JP4735142B2 - Driving force distribution control device for front and rear wheel drive vehicles - Google Patents

Description

  The present invention relates to a driving force distribution control device used for front and rear wheel drive vehicles.

  Conventionally, as a driving force distribution control device used in front and rear wheel drive vehicles capable of arbitrarily distributing driving force to front and rear wheels, there is a driving force distribution control device as described in Patent Document 1, which provides high acceleration performance at the time of starting. As a driving force distribution ratio to obtain, a technique is known in which a driving force distribution ratio (for example, front wheel torque: rear wheel torque = 50: 50) having a four-wheel drive tendency is set in advance. However, with such a driving force distribution ratio, a so-called tight corner braking phenomenon (a phenomenon in which braking torque is generated in the direct drive system due to the difference in the average turning radius of the front and rear wheels during turning) occurs when the vehicle starts turning. However, there is a problem that the user feels uncomfortable due to deceleration.

  In order to prevent such an uncomfortable feeling of deceleration due to the tight corner braking phenomenon, the turning state is estimated from the wheel speed difference between the front and rear, left and right, lateral acceleration, snake angle, yaw rate, etc. Is known to control the driving force distribution to two-wheel drive, and more specifically, when the turning radius is estimated and the turning radius is equal to or less than a predetermined threshold, the tight corner brake It is determined that the vehicle is in a turning state in which a phenomenon occurs.

  However, in estimating the turning radius, for example, in the method using the front / rear / left / right wheel speed difference, lateral acceleration, and yaw rate, the measured values of these measurement items are small immediately after starting, so whether or not the vehicle is in a straight traveling state. Although it can be judged, it is not possible to quickly determine whether or not it is a small turning radius that causes a tight corner braking phenomenon, and therefore it is possible to prevent a tight corner braking phenomenon in advance even at a turning radius that does not cause a tight corner braking phenomenon. Therefore, it is necessary to set the driving force distribution of the two-wheel drive tendency rather than the four-wheel drive tendency of the driving force distribution focusing on the start acceleration performance, and it is difficult to always obtain a high start possibility.

In addition, there is a method of estimating the turning radius from the start using the snake angle when estimating the turning radius, but when the snake angle is small and the turning radius is judged to be a large turning radius, the driving force distribution of the four-wheel drive tendency is assumed. However, if it is determined that the turning radius is such that the snake angle is large and the tight corner braking phenomenon occurs, the driving force distribution of the two-wheel drive tendency must be made in advance before starting, and a high starting driving force is required. On the friction road surface (low μ road surface), it is not possible to achieve torque distribution with an emphasis on high start acceleration performance.
JP 2000-335272 A

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, and to provide a driving force distribution control device for front and rear wheel drive vehicles that can prevent uncomfortable deceleration due to a tight corner braking phenomenon and can realize high start acceleration performance. There is to do.

Driving force distribution control device for a front and rear wheel drive vehicle according to the present invention, the turning state and the acceleration state of the vehicle, as well as detecting the presence or absence of tight-corner braking phenomenon, when detecting the tight-corner braking phenomenon, the engine torque with increasing, when increasing the engine torque, which comprises carrying out the torque limit process of the engine torque with a torque limiter value corresponding to the 4WD engagement force.

According to this, in the prior art, when the tight corner brake phenomenon is detected from the turning state of the vehicle, switching from the four-wheel drive tendency to the two-wheel drive tendency prevents the uncomfortable feeling of deceleration due to the tight corner brake phenomenon. compared to, when detecting the tight-corner braking phenomenon from turning state of the vehicle, along with increasing the engine torque, when increasing the engine torque, torque of the engine torque with a torque limiter value corresponding to the 4WD engagement force By carrying out the limit processing, it is possible to prevent a feeling of strangeness of deceleration due to the tight corner braking phenomenon. As a result, it is possible to achieve both the prevention of an uncomfortable feeling of deceleration due to the tight corner brake phenomenon and the realization of a high start acceleration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a flowchart showing the contents of control as one embodiment of a driving force distribution control device for front and rear wheel drive vehicles according to the present invention.

