Control method for electric vehicle and control device for electric vehicle

Abstract

The controller (20) sets a front basic slip amount upper limit value (Svfr) based on the accelerator opening degree (θa) and the vehicle body speed (Vm) in the case where the drive mode is the sand mode. The controller (20) performs addition operation processing of adding the superimposed slip amount (Svb) to the front basic slip amount upper limit value (Svfr) to finally determine a front slip amount upper limit value (Svfm) in the case where the acceleration request of the driver is determined. The controller (20) sets a rear slip amount upper limit value (Svrm) based on the accelerator opening degree (θa) and the vehicle body speed (Vm). Also, the controller (20) controls the slip amount of the front wheels (2f) to be less than or equal to the front slip amount upper limit value (Svfm), and controls the slip amount of the rear wheels (2r) to be less than or equal to the rear slip amount upper limit value (Svrm).

Description

Technical Field

[0001] This invention relates to a control method and a control device for electric vehicles. Background Technology

[0002] Patent Document 1 discloses a vehicle driving control device that controls the driving torque applied to the drive wheels according to a control mode corresponding to the type of road surface the vehicle is traveling on. When the vehicle driving control device determines that a mode selection condition has been met, it selects a control mode from a predetermined plurality of control modes as the operating control mode based on at least one of the road surface deformation and the slip of all drive wheels, in a manner that corresponds to the type of road surface. The vehicle driving control device controls the driving torque applied to the drive wheels according to the operating control mode. Furthermore, for drive wheels with slip exceeding a predetermined threshold slip determined corresponding to the operating control mode, the vehicle driving control device reduces the driving force so that the slip is less than or equal to the threshold slip.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2020-59421 Summary of the Invention

[0004] In the method disclosed in Patent Document 1, a threshold slip amount is uniformly set corresponding to the control mode. When driving on sandy terrain with accumulated gravel, the driving resistance is high, resulting in a difficulty in obtaining a sense of acceleration compared to driving on paved roads.

[0005] The purpose of this invention is to provide a control method and control device for an electric vehicle that can achieve good acceleration even when driving on sandy terrain with accumulated gravel.

[0006] One aspect of the present invention relates to a control method for an electric vehicle, which includes the following processing: when the driving mode of the electric vehicle is sand mode, based on the accelerator opening and vehicle speed, respectively setting upper limits for the allowable slip amount of the front wheels (i.e., the upper limit of front slip amount) and the upper limits for the allowable slip amount of the rear wheels (i.e., the upper limit of rear slip amount). Furthermore, the control method for the electric vehicle includes the following processing: when a driver's acceleration request is determined, performing an addition operation to determine the upper limit of front slip amount by adding the upper limit of forward slip amount to the value obtained by superimposing slip amount.

[0007] The effects of the invention

[0008] According to one aspect of the present invention, a good sense of acceleration can be obtained even when driving on sand. Attached Figure Description

[0009] Figure 1This is a schematic diagram illustrating the structure of the electric vehicle according to this embodiment.

[0010] Figure 2 This is a diagram illustrating the functionality of the controller.

[0011] Figure 3 This is a flowchart illustrating the control method for electric vehicles.

[0012] Figure 4 This diagram illustrates the computational processing involved in the upper limit of the slip amount.

[0013] Figure 5 This is a diagram illustrating the upper limit of the basic slip.

[0014] Figure 6 This is a diagram illustrating the first superimposed slip.

[0015] Figure 7 This is a diagram illustrating the second superimposed slip.

[0016] Figure 8 This is a diagram illustrating the superimposed slip gain.

[0017] Figure 9 This is a timing diagram illustrating an example of slip control involved in this embodiment.

[0018] Figure 10 This is a timing diagram illustrating an example of slip control involved in this embodiment. Detailed Implementation

[0019] Reference Figure 1 The electric vehicle 1 (hereinafter referred to as "vehicle 1") according to this embodiment will be described. Vehicle 1 in this embodiment is a vehicle that uses the power of an electric motor as a driving force, such as an electric vehicle, a hybrid electric vehicle, or a fuel cell vehicle. Vehicle 1 is a four-wheel drive vehicle that can independently drive the front wheels 2f and the rear wheels 2r.

