Drive control system for electric vehicles

Abstract

To provide a driving control device of an electric vehicle that can suppress both slip and slide-down of a vehicle when the vehicle is travelling on an upward slope on which the vehicle may slip.SOLUTION: A driving control device of an electric vehicle is mounted on the electric vehicle equipped with driving wheels and an electric motor that drives the driving wheels, which is provided with a controller that controls torque that is outputted from the electric motor, on the basis of an accelerator operation amount and a condition of the vehicle. The controller limits a change rate of torque in a first limitation mode when the torque is less than threshold torque, in a period of time of a first travelling state where the vehicle is travelling on an upward slope in which a degree of occurrence of slip is estimated to be above a threshold, and limits the change rate of torque in a second limitation mode that is milder than in the first limitation mode, when the torque is above the threshold torque.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a drive control device for an electric vehicle.

Background Art

[0002] Patent Document 1 shows torque control for a four-wheel drive vehicle. In this torque control, a parameter regarding the change rate of torque is set based on the estimated road surface gradient. Patent Document 1 describes that by the above setting, it is possible to avoid simultaneous slipping of the front wheels and the rear wheels at the start of ascending a slope, and to prevent vehicle slip-down and the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] During travel on an ascending slope with low frictional resistance, by limiting the change rate of torque to a small value, a rapid change in torque can be suppressed, and the occurrence of slip can be reduced. However, if the change rate of torque is limited to a small value, when the torque once becomes small, even if the driver quickly performs an accelerator operation, it takes time until torque capable of supporting the vehicle weight along the gradient is output, and there is a risk of vehicle slip-down.

[0005] An object of the present invention is to provide a drive control device for an electric vehicle that can suppress both slip and vehicle slip-down during travel on an ascending slope where slip is likely to occur.

Means for Solving the Problems

[0006] (1) A drive control device for an electric vehicle according to one aspect of the present invention is: A drive control device for an electric vehicle, which is mounted on an electric vehicle equipped with drive wheels and an electric motor that drives the drive wheels, The system includes a controller that controls the torque output from the electric motor based on the accelerator pedal input and the vehicle status. The aforementioned controller, During a first driving state, which is driving uphill where the likelihood of slippage is estimated to be above a threshold, the rate of change of the torque is limited by a first limiting mode when the torque is below the threshold torque, while the rate of change of the torque is limited by a second limiting mode that is less restrictive than the first limiting mode when the torque is above the threshold torque. Furthermore, the controller determines that the vehicle is in the first driving state if it detects that a slip has occurred while driving uphill. The first limiting mode is a mode of limiting the change rate that is applied during a second driving state in which no slip occurs of the drive wheels, The second limiting mode is a mode of limiting the change rate that is applied during a third driving state in which slip of the drive wheels occurs other than on an uphill slope, The threshold torque is set to a value that has a positive correlation with the torque at the time of slip occurrence. (2) A drive control device for an electric vehicle according to another aspect of the present invention is: A drive control device for an electric vehicle, which is mounted on an electric vehicle equipped with drive wheels and an electric motor that drives the drive wheels, The system includes a controller that controls the torque output from the electric motor based on the accelerator pedal input and the vehicle status. The aforementioned controller, During a first driving state, which is driving uphill where the likelihood of slippage is estimated to be above a threshold, the rate of change of the torque is limited by a first limiting mode when the torque is below the threshold torque, while the rate of change of the torque is limited by a second limiting mode that is less restrictive than the first limiting mode when the torque is above the threshold torque. When the vehicle transitions to the first driving state due to slippage, the controller changes the torque to the first torque if the accelerator pedal input is greater than zero, and then fixes the torque to the first torque if the accelerator pedal input remains greater than zero for a threshold time or longer. The first torque is characterized by being set to a value that has a positive correlation with the torque at the time of slip. [Effects of the Invention]

[0007] According to the present invention, during the first driving state, if the torque output from the electric motor is greater than or equal to the threshold torque, the rate of change of the torque is limited by the second limiting mode, thereby suppressing abrupt changes in the torque output to the drive wheels. Therefore, the occurrence of slip of the drive wheels can be suppressed. On the other hand, during the first driving state, if the torque output from the electric motor is less than the threshold torque, the rate of change of the torque is limited by the first limiting mode, allowing the torque to be increased relatively quickly. Therefore, it is possible to quickly output torque that can support the weight of the vehicle along a gradient, thereby reducing the likelihood of the vehicle sliding backward. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram showing an electric vehicle and a drive control device according to Embodiment 1 of the present invention. [Figure 2A] This diagram illustrates the first limiting mode of the torque change rate. [Figure 2B] This diagram illustrates a second limiting mechanism for the rate of change of torque. [Figure 3A] This figure shows an example of the change in torque when the first limiting mode is applied. [Figure 3B] This figure shows an example of the change in torque when the second limiting mode is applied. [Figure 4] This is a time chart showing an example of the operation of an electric vehicle according to Embodiment 1. [Figure 5]It is a flowchart showing the drive control process executed by the controller of Embodiment 1. [Figure 6] It is a time chart showing the first example of the operation of the electric vehicle according to Embodiment 2. [Figure 7] It is a time chart showing the second example of the operation of the electric vehicle according to Embodiment 2. [Figure 8] It is a part of a flowchart showing the drive control process executed by the controller according to Embodiment 2. [Figure 9] It is a part of a flowchart showing the drive control process executed by the controller according to Embodiment 2.

Mode for Carrying Out the Invention

[0009] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings.

