Vehicle differential limiting control system

Abstract

The present invention provides a differential limiting control device that can suppress control delays, such as delays in attitude changes during turning, as much as possible. [Solution] The controller includes a limit amount calculation unit (step S6) that determines a second limit amount to limit differential rotation based on road surface information detected by road surface information detection means (steps S3 to S5), a limit amount selection unit (step S7) that selects the smaller of the first limit amount (step S2) and the second limit amount, and an output unit (step S8) that outputs the smaller limit amount selected by the limit amount selection unit as a differential limit command value for the differential limiting mechanism.

Description

Technical Field

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[0003]

[0001] The present invention relates to a control device for restricting differential rotation of left and right wheels and front and rear wheels of a vehicle, and particularly to a device for performing differential restriction by electronic control.

Background Art

[0002] When a vehicle turns, the left and right wheels as well as the front and rear wheels need to rotate at different rotational speeds. Therefore, in a two-wheel drive vehicle, a differential mechanism (differential gear) is arranged between the left and right drive wheels, and in a four-wheel drive vehicle, a center differential is interposed between the front and rear wheels. However, if any of the wheels connected to the differential mechanism disengages or slips, so-called torque loss occurs, causing abnormalities in the vehicle's running. Therefore, conventionally, when a rotational speed difference or torque difference occurs between wheels, the differential function of the differential mechanism is restricted. As differential restriction methods, a mechanical (rotation-sensitive) method, a torsen method, or a helical method is known, and an electronic control method is known as a method for performing more advanced control.

[0003] Patent Document 1 describes an electronic control type differential restriction device. As control modes, for example, a plurality of modes corresponding to the road surface μ are prepared, and a driver selects a predetermined control mode from among these control modes, and differential restriction is automatically performed according to the selected control mode.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Differential limiting is primarily performed to ensure stable driving by securing driving and braking forces between the tires and the road surface. Therefore, its control is based on vehicle speed, steering angle, and accelerator opening (driving requirement). The required control amount (differential limiting amount) varies depending on the road surface conditions, such as the road surface friction coefficient (road surface μ). As described above, the invention in Patent Document 1 is configured to provide multiple control modes according to the road surface conditions, allowing the driver to select a control mode. However, the road surface usually changes moment by moment while the vehicle is traveling, and not only the road surface μ but also the turning radius and gradient change frequently. In the device described in Patent Document 1, the driver switches the control mode in response to such changes in road surface conditions. However, in addition to the unavoidable delay of the differential limiting mechanism, there is a delay in manually switching the control mode, which may result in transient or temporary abnormalities in the vehicle's operation. For example, when a vehicle turns, it is required to allow sufficient differential rotation between the inner and outer wheels. However, if the differential rotation is significantly restricted just before the vehicle turns, and this restriction is released or reduced by switching control modes, the differential rotation between the inner and outer wheels may be restricted in the initial stages of the turn, potentially hindering smooth turning by causing understeer or a decrease in driving force.

[0006] This invention has been made in view of the above technical problems, and aims to provide a differential limit control device that can suppress control delays, such as delays in attitude changes during turning, as much as possible. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides a differential limit control device for a vehicle, comprising: a differential mechanism that generates differential rotation between the left and right wheels of a vehicle or differential rotation between the front and rear wheels; a differential limiting mechanism that limits the differential rotation by the differential mechanism and can change the amount of the differential rotation limit; and a first limit amount determined based on a driving operation amount including vehicle speed, drive request amount, or steering angle, wherein the device comprises: road surface information detection means for detecting road surface information in front of the vehicle on which it is traveling; and a controller for controlling the limit amount, the controller comprising: a limit amount calculation unit that determines a second limit amount for limiting the differential rotation based on the road surface information detected by the road surface information detection means; a limit amount selection unit that selects the smaller of the first limit amount and the second limit amount; and an output unit that outputs the smaller limit amount selected by the limit amount selection unit as a differential limit command value to the differential limiting mechanism. [Effects of the Invention]

[0008] The control device of the present invention acquires road surface information in front of the vehicle and calculates a second limiting amount by the differential limiting mechanism based on that road surface information. It compares this second limiting amount with a first limiting amount determined based on driving operation amounts such as the required drive amount for driving the vehicle and the resulting vehicle speed, and outputs the smaller limiting amount as the differential limiting command value. In other words, the control command is the smaller of the limiting amount based on the current state and the limiting amount based on the future state. Therefore, for example, if the differential limiting is currently set to be relatively large and a turn is acquired as the future state ahead, the differential limiting amount will be reduced based on the future state. As a result, the differential limiting is released or the limiting amount is reduced when the turn begins, so a smooth turn in which the inner and outer wheels rotate differentially sufficiently can be started without delay. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram illustrating the parts of a vehicle related to the present invention in an embodiment of the present invention. [Figure 2] This is a block diagram showing the functional configuration of the controller. [Figure 3] This figure shows an example of a map for determining the first limit based on the amount of driving maneuvers. [Figure 4] This is a flowchart illustrating an example of control performed in an embodiment of the present invention. [Modes for carrying out the invention]

[0010] Next, embodiments of the present invention will be described with reference to the attached drawings. Note that the embodiments described below are merely examples of how the present invention can be implemented and do not limit the invention.

