JP2662959B2 - Slip detector for four-wheel drive vehicles - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slip detection device used for traction control or the like for preventing wheel slip in a full-time four-wheel drive vehicle with a center differential device. 2. Description of the Related Art Regarding slip of a four-wheel drive vehicle with a center differential,
There is a two-wheel slip on one of the front and rear wheels and a four-wheel slip on both. Here, in the case of a two-wheel slip, the slip can be eliminated by diff-locking the center differential, but the turning performance is significantly deteriorated because the differential limit is uniquely determined. Further, when the differential lock is performed, the slip state of the wheel cannot be determined, and therefore, it is impossible to automatically control the release of the differential lock. Therefore, such a differential lock is generally operated manually at the time of emergency evacuation or when traveling on a special low μ road such as a snowy road. Therefore, in recent years, regarding the two-wheel slip, it has been considered to control the torque split so as to increase the torque distribution of the grip-side wheels. In such torque split control, two-wheel slip is avoided by torque distribution between the front and rear wheels, so that the turning performance of the center differential is not lost,
Driving force is also ensured, which has a traction effect. Further, in this case, since the rotation difference between the front and rear wheels is always feedback-controlled to the target value, the normal control is immediately performed as soon as the slip escape state occurs in the two wheels. Here, if the torque split control for the two-wheel slip is performed, the torque is distributed as much as possible without causing the two-wheel slip.
Wheel slip occurs, and the higher the accuracy of torque split control, the less likely it is for two-wheel slip to occur and the better the marginal performance, but the more difficult it is to control when four wheels slip at the same time, and this four-wheel slip is eliminated by torque split. It is not possible to do so, and there is no other choice but to rely on traction control to lower the power by lowering the engine output. Thus, the traction control for reducing the torque split and the power of the four-wheel drive vehicle is performed in relation to the wheel slip, so that slip detection is required. Here, in a four-wheel drive vehicle, since four wheels are drive wheels and there is a possibility of slip, detecting a slip of two or four wheels only with this wheel speed increases the error, and therefore, the detection accuracy is reduced. It needs to be devised to improve. Conventionally, with respect to slip detection of a four-wheel drive vehicle, for example, there is a prior art in Japanese Utility Model Laid-Open No. 59-99827. Here, a vehicle speed sensor for detecting the speed of the vehicle and a tire rotation sensor for detecting the rotation of the tire are shown, and the idling of the tire is detected based on the vehicle speed and the rotation of the tire. However, if the prior art vehicle speed sensor is attached to, for example, a transmission output side and calculates the vehicle speed based on its rotation, the vehicle speed sensor calculates the vehicle speed based on the actual vehicle speed at the time of driving wheel slip. The value is greatly out of range. Also, four-wheel slip cannot be detected. In view of the foregoing, an object of the present invention is to provide a slip detection device capable of detecting a four-wheel slip and a grip of a four-wheel drive vehicle with high accuracy. [MEANS FOR SOLVING THE PROBLEMS] In order to achieve the above object, the present invention relates to a slip detection device for a four-wheel drive vehicle, a front and rear wheel speed detection unit for detecting front and rear wheel speeds, and a vehicle body acceleration detection. A two-wheel slip detector for determining one of the front and rear wheel slips from the front and rear wheel speeds, a wheel speed calculator for calculating a wheel speed obtained by averaging the front and rear wheel speeds, A vehicle speed calculation unit for calculating the vehicle speed by integrating the acceleration, and a two-wheel slip detection by the two-wheel slip detection unit,
A four-wheel slip detection unit that determines a four-wheel slip when a deviation between the wheel speed and the vehicle body speed is equal to or greater than a predetermined value. In addition, after the four-wheel slip detection by the four-wheel slip detection unit, a four-wheel grip detection unit that determines that the wheel is a four-wheel grip when a deviation between the wheel speed and the vehicle speed becomes equal to or less than a second predetermined value. It is characterized by the following. Further, when the two-wheel slip is detected by the two-wheel slip detector, torque split control of the four-wheel drive vehicle is performed,
When the four-wheel slip is detected by the four-wheel slip detection, traction control for reducing the engine output is performed. According to the above configuration, under the conditions of slip or grip of four wheels excluding the slip condition of one of the front and rear wheels, if the wheel speed becomes equal to or more than the set value for slip with respect to the vehicle speed due to the vehicle acceleration, the four wheel slip. Is determined, and when the wheel speed becomes equal to or less than the set value for grip in the four-wheel slip state, the four-wheel grip is determined. Thus, in the present invention, under the conditions excluding the two-wheel slip,
The four-wheel slip and the grip can be accurately detected using the vehicle speed due to the vehicle acceleration. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, as a drive system of a four-wheel drive vehicle capable of performing traction control with a torque split and a traction control to which the present invention is applied, a front engine which is vertically installed and has an automatic transmission with a torque converter. In other words, the engine 1, the torque converter 2, and the automatic transmission 3 are arranged in the front-rear direction of the vehicle, and are connected so that power can be transmitted. The output shaft 4 of the automatic transmission 3 is input to a center differential device 20, and a torque split device 25 is provided in the center differential device 20 in a bypass manner. The center differential device 20 is of a planetary gear type and includes a sun gear 21, a ring gear 22, a pinion 23 meshing with the sun gear 21 and the ring gear 22, and a carrier 24.