[0010] (Embodiment 1) FIG. 1 is a block diagram showing an electric vehicle 1 and a drive control device 20 according to Embodiment 1 of the present invention. The electric vehicle 1 according to Embodiment 1 includes drive wheels 2d, an electric motor 3 that drives the drive wheels 2d, an inverter 4 that outputs a drive current to the electric motor 3, a battery 5 that stores electric power supplied to the electric motor 3, and a braking device 6 that brakes the electric vehicle 1. The electric vehicle 1 further includes a driving operation unit 11 operated by a driver or the like, and a controller 21 that performs drive control of the electric motor 3 based on the operation of the driving operation unit 11 and the vehicle state. The electric vehicle 1 further includes, as devices for detecting the vehicle state, a vehicle speed sensor 31 that detects the vehicle speed, a first detection device 32 that can detect the gradient of the traveling road surface, and a second detection device 33 for determining the occurrence of slip of the drive wheels 2d. The electric vehicle 1 further includes switches 35 and 36 that can be selectively operated by the driver regarding torque control. The switches 35 and 36 may be located on the panel of the driver's seat or on the steering unit (steering wheel) 11c.

[0011] The drive control device 20 according to Embodiment 1 includes a controller 21, a first detection device 32, and switches 35 and 36 among the above configurations.

[0012] The operation operation unit 11 includes a brake operation unit (for example, a brake pedal) 11a, an accelerator operation unit (for example, an accelerator pedal) 11b, and a steering unit (for example, a steering wheel) 11c. Signals indicating the operation amount of the brake operation unit 11a and the operation amount of the accelerator operation unit 11b are sent to the controller 21. Hereinafter, the operation amount of the accelerator operation unit 11b is referred to as "accelerator operation amount".

[0013] The vehicle speed sensor 31 has a configuration for detecting the rotational speed of a plurality of wheels 2 including the drive wheels 2d, a configuration in which an acceleration sensor is added to the said configuration, or a configuration for obtaining the vehicle speed from a positioning device such as GPS (Global Positioning System) and positioning results for a plurality of times. As long as the vehicle speed sensor can detect the vehicle speed, any other configuration may be adopted.

[0014] The first detection device 32 for detecting the gradient is a configuration in which a plurality of acceleration sensors are arranged at the front and rear of the electric vehicle 1, or a combination of a gyro sensor and a magnetic sensor. As long as the first detection device 32 can detect the gradient of the traveling road, any other configuration may be adopted in other cases.

[0015] The second detection device 33 for determining the slip of the drive wheels 2d is a configuration in which a wheel speed sensor of the drive wheels 2d and a wheel speed sensor of the driven wheels are combined, or a configuration in which a wheel speed sensor and an acceleration sensor are combined. Alternatively, the second detection device 33 is a configuration in which a wheel speed sensor of the drive wheels 2d and various vehicle speed sensors are combined. When slip occurs in the drive wheels 2d, the wheel speed of the drive wheels 2d becomes a value that does not correspond to the wheel speed of the other wheels 2 or the speed or acceleration of the electric vehicle 1. By detecting such an event, the second detection device 33 can detect the occurrence of slip of the drive wheels 2d. As long as the second detection device 33 can detect a physical quantity for determining the occurrence of slip of the drive wheels 2d, any other configuration may be adopted.

[0016] The controller 21 includes one ECU (Electronic Control Unit) or multiple ECUs that communicate with each other and operate in cooperation. The controller 21 includes a storage device 22 that stores control programs and control data, and controls the drive of the electric motor 3 by executing the control programs stored in the storage device 22. The controller 21 can control the torque output from the electric motor 3 by controlling the operation of the inverter 4. Furthermore, the controller 21 can control the braking force of the electric vehicle 1 by driving the braking device 6.

[0017] The controller 21 calculates the command torque according to the vehicle speed and accelerator input, and determines the torque to be actually output from the electric motor 3 based on the command torque and the currently generated torque. Once the torque is determined, the controller 21 controls the inverter 4 so that the torque is output, and the torque is output from the electric motor 3.

[0018] When the controller 21 determines the torque from the commanded torque, it limits the rate of change of the torque to prevent the torque from changing abruptly. The controller 21 determines the mode of limiting the rate of change of the torque according to the driving state of the electric vehicle 1, as follows.

[0019] In other words, during a first driving state, which is when driving uphill where the likelihood of slippage is estimated to be above a threshold, the controller 21 limits the rate of change of torque in a first limiting mode if the torque is below the threshold torque. On the other hand, during the first driving state, if the torque is above the threshold torque, the controller 21 limits the rate of change of torque in a second limiting mode that is less restrictive than the first limiting mode.

[0020] Here, the estimation methods for "driving uphill," "degree of likelihood of slipping," "first limiting mode," "second limiting mode," and "threshold torque" are defined as follows.

[0021] In other words, "driving uphill" means driving on a road surface with a gradient of a predetermined angle or greater in the uphill direction (gradient of the longitudinal section along the direction of travel), such as 5° or more. Therefore, driving uphill with a small gradient less than the predetermined angle may be excluded from the above definition of "driving uphill."

[0022] The above method for estimating the "degree of likelihood of slipping" may be an estimation method based on whether or not slippage of the drive wheel 2d actually occurred. That is, the controller 21 may be configured to estimate that the degree of likelihood of slipping on the uphill slope is above a threshold when slippage occurs. If the estimation is made as described above, the controller 21 may maintain the above estimation result until the vehicle returns to a flat road, or until the electric vehicle 1 stops in the parking range, or until the system of the electric vehicle 1 is powered off. Alternatively, the electric vehicle 1 may be equipped with a device for detecting the condition of the road surface. Furthermore, if the controller 21 determines that slippage has occurred on the uphill slope, it may estimate that the degree of likelihood of slipping on the uphill slope is above a threshold until the road surface conditions change to a road surface that is less prone to slipping, such as a dry paved road surface.