[0020] Vehicle 1 has a front drive motor 10f that drives the front wheels 2f, a rear drive motor 10r that drives the rear wheels 2r, and a controller 20.

[0021] The front drive motor 10f is controlled by the controller 20. Under the control of the controller 20, the front drive motor 10f is supplied with drive current from an inverter that performs on-off operations, generating a drive torque corresponding to the drive current. The front wheel 2f rotates according to the drive torque output from the front drive motor 10f.

[0022] The rear drive motor 10r is controlled by the controller 20. Under the control of the controller 20, the rear drive motor 10r is supplied with drive current from an inverter that performs on-off operations, generating a drive torque corresponding to the drive current. The rear wheel 2r rotates according to the drive torque output from the rear drive motor 10r.

[0023] The controller 20 consists of a computer with a hardware processor such as a CPU (Central Processing Unit), memory, and various interfaces. The CPU reads various computer programs stored in memory and other containers, and executes the various commands contained in the programs. By executing the programs, the controller 20 functions as one of the multiple information processing circuits described later. Furthermore, the controller 20 implements the functions of each information processing circuit through software, but it can also implement its functions through dedicated hardware.

[0024] The controller 20 controls the front drive motor 10f and the rear drive motor 10r. Specifically, the controller 20 calculates the front torque command value of the front drive motor 10f, which corresponds to the driving force of the vehicle 1. Based on the front torque command value, the controller 20 calculates the front current command value supplied to the front drive motor 10f. According to the front current command value, the controller 20 causes the inverter to switch on and off, supplying drive current to the front drive motor 10f from the inverter. Similarly, the controller 20 calculates the rear torque command value of the rear drive motor 10r, which corresponds to the requested driving force of the vehicle 1. Based on the rear torque command value, the controller 20 calculates the rear current command value supplied to the rear drive motor 10r. According to the rear current command value, the controller 20 causes the inverter to switch on and off, supplying drive current to the rear drive motor 10r from the inverter.

[0025] Various signals are input to the controller 20.

[0026] The vehicle speed signal represents the vehicle speed Vm. The vehicle speed Vm can be calculated by controller 20 or a higher-level controller (not shown) based on position information obtained from a GPS sensor, or based on data detected by an acceleration sensor. Alternatively, the vehicle speed Vm can also be calculated based on the rotational speeds of the front wheels 2f and the rear wheels 2f.

[0027] The accelerator opening signal represents the accelerator opening degree θa. θa is detected by the accelerator opening degree sensor and varies according to the amount of pressure applied to the accelerator pedal by the driver. The steering angle signal represents the steering angle θs. θs is detected by the steering angle sensor and varies according to the amount of steering input by the driver.

[0028] The front wheel speed signal represents the rotational speed of the front wheel 2f, i.e., the front wheel speed Vwf. The front wheel speed Vwf is detected by a wheel speed sensor located on the front wheel 2f. The rear wheel speed signal represents the rotational speed of the rear wheel 2r, i.e., the rear wheel speed Vwr. The rear wheel speed Vwr is detected by a wheel speed sensor located on the rear wheel 2r.

[0029] The drive mode signal Sd represents the drive mode. The drive mode is used to set the vehicle's operating characteristics, specifically the control characteristics of vehicle control devices such as the front drive motor and rear drive motors 10f and 10r. Based on the drive mode, characteristics such as drive force gain and the upper limit of slippage for the front wheels 2f and rear wheels 2r are adjusted.

[0030] Vehicle 1 has multiple driving modes corresponding to different road surfaces. For example, vehicle 1 includes four driving modes: Standard, Snow, Sand, and Rock. If the driver operates an operation switch (not shown) to select one of the four driving modes, the signal indicating the selected driving mode is output to the controller 20 as the driving mode signal Sd.

