Vehicle speed estimation method and vehicle speed estimation device

Abstract

This disclosure relates to a vehicle speed estimation method and a vehicle speed estimation device. The vehicle speed estimation method of the present invention, applied to a four-wheel drive vehicle, includes: obtaining an estimated vehicle speed based on the wheel speed or front-rear acceleration of the vehicle; determining whether a working condition, including at least the estimated vehicle speed being higher than a working determination speed, is met; if the working condition is met, executing a torque limitation that reduces the torque of a portion of the wheels of the vehicle; determining whether a termination condition, including the estimated vehicle speed becoming below the termination determination speed or the wheel acceleration of the portion of the wheels remaining greater than zero for a certain period of time, is met; and if the termination condition is met, ending the torque limitation.

Description

Technical Field

[0001] This disclosure relates to a method and apparatus for inferring vehicle speed. Background Technology

[0002] Japanese Patent Application Publication No. 2003-002079 discloses a drive force control device for a four-wheel drive vehicle. This four-wheel drive vehicle includes a friction clutch positioned midway between the engine-driven system and the rear wheels. The drive force control device variably controls the drive force distribution ratio between the front and rear wheels by controlling the clutch engagement force of the friction clutch. Furthermore, the drive force control device detects wheel slippage and performs traction control to reduce the drive force on the drive wheels.

[0003] Japanese Patent Application Publication No. 5-185922 discloses a method for calculating and inferring vehicle speed. When the wheels do not slip excessively or spin excessively, the vehicle speed is inferred from the wheel speed. Conversely, when the wheels slip excessively or spin excessively, the vehicle speed is inferred from the output of a gravity-type accelerometer.

[0004] Japanese Patent Application Publication No. 2016-103867 discloses a vehicle body speed estimation device. The vehicle has braking force generating units at all wheels capable of generating driving and braking forces. The vehicle body speed estimation device infers the vehicle body speed based on the wheel speeds of each wheel. The inferred vehicle body speed is used for traction control and anti-lock braking control.

[0005] Consider inferring the vehicle speed of a four-wheel-drive vehicle. For example, if all four wheels slip, the inferred vehicle speed based on the wheel speeds will be higher than the actual vehicle speed. This results in an "increase" in the inferred vehicle speed. This discrepancy between the inferred and actual vehicle speed leads to a reduction in the accuracy of vehicle control or information processing that utilizes the inferred vehicle speed. Summary of the Invention

[0006] This disclosure provides a vehicle speed estimation method and a vehicle speed estimation device that ensure the accuracy of the estimated vehicle speed for a four-wheel drive vehicle.

[0007] The first viewpoint relates to a method for inferring vehicle speed in a four-wheel drive vehicle. The method includes: obtaining an inferred vehicle speed based on the vehicle's wheel speed or front-rear acceleration; determining whether a working condition, including at least an inferred vehicle speed higher than a working determination speed, is met; if the working condition is met, implementing a torque limit that reduces the torque of a portion of the vehicle's wheels; determining whether a termination condition, including the inferred vehicle speed becoming below the termination determination speed or the wheel acceleration of the aforementioned portion of the wheels remaining greater than zero for a certain period of time, is met; and if the termination condition is met, ending the torque limit.

[0008] The second viewpoint relates to a vehicle speed estimation device applied to a four-wheel drive vehicle. The vehicle speed estimation device includes one or more processors. The one or more processors are configured to: obtain an estimated vehicle speed based on the vehicle's wheel speed or front-rear acceleration; determine whether an operating condition, including at least one condition that the estimated vehicle speed is higher than a working determination speed, is met; if the operating condition is met, execute a torque limit that reduces the torque of a portion of the vehicle's wheels; determine whether a termination condition, including one that the estimated vehicle speed becomes lower than a termination determination speed, or one that the wheel acceleration of the aforementioned portion of the wheels remains greater than zero for a certain period of time, is met; and if the termination condition is met, terminate the torque limit.

[0009] It can also be configured such that, based on the first point above, the torque limitation does not reduce the torque of the front wheel but reduces the torque of the rear wheel.

[0010] It can also be configured as follows: based on the first point above, the working determination speed is calculated based on the integral of the acceleration before and after.

[0011] It can also be configured as follows: based on the first point above, the above-mentioned end determination velocity is calculated based on the integral of the above-mentioned acceleration before and after.

[0012] It can also be configured as follows: Based on the first point above, the above-mentioned ending determination speed is the sum of the value calculated by the integral of the above-mentioned acceleration before and after and a certain value.

[0013] It can also be configured as follows: Based on the first point of view above, the above-mentioned inferred vehicle speed is the first inferred vehicle speed inferred from the above-mentioned wheel speed.

[0014] It can also be configured as follows: Based on the first point above, the above-mentioned inferred vehicle speed is a second inferred vehicle speed inferred based on the integral of the sum of the above-mentioned front and rear accelerations and offset.

[0015] Alternatively, based on the first point above, the vehicle speed inference method may further include: obtaining a first inferred vehicle speed based on the wheel speed; calculating a second inferred vehicle speed based on the integral of the sum of the front and rear accelerations and the offset; determining whether a slippage determination condition, including at least the first inferred vehicle speed being higher than the second inferred vehicle speed, is met; if the slippage determination condition is not met, setting the first inferred vehicle speed as the inferred vehicle speed; and if the slippage determination condition is met, setting the second inferred vehicle speed as the inferred vehicle speed.

[0016] It can also be configured such that, based on the first and second points above, one or more processors of the vehicle speed inference method or vehicle speed inference device further include determining whether wheel slippage has occurred, and the above working conditions include at least the occurrence of the above wheel slippage and the above inferred vehicle speed being higher than the above working determination speed.

[0017] It can also be configured as follows: based on the first and second viewpoints above, the above working conditions include the occurrence of the above wheel slippage and the state inferred vehicle speed being higher than the above working determination speed for a certain period of time.