[0023] The method for estimating the "degree of likelihood of slipping" is not limited to the above example. For example, a method of estimating the degree based on the detection of the condition of the road surface may be employed. The device for detecting the condition of the road surface may include a camera and road surface image analysis device, a vibration sensor, a road surface temperature sensor, a map database showing road surface conditions and a positioning device, or a combination thereof. Based on the detection results of these devices, the controller 21 may, for example, determine that a slip will occur on an uphill slope when a predetermined torque is output to the drive wheel 2d, and estimate that the degree of likelihood of slipping on that uphill slope is above a threshold. In this case, the predetermined torque described above may be set as the threshold torque at which slipping is estimated to occur.

[0024] Figure 2A illustrates the first limitation mode for the rate of change of torque. Figure 2B illustrates the second limitation mode for the rate of change of torque. Figure 3A shows an example of torque change when the first limitation mode is applied. Figure 3B shows an example of torque change when the second limitation mode is applied.

[0025] The "first limiting mode" mentioned above refers to one mode of limiting the rate of change of torque. The first limiting mode may be a mode in which the limited rate of change changes according to the torque difference, which is the difference between the commanded torque and the currently generated torque, and the elapsed time since the torque difference occurred, as follows: That is, as shown in Figure 2A, when the torque difference is small and the elapsed time is small, the rate of change changes to a small value, and when the torque difference is small and the elapsed time is large, the rate of change changes to a moderate value. Also, when the torque difference is large and the elapsed time is small, the rate of change changes to a small value, and when the torque difference is large and the elapsed time is large, the rate of change changes to a large value.

[0026] Figure 3A shows the change in torque when a sudden accelerator operation is performed from zero torque, resulting in a large command torque, while the first limiting mode is in effect. When this accelerator operation is performed, in region W1 where the elapsed time is short, the torque increases at a small rate of change even if the torque difference is large, and as the elapsed time increases (region W2), the torque increases at a large rate of change. Furthermore, as the elapsed time increases but the torque difference becomes small (region W3), the torque approaches the command torque at a small rate of change.

[0027] The "first limiting mode" may also be a mode of limiting the rate of change used by the controller 21 when calculating torque from the command torque in a second driving state (for example, a normal driving state) in which there is no slip of the drive wheel 2d. According to the first limiting mode, a relatively quick torque response to accelerator operation can be obtained.

[0028] The "first limiting mode" is not limited to the above example; for example, it may be a mode in which the torque change rate is fixed to a predetermined value. Even in that case, the value of the change rate is set to a value greater than the torque change rate in the second limiting mode.

[0029] The "second limiting mode" described above is one mode of limiting the rate of change of torque, and is a mode in which a gentler rate of change is applied than that of the first limiting mode. The second limiting mode may be a mode in which the limited rate of change changes according to the torque difference, which is the difference between the commanded torque and the currently generated torque, and the elapsed time since the torque difference occurred, as follows: That is, as shown in Figure 2B, when the torque difference is small and the elapsed time is small, the rate of change changes to a small value, and when the torque difference is small and the elapsed time is large, the rate of change changes to a small value. Also, when the torque difference is large and the elapsed time is small, the rate of change changes to a small value, and when the torque difference is large and the elapsed time is large, the rate of change changes to a moderate value.

[0030] Figure 3B shows the torque change when the second limiting mode is applied and a sudden accelerator operation is performed from zero torque, resulting in a large command torque value. In this case, the torque changes at a smaller rate of change compared to the first limiting mode in each of the following regions: region W11 with a short elapsed time, region W12 with a long elapsed time, and region W13 with a long elapsed time but a small torque difference.

[0031] The "second limiting mode" may also be a limiting mode for the rate of change used by the controller 21 when calculating torque in a third driving state (for example, a low-friction resistance road driving state) in which slippage of the drive wheel 2d occurs other than on an uphill slope. According to the second limiting mode, the torque responsiveness to accelerator operation is lower compared to the first limiting mode.

[0032] The "second limiting mode" is not limited to the above example; for example, it may be a mode in which the torque change rate is fixed to a predetermined value. Even in that case, the value of the change rate is set to a value smaller than the torque change rate in the first limiting mode.

[0033] The change rate of the second limiting mode is said to be more gradual than the change rate of the first limiting mode, meaning that, given the same conditions (e.g., torque difference and elapsed time), the value of the change rate of the second limiting mode is less than or equal to the value of the change rate of the first limiting mode.

[0034] The "threshold torque" mentioned above is set to a value estimated as the torque at which the drive wheel 2d begins to slip, or the torque immediately before slippage. If the drive wheel 2d slips and the first driving state is determined, the controller 21 sets the torque that was output at the time of slippage as the threshold torque. In this setting, the torque output at the time of slippage and the threshold torque have a positive correlation. That is, if the torque output at the time of slippage is small, the threshold torque will be a small value, and if the torque output at the time of slippage is large, the threshold torque will be a large value.

