Vehicle driving force control method and device

Abstract

To realize rapid start in addition to slip suppression at the time of ascending slope start in a snowy road.SOLUTION: Road surface information is acquired by an on-vehicle camera to estimate frictional coefficient μ of a road surface and surface resistance (rolling resistance) R thereof. Gradient resistance is obtained by G sensor. A point A is defined to have slip limit driving force Fs corresponding to the frictional coefficient μ at a second accelerator opening degree APO2 which is specified, and a point B is defined to have larger driving force than the reference driving force F0 according to travel resistance (surface resistance R and gradient resistance) at a first accelerator opening degree APO1 which is specified. The driving force is larger than the reference driving force along a characteristic line L1 until the first accelerator opening degree APO1, and the driving force is gradually changed along a characteristic line L2 between the first accelerator opening degree APO1 and the second accelerator opening degree APO2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a vehicle driving force control that optimally controls the driving force generated by a driving source in response to accelerator operation by a driver, and particularly to a driving force control on a road surface with a low coefficient of friction (so-called low μ road) such as a snowy road. [Background technology]

[0002] An example of drive force control for road surfaces with a low coefficient of friction, such as snowy roads, is disclosed in Patent Document 1. The technology in Patent Document 1 calculates the balancing torque that should be output when starting on a slope when the snowy road driving mode is set to prevent the vehicle from rolling down due to the gradient of the road surface, and makes the characteristics of the drive torque relative to the accelerator opening the same as those in the normal driving mode in the range up to this balancing torque, and makes the characteristics of the drive torque relative to the accelerator opening lower than those in the normal driving mode in the range beyond the balancing torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-42528 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned conventional technology, the vehicle can be prevented from rolling downhill by using the characteristics of the normal driving mode until the balanced torque is reached, but it is not possible to perform a quick start, and it is not possible to meet the needs of drivers who prefer to start quickly even on snowy uphill roads, for example. [Means for solving the problem]

[0005] The driving force control of the vehicle of the present invention comprises: Detects the friction coefficient of the road surface and the running resistance of the vehicle, Calculate the slip limit driving force according to the friction coefficient, Up to the first predetermined throttle opening Within the range of the slip limit driving force mentioned above The driving force is set in accordance with a low opening range characteristic in which the driving force becomes larger than the reference driving force as the running resistance increases, Between the first accelerator opening and a predetermined second accelerator opening greater than the first accelerator opening, the driving force is set in accordance with a medium opening range characteristic that continuously changes from the driving force corresponding to the first accelerator opening based on the low opening range characteristic to a slip limit driving force at the second accelerator opening. [Effects of the Invention]

[0006] According to this invention, the greater the running resistance, the greater the driving force that is applied than the reference driving force up to the first accelerator opening within the range of the slip limit driving force according to the road surface friction coefficient, so that, for example, on snowy roads, it is possible to achieve quick starts while suppressing excessive slippage. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an explanatory diagram showing a system configuration according to an embodiment. [Figure 2] FIG. 2 is a functional block diagram showing a driving force control according to an embodiment. [Figure 3] FIG. 4 is a characteristic diagram showing an example of driving force characteristics when running resistance is large on a low μ road. DETAILED DESCRIPTION OF THE INVENTION

[0008] FIG. 1 is an explanatory diagram showing the system configuration of one embodiment in which this invention is applied to a series hybrid vehicle. The series hybrid vehicle is configured to include a power-generating motor-generator 1 that operates primarily as a generator, an internal combustion engine 2 used as a power-generating internal combustion engine that drives the power-generating motor-generator 1 in response to power demands, a traction motor-generator 4 that operates primarily as a motor to drive drive wheels 3, and a battery 5 that temporarily stores the generated power. The power obtained by the internal combustion engine 2 driving the power-generating motor-generator 1 is stored in the battery 5 via an inverter device (not shown). The traction motor-generator 4 is driven and controlled using the power from the battery 5. The power generated by the traction motor-generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

[0009] The operation of motor generators 1 and 4, the charging and discharging of battery 5, and the operation of internal combustion engine 2 are controlled by controller 6. Controller 6 is composed of multiple controllers connected to each other so that they can communicate with each other, such as motor controller 7 that controls motor generators 1 and 4, engine controller 8 that controls internal combustion engine 2, and battery controller 9 that manages battery 5. Information such as the opening (depression amount) of accelerator pedal 13, the operation amount of brake pedal 14, and vehicle speed detected by vehicle speed detection means 15 is input to controller 6. The driving force required for the vehicle is calculated based on this information, and traction motor generator 4 is controlled via motor controller 7 to satisfy this driving force. Furthermore, when brake pedal 14 is depressed, so-called cooperative regenerative braking control is executed, in which part of the required braking force is provided by regenerative braking and the shortfall is provided by the friction brake mechanisms of each wheel.