[0018] It can also be configured such that, based on the first and second viewpoints above, determining whether the aforementioned wheel slippage has occurred includes: obtaining a first inferred vehicle speed based on the aforementioned wheel speed; calculating a second inferred vehicle speed based on the integral of the sum of the aforementioned front-rear acceleration and offset; determining whether a slippage determination condition, including at least the aforementioned first inferred vehicle speed being higher than the aforementioned second inferred vehicle speed, is met; and determining that the aforementioned wheel slippage has occurred if the aforementioned slippage determination condition is met.

[0019] According to this disclosure, the vehicle body speed is inferred based on wheel speed or front-rear acceleration. When at least one working condition, including the inferred vehicle body speed being higher than the working determination speed, is met, a torque limit is applied to reduce the torque of a portion of the wheels. Subsequently, when a termination condition is met, the torque limit ends. This torque limit eliminates the "lift" in the inferred vehicle body speed, thereby restoring the accuracy of the inferred vehicle body speed. In other words, the accuracy of the inferred vehicle body speed is ensured.

[0020] Furthermore, according to the viewpoint of this disclosure, since there is a termination condition for torque limiting, the torque limiting is suppressed from lasting too long. As a result, vehicle stalling is suppressed.

[0021] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements. Attached Figure Description

[0022] Figure 1 This is a schematic diagram used to explain the outline of the vehicle and body speed estimation device according to the first embodiment.

[0023] Figure 2 This is a schematic diagram used to illustrate the torque limitation involved in the first embodiment.

[0024] Figure 3 This is a timeline showing an example of the torque limitation involved in the first embodiment.

[0025] Figure 4 This is a block diagram illustrating a structural example of the vehicle control system according to the first embodiment.

[0026] Figure 5 This is a flowchart illustrating an example of a process related to torque limiting as described in the first embodiment.

[0027] Figure 6 This is a flowchart illustrating the first example of operating conditions for torque limitation.

[0028] Figure 7 This is a flowchart illustrating the second example of operating conditions for torque limitation.

[0029] Figure 8 This is a flowchart illustrating the third example of operating conditions for torque limitation.

[0030] Figure 9 This is a flowchart illustrating the fourth example of operating conditions for torque limitation.

[0031] Figure 10 This is a schematic diagram illustrating an example of the torque limit applied during torque limiting.

[0032] Figure 11 This is a flowchart illustrating an example of the termination condition for torque limiting.

[0033] Figure 12 This is a schematic diagram used to illustrate the torque limitation involved in the second embodiment.

[0034] Figure 13 This is a flowchart illustrating the processing related to torque limiting as described in the second embodiment.

[0035] Figure 14 This is a flowchart illustrating a variation of the processing related to torque limitation as described in the second embodiment. Detailed Implementation

[0036] The embodiments of this disclosure will be described with reference to the accompanying drawings.

[0037] 1. First Implementation Method

[0038] 1-1. Overview of Vehicle and Body Speed ​​Inference Device

[0039] Figure 1 This is a schematic diagram illustrating the general outline of the vehicle 1 and the vehicle speed estimation device 10 according to the first embodiment. The vehicle 1 has a plurality of wheels 5. The plurality of wheels 5 includes front wheels 5F and rear wheels 5R. In this embodiment, the vehicle 1 is configured to be capable of four-wheel drive. That is, the vehicle 1 is configured to be able to drive the front wheels 5F and the rear wheels 5R. Typically, the vehicle 1 can drive the front wheels 5F and the rear wheels 5R independently.

[0040] The vehicle speed inference device 10 infers the vehicle speed of the vehicle 1. Hereinafter, the inferred vehicle speed will be referred to as "inferred vehicle speed Ve". The inferred vehicle speed Ve is inferred based on the vehicle state detected by sensors mounted on the vehicle 1. Examples of vehicle states of the vehicle 1 include wheel speed, front-rear acceleration, etc. Typically, the vehicle speed inference device 10 is mounted on the vehicle 1 and obtains the inferred vehicle speed Ve based on the vehicle state detected by sensors. As another example, the vehicle speed inference device 10 may also be distributed between the vehicle 1 and external systems.

[0041] The inferred vehicle speed Ve can be used for various vehicle control and information processing applications. To achieve accurate vehicle control or information processing, a high-precision inferred vehicle speed Ve is required.

[0042] For example, the inferred vehicle speed Ve can be used for traction control of vehicle 1. Traction control (hereinafter, sometimes simply referred to as "TRC") is a vehicle driving control mechanism used to suppress the spinning of the wheels 5 (drive wheels) of vehicle 1 during start-up or acceleration. More specifically, the slip rate of each wheel 5 is calculated based on the wheel speed of each wheel 5 and the inferred vehicle speed Ve. TRC activates when the slip rate of a wheel 5 exceeds a threshold. Hereinafter, the wheel 5 whose slip rate exceeds the threshold is referred to as the "TRC target wheel 5t". TRC reduces the torque of the TRC target wheel 5t by reducing its slip rate to a target slip rate. The actual torque of the TRC target wheel 5t can be reduced by reducing the output of the drive unit or by applying braking force. This suppresses the spinning of the TRC target wheel 5t. Thus, the inferred vehicle speed Ve is used to calculate the slip rate of the wheel 5. To implement TRC with high accuracy, a high-precision inferred vehicle speed Ve is required.

[0043] 1-2. Torque Limiting Treatment

[0044] In the first embodiment, a deduced vehicle body speed Ve based on the wheel speed of the wheels 5 is considered. For convenience, the deduced vehicle body speed Ve based on the wheel speed is referred to as "first deduced vehicle body speed Ve1" below. The first deduced vehicle body speed Ve1 based on the wheel speed is well known, and its deduction method is not particularly limited in this embodiment. For example, the lowest wheel speed among the individual wheel speeds of the plurality of wheels 5 is obtained as the first deduced vehicle body speed Ve1. As another example, the second lowest wheel speed among the individual wheel speeds of the plurality of wheels 5 may also be obtained as the first deduced vehicle body speed Ve1.

