Differential limiting characteristic estimation device

Abstract

To provide a differential limiting characteristic estimation device that is able to estimate a differential limiting characteristic of a differential device that distributes the driving force of a drive source to right and left steering wheels while allowing a differential.SOLUTION: A differential limiting characteristic estimation device 5 is mounted on a vehicle 1 including: a differential device 2 that distributes a driving force of an engine 11 to right and left front wheels 13, 14 while allowing a differential; and a control device 46 that controls an assist motor 44 of an electric power steering device 4, based on a magnitude of the driving force transmitted to each of the right and left front wheels 13, 14. The differential limiting characteristic estimation device 5 includes: vehicle information acquisition means 51 that acquires vehicle information including information on a magnitude of the driving force generated by the engine 11 and information on a steering angle; and characteristic value identifying means 52 that identifies a characteristic value indicating a differential limiting characteristic of the differential device 2, based on a wheel speed difference between the right and left front wheels 13, 14 during turning travel in which the magnitude of the driving force generated by the engine 11 is equal to or greater than a predetermined value and the steering angle is equal to or larger than a predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a differential limiting characteristic estimation device that estimates the differential limiting characteristic of a differential device that distributes driving force of a drive source of a vehicle to left and right steered wheels while allowing differential motion. [Background technology]

[0002] In a vehicle in which the driving force of a driving source is transmitted to the left and right steered wheels, the driving force transmitted to the steered wheels may affect the steering characteristics. Patent Documents 1 and 2 describe a control method for an electric power steering device for providing a good steering feel to the driver by suppressing the effect of the driving force transmitted to the steered wheels on the steering characteristics.

[0003] The method described in Patent Document 1 determines the torque to be applied to the steering rack using an application gain obtained by multiplying a first gain G1 representing the strength of the torque steer phenomenon by a second gain G2 representing the probability of entering a driving situation that may cause the occurrence of the torque steer phenomenon. The first gain G1 is determined according to the wheel torque, and the second gain G2 is determined according to the steering angle and the difference in rotation speed between the left and right wheels.

[0004] The method described in Patent Document 2 relates to the control of an electric power steering device in a vehicle in which driving force is transmitted to left and right wheels via a differential gear equipped with a differential limiting function that suppresses differential rotation between the left and right wheels, and provides the driver with a good steering feel by having the power steering motor compensate for phenomena such as freezing (loss of return motion) that are induced in the steering mechanism by the differential limiting function of the differential gear. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2021-524417 [Patent Document 2] Special Publication No. 2018-524224 Summary of the Invention [Problem to be solved by the invention]

[0006] In a vehicle in which the driving force of the driving source is distributed to the left and right steered wheels by a differential device having a differential limiting function, if the differential limiting force changes due to deterioration of the differential device over time, for example, even if the control is performed as described above in an electric power steering device, the expected performance may not be fully exhibited. In addition, if the vehicle user replaces the differential device, the differential limiting force of the differential device changes, and the same problem may occur.

[0007] The inventors of the present application have come up with the present invention based on the finding that, in order to solve such problems, it is desirable to estimate the differential limiting characteristic after a change in the differential limiting characteristic of a differential device from information obtained by various on-board sensors and to control the vehicle based on the estimated result. That is, an object of the present invention is to provide a differential limiting characteristic estimation device capable of estimating the differential limiting characteristic of a differential device that distributes the driving force of a drive source to left and right steered wheels while allowing a differential. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a differential limiting characteristic estimation device that is mounted on a vehicle equipped with a differential gear that distributes the driving force of a driving source to left and right steered wheels while allowing differential distribution, and a control device that controls the vehicle based on the magnitude of the driving force transmitted to the left and right steered wheels, respectively, and has: vehicle information acquisition means that acquires vehicle information including information on the magnitude of the driving force generated by the driving source and information on the steering angle; and characteristic value identification means that identifies a characteristic value indicative of the differential limiting characteristic of the differential gear based on the wheel speed difference between the left and right steered wheels during a cornering run when the magnitude of the driving force generated by the driving source is equal to or greater than a predetermined value and the steering angle is equal to or greater than a predetermined value. Effect of the Invention