[0035] Furthermore, the threshold torque is not limited to the above example and may be set to a value greater than or equal to the torque value that can stop the electric vehicle 1 from sliding down, calculated from the gradient of the uphill slope and the vehicle weight. Also, the threshold torque is a value that is positively correlated with the torque that was output when the vehicle slipped, and may be set to a value smaller or larger than the torque that was output when the vehicle slipped.

[0036] <Example of operation> Figure 4 is a time chart showing an example of the operation of an electric vehicle according to Embodiment 1. When slippage occurs in the drive wheel 2d while driving uphill (timing t1), the controller 21 determines that the vehicle is in a first driving state and starts torque control for the first driving state. Here, the controller 21 stores the torque that was output to the drive wheel 2d when the slippage occurred as the threshold torque Tqth.

[0037] After a slip occurs, the driver can apply the brakes or reduce the accelerator input to bring the electric vehicle 1 to a stop or near-stop state (action c1). Alternatively, the controller 21 can perform torque control to compensate for the slip, reducing the torque of the electric vehicle 1 and bringing the electric vehicle 1 to a near-stop state (action c1).

[0038] Then, when the driver operates the accelerator to continue driving the electric vehicle 1, the controller 21 calculates the torque by applying the rate of change of the first limiting mode within the range where the torque is less than the threshold torque Tqth (period T1). By applying the first limiting mode, the torque increases with relatively high responsiveness, which suppresses the electric vehicle 1 from sliding backward due to its own weight on an uphill slope.

[0039] On the other hand, when the driver operates the accelerator while the torque is above the threshold torque Tqth (period T2), the controller 21 calculates the torque by applying the change rate of the second limiting mode. Therefore, sudden changes in torque are suppressed, and the driver can continue driving in a way that is less prone to slippage.

[0040] <Drive control processing> Next, we will explain the drive control process that realizes the operation of the electric vehicle 1 described above. Figure 5 is a flowchart of the drive control process executed by the controller 21.

[0041] The drive control process is initiated when the electric vehicle 1 system is started and is continuously executed by the controller 21 while the system is operating. When the drive control process is initiated, the controller 21 first acquires detection information from the vehicle speed sensor 31, the first detection device 32 and the second detection device 33, as well as operation signals from the driving operation unit 11 and the switch 35 (step S1).

[0042] Next, the controller 21 calculates the command torque based on the vehicle speed and accelerator pedal input from the acquired detection information and operation signals (step S2). The electric motor 3 has a torque characteristic in which the maximum torque is large at low rotational speeds and small at high rotational speeds. In step S2, the controller 21 may calculate the command torque in accordance with the torque characteristics of the electric motor 3. For example, the controller 21 may calculate the specified torque such that when the accelerator pedal input is at its maximum, the command torque is equal to or near the maximum torque of the electric motor 3 corresponding to the rotational speed at that time (rotational speed converted from the vehicle speed). Furthermore, the controller 21 may calculate the specified torque such that, when the rotational speed of the electric motor 3 is the same, the torque gradually decreases from the maximum torque corresponding to that rotational speed as the accelerator pedal input decreases.

[0043] Next, the controller 21 determines the driving state of the electric vehicle 1 based on the signal acquired in step S1 (step S3). The conditions for the first driving state, second driving state, and third driving state determined here are as described above. In the drive control process of this embodiment, the controller 21 estimates that the degree of likelihood of slippage is above a threshold due to the occurrence of slippage, and determines the first driving state.

[0044] If the determination process in step S3 determines that the second driving state (for example, the normal driving state) is in effect, the controller 21 applies the rate of change of the first limiting mode based on the commanded torque and the currently outputting torque to determine the torque that the electric motor 3 should actually output (step S4).

[0045] The controller 21 then controls the inverter 4 so that the determined torque is output (step S10). The controller 21 then returns the process to step S1.

[0046] On the other hand, if the determination process in step S3 determines that a slip has occurred, the controller 21 sets the first flag indicating that a slip has occurred to "1" (step S5), and sets the torque that was being output from the electric motor 3 at that time as the threshold torque (step S6). Furthermore, the controller 21 performs a process to deal with the slip, such as temporarily reducing the torque (step S7). Then, after the torque output process in step S10, the controller 21 returns to step S1.

[0047] In the determination process of step S3, the controller 21 determines that a slip has occurred if the first flag is "1", and if it is not an uphill slope, it determines that it is in the third driving state (a driving state in which a slip of the drive wheel 2d has occurred on a non-uphill slope). In this case, the controller 21 applies the change rate of the second limiting mode based on the command torque and the currently output torque to determine the torque that the electric motor 3 should actually output (step S8).

[0048] The controller 21 then controls the inverter 4 so that the determined torque is output (step S10). The controller 21 then returns the process to step S1.

[0049] On the other hand, if the determination process in step S3 determines that the vehicle is in the first driving state (a driving state on an uphill slope where the drive wheel 2d has slipped), the controller 21 determines whether the currently outputting torque is less than or equal to the threshold torque (step S9). If the result is equal to or equal to the threshold torque, the controller 21 applies the change rate of the second limiting mode based on the command torque and the currently outputting torque to determine the torque that the electric motor 3 should actually output (step S8).

[0050] On the other hand, if the result of the determination in step S9 is less than the threshold torque, the controller 21 applies the rate of change of the first limiting mode based on the command torque and the currently output torque to determine the torque that the electric motor 3 should actually output (step S4).

[0051] Once the torque is determined in step S4 or step S9, the controller 21 then controls the inverter 4 so that the determined torque is output (step S10). The controller 21 then returns the process to step S1.

