JPH0794206B2 - Transmission torque control device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a transmission torque control means for a four-wheel drive vehicle, and more specifically, it can maintain a constant torque distribution ratio to front and rear wheels. The present invention relates to a transmission torque control means for a wheel drive vehicle.

(Prior Art) As a four-wheel drive vehicle, for example, as shown in Japanese Utility Model Publication No. 56-122630, a first drive shaft directly connected to a power plant including an engine, a transmission, and the like,
A second drive shaft connected to a power plant via a power transmission means such as a clutch mechanism is provided, and two-wheel drive and four-wheel drive can be switched by controlling engagement and disengagement of the clutch mechanism. It is known what can be done.

To adjust the torque distribution ratio to the front and rear wheels in a four-wheel drive vehicle,
For example, it can be performed by adjusting the engaging force of the clutch mechanism for switching between the two-wheel drive and the four-wheel drive described above and controlling the amount of torque transmitted by the clutch mechanism. However, when the torque distribution ratio of the front and rear wheels is adjusted by this mechanism, if the output torque of the power plant fluctuates, the engaging force of the clutch mechanism must be adjusted to change the amount of transmitted torque. The torque distribution ratio cannot be kept constant. This is because the transmission torque of the clutch mechanism fluctuates only due to fluctuations in its engaging force.

In order to control the amount of transmission torque of the clutch mechanism that accompanies fluctuations in the output torque of the power plant, for example, the output torque of the power plant is detected using a torque detector, and the engagement force of the clutch mechanism is adjusted based on the detected amount. Good.
However, the torque detector is extremely expensive, which causes a problem that the entire device becomes expensive.

Therefore, in order to solve this problem, the fact that the rotational speed difference between the front and rear wheels fluctuates with the fluctuation of the output torque of the power plant is utilized, and the amount of transmission torque of the power transmission means is adjusted based on this rotational speed difference. As a result, the torque distribution ratio of the front and rear wheels can be maintained at a desired value.

That is, at least one of the torque transmission paths for transmitting torque from the power plant to the front and rear wheels is provided with a power transmission means for varying the amount of torque transmission, and the power transmission means is variably controlled to distribute the torque to the front and rear wheels. Control 4
In a transmission torque control device for a wheel drive vehicle, output from vehicle speed detecting means for detecting vehicle speed, steering angle detecting means for detecting steering angle, rotational speed difference detecting means for detecting front and rear wheel rotational speed difference, and the three detecting means Control means for receiving the signal and controlling the torque transmission amount of the power transmission means based on the output signals from the three detection means so that the front and rear wheel torque distribution ratio always becomes a desired constant distribution ratio. Due to
The torque distribution ratio is maintained at a predetermined value.

(Problems to be Solved by the Invention) However, when the control is performed according to one fixed control mode by the above-mentioned configuration, each traveling state during braking, low slip, low speed, and high speed small steering angle It is not possible to perform appropriate control according to. This will be described below.

During braking During braking, the front and rear wheels are not locked at the same time, and either wheel is locked early.
In order to improve the braking effect, it is necessary to increase this lock limit and prevent the wheels from locking prematurely.
However, for example, when the power transmission means is provided and the torque distribution of the front and rear wheels is controlled, the coupling state between the front and rear wheels is low due to the power transmission means even during the control.
It is not possible to drive the wheel that is early locked by the wheel that is not locked to increase the lock limit.

At the time of low slip As the power transmission means, for example, a clutch mechanism is used, but the front and rear wheels always have a rotational speed difference, and in the latch mechanism, when the front and rear wheel rotational speed difference is a predetermined value or less, If the torque is distributed even during (low slip), the clutch mechanism will always slip.
It is not preferable in terms of durability and power loss.

At low speed During low speed running, the gradient of the control characteristic becomes large, and a slight fluctuation in the rotational speed difference causes a large torque fluctuation, resulting in unstable vibration.

High speed small steering angle When the vehicle is running at high speed and the steering angle is small, traveling is unstable unless the front and rear wheels are directly connected, and the slippage of the power transmission means causes large loss and poor durability. There is.