[0010] Here, a map of reference driving force characteristics that assigns a reference driving force value to be output by the traction motor generator 4 to the opening of the accelerator pedal 13 operated by the driver, i.e., accelerator opening APO, is stored in the storage device 10 of the controller 6, and the vehicle driving force (i.e., the output of the traction motor generator 4) is basically controlled in accordance with this reference driving force characteristic. Then, when the vehicle starts moving, this reference driving force characteristic is modified in accordance with the friction coefficient of the road surface on which the vehicle is traveling and the running resistance of the vehicle, so that the driving force is controlled more optimally, as will be described later.

[0011] To correct or set the driving force in accordance with the road surface friction coefficient, the vehicle is equipped with an on-board camera 17 that acquires information about the road surface on which the vehicle is traveling. Furthermore, to acquire information about the road surface gradient, particularly when the vehicle is traveling uphill, the vehicle is equipped with a G-sensor 18 that detects the vehicle's inclination. The on-board camera 17 constantly captures images of the road surface, for example, several meters to several tens of meters ahead of the vehicle. The controller 6 processes the images acquired by the on-board camera 17 to estimate the road surface friction coefficient (μ) and road surface resistance (rolling resistance) (R). For example, image processing can distinguish whether the road is snowy, icy, wet paved, dry paved, gravel, sandy, or muddy, and thereby estimate the friction coefficient. Furthermore, as is well known, road surface resistance is high on sandy, gravel, or muddy surfaces, and this road surface resistance can also be estimated from the road surface conditions acquired by the on-board camera 17. Furthermore, the G sensor 18 provides information on the climbing resistance, which is a part of the running resistance and corresponds to the road surface gradient. In this embodiment, the running resistance of the vehicle includes both the road surface resistance corresponding to the road surface characteristics and the climbing resistance corresponding to the road surface gradient. Note that the present invention may include only one of the road surface resistance and the climbing resistance, or may include other types of running resistance.

[0012] FIG. 3 is a characteristic diagram showing an example of driving force characteristics when the vehicle is on a low μ road, such as a snowy road, and the running resistance is high. The horizontal axis represents accelerator pedal opening APO, and the vertical axis represents driving force F. The dotted line L0 indicates the reference driving force characteristic. In the illustrated example, the reference driving force characteristic is set to a relatively simple characteristic in which the driving force F increases at a substantially constant rate as the accelerator pedal opening APO increases.

[0013] In one embodiment, a first predetermined accelerator pedal opening APO1 is set to a relatively small opening, and a second predetermined accelerator pedal opening APO2 is set to a larger opening, in order to obtain more preferable driving force characteristics, including when starting the vehicle on a low-μ road. For example, the first accelerator pedal opening APO1 can be set to about 20%, and the second accelerator pedal opening APO2 can be set to about 80%. The second accelerator pedal opening APO2 is set taking into account the accelerator pedal operation range used by the driver when starting a vehicle in a typical manner, and the vehicle is usually started within a range not exceeding this second accelerator pedal opening APO2.

[0014] Meanwhile, a slip limit driving force Fs is set according to the friction coefficient μ estimated from an image of the road surface. This slip limit driving force Fs is the limit driving force at which a driving force greater than this could cause slippage of the drive wheels. Point A at which the slip limit driving force Fs is reached at the second accelerator opening APO2 (in other words, the limit driving force at which slip does not occur at the second accelerator opening APO2) is determined. This point A is a driving force smaller than the reference driving force characteristic at the second accelerator opening APO2.

[0015] Furthermore, the target driving force (shown as point B) at the first accelerator opening APO1 is set as a driving force greater than the reference driving force. Specifically, the driving force at point B is set so that the greater the running resistance (hill resistance and road resistance), the greater the driving force becomes compared to the reference driving force. For example, a predetermined amount of driving force necessary for initial vehicle start is added to a driving force that balances the hill resistance and a driving force corresponding to the road resistance, and the driving force at point B is set as the sum of both.

[0016] If the target driving force at point B is calculated to be greater than the target driving force at point A (in other words, the slip limit driving force Fs), the target driving force at point B is corrected so that it is less than the target driving force at point A.

