JPH04169328A - Unequal torque distributional controller of four-wheel driving car - Google Patents

Abstract

PURPOSE:To ensure the prevention of slipping of four wheels, so as to ensure stable operability by judging the slipping of four wheels easily and appropriately based on the wheel acceleration in a slip mode, and by carrying out up-shifting through the judgement of the slipping of four wheels. CONSTITUTION:Each detection signal of the rotational number of front wheel, the rotational number of rear wheel, a shift position, and of throttle opening, from each sensor 40-45, is input to a control unit 50, while a car speed and a front/rear rotational ratio are calculated by each calculation part 51, 52. Each signal is input to each mode judging part 53-59, so as to judge each running condition of normal mode, starting, turning and steering, slipping, braking, one-range, and of ABS control. The acceleration of wheel is detected by an acceleration detection part 75 to which the rotational number of front/rear wheel is input. The acceleration and the slip signal of a slip mode judging part 56 are input to a four wheel slipping judging part 76, so as to judge whether there is slipping of four wheels, while the signal of slipping of four wheels is input to a speed change step set part 77, and by selecting a fixed high speed step, a shift signal is output to an automatic transmission 3.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a four-wheel drive vehicle that is equipped with a center differential device and whose torque distribution is controlled. The present invention relates to an unequal torque distribution control device, and specifically relates to measures to prevent four-wheel slippage when slipping on a low μ road.

[Conventional technology]

In a full-time four-wheel drive vehicle equipped with a center differential device, the standard torque distribution of the center differential device is set to be biased toward the rear wheels. Furthermore, a differential limiting device is attached to the center differential device to electronically control the differential limiting torque between the vehicle weight distribution when the rear wheel bias is directly connected. This unequal torque distribution control system always causes the rear wheels to slip first to prevent four-wheel slip, improves maneuverability, turning performance, etc. with FR-oriented driving, and provides a wider control range. Already proposed by the applicant. In this wide control range, it has been developed to appropriately determine differential limiting torque according to each driving condition and to perform optimal electronic control.

In the unequal torque distribution control system based on rear wheel bias, when a slip occurs on a low μ road, the differential limiting torque is controlled to increase in slip mode according to the slip condition, and the front wheel This is designed to avoid slipping on one side of the rear wheels. However, when the differential limiting torque is increased, the drive system tends to be directly connected, which may cause four-wheel slip under the worst driving conditions. When this four-wheel slip occurs, steering stability deteriorates, so
Even if drivability is reduced in consideration of safety, it is necessary to reliably prevent four-wheel slippage, and for this reason, it is desirable to be equipped with measures to prevent four-wheel slippage.

Therefore, regarding the above-mentioned slip prevention measures, there is a prior art, for example, in Japanese Patent Application Laid-Open No. 61-70254.

Here, it is shown that if the difference between the vehicle speed calculated from the actual vehicle speed and the output shaft rotational speed is equal to or greater than a set value, slipping is determined and the transmission is upshifted to prevent the recurrence of slipping.

[Problem to be solved by the invention]

By the way, in the prior art described above, since the upshift is performed immediately upon detection of a slip, even if the steering stability is sufficient even if one of the front and rear wheels slips, the drivability is significantly reduced. Therefore, such measures are desirable for use in emergencies that cannot be prevented by other means.

The present invention has been made in view of the above, and its purpose is to control the unequal torque distribution to control the torque between the front and rear wheels in a wide range of vehicle weight distribution from rear wheel bias through differential limiting torque. An object of the present invention is to provide an unequal torque distribution control device for a four-wheel drive vehicle that can reliably detect four-wheel slip when slip occurs and can prevent the four-wheel slip.