Therefore, the present invention provides a four-wheel drive vehicle in which torque distribution to the front and rear wheels is controlled according to the front and rear wheel rotation difference,
It is an object of the present invention to improve traveling performance by performing control according to an appropriate control mode selected according to the traveling state.

(Means for Solving Problems) According to the present invention, a torque transmission amount variable power transmission means is provided in a torque transmission path for transmitting torque from a power plant to front and rear wheels, respectively, and the power transmission means is variably controlled. In a transmission torque control device for a four-wheel drive vehicle that controls torque distribution to the front and rear wheels by means of a running state detecting means for detecting a running state of the vehicle, and a running state of the vehicle based on an output from the running state detecting means. Correspondingly, one of a plurality of preset control modes is selected, and the front and rear wheel torque distribution ratio becomes a desired distribution ratio based on the selected control mode.
A control means for controlling the amount of torque transmission of the power transmission means, wherein the control modes are normal traveling, braking, traveling with a difference in rotational speed between the front and rear wheels of a predetermined value or less, low speed traveling, and high speed small. It is characterized in that each of them is set corresponding to at least two traveling states during the steering angle traveling.

(Effects of the Invention) In the transmission torque control device for a four-wheel drive vehicle according to the present invention,
The running state of the vehicle is detected from various angles, and the torque distribution between the front and rear wheels is controlled according to the running state. Among the running conditions of this vehicle, there are environmental factors surrounding the running vehicle such as road friction coefficient, outside air temperature, atmospheric pressure, etc., and external factors, and behavior of the vehicle itself such as vehicle speed, front and rear wheel rotation speed difference, brake operation state, etc. There is an internal factor that represents the driving state of the vehicle related to. According to the present invention, factors that widely indicate the traveling state are detected, including the internal factors and the external factors, and the torque transmission amount of the power transmission means is controlled based on the measured values of the factors that represent the traveling states. Therefore, even when the output torque of the engine changes, the torque distribution ratio of the front and rear wheels can be controlled to a desired value, and therefore, without using an expensive torque sensor or the like,
Highly accurate front and rear wheel torque distribution control is possible.

In particular, in the four-wheel drive state, the torque based on at least one driving state of the vehicle such as the front-rear wheel rotational speed difference, the vehicle speed, the vehicle body speed ratio, and the like, which are internal factors, among the detected traveling states is detected. Since the distribution control mode is selected and the control is performed according to the selected appropriate control mode, accurate torque distribution control corresponding to the driving operation of the driver can be quickly performed, and therefore, the traveling performance can be improved. it can. Hereinafter, each control mode will be described.

Braking mode During braking, the torque transmission amount of the power transmission means is controlled to increase, and the wheel on the side where the early lock occurs is driven by another wheel and the lock is delayed, and the lock limit is reached. And the stability at the time of braking is improved, and a decrease in braking force due to locking can be prevented.

Low slip mode When the rotational speed difference between the front and rear wheels is less than or equal to a predetermined value, the control of the torque transmission amount of the power transmission means is prohibited, that is, two-wheel drive is performed, and the control becomes stable and the running resistance In addition, the durability of the power transmission means can be improved, and vibration due to a minute slip in the power transmission means can be prevented.

At low speeds When driving at low speeds, the control characteristics are fixed to the lowest speed that allows stable running, and unstable vibration can be prevented.

High speed small rudder angle When the vehicle is running at high speed and the rudder angle is small, the torque transmission amount of the power transmission means is set to the maximum value so that slippage of the power transmission means does not occur. The low loss and durability of the device can be improved.

(Embodiment) Hereinafter, a transmission torque control device for a four-wheel drive vehicle according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

3 and 4 show an embodiment of the present invention. In FIG. 3, reference numeral 1 indicates a power plant, and the power plant 1 is composed of an engine, a transmission and the like. A front side propeller shaft 4 is connected to an output shaft 2 of the power plant 1 via a gear train 3, and a rear side propeller shaft 6 is connected to the output shaft 2 via a hydraulic variable clutch 5 which is a power transmission means. ing. The front side propeller shaft 4 is connected to a front wheel 8 via a final gear unit 7, and the rear side propeller shaft 6 is connected to a rear wheel 10 via a final gear unit 9. In the above configuration,
The pressure of the hydraulic oil applied to the clutch 5 is changed to change the amount of transmission torque of the clutch 5, thereby adjusting the torque distribution ratio of the front and rear wheels.