[0052] On the other hand, if the determination process in step S3 determines that the electric vehicle 1 has stopped in the parking range, or that the switch 35 has been turned off, the controller 21 resets the first flag indicating the occurrence of slip to "0" (step S11). Then, the controller 21 returns to step S1.

[0053] The process in step S11 terminates torque control in the first or third driving state, and returns to torque control in the second driving state (normal driving state).

[0054] Through the drive control process described above, the operation of the electric vehicle 1, as explained with reference to Figure 4, is realized.

[0055] The program for the drive control process described above is stored in a non-transient computer-readable medium included in the storage device 22. The controller 21 may be configured to read the program stored in the portable non-transient recording medium and execute the program. The portable non-transient storage medium may store the program for the drive control process described above.

[0056] In the drive control process shown in Figure 5, if the controller 21 determines that the switch 35 has been turned off, it may perform the following branch in the subsequent determination process in step S3. That is, if the switch 35 is turned off, the controller 21 may proceed to the branch (step S8) for when the vehicle is determined to be in the third driving state, regardless of whether it is determined to be in the first driving state. Through this process, the driver can stop the torque control in the first driving state, even when the drive wheels 2d are slipping on an uphill slope, by turning off the switch 35. Then, the torque control, which switches between the first and second limiting modes of the rate of change depending on the magnitude of the torque, stops, and switches to torque control where the gentler second limiting mode is applied.

[0057] As described above, according to the drive control device 20 of the electric vehicle 1 of Embodiment 1, during the first driving state, which is when driving uphill where the likelihood of slippage is estimated to be above a threshold, if the torque is below the threshold torque, the torque change rate is limited by a first limiting mode. Furthermore, if the torque is above the threshold torque, the torque change rate is limited by a second limiting mode that is gentler than the first limiting mode. Therefore, when the torque is small, the application of the first limiting mode allows for the rapid output of torque to support the weight of the electric vehicle 1 along the gradient on an uphill slope, thereby suppressing the downward movement of the electric vehicle 1. On the other hand, when the torque is large, the application of the second limiting mode allows for the avoidance of sudden torque changes and the suppression of slippage of the drive wheels 2d.

[0058] Furthermore, according to the drive control device 20 of the electric vehicle 1 of Embodiment 1, the controller 21 determines that a first driving state is in effect when it detects the occurrence of slippage while driving uphill. Therefore, additional detection equipment required for determining the first driving state can be omitted, and the cost of the drive control device 20 can be reduced. Moreover, since the first driving state is determined based on the actual occurrence of slippage, it is possible to accurately determine that the degree of likelihood of slippage is above a threshold on the uphill slope.

[0059] Furthermore, according to the drive control device 20 of the electric vehicle 1 of Embodiment 1, the first mode of limiting the torque change rate is a mode of limiting the change rate that is applied during a second driving state in which there is no slip of the drive wheels 2d (for example, during normal driving). Therefore, the driver can perform accelerator operations to avoid the electric vehicle 1 sliding down on an uphill slope in the same way as accelerator operations in the second driving state, reducing the sense of unnaturalness in accelerator operation.

[0060] Furthermore, according to the drive control device 20 of the electric vehicle 1 of Embodiment 1, the second mode of limiting the torque change rate is a mode of limiting the change rate that is applied during a third driving state in which slip of the drive wheel 2d occurs other than on an uphill slope (for example, when driving on a low-friction resistance road). Therefore, the driver can perform accelerator operations that are controlled to prevent sudden torque changes so as not to cause slip, in the same way as accelerator operations in the third driving state, and the feeling of discomfort in accelerator operation is reduced.

[0061] Furthermore, according to the drive control device 20 of the electric vehicle 1 of Embodiment 1, the threshold torque is set to a value that has a positive correlation with the torque at the time of slip. Therefore, the threshold torque is set to be smaller the more likely slip is to occur, and a second limiting mode can be applied in the torque range in which slip is likely to occur, which makes it easier to avoid sudden changes in torque.

[0062] (Embodiment 2) The electric vehicle 1 and drive control device 20 according to Embodiment 2 differ from Embodiment 1 in that the torque control when slip occurs and the vehicle transitions to the first driving state is different. Otherwise, they are almost the same as Embodiment 1. The differences will be explained in detail below.

[0063] When slippage occurs on an uphill slope and the vehicle transitions to the first driving state, the controller 21 first performs control to address the slippage (such as temporarily reducing the torque), and then first executes the following torque control. That is, when transitioning to the first driving state, if the accelerator input is greater than zero, the controller 21 sets the commanded torque to the first torque.

[0064] The first torque may be set to a threshold torque. Alternatively, the first torque may be set to the torque at which slip occurs. Alternatively, the first torque may have a positive correlation with the torque at which slip occurs and may be set to a value smaller or larger than the torque at which slip occurs. In the following explanation, we will assume that the first torque = threshold torque = torque at which slip occurs.

[0065] After setting the specified torque to the first torque, the controller applies the rate of change of the first limiting mode to increase the torque to the first torque. Once the torque reaches the first torque, the controller 21 determines whether the electric vehicle 1 is moving forward. This determination is referred to as the "first forward determination".

[0066] If the determination shows that the electric vehicle 1 is moving forward and the accelerator input is fixed at an amount greater than zero for a threshold time or longer, the controller 21 fixes the torque to the first torque. The term "fixed accelerator input" is not limited to a fixed amount in the strict sense, but is a concept that includes accelerator inputs that have minute fluctuations that the driver perceives as a fixed input.

