Control method for electric vehicle and control system for electric vehicle

Abstract

Provided is a control method for an electric vehicle. The control method executes, on a torque command value, a filtering process that causes torque to stagnate when torque is not transmitted to a drive shaft, using a vehicle model representing the torque response of a driving force transmission system having a dead zone section, in which torque is not transmitted to the drive shaft, and controls a drive motor on the basis of the torque command value after the filtering process. The control method includes: a setting step for setting, while the electric vehicle is stopped, the torque command value to a predetermined first torque command value and thereafter setting the torque command value to a predetermined second torque command value having a sign opposite to that of the first torque command value; an estimation step for estimating an actual backlash amount of the driving force transmission system on the basis of the amount of change in a parameter related to the rotational speed of the drive motor when the torque command value is changed from the first torque command value to the second torque command value; and an updating step for updating a set backlash amount for setting an upper limit and a lower limit of the dead zone section on the basis of the actual backlash amount.

Description

Electric vehicle control method and electric vehicle control system

[0001] The present invention relates to a control method for an electric vehicle and a control system for an electric vehicle.

[0002] JP2009-185738A discloses a configuration for a vehicle control device that transmits the torque of an internal combustion engine to a transmission, in which a torsion model of a driving force transmission system is used to estimate the current amount of backlash in backlash elements, and the total amount of backlash in the backlash elements is compared with the estimated current amount of backlash to determine the timing for increasing or decreasing engine torque.

[0003] As in JP2009-185738A, estimating the amount of backlash in a transmission connected to an internal combustion engine to grasp the difference between the design value and individual variations and reflecting this in a control device is also effective for reducing shock in the control of electric vehicles. However, drivers have high expectations for a reduction in shock caused by backlash in the driving force transmission system of electric vehicles, and it is difficult to meet these expectations with the technology disclosed in JP2009-185738A.

[0004] Therefore, an object of the present invention is to provide a control method for an electric vehicle and a control system for an electric vehicle that efficiently reduces shock caused by eliminating backlash by accurately estimating the actual amount of backlash in the driving force transmission system of the electric vehicle.

[0005] According to one aspect of the present invention, there is provided a method for controlling an electric vehicle, in which a torque command value is set based on vehicle information to control the torque of a drive motor connected to a drive wheel, the method performs filtering on the torque command value using a vehicle model representing the torque response of a drive force transmission system having a dead-band section in which torque is not transmitted to the drive shaft, thereby stagnating torque when torque is not transmitted to the drive shaft, and controls the drive motor based on the filtered torque command value. This control method includes a setting step of setting the torque command value to a first backlash-reducing torque for reducing backlash in the drive force transmission system while the electric vehicle is stopped, and then setting the torque command value to a second backlash-reducing torque having a positive / negative sign opposite to that of the first backlash-reducing torque, an estimation step of estimating an actual amount of backlash in the drive force transmission system based on changes in parameters related to drive motor rotation when the torque command value is changed from the first backlash-reducing torque to the second backlash-reducing torque, and an updating step of updating a set backlash that sets upper and lower limits of the dead-band section based on the actual amount of backlash.

[0006] FIG. 1 is a diagram showing the main configuration of an electric vehicle to which the control system for an electric vehicle of this embodiment is applied. FIG. 2 is a flow chart showing the flow of processing performed by a motor controller. FIG. 3 is a diagram showing an example of an accelerator opening-torque table. FIG. 4 is a diagram showing the main configuration of the control system for an electric vehicle of this embodiment. FIG. 5 is a diagram showing a model of the driving force transmission system of the vehicle. FIG. 6 is a flow chart of the set backlash amount update process. FIG. 7 is a time chart of the set backlash amount update process. FIG. 8 is a diagram showing the relationship between the shock occurring when backlash is eliminated when the initial value of the set backlash is set corresponding to the actual backlash amount of the driving force transmission system, and the shock occurring when the set backlash amount is maintained at the initial value and the actual backlash amount subsequently changes due to long-distance driving of the electric vehicle. Fig. 9 shows changes in longitudinal acceleration, motor rotation speed, and feedback torque during backlash elimination when the initial value of the set backlash is set corresponding to the actual backlash of the driving force transmission system, and Fig. 10 shows changes in shock during backlash elimination when the set backlash is updated to match the actual backlash that has changed due to long-distance driving of the electric vehicle. Fig. 11 shows changes in longitudinal acceleration, motor rotation speed, and motor torque during backlash elimination when the set backlash is updated to match the actual backlash that has changed due to long-distance driving of the electric vehicle.

[0007] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0008] 1 is a diagram showing the main configuration of an electric vehicle 100 to which the control system for the electric vehicle 100 of this embodiment is applied. The electric vehicle 100 is a vehicle that has a drive motor 4 as part or all of the vehicle's drive source and can run using the driving force of the drive motor 4, and includes not only electric vehicles but also hybrid vehicles and fuel cell vehicles.

[0009] The motor controller 2 receives digital signals indicating vehicle conditions such as vehicle speed (V), accelerator opening (θ), rotor phase (α) of the drive motor 4, current (iu, iv, iw) of the drive motor 4, and a shift signal (not shown), and generates a PWM signal for controlling the drive motor 4 based on the received signals. The motor controller 2 also generates a drive signal for the inverter 3 in accordance with the generated PWM signal. The motor controller 2 is also programmed to execute the control system (control method) for the electric vehicle 100 of this embodiment.

[0010] The inverter 3 has, for example, two switching elements (e.g., power semiconductor elements such as IGBTs and MOS-FETs) for each phase, and by turning the switching elements on and off in response to a drive signal, converts the direct current supplied from the battery 1 into alternating current and passes the desired current through the drive motor 4.