Starting in S1, it is determined in S2 whether or not the vehicle is turning based on the difference between the left and right wheel speeds of the driven wheels. Whether the vehicle is in a turning state is determined by estimating the turning radius.
Circl_r: Estimated turning radius (m)
a: Turning radius conversion factor 1 (tread on FF vehicle base: tread is the distance between the left and right center of the tire)
b: Turning radius conversion factor 2 (not used on the FF vehicle base)
Assuming that VWJUD_RH is the wheel speed of the right driven wheel and VWJUD_LH is the wheel speed of the left driven wheel, the estimated turning radius circul_r is expressed by the following equation.
[Equation 1]
Circl_r = a * min (VWJUD_RH, VWJUD_LH) / abs (VWJUD_RH−VWJUD_LH) + b

  When the estimated turning radius (m) circul_r <turning determination radius senkai_R, turn determination (f_senkai = 1) is set. The value of the turning discriminating radius senkai_R can be larger than the tight corner turning discriminating radius height_R. According to this, the judgment of the turning state is made earlier than the judgment of the turning state in which the tight corner braking phenomenon occurs. Can be done. Here, an example in which it is determined whether the vehicle is in a turning state using the wheel speed has been described, but lateral acceleration, yaw rate, snake angle, or the like may be used.

If it is determined in S2 that the vehicle is in a turning state, the process proceeds to S3, and driver requested acceleration is calculated.
xg_drrrq: Driver requested acceleration etrq_dr: Driver requested engine torque k_dt1: Engine torque-driving force conversion coefficient (mission gear ratio * final gear ratio / tire dynamic radius)
xg_reg: Running resistance (mainly resistance due to turning)
If wg: vehicle weight, driver required acceleration xg_drrrq is expressed by the following equation.
[Equation 2]
xg_drrrq = (etrq_dr * k_dt1-xg_reg) / wg

  The driver required acceleration may be obtained from a map of accelerator opening, vehicle speed, snake angle, etc., and is equivalent to the acceleration that occurs when the vehicle is turning in a two-wheel drive tendency, with respect to the driver acceleration request operation amount (accelerator opening). Any acceleration that does not give the driver a sense of incongruity is acceptable.

Next, in S4, when the driver required acceleration (xg_drrrq) is larger than the actual acceleration (xgs) by a certain rate or a certain value or more, engine torque increase request determination 1 (f_trqup1) as an increase in driving force is performed.
here,
xgs_trqup: engine torque up threshold value kxg_trqupjdg: engine torque up threshold coefficient (Example 0.15)
Then,
If xg_drrrq-xgs> max (xg_drrrq * kxg_trqupjdg, xgs_trqup), torque-up request determination 1 (f_trqup1) is performed.

In this state, the process proceeds to S5 to check whether the torque increase request is sufficiently accepted, that is, whether the engine torque can be increased.
here,
V_APO: Throttle opening apol: Throttle opening request possible judgment throttle opening threshold (Example 75%)
Then,
When V_APO <apol, torque increase request determination 2 (f_trcup2 = 1) is set.

  Thereafter, the process proceeds to S6, and when the turning state (f_senkai = 1), the torque-up request determination 1 (f_trqup1 = 1) and the torque-up possible determination (f_trqup2), the engine torque-up request value (rq_etrq_ets) is determined. Request torque up.

This engine torque increase request value rq_etrq_ets is
here,
rq_etrq_ets0: engine torque increase request value 0
rq_etrq_ets1: Engine torque increase request value 1 (after engagement torque limiter)
TETS: 4WD fastening force k_dt2: Driving force conversion coefficient (final gear ratio / tire dynamic radius)
rq_etrq_ets: engine torque request
The engine torque increase request value 0 is expressed by the following equation.
[Equation 3]
rq_etrq_ets0 = xg_drrrq-xgs) * wg
The engine torque increase request value 1 is expressed by the following equation.
[Equation 4]
rq_etrq_ets1 = min (TETS * k_dt2, rq_etrq_ets0)
Further, the engine torque request is expressed by the following equation.
[Equation 5]
rq_etrq_ets = rq_etrq_ets1 / k_dt1

  Here, the reason for performing the torque limiter converted from TETS is that the running resistance by the internal circulation torque, that is, the tight corner braking force, does not exceed the clutch engagement torque. As a result, an unnecessary increase in engine torque can be prevented.