[0031] The following is a brief explanation of each drive mode. Standard mode provides driving characteristics suitable for paved roads and other repaired surfaces. Snow mode provides driving characteristics suitable for snow-covered or icy roads. Sand mode provides driving characteristics suitable for sandy terrain such as deserts or beaches. Rock climbing mode provides driving characteristics suitable for rocky surfaces.

[0032] The drive force gain is the gain multiplied by the vehicle's drive force, which is determined based on the accelerator opening and vehicle speed Vm. The drive force gain in standard mode is set to a neutral value (e.g., "1"), while the drive force gain in snow, sand, and rock climbing modes is set to a smaller value than that in standard mode. When snow, sand, or rock climbing modes are selected, the control makes the drive force response slower compared to when standard mode is selected.

[0033] The maximum slip amount is the upper limit of the allowable slip amount for the front wheels 2f and the rear wheels 2r. The maximum slip amount for Sand Mode is set to a larger value than that for Standard Mode, Snow Mode, and Rock Climbing Mode. When Standard Mode, Snow Mode, and Rock Climbing Mode are selected, Vehicle 1 is controlled to move without slipping the front wheels 2f and the rear wheels 2r. When Sand Mode is selected, Vehicle 1 is controlled to move while slipping the front wheels 2f and the rear wheels 2r.

[0034] One feature of this embodiment is that, when the driving mode is sand mode, the controller 20 controls the slippage of the front wheel 2f and the rear wheel 2r to an optimal level. Here, sand mode envisions sand as a surface where fine gravel is piled up without being solidified. Specifically, sand has a surface layer to the extent that the vehicle 1 can drive on it when the slippage is small. In addition, the sand is piled up with gravel to such an extent that, when the slippage is large, the gravel is scraped out by the rotation of the wheels, and part of the wheel sinks to the lower side of the surface.

[0035] Reference Figure 2 The functions of the controller 20 will be explained below. As multiple information processing circuits, the controller 20 has a slip upper limit value calculation unit 21, a front torque upper limit value calculation unit 22f, a rear torque upper limit value calculation unit 22r, a front torque command value calculation unit 23f, and a rear torque command value calculation unit 23r.

[0036] The slip limit calculation unit 21 calculates the front slip limit value Svfm and the rear slip limit value Svrm based on the vehicle speed Vm, steering angle θs, accelerator opening θa, and accelerator opening speed Δθa. The front slip limit value Svfm is the upper limit of the slip allowed for the front wheels 2f. That is, even if the front wheels 2f slip while the vehicle is moving, slippage of the front wheels 2f is allowed until the slippage reaches the front slip limit value Svfm. Similarly, the rear slip limit value Svrm is the upper limit of the slip allowed for the rear wheels 2r. The accelerator opening speed Δθa is the change in accelerator opening θa per unit time, calculated based on the accelerator opening θa. Details of the calculation methods for the front slip limit value Svfm and the rear slip limit value Svrm will be described later.

[0037] The front torque upper limit calculation unit 22f calculates the upper limit of the driving torque allowed by the front drive motor 10f, namely the front torque upper limit value Ttfm, based on the front slip upper limit value Svfm and the slip amount of the front wheel 2f, namely the front slip amount Svf. That is, the front torque upper limit value Ttfm is equivalent to the driving torque required for the front wheel 2f to rotate under the condition of the front slip upper limit value Svfm. Similarly, the rear torque upper limit calculation unit 22r calculates the upper limit of the driving torque allowed by the rear drive motor 10r, namely the rear torque upper limit value Ttrm, based on the rear slip upper limit value Svrm and the slip amount of the rear wheel 2r, namely the rear slip amount Svr.