(Principle of controlling the torque distribution ratio of front and rear wheels according to the rotational speed difference between the front and rear wheels) First, the power transmission means is provided on the rear side, and the power plant output torque is T _p and the front and rear side torques are T _f respectively. , T _r , and the target rear torque distribution ratio are u, the following equation holds.

T _p ＝ T _f ＋ T _r …… (1) T _r ＝ uT _p …… (2) The front and rear driving forces are F _f and F _r , the front and rear tire slip ratios are S _f and S _r , the front and rear tire angular velocities are ω _f and ω _r , and the front and rear ground loads are N _f and N _r , respectively. _Let R _f and R _{r be} the dynamic effective radii of the front and rear tires, V _f and V _r be the front and rear body speeds averaging the left and right _sides , the driving coefficient be μ, and the constant determined by the tire slip characteristics be k The formula of is established.
The driving coefficient μ and the constant k are values obtained from the slip characteristics peculiar to the tire to be used as shown in FIG. 9 μ = F / N (F; driving force, N; ground load) k = μ / It is S (S; slip ratio).

F _f ＝ μN _f ＝ kS _f N _f …… (4) F _r ＝ μN _r ＝ kS _r N _r …… (5) Furthermore, front and rear gear ratio (propeller shaft /
The half shafts are denoted by G _f and G _r , and the speeds of the front and rear propeller shafts are denoted by n _f and n _r , respectively, and the relationship between the angular rotational speeds of torque can be expressed by the following equation.

n _f = G _f ω _f (10) n _r = G _r ω _r (11) From equations (4), (6), (8) and (10) From equations (5), (7), (9), (11) From equation (12) From equation (13) The front-rear body speed ratio t is Can be expressed as From equations (14), (15), and (16) The relationship between the rear torque and each rotation speed is expressed by equations (3) and (17).
Can be expressed as follows.

The relationship between the rear torque and the rotational speed difference between the front and rear wheels, Δ _n , can be shown as follows.

_{Δ n = n r -n r ......} (19) ∴n r = n f -Δn ...... (20) Equation (18) and (20) Therefore, the driving conditions of the vehicle (for example, vehicle speed and cornering)
In order to make the target rear torque distribution ratio u preset according to the above, the front-rear wheel rotation speed difference Δn, the front side propeller shaft angular speed n _f and the vehicle body speed ratio t are measured and fitted to the above equation (21), The side torque T _r may be set to the obtained value. The rear torque obtained from the above equation (21) when the steering angle is constant and when the vehicle speed is constant
The relationship between T _r and the rotational speed difference Δn is shown in FIGS. 1 and 2.

Note that the front wheel spacing is b ₁ , the rear wheel spacing is b ₂ , the front and rear wheel spacing is l, the steered angle of the inner front wheel in the steered state is α ₁ , the steered angle of the outer front wheel is α ₂ , and the center of rotation is From the inner and outer front wheels to the inner and outer rear wheels by R ₁ , R ₂ ,
If R ₃ and R ₄ are used, the vehicle body speed ratio t can be expressed as follows.

Therefore, if the steering angle is known, the vehicle speed ratio t can be known.

Based on the above principle, the torque distribution ratio of the front and rear wheels can be controlled according to the rotational speed difference of the front and rear wheels to make the torque distribution ratio constant.

Next, the hydraulic control system for the clutch 5 will be described with reference to FIG. Oil tank as shown
The hydraulic oil in 11 is sucked up by the pump 12 and discharged at a predetermined pressure, and the hydraulic oil in the clutch 5 is passed through the hydraulic control valve 13.
Is supplied to the hydraulic oil chamber 5a. The hydraulic control valve 13 is controlled by the control unit 14 to adjust its operating hydraulic pressure. As a result, the pressure of the hydraulic oil to the hydraulic oil chamber 5a of the clutch 5 is adjusted, and the engagement force of the clutch 5 is controlled.