[0011] The drive motor 4 (three-phase AC motor) generates driving force using the AC current supplied from the inverter 3, and transmits the driving force to the left and right drive wheels 9a, 9b via the speed reducer 5 and the drive shaft 8. When the drive motor 4 rotates along with the drive wheels 9a, 9b while the vehicle is running, it generates regenerative driving force, thereby recovering the vehicle's kinetic energy as electrical energy. In this case, the inverter 3 converts the AC current generated during regenerative operation of the drive motor 4 into DC current and supplies it to the battery 1.

[0012] The current sensor 7 detects three-phase AC currents (iu, iv, iw) flowing through the drive motor 4. However, since the sum of the three-phase AC currents (iu, iv, iw) is zero, the currents of any two phases may be detected and the current of the remaining phase may be calculated.

[0013] The rotation sensor 6 is, for example, a resolver or an encoder, and detects the rotor phase (α) of the drive motor 4 .

[0014] [Motor Controller 2] Fig. 2 is a flow chart showing the flow of processing performed by the motor controller 2. Fig. 3 is a diagram showing an example of an accelerator opening-torque table.

[0015] In step S201, signals indicating the vehicle state are input, including the vehicle speed (V) [km / h], accelerator opening (θ) [%], rotor phase (α) [rad] of the drive motor 4, rotation speed (Nm) [rpm] of the drive motor 4, rotor angular velocity (ω) [rad / s], current (iu, iv, iw) of the drive motor 4, shift signal, and DC voltage value (Vdc) [V] between the battery 1 and inverter 3.

[0016] The vehicle speed (V) [km / h] is acquired by communication from a vehicle speed sensor (not shown) or another controller (not shown), such as a brake controller. Alternatively, the vehicle speed (V) [m / s] is calculated by multiplying the motor rotation speed (ωm) by the tire dynamic radius (R) and dividing by the gear ratio of the final gear, and the unit is converted by multiplying it by 3600 / 1000 to calculate the vehicle speed (V) [km / h].

[0017] The accelerator opening (θ) [%] is obtained from an accelerator opening sensor (not shown) or is obtained by communication from another controller (not shown) such as a vehicle controller.

[0018] The rotor phase (α) [rad] of the drive motor 4 is acquired from the rotation sensor 6. The rotation speed (Nm) [rpm] of the drive motor 4 is calculated by dividing the rotor angular velocity (ω) (electrical angle) by the number of pole pairs of the drive motor 4 to obtain the motor rotation speed (ωm) [rad / s], which is the mechanical angular velocity of the drive motor 4, and then multiplying the motor rotation speed (ωm) by 60 / (2π). The rotor angular velocity (ω) [rad / s] is calculated by differentiating the rotor phase (α).

[0019] The current (iu, iv, iw) [A] of the drive motor 4 is acquired from the current sensor 7 .

[0020] The DC voltage (Vdc) [V] is determined from a voltage sensor (not shown) provided on the DC power supply line between the battery 1 and the inverter 3, or from a power supply voltage value transmitted from a battery controller (not shown).

[0021] In step S202, the first torque command value (Tm1 ＊Specifically, the first torque command value (Tm1) is set by referring to the accelerator opening-torque table shown in FIG. 3 based on the accelerator opening (θ) and vehicle speed (V) input in step S201. ＊ ) to set the

[0022] In step S203, a process for updating the set backlash amount used in step S204 is executed. Details of this update process will be described later.

[0023] In step S204, the first torque command value (Tm1 ＊ ) and the motor rotation speed (ωm), and calculates a final torque command value (Tm2 ＊ ) is set. ＊ ) will be described in detail later.

[0024] In step S205, the final torque command value (Tm2 ＊ ), the motor rotation speed (ωm), and the DC voltage (Vdc), the d-axis current target value (id ＊ ), q-axis current target value (iq ＊ ) is required.

[0025] In step S206, the d-axis current (i d ) and the q-axis current (i q ) are respectively set to the d-axis current target value (i d ＊ ) and the q-axis current target value (iq ＊ ) is controlled to match the d-axis current (id) and the q-axis current (iq). For this purpose, first, the d-axis current (id) and the q-axis current (iq) are calculated based on the three-phase AC current values ​​(iu, iv, iw) input in step S201 and the rotor phase (α) of the drive motor 4. Next, the d-axis and q-axis current command values ​​(id ＊ , iq ＊ The d-axis and q-axis voltage command values ​​(vd, vq) are calculated from the deviation between the d-axis and q-axis currents (id, iq) and the d-axis and q-axis voltage command values ​​(vd, vq).

[0026] Next, three-phase AC voltage command values ​​(vu, vv, vw) are calculated from the d-axis and q-axis voltage command values ​​(vd, vq) and the rotor phase (α) of the drive motor 4. Then, PWM signals (tu, tv, tw) [%] are calculated from the calculated three-phase AC voltage command values ​​(vu, vv, vw) and the DC voltage (Vdc). By opening and closing the switching elements of the inverter 3 using the PWM signals (tu, tv, tw) calculated in this way, the drive motor 4 can be driven at the desired torque specified by the torque command value.

[0027] [Control System] Figure 4 is a diagram showing the main configuration of the control system for the electric vehicle 100 of this embodiment. The control system for the electric vehicle 100 of this embodiment is composed of a vibration suppression control feedforward compensator (FF compensator 21), a vibration suppression control feedback compensator (FB compensator 22), and an adder 23, and performs vibration suppression control during traveling (reducing torsional vibration in the drive shaft 8 and shock when backlash is eliminated). Note that backlash elimination refers to preventing play from occurring in the drive force transmission mechanism (free rotation of the drive motor 4 due to backlash) when transmitting the driving force (torque) of the drive motor 4 to the drive shaft 8.