[0038] The front torque command value calculation unit 23f calculates the smaller of the front target torque Ttf and the front torque upper limit value Ttfm as the front torque command value Tcf. The rear torque command value calculation unit 23r calculates the smaller of the rear target torque Ttr and the rear torque upper limit value Ttrm as the rear torque command value Tcr. The front target torque Ttf is calculated based on the accelerator opening θa and the vehicle speed Vm through correspondence graph calculations, etc. Similarly, the rear target torque Ttr is calculated based on the accelerator opening θa and the vehicle speed Vm through correspondence graph calculations, etc.

[0039] Reference Figure 3 The control method for vehicle 1, specifically the control of the slip amount of the front wheel 2f and the rear wheel 2r when the sand mode is selected, is explained. Figure 3 The flowchart shown is executed periodically by controller 20.

[0040] In step S10, the controller 20 determines whether the sand mode has been selected based on the drive mode signal Sd. If the sand mode is not selected, step S10 determines no and ends the process. If the sand mode is selected, step S10 determines yes and proceeds to step S11.

[0041] In step S11, the controller 20 calculates the upper limit value of the basic slip amount. Specifically, as follows: Figure 4 As shown, the slip upper limit calculation unit 21 has a first calculation unit 21a and a second calculation unit 21b.

[0042] The first calculation unit 21a calculates the upper limit of the basic slip amount related to the front wheel 2f, namely the upper limit of the front basic slip amount Svfr. For example... Figure 5 As shown, the first calculation unit 21a stores a graph that defines the relationship between the vehicle speed Vm, the accelerator opening θa, and the upper limit of the front basic slip amount Svfr. The first calculation unit 21a calculates the upper limit of the front basic slip amount Svfr based on the vehicle speed Vm and the accelerator opening θa. The upper limit of the front basic slip amount Svfr is set to a larger value as the vehicle speed Vm increases; even at the same vehicle speed Vm, the upper limit is set to a larger value as the accelerator opening θa increases.

[0043] The second calculation unit 21b calculates the upper limit of the basic slip amount related to the rear wheel 2r, i.e., the upper limit of the rear basic slip amount. Similar to the first calculation unit 21a, the second calculation unit 21b calculates the upper limit of the rear basic slip amount based on the vehicle speed Vm and the accelerator opening θa. When the vehicle speed Vm and the accelerator opening θa are the same, the upper limit of the rear basic slip amount is the same as the upper limit of the front basic slip amount Svfr. The second calculation unit 21b outputs the calculated upper limit of the rear basic slip amount directly as the upper limit of the rear slip amount Svrm.

[0044] In step S12, the controller 20 determines whether braking is not being performed in vehicle 1. The controller 20 determines this by checking whether the brake pedal has been operated, or whether the front drive motor and rear drive motors 10f and 10r are performing regenerative braking. If braking is being performed in vehicle 1, step S12 determines no, and the process ends. If braking is not being performed in vehicle 1, step S12 determines yes, and the process proceeds to step S13.

[0045] In step S13, the controller 20 determines whether it is the initial period of acceleration. The initial period refers to a certain period during which the driver's acceleration request continues, starting from the beginning of the acceleration request. The acceleration request can be determined based on the vehicle speed Vm and the accelerator opening θa. The acceleration request includes not only acceleration requests starting from a state of zero speed, but also acceleration requests starting from a state of speed above zero. If it is not the initial period of acceleration, the determination in step S13 is negative, and the process proceeds to step S18 described later. If it is the initial period of acceleration, the determination in step S13 is positive, and the process proceeds to step S14.

[0046] In step S14, the controller 20 calculates the superimposed slip amount to be added to the previous basic slip upper limit value Svfr. Specifically, as... Figure 4 As shown, the slip upper limit calculation unit 21 has a third calculation unit 21c and a fourth calculation unit 21d.