4, the transmission output shaft 4 is coaxially connected. Also, the sun gear 21 and the ring gear 2 on the two output sides of the center differential device 20
2, the large-diameter ring gear 22 is connected to a front drive shaft 7 parallel to the output shaft 4 via reduction gears 5 and 6 rotatably provided on the transmission output shaft. The gears are transmitted to the left and right front wheels 10L and 10R via the differential device 8 and the axle 9. On the other hand, the small-diameter sun gear 21 is connected to the rear drive shaft 11, and the rear drive shaft 11 is configured to transmit power to the left and right rear wheels 14L, 14R via the rear differential device 12, the axle 13, and the like. Thus, the center differential device 20 transmits the transmission output to the front and rear wheels with a predetermined torque distribution, and absorbs the rotation difference between the front and rear wheels. Here, the above-described drive system corresponds to the case where the front side of the vehicle body has a larger static load than the rear side, and the torque transmitted from the ring gear 22 to the front wheels is larger than the torque transmitted from the sun gear 21 to the rear wheels. ing. The torque split device 25 has a bypass shaft 26 coaxial with the front drive shaft 7 and a hydraulic clutch 27 as a clutch capable of variably controlling the torque. The bypass shaft 26 is connected to a hub 27a of the hydraulic clutch 27, and its drum 27b is Gear 2
It is configured to transmit power to the rear drive shaft 11 via 8, 29. Here, the reduction gears 5 and 6 are also components in this case, and the gear ratio thereof is set to, for example, “1”, and the gear ratios of the gears 28 and 29 are set slightly smaller than that. Also hydraulic clutch
Numeral 27 is such that clutch torque can be generated by supply of hydraulic oil from the hydraulic unit 30. Thus, in the hydraulic clutch 27, the drum 2 is
7b produces a slightly lower rotation difference, and when clutch pressure is applied to the hydraulic clutch 27 to generate clutch torque, the torque moves from the front wheel side of the hub 27a to the rear wheel side of the drum 27b according to the clutch pressure and the like. To vary the torque distribution between the front wheel side and the rear wheel side. That is, assuming that the input torque of the center differential device 20 is Ti and the front side distribution ratio of the center differential device 20 is γ, the transmission torque of the front drive shaft 7 is γ
The torque of the rear drive shaft 11 is allocated to (1−γ) · Ti. Therefore, assuming that the clutch torque is Tc and the gear ratio of the gears 28 and 29 is K, the torque TF and TR of the front drive shaft 7 and the rear drive shaft 11 by the torque movement are as follows: TF = γ · Ti−Tc TR = (1− γ) · Ti + KTc. Thus, the distribution ratio of the front side torque TF continuously changes below the distribution ratio in the center differential device 20 due to the change in the clutch torque Tc, and the distribution ratio of the rear side torque TR continuously increases above the distribution ratio in the center differential device 20. And acts as a torque split. An actuator 16 such as a motor is attached to the throttle valve 15 of the engine 1, and the actuator 16 enables electronic control of the throttle valve opening. As the electronic control system, left and right front wheel and rear wheel speed sensors 40
L, 40R, 41L, 41R, a vehicle body acceleration sensor 42, an accelerator opening sensor 43, a throttle opening sensor 44, and a steering angle sensor 45. These sensor signals are input to the control unit 50.
The control unit 50 processes the sensor signal to determine a slip state, and outputs a clutch pressure control signal to the hydraulic unit 30 and a throttle control signal to the actuator 16. In FIG. 2, the control unit 50 will be described. The control unit 50 includes a slip detection unit 51, a torque split control unit 52, and a traction control unit 53 for reducing power.