[0009] According to the present invention, it is possible to estimate the differential limiting characteristic of a differential device, and it is possible to perform good vehicle control based on the differential limiting characteristic obtained by estimation. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing an example of the general configuration of a vehicle equipped with a differential limiting characteristic estimation device according to an embodiment of the present invention; [Diagram 2] 1A is a cross-sectional view of the differential gear in a cross section parallel to the axial direction, and FIG. 1B is a cross-sectional view of the differential gear in a cross section perpendicular to the axial direction. [Diagram 3] FIG. 2 is a perspective view showing a differential device with a part cut away. [Figure 4] 1A and 1B are explanatory diagrams showing an example of forces acting on a wheel when a vehicle is turning while driving. [Diagram 5] 1A to 1D are explanatory diagrams showing map information, which is an example of relationship information stored in a storage means, as a three-dimensional map. [Figure 6] 10 is a flowchart showing a specific example of a process executed by a characteristic value identifying means. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Embodiment Mode] An embodiment of the present invention will be described with reference to Figures 1 to 6. Note that the embodiment described below is shown as a preferred specific example for carrying out the present invention, and while there are some parts that specifically exemplify various technical matters that are technically preferable, the technical scope of the present invention is not limited to this specific embodiment.

[0012] 1 is a schematic diagram showing an example of the general configuration of a vehicle 1 equipped with a differential limiting characteristic estimation device 5 according to an embodiment of the present invention. The vehicle 1 has an engine 11 as a drive source, and a transmission 12 that changes the speed of the output rotation of the engine 11, and drives left and right front wheels 13, 14 as steered wheels by the driving force of the engine 11. The vehicle 1 also has a differential gear 2 to which the driving force of the engine 11 is input via the transmission 12, drive shafts 31, 32 between the differential gear 2 and the left and right front wheels 13, 14, and an electric power steering device 4 that steers the left and right front wheels 13, 14 in response to the steering operation of a steering wheel 40 by a driver.

[0013] The differential device 2 has a differential limiting function that suppresses differential rotation between the left and right front wheels 13, 14, and distributes the driving force of the engine 11 while allowing differential rotation between the left and right front wheels 13, 14. The differential limiting characteristic estimation device 5 estimates the differential limiting characteristic of the differential device 2, and outputs the estimation result to a control device 46 of the electric power steering device 4.

[0014] The drive source is not limited to the engine 11, but may be an electric motor, or a so-called hybrid system that combines an engine and an electric motor may be used. The vehicle configuration is not limited to a two-wheel drive vehicle that drives only the left and right front wheels 13, 14, but may be a four-wheel drive vehicle in which the drive force of the drive source is distributed to the left and right front wheels 13, 14 and the left and right rear wheels 15, 16.

[0015] The electric power steering device 4 has a steering shaft 41 connected to the steering wheel 40, a rack shaft 42 extending in the vehicle width direction, left and right tie rods 43 swingably connected to both ends of the rack shaft 42, an assist motor 44 that generates a steering assist force to assist the driver in steering the steering wheel 40, a reduction mechanism 45 that reduces the output rotation of the assist motor 44, and a control device 46 that controls the assist motor 44.

[0016] The left and right tie rods 43 are connected to knuckles 33, 34 provided corresponding to the left and right front wheels 13, 14, respectively. A pinion gear 411 is provided at the tip of the steering shaft 41. A rack tooth portion 421 that meshes with the pinion gear 411 is provided on the rack shaft 42. When the steering shaft 41 rotates, the rack shaft 42 moves in the vehicle width direction, and the left and right front wheels 13, 14 are steered.

[0017] 1, the reduction mechanism 45 is a worm gear mechanism provided in correspondence with the steering shaft 41, and includes a worm 451 fixed to the output shaft 441 of the assist motor 44, and a worm wheel 452 meshed with the worm 451. The worm wheel 452 rotates together with the steering shaft 41. However, this is not limiting, and the electric power steering device 4 may be configured so that the steering assist force generated by the assist motor 44 is transmitted to the rack shaft 42.

[0018] The vehicle 1 is equipped with a plurality of on-board sensors that detect the state of each part of the vehicle 1. The differential limiting characteristic estimation device 5 and the control device 46 of the electric power steering device 4 can acquire information on the detection results of these on-board sensors through an on-board network such as a controller area network (CAN). The multiple on-board sensors include an engine torque sensor 61 that detects engine torque, which is the magnitude of the driving force generated by the engine 11, a steering angle sensor 62 that detects the steering angle of the steering wheel 40, and wheel speed sensors 63-66 that detect wheel speeds, which are the rotational speeds of the front wheels 13, 14 and the rear wheels 15, 16. The wheel speed sensors 63-66 are attached to hubs 35-38 that support the front wheels 13, 14 and the rear wheels 15, 16, respectively.