[0047] The third calculation unit 21c calculates the first superimposed slip amount Sva1 based on the vehicle speed Vm and the accelerator opening θa. For example... Figure 6As shown, the third calculation unit 21c stores a correspondence diagram defining the relationship between the vehicle speed difference, the accelerator opening θa, and the first superimposed slip amount Sva1. The vehicle speed difference is the difference between the vehicle speed Vm after acceleration (current) and the vehicle speed Vm at the start of the acceleration request. The first superimposed slip amount Sva1 is generated during the period from the start of the acceleration request until the vehicle speed Vm increases by a certain amount, with the initial period as the upper limit. In the region where the vehicle speed difference is small, the first superimposed slip amount Sva1 increases with the increase of the vehicle speed difference. In the region where the vehicle speed difference is in the middle, the first superimposed slip amount Sva1 is a constant value regardless of whether the vehicle speed difference increases. As described above, the first superimposed slip amount Sva1 increases as the initial period passes. Furthermore, after a period where the rate of change of the first superimposed slip amount Sva1 is large, it transitions to a period where the rate of change of the first superimposed slip amount Sva1 is small. Moreover, in the region where the vehicle speed difference is large, the first superimposed slip amount Sva1 decreases with the increase of the vehicle speed difference. The first superimposed slip amount Sva1 is set to a larger value as the accelerator opening θa increases, even at the same vehicle speed difference.

[0048] The fourth calculation unit 21d calculates the second superimposed slip amount Sva2 based on the accelerator opening speed Δθa and the elapsed time during the initial period. For example... Figure 7 As shown, the fourth calculation unit 21d stores a graph relating the accelerator opening speed Δθa, the elapsed time of the initial period, and the second superimposed slip amount Sva2. The second superimposed slip amount Sva2 is generated during the initial period. In the first half of the initial period, the second superimposed slip amount Sva2 increases with the elapsed time. In the middle of the initial period, the second superimposed slip amount Sva2 becomes a constant value regardless of the elapsed time. As described above, the second superimposed slip amount Sva2 increases with the elapsed time; furthermore, after a period where the rate of change of the second superimposed slip amount Sva2 is large, a period where the rate of change of the second superimposed slip amount Sva2 is small is entered. And, in the second half of the initial period, the second superimposed slip amount Sva2 decreases with the elapsed time. The second superimposed slip amount Sva2 is also set to a larger value as the accelerator opening θa increases for the same elapsed time.

[0049] like Figure 4 As shown, the slip upper limit calculation unit 21 has a first adder 21e. In the first adder 21e, the first superimposed slip amount Sva1 calculated in the third calculation unit 21c and the second superimposed slip amount Sva2 calculated in the fourth calculation unit 21d are added together. The first adder 21e outputs the sum Sva, which is the sum of the first superimposed slip amount Sva1 and the second superimposed slip amount Sva2.

[0050] exist Figure 3 In step S15, the controller 20 calculates the superimposed slip gain. For example... Figure 4 As shown, the slip upper limit calculation unit 21 has a fifth calculation unit 21f that calculates the superimposed slip gain Ks.

[0051] like Figure 8 As shown, the fifth calculation unit 21f stores a graph that defines the relationship between the absolute values ​​of the vehicle speed Vm and the steering angle θs and the superimposed slip gain Ks. The superimposed slip gain Ks is set to a value less than 1 when the absolute value of the steering angle θs is greater than or equal to a specified angle; the larger the absolute value of the steering angle θs, the smaller the value. At the same steering angle θs, the superimposed slip gain Ks is also set to a value closer to 0 as the vehicle speed Vm decreases.

[0052] exist Figure 3 In step S16, the controller 20 determines the final superimposed slip amount Svb. For example... Figure 4 As shown, the slip upper limit calculation unit 21 has a multiplier 21g. In the multiplier 21g, the sum of the slip values ​​Sva1 and Sva2 added to the first and second slip values ​​Sva1 and Sva2 is multiplied by the slip gain Ks. The output from the multiplier 21g becomes the final slip value Svb.

[0053] exist Figure 3 In step S17, the controller 20 calculates the upper limit value of the forward slip amount Svfm. For example... Figure 4 As shown, the slip upper limit calculation unit 21 has a second adder 21h. The second adder 21h adds the superimposed slip amount Svb and the previous basic slip upper limit value Svfr. The second adder 21h outputs the sum of the superimposed slip amount Svb and the previous basic slip upper limit value Svfr as the previous slip upper limit value Svfm.