[0028] The FF compensator 21 calculates the first torque command value (Tm1 ＊ ) is input, and a filtering process (described later) is performed to suppress torsional vibration in the drive shaft 8, thereby obtaining an FF compensation value (Tm11 ＊ ) and outputs the FF compensation value (Tm11 ＊ The motor angular velocity estimated value (ωm^) is calculated in the process of calculating the FF compensator 21. The calculation of the FF compensator 21 will be described in detail later.

[0029] The FB compensator 22 receives the motor rotation speed (ωm) and the motor angular velocity estimate (ωm^) and calculates an FB compensation value (Tm12 ＊ The calculation of the FB compensator 22 will be described in detail later.

[0030] The adder 23 calculates the FF compensation value (Tm11 ＊ ) and FB compensation value (Tm12 ＊ ) to obtain the final torque command value (Tm2 ＊) is output. As a result, for example, the first torque command value (Tm1 ＊ ) switches from negative to positive (or from positive to negative), causing backlash in the driving force transmission system to be eliminated (the driving force of the drive motor 4 is not transmitted to the drive shaft 8). ＊ ) can be stagnated (set to a value close to zero), reducing the shock when removing backlash (the excitation force caused by teeth hitting when removing backlash in the gears that make up the drive force transmission system).

[0031] The FF compensator 21 is configured with a vehicle model 211 that is configured with a dead zone model that simulates vehicle parameters and gear backlash, and a first torque command value (Tm1 ＊ ) to the pseudo torsional angular velocity using the feedback gain (K ＦＢ１ and a drive shaft torsional angular velocity FB model 212 that subtracts the integrated value of the above.

[0032] [Vibration Suppression Control] <Vehicle Model 211> Fig. 5 is a diagram showing a model of a driving force transmission system of a vehicle. The equations of motion of the vehicle are expressed by the following equations (1) to (6).

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] Here, the parameters are as follows:

[0040] J ｍ : Motor inertia J ｗ : Drive shaft inertia (for one shaft) M: Vehicle mass K ｄ : Torsional rigidity of drive shaft K ｔ : Coefficient of friction between tire and road surface N: Overall gear ratio r: Tire load radius ω ｍ : Motor angular velocity θ ｍ: Motor rotation angle ω ｗ : Drive wheel angular velocity θ ｗ : Drive wheel rotation angle T ｍ : Motor torque T ｄ : Drive shaft torque F: Driving force (for one shaft) V: Vehicle speed θ ｄ : Torsion angle of the drive shaft

[0041] Equations (1) to (6) are Laplace transformed to obtain the motor torque (T ｍ ) to the motor rotation angular velocity (ω ｍ ) and obtain the transfer characteristics as shown in equations (7) and (8) below.

[0042]

[0043]

[0044] However, each parameter is as shown in the following equation (9).

[0045] In addition, the motor torque (T ｍ ) to the drive shaft torque (T ｄ ) is expressed by the following equation (10).

[0046] From equations (1), (3), (4), and (5), the motor rotation angular velocity (ω ｍ ) to the driving wheel rotation angular velocity (ω ｗ ) is calculated as the following equation (11).

[0047] From equations (7), (8), and (11), the motor torque (T ｍ ) to the driving wheel rotation angular velocity (ω ｗ ) is expressed by the following equation (12).

[0048] From equations (10) and (12), the drive shaft torque (T ｄ ) to the driving wheel rotation angular velocity (ω ｗ ) is expressed by the following equation (13).

[0049] Transforming equation (13) yields equation (14) below.

[0050] Therefore, from equations (13) and (14), the drive shaft torsional angular velocity (ω ｄ ) can be expressed by the following formula:

[0051] However, H in equation (15) ｗ (s) is as follows: is.

[0052] Furthermore, equation (15) is Here, "ζ ｐ " is the damping coefficient of the drive shaft torque transmission system, "ω ｐ " is the natural vibration frequency of the drive shaft torque transmission system.

[0053] Furthermore, when we examine the poles and zeros of equation (17), we find that "α ≒ c ０ / c １ " Therefore, when pole-zero cancellation is performed, the following equation (18) is obtained.

[0054] Final torque command value (T ｍｆ ＊ )of Then, it can be rewritten as the following equation (20).

[0055] "T ｍ =T ｍｆ ＊ " and substituting equation (20) into equation (18), it can be rearranged as shown in equation (21) below.

[0056] When the reference response from the motor torque to the drive shaft torque is expressed by the following equation (22), The condition under which equations (21) and (22) coincide is given by equation (23) below.

[0057] Next, by applying equations (1) to (16), the backlash characteristics from the drive motor 4 to the drive shaft 8 are modeled in a dead zone.

[0058] Drive shaft torque (T ｄ ) is expressed by the following equation (24). Here, "θ ｄｅａｄ" is the overall backlash amount (set backlash amount) from the drive motor 4 to the drive shaft 8. As a result, the vehicle model 211 becomes a model that includes the transfer characteristic (Gp(s)) and has a dead band section in which the torque of the drive motor 4 is not transmitted to the drive shaft 8 of the electric vehicle 100.

[0059] <Torsion angular velocity FB model 212> The torsion angular velocity FB model 212 calculates the drive shaft torsion angular velocity FB command value (T ＦＢ ) is calculated. ＦＢ ) is expressed by the following equation using the drive shaft torsional angular velocity estimate value (ωd^=(ωm / N)−ωw) calculated from the vehicle model 211:

[0060] Furthermore, the above equation can be rewritten as follows using equations (4) and (6):

[0061] Moreover, equation (10) can be transformed into the following equation (27).