[0011] Figure 1 is a schematic diagram showing the part of a vehicle 1 in an embodiment of the present invention that is relevant to the present invention. The vehicle 1 shown here is a so-called front-engine, rear-wheel-drive (FR) vehicle, in which the left and right rear wheels 2R and 2L are drive wheels and the left and right front wheels 3R ​​and 3L are steering wheels. The power source 4, consisting of an engine or motor, is mounted facing rearward on the front side of the vehicle 1, and its output shaft (e.g., propeller shaft) 5 is connected to a rear differential gear (hereinafter referred to as rear differential) 6, which is the final reduction gear.

[0012] The rear differential 6 is basically a rear differential similar to those conventionally known, with a pinion held by a differential case positioned between a pair of side gears. Torque is input from a ring gear integrated into the differential case, and the pinion revolves around the central axis of the side gears, transmitting torque to the side gears. The pinion also rotates on its own, causing the left and right side gears to rotate differentially. Therefore, this rear differential 6 corresponds to the differential mechanism in the embodiment of the present invention.

[0013] The rear differential 6 is equipped with a differential limiting clutch 7. The differential limiting clutch 7 is installed between two predetermined members, such as between the side gear and the differential case, or between the side gears themselves, and is a clutch that transmits torque by friction. Therefore, that torque is the differential limiting torque, and a torque corresponding to that differential limiting torque is transmitted between the left and right side gears, in other words, between the left and right rear wheels 2R and 2L. The differential limiting clutch 7 is also equipped with an electrically controlled actuator (not shown), and is configured to operate by this actuator to appropriately set the differential limiting torque.

[0014] Vehicle 1 is equipped with an accelerator pedal 8 for acceleration and deceleration. The amount of depression (depression angle) of the accelerator pedal 8 corresponds to the amount of drive required, and the amount of intake air, fuel injection amount, or driving power is controlled according to the accelerator opening, which is the amount of depression, so that the output of the driving force source 4 changes in magnitude. The accelerator opening is detected by a sensor (not shown).

[0015] Furthermore, Vehicle 1, like conventional vehicles, is equipped with a steering mechanism 10 including a steering wheel 9, and is configured to steer the front wheels 3R ​​and 3L to the left and right by rotating the steering wheel 9. The angle by which the steering wheel 9 is rotated is the steering angle, and the steering angle is detected by the steering angle sensor 11.

[0016] Furthermore, vehicle 1 is equipped with a camera 12 that captures images of the area in front of vehicle 1. Camera 12 is a so-called advanced safety camera for acquiring information to assist driving, and it detects road surface conditions such as smooth, uneven, or muddy surfaces, as well as road curvature and slope. Therefore, camera 12 corresponds to the road surface information detection means in the embodiment of the present invention.

[0017] A controller 13 is provided that performs differential limiting control to limit the differential function of the rear differential 6 by operating the differential limiting clutch 7 described above. The controller 13 is an electronic control device mainly composed of a microcomputer consisting of an arithmetic element (CPU), memory elements (RAM, ROM), and various interfaces, and is configured to perform calculations according to a preset program using input data and pre-stored data, and to output the result of the calculation as a control command signal. The input data is the vehicle speed v, accelerator opening ACC, steering angle θ, and image data from the camera 12. The pre-stored data is, for example, a map that defines the differential limiting amount according to driving operations such as the vehicle speed v, accelerator opening ACC, and steering angle θ, and a map that defines the differential limiting amount according to road surface information detected by the camera 12.

[0018] The controller 13 performs calculations using the data described above and outputs a differential limit command value as a result of those calculations. The functional configuration for performing this control is shown in a block diagram in Figure 2. The controller 13 includes a limit amount calculation unit 13a. Here, the limit amount is a first limit amount based on the aforementioned driving operation amount and a second limit amount based on the road surface information in front of the vehicle 1.

[0019] The first limit can be determined in the same way as with conventional differential limit control, for example, from the map shown in Figure 3. Figure 3 is a map in which the differential limit is defined by the lateral acceleration (lateral G) corresponding to the steering angle θ and the longitudinal acceleration (longitudinal G) corresponding to the accelerator opening ACC. The limit calculation unit 13a calculates the first limit from the input steering angle θ and accelerator opening ACC and the map. The second limit is calculated, for example, from a map in which the second limit is defined in relation to road surface information.

[0020] The controller 13 includes a limit quantity selection unit 13b. The limit quantity calculation unit 13a is a functional means for selecting the smaller one of the above-mentioned first limit quantity and the second limit quantity. And an output unit 13c is provided in the controller 13 that outputs the selected smaller limit quantity as a differential limit command value. Based on this differential limit command value, the differential limit clutch 7 is controlled, and a differential limit torque corresponding to the differential limit command value is set.