[0017] In this way, the target driving forces (points B and A) for the first accelerator opening APO1 and the second accelerator opening APO2 are set, respectively, and characteristic lines L1, L2, L3, and L4 showing the driving force characteristics are determined accordingly. The driving force F is then controlled along these characteristic lines.

[0018] That is, when the accelerator pedal opening APO is between 0 and a first accelerator pedal opening APO1, the target driving force is set along characteristic line L1, which represents a low-opening region characteristic where the driving force is greater than the reference driving force characteristic. Characteristic line L1 has a characteristic where the driving force F increases at a substantially constant rate as the accelerator pedal opening APO increases, but the slope (i.e., the rate of increase) increases as the running resistance (climbing resistance and road surface resistance) increases. Therefore, when starting on an uphill road, for example, the vehicle can overcome the running resistance and start quickly.

[0019] Furthermore, characteristic line L2 exhibits a characteristic such that the driving force changes continuously in response to accelerator pedal position APO from the target driving force at point B at the first accelerator pedal position APO1 to the driving force at point A (slip limit driving force Fs) at the second accelerator pedal position APO2. In one embodiment, characteristic line L2 is set as a straight line connecting points B and A. Therefore, between the first accelerator pedal position APO1 and the second accelerator pedal position APO2, the driving force F is controlled along characteristic line L2 as a medium-opening range characteristic. As is clear from the fact that the slope of characteristic line L2 is smaller than the slopes of characteristic line L1 and reference driving force characteristic L0 in this range, the change in the vehicle's driving force in response to accelerator pedal operation is gradual. Furthermore, up to the second accelerator pedal position APO2, the slip limit driving force Fs, which is based on the road surface's friction coefficient, is not exceeded, ensuring that slippage is suppressed even on low-μ roads.

[0020] When the accelerator pedal depression APO is greater than the second accelerator pedal depression APO2, the driving force is controlled along characteristic lines L3 and L4. Characteristic line L4 is a characteristic that follows the reference driving force characteristic, and characteristic line L3 is a buffer zone that prevents the driving force characteristic from changing stepwise at the second accelerator pedal depression APO2. Therefore, if the driver intentionally depresses the accelerator pedal 13 to an angle greater than the second accelerator pedal depression APO2, the vehicle can travel with a large driving force while slipping.

[0021] In a preferred embodiment, the driving force control according to the characteristics shown in Figure 3 is cancelled when a predetermined vehicle speed is reached, and the control is switched to normal control according to the reference driving force characteristics. In other words, the characteristics shown in Figure 3 are particularly suitable for starting, and normal control is used after starting.

[0022] In a preferred embodiment, the driving force control can be configured to be performed only in a specific driving mode selected by the driver. For example, if an auto mode, a sport mode, and a snow mode are selectable, the driving force control can be performed only in the auto mode. This allows the driving force characteristics shown in Figure 3 to be obtained when starting without the driver having to actively operate the vehicle.

[0023] In the driving force control of the above embodiment, in the low accelerator pedal opening range up to the first accelerator pedal opening APO1, a driving force greater than the reference driving force is output in accordance with the running resistance regardless of the friction coefficient of the road surface, which not only prevents the vehicle from sliding downhill on an uphill road but also improves the vehicle's response when starting. Furthermore, up to the second accelerator pedal opening APO2, the driving force increases gradually without exceeding the slip limit driving force Fs, which enables quick starting on, for example, snowy uphill roads without requiring any special driving technique.

[0024] On a flat road such as a paved road where the road surface resistance (rolling resistance) is not particularly high, point B is on or close to the reference driving force characteristic L0. Similarly, on a dry paved road where the road surface friction coefficient μ is not particularly small, point A is on or close to the reference driving force characteristic L0.