[0062] Here, ζp is the damping coefficient of the drive torque transmission system, and ωp is the natural vibration frequency of the drive torque transmission system. Furthermore, by examining the poles and zeros of equation (27), α ≒ c ０ / c １ Therefore, when poles and zeros are cancelled out, the following equation is obtained.

[0063] From equations (24), (26), and (28), the drive shaft torque (Td) is expressed by the following equation:

[0064] By modifying equation (29), the transfer characteristic of the drive shaft torsional angular velocity FB system is expressed by the following equation.

[0065] An idealized standard response of the torque response from the drive motor 4 to the drive shaft 8 is expressed by the following equation, assuming that the response from Tm to Td does not become an oscillatory system (becomes an undershoot).

[0066] The condition under which the transfer characteristic of the drive shaft torsional angular velocity FB system matches the reference response is given by the following equation.

[0067] From equation (31), the feedback gain (K ＦＢ１ ) is defined by the following formula:

[0068] The torsional angular velocity FB model 212 calculates the first torque command value (Tm1 ＊ ) to the drive shaft torsional angular velocity FB command value (T ＦＢ ) is subtracted from the FF compensation value (Tm11 ＊ ) to the vehicle model 211 and the adder 23.

[0069] <FB compensator 22> The FB compensator 22 outputs an FB correction value (Tm12) through a filter (H(s) / Gp(s)) consisting of the inverse characteristic of the transfer characteristic (Gp(s)) (Equation (8)) and a band-pass filter (H(s)) to the difference between the motor angular velocity estimated value (ωm^) calculated by the vehicle model 211 and the motor angular velocity detected value (ωm). ＊ ) is calculated.

[0070] Here, the bandpass filter H(s) is set so that the attenuation characteristics of the low-pass side and the high-pass side are approximately the same and the torsional resonance frequency of the driving force transmission system is near the center of the passband on a logarithmic axis (Log scale). For example, when H(s) is configured with a first-order high-pass filter and a first-order low-pass filter, the frequency fp is the torsional resonance frequency of the driving force transmission system, and f ＬＣ is the low-frequency cutoff frequency, f ＨＣ is the high-frequency cutoff frequency, and k is an arbitrary value, and is constructed as shown in equation (34).

[0071] where τ Ｌ = 1 / (2πf ＨＣ ), f ＨＣ = k fp, τ Ｈ = 1 / (2πf ＬＣ ), f ＬＣ = fp / k.

[0072] However, JP2009-185738A has the following problems: it cannot estimate the overall actual backlash of the driving force transmission system that satisfies the requirements of the electric vehicle 100 and reflect it as the set backlash. (1) The actual backlash of the driving force transmission system is estimated based on the difference between the transmission input and output rotational speeds. However, the input and output rotational speeds fluctuate during driving due to vibrations, and are filtered. This filter reduces the accuracy of the estimated backlash. (2) The torsional angle when driven is corrected based on the estimated wheel torque when driven and the drive shaft torsional stiffness value. However, errors between the estimated wheel torque and the actual wheel torque and variations in the drive shaft torsional stiffness directly contribute to errors in the estimated backlash. (3) Although the system has a function for learning the actual backlash, the actual backlash is also estimated using corrections of the estimated torque and torsional stiffness, which, like (3), contributes to errors in the total backlash.

[0073] Therefore, in this embodiment, in order to solve the above problems (1) to (3), the actual backlash amount is estimated when the electric vehicle 100 is stopped.

[0074] 6 is a flow diagram of the set backlash updating process. In step S501, the motor controller 2 determines whether the preconditions for the set backlash updating process are met. If the result is YES, the process proceeds to step S502. If the result is NO, the process proceeds to END (the set backlash updating process is not executed). Here, the preconditions include, for example, that the electric vehicle 100 has traveled approximately 1000 km since the last time the set backlash updating process was performed, and that the road surface on which the electric vehicle 100 is traveling is flat (with almost no incline).

[0075] In step S502, the motor controller 2 determines whether the brake (mechanical brake or regenerative brake) that brakes the drive wheels 9a, 9b is on or not, and if YES, proceeds to step S503, and if NO, proceeds to END.

[0076] In step S503, the motor controller 2 determines whether or not the torque command value is zero (creep cut), and if YES, proceeds to step S504, and if NO, proceeds to END.

[0077] In step S504, the motor controller 2 determines whether the vehicle is stopped (whether the vehicle speed (V) is zero), and if YES, proceeds to step S505, and if NO, proceeds to END.

[0078] In step S505, the motor controller 2 determines whether a first predetermined time (for example, 5 seconds) has elapsed since the vehicle stopped, and if YES, proceeds to step S506, and if NO, remains in step S505.

[0079] In step S506, the motor controller 2 calculates the torque command value (first torque command value (Tm1 ＊ )) is set as the first backlash-reducing torque. Here, the first backlash-reducing torque is a minute negative torque that allows backlash reduction in the driving force transmission system, and is set in the range of, for example, -2 [Nm] to -3 [Nm]. This reduces backlash in the driving force transmission system in the direction in which the electric vehicle 100 moves backward, but because the torque is minute, no twisting of the drive shaft 8 occurs, and backlash reduction is performed while maintaining the rigidity of the driving force transmission system. Note that the internal combustion engine disclosed in JP 2009-185738 A and the like cannot generate minute torque when the vehicle is stopped, making it difficult to implement the present invention.

[0080] In step S507, the motor controller 2 starts reading the detection value (electrical angle) of the rotation sensor 6 (resolver) after a second predetermined time (e.g., 2 seconds) has elapsed since the execution of the processing of step S506 (after the backlash elimination in step S506 has been completed).