  In S2, it is determined that the vehicle is turning (f_senkai = 1). In S4, torque-up request determination 1 (f_trqup1) is performed. In S5, torque-up possible determination 2 (f_trcup2 = 0) is performed. In S7, the 4WD fastening force is reduced. If it is determined, a 4WD fastening force down determination (f_tetsdn1 = 1) is performed in S8, and the 4WD fastening force is reduced. Alternatively, even when the torque increase possibility determination 2 (f_trqup2 = 0) is not made in S5, the 4WD engagement force down determination (f_tetsdn1 = 1) is performed in S8 to decrease the 4WD engagement force.

In addition, the determination of 4WD fastening force down in S7 is
xgs_tstsdn: TETS engagement amount down threshold kxg_tstsdnjdg: driver requested acceleration correction coefficient (Example 0.7)
Then,
It is performed when xg_drrrq * kxg_tetsdnjdg_xgs> xgs_tstsdn.

In addition, the 4WD fastening force is
TETS: 4WD fastening force,
trlim: Control torque lower limit limiter at tight corner,
Then, it is calculated by the following formula. The meaning of applying the tight corner control lower limit limiter trlim is to prevent more torque reduction than necessary. When the running resistance is large and the actual acceleration is low due to a gradient or the like, the 4WD fastening force is lowered too much to improve the 4WD performance. This is because it does not deteriorate significantly.
[Equation 6]
TETS = max (TETS − ((xg_drrrq * wg−rq_etrq_ets) / k_dt2), trlim)

  As described above with reference to the flowchart of FIG. 1, when the tight corner braking phenomenon is detected in S5 and below, it is impossible to increase the driving force, or the amount of increase in the driving force is sufficiently increased. When it cannot be taken, control is performed to reduce the 4WD fastening force. (Equivalent to claim 2)

  According to this, even when the driving force cannot be increased or cannot be sufficiently increased, by reducing the 4WD fastening force, the driving force distribution is made to be a two-wheel drive tendency, and the uncomfortable deceleration due to the tight corner braking phenomenon can be prevented. it can.

  Alternatively, instead of the control described above, the presence or absence of a tight corner brake phenomenon is detected from the turning state and acceleration state of the vehicle, and when the tight corner brake phenomenon is detected, the driving force is increased and the 4WD fastening force is increased. It can also be reduced. (Equivalent to claim 3)

According to this, it is possible to prevent an uncomfortable feeling of deceleration due to the tight corner braking phenomenon more smoothly than when either increasing the driving force or reducing the 4WD fastening force is performed.
If it is determined in S2 of FIG. 1 that the vehicle is not in a turning state, if the target acceleration-actual acceleration is less than or equal to a predetermined threshold value in S4, or if it is determined in S7 that the 4WD fastening force is not reduced, the process proceeds to S9. And perform normal control.

FIG. 2 is a system configuration diagram of a front and rear wheel drive vehicle to which the driving force distribution control device for front and rear wheel drive vehicles according to the present invention can be applied.
The engine 1 is disposed on the front wheel side, and the driving force is transmitted to the rear wheel 6 as the driving wheel via the transmission 2, the transfer 3, the rear propeller shaft 4, and the rear final drive 5, and the transmission 2, 4WD clutch 7 Then, it is transmitted to the front wheel 10 as a driven wheel via the front propeller shaft 8 and the front final drive 9. The driving force distribution ratio of the front and rear wheels is changed by controlling the 4WD engagement force of the 4WD clutch 7 by the 4WD controller 11.