Having. The slip detector 51 includes a front wheel speed calculator 54 to which the left and right front wheel rotation speeds NFL and NFR of the rotation speed sensors 40L and 40R are input, and a rear wheel to which left and right rear wheel rotation speeds NRL and NRR of the rotation speed sensors 41L and 41R are input. The calculation unit 55 is provided. The front and rear wheel speeds NF and NR are calculated by the front wheel speed calculation unit 54 and the rear wheel speed calculation unit 55 as follows. NF = (NFL + NFR) / 2 NR = (NRL + NRR) / 2 The front and rear wheel speeds NF and NR are input to a front wheel slip detecting unit 56, and a target front and rear wheel speed difference setting unit 62 is used based on an output value λ from the steering angle sensor 45 and the like. Target front and rear wheel speed difference Δ theoretically set by
With Ns (≧ 0), to detect the front wheel slip in the case of _{NF-NR> ΔNs + K 1} . The front and rear wheel speeds NF, NR is input to the rear-wheel slip detector 57 detects the rear wheel slip in the case of _{NF-NR <ΔNs-K 2} . Here, K ₁ and K ₂ are dead zone widths determined by the accuracy of the rotation speed sensor. These two-wheel slip signals are input to the torque split control unit 52, and in the case of front wheel slip, the amount of movement torque from the front wheel side to the rear wheel side is increased together with the clutch pressure of the hydraulic clutch 27 to distribute torque toward the rear wheel. In the case of rear wheel slip, the clutch pressure is reduced to control the torque distribution toward the front wheels, and this clutch pressure control signal is output to the hydraulic unit 30 that supplies the clutch pressure to the hydraulic clutch 27. On the other hand, the front and rear wheel speeds NF and NR are input to the wheel speed
The wheel speed V corresponding to the vehicle speed on the wheel average is calculated as follows. V = (NF + NR) / 2 Further, the vehicle body acceleration G of the vehicle body acceleration sensor 42 is input to the vehicle body acceleration calculating section 59, and the vehicle body acceleration G is integrated as follows to calculate the vehicle body speed Vg corresponding to the vehicle speed. Vg = ∫Gdt These wheel speed V and body speed Vg are the four-wheel slip detector
60, where the front wheel slip detector 56,
The two-wheel slip signal of the rear-wheel slip detection unit 57 is input, and the following determination is made only under the four-wheel slip or grip condition other than the two-wheel slip condition. That is, V>
From the relationship of Vg, a speed difference ΔV between the two is obtained by ΔV = V−Vg, and using a predetermined slip setting value ΔVs, ΔV> ΔVs
In the case of, a four-wheel slip is detected. The signal of the four-wheel slip is input to the traction control unit 53 for reducing the power, and at the time of the four-wheel slip, a throttle control signal corrected so as to restrict the engine output by reducing the throttle opening is output. The four-wheel slip detecting unit 60 has a four-wheel grip detecting unit 61. The output of the four-wheel throttle detecting unit 60 is input together with the wheel speed V and the vehicle speed Vg. 4-wheel grip detector 61
Has a grip setting value ΔVs ′ smaller than the grip setting value ΔVs, for example, and ΔV <ΔVs ′ after four-wheel slip detection.
In this case, the four-wheel grip is detected, and the traction control unit 53 that reduces the power is gradually returned, for example, to control the throttle opening to follow the accelerator opening. Next, the operation of the four-wheel drive vehicle configured as described above will be described. First, when the automatic transmission 3 is shifted to a drive range such as a drive (D) while the vehicle is running, the power of the engine 1 is input to the automatic transmission 3 via the torque converter 2 and the power for shifting is output. Carrier 24 of center differential device 20
To communicate. The ring gear 22 and the sun gear 21 distribute the static load to the front and rear wheels at a torque distribution ratio of, for example, 60:40 to the wheels of the vehicle. The power from the ring gear 22 is transmitted through the reduction gears 5, 6, the front drive shaft 7, the front differential device 8, etc., to the front wheels 10L, 10R.
Further, the power from the sun gear 21 is transmitted to the rear wheels 14L, 14R via the rear drive shaft 11, the rear differential device 12, and the like, and thus, a full-time four-wheel drive traveling with a center differential is provided. At this time, the hydraulic clutch 27 of the torque split device 25
Is rotated with a rotation difference caused by the gear ratio between the reduction gears 5, 6 and the gears 28, 29, so that torque can be transferred to the rear wheels. On the other hand, various information is detected by each sensor of the electronic control system, and is input to the control unit 50. Then, various controls are performed by detecting a two-wheel or four-wheel slip. This will be described with reference to the flowchart of FIG. First, the slip flag is cleared and initialized, and the front wheel speed calculation unit 54 and the rear wheel calculation unit 55 of the slip detection unit 51 are set.