[0081] In step S508, after the processing of step S507, the motor controller 2 sets the torque command value to a second backlash-reducing torque. Here, the second backlash-reducing torque is a small positive torque that is large enough to eliminate backlash in the driving force transmission system, and is set in the range of 2 [Nm] to 3 [Nm], for example. This eliminates backlash in the driving force transmission system in the direction in which the electric vehicle 100 travels, but because the torque is small, no twisting of the drive shaft 8 occurs, and backlash elimination is performed while maintaining the rigidity of the driving force transmission system.

[0082] In step S509, after a third predetermined time (for example, 2 seconds) has elapsed since the execution of the process of step S508 (after the backlash elimination in step S508 has been completed), the torque command value is set to zero.

[0083] In step S510, the motor controller 2 estimates the amount of change in the detected value of the rotation sensor 6 (resolver) as the actual amount of backlash in the driving force transmission system.

[0084] In step S511, the motor controller 2 calculates the set backlash (θ ｄｅａｄ ) to update.

[0085] In step S507, instead of reading the detection value of the rotation sensor 6 (resolver), the motor controller 2 starts reading the motor angular velocity (ωm), and in step S508, integrates the motor angular velocity (ωm) over a time range in which it becomes a predetermined value as backlash elimination occurs and then becomes zero as backlash elimination ends, and estimates the integrated value as the actual amount of backlash in the driving force transmission system.

[0086] 7 is a time chart of the process of updating the set backlash. In the initial state, the electric vehicle 100 is traveling (stopped) on a flat road, and has traveled approximately 1000 km (a distance over which the actual backlash of the driving force transmission system may change) since the last time the set backlash was updated.

[0087] Before time t0, the vehicle speed and the motor rotation speed are reduced by the brake being applied, and if the brake is a regenerative brake, the torque command value (first torque command value (Tm1 ＊ ) is set to a negative value, and the motor torque (torque applied to the drive motor 4) also becomes a negative value.

[0088] When the vehicle speed becomes equal to or lower than a predetermined low speed at time t0, the torque command value (first torque command value (Tm1 ＊ ) becomes zero, the motor torque starts to converge to zero, and at time t1, the vehicle speed, motor torque, and motor rotation speed become zero.

[0089] At time t1, the drive force transmission system is in a state where backlash elimination in the direction in which the electric vehicle 100 travels has been completed, or where the backlash elimination is incomplete.

[0090] At time t2 (for example, 5 seconds after time t0), the torque command value is set to a first backlash-reducing torque (-3 Nm). This reduces backlash in the driving force transmission system in the direction in which the electric vehicle 100 moves backward. The set time is approximately 3 seconds.

[0091] When the torque command value is set to the first backlash-reducing torque at time t2, the motor torque changes monotonically in the negative direction in accordance with the transmission characteristics of the driving force transmission system, and when backlash reduction is completed at time t3, the motor torque becomes the same value as the first backlash-reducing torque.

[0092] When backlash elimination in the direction in which the electric vehicle 100 moves backward begins at time t2, the motor rotation speed (angular velocity) of the drive motor 4 changes from zero to a negative value, but when backlash elimination is completed at time t3, it converges to zero.

[0093] At time t4, reading of the detected value of the rotation sensor 6 (resolver) begins. However, the detected value (initial value) does not change until time t6, which will be described later.

[0094] At time t5, the torque command value is set to a second backlash-removing torque (3 [Nm]) for a set time of approximately 3 [sec]. This causes backlash to be removed in the driving force transmission system in the forward direction of electric vehicle 100.

[0095] When the torque command value is set to the second backlash-reducing torque at time t5, the motor torque changes monotonically in the positive direction in accordance with the transfer characteristics of the driving force transmission system until time t7, which will be described later. At time t6, the motor torque becomes zero, and backlash reduction in the driving force transmission system in the direction in which the electric vehicle 100 moves backward (and forward) is released. At time t7, backlash reduction in the driving force transmission system in the direction in which the electric vehicle 100 moves forward is completed, and the motor torque becomes the same value as the second backlash-reducing torque.

[0096] When backlash elimination in the forward direction of the electric vehicle begins at time t6, the motor rotation speed of the drive motor 4 increases from zero to a positive value, but when backlash elimination is completed at time t7, it converges to zero.

[0097] At time t6, the detection value of the rotation sensor 6 (resolver) starts to rise from the initial value, and the amount of change in the detection value becomes the integral value of the motor rotation speed. Then, when the motor rotation speed converges to zero at time t7, the change in the detection value of the rotation sensor 6 (resolver) also stops. Then, the difference between the final detection value and the initial value becomes the set backlash amount (θ ｄｅａｄ ) and reflects the actual amount of play in the current drive force transmission system.

[0098] Thereafter, at time t8, the torque command value is set to zero, and the motor torque also converges to zero. Note that the first backlash-reducing torque may be a positive value, and the second backlash-reducing torque may be a negative value.

[0099] [Longitudinal acceleration when eliminating backlash] Figure 8 shows the longitudinal acceleration when eliminating backlash (θ ｄｅａｄ The shock when eliminating backlash when the initial value of θ is set according to the actual backlash of the driving force transmission system, and the set backlash (θ ｄｅａｄ 9 is a diagram showing the relationship between the set amount of backlash (θ ) and the shock when the actual amount of backlash changes after the electric vehicle 100 has traveled a long distance while the set amount of backlash (θ ) is maintained at the initial value. ｄｅａｄ The initial value of θ ) is set according to the actual amount of backlash in the driving force transmission system. The transition of the longitudinal acceleration, motor rotation speed, and feedback torque during backlash elimination and the set backlash amount (θ ｄｅａｄ 10A and 10B are diagrams showing changes in longitudinal acceleration, motor rotation speed, and feedback torque during backlash elimination when the actual backlash amount changes as the electric vehicle 100 travels long distances while the initial value of the backlash is maintained.