Means for Solving Problem C] In order to achieve the above object, the unequal torque distribution control device for a four-wheel drive vehicle of the present invention includes a center differential device that sets a reference torque distribution to an unequal torque distribution with a bias toward the rear wheels. In a four-wheel drive vehicle with a center differential device that has a differential limiting device Z that controls the front wheel biased torque distribution by limiting the differential, the control unit that controls the differential limiting device controls at least the rotation ratio of the front and rear wheels. a slip mode determining means for determining whether a front or rear wheel slip has occurred, a torque setting means for setting a basic torque according to the state when a slip occurs, and a differential limiting torque based on the basic torque and a correction coefficient during steering. a differential limit torque calculation means for calculating a differential limit torque; a four-wheel slip determination means for determining four-wheel slip from wheel acceleration in slip mode; and a gear setting means for outputting a shift signal for a predetermined high-speed gear when four wheels slip. It is equipped with the following.

[For production]

Based on the above configuration, when the vehicle is running in four-wheel drive, the control unit determines whether or not at least one of the front and rear wheels is slipping, and when slipping occurs, the differential limiting torque of the differential limiting device is controlled to increase to prevent slipping. do. In this slip mode, when the drive system is substantially directly connected, four-wheel slip is reliably determined when the wheel acceleration exceeds a set value.

At this time, the vehicle is controlled to upshift to a high speed gear and reduce the wheel driving force, thereby appropriately preventing four-wheel slip and preventing deterioration of steering stability.

〔Example〕

Hereinafter, practical examples of the present invention will be explained based on the drawings.

In Fig. 2, the outline of the drive system of a full-time four-wheel drive vehicle equipped with a center differential device is described. The reference numeral 1 is the engine, 2 is the clutch, and 3 is the transmission. The output shaft 4 of the transmission is at the center. It is input to the differential device f20. A front drive shaft 5 outputs to the front of the center differential device 2o, and a rear drive shaft 6 outputs to the rear of the center differential device 2o. to the left and right front wheels 9 via the axle 8,
The rear drive shaft 6 is a propeller shaft 10. Rear differential device 11. It is connected to the left and right rear wheels 13 via an axle [2] to form a power transmission structure.

The center differential device 20 is of a composite planetary gear type, and has a first sun gear 2 integrated with the transmission output shaft 4.
1. A second sun gear 22 integrated with the rear drive shaft 6. The first pinion 23 gear 23a of the binion 23 is connected to the first sun gear 21, and the second pinion 23 gear 23 is connected to the first sun gear 21.
3b mesh with the second sun gear 22, respectively. In addition, a drive gear 25 of a beam reduction is attached to the transmission output shaft 4.
is rotatably provided, and a pinion 23 is pivotally supported by a carrier 24 that is integrated with the drive gear 25. The drive gear 25 is configured to mesh with a driven gear 26 that is integrated with the front drive shaft 5.

On the other hand, the center differential device 20 includes:
A hydraulic clutch 27 is attached as a differential limiting device. This hydraulic clutch 27 moves the drum 27a to the carrier 2 using the immediate force of the center differential device 20, for example.
4, the /1 tabs 27b are respectively coupled to the rear drive shaft 6 and arranged coaxially.

With this configuration of the center differential device 20, the shift power input to the first sun gear 21 is transferred to the carrier 2.
4 and second sun gear 22 in a predetermined reference torque distribution. Furthermore, the difference in rotation between the front and rear wheels during turning is absorbed by the planetary rotation of the binion 23. Here, the reference torque distribution is freely set based on the pitch circle radius of the four gear meshes of the two outer gears 21 and 22 and the two pinion gears 23a and 23b. Therefore, the standard torque distribution e'rs for front wheel torque TF and rear wheel torque TR is
For example, it is possible to set the weight to be sufficiently biased to the rear wheels as shown below.

e TS-TF: TR"=34: 6B In the case of a front engine installation, the static weight distribution ew between the front wheel weight WF and the rear wheel weight WR of the vehicle is, for example, as follows.

e w = WF + Wit≠62:38 Therefore, in the case of direct connection due to differential restriction of the hydraulic clutch 27, torque is distributed to the front wheels in accordance with this weight distribution. As described above, by controlling the differential limiting torque of the hydraulic Kurasochi 27, it is possible to control the torque distribution between the front and rear wheels in a wide range between the standard torque distribution eTs with a biased weight on the rear wheels and the weight distribution ew with a biased weight on the front wheels. It becomes possible.