Calculates the front and rear wheel speeds NF and NR, and this is the front wheel slip detector
56, which is input to the rear wheel slip detector 57, and the difference between the two is compared with the target front and rear wheel speed difference ΔNs. Then, ΔNs−K ₂ <NF−
NR <detecting a slip of the front wheels or the rear wheels when the condition is not satisfied in .DELTA.Ns + K _1, inputs the slip signal to the torque split controller 52, the clutch pressure control signal corresponding to the slip state is input to the hydraulic unit 30 Hydraulic clutch
Control 27 clutch pressures. Therefore, in front wheel slip, torque split control is performed to increase torque distribution toward the rear wheel by increasing the clutch pressure, and in rear wheel slip, torque split control is performed to distribute torque toward the front wheel by decreasing the clutch pressure, thereby ensuring the driving force,
Shift to avoid slip. If two-wheel slip does not occur, torque split control is performed by other factors according to the running conditions. On the other hand, the four-wheel slip detection unit 60 can detect the wheel speed under conditions other than the two-wheel slip condition, and obtains a difference ΔV between the wheel speed V and the speed Vg obtained by integrating the vehicle acceleration G. Here, when the slip flag is cleared, the slip flag is compared with the slip set value ΔVs. When the difference ΔV is smaller than the slip set value ΔVs,
That is, when the wheel speed V increases substantially along the vehicle speed Vg, it is determined that the vehicle is traveling stably, and a throttle control signal corresponding to the accelerator opening is input to the actuator 16 from the traction control unit 53 that reduces the power. By opening and closing the throttle valve 15, the throttle opening is controlled so as to correspond to the accelerator opening. On the other hand, only the wheel speed V sharply increases as shown in FIG.
If the slip set value ΔVs or more is reached, at this time t ₁ , a four-wheel slip is detected, a slip flag is set, and the traction control unit 53 narrows the throttle opening. As a result, the output of the engine 1 decreases, and the wheel speed V
Rise is suppressed and falls. During this four-wheel slip enables detection four-wheel grip detection unit 61, after the four-wheel slip detection, the difference between the wheel speed V and the vehicle speed Vg becomes a set value .DELTA.Vs' or grip, 4-wheel at the time t ₂ Detects grip and clears slipblag. Therefore, the throttle opening gradually returns to its original value, and the wheel speed V increases with the engine output. Such control is repeated once or several times to avoid a four-wheel slip, and the wheel speed V is reduced to the vehicle speed. The speed substantially follows the speed Vg. Although the embodiment of the present invention has been described above, the front and rear wheel speeds N
F and NR may be directly detected by the drive system. The torque split control for two-wheel slip is not limited to the above. Various values of the set values ΔVs, ΔVs ′ for slip and grip can be selected, and may be changed by other factors. In this embodiment, the traction control unit for reducing the power is configured to adjust the throttle opening. However, the present invention is not limited to this, and the power may be reduced by brake control, ignition timing control, or the like. good. As described above, according to the present invention, in a four-wheel drive vehicle, four-wheel slip can be accurately detected based on the wheel speed and the vehicle body speed based on the vehicle body acceleration. Since the detection of the four-wheel slip is performed under the condition of the slip or grip of the four wheels other than the condition of the two-wheel slip, confusion between the two can be prevented. Since the detection of the four-wheel grip after the detection of the four-wheel slip is performed using each set value different from the case of detecting the four-wheel slip, the four-wheel grip can be optimally detected together with the four-wheel slip. By detecting the slip and grip of the four wheels, the throttle control is most effectively performed, and the slip of the four wheels can be accurately prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram schematically showing a four-wheel drive vehicle to which the present invention is applied, FIG. 2 is a block diagram of an embodiment of a slip detecting device and a control system, and FIG. FIG. 4 is a time chart showing a state in which four-wheel slip is prevented. 51: Slip detecting unit, 54: Front wheel speed calculating unit, 55: Rear wheel speed calculating unit, 58: Wheel speed calculating unit, 59: Body speed calculating unit, 60: 4-wheel slip detecting unit, 61 …… 4 wheel grip detector

Claims (1)

(57) [Claims] 1. In a slip detection device for a four-wheel drive vehicle, a front and rear wheel speed detection unit for detecting front and rear wheel speeds, a vehicle body acceleration detection unit for detecting vehicle body acceleration, and the front and rear wheels A two-wheel slip detector for determining one of the front and rear wheels from two-wheel slip, a wheel speed calculator for calculating a wheel speed obtained by averaging the front and rear wheel speeds, and a vehicle body for integrating the vehicle acceleration to obtain a vehicle speed A speed calculating unit; and a four-wheel slip detecting unit that determines a four-wheel slip when a deviation between the wheel speed and the vehicle speed is equal to or more than a predetermined value except when the two-wheel slip is detected by the two-wheel slip detecting unit. A slip detection device for a four-wheel drive vehicle. 2. After the four-wheel slip detection by the four-wheel slip detection unit, a four-wheel grip detection unit that determines a four-wheel grip when a deviation between the wheel speed and the vehicle speed becomes equal to or less than a second predetermined value. Claims 1
Item 4. A slip detection device for a four-wheel drive vehicle according to claim 1. 3. When the two-wheel slip is detected by the two-wheel slip detector, the torque split control of the four-wheel drive vehicle is performed.
The slip detection device for a four-wheel drive vehicle according to claim 1, wherein traction control for reducing engine output is performed when four-wheel slip is detected by detecting wheel slip.