[0067] When the accelerator input is fixed, the torque is fixed to the first torque, and the electric vehicle 1 is moving forward, the controller 21 monitors the gradient of the road and corrects the first torque according to the change in gradient when the gradient of the road changes. That is, if the gradient changes to a steep angle, the first torque is reduced, and if the gradient changes to a gentle angle, the first torque is increased. The torque output from the electric motor 3 is similarly corrected by the correction of the first torque. When correcting the first torque, the controller 21 may also correct the threshold torque in the same way.

[0068] Furthermore, when the accelerator input is fixed, the torque is fixed to the first torque, and the electric vehicle 1 is moving forward, if the accelerator input changes, the controller 21 returns the process to the original torque control for the first driving state. That is, the controller 21 calculates the command torque according to the accelerator input and vehicle speed, and if the torque is less than the threshold torque, it limits the rate of change in the first limiting mode and determines the torque to be output in the next output process from the command torque and the currently output torque. On the other hand, if the torque is greater than or equal to the threshold torque, it limits the rate of change in the second limiting mode, which is less restrictive than the first limiting mode, and determines the torque to be output in the next output process from the specified torque and the currently output torque.

[0069] On the other hand, if the electric vehicle 1 is determined to be stopped in the first forward movement determination described above, the controller 21 fixes the torque to the first torque, provided that the accelerator pedal input is fixed (fixed for a threshold time or longer). Then, if the accelerator pedal input increases, the controller 21 increases the torque (slightly) regardless of the accelerator pedal input and determines whether the electric vehicle 1 will move forward. This determination is referred to as the "second forward movement determination".

[0070] If the second forward determination determines that forward movement is warranted, the controller 21 executes a user interface process that allows the driver to choose between continuing automatic forward driving with the aforementioned torque increase (slight increase) or switching to driving that responds to the accelerator pedal input. The driver can make this selection using the switch 36.

[0071] As a result, if the switch 36 is not operated and the continuation of automatic forward driving is selected, the controller 21 continues automatic forward driving with the increased (slightly increased) torque. On the other hand, if the switch 36 selects driving according to the accelerator operation amount, the controller 21 returns to the original torque control of the first driving state. That is, the controller 21 calculates the command torque according to the accelerator operation amount and vehicle speed, and if the torque is less than the threshold torque, it limits the rate of change in the first limiting mode and determines the torque to be output in the next output processing from the command torque and the currently output torque. On the other hand, if the torque is greater than or equal to the threshold torque, it limits the rate of change in the second limiting mode, which is less restrictive than the first limiting mode, and determines the torque to be output in the next output processing from the specified torque and the currently output torque.

[0072] On the other hand, if the first forward movement determination results in the aforementioned determination that the electric vehicle 1 is sliding backward, the controller 21 drives the braking device 6 to stop the electric vehicle 1 from sliding backward. Also, if the second forward movement determination results in the aforementioned determination that the electric vehicle 1 is sliding backward, the controller 21 drives the braking device 6 to stop the electric vehicle 1 from sliding backward. After these actions, the controller 21 outputs information to the driver explaining the situation and then terminates the torque control.

[0073] <Example of operation> Figures 6 and 7 are time charts showing an example of the operation of an electric vehicle according to Embodiment 2. Figures 6 and 7 show the operation of electric vehicle 1 when traveling uphill with very low frictional resistance.

[0074] As shown in Figures 6 and 7, when the electric vehicle 1 is traveling uphill with low frictional resistance and slip occurs in the drive wheels 2d (timing t11), the controller 21 first performs a process to deal with the slip (operation c11). Then, torque control for when the vehicle transitions to the first driving state is started (timing t12). Because the slip occurred with a small torque, it is expected that the driver will fix the accelerator input at an amount greater than zero (operation c12). When this operation occurs, the controller 21 sets the command torque to the first torque Tq1 (= threshold torque Tqth = torque at the time of slip), and when the torque reaches the first torque Tq1, it fixes the torque at the first torque Tq1 (period T11).

[0075] As shown in Figure 6, if the electric vehicle 1 moves forward and the accelerator pedal input remains fixed, the controller 21 continues to output the first torque, and the electric vehicle 1 continues to move forward. When the driver changes the accelerator pedal input (timing t13), the controller 21 switches the processing back to the original torque control for the first driving state. This switch allows the driver to then drive in accordance with the accelerator pedal input (period T12).

[0076] Furthermore, as shown in Figure 7, when the accelerator input is fixed and the torque is fixed to the first torque Tq1 (period T11), if the electric vehicle 1 is stopped, the controller 21 continues to output the first torque Tq1. In this case, it is assumed that the driver will increase the accelerator input after some time has elapsed (operation c13) and attempt to move forward. When the above operation (operation c13) occurs, the controller 21 increases the torque (slightly) (operation c14) regardless of the amount of increase in accelerator input and determines whether the electric vehicle 1 will move forward. If it moves forward as a result, the electric vehicle 1 continues to move forward with the increased (slightly increased) torque (period T13). During this period T13, the controller 21 outputs information to the driver that it is possible to select a torque control method. If the switch 36 is not operated and automatic forward driving control is selected, the electric vehicle 1 continues to move forward with the increased (slightly increased) torque.

[0077] On the other hand, when a request to switch to driving in response to accelerator operation ("1" in Figure 7) is made by operating switch 36 (timing t14), the controller 21 switches the processing back to torque control of the original first driving state. Therefore, the driver can then drive in response to accelerator operation (period T14).