Next, the hydraulic control system of the hydraulic clutch 27 will be described.

First, when the transmission is an automatic transmission, it is configured using line pressure obtained by regulating the oil pressure of the oil pump 30 of the hydraulic control system with the regulator valve 31. Therefore, the line pressure oil passage 32 is connected to the clutch control valve 33. It communicates with the hydraulic clutch 27 via an oil passage 34. The line pressure oil passage 32 also communicates with a solenoid valve 38 through an oil passage 37 having a pilot valve 35 and an orifice 3B, and duty pressure from the solenoid valve 38 acts on the control side of the clutch control valve 33 via an oil passage 39. . The solenoid valve 38 is connected to the control unit 5
When a duty signal corresponding to each running condition from 0 is input, the hydraulic pressure is drained to generate duty pressure, and the clutch control valve 33 is operated according to this duty pressure, and the differential of the hydraulic clutch 27 is The limit torque is variably controlled.

Referring to FIG. 1, an electronic control system of an embodiment of the unequal torque distribution control device of the present invention, which is applied to the above-mentioned four-wheel drive vehicle, will be described.

First, the front wheel rotation sensor 40 detects the rotation speed NF of the front wheels as input information. Rear wheel rotation sensor 41 that detects the rotation speed Nλ of the rear wheel. A throttle opening sensor 42, a shift position sensor 43 that detects the shift position of the transmission. Brake switch 44. It has an engine rotation speed sensor 45 and the like.

The control unit 50 includes a vehicle speed detection section 511 and a longitudinal rotation ratio calculation section 52 to which the front wheel rotation speed NF and the rear wheel rotation speed N are input. When the engine speed Ne is equal to or higher than the set value, the vehicle speed detection unit 51 detects, for example, the front wheel rotation speed NF and the rear wheel rotation speed N11j.
The vehicle speed V is calculated from the average value of .

The longitudinal rotation ratio calculation unit 52 calculates slip, steering, and other driving conditions that are important in this control, as well as conditions such as slip.
This is provided considering that judgment and detection can be made based on the rotation ratio. Therefore, the rotation ratio eN is set as follows using the front wheel rotation speed NF and the rear wheel rotation speed NH.

e N-N FL / NF In addition, the control unit 50 controls the vehicle speed V1 longitudinal rotation ratio e
N + Normal mode determination unit 531 to which signals of throttle opening θ and shift position are input Start mode determination unit 54. Steering mode determination section 55. It has a slip mode determination section 56. Also, a braking mode determining section 57 receives the throttle opening θ and the brake switch signal, and a lunge mode determining section 58 receives the lunge signal at the shift position. It has an ABS mode determination section 59 to which ABS operation and brake switch signals are input.

The normal mode determination section 53 determines the normal driving state based on the shift position of forward 1st to 4th speed or reverse speed, and θ, ■.The torque setting section 60 uses this mode determination signal to determine the differential limiting Define the basic torque Tc1.

Torque Tc1 is given to the torque setting section 60 by a map in the relationship between θ and V for each shift position, and the map M1 for 1st speed or reverse speed shows that torque Tc1 is θ as shown in FIG. 3(a). An increasing function is set for , and a decreasing function is set for ■. That is, in the region where θ is small, the torque Tc1 is reduced to prevent the tight corner braking phenomenon during large steering turns, and in this case, the lower V is, the more the torque Tc1 is increased to improve running performance.

On the other hand, if the high speeds of 2nd and higher gears are set in the same manner as the above map, when the accelerator is released after turning and accelerating in high speeds, the torque will decrease as θ decreases, and the rear wheel brake torque will increase. Tends to spin. Therefore, in the map M2 for the second or higher speed gears, as shown in FIG. 2(b), the torque Tc1 is set to be large in the region where θ is small, so that the differential limiting torque is increased and maintained even after the accelerator is released.

The start mode determination unit 54 determines whether to start traveling if V is zero and the rotation ratio eN is equal to or greater than a set value, and it is determined that the vehicle is traveling straight. Then, using this mode determination signal, the torque setting section 6I determines the torque Tc2 at the time of starting. In this case, the torque Tc2 is set by a high level increasing function with respect to θ, as shown in map M3 in the same figure (C). has been done.