[0054] In step S18, the controller 20 calculates the forward slip Svf and the rear slip Svr respectively. The forward slip Svf is calculated by subtracting the vehicle speed Vm from the front wheel speed Vwf, and the rear slip Svr is calculated by subtracting the vehicle speed Vm from the rear wheel speed Vwr.

[0055] In step S19, the controller 20 calculates the upper limit value of the front torque Ttfm based on the front slip amount Svf and the upper limit value of the front slip amount Svfm. Furthermore, if the determination in step S13 is yes, that is, during the initial period of an acceleration request, the upper limit value of the front slip amount Svfm is ultimately determined to be the value calculated in step S17. On the other hand, if the determination in step S13 is no, that is, after the initial period of an acceleration request has elapsed or there is no acceleration request, the upper limit value of the front slip amount Svfm is ultimately determined to be the upper limit value of the front basic slip amount Svfr calculated in step S11. Similarly, the controller 20 calculates the upper limit value of the rear torque Ttrm based on the rear slip amount Svr and the upper limit value of the rear slip amount Svrm. The upper limit value of the rear slip amount Svrm is directly and ultimately determined to be the upper limit value of the rear basic slip amount calculated in step S11.

[0056] In step S20, the controller 20 calculates the smaller of the front target torque Ttf and the front torque upper limit value Ttfm as the front torque command value Tcf. Similarly, the controller 20 calculates the smaller of the rear target torque Ttr and the rear torque upper limit value Ttrm as the rear torque command value Tcr.

[0057] If the front torque command value Tcf and the rear torque command value Tcr are calculated through this series of processes, then the controller 20 calculates the current command value supplied to the front drive motor 10f based on the front torque command value Tcf. The controller 20 then switches the inverter on and off according to the current command value, supplying drive current to the front drive motor 10f from the inverter. Similarly, the controller 20 calculates the current command value supplied to the rear drive motor 10r based on the rear torque command value Tcr. The controller 20 then switches the inverter on and off according to the current command value, supplying drive current to the rear drive motor 10r from the inverter. At this time, the slip of the front wheel 2f is controlled to be less than or equal to the upper limit of the front slip value Svfm, and the slip of the rear wheel 2r is controlled to be less than or equal to the upper limit of the rear slip value Svrm.

[0058] Thus, in this embodiment, when the driving mode is sand mode, the controller 20 executing the vehicle 1 control method sets a front basic slip upper limit value Svfr based on the accelerator opening θa and the vehicle speed Vm. Upon determining a driver's acceleration request, the controller 20 performs an addition operation, adding the superimposed slip amount Svb to the front basic slip upper limit value Svfr, ultimately determining the front slip upper limit value Svfm as the final value. The controller 20 sets a rear slip upper limit value Svrm based on the accelerator opening θa and the vehicle speed Vm. Furthermore, the controller 20 controls the slip of the front wheel 2f to be less than or equal to the front slip upper limit value Svfm, and controls the slip of the rear wheel 2r to be less than or equal to the rear slip upper limit value Svrm.

[0059] Figure 9 The shifts in front wheel speed Vwf, rear wheel speed Vwr, vehicle speed Vm, drive torque Trf of front wheel 2f, and drive torque Trr of rear wheel 2r when an acceleration request is received are shown. In sand mode, the upper limits of front and rear slip are greater than in other driving modes. Since the front wheel speed Vwf and rear wheel speed Vwr are set greater than the vehicle speed Vm, vehicle 1 moves while its front and rear wheels 2f and 2r slip. Furthermore, in sand mode, when a driver's acceleration request is detected, the upper limit of front slip Svfm includes a superimposed slip amount Svb. The slip of front wheel 2f is greater than the slip of rear wheel 2r; therefore, the front wheel speed Vwf is greater than the rear wheel speed Vwr. By scraping away the gravel with the front wheel 2f, the gravel is excavated, thereby imparting acceleration to vehicle 1 due to the nose-down motion. Thus, even when driving on sand, the driver can experience good acceleration.