[0078] <Drive control processing> Figures 8 and 9 are flowcharts showing the drive control process executed by the controller 21 according to Embodiment 2. In the drive control process of Embodiment 2, steps identical to those in Embodiment 1 are denoted by the same reference numerals and detailed descriptions are omitted. In Figure 8, the illustration of a series of steps identical to those in Embodiment 1 is omitted.

[0079] In the drive control process of Embodiment 2, if it is determined in step S3 that the vehicle is in a second or third driving state, the controller 21 sets the second flag to "1" (steps S21, S22). The second flag is used to determine whether or not the vehicle has just transitioned to the first driving state.

[0080] Furthermore, if the first driving state is determined in step S3, the controller 21 determines whether the second flag is "1" or "0" (step S31). If the result is "0", the controller 21 proceeds to the torque control processing for the first driving state (steps S9~) similar to that in Embodiment 1. After that, the processing in steps S1~S3, S31, and S9~ is repeated, and the torque control processing for the first driving state continues.

[0081] On the other hand, if the result of the determination in step S31 is that the second flag is "1", then the controller 21 determines whether the accelerator operation amount is greater than zero, as it has just transitioned to the first driving state (step S32). If the result of the determination is YES, the controller 21 sets the command torque to the first torque, calculates the torque by applying the first limiting mode to the command torque, and outputs the torque, thereby changing the torque to the first torque (step S33). Then, the controller 21 determines whether the accelerator operation amount is greater than zero and fixed for a threshold time or longer (step S34), and if it is YES, it further determines whether the electric vehicle 1 is moving forward, stopped, or sliding backward (step S35).

[0082] If the result of the determination in step S32 is NO, or if the result of the determination in step S34 is NO, the controller 21 sets the second flag to "0" (step S36) and proceeds to step S9. By proceeding to step S9, the process then proceeds to torque control of the first driving state, similar to Embodiment 1.

[0083] On the other hand, if the result of the determination in step S35 is forward, the controller 21 proceeds to the loop processing of steps S41 to S44. In the loop processing, the controller 21 performs a determination process (step S41) to determine whether or not a change has occurred in the accelerator operation amount, and a determination process (step S42) to determine whether or not a change has occurred in the gradient based on the input from the first detection device 32. If there is a change in the gradient, the controller 21 corrects the first torque according to the change and performs a torque calculation process (step S43) using the corrected first torque as the command torque. Then, the controller 21 performs a torque output process (step S44). If the controller 21 does not determine in step S41 that there has been a change in the accelerator operation amount, it repeats the above loop processing.

[0084] If the result of step S41 is YES (a change has occurred), the controller 21 sets the second flag to "0" (step S36) and proceeds to step S9. By proceeding to step S9, the process then moves to torque control of the first driving state, similar to Embodiment 1.

[0085] If the result of the determination in step S35 is that the electric vehicle 1 is stopped, the controller 21 proceeds to the loop processing of steps S51 to S56. In the loop processing, the controller 21 first performs a determination process (step S51) to determine whether or not there is an increase in the accelerator operation amount. If there is an increase, the controller 21 slightly increases the command torque from the first torque and performs a torque calculation process (step S52) using the slightly increased first torque as the specified torque. Furthermore, the controller 21 performs a process to output the torque (step S53) and a process to determine how the behavior of the electric vehicle 1 has changed when the first torque has been slightly increased (step S54). If the electric vehicle 1 moves forward, the controller 21 performs a user interface process (step S55) that outputs information allowing the driver to choose between automatic forward driving or driving in response to accelerator operation. Finally, the controller 21 performs a process (step S56) to determine whether the switch 36 has been switched to driving in response to accelerator operation. The controller 21 repeats this loop process unless it is determined in step S54 that the electric vehicle 1 is sliding backward, or unless a specific selection is made in step S56.

[0086] Then, if the result of the determination in step S56 is YES, the controller 21 sets the second flag to "0" (step S36) and proceeds to step S9. By proceeding to step S9, the process then moves to torque control of the first driving state, similar to Embodiment 1.

[0087] Furthermore, if the result of the judgment in step S35 is that the vehicle is sliding down, or if the result of the judgment in step S54 is that the vehicle is sliding down, the controller 21 drives the braking device 6 to stop the electric vehicle 1 from sliding down (step S61). Next, the controller 21 outputs information explaining the situation to the driver (step S62) and then terminates the drive control process.

[0088] The torque control described above in Embodiment 2 is achieved through the drive control process described above.

[0089] The program for the drive control process described above is stored in a non-transient storage medium included in the storage device 22. The controller 21 may be configured to read a program stored in a portable non-transient recording medium and execute the program. The portable non-transient storage medium may store the program for the drive control process described above.

[0090] As described above, the drive control device 20 for the electric vehicle 1 of Embodiment 2 provides the following effects in addition to the effects of Embodiment 1. Specifically, with the drive control device 20 for the electric vehicle 1 of Embodiment 2, when the vehicle transitions to the first driving state due to slippage, the controller 21 changes the torque to the first torque Tq1 if the accelerator pedal input is greater than zero. Furthermore, the controller 21 then fixes the torque to the first torque Tq1 if the accelerator pedal input remains greater than zero for a threshold time or longer, and the electric vehicle 1 is moving forward (see Figure 6). Moreover, the first torque Tq1 is set to a value that has a positive correlation with the torque at the time of slippage (for example, the same value as the torque at the time of slippage). Therefore, in cases where slippage occurs with small accelerator pedal input on an uphill slope with very low road surface friction resistance, appropriate torque control can be activated for the driver's accelerator input (fixed at an accelerator pedal input greater than zero), which is often anticipated. In other words, torque control can be quickly activated to prevent the electric vehicle 1 from sliding backward, and the electric vehicle 1 can continue to move forward.