The slip mode determination unit 56 determines front wheel slip when the rotation ratio eN is less than or equal to a set value, and determines rear wheel slip when it is greater than or equal to the set value. Then, using this slip determination signal, the torque setting section 63 determines the torque Tc3 using a map M4 using θ and V as parameters. In this case, when the rear wheel slips, the torque Tc3 is increased as shown by the solid line in FIG. 2(d), but when the front wheel slips, the torque Tc3 is decreased as shown by the broken line.

Furthermore, the steering mode determination $59 is determined when the rotation ratio eN is within the range between the lower limit setting value for full steering and the upper limit setting value for minute steering.
Determine whether the vehicle is turning by turning the steering wheel. In this steering mode, the torque during traveling in each of the above modes may be corrected to decrease so as not to cause a tight corner braking phenomenon. Therefore,
In the correction coefficient setting section 62, as shown in map M5 in FIG. The correction coefficient k is determined to be small.

The braking mode determining unit 57 determines normal braking when the throttle is fully open and the ON signal of the brake switch 44 is manually input. Then, in response to this braking signal, the torque setting section 64 sets the differential limiting torque to zero, thereby maximizing the braking performance.

The lunge mode determination unit 58 makes a determination based on the input of the lunge shift signal, and in this case, it forcibly sets the slip mode torque Tc3 to enable escape from the rough road.

Furthermore, the ABS mode determination section 59 turns on the brake switch.
The torque setting section 65 sets a predetermined small torque Tc4 to prompt the wheel rotation to return.

Torques Tc1 to Tc4 set in each of these modes.
The correction coefficient is input to the differential limit torque calculation unit 7o. The calculation unit 7o selects the starting and slipping mode torque Tc2 or Tc3 with priority over the normal mode torque Tc1, and multiplies the selected torque by a correction coefficient k to obtain the differential limiting torque Ts. is calculated as follows.

Ts-kIITc (Tc shoulder Tc1, Tc2, Tc3, Tc4)
The differential limiting torque Ts is manually inputted to the duty ratio conversion section 71, and the torque Ts is converted into a duty ratio using a conversion map M6 of <n in the figure, and the signal of this duty ratio is sent to the drive section 72. The output signal is configured to be output to the solenoid valve 38 via the solenoid valve 38.

Next, measures to prevent four-wheel slippage will be explained.

In a configuration in which torque distribution is controlled using differential limiting torque as in this example, when one of the front and rear wheels slips, the slip is prevented by increasing the differential limiting torque, and the wheels are driven to rotate with the same acceleration as in the non-slip case. are doing. Therefore,
In this slip mode, if the wheel acceleration G is larger than the set value Go corresponding to the normal maximum value (for example, 0.6 G), it can be determined that four-wheel slip has occurred.

Therefore, an acceleration detection section 75 is provided to which the rotation speeds NF and NIt of the front and rear wheels are input, and the acceleration G of the wheels is detected. This acceleration G and the slip signal of the slip mode determination section 56 are 4
The acceleration G in the slip mode is inputted to the wheel slip determination section 76 and compared with the set value GO to determine whether there is a four-wheel slip. The four-wheel slip signal is sent to the gear setting section 77.
is input, a predetermined high speed gear is selected, and the shift signal is output to the automatic transmission 3.

Next, the operation of this embodiment will be explained.

First, when the vehicle is running, the power of the engine 1 is input to the transmission 3 via the clutch 2, and the shifting power is input to the first sun gear 21 of the center differential device 20. Here, since the reference torque distribution is set to be biased toward the rear wheels according to the specifications of each gear of the center differential device 20, the power is distributed to the carrier 24 and the second sun gear 22 according to this torque distribution, and power is output.

On the other hand, at this time, the control unit 50 of the electronic control system records the front wheel rotation speed NF, the rear wheel rotation speed N, and the shift position.