[0045] When no wheel slippage occurs, the accuracy of the first inferred vehicle speed Ve1 is high. However, for example, when all wheels 5 slip, the first inferred vehicle speed Ve1, inferred from the wheel speed, is higher than the actual vehicle speed Vt. That is, there is an "increase" in the first inferred vehicle speed Ve1. This deviation between the first inferred vehicle speed Ve1 and the actual vehicle speed Vt leads to a decrease in the accuracy of vehicle control or information processing that utilizes the first inferred vehicle speed Ve1, which is therefore undesirable.

[0046] The vehicle speed estimation device 10 according to this embodiment has the function of suppressing the deviation between the first estimated vehicle speed Ve1 and the actual vehicle speed Vt. More specifically, the vehicle speed estimation device 10 determines whether an "increase" in the first estimated vehicle speed Ve1 has occurred. If an "increase" in the first estimated vehicle speed Ve1 is determined to have occurred, the vehicle speed estimation device 10 performs a "torque limiting" that reduces the torque of a portion of the wheels 5. By performing the torque limiting, the wheel speed of a portion of the wheels 5 is reduced, thereby eliminating the "increase" in the first estimated vehicle speed Ve1.

[0047] Figure 2 This is a schematic diagram used to explain in detail the torque limitation involved in the first embodiment.

[0048] First, the vehicle speed estimation device 10 determines whether the "operating condition" of the torque limit is met. The operating condition of the torque limit is that a "rise" in the first estimated vehicle speed Ve1 occurs. In order to detect such a "rise" in the first estimated vehicle speed Ve1, the "operating determination speed Va" is used.

[0049] The working determination speed Va is set in a manner that is higher than the first inferred vehicle speed Ve1 in the state without wheel slippage and lower than the first inferred vehicle speed Ve1 in the state with wheel slippage. At least the working determination speed Va does not depend on the wheel speed. For example, the vehicle speed inference device 10 calculates the working determination speed Va based on the integral of the front and rear acceleration of the vehicle 1. The working determination speed Va based on the integral of the front and rear acceleration of the vehicle 1 is expressed, for example, by the following equation (1).

[0050] Equation (1): Va = (Gx × α) × actual time

[0051] In equation (1), Gx is the front-to-rear acceleration (after filtering) detected by the acceleration sensor mounted on vehicle 1. α is a gain greater than 1. The gain α is preset to account for the error of the acceleration sensor. It can be said that the working determination speed Va, expressed by equation (1), is the inferred vehicle speed inferred based on the integral of the front-to-rear acceleration Gx.

[0052] As another example, the work determination speed Va can also be expressed by the following equation (2).

[0053] Equation (2): Va=(Gx×α)×actual time+β

[0054] In equation (2), β is a constant value (positive value). For example, the constant value β is the value of wheel slippage that produces moderate grip in wheel 5. It can be said that the working judgment speed Va expressed by equation (2) is the sum of "the inferred vehicle speed inferred from the integral of the front and rear acceleration Gx" and "the constant value β that is equivalent to a certain amount of slippage".

[0055] The working judgment speed Va described above is lower than the first inferred vehicle speed Ve1 under the condition of wheel slippage, that is, it is closer to the actual vehicle speed Vt. The first inferred vehicle speed Ve1 exceeding the working judgment speed Va means that the first inferred vehicle speed Ve1 has been "lifted".

[0056] Based on the above viewpoints, the torque limiting operating condition is set in a manner that includes at least "the first inferred vehicle speed Ve1 is higher than the operating determination speed Va". The torque limiting operating condition may also include "the state of the first inferred vehicle speed Ve1 being higher than the operating determination speed Va lasting for a certain period of time".

[0057] When the operating conditions are met, the vehicle speed estimation device 10 performs torque limiting. In torque limiting, the vehicle speed estimation device 10 reduces the torque of a portion of the wheels 5 compared to before torque limiting was performed. For example, the vehicle speed estimation device 10 performs torque limiting by multiplying the torque of a portion of the wheels 5 by a gain of less than 1. For example, the vehicle speed estimation device 10 reduces the torque of the rear wheels 5R without reducing the torque of the front wheels 5F. From the viewpoint of vehicle stability, it is preferable to reduce the torque of the rear wheels 5R without reducing the torque of the front wheels 5F. As another example, the vehicle speed estimation device 10 may also reduce the torque of the front wheels 5F without reducing the torque of the rear wheels 5R.

[0058] By implementing this torque limiting, the wheel speed of some wheels 5 is reduced, thereby mitigating the slippage of some wheels 5. As a result, the first inferred vehicle speed Ve1 also decreases, approaching the actual vehicle speed Vt.

[0059] Prolonged torque limiting can affect the acceleration of vehicle 1, potentially causing it to stall. Therefore, after the torque limiting begins, the vehicle speed estimation device 10 determines whether the "end condition" of the torque limiting is met. The end condition of the torque limiting is the elimination of the "rise" in the first estimated vehicle speed Ve1.

[0060] For example, the termination condition for torque limiting includes "the first inferred vehicle speed Ve1 becomes below the termination determination speed Vb". The termination determination speed Vb is set based on the same viewpoint as the working determination speed Va mentioned above. For example, the termination determination speed Vb is expressed by the following equation (3) or equation (4).

[0061] Equation (3): Vb=(Gx×α)×actual time

[0062] Equation (4): Vb=(Gx×α)×actual time+β

[0063] The vehicle speed inference device 10 calculates the final judgment speed Vb based on the integral of the front and rear acceleration Gx of the vehicle 1. It can be said that the final judgment speed Vb, expressed by equation (3), is the inferred vehicle speed inferred based on the integral of the front and rear acceleration Gx. It can also be said that the final judgment speed Vb, expressed by equation (4), is the sum of "the inferred vehicle speed inferred based on the integral of the front and rear acceleration Gx" and "a certain value β equivalent to a certain amount of slippage".