[0021] An example of the control by the above-mentioned controller 13 will be described based on the flowchart shown in FIG. 4. The routine shown in FIG. 4 is repeatedly executed by the controller 13 at every predetermined short time when the vehicle 1 is running. First, in step S1, the above-mentioned driving operation amount is acquired. The driving operation amount is, in the embodiment described here, the vehicle speed v, the accelerator opening ACC, and the steering angle θ. Based on the acquired driving operation amount, a first limit quantity is calculated (step S2). These steps S1 and step S2 are controls based on the current driving state of the vehicle 1.

[0022] On the other hand, in parallel with steps S1 and step S2, the image information obtained by the above-mentioned camera 12 is acquired (step S3). Next, the state of the road surface or the road is recognized (step S4). Based on the recognition, the driving route is determined (step S5). The determination of the driving route includes the determination that the front of the vehicle 1 is a straight road, the determination of the road surface state when it is a straight road, and the determination of a curved road. Note that the determination of the road surface state is the determination of the state of the road surface on which the vehicle 1 will travel after a predetermined time from the current time, such as the height and low of the road surface μ, the presence or absence of unevenness, and the inclination.

[0023] Next, based on the determination result of the driving route, a second limit quantity is calculated (step S6). If the result of the determination based on the road surface information is a straight road, differential limitation based on driving operation amounts such as the vehicle speed v and the accelerator opening ACC will be performed. Also, when the road surface state is a smooth road with a large road surface μ, there is no need for differential limitation based on the road surface state. Therefore, in this case, a second limit quantity having the same magnitude as the first limit quantity obtained in steps S1 and step S2 described above is calculated.

[0024] Conversely, if the road surface is uneven, a certain degree of differential limiting is applied to avoid or suppress wheel slip or spin due to bump rebound. This limiting amount is pre-stored as a constant value or a value corresponding to the unevenness of the surface, and this is read out as the second limiting amount. Furthermore, if it is determined that the vehicle is on a turn, it is preferable that the differential limiting is as small as possible on a turn, so a small limiting amount sufficient to ensure attitude stability in the initial stages of turning is pre-stored, and this is read out as the second limiting amount.

[0025] As described above, the second limit amount can be varied depending on the determination of the driving path. Furthermore, it is sometimes preferable that the vehicle's behavior due to differential limiting be in line with the driver's driving intention. The driver's driving intention can be determined, for example, by whether sport driving is determined, the driving mode selected by the drive mode switch, or the accelerator opening. In order to achieve vehicle behavior that is in line with such driving intention, it is preferable to vary the differential limit according to the driver's driving intention. Therefore, the calculation of the second limit amount in step S6 may be performed in accordance with the driver's driving intention. For example, second limit amounts corresponding to sport driving, the driving mode selected by the drive mode switch, and the accelerator opening may be prepared in advance, or correction coefficients may be prepared, and the second limit value may be determined using this pre-prepared data. The control in step S6 and the aforementioned step S2 corresponds to the control performed by the limit amount calculation unit 13a in the embodiment of the present invention.

[0026] Next, the smaller of the first and second limit amounts mentioned above is selected (step S7). This is known as a minimum select (Min select). Then, the selected limit amount is output as a differential limit command value by feedforward control (step S8), and the routine shown in Figure 4 is terminated.

[0027] Therefore, the control device in the embodiment of the present invention that performs the control shown in Figure 4 performs small differential limiting based on the expected road conditions. As a result, when encountering uneven surfaces or turning sections, the differential limiting is adjusted according to the road surface conditions, making it possible to appropriately control the vehicle's behavior without causing a delay in control.

[0028] It should be noted that the present invention is not limited to the embodiments described above, and can be implemented with appropriate modifications without departing from the spirit of the invention. For example, the differential mechanism is not limited to a mechanism for differential rotation of the left and right wheels, but may be a mechanism for differential rotation of the front and rear wheels. Also, the differential limiting mechanism is not limited to a friction clutch, as it is a mechanism that can electrically control the differential limiting amount. [Explanation of Symbols]

[0029] 1 vehicle 2R,2L rear wheel 3R,3L front wheel 4. Power source 5. Output shaft (propeller shaft) 6 Rear differential 7. Differential limiting clutch 8. Accelerator pedal 9 Steering wheel 10. Steering mechanism 11. Steering angle sensor 12 cameras 13 Controllers 13a Limit Calculation Unit 13b Limit selection section 13c output section θ Steering angle ACC accelerator pedal position v Vehicle speed

Claims

[Claim 1] A differential limiting control device for a vehicle, comprising a differential mechanism that generates differential rotation between the left and right wheels or between the front and rear wheels of a vehicle, and a differential limiting mechanism that limits the differential rotation by the differential mechanism and can change the amount of the differential rotation limit, wherein a first limiting amount is determined based on a driving operation amount that includes either the vehicle speed, the drive request amount, or the steering angle, A road surface information detection means for detecting road surface information ahead of the vehicle, It has a controller that controls the aforementioned limit amount, The aforementioned controller, A limit amount calculation unit that determines a second limit amount for limiting the differential rotation based on the road surface information detected by the road surface information detection means, A limit amount selection unit that selects the smaller of the first limit amount and the second limit amount, An output unit that outputs the small limit amount selected by the limit amount selection unit as a differential limit command value for the differential limiting mechanism. It is equipped with A differential limiting control device for a vehicle, characterized by the following features.

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