Each signal of the throttle opening θ is input, and the vehicle speed V1 longitudinal rotation ratio eN is calculated. Then, these signals are input to each mode determining section 53 to 59, and one normal start is performed.

The driving conditions of steering, slip, braking, lunge, and ABS control are determined.

Therefore, when starting on a high μ road, the mode determination unit 54 makes a determination, and the high torque Tc2 is determined by the map M3 in this case.
This duty signal is manually applied to the solenoid valve 38. Then, high duty pressure PD acts on the clutch control valve 33 from the solenoid valve 38 of the hydraulic control system,
Correspondingly, the amount of oil supplied to the hydraulic clutch 27 increases, the clutch pressure Pc rises, and a predetermined high differential limiting torque Ts is generated.

Therefore, the differential is limited in the center differential device 20, and the power is bypassed and transmitted from the second sun gear 22 to the carrier 24 side according to the differential limit torque Ts, changing the torque distribution state from being biased to the rear wheels to being biased to the front wheels. Become. Then, power is transmitted from the carrier 24 to the front wheels and from the second sun gear 22 to the rear wheels, resulting in four-wheel drive running with unequal torque distribution as shown at point P2 in FIG. This will accelerate the start.

When the rotational speeds NF and N11l of the front and rear wheels become substantially equal after the vehicle starts, and the rotational ratio eN is within the set value, the determination unit 53 determines that the normal mode is present. At this time, in low gears such as 1st gear and reverse speed, the map M1 sets a relatively low torque Tc1, and based on this, the hydraulic pressure is controlled, and the hydraulic clutch 27
The differential limiting torque Ts is controlled to be low. For this reason, the torque distribution between the front and rear wheels is approximately in accordance with the standard torque distribution, and the torque distribution is biased toward the rear wheels toward point P1 in Fig. 5, resulting in a FR-like, FR-like torque distribution even though it is a four-wheel drive system, resulting in improved turning and maneuverability. becomes better. In this case, especially when turning in a region where θ is small,
The center differential device 20 becomes substantially free, and it becomes possible to turn freely while absorbing the rotational difference ΔN between the front and rear wheels.

Further, when traveling in the above-described start 1 normal mode, under high load conditions where θ is large, the differential limiting torque Ts is controlled to increase, so that the front and rear wheels are more likely to be directly connected to fully exhibit running performance. On the other hand, especially when the steering is performed under such driving conditions, it is detected by the steering mode determining section 55, and the rotation ratio e
A correction coefficient k is set according to N, etc. Then, the larger the steering, the more the differential limiting torque Ts is temporarily corrected to be reduced, and therefore it becomes possible to turn without producing a tight corner braking phenomenon.

When braking is performed by normal brake operation, this is determined by the braking mode determination unit 57, and the differential restriction is canceled, so that sufficient braking performance can be exerted on the four wheels.

Next, when driving on a low μ road, the presence or absence of slip is determined by the slip mode determination unit 56, and when a normal slip occurs, the rear wheels always slip first due to unequal torque distribution with a bias toward the rear wheels, and the four wheels slips are avoided. When this rear wheel slips, the differential limiting torque Ts is controlled to be high by the map M4, thereby limiting the differential of the center differential device 20, and shifting to a front wheel-biased torque distribution as shown at point P3 in FIG. It turns out. Conversely, when front wheel slip is determined, the differential limiting torque Ts is reduced to control the torque distribution to favor the rear wheels.In this way, the control is performed so that the driving force of the non-slip side wheel is constantly increased. Anti-slip.

In addition, in this slip mode, not only when the rotation ratio eN deviates from the set value, but also when the vehicle speed V increases or the throttle opening θ decreases and slip avoidance is determined, the slip mode control is disabled. It is released and returns to normal mode control.

When braking on this low μ road, the wheels lock and the brake system causes A.
When the BS control is activated, the ABS mode determination section 59
It will be judged as follows. In this case, since the differential limiting torque is set to a small value, the ABS control function is promoted by prompting the wheel rotation to return without impairing the braking function.