[0064] Furthermore, the working decision speed Va and the ending decision speed Vb can be the same or different. The gain α in equation (1) or equation (2) can be the same or different from the gain α in equation (3) or equation (4). The fixed value β in equation (2) can be the same or different from the fixed value β in equation (4). By adjusting the gain α and the fixed value β, the working decision speed Va and the ending decision speed Vb can be appropriately adjusted. In any case, the working decision speed Va and the ending decision speed Vb are lower than the first inferred vehicle speed Ve1 in the state of wheel slippage, that is, closer to the actual vehicle speed Vt.

[0065] If the first inferred vehicle speed Ve1 falls below the termination determination speed Vb, i.e., if the termination condition is met, the vehicle speed inference device 10 terminates (releases) the torque limitation. For example, the vehicle speed inference device 10 terminates by multiplying the torque of wheel 5, which is part of the torque limitation, by the aforementioned gain of less than 1. As a result, the first inferred vehicle speed Ve1 returns to the termination determination speed Vb, which is close to the actual vehicle speed Vt. That is, the accuracy of the first inferred vehicle speed Ve1 is improved (restored). In other words, the accuracy of the first inferred vehicle speed Ve1 is ensured. In addition, since the torque limitation does not last too long, vehicle 1 stalling is also prevented.

[0066] In particular, the final determination speed Vb, expressed by the above formula (4), includes a certain value β equivalent to the amount of wheel slippage that produces moderate grip in wheel 5. By using the final determination speed Vb, expressed by the above formula (4), "excessive return" of the first inferred vehicle speed Ve1 can be prevented. That is, the accuracy of the first inferred vehicle speed Ve1 can be properly restored and vehicle 1 can be prevented from stalling more reliably.

[0067] Furthermore, due to important factors such as acceleration sensor error and changes in road slope, there is a possibility that the final determination speed Vb may be lower than the actual vehicle speed Vt. In this case, the termination condition of "the first inferred vehicle speed Ve1 becoming below the final determination speed Vb" may not be met, and the torque limit may continue. Therefore, as a variation of the torque limit termination condition, it is also possible to add "the wheel acceleration of wheel 5, which is part of the torque limit, remains greater than zero for a certain period of time." This is because the state of wheel acceleration being greater than zero for a certain period of time refers to wheel slippage and convergence.

[0068] Thus, the termination conditions for the torque limitation involved in this embodiment include "the first inferred vehicle speed Ve1 becomes below the termination determination speed Vb" or "the wheel acceleration of the wheel 5 to which the torque limitation is applied remains greater than zero for a certain period of time". Because of these termination conditions, unnecessary continuation of the torque limitation is prevented. As a result, vehicle 1 is prevented from stalling.

[0069] Figure 3 This is a time graph illustrating an example of torque limiting. The horizontal axis represents time, and the vertical axis represents various vehicle speeds (first inferred vehicle speed Ve1, operating speed Va, ending speed Vb, and actual vehicle speed Vt). During acceleration of vehicle 1, wheel slippage occurs, resulting in a "rise" in the first inferred vehicle speed Ve1. If the first inferred vehicle speed Ve1 remains above the operating speed Va for a certain period, torque limiting is activated. As a result of torque limiting, the first inferred vehicle speed Ve1 decreases. If the first inferred vehicle speed Ve1 falls below the ending speed Vb, torque limiting ends. Consequently, the first inferred vehicle speed Ve1 returns to a value close to the actual vehicle speed Vt.

[0070] 1-3. Effects

[0071] As explained above, according to this embodiment, a first inferred vehicle speed Ve1 is obtained based on the wheel speed. When at least one working condition, including the first inferred vehicle speed Ve1 being higher than the working determination speed Va, is met, a torque limitation is applied to reduce the torque of a portion of the wheels 5. Subsequently, when a termination condition is met, the torque limitation ends. Through this torque limitation, the "increase" in the first inferred vehicle speed Ve1 is eliminated, and the accuracy of the first inferred vehicle speed Ve1 is improved (restored). That is, the accuracy of the first inferred vehicle speed Ve1 is ensured.

[0072] Furthermore, according to this embodiment, there is a termination condition for the torque limitation. Therefore, the torque limitation is prevented from lasting too long. As a result, vehicle 1 is prevented from stalling. In particular, by using the termination determination speed Vb expressed by the above formula (4), the "excessive return" of the first inferred vehicle speed Ve1 can be prevented. That is, the accuracy of the first inferred vehicle speed Ve1 can be properly restored and vehicle 1 stalling can be prevented more reliably.

[0073] The wheel 5 for which torque limiting is applied can also be the rear wheel 5R instead of the front wheel 5F. From the viewpoint of vehicle stability, it is preferable to reduce the torque of the rear wheel 5R without lowering the torque of the front wheel 5F.

[0074] By ensuring the accuracy of the first inferred vehicle speed Ve1, the accuracy of vehicle control or information processing that utilizes the first inferred vehicle speed Ve1 is also ensured.

[0075] For example, the first inferred vehicle speed Ve1 is used in TRC. Specifically, the slip rate of each wheel 5 is calculated based on the wheel speed of each wheel 5 and the first inferred vehicle speed Ve1. By ensuring the accuracy of the first inferred vehicle speed Ve1, the accuracy of TRC is also ensured. From the viewpoint of acceleration and vehicle stability, this setting is preferred.

