JPS6250228A - Transmission torque controlling device for four-wheel-drive vehicle - Google Patents

Abstract

PURPOSE:To improve the running performance by allowing the transmitted torque amount of a power transmission means to be selected and controlled based on the measurement of such items as the difference in rotation speed between a front and a rear wheel, a car speed, and a car body speed ratio so as to keep a torque distribution ratio between the front and rear wheels constant. CONSTITUTION:Such signals as Sv, Sa, and SDELTAn from each of sensors are inputted into a control unit 14 so as to allow Sa to form a judgement as to whether a car is running straight ahead or is making a turn. Then a control mode corresponding to the running condition is selected out of torque distribution ratio control modes which are set in a form of a control map M1 and the like and operation formulas. Then the selected mode is checked up with the signal SDELTAn for the difference in rotation speed so as to determine controlling electric current 'i'. And a hydraulic pressure proportional to the current is applied to a clutch 5 by a hydraulic control valve 13 so that the clutch is joined so as to transmit the torque Tr corresponding to the control mode to a propeller shaft 6 of the rear wheel side. With this, the torque distribution between the front and rear wheel which corresponds to the running condition, is controlled so as to improve the running performance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a transmission torque control means for a four-wheel drive vehicle, and more specifically, to a four-wheel drive vehicle capable of maintaining a constant torque distribution ratio between 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 the publication, a first drive shaft is directly connected to a power plant consisting of an engine, a transmission, etc., and a second drive shaft is connected to the power plant via a power transmission means such as a clutch mechanism. There is known a vehicle that can switch between two-wheel drive and four-wheel drive by controlling the engagement and release of the clutch mechanism.

To adjust the torque distribution ratio between front and rear wheels in a four-wheel drive vehicle,
For example, this can be done by adjusting the engagement force of a clutch mechanism that switches between two-wheel drive and four-wheel drive as described above, and controlling the amount of torque transmitted by this clutch mechanism. However, when the torque distribution ratio between the front and rear wheels is adjusted using this mechanism, if the output torque of the power plant fluctuates, the engagement force of the clutch mechanism must be adjusted to vary the amount of transmitted torque. It is not possible to keep the torque distribution ratio constant. This is because the transmission torque of the clutch mechanism varies only due to variations in its engagement force.

In order to control the amount of torque transmitted by the clutch mechanism as the power plant output torque fluctuates, for example, the power plant output torque can be detected using a torque detector, and the engagement force of the clutch mechanism can be adjusted based on this detected amount. good.

However, the torque detector described in item 1 is extremely expensive, and therefore, there is a problem in that the entire device becomes expensive.

Therefore, in order to solve this problem, we took advantage of the fact that the rotational speed difference between the front and rear wheels fluctuates as the power plant output torque fluctuates, and adjusted the amount of torque transmitted by the power transmission means based on this rotational speed difference. However, this allows the torque distribution ratio between the front and rear wheels to be maintained at a desired value.

That is, at least one of the torque transmission paths that transmits torque from the power plant to the front and rear wheels is provided with a power transmission means that can vary the amount of torque transmission, and this 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, a vehicle speed detection means for detecting vehicle speed, a steering angle detection means for detecting a steering angle, a rotational speed difference detection means for detecting a difference in rotational speed between front and rear wheels, and a Control means is provided for receiving the output signal and controlling the amount of torque transmitted by the power transmission means so that the front and rear wheel torque distribution ratio always becomes a desired constant distribution ratio based on the output signals from the three detection means. As a result, the torque distribution ratio is maintained at a predetermined value.

(Problem to be Solved by the Invention) However, with the configuration described above, if control is performed according to one fixed control mode, each driving state during braking, low slip, low speed, and high speed small steering angle It is not possible to perform appropriate control depending on the situation. This will be explained below.

During braking During braking, the front and rear wheels are not completely locked simultaneously, but one of the wheels is locked early.

In order to improve braking effectiveness, it is necessary to increase this locking limit to prevent the wheels from locking prematurely.