Furthermore, when shifting to Lunge on rough roads, etc., the differential limiting torque is set to a large value similar to slip mode, improving drivability.

FIG. 6 shows a summary of the mode control under each driving condition described above.

Furthermore, in the slip mode control described above, the flowchart of FIG. 4 is executed. That is, step S
When the slip mode is determined in step I, the process proceeds to step S2, where the wheel acceleration G is compared with a set value Go. Therefore,
If one of the front and rear wheels slips, slip prevention control is performed by increasing the differential limiting torque Tc3 as described above, and the acceleration G becomes equal to or less than the set value GO. Therefore, control is maintained in this slip mode.

On the other hand, under the worst conditions, such as when the road surface is very slippery and the vehicle is driven with increased output in low gears, the differential limiting torque Tc3 becomes maximum and directly connects the drive system to prevent slips to the maximum extent possible. However, on the other hand, this results in a situation where four-wheel slip is likely to occur. Therefore, at this time, if the wheel acceleration G increases to a set value of 60 or more and four-wheel slip occurs, this is immediately detected, the process proceeds from step S2 to step S3, a high gear shift signal is output, and the automatic transmission 3 is automatically upshifted. For this reason, the driving force on the wheel side is rapidly reduced, and four-wheel slip is thereby prevented.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto.

〔Effect of the invention〕

As explained above, according to the present invention, in a four-wheel drive vehicle equipped with a center differential device, in a control system that performs at least slip prevention control using differential limiting torque, there is a means for determining four-wheel slip and upshifting. Since this is added, it is possible to reliably prevent four-wheel slippage, ensure maneuverability, and improve safety.

Since the four-wheel slip is determined based on the wheel acceleration in the slip mode, the four-wheel slip can be easily and appropriately determined.

[Brief explanation of the drawing]

1 is a skeleton diagram showing an electronic control system of an embodiment of the unequal torque distribution control device of the present invention; FIG. 2 is a configuration diagram showing the overall configuration of a four-wheel drive vehicle to which the present invention is applied; Figures (a) to ``)'' show each map, Figure 4 is a flowchart of the action when four wheels slip, Figure 5 is a diagram showing the control state of unequal torque distribution, and Figure 6 is a diagram showing the control state of unequal torque distribution. It is a diagram showing the control state of each mode under each driving condition. 1... Engine, 9... Front wheels, 13... Rear wheels, 2
0...Center differential device, 27...
Differential limiting hydraulic clutch, 33...clutch control valve,
38... Solenoid valve, 50... Control unit, 5
3... Normal mode determining section, 54... Starting mode determining section, 55... Steering mode determining section, 56... Slip mode determining section, 57... Braking mode determining section, 58...
・l range mode determination unit, 59...ABS mode determination unit, 60, 61.83, 84.65...torque setting unit, 62...correction coefficient setting unit, 70...differential limit torque calculation Part, 76... 4-wheel slip judgment part, 77...
Gear stage setting section. Patent Applicant Fuji Heavy Industries Co., Ltd. Agent Patent Attorney Nobu Kobashi Slag Volume Patent Attorney Wataru Ogura Figure 5 Clutch Pressure Pc Figure 6

Claims (1)

[Scope of Claims] A center differential device having a differential limiting device that sets a reference torque distribution to an unequal torque distribution with a biased weight on the rear wheels by limiting the differential of the center differential device to control torque distribution with a biased weight on the front wheels. In a four-wheel drive vehicle, the control unit that controls the differential limiting device includes at least a slip mode determining means that determines the occurrence of slip in the front or rear wheels based on the rotation ratio of the front and rear wheels, and a basic torque determination unit that determines the occurrence of slip in the front or rear wheels when slip occurs. a torque setting means for setting the differential limit torque, a differential limit torque calculating means for calculating the differential limit torque from the basic torque and a correction coefficient during steering, and a four-wheel slip controller for determining the four-wheel slip from the wheel acceleration in slip mode. 1. An unequal torque distribution control device for a four-wheel drive vehicle, comprising a determining means and a gear setting means for outputting a shift signal for a predetermined high speed gear when four wheels slip.