[0076] 1-4. Example of vehicle control system structure

[0077] Figure 4 This is a block diagram illustrating a structural example of the vehicle control system 100 according to the first embodiment. The vehicle control system 100 controls the vehicle 1. Typically, the vehicle control system 100 is mounted on the vehicle 1. Alternatively, at least a portion of the vehicle control system 100 may be included in a remote system external to the vehicle 1 and remotely control the vehicle 1. That is, the vehicle control system 100 may also be distributed between the vehicle 1 and the remote system.

[0078] The vehicle control system 100 includes a sensor group 20, a driving device 30, and a control device 110.

[0079] Sensor group 20 is mounted on vehicle 1 to detect the vehicle status of vehicle 1. Sensor group 20 includes wheel speed sensor 21, acceleration sensor 22, etc. Wheel speed sensor 21 detects the wheel speed of each wheel 5. Acceleration sensor 22 detects various accelerations, including the front-rear acceleration Gx of vehicle 1.

[0080] A driving device 30 is mounted on the vehicle 1. The driving device 30 includes a drive unit 31 and a braking device 32. The drive unit 31 drives the wheels 5. The drive unit 31 is capable of independently driving the front wheels 5F and the rear wheels 5R. For example, the drive unit 31 includes a front wheel motor that drives the front wheels 5F and a rear wheel motor that drives the rear wheels 5R. The drive unit 31 may also include in-wheel motors disposed on each wheel 5. The braking device 32 independently applies braking force to each wheel 5.

[0081] The control device 110 is a computer that controls the vehicle 1. The control device 110 includes one or more processors 120 (hereinafter simply referred to as processors 120) and one or more storage devices 130 (hereinafter simply referred to as storage devices 130). The processor 120 performs various processes. For example, the processor 120 includes a CPU (Central Processing Unit). The storage device 130 stores various information. Examples of storage devices 130 include volatile memory, non-volatile memory, HDD (Hard Disk Drive), SSD (Solid State Drive), etc. The control device 110 may also include one or more ECUs (Electronic Control Units). A portion of the control device 110 may also be an external information processing device to the vehicle 1. In this case, a portion of the control device 110 communicates with the vehicle 1 and remotely controls the vehicle 1.

[0082] Vehicle status information 200 represents the vehicle status detected by sensor group 20. Specifically, vehicle status information 200 includes the wheel speeds of each wheel 5 detected by wheel speed sensor 21, the front-rear acceleration Gx detected by acceleration sensor 22, etc. Control device 110 (processor 120) obtains vehicle status information 200 from sensor group 20. Vehicle status information 200 is stored in storage device 130.

[0083] The vehicle control program 300 is a computer program executed by the processor 120. By executing the vehicle control program 300 through the processor 120, various processes based on the control device 110 (processor 120) are implemented. The vehicle control program 300 is stored in the storage device 130. The vehicle control program 300 may also be recorded on a computer-readable recording medium.

[0084] The control unit 110 (processor 120) performs torque control (drive force control) related to each wheel 5. More specifically, the control unit 110 calculates the target torque for each wheel 5. Furthermore, the control unit 110 controls the operation of the drive unit 31 and the braking unit 32 in a manner that obtains the target torque for each wheel 5.

[0085] Additionally, the control unit 110 (processor 120) performs traction control (TRC) as needed. More specifically, the control unit 110 obtains the inferred vehicle speed Ve based on the vehicle state information 200. Moreover, the control unit 110 calculates the slip rate of each wheel 5 based on the wheel speed of each wheel 5 and the inferred vehicle speed Ve. If the slip rate of a certain wheel 5 exceeds a threshold, the control unit 110 activates TRC. The TRC target wheel 5t is the wheel 5 whose slip rate exceeds the threshold. For example, the control unit 110 performs torque control in a manner that reduces the slip rate of the TRC target wheel 5t to a target slip rate (e.g., 10-15%).

[0086] The control device 110 also has the function of the "vehicle speed estimation device 10" according to this embodiment. The control device 110 obtains the estimated vehicle speed Ve based on the vehicle state information 200. Furthermore, the control device 110 performs the aforementioned "torque limiting" as needed. Hereinafter, a processing example related to the torque limiting performed by the control device 110 according to this embodiment will be described.

[0087] 1-5. Examples of processing procedures related to torque limiting

[0088] Figure 5 This is a flowchart illustrating an example of a process related to torque limiting performed by the control device 110 according to the first embodiment. It is repeatedly executed at regular intervals. Figure 5 The processing flow is shown below.

[0089] 1-5-1. Step S100

[0090] In step S100, the control device 110 performs a "vehicle speed calculation process" to calculate various vehicle speeds based on the vehicle state information 200. Specifically, the control device 110 infers a first inferred vehicle speed Ve1 based on the wheel speed. In addition, the control device 110 calculates the working determination speed Va and the ending determination speed Vb based on the integral of the front and rear acceleration Gx (refer to the above equations (1) to (4)). Furthermore, the control device 110 calculates a "second inferred vehicle speed Ve2" expressed by the following equation (5).

[0091] Equation (5): Ve2 = (Gx × α + OFST) × actual time

[0092] In equation (5), Gx is the forward and backward acceleration (after filtering) detected by accelerometer 22. α is a gain greater than 1 (e.g., α = 1.15). The gain α is set to account for the error of accelerometer 22. To avoid the second inferred vehicle speed Ve2 being underestimated when vehicle 1 moves from a flat road to a downhill road, an offset OFST is added. It can be said that the second inferred vehicle speed Ve2, expressed by equation (5), is an inferred vehicle speed inferred based on the integral of the sum of forward and backward acceleration Gx and offset OFST.

[0093] 1-5-2. Step S200

[0094] In step S200, the control device 110 performs a "slippage determination process" to determine whether wheel slippage has occurred. For example, the slippage determination condition includes at least "a first inferred vehicle speed Ve1 based on wheel speed is higher than a second inferred vehicle speed Ve2 based on front and rear acceleration". The slippage determination condition may also include "the state in which the first inferred vehicle speed Ve1 is higher than the second inferred vehicle speed Ve2 lasts for a certain period of time".