[0100] In the electric vehicle 100, there may be variations in the actual amount of backlash in the driving force transmission system. For this reason, the vehicle model 211 sets a set amount of backlash (θ ｄｅａｄThis makes it possible to control the motor torque to stagnate (set to almost zero) when, for example, the motor torque switches from negative to positive and backlash (backlash) occurs in the drive force transmission system, and then increase the motor torque in the positive direction when backlash elimination is complete, thereby reducing shock when backlash is eliminated.

[0101] It is also known that the amount of actual backlash in the driving force transmission system increases in proportion to the travel distance of the electric vehicle 100. This increase in the amount of actual backlash occurs due to wear of the gears that make up the driving force transmission system, etc.

[0102] Therefore, if the set amount of backlash in vehicle model 211 is set, for example, to match the actual amount of backlash in the driving force transmission system at the time of manufacturing electric vehicle 100, the actual amount of backlash will become larger than the set amount as the traveling distance of electric vehicle 100 increases thereafter. For this reason, if it is determined that backlash elimination has been completed in vehicle model 211 and torque is increased, the torque will be increased before backlash elimination in the driving force transmission system has been completed, and a shock (longitudinal acceleration) will occur when backlash elimination is completed.

[0103] As shown in Figure 8, when the actual amount of backlash in the driving force transmission system of electric vehicle 100 is 1.75 degrees, the initial value of the set amount of backlash in vehicle model 211 is set to the same value as the actual amount of backlash, and the longitudinal acceleration when backlash is subsequently eliminated is used as a reference. As electric vehicle 100 travels a long distance and the actual amount of backlash increases, the longitudinal acceleration generated when backlash is eliminated tends to increase. For example, when the actual amount of backlash becomes 2.75 degrees, the longitudinal acceleration generated when backlash is eliminated increases by 0.017 G.

[0104] 9 shows a case where the torque applied to the drive motor 4 changes from negative to positive torque. When the torque applied to the drive motor 4 is zero (time t=2 [sec] in FIG. 9), the longitudinal acceleration becomes zero, and around this time, the drive force transmission system of the electric vehicle 100 begins to eliminate backlash in the forward direction of the electric vehicle 100 and this is completed, resulting in a shock.

[0105] However, as shown in FIG. 9, when the initial value (1.75 [deg]) of the set amount of backlash in the vehicle model 211 is set to the same value as the actual amount of backlash (1.75 [deg]) of the driving force transmission system, the sudden increase in the motor rotation speed during backlash elimination (the sudden increase in the motor rotation speed due to the increase in torque during backlash elimination) is suppressed, and as a result, the feedback torque (FB compensation value (Tm12 ＊ Therefore, a sudden change (shock) in the longitudinal acceleration immediately after the longitudinal acceleration becomes zero is suppressed.

[0106] On the other hand, if the actual backlash becomes 2.75 degrees while the initial set backlash value (1.75 degrees) is maintained, the torque will increase before the backlash is eliminated as described above, causing the motor rotation speed to increase at time t = 2 seconds, and the feedback torque will not be able to absorb the vibration caused by this increase. As a result, a large peak (shock) will occur in the longitudinal acceleration around time t = 2.05 seconds.

[0107] [Longitudinal acceleration when eliminating backlash after updating the set backlash amount] FIG. 10 shows the longitudinal acceleration when eliminating backlash after updating the set backlash amount (θ ｄｅａｄ 11 is a diagram showing a change in shock when the set amount of backlash (θ ) is updated to match the actual amount of backlash that has changed due to long-distance traveling of the electric vehicle 100. ｄｅａｄ 10A and 10B are diagrams showing changes in longitudinal acceleration, motor rotation speed, and motor torque during backlash elimination when the backlash amount is updated to match the actual backlash amount that has changed due to long-distance driving of the electric vehicle 100.

[0108] FIG. 10 shows the result of adding longitudinal acceleration (shock) when the set backlash amount is updated to the actual backlash amount of the driving force transmission system after the set backlash amount has increased due to long-distance driving of the electric vehicle 100, compared to FIG. 8, and is applied when the actual backlash amount is 2.75 [deg] and 3.75 [deg].

[0109] When the actual backlash is 2.75 [deg] and the set backlash is 1.75 [deg], the longitudinal acceleration is increased by 0.017 [G] compared to when the actual backlash is 1.75 [deg] and the set backlash is 1.75 [deg].

[0110] On the other hand, when the actual backlash is 2.75 [deg] and the set backlash is updated to 2.75 [deg], the longitudinal acceleration improves to the same level as when the actual backlash is 1.75 [deg] and the set backlash is 1.75 [deg].

[0111] When the actual backlash is 3.75 [deg] and the set backlash is 1.75 [deg], the longitudinal acceleration is increased by 0.027 [G] compared to when the actual backlash is 1.75 [deg] and the set backlash is 1.75 [deg].

[0112] On the other hand, when the actual backlash is 3.75 [deg] and the set backlash is updated to 3.75 [deg], the longitudinal acceleration improves to about 0.003 [G] higher than when the actual backlash is 1.75 [deg] and the set backlash is 1.75 [deg].

[0113] The longitudinal acceleration (dashed line) and motor rotation speed (dashed line) in FIG. 11 are the same as the longitudinal acceleration (solid line) and motor rotation speed (solid line) in FIG.