[0019] The driving force generated by the engine 11 may be positive or negative. When the engine 11 generates a positive driving force, the vehicle 1 accelerates or runs at a constant speed. When the engine 11 generates a negative driving force, the vehicle 1 decelerates. The negative driving force is, for example, engine braking. If the vehicle 1 is a freight vehicle or the like, the negative driving force may be generated by an exhaust brake. If the vehicle 1 has an electric motor as a driving source, the negative driving force may be generated by a regenerative brake.

[0020] Hereinafter, when the term "magnitude of driving force" or "magnitude of engine torque" is used, it refers to the absolute value of the driving force or engine torque. In addition, when the vehicle 1 runs with the engine 11 generating a positive driving force, it is called drive running, and when the vehicle 1 runs with the engine 11 generating a negative driving force, it is called coast running.

[0021] Fig. 2(a) is a cross-sectional view of the differential gear 2 taken along a cross section parallel to the axial direction. Fig. 2(b) is a cross-sectional view of the differential gear 2 taken along a cross section perpendicular to the axial direction. Fig. 3 is a perspective view showing a part of the differential gear 2 cut away.

[0022] The differential device 2 has left and right side gears 21, 22, a plurality of pinion gear sets 23, a differential case 24 that houses them, a center washer 25 arranged between the left and right side gears 21, 22, and a pair of side washers 26, 27 arranged between the left and right side gears 21, 22 and the differential case 24, respectively. The driving force of the engine 11 is input to the differential case 24 from a ring gear 20 fixed to the outer periphery of the differential case 24. One end of each of the drive shafts 31, 32 is connected to the left and right side gears 21, 22 so as not to rotate relative to each other. The differential case 24 has a plurality of holding holes 240 that respectively hold the plurality of pinion gear sets 23.

[0023] Each pinion gear set 23 has a first pinion gear 231 meshing with the left side gear 21 and two second pinion gears 232 meshing with the left side gear 22. The first pinion gear 231 meshes with the two second pinion gears 232 on the outer periphery of the right side gear 22. In this embodiment, three pinion gear sets 23 are held in the differential case 24. The first pinion gear 231, the second pinion gear 232, and the side gears 21 and 22 are formed with helical teeth whose tooth traces are inclined with respect to the axial direction.

[0024] When the left and right side gears 21, 22 rotate differentially, the first pinion gear 231 and the second pinion gear 232 rotate about their respective central axes within the retaining hole 240. At this time, the tooth tip surface 231a of the first pinion gear 231 and the tooth tip surface 232a of the second pinion gear 232 slide on the inner surface 240a of the retaining hole 240, generating frictional resistance. In addition, frictional resistance is also generated between the side gears 21, 22 and the center washer 25 or the pair of side washers 26, 27 due to an axial thrust force generated in the side gears 21, 22 by the meshing of the side gears 21, 22 with the first pinion gear 231 and the second pinion gear 232.

[0025] These frictional resistance forces become a differential limiting force that suppresses differential rotation between the left front wheel 13 and the right front wheel 14. Due to this differential limiting force, for example, even when slippage occurs in the left front wheel 13, driving force is transmitted to the right front wheel 14. The differential limiting characteristic of the differential device 2 is expressed by a torque bias ratio (hereinafter referred to as TBR), which is a characteristic value thereof. The TBR of the differential device 2 is a value obtained by dividing the magnitude of torque output from the side gear on the high torque side of the side gears 21, 22 by the magnitude of torque output from the side gear on the low torque side when the side gears 21, 22 are rotating differentially. The larger the TBR value, the stronger the suppression of differential rotation between the left front wheel 13 and the right front wheel 14.

[0026] The axial thrust force generated in the side gears 21, 22 is in the opposite direction during drive running and during coast running, and for example, when a thrust force toward the center washer 25 is generated in the side gears 21, 22 during drive running, a thrust force toward each of the pair of side washers 26, 27 is generated in the side gears 21, 22 during coast running. Therefore, the differential limiting characteristic of the differential device 2 may differ between drive running and coast running. In this embodiment, the differential limiting characteristic estimation device 5 estimates the differential limiting characteristic of the differential device 2 for each of drive running and coast running.