[0095] If the slippage determination condition is not met, the control device 110 determines that no wheel slippage has occurred. On the other hand, if the slippage determination condition is met, the control device 110 determines that wheel slippage has occurred. The result of the slippage determination process is used later.

[0096] 1-5-3. Step S300

[0097] In step S300, the control device 110 performs a "working condition determination process" to determine whether the working condition for torque limitation is met. If the working condition for torque limitation is met (step S300: Yes), the process proceeds to step S400. On the other hand, if the working condition for torque limitation is not met (step S300: No), the process skips step S400 and proceeds to step S500.

[0098] The operating conditions for torque limiting are defined based on the relationship between the inferred vehicle speed Ve and the working determination speed Va. Various examples of the operating conditions for torque limiting will be described below. Furthermore, in the first embodiment, the inferred vehicle speed Ve is a first inferred vehicle speed Ve1 (Ve=Ve1) inferred from the wheel speed.

[0099] <Example 1 of working conditions>

[0100] Figure 6 This is a flowchart illustrating the first example of a torque-limiting operating condition. The first example of a torque-limiting operating condition is "wheel slippage occurs, and it is inferred that the vehicle speed Ve is higher than the operating determination speed Va". In step S310, the control device 110 determines whether wheel slippage has occurred and infers whether the vehicle speed Ve is higher than the operating determination speed Va. If the result of step S310 is negative (step S310: No), the operating condition is not met (step S300: No). On the other hand, if the result of step S310 is positive (step S310: Yes), the operating condition is met (step S300: Yes).

[0101] <Example 2 of working conditions>

[0102] Figure 7 This is a flowchart illustrating the second example of the operating conditions for torque limiting. The second example of the operating conditions for torque limiting is "TRC is in operation, wheel slippage occurs, and the vehicle speed Ve is inferred to be higher than the operating determination speed Va". In step S320, the control device 110 determines whether TRC is in operation, whether wheel slippage has occurred, and whether the vehicle speed Ve is inferred to be higher than the operating determination speed Va. If the result of step S320 is negative (step S320: No), the operating condition is not met (step S300: No). On the other hand, if the result of step S320 is positive (step S320: Yes), the operating condition is met (step S300: Yes).

[0103] <Example 3 of working conditions>

[0104] Figure 8This is a flowchart illustrating the third example of the torque-limiting operating condition. The third example is a variation of the first example. The third example of the torque-limiting operating condition is "a state in which wheel slippage occurs and the vehicle speed Ve is inferred to be higher than the operating determination speed Va for a certain period of time." If the result of step S310 is positive (step S310: Yes), the control device 110 increments the timer by 1 (step S330). On the other hand, if the result of step S310 is negative (step S310: No), the control device 110 resets the timer (step S340). If the timer is less than the threshold (step S350: No), the operating condition is not met (step S300: No). On the other hand, if the timer is above the threshold (step S350: Yes), the operating condition is met (step S300: Yes).

[0105] <Example 4 of working conditions>

[0106] Figure 9 This is a flowchart illustrating the fourth example of the torque-limiting operating condition. The fourth example is a variation of the second example. The fourth example of the torque-limiting operating condition is: "The TRC is in operation, wheel slippage occurs, and the vehicle speed Ve is inferred to be higher than the operating determination speed Va for a certain period of time." If the result of step S320 is positive (step S320: Yes), the control device 110 increments the timer by 1 (step S330). On the other hand, if the result of step S320 is negative (step S320: No), the control device 110 resets the timer (step S340). If the timer is less than the threshold (step S350: No), the operating condition is not met (step S300: No). On the other hand, if the timer is above the threshold (step S350: Yes), the operating condition is met (step S300: Yes).

[0107] 1-5-4. Step S400

[0108] In step S400, the control device 110 performs torque limiting. Specifically, the control device 110 reduces the torque of a portion of the wheels 5 compared to before the torque limiting was performed. For example, the control device 110 reduces the torque of the rear wheels 5R without reducing the torque of the front wheels 5F. From the viewpoint of vehicle stability, it is preferable to reduce the torque of the rear wheels 5R without reducing the torque of the front wheels 5F. As another example, the control device 110 may also reduce the torque of the front wheels 5F without reducing the torque of the rear wheels 5R.

[0109] Figure 10This is a schematic diagram illustrating an example of torque limiting during torque limiting operation. "Front torque Tf" and "Rear torque Tr" are the target torques for the front wheel (5F) and rear wheel (5R) respectively when the TRC is not engaged. The front torque Tf and rear torque Tr are calculated based on factors such as accelerator pedal engagement. "Front TRC torque Tf_trc" and "Rear TRC torque Tr_trc" are the target torques for the front wheel (5F) and rear wheel (5R) respectively when the TRC is engaged. The front TRC torque Tf_trc and rear TRC torque Tr_trc are required by the TRC. Furthermore, the front TRC torque Tf_trc and rear TRC torque Tr_trc are both less than the front torque Tf and rear torque Tr, respectively.

[0110] First, let's explain the case where the torque limiting is applied to the rear wheel 5R. The torque limit TRr is the target torque for limiting the torque of the rear wheel 5R. This is in the case where TRC is not engaged (refer to...). Figure 6 , Figure 8 The limiting torque TRr is either the product of the front torque Tf and the gain γ, or the product of the rear torque Tr and the gain γ. Here, the gain γ is a constant greater than 0 and less than 1 (0 < γ < 1). On the other hand, when TRC is operating (see...), Figure 7 , Figure 9 This can be adjusted. For example, the output can be the smaller of the product of the front TRC torque Tf_trc and the gain γ and the rear TRC torque Tr_trc. Alternatively, the rear torque TRr can also be limited to the product of the rear TRC torque Tr_trc and the gain γ.