[0114] As shown in Figure 11, when the actual backlash is 2.75 [deg] and the set backlash is 1.75 [deg], the motor torque stops stagnating and begins to rise at a time (time t = 1.98 [sec]) before the removal of backlash in the driving force transmission system is completed, so the amount of increase in motor rotation speed increases and a peak (shock) in the longitudinal acceleration appears at time t = 2.05 [sec].

[0115] On the other hand, when the actual backlash is 2.75 degrees and the set backlash is set to 2.75 degrees, the motor torque stops stagnating and begins to increase almost simultaneously with the completion of backlash elimination in the driving force transmission system (time t = 2.01 seconds), and the increase in motor rotation speed and the peak (shock) in the longitudinal acceleration at time t = 2.05 seconds are also reduced.

[0116] [Effects of this embodiment] The control method for the electric vehicle 100 of this embodiment calculates a torque command value (first torque command value (Tm1 ＊In the case where the torque of the drive motor 4 connected to the drive wheels 9 a, 9 b is controlled by setting a torque command value (first torque command value (Tm1)) and using a vehicle model 211 that represents the torque response of the drive force transmission system having a dead zone section in which torque is not transmitted to the drive shaft 8, a filtering process that stagnates the torque when torque is not transmitted to the drive shaft 8 is performed as a torque command value (first torque command value (Tm1) ＊ )) and the torque command value after filtering (final torque command value (Tm2 ＊ a torque command value (first torque command value (Tm1)) while the electric vehicle is stopped; ＊ )) is set as a first torque command value (Tm1) for eliminating backlash in the driving force transmission system. ＊ a setting step of setting the torque command value (first torque command value (Tm1)) to a second torque command value (Tm2) having a positive or negative sign different from that of the first torque command value (Tm3) ＊ The method includes an estimation process (steps S506 and S508) for estimating the actual amount of backlash in the driving force transmission system based on changes in parameters (electrical angle of the resolver, motor rotation speed) related to the rotation of the drive motor 4 when the torque (θdead) is changed from the first backlash-eliminating torque to the second backlash-eliminating torque, and an updating process (step S511) for updating a set amount of backlash (θdead) that sets the upper and lower limits of the dead band section based on the actual amount of backlash.

[0117] The above method provides the following advantages (1) to (5) in this embodiment. (1) Because the actual backlash is estimated while the vehicle is stopped, fluctuations in the motor rotation speed are extremely small, allowing for accurate estimation of the actual backlash. (2) The first backlash-eliminating torque and the second backlash-eliminating torque generated while the vehicle is stopped are set to the minute torques required for backlash elimination. Therefore, the generated motor torque is also small, and the torsion angle of the driving force transmission system is also extremely small, allowing for accurate backlash estimation. (3) Although the actual backlash increases with increasing travel distance, for example, by periodically estimating the actual backlash and updating the set backlash based on this, it is possible to reduce the worsening of shock during backlash elimination that occurs when the motor torque changes from negative to positive (or from positive to negative). (4) Because the actual backlash varies among electric vehicles 100, the shock can be reduced by individually estimating and updating the actual backlash. (5) In 4WD vehicles (especially 4WD vehicles that use wound-field motors or induction motors and that turn off the gate when driven), the shock caused by the clearance that occurs when the front-to-rear torque distribution is changed (for example, changing the front-to-rear ratio from 0:100 to 100:0) occurs regardless of the driver's intentions, so the requirement for shock reduction is higher than in 2WD vehicles.However, by learning the actual amount of clearance each time, it is possible to reduce variations in the actual amount of clearance (set amount of clearance) and factors such as deterioration over time, and vehicle requirements can be met.

[0118] In this embodiment, the parameter is a detected value (electrical angle) of a rotation sensor 6 (resolver) attached to the drive motor 4, and the actual backlash amount is estimated based on the amount of change in the detected value.

[0119] The above method allows the actual amount of backlash to be estimated in a simple manner.

[0120] In this embodiment, the parameter is the rotation speed of the drive motor 4 (motor rotation speed (ωm)), and the actual backlash amount is estimated from the integral of the rotation speed (motor rotation speed (ωm)).

[0121] The above method allows the actual amount of backlash to be estimated in a simple manner.

[0122] In this embodiment, the setting step, the estimation step, and the updating step are executed when the electric vehicle 100 is stopped and the driving wheels 9a, 9b are braked.

[0123] The above method can prevent the electric vehicle 100 from unexpectedly moving forward and backward while stopped, and can also reduce the occurrence of errors in the actual amount of backlash due to such movement.

[0124] In this embodiment, when the electric vehicle 100 is stopped and the torque command value (first torque command value (Tm1 ＊ )) is zero, the setting, estimation, and update steps are performed.

[0125] The above method can reduce the torsion angle in the driving force transmission system and improve the accuracy of estimating the actual backlash amount.

[0126] In this embodiment, the setting step, the estimation step, and the update step are executed when the electric vehicle 100 is stopped and the road surface on which the electric vehicle 100 is stopped is flat.

[0127] The above method can reduce the torsion angle in the driving force transmission system and improve the accuracy of estimating the actual backlash amount.

[0128] In this embodiment, the absolute values ​​of the first and second backlash eliminating torques are set in the range of 2 [N·m] to 3 [N·m].

[0129] The above method can eliminate backlash without generating a torsion angle in the driving force transmission system, thereby improving the accuracy of estimating the actual amount of backlash.