To the control unit 14 detects the vehicle speed, the vehicle speed signal S _v vehicle speed sensor 15 which outputs a detect the steering angle, the steering angle sensor 16 outputs a Sα steering angle signal, and the front-end and rear propeller shaft 4 detects the rotational speed difference Δn of 6, the speed difference sensor 17 which outputs a speed difference signal Esuderuta _n are connected. As the vehicle speed sensor 15, a rotation speed sensor that detects the rotation speed of the front side propeller shaft 4 can be used. Further, in _order to obtain the rotation speed difference Δ _n , a rotation speed sensor for detecting the rotation speed of the rear side propeller shaft 6 is connected to the control unit 14 without using the speed difference sensor, and the control unit calculates the difference. You may

The control unit 14 controls the above three signals S _v , S α and S Δ.
_n is input, and the first and second control maps M ₁ and M ₂ of FIGS. 5 and 6 stored in advance are read out, and this control map is read.
A control current i is supplied to the hydraulic control valve 13 according to M ₁ and M ₂ . These first and second control maps M ₁ and M ₂ are defined based on the characteristic diagrams shown in FIGS. 1 and 2, and the vertical axis represents the control current i and the horizontal axis represents the control current i. the rotational speed difference △ _n
Is shown. The first control map M ₁ is for straight traveling, and is provided with a plurality of control lines l ₁ , l ₂ , and l ₃ that move to the side where the rotational speed difference is large as the vehicle speed increases. On the other hand, the second control map M ₂ is for steering, and includes a plurality of control lines that move to the larger rotational speed difference side as the steering angle increases.
It has l ₄ , l ₅ , and l ₆ .

Next, the operation of the transmission torque control device will be described.

The control unit 14 receives a vehicle speed signal from each sensor 15, 16, 17
S _v , the steering angle signal Sα and the rotational speed difference signal SΔ _n are input, and then it is determined from the steering angle signal Sα whether the vehicle is in a straight traveling state or a steered state. When the vehicle is in a straight traveling state, the first control map M _{1 is changed} to the steered state. In the case of, the second control map M ₂ is read out. First, the control in the straight traveling state will be described. According to the vehicle speed signal S _v , an appropriate control line from the first control map M ₁ will be described.
Select l _1, l ₂ or l _3, irradiation to determine the control current i a rotational speed difference signal S △ _n to the control line. This control current i
Is supplied to the hydraulic control valve 13, and the hydraulic control valve 13 supplies the hydraulic oil having the pressure P proportional to the current i to the clutch 5 according to the control current i. The clutch 5 is engaged at a pressure corresponding to the pressure P of the hydraulic oil, and the torque _Tr proportional to the engagement pressure is transmitted to the rear side propeller shaft 6.

On the other hand, when the turning state, the depending on Sα steering angle signal and select the appropriate control line l _4, l ₅ or l ₆ from the second control map, irradiation to the rotational speed difference signal Esuderuta _n to the control line The control current i is determined and the same control as above is performed thereafter. Thus, knowing the rotation speed difference delta _n, to maintain the torque distribution ratio u of the rear wheels constant. The rear wheel torque distribution u can be a fixed value that is preset according to the specifications of the vehicle or a value that is changed according to the running conditions of the vehicle. Further, although the above-mentioned control has been described in the form in which the control current i is obtained using the control map, it may be in the form obtained by calculation.

Next, in the present invention, a plurality of torque distribution ratio control modes are set according to the traveling state, a control mode corresponding to the traveling state is selected, and control is performed in accordance with the selected control mode. This will be described below.

FIG. 7 shows the normal traveling mode, the braking mode, the low slip mode, the low speed traveling mode, and the high speed small steering angle traveling mode described above.

