slip ratio is included in the appropriate slip ratio range; and The determination unit: Performing a first step of determining whether there is an inflection slip point at which the decrease width of the friction coefficient with respect to the slip ratio becomes a certain value or more on the μ-S characteristic map; Performing a second step of determining whether the wheel angular acceleration of the vehicle becomes equal to or less than a predetermined threshold angular acceleration. When both determination results in the first step and the second step are affirmative, it is determined that the driving road surface is the muddy road surface, and in other cases, it is determined that the driving road surface is not the muddy road surface. Vehicle driving force control device.