[0060] In this embodiment, the addition operation is performed during an initial period that spans a certain timeframe from the start of the acceleration request. If the slippage of the front wheel 2f is increased to achieve a sense of acceleration, there is a risk of vehicle 1 getting stuck. The acceleration process is not performed throughout the entire period during which the acceleration request exists, but is limited to the initial period. Therefore, it is possible to improve the sense of acceleration and suppress the risk of getting stuck.

[0061] In this embodiment, the superimposed slip amount Svb increases as the initial period progresses, and after a period with a high rate of change of the superimposed slip amount Svb, it transitions to a period with a low rate of change of the superimposed slip amount Svb. According to this method, the amount of head movement of the driver can be reduced, thus providing a change in acceleration that is not uncomfortable for the driver.

[0062] Figure 10The diagram shows the shifts in front wheel speed Vwf, rear wheel speed Vwr, vehicle speed Vm, drive torque Trf of front wheel 2f, and drive torque Trr of rear wheel 2r when an acceleration request is requested, all under a large steering angle θs. When the steering angle θs is large, the risk of vehicle 1 jamming is high. Therefore, in this embodiment, the addition operation process includes suppressing the superimposed slip amount Svb as the steering angle θs of the front wheel 2f increases. Thus, when the steering angle θs is large, the superimposed slip amount Svb decreases, thereby suppressing the upper limit of the front slip amount Svfm, and the front wheel speed Vwf becomes a value close to or the same as the rear wheel speed Vwr. This suppresses the risk of vehicle 1 jamming.

[0063] In this embodiment, the addition operation includes setting a superimposed slip amount Svb based on a first superimposed slip amount Sva1 corresponding to the accelerator opening θa and the vehicle speed Vm. According to this method, the superimposed slip amount Svb corresponding to the driver's acceleration request can be appropriately set.

[0064] In this embodiment, the addition operation process calculates a second superimposed slip amount Sva2 corresponding to the accelerator opening speed Δθa and the elapsed time of the initial period. The addition operation process includes setting a superimposed slip amount Svb based on the value obtained by adding the first and second superimposed slip amounts Sva1 and Sva2. According to this method, the superimposed slip amount Svb corresponding to the intensity of acceleration required by the driver can be appropriately set.

[0065] In this embodiment, the controller 20 determines the acceleration request based on the accelerator opening θa and the vehicle speed Vm. According to this method, the acceleration request can be appropriately determined.

[0066] Furthermore, a control device for the vehicle 1, which includes a front drive motor 10f and a rear drive motor 10r, is also included as part of this embodiment. The control device for the vehicle 1 includes the aforementioned controller 20, which controls the slippage of the front wheel 2f and the slippage of the rear wheel 2r. According to this control device for the electric vehicle 1, the driver can obtain a good sense of acceleration even when driving on sand.

[0067] Furthermore, in the above embodiment, vehicle 1 is configured such that a single front drive motor 10f drives the left and right front wheels 2f, and a single rear drive motor 10r drives the left and right rear wheels 2r. However, vehicle 1 may also have a structure having a pair of front drive motors 10f that drive the left and right front wheels 2f respectively, and a pair of rear drive motors 10r that drive the left and right rear wheels 2r respectively. In this case, the above-described control method is applied to both the pair of front drive motors 10f and the pair of rear drive motors 10r.

[0068] As described above, embodiments of the present invention have been presented, but it should not be construed that the descriptions and drawings, which form part of the present invention, are limiting of the present invention. Based on the present invention, those skilled in the art can recognize various alternative embodiments, examples, and techniques employed.