[0025] 2 is a functional block diagram of the driving force control described above, and includes a slip limit driving force setting unit 21 that determines point A, a low opening range characteristics setting unit 22 that determines point B, and a target driving force setting unit 23 that determines the final driving force characteristics based on the outputs of both units. The value of the road friction coefficient μ estimated using the on-board camera 17 is input to a block 24 that calculates slip limit driving force Fs, and block 24 inputs the slip limit driving force Fs to the slip limit driving force setting unit 21. As a result, the slip limit driving force setting unit 21 sets the target driving force for the second accelerator opening APO2, i.e., point A. The value of road resistance R estimated using the on-board camera 17 is input to block 25, and block 25 outputs a value obtained by adding a predetermined amount of driving force necessary for initial vehicle start to the driving force corresponding to the road resistance. Similarly, the value of the climbing resistance estimated using the G sensor 18 is input to block 26, which outputs a value obtained by adding a predetermined amount of driving force required for initial vehicle start to the driving force corresponding to the climbing resistance. These two required driving force values ​​are added in block 27 and input to low opening range characteristic setting unit 22. Point B is set based on this sum. The outputs of slip limit driving force setting unit 21 and low opening range characteristic setting unit 22 are then input to target driving force setting unit 23 via addition block 28, and the driving force control described above is performed.

[0026] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible.

[0027] For example, although the above embodiment has been described taking a series hybrid vehicle as an example, the present invention can be widely applied to other types of hybrid vehicles, electric vehicles, and even engine-driven vehicles.

[0028] In the above embodiment, the road surface conditions are acquired using the on-board camera 17, but it is also possible to acquire road surface information from outside the vehicle using communication technologies such as road-to-vehicle communication or vehicle-to-vehicle communication or connected car technology, or to obtain road surface information, such as whether the road is paved or gravel, and the road surface gradient, from map information in a car navigation system.

[0029] Furthermore, the first accelerator opening degree APO1 and the second accelerator opening degree APO2 do not have to be fixed values, but can be configured to be variably set depending on, for example, the driving mode selected by the driver or other conditions.

[0030] In FIG. 3, the characteristic lines L0 to L4 are drawn as straight lines, but are not necessarily limited to linear characteristics. [Explanation of symbols]

[0031] 1...Power generating motor generator 2...Internal combustion engine 4...Traction motor generator 5. Battery 6...Controller 7...Motor controller 17...In-car camera 18...G sensor

Claims

1. The reference driving force characteristic is set to a reference driving force relative to the accelerator opening. Detects the accelerator opening, Detects the friction coefficient of the road surface and the running resistance of the vehicle, Calculate the slip limit driving force according to the friction coefficient, a driving force is set in accordance with a low opening range characteristic in which the driving force becomes larger than the reference driving force as the running resistance increases up to a predetermined first accelerator opening within a range less than the slip limit driving force; Between the first accelerator opening and a predetermined second accelerator opening greater than the first accelerator opening, the driving force is set in accordance with a medium opening range characteristic that continuously changes from the driving force corresponding to the first accelerator opening based on the low opening range characteristic to a slip limit driving force at the second accelerator opening. A method for controlling the driving force of a vehicle.

2. 2. The vehicle driving force control method according to claim 1, wherein the running resistance includes at least one of a climbing resistance corresponding to a road surface gradient and a road surface resistance corresponding to a road surface property.

3. 3. The vehicle driving force control method according to claim 1, further comprising correcting the low opening range characteristics so that the driving force at the first accelerator opening based on the low opening range characteristics is less than the slip limit driving force.

4. 4. The vehicle driving force control method according to claim 1, wherein when the accelerator opening is greater than the second accelerator opening, the driving force is set in accordance with the reference driving force characteristic.

5. 5. The vehicle driving force control method according to claim 1, wherein when the vehicle speed reaches a predetermined vehicle speed, the control is switched to normal control in accordance with the reference driving force characteristic.

6. 6. A method for controlling driving force of a vehicle according to claim 1, further comprising the steps of: acquiring an image of the road surface using an on-board camera; and estimating the coefficient of friction of the road surface and the road surface resistance that becomes the running resistance from the image.

7. an accelerator opening sensor for detecting an accelerator opening of a vehicle; a device for acquiring information about the friction coefficient of the road surface on which the vehicle is traveling and the running resistance of the vehicle; a controller that controls the driving force of a driving source of the vehicle based on an accelerator opening degree; Equipped with The above controller is The reference driving force characteristic is set to a reference driving force relative to the accelerator opening. determining a slip limit driving force according to the friction coefficient; a driving force is set in accordance with a low opening range characteristic in which the driving force becomes larger than the reference driving force as the running resistance increases up to a predetermined first accelerator opening within a range less than the slip limit driving force; Between the first accelerator opening and a predetermined second accelerator opening greater than the first accelerator opening, the driving force is set in accordance with a medium opening range characteristic that continuously changes from the driving force corresponding to the first accelerator opening based on the low opening range characteristic to a slip limit driving force at the second accelerator opening. A vehicle driving force control device.

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