In FIG. 7, when the brake is ON, the braking mode is set, and T
- △ _{n-characteristic} in the high gradient and strongly coupled state, reference characteristic l _b1, l _b2 of the 10, 11 view), take the normal running mode in the accelerator ON. Moreover, (the V _min slowest possible stable running) vehicle speed V ≦ V _min is slow running mode to be, T-△ _{n-characteristic} is fixed to the characteristics of stable running possible minimum speed (in FIG. 14 JP
l ₀ ), and when the vehicle speed V> V _min , the normal traveling mode is set. When the vehicle speed V ≧ the predetermined vehicle speed V _F and the steering angle α ≦ the predetermined steering angle α _o , the high speed small steering angle mode is set, and the torque T = the maximum torque T.
Direct connection for _max (see Fig. 17A, 17B, 17C), V
If <V _F or α _o <α, the normal traveling mode is set.
In the normal running mode described above, the difference in rotation speed Δ
If it is _n ≦ predetermined rotational speed difference △ n _o, is the torque T = 0 as a low slip mode transmission is prevented (see 12 and 13 FIG.), if it is △ _n0 <△ _n, at high slip state Therefore, the normal torque distribution ratio control described above is performed. In addition,
In each of the above modes, the braking mode has the highest priority. Further, in FIG. 7, it is possible not only to select each mode in accordance with each of the above conditions, but also to allow selection by manual operation.

Hereinafter, each of the above modes, that is, the braking mode, the low slip mode, the low speed traveling mode, and the high speed small steering angle traveling mode will be described in detail.

Braking Mode The control unit 14 shown in FIG. 4 is connected to a brake switch 18 that outputs the brake signal S _b for displaying the operation of the brake device.
When the brake signal S _b is received from 18, the current i is controlled based on the control lines l _b1 and l _b2 by the _third and fourth control maps M ₃ and M ₄ of FIGS. Control lines l of this map M ₃ , M _{4
At b1} and l _b2 , the current i is controlled so as to be considerably larger than in the normal control, and thus the hydraulic control valve is controlled.
The pressure p of the hydraulic oil generated by 13 also becomes large. Thus, although the clutch 5 is not completely engaged, it is almost in the engaged state, whereby the rear wheel 10 is locked with a slight delay after the front wheel 8, and a desired braking state is obtained, and stability during braking is improved. To do.

Low slip mode The fifth and sixth control maps M ₅ and M ₆ in the low slip mode are
As shown in Figures 12 and 13, each control line l ₁ , l ₂ , l ₃ , l ₄ ,
In l _5, l _6, the rotational speed difference △ _n is a predetermined value △ _{n01,
△ n02, △ n03, △ n04} , △ n05, the first time is set as the control current i out, and such hydraulic fluid pressure transmission torque of the clutch 5 becomes unstable when it is more than △ _n06 The current i is not generated. Then, the control unit 14 determines that the rotational speed difference Δ _n is Δ _n01 , Δ _n02 ,
_{△ n03, △ n04, △ n05} , when less than △ _n06 is not supplied with current i, in this case therefore be front-wheel drive, control is stabilized.

Low-speed traveling mode In the first control map M ₇ of FIG. 14, in the case of low-speed traveling, the slope of the control characteristic becomes large as indicated by the control characteristic l ′ indicated by the broken line, and the control characteristic having such a large slope is shown. When performing control according to l ', by a slight variation in the rotational speed difference △ _n, caused a large torque fluctuation, this also causes the variation in the new rotational speed difference △ _n, Therefore, the unstable vibration It is easy to occur.

Therefore, the minimum speed V _min that allows stable running is calculated, and the vehicle speed V ≤
In the case of V _min is fixed to the control characteristics l ₀ in the case of V = V _min, by performing control according to the fixed control characteristic l _0,
Prevents unstable vibration. The flowchart at this time is
Shown in Figure 15 and starting with Start 100, Step 1
In 02, the vehicle speed V and the low speed vehicle speed V _min are compared, and if V ≦ V _min , the control characteristic is fixed to l ₀ as the low speed traveling mode in step 104, and when V> V _min Performs normal torque distribution ratio control in the normal traveling mode.

High-speed small steering angle traveling mode When the vehicle is traveling at high speed and the steering angle is small, the clutch 5
The maximum torque transmission amount is. This will be described with reference to the flowchart of FIG. 16. If the vehicle speed V ≧ the predetermined vehicle speed V _F in step 202, the process proceeds to step 204, and in step 204 the steering angle α ≦ the predetermined steering angle α ₀
Then, in step 206, control current i = maximum control current i
_Set to _max . If the vehicle speed V <V _F in step 202 and the steering angle α> α ₀ in step 204, the routine proceeds to step 208, where normal torque distribution ratio control is performed.
Then, in step 206, the control current i = the maximum control current i
_When it is _max , as shown in the graphs of FIGS. 17A, 17B and 17C, the pressure P of the hydraulic oil to the power transmission means becomes the maximum pressure P _max , and the rear torque T becomes the maximum torque T _max . When the rear torque T = T _max , slippage of the power transmission means is less likely to occur, and the front and rear wheels are actually directly connected. By directly connecting the front and rear wheels in this way, high-speed straightness can be stabilized, and low slippage and durability can be improved by preventing slippage of the power transmission means.