[0027] 4(a) and (b) are explanatory diagrams showing an example of the force acting on a wheel (here, the left wheel 13) when the vehicle 1 is turning while driving. Fig. 4(a) shows the self-aligning torque, and Fig. 4(b) shows the moment generated around the vertical axis of the wheel by the driving force transmitted to the wheel. The same applies to the right front wheel 14.

[0028] 4(a) and (b) show the wheels of the vehicle 1 when turning right, viewed from above in the vertical direction, together with the vehicle body 10. In Fig. 4(a) and (b), the straight line L indicates a direction passing through the center of the wheel and perpendicular to the rotation axis of the wheel, the arrow A indicates the instantaneous traveling direction of the wheel, θa indicates the steering angle, and θs indicates the sideslip angle (slip angle).

[0029] As shown in Figure 4(a), the self-aligning torque SAT is generated when the application point P1 of the cornering force CF is located behind the vertical axis Va passing through the center of the wheel in the direction of travel, and acts in the direction to reduce the steering angle θa, i.e., in the direction to return the wheel to a straight traveling state. The distance D between the force application point P1 and the intersection P2 where the vertical axis Va intersects with the road surface becomes a moment arm generally called pneumatic trail, and the self-aligning torque SAT is generated according to the magnitude of the cornering force and the distance D.

[0030] FIG. 4(b) shows a point of action P3 of the frictional force generated between the wheel (tire) and the road surface by the driving force transmitted to the wheel, and a vector V of the frictional force having the point of action P3 as an end point. As shown in FIG. 4(b), when the driving force is transmitted to the wheel in a state where the steering angle θa is large and a large centrifugal force is acting on the vehicle body 10, a force that pushes the wheel forward acts on the point of action P3 located on the outer side of the turn from the straight line L. This force shown by the vector V acts in a direction that increases the steering angle θa, that is, in a direction that causes the wheel to turn on the inside of the turn around the vertical axis Va. Hereinafter, this force around the vertical axis Va is referred to as a turning torque. In FIG. 4(b), the arrow representing the turning torque is indicated by the symbol T.

[0031] The control device 46 of the electric power steering device 4 controls the assist motor 44 so as to suppress the turning torque. Since the turning torque increases according to the magnitude of the driving force transmitted to the wheels, the control device 46 controls the assist motor 44, i.e., the vehicle, based on the magnitude of the driving force transmitted to the wheels. Here, when turning, torque is transmitted from the wheel on the outside of the turn that rotates at high speed (e.g., the left front wheel 13) to the wheel on the inside of the turn that rotates at low speed (e.g., the right front wheel 14) via the differential device 2. In other words, a larger driving force is distributed to the wheel on the inside of the turn than to the wheel on the outside of the turn.

[0032] Since the torque transmitted from the wheel on the outside of the turn to the wheel on the inside of the turn varies depending on the TBR of the differential 2, the control device 46 uses the TBR to calculate the driving force transmitted to each of the left front wheel 13 and the right front wheel 14, and controls the assist motor 44 to suppress the turning torque. The control device 46 obtains the value of the TBR from the differential limiting characteristic estimation device 5.

[0033] Incidentally, the TBR of the differential gear 2 may change due to deterioration over time, etc. In addition, the TBR also changes when a vehicle user or the like replaces the differential gear 2 from the one that was installed when the vehicle was new with another one. For this reason, if the control device 46 performs the above calculations using the TBR of the differential gear 2 when the vehicle was new, there is a risk that the effect of suppressing the turning torque, that is, the effect of controlling the vehicle based on the magnitude of the driving forces transmitted to the left front wheel 13 and the right front wheel 14, may not be fully achieved.

[0034] In this embodiment, the differential limiting characteristic estimation device 5 estimates the TBR of the differential 2 from information obtained by an on-board sensor. The control device 46 acquires the information on the TBR estimated by the differential limiting characteristic estimation device 5 via, for example, an on-board network, and controls the assist motor 44 based on the acquired TBR information.

[0035] As shown in FIG. 1, the differential limiting characteristic estimation device 5 has a vehicle information acquisition means 51 that acquires vehicle information, which is information indicating the state of each part of the vehicle 1 obtained from multiple on-board sensors, etc., a characteristic value identification means 52 that identifies TBR, which is a characteristic value that indicates the differential limiting characteristic of the differential device 2, and a memory means 53 that stores multiple pieces of related information referenced by the characteristic value identification means 52.