[0130] The control system for the electric vehicle 100 of this embodiment calculates a torque command value (first torque command value (Tm1 ＊ In the case where the torque of the drive motor 4 connected to the drive wheels 9 a, 9 b is controlled by setting a torque command value (first torque command value (Tm1)) and using a vehicle model 211 that represents the torque response of the drive force transmission system having a dead zone section in which torque is not transmitted to the drive shaft 8, a filtering process that stagnates the torque when torque is not transmitted to the drive shaft 8 is performed as a torque command value (first torque command value (Tm1) ＊ )) and the torque command value after filtering (final torque command value (Tm2 ＊a torque command value (first torque command value (Tm1)) while the electric vehicle is stopped; ＊ )) is set as a first torque command value (Tm1) for eliminating backlash in the driving force transmission system. ＊ a setting means (motor controller 2) for setting the torque command value (first torque command value (Tm1)) to a predetermined second torque command value (Tm2) having a sign different from that of the first torque command value (Tm3) ＊ )) is changed from the first backlash-reducing torque to the second backlash-reducing torque, the torque is changed based on the change in the parameters (electrical angle of the resolver, motor rotation speed) related to the rotation of the drive motor 4, and the set backlash (θ ｄｅａｄ and an updating means (motor controller 2) for updating the motor speed.

[0131] With the above configuration, this embodiment has the following advantages (1) to (5). (1) Because the actual backlash is estimated while the vehicle is stopped, fluctuations in the motor rotation speed are extremely small, allowing for accurate estimation of the actual backlash. (2) The first backlash-eliminating torque and the second backlash-eliminating torque generated while the vehicle is stopped are set to the minute torques required for backlash elimination. Therefore, the generated motor torque is also small, and the torsion angle of the driving force transmission system is also extremely small, allowing for accurate backlash estimation. (3) Although the actual backlash increases with increasing mileage, for example, by periodically estimating the actual backlash and updating the set backlash based on this, it is possible to reduce the worsening of shock during backlash elimination that occurs when the motor torque changes from negative to positive (or from positive to negative). (4) Because the actual backlash varies among electric vehicles 100, the shock can be reduced by individually estimating and updating the actual backlash. (5) In 4WD vehicles (especially 4WD vehicles that use wound-field motors or induction motors and that turn off the gate when driven), the shock caused by the clearance that occurs when the front-to-rear torque distribution is changed (for example, changing the front-to-rear ratio from 0:100 to 100:0) occurs regardless of the driver's intentions, so the requirement for shock reduction is higher than in 2WD vehicles.However, by learning the actual amount of clearance each time, it is possible to reduce variations in the actual amount of clearance (set amount of clearance) and factors such as deterioration over time, and vehicle requirements can be met.

[0132] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

Claims

1. A control method for an electric vehicle in which, when setting a torque command value based on vehicle information and controlling the torque of a drive motor connected to a drive wheel, a filtering process is performed on the torque command value using a vehicle model representing the torque response of a drive force transmission system having a dead band section in which the torque is not transmitted to the drive axle, causing the torque to stagnate when the torque is not transmitted to the drive axle, and the drive motor is controlled based on the torque command value after the filtering process, the control method comprising: a setting step of setting the torque command value to a first backlash-reducing torque for reduc- ing backlash in the drive force transmission system while the electric vehicle is stopped, and then setting the torque command value to a second backlash-reducing torque having a different sign from the first backlash-reducing torque; an estimation step of estimating an actual amount of backlash in the drive force transmission system based on changes in parameters related to the rotation of the drive motor when the torque command value is changed from the first backlash-reducing torque to the second backlash-reducing torque; and an update step of updating a set backlash that sets an upper and lower limit of the dead band section based on the actual amount of backlash.

2. A method for controlling an electric vehicle according to claim 1, wherein the parameter is a detected value of a rotation sensor attached to the drive motor, and the actual amount of backlash is estimated based on the amount of change in the detected value.

3. The method for controlling an electric vehicle according to claim 1, wherein the parameter is the rotation speed of the drive motor, and the actual backlash amount is estimated from the integral of the rotation speed.

4. The method for controlling an electric vehicle according to claim 1, wherein the setting step, the estimation step, and the updating step are performed when the electric vehicle is stopped and a brake operation is being performed on the drive wheels.

5. The method for controlling an electric vehicle according to claim 1, wherein the setting step, the estimation step, and the updating step are executed when the electric vehicle is stopped and the torque command value is zero.

6. The method for controlling an electric vehicle according to claim 1, wherein the setting step, the estimation step, and the updating step are performed when the electric vehicle is stopped and the road surface on which the electric vehicle is stopped is flat.

7. A control method for an electric vehicle according to claim 1, wherein the absolute values ​​of the first backlash eliminating torque and the second backlash eliminating torque are set in the range of 2 [N·m] to 3 [N·m].

8. A control system for an electric vehicle that, when setting a torque command value based on vehicle information and controlling the torque of a drive motor connected to a drive wheel, performs filtering on the torque command value using a vehicle model representing the torque response of a drive force transmission system having a dead band section in which the torque is not transmitted to the drive axle, causing the torque to stagnate when the torque is not transmitted to the drive axle, and controls the drive motor based on the torque command value after filtering, the control system for an electric vehicle comprising: setting means for setting the torque command value to a first backlash-reducing torque for reduc- ing backlash in the drive force transmission system while the electric vehicle is stopped, and then setting the torque command value to a predetermined second backlash-reducing torque having a different sign from the first backlash-reducing torque; estimating means for estimating an actual amount of backlash in the drive force transmission system based on changes in parameters related to the rotation of the drive motor when the torque command value is changed from the first backlash-reducing torque to the second backlash-reducing torque; and updating means for updating a set backlash that sets an upper and lower limit of the dead band section based on the actual amount of backlash.

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