[0111] Next, we will explain the case where the torque limiting is applied to the front wheel 5F. The front torque limiter TRf is the target torque for limiting the torque of the front wheel 5F. This is in the case where TRC is not engaged (see [reference]). Figure 6 , Figure 8 The limiting torque TRf is either "the product of the rear torque Tr and the gain γ" or "the product of the front torque Tf and the gain γ". On the other hand, when TRC is operating (see...), Figure 7 , Figure 9 This can be adjusted. For example, the output can be the smaller of the product of the rear TRC torque Tr_trc and the gain γ and the front TRC torque Tf_trc. Alternatively, the front torque TRf can also be limited to the product of the front TRC torque Tf_trc and the gain γ.

[0112] 1-5-5. Step S500

[0113] In step S500, the control device 110 determines whether the torque limit is active. If the torque limit is active (step S500: Yes), the process proceeds to step S600. On the other hand, if the torque limit is not active (step S500: No), the processing in this cycle ends.

[0114] 1-5-6. Step S600

[0115] In step S600, the control device 110 performs an "end condition determination process" to determine whether the end condition for torque limitation is met. If the end condition for torque limitation is met (step S600: Yes), the process proceeds to step S700. On the other hand, if the end condition for torque limitation is not met (step S600: No), the process in this loop ends.

[0116] Figure 11 This is a flowchart illustrating an example of the termination condition for torque limiting. For example, the termination condition for torque limiting includes "the inferred vehicle speed Ve becomes below the termination determination speed Vb" or "the wheel acceleration of wheel 5, to which a portion of the torque limiting is applied, remains greater than zero for a certain period of time" (see Sections 1-2). In step S610, the control device 110 determines whether the termination condition is met.

[0117] 1-5-7. Step S700

[0118] In step S700, the control device 110 terminates the torque limiting. This ensures the accuracy of the inferred vehicle speed Ve.

[0119] 2. Second Implementation Method

[0120] Figure 12 This is a schematic diagram used to explain the torque limitation involved in the second embodiment. In the second embodiment, the "second inferred vehicle speed Ve2" expressed by the above formula (5) is used as the inferred vehicle speed Ve. The second inferred vehicle speed Ve2 is the inferred vehicle speed inferred based on the integral of the sum of the front and rear acceleration Gx and the offset OFST. In order to prevent the second inferred vehicle speed Ve2 from being evaluated too small when the vehicle 1 moves from a flat road to a downhill road, the offset OFST is added. Since the offset OFST is added, the second inferred vehicle speed Ve2 tends to be inferred to be larger. That is, there is also a possibility of "lifting" with respect to the second inferred vehicle speed Ve2. Therefore, the torque limitation treatment is also effective for the second inferred vehicle speed Ve2.

[0121] The working determination speed Va and the ending determination speed Vb are the same as in the first embodiment. The structure of the vehicle control system 100 is also the same as in the first embodiment. Descriptions that are repeated in the first embodiment are omitted as appropriate.

[0122] Figure 13 This is a flowchart illustrating the processing related to torque limiting as described in the second embodiment. (The last sentence appears to be incomplete and possibly refers to a previous statement.) Figure 5 Step S250 is added between steps S200 and S300 shown.

[0123] As described above, in step S200, the control device 110 determines whether wheel slippage has occurred. For example, the slippage determination condition includes "the first inferred vehicle speed Ve1 is higher than the second inferred vehicle speed Ve2". The slippage determination condition may also include "the state in which the first inferred vehicle speed Ve1 is higher than the second inferred vehicle speed Ve2 lasts for a certain period of time".

[0124] In step S250, the control device 110 switches the inferred vehicle speed Ve based on the result of step S200. More specifically, if no wheel slippage occurs (step S251: No), the control device 110 sets the first inferred vehicle speed Ve1 as the inferred vehicle speed Ve. On the other hand, if wheel slippage occurs (step S251: Yes), the control device 110 sets the second inferred vehicle speed Ve2 as the inferred vehicle speed Ve.

[0125] When there is no wheel slippage, the accuracy of the first inferred vehicle speed Ve1 is high. However, when wheel slippage occurs, the accuracy of the first inferred vehicle speed Ve1, which depends on wheel speed, decreases, while the accuracy of the second inferred vehicle speed Ve2, which does not depend on wheel speed, becomes higher than that of the first inferred vehicle speed Ve1. Therefore, by switching the inferred vehicle speed Ve from the first inferred vehicle speed Ve1 to the second inferred vehicle speed Ve2, the accuracy of the inferred vehicle speed Ve is improved.

[0126] As mentioned above, the accuracy of the second inferred vehicle speed Ve2 is not necessarily high. Due to the addition of the offset OFST, there is a possibility of "lifting" the second inferred vehicle speed Ve2. Therefore, torque limiting is also applied to the second inferred vehicle speed Ve2. If the torque limiting results in a decrease in the wheel speed of some wheels 5, wheel slippage is eliminated. If wheel slippage is eliminated (step S251: No), the inferred vehicle speed Ve is switched from the second inferred vehicle speed Ve2 to the first inferred vehicle speed Ve1 (step S252). That is, the inferred vehicle speed Ve is reset to the high-precision first inferred vehicle speed Ve1. This ensures the accuracy of the inferred vehicle speed Ve.

[0127] Figure 14 This section describes a variation of the second embodiment. In this variation, two second inferred vehicle speeds, Ve21 and Ve22, are used. The second inferred vehicle speeds Ve21 and Ve22 are represented by the following equations (6) and (7).

[0128] Equation (6): Ve21=(Gx×α1+OFST1)×actual time

[0129] Equation (7): Ve22=(Gx×α2+OFST2)×actual time

[0130] The gain α2 in equation (7) is less than the gain α1 in equation (6). The offset OFST2 in equation (7) is less than the offset OFST1 in equation (6). That is, the second inferred vehicle speed Ve22 is lower than the second inferred vehicle speed Ve21.