[0036] The vehicle information acquisition means 51 is configured to have a communication interface circuit with an in-vehicle network. The characteristic value identification means 52 is realized by a CPU (Central Processing Unit) executing the processing of a flowchart described later. The storage means 53 is realized by a non-volatile memory. In this embodiment, the storage means 53 stores a plurality of pieces of related information for each of drive driving and coast driving.

[0037] The vehicle information acquisition means 51 is capable of acquiring information on the magnitude of engine torque, information on the steering angle of the steering wheel 40, and information on the wheel speeds of the left and right front wheels 13, 14. The information on the magnitude of engine torque is information acquired from an engine torque sensor 61. The information on the steering angle of the steering wheel 40 is information acquired from a steering angle sensor 62. The information on the wheel speeds of the left front wheel 13 and the right front wheel 14 is information on the actual wheel speed values ​​acquired from wheel speed sensors 63, 64.

[0038] 5(a) to 5(d) are explanatory diagrams showing, as a three-dimensional map, map information, which is an example of relationship information stored in the storage means 53. The storage means 53 stores, in map format, a plurality of pieces of relationship information indicating the relationship between the magnitude of engine torque, the steering angle, and the wheel speed difference between the left and right front wheels 13, 14 for a plurality of different TBR values.

[0039] FIG. 5(a) shows a three-dimensional map when the TBR is low. FIG. 5(b) shows a three-dimensional map when the TBR is medium. FIG. 5(c) shows a three-dimensional map when the TBR is high. FIG. 5(d) shows a three-dimensional map when the TBR is even higher. In these three-dimensional maps, the X-axis indicates the turning curvature calculated based on the steering angle, the Y-axis indicates the magnitude of the engine torque, and the Z-axis indicates the absolute value of the wheel speed difference between the left and right front wheels 13, 14. As shown in FIG. 5(a) to (d), the wheel speed difference between the left and right front wheels 13, 14 tends to become smaller as the TBR increases.

[0040] The turning curvature is the reciprocal of the turning radius of the center of gravity of the vehicle 1 when turning. The turning radius can be calculated, for example, by the following formula (1): In formula (1), R is the turning radius, SF is the stability factor, VS is the vehicle speed, L is the wheelbase, and θ is the steering angle.

number

[0041] These map information are set based on the results obtained, for example, from an experiment using an actual vehicle or a vehicle simulation in which the operation of the vehicle 1 is simulated on a computer. As shown in Figs. 5(a) to (d), the relationship between the magnitude of engine torque, the steering angle (turning curvature), and the wheel speed difference between the left and right front wheels 13, 14 varies depending on the TBR. The storage means 53 stores relationship information for each of a plurality of TBRs, for example, from 1.00 to 10.00 in increments of 0.05. The characteristic value identification means 52 identifies the TBR by extracting the most relevant one of the plurality of relationship information based on the information obtained by the vehicle information acquisition means 51. Next, a specific example of the process executed by the characteristic value identification means 52 will be described in detail with reference to Fig. 6.

[0042] 6 is a flowchart showing a specific example of the processing executed by the characteristic value identifying means 52. The characteristic value identifying means 52 repeatedly executes a series of processing shown in this flowchart at a predetermined time interval. Note that, when a new vehicle is manufactured, one piece of relationship information corresponding to the state of the differential gear 2 mounted on the vehicle 1 is pre-selected from among the multiple pieces of relationship information stored in the storage means 53.

[0043] In the processing of the flowchart shown in FIG. 6, the characteristic value identification means 52 first judges whether or not the vehicle is turning when the magnitude of the engine torque is equal to or greater than a predetermined value and the steering angle is equal to or greater than a predetermined value (step S1). More specifically, it judges whether or not the absolute value of the engine torque is equal to or greater than a threshold value S1 and the absolute value of the steering angle is equal to or greater than a threshold value S2. The threshold value S1 is an engine torque value that is large enough to maintain the vehicle speed even during high-speed driving, for example. The threshold value S2 is, for example, about 10°. If the result of the judgment in step S1 is negative (No), the processing of the flowchart shown in FIG. 6 is terminated.