However, if, for example, the power transmission means is provided and the torque distribution between the front and rear wheels is controlled, the state of coupling between the front and rear wheels is low due to the power transmission means even during braking.
It is not possible to increase the locking limit by driving the wheels on the side that are prematurely locked by the wheels on the unlocked side.

For example, a clutch mechanism is used as the above-mentioned power transmission means during low slip, but there is always a difference in rotational speed between the front and rear wheels, and in the case of a latch mechanism, when the difference in rotational speed between the front and rear wheels is below a predetermined value, If you perform torque distribution even during low slip conditions, the clutch mechanism will always be slipping.
This is unfavorable in terms of durability and power loss.

When the vehicle is running at low speeds, the slope of the control characteristics becomes large, and a slight variation in the rotational speed difference causes large torque fluctuations and unstable vibrations.

When the vehicle is running at high speed and the steering angle is small, if the front and rear wheels are not directly connected, the vehicle will run unstable, and the power transmission means will slip, resulting in large losses and poor durability. There is a problem.

Therefore, the present invention provides a four-wheel drive vehicle in which the torque distribution between the front and rear wheels is controlled according to the rotation difference between the front and rear wheels.
The purpose is to improve driving performance by performing control according to an appropriate control mode selected according to driving conditions.

(Means for Solving the Problem) In the present invention, the control means includes a control mode setting means for setting a plurality of control modes of the torque distribution ratio depending on the driving state, and a driving state based on the output signal from the detection means. and selecting means for selecting a control mode corresponding to the selected control mode and performing control according to the selected control mode.

(Effect of the invention) In the transmission torque control device for a four-wheel drive vehicle of the present invention,
Even if the output torque of the engine changes, the torque distribution between the front and rear wheels can be improved by simply measuring the difference in rotational speed between the front and rear wheels, the vehicle speed, and the vehicle speed ratio, and controlling the amount of torque transmitted by the power transmission means based on these measurements. The ratio can be maintained constant, and therefore, highly accurate torque distribution control between the front and rear wheels can be performed without using an expensive torque sensor or the like.

Further, in the transmission torque control device for a four-wheel drive vehicle of the present invention, since control is performed according to an appropriate control mode selected depending on the driving condition, driving performance can be improved. Each control mode will be described below.

Braking mode When braking, the amount of torque transmitted by the power transmission means is controlled to increase, and the wheel on the side where early locking occurs is driven by the other wheels, and the locking is delayed, causing the locking limit to be increased. This increases stability during braking, and prevents a reduction in braking force due to locking.

Low slip mode When the difference in rotational speed between the front and rear wheels is below a predetermined value, control of the amount of torque transmitted by the power transmission means is prohibited, in other words, two-wheel drive is set, which stabilizes the control and reduces running resistance. In addition, the durability of the power transmission means can be improved, and vibrations caused by minute slips in the power transmission means can be prevented.

When driving at low speeds, the control characteristics are fixed at the lowest speed that allows stable driving, thereby preventing unstable vibrations.

When the vehicle is running at high speed and the steering angle is small, the amount of torque transmitted by the power transmission means is set to the maximum value to prevent slippage of the power transmission means, which stabilizes high-speed straight-line performance. It can improve the low loss and durability of the device.

(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 this power plant 1 consists of an engine, a transmission, and the like.

A front propeller shaft 4 is connected to the output shaft 2 of the power plant 1 via a gear train 3, and a rear propeller shaft 6 is connected via a hydraulic variable clutch 5, which is a power transmission means. ing. The front propeller shaft 4 is connected to a front wheel 8 via a final gear unit 7, and the rear 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 torque transmitted by the clutch 5, thereby adjusting the torque distribution ratio between the front and rear wheels.

(Principle of controlling the torque distribution ratio between the front and rear wheels according to the rotational speed difference between the front and rear wheels) First, the power transmission means described above is provided on the rear side, the power plant output torque is Tp, and the front and rear side torques are respectively Tp. f % Tr % If the target rear torque distribution rate is U, then the following formula holds true.