[0091] Furthermore, the drive control device 20 of the electric vehicle 1 in Embodiment 2 includes a first detection device 32 capable of detecting the gradient of the travel path. The controller 21 fixes the torque to a first torque Tq1, and when the electric vehicle 1 is moving forward, corrects the value of the first torque Tq1 based on the output of the first detection device 32 if the gradient of the travel path changes. Therefore, even if the gradient changes and the degree to which slippage occurs on an uphill slope changes, the torque changes in response to the change, making it easier to continue moving the electric vehicle 1 forward while suppressing slippage.

[0092] Furthermore, according to the drive control device 20 of the electric vehicle 1 of Embodiment 2, when the vehicle transitions to the first driving state due to slippage, the controller 21 changes the torque to the first torque Tq1 if the accelerator pedal input is greater than zero. Subsequently, if the accelerator pedal input remains greater than zero for a threshold time or longer and the electric vehicle 1 is stopped, the controller 21 fixes the torque to the first torque Tq1. Then, when the accelerator pedal input increases, the controller 21 increases the torque (slightly) regardless of the accelerator pedal input and determines whether the electric vehicle has moved forward due to the increase in torque. If the determination shows that the vehicle has moved forward, the controller 21 executes a user interface process that allows the driver to choose between automatic forward driving or driving according to the accelerator pedal input (see Figure 7). Therefore, even on uphill slopes where both slippage and backward sliding are likely to occur, the possibility of moving the electric vehicle 1 forward can be increased by the torque control that does not depend on the accelerator pedal input as described above. Furthermore, the driver can choose to return to driving according to the accelerator pedal input.

[0093] Embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. For example, although the above embodiments described a drive control device for an electric vehicle having driven wheels, the present invention may also be applied to a drive control device for an all-wheel drive electric vehicle that does not have driven wheels. In that case, the torque to be controlled may be the total torque, or it may be the front wheel torque or the rear wheel torque. Also, in the above embodiments, the electric vehicle 1 on which the drive control device is installed was shown as an electric vehicle without an engine, such as an internal combustion engine, but the electric vehicle may be an HEV (Hybrid Electric Vehicle) that has an engine. Also, in the above embodiments, the accelerator operation amount was shown as the amount by which the driver operates the accelerator operation unit 11b, but the accelerator operation amount may be the amount of accelerator operation by the automatic driving system. Furthermore, details shown in the embodiments can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0094] 1. Electric Vehicle 20 Drive control device 2 wheels 2d drive wheels 3 Electric motor 4 Inverters 5 batteries 6 Braking device 11. Operating controls 11a Brake operating section 11b Accelerator control unit 11c Steering Section 21 Controllers 22 Storage device 31. Vehicle speed sensor 32 First detection device (detection device) 33 Second detection device 35, 36 switches Tqth threshold torque Tq1 First Torque

Claims

1. A drive control device for an electric vehicle, which is mounted on an electric vehicle equipped with drive wheels and an electric motor that drives the drive wheels, The system includes a controller that controls the torque output from the electric motor based on the accelerator pedal input and the vehicle status. The aforementioned controller, During a first driving state, which is driving uphill where the likelihood of slippage is estimated to be above a threshold, the rate of change of the torque is limited in a first limiting mode when the torque is below the threshold torque, while the rate of change of the torque is limited in a second limiting mode that is less restrictive than the first limiting mode when the torque is above the threshold torque. Furthermore, the controller determines that the vehicle is in the first driving state when it detects that a slip has occurred while driving uphill. The first limiting mode is a mode of limiting the change rate that is applied during a second driving state in which no slip occurs of the drive wheels, The second limitation mode is a limitation mode of the change rate that is applied during the period of the third driving state in which slip of the drive wheels occurs other than on an uphill slope, The drive control device for an electric vehicle is characterized in that the threshold torque is set to a value that has a positive correlation with the torque at the time of slip.

2. A drive control device for an electric vehicle, which is mounted on an electric vehicle equipped with drive wheels and an electric motor that drives the drive wheels, The system includes a controller that controls the torque output from the electric motor based on the accelerator pedal input and the vehicle status. The aforementioned controller, During a first driving state, which is driving uphill where the likelihood of slippage is estimated to be above a threshold, the rate of change of the torque is limited in a first limiting mode when the torque is below the threshold torque, while the rate of change of the torque is limited in a second limiting mode that is less restrictive than the first limiting mode when the torque is above the threshold torque. When the vehicle transitions to the first driving state due to slippage, the controller changes the torque to a first torque if the accelerator pedal input is greater than zero, and then fixes the torque to the first torque if the accelerator pedal input remains greater than zero for a threshold time or longer. The drive control device for an electric vehicle is characterized in that the first torque is set to a value that has a positive correlation with the torque at the time of slip.

3. Equipped with a detection device capable of detecting the gradient of the road, The drive control device for an electric vehicle according to claim 2, characterized in that the controller fixes the torque to the first torque, and when the electric vehicle is moving forward, it acquires the output of the detection device, and when it is determined that the gradient of the road has changed based on the output, it corrects the value of the first torque according to the gradient.

4. The controller fixes the torque to the first torque, and when the electric vehicle is stopped, it determines whether the accelerator operation amount has increased, and if the accelerator operation amount has increased, it increases the torque regardless of the accelerator operation amount, as described in claim 2 or 3.

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