[0044] If the result of the determination in step S1 is affirmative (Yes), the characteristic value identifying means 52 determines whether or not the vehicle is in drive driving, in which the engine torque is positive, based on the information obtained from the engine torque sensor 61 (step S2). If the determination in step S2 is affirmative (Yes), the characteristic value identifying means 52 refers to one piece of relationship information selected from the plurality of pieces of relationship information stored in the storage means 53 as information for drive driving, and obtains the wheel speed difference between the left and right front wheels 13, 14 by applying the turning curvature and the magnitude of the engine torque based on the information obtained by the vehicle information obtaining means 51 (step S3).

[0045] This wheel speed difference is an estimated value of the wheel speed difference between the left and right front wheels 13, 14 based on the relationship information stored in the characteristic value identification means 52. Hereinafter, the estimated value of the wheel speed difference obtained by referring to the relationship information stored in the storage means 53 is referred to as ΔSe.

[0046] Next, the characteristic value identification means 52 calculates an absolute value of an actual wheel speed difference between the left and right front wheels 13, 14 based on the information of the actual measured wheel speed values ​​of the left and right front wheels 13, 14 acquired by the vehicle information acquisition means 51 (step S4). Hereinafter, the absolute value of the wheel speed difference based on the information of the actual measured wheel speed values ​​is referred to as ΔSa.

[0047] Next, the characteristic value identifying means 52 obtains the deviation rate between ΔSe and ΔSa (step S5). The deviation rate is, for example, a value obtained by dividing the absolute value of the difference between ΔSe and ΔSa by ΔSa.

[0048] Next, the characteristic value identification means 52 judges whether the deviation rate obtained in step S5 is less than a predetermined value (step S6). Specifically, it judges whether the deviation rate obtained in step S5 is less than a threshold value S3 set to a value corresponding to the TBR increment (0.05 in the above example) of the multiple pieces of relationship information stored in the storage means 53. If the judgment result in step S6 is affirmative (Yes), it is judged that the relevance of the currently selected relationship information is high and the TBR value corresponding to this relationship information is appropriate, and therefore the process of the flowchart shown in FIG. 6 is terminated.

[0049] If the result of the determination in step S6 is negative (No), the characteristic value identification means 52 newly extracts one piece of relationship information with the highest applicability from among the multiple pieces of relationship information stored in the storage means 53, thereby identifying a new TBR (step S7). Specifically, for example, if ΔSe is greater than ΔSa, it is considered that a TBR with a value smaller than the actual value has been identified. Therefore, ΔSe is obtained by referring to relationship information corresponding to a TBR higher than the currently selected relationship information, the deviation rate between the ΔSe and ΔSa is obtained, and it is determined whether the deviation rate is less than the threshold value S3. If the result of this determination is positive (Yes), the value of the TBR corresponding to that relationship information is adopted, and if the result is negative (No), ΔSe is obtained by referring to another piece of relationship information, and the same process is repeated until the deviation rate between ΔSe and ΔSa becomes less than the threshold value S3. As a result, one piece of relationship information with the highest applicability is newly extracted from among the multiple pieces of relationship information stored in the storage means 53, and the TBR is identified.

[0050] On the other hand, if the determination in step S2 is negative (No), the characteristic value identification means 52 refers to a plurality of pieces of related information stored in the storage means 53 as information for coasting, and performs the processes of steps S8 to S12. The contents of the processes of steps S8 to S12 are the same as those of steps S3 to S7 described above, except that the plurality of pieces of related information stored as information for coasting are referred to, and therefore detailed explanations will be omitted.

[0051] (Effects of the embodiment) According to the present embodiment described above, the differential limiting characteristic of the differential gear 2 mounted on the vehicle 1 can be appropriately estimated. Therefore, even if the differential limiting force changes due to deterioration over time of the differential gear 2 or the differential gear 2 is replaced by the user of the vehicle 1, it is possible to perform good vehicle control based on the differential limiting characteristic obtained by estimation. In addition, in this embodiment, when the magnitude of the engine torque is equal to or greater than a predetermined value and the steering angle is equal to or greater than a predetermined value during turning, the characteristic value identifying means 52 performs the process from step S2 onward, so that a highly accurate TBR can be identified. In addition, in this embodiment, the process of identifying a new TBR is performed only when the deviation rate is less than a predetermined value, so that the calculation load of the characteristic value identifying means 52 can be reduced. Furthermore, in this embodiment, the TBR is identified for each of driving and coasting, so that good vehicle control can be performed in both driving and coasting.