[0131] In step S200, the second estimated vehicle speed Ve21 is used. If wheel slippage does not last for a certain period of time (step S254: No), the control device 110 sets the second estimated vehicle speed Ve21 as the estimated vehicle speed Ve (step S255). On the other hand, if wheel slippage lasts for a certain period of time (step S254: Yes), the control device 110 sets the second estimated vehicle speed Ve22 as the estimated vehicle speed Ve (step S256).

[0132] In this way, even when wheel slippage occurs, the estimated vehicle speed Ve can be reduced in stages. This allows for a more precise improvement in the accuracy of the estimated vehicle speed Ve.

Claims

1. A method for inferring vehicle speed, applied to a four-wheel drive vehicle, characterized in that, The method for inferring vehicle speed includes: The vehicle speed is inferred based on the vehicle's wheel speed or front-rear acceleration; Determine whether the working conditions, including at least the inferred vehicle speed being higher than the working determination speed, are met. When the operating conditions are met, a torque limit is applied to reduce the torque of a portion of the wheels of the vehicle. The determination includes whether the termination condition, including the inferred vehicle speed falling below the termination determination speed or the wheel acceleration of a portion of the wheels remaining greater than zero for a certain period of time, is met; and If the termination condition is met, the torque limitation is terminated. The working determination speed and the ending determination speed are not dependent on the wheel speed, and are set to be higher than the first inferred vehicle speed in the state where wheel slippage has not occurred and lower than the first inferred vehicle speed in the state where wheel slippage has occurred.

2. The vehicle speed estimation method according to claim 1, characterized in that, The torque limit does not reduce the torque of the front wheels but reduces the torque of the rear wheels.

3. The vehicle speed estimation method according to claim 1 or 2, characterized in that, The working determination speed is calculated based on the integral of the preceding and following accelerations.

4. The method for inferring vehicle speed according to any one of claims 1 to 3, characterized in that, The termination determination velocity is calculated based on the integral of the preceding and following accelerations.

5. The vehicle speed estimation method according to claim 4, characterized in that, The termination determination speed is the sum of the integral calculated from the preceding and following accelerations and a certain value.

6. The method for inferring vehicle speed according to any one of claims 1 to 5, characterized in that, The inferred vehicle speed is a first inferred vehicle speed inferred based on the wheel speed.

7. The method for inferring vehicle speed according to any one of claims 1 to 5, characterized in that, The inferred vehicle speed is a second inferred vehicle speed inferred based on the integral of the sum of the front and rear accelerations and the offset.

8. The method for inferring vehicle speed according to any one of claims 1 to 5, characterized in that, The vehicle speed inference method also includes: The first inferred vehicle speed is obtained based on the wheel speed; The second inferred vehicle speed is calculated based on the integral of the sum of the front and rear accelerations and the offset. Determine whether the slippage determination condition, including at least the first inferred vehicle speed being higher than the second inferred vehicle speed, is met; If the slippage determination condition is not met, the first inferred vehicle speed is set to the inferred vehicle speed; and If the slippage determination condition is met, the second inferred vehicle speed is set as the inferred vehicle speed.

9. The method for inferring vehicle speed according to any one of claims 1 to 8, characterized in that, The vehicle speed inference method also includes determining whether wheel slippage has occurred. The operating conditions include at least the occurrence of wheel slippage and the inferred vehicle speed being higher than the operating determination speed.

10. The vehicle speed estimation method according to claim 9, characterized in that, The operating conditions include the occurrence of wheel slippage and the state in which the inferred vehicle speed is higher than the operating determination speed for a certain period of time.

11. The vehicle speed estimation method according to claim 9 or 10, characterized in that, Determining whether the wheel slippage has occurred includes: The first inferred vehicle speed is obtained based on the wheel speed; The second inferred vehicle speed is calculated based on the integral of the sum of the front and rear accelerations and the offset. Determine whether the slippage determination condition, including at least the first inferred vehicle speed being higher than the second inferred vehicle speed, is met; and If the slippage determination condition is met, it is determined that the wheel slippage has occurred.

12. A vehicle speed estimation device, applied to a four-wheel drive vehicle, comprising one or more processors, characterized in that, The one or more processors are configured as follows: The vehicle speed is inferred based on the vehicle's wheel speed or front-rear acceleration; Determine whether the working conditions, including at least the inferred vehicle speed being higher than the working determination speed, are met. When the operating conditions are met, a torque limit is applied to reduce the torque of a portion of the wheels of the vehicle. Determine whether the termination conditions, including the inferred vehicle speed becoming below the termination determination speed or the wheel acceleration of a portion of the wheels being greater than zero for a certain period of time, are met. as well as If the termination condition is met, the torque limitation is terminated. The working determination speed and the ending determination speed are not dependent on the wheel speed, and are set to be higher than the first inferred vehicle speed in the state where wheel slippage has not occurred and lower than the first inferred vehicle speed in the state where wheel slippage has occurred.

13. The vehicle speed estimation device according to claim 12, characterized in that, The one or more processors are configured to determine whether wheel slippage has occurred. The operating conditions include at least the occurrence of wheel slippage and the inferred vehicle speed being higher than the operating determination speed.

14. The vehicle speed estimation device according to claim 13, characterized in that, The operating conditions include the occurrence of wheel slippage and the state in which the inferred vehicle speed is higher than the operating determination speed for a certain period of time.

15. The vehicle speed estimation device according to claim 13 or 14, characterized in that, The one or more processors are further configured as follows: The first inferred vehicle speed is obtained based on the wheel speed; The second inferred vehicle speed is calculated based on the integral of the sum of the front and rear accelerations and the offset. Determine whether the slippage determination condition, including at least the first inferred vehicle speed being higher than the second inferred vehicle speed, is met; as well as If the slippage determination condition is met, it is determined that the wheel slippage has occurred.

Images