As described above, the control is performed in the control mode, the low slip mode, the low speed traveling mode, the high speed small steering angle traveling mode, or the normal traveling mode according to the traveling state, so that the traveling performance can be improved.

In the above embodiment, the front side propeller shaft 4 is always connected to the output shaft 2 of the power plant 1,
A clutch 5 is provided between the rear side propeller shaft 6 and the output shaft 2.
However, the second clutch 20 and the gear train 21 may be connected to the output shaft 2 and the front side propeller shaft 4 as shown in FIG.
It may be provided between the two so that the propeller shaft directly connected thereto can be selected. In this case, it is necessary to provide the second hydraulic control flight 22.

[Brief description of drawings]

Figure 1 is a torque distribution ratio constant, the transmission torque T _r when the steering angle constant - graph showing the rotational speed difference △ _n characteristic, FIG. 2, the transmission torque when the torque distribution ratio constant, the vehicle speed constant T _r - graph showing the rotational speed difference △ _n characteristic, FIG. 3 is a schematic view showing a 4-wheel drive vehicle drive system, Figure 4 is a schematic diagram of a transmission torque control device according to an embodiment of the present invention, FIG. 5 and FIG. 6 are the first and the second used for the transmission torque control in the transmission torque control device, respectively.
FIG. 7 is a graph showing a control map, FIG. 7 is an explanatory view showing a normal traveling mode, a braking mode, a low slip mode, a low speed traveling mode, a high speed small steering angle traveling mode, and FIG. 8 is another embodiment of the present invention. FIG. 9 is a schematic diagram of a transmission torque control device, FIG. 9 is a characteristic diagram showing a slip characteristic peculiar to a tire, and FIGS. 10 and 11 are third and fourth control maps M ₃ in braking mode.
A graph showing M ₄ , FIGS. 12 and 13 are graphs showing fifth and sixth control maps M ₅ and M ₆ in the low slip mode, and FIG. 14 is a seventh control map M _{7 in} the low speed running mode. Graph FIG. 15 is a flow chart diagram for dividing the low speed traveling mode and the normal traveling mode, and FIG. 16 is a flowchart diagram showing a flow for making the control current i = i _max based on the vehicle speed and the steering angle, 17A, 17B, FIG. 17C is a graph showing the maximum control current, the maximum pressure, and the maximum torque, respectively. 1 ... Power plant, 2 ... Output shaft, 4 ... Front side propeller shaft, 5 ... Clutch, 6 ... Rear side propeller shaft, 13 ... Hydraulic control valve, 14 ... Control unit, 15 ... Vehicle speed Sensor, 16 …… Steering angle sensor, 17 …… Speed difference sensor, 18 …… Brake switch.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Nikita 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) References JP 61-146636 (JP, A) JP 61- 157437 (JP, A) JP 61-71226 (JP, A)

Claims (1)

[Claims] 1. Power transmission means for varying the amount of torque transmission is provided in a torque transmission path for transmitting torque from a power plant to the front and rear wheels respectively, and the power transmission means is variably controlled to control torque distribution to the front and rear wheels. In a transmission torque control device for a four-wheel drive vehicle, a plurality of driving state detection means for detecting a traveling state of the vehicle and a plurality of preset driving states corresponding to the traveling state of the vehicle are output based on the output from the traveling state detection means. A control means for selecting one of the control modes, and controlling the torque transmission amount of the power transmission means so that the front and rear wheel torque distribution ratio becomes a desired distribution ratio based on the selected control mode. The control mode corresponds to at least two driving states of normal traveling, braking, traveling in which the rotational speed difference between the front and rear wheels is a predetermined value or less, low speed traveling, and high speed small steering angle traveling. Transmission torque control device for a four-wheel drive vehicle, characterized in that it is respectively set.