  A front wheel speed sensor 12 and a rear wheel speed sensor 13 are provided on the front wheel 10 and the rear wheel 6, respectively, and the respective wheel speeds detected by the sensors are input to the 4WD controller 11. The 4WD controller 11 is connected to the engine control unit 14 by CAN, and outputs an engine torque increase request signal from the 4WD controller 11 to the engine control unit 14. The engine control unit 14 sends an estimated value or actual measurement of the engine torque to the 4WD controller 11. Value and driver request engine torque are output. A vehicle body (not shown) is provided with an acceleration G / yaw rate sensor 15 and a snake angle sensor 16, and the acceleration G, yaw rate and snake angle detected by these sensors are input to the 4WD controller 11.

FIG. 3 is a schematic diagram showing the contents of control by the driving force distribution control device for front and rear wheel drive vehicles according to the present invention.
3, the horizontal axis represents time, the vertical axis in FIG. 3 (a) is the turning radius, the vertical axis in FIG. 3 (b) is the targeted speed and actual acceleration, and in FIG. 3 (c). The vertical axis represents the accelerator opening and the throttle opening, the engine torque and the driver request engine torque in FIG. 3 (d), and the 4WD engagement torque in FIG. 3 (e).

  As shown in FIG. 3A, when the turning radius is equal to or less than the threshold value 17, a tight corner braking phenomenon occurs. In this case, the control performed to prevent the uncomfortable feeling of deceleration due to the tight corner braking phenomenon is performed in the region α where the accelerator opening is small and the engine torque can be sufficiently increased as the driving force as shown in FIG. Then, the throttle valve opening is increased as shown in FIG. 3 (c), and the engine torque is increased as shown in FIG. 3 (d).

As shown in FIG. 3A, in the region β where the accelerator opening is large and the engine torque cannot be increased sufficiently, the throttle valve opening is increased as shown in FIG. The engine torque is increased as shown in FIG. 3B, and the 4WD fastening force is reduced simultaneously as shown in FIG.
As shown in FIG. 3A, in the region γ where the accelerator opening is fully open and the engine torque cannot be increased, the 4WD fastening force is reduced as shown in FIG.

  As a result, as shown in FIG. 3B, the actual acceleration can be made to coincide with the target acceleration, thereby preventing the uncomfortable deceleration caused by the tight corner braking phenomenon. A broken line in FIG. 3B indicates an actual acceleration when the control according to the present invention is not performed.

  In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible.

  The driving force distribution control device for front and rear wheel drive vehicles according to the present invention is suitable for use in front and rear wheel drive vehicles, and can achieve both prevention of uncomfortable deceleration due to the tight corner braking phenomenon and high start acceleration performance. It can be done.

It is a flowchart which shows the control content which is one Embodiment of the driving force distribution control apparatus of the front-and-rear wheel drive vehicle which concerns on this invention. 1 is a system configuration diagram of a front and rear wheel drive vehicle to which a driving force distribution control device for front and rear wheel drive vehicles according to the present invention can be applied. It is a schematic diagram which shows the control content by the driving force distribution control apparatus of the front-and-rear wheel drive vehicle which concerns on this invention.

Explanation of symbols

1 Engine 2 Transmission 3 Transfer 4 Rear Propeller Shaft 5 Rear Final Drive 6 Rear Wheel 7 4WD Clutch 8 Front Propeller Shaft 9 Front Final Drive 10 Front Wheel 11 4WD Controller 12 Front Wheel Speed Sensor 13 Rear Wheel Speed Sensor 14 Engine Control Unit 15 Acceleration G and yaw rate sensor 16 Snake angle sensor

Claims (2)

From the turning state and the acceleration state of the vehicle, as well as detecting the presence or absence of tight-corner braking phenomenon, when detecting the tight-corner braking phenomenon, along with increasing the engine torque,
A driving force distribution control device for front and rear wheel drive vehicles, wherein when the engine torque is increased, torque limit processing of the engine torque is performed using a torque limiter value corresponding to a 4WD fastening force . When detecting the tight-corner braking phenomenon, if it is impossible to increase the driving amount, or in case of insufficient take the increased amount of the driving force, characterized by reducing the 4WD engagement force The driving force distribution control device for a front and rear wheel drive vehicle according to claim 1.

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