[0052] (Additional Note) The present invention has been described above based on the embodiments, but the invention according to the claims is not limited to these embodiments. It should be noted that not all of the combinations of features described in the embodiments are essential to the means for solving the problems of the invention. The present invention can be modified as appropriate by omitting some configurations or adding or replacing configurations within the scope of the gist of the invention. Furthermore, some configurations of the above-mentioned embodiments can be combined with each other, and can be modified, for example, as follows.

[0053] In the above embodiment, the control device 46 of the electric power steering device 4 has been described as an example of a control device that performs vehicle control based on the magnitude of the driving force transmitted to the left and right front wheels 13, 14, respectively. However, this is not limited to this. For example, a control device that performs vehicle behavior stabilization control to stabilize the behavior of the vehicle 1 by generating a braking force on at least one of the left and right front wheels 13, 14 may perform control using the TBR identified by the differential limiting characteristic estimation device 5.

[0054] In the above embodiment, the case has been described where the TBR is identified by referring to the relational information based on the information on the magnitude of the engine torque and the information on the steering angle of the steering wheel 40, but the TBR may be identified by further taking other information into consideration. Examples of the other information include information on the gear ratio of the transmission 12 and information on the vehicle speed. The information on the gear ratio of the transmission 12 can be obtained, for example, from a control device that controls the transmission 12. The information on the vehicle speed can be obtained, for example, from the detection results of the wheel speed sensors 63-66.

[0055] In the above embodiment, the X-axis of the three-dimensional map shown in Figures 5(a) to (d) is the turning curvature, but the X-axis may be the turning radius or the steering angle. The Y-axis may be the driving force input to the differential device 2. In other words, the relationship information only needs to directly or indirectly indicate the relationship between the magnitude of the driving force generated by the engine 11, the steering angle, and the wheel speed difference between the left and right front wheels 13, 14. The driving force input to the differential device 2 can be calculated based on, for example, the engine torque and the gear ratio of the transmission 12.

[0056] In the above embodiment, the engine torque is detected by the engine torque sensor 61. However, the present invention is not limited to this. For example, engine torque information may be obtained from an engine control device that controls the engine 11. [Explanation of symbols]

[0057] 1...vehicle 2...differential 5... Differential limiting characteristic estimation device 11... Engine (drive source) 13...Left front wheel (steerable wheel) 14...Right front wheel (steerable wheel) 46: Control device 51: Vehicle information acquisition means 52: characteristic value identification means 53: storage means

Claims

1. The vehicle is equipped with a differential device that distributes the driving force of a driving source to left and right steered wheels while allowing a differential, and a control device that controls the vehicle based on the magnitude of the driving force transmitted to the left and right steered wheels, a vehicle information acquisition means for acquiring vehicle information including information on the magnitude of the driving force generated by the driving source and information on the steering angle; a characteristic value identifying means for identifying a characteristic value indicative of a differential limiting characteristic of the differential device based on a wheel speed difference between the left and right steered wheels during a turning run in which the magnitude of the driving force generated by the driving source is equal to or greater than a predetermined value and the steering angle is equal to or greater than a predetermined value; A differential limiting characteristic estimation device having the following.

2. the characteristic value is a torque bias ratio between the left and right steered wheels, a storage means for storing a plurality of pieces of relationship information indicating a relationship between a magnitude of a driving force generated by the driving source, the steering angle, and a wheel speed difference between the left and right steered wheels for a plurality of different values ​​of the torque bias ratio; The characteristic value identification means identifies the torque bias ratio by extracting one piece of relationship information having the highest applicability from among the plurality of pieces of relationship information based on the information obtained by the vehicle information acquisition means. The differential limiting characteristic estimation device according to claim 1 .

3. the vehicle information acquisition means is capable of acquiring actual measured values ​​of wheel speeds of the left and right steered wheels detected by wheel speed sensors, the characteristic value identification means calculates a deviation rate between the wheel speed difference between the left and right steered wheels obtained by referring to the one piece of relationship information based on information on the magnitude of the driving force generated by the driving source and information on the steering angle obtained by the vehicle information acquisition means, and the wheel speed difference between the left and right steered wheels obtained from the actual measurement values, and when the deviation rate is equal to or greater than a predetermined value, newly extracts one piece of relationship information that is most applicable from among the plurality of pieces of relationship information. The differential limiting characteristic estimation device according to claim 2 .

4. The characteristic value identification means identifies the characteristic value when the vehicle is driving and when the vehicle is coasting. The differential limiting characteristic estimation device according to any one of claims 1 to 3.

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