[0069] Explanation of the label

[0070] 1. Electric vehicles

[0071] 2f, 2r: Front wheel, Rear wheel

[0072] 10f, 10r: Front drive motor, rear drive motor

[0073] 20 Controllers

[0074] 21 Slip Upper Limit Calculation Unit

[0075] 21a First Arithmetic Division

[0076] 21b Second Operations Unit

[0077] 21c Third Arithmetic Division

[0078] 21d Fourth Arithmetic Division

[0079] 21e First Adder

[0080] 21f Fifth Arithmetic Division

[0081] 21g multiplier

[0082] 21h Second Adder

[0083] 22f Front Torque Upper Limit Calculation Unit

[0084] 22r Rear Torque Upper Limit Calculation Unit

[0085] 23f Front Torque Command Value Calculation Unit

[0086] 23r Rear Torque Command Value Calculation Unit

Claims

1. A control method for an electric vehicle, the electric vehicle having a front drive motor for driving the front wheels and a rear drive motor for driving the rear wheels. In the control method of this electric vehicle, Determine whether the drive mode of the electric vehicle, which sets its operating characteristics, is a sand driving mode suitable for driving on sandy terrain with accumulated gravel. When the driving mode is the sand mode, based on the accelerator opening and vehicle speed, the upper limit values ​​for the allowable slip of the front wheels (i.e., the front slip limit value) and the upper limit values ​​for the allowable slip of the rear wheels (i.e., the rear slip limit value) are set respectively. If the driver's acceleration request is detected, an addition operation is performed to add the superimposed slip amount to the upper limit of the forward slip amount, and the resulting value is ultimately determined as the upper limit of the forward slip amount. The slippage of the front wheel is controlled to be less than or equal to the upper limit of the front slippage, and the slippage of the rear wheel is controlled to be less than or equal to the upper limit of the rear slippage.

2. The control method for an electric vehicle according to claim 1, wherein, The addition operation is performed during an initial period that spans a certain timeframe from the start of the acceleration request.

3. The control method for an electric vehicle according to claim 2, wherein, The amount of superimposed slip increases as the initial period passes. After a period of high rate of change of the superimposed slip, the period transitions to a period of low rate of change of the superimposed slip.

4. The control method for an electric vehicle according to claim 3, wherein, The addition operation process includes the following process: as the steering angle of the front wheel increases, the amount of superimposed slip is suppressed.

5. The control method for an electric vehicle according to any one of claims 2 to 4, wherein, The addition operation process includes the following process: setting the superimposed slip amount based on the first superimposed slip amount corresponding to the accelerator opening and the vehicle speed.

6. The control method for an electric vehicle according to claim 5, wherein, The addition operation process includes the following process: based on the value obtained by adding the second superimposed slip amount and the first superimposed slip amount, the superimposed slip amount is set, and the second superimposed slip amount corresponds to the change in the accelerator opening per unit time, i.e., the accelerator opening speed and the elapsed time of the initial period.

7. The control method for an electric vehicle according to any one of claims 1 to 6, wherein, It also includes the following process: determining the acceleration request based on the accelerator opening and the vehicle speed.

8. A control device for an electric vehicle, the electric vehicle having a front drive motor for driving the front wheels and a rear drive motor for driving the rear wheels. The control device of the electric vehicle includes controllers that separately control the slippage of the front wheels and the slippage of the rear wheels. The controller determines whether the drive mode for setting the operating characteristics of the electric vehicle is a sand driving mode suitable for driving on sandy terrain with accumulated gravel. When the driving mode is the sand mode, based on the accelerator opening and vehicle speed, the upper limit values ​​for the allowable slip of the front wheels (i.e., the front slip limit value) and the upper limit values ​​for the allowable slip of the rear wheels (i.e., the rear slip limit value) are set respectively. If the driver's acceleration request is detected, an addition operation is performed to add the superimposed slip amount to the upper limit of the forward slip amount, and the resulting value is ultimately determined as the upper limit of the forward slip amount. The slippage of the front wheel is controlled based on the upper limit of the front slippage, and the slippage of the rear wheel is controlled based on the upper limit of the rear slippage.

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