Tp=Tr+Tr−・”(1)T,
-uT, ......(2)1" Also, the front and rear driving forces are each F f %
Fr % front and rear tire slip ratio
F, Sr s - front and rear tire angular velocity n
f11, front and rear ground contact load is ω N f % Nr % front and rear tire dynamic effective radius is R,, R,, front and rear vehicle speed averaged from left and right is ■1, ■1, drive coefficient is μ , Th is a constant determined by the slip characteristics of the tire, then the following equation holds true. In addition, the driving coefficient μ and the constant are values obtained from the slip characteristics specific to the tires used as shown in Fig. 9, and μ-F/N (F: driving force, N: ground contact load)k- μ/
S (S; slip rate).

Fr = μNr = k Sr Nr --(4)
Fr -μNr -kSrNr (5) Furthermore, the front and rear gear ratios (pellet shaft/half shaft) are G, Gr, and the speeds of the front and rear propeller shafts are nf and nr, respectively. Then, the relationship between torque and angular rotation speed can be expressed by the following equation.

nf −Gr ω, ...
...0Qnr = Gr ω,
・・・−[111 Formulas (4), (6), (8), from 00……(12) Formulas (5), (7), (9), from the circle…… ...(13) From equation (12)... (14) From equation (13)... f151 The front and rear vehicle speed ratio t is... (17) The relationship between rear torque and each rotation speed is expressed by equations (3) and (17
), it can be expressed as follows.

, °, T, = (18) The relationship between the rear torque and the rotational speed difference between the front and rear wheels of 80 can be expressed as follows.

△, =n, nr (19
) Pa・η・−nf−△n ・・・・・・(20)
From formulas (18) and (20), 2 〆I 〆 ← Therefore, vehicle running conditions (e.g. vehicle speed and cornering)
In order to keep the target rear torque distribution ratio U set in advance in accordance with The value obtained by torque Tr may be used. Note that the rear torque T obtained from the above equation (21) when the steering angle is constant and when the vehicle speed is constant.

The relationship between the rotational speed difference Δn and the rotational speed difference Δn is shown in FIGS. 1 and 2.

In addition, the distance between the front wheels is bl, the distance between the rear wheels is b2, the distance between the front and rear wheels is l, the steering angle of the inside front wheel in the steered state is α1, the steering angle of the outside front wheel is α2, and the inside and outside from the rotation center. The distances to the front wheels and the inner and outer rear wheels are respectively RI,
Assuming R2, R3, and R4, the vehicle speed ratio t can be expressed as follows.

tan α, tan α2 Therefore, if the steering angle is known, the vehicle speed ratio t can be known.

Based on the above principle, it is possible to control the torque distribution ratio between the front and rear wheels according to the rotational speed difference between the front and rear wheels, thereby making the torque distribution ratio constant.

Next, with reference to FIG.
The internal pressure control system will be explained. As shown in the figure, the hydraulic oil in the oil tank 11 is sucked up by the pump 12, discharged at a predetermined pressure, and supplied to the hydraulic oil chamber 5a of the clutch 5 via the hydraulic control valve 13. Hydraulic control valve 13
is controlled by a control unit 14, and its working oil pressure is adjusted. As a result, the pressure of the hydraulic oil in the hydraulic oil chamber 5a of the clutch 5 is adjusted, and the engagement force of the clutch 5 is controlled.

The control unit 14 detects the vehicle speed and receives a vehicle speed signal S.
A vehicle speed sensor 15 outputs a steering angle signal Sα, a steering angle sensor 16 detects a steering angle and outputs a steering angle signal Sα, and a rotational speed difference Δn between the front and rear propeller shafts 4.6 is detected and a speed difference signal SΔ . A speed difference sensor 17 is connected to output the speed difference sensor 17. In addition, as the vehicle speed sensor 15,
A rotational speed sensor that detects the rotational speed of the front propeller shaft 4 can be used. Also, the rotational speed difference △. In order to obtain the above, instead of using the speed difference sensor, a rotational speed sensor for detecting the rotational speed of the rear propeller shaft 6 may be connected to the control unit 14, and the calculation may be performed by the control unit.

The control unit 14 inputs the three signals SV%Sα and SΔ, reads out the first and second control maps M1 and M2 of FIG. 5.6 stored in advance, and outputs the control maps M, , Control current 1 is applied to hydraulic control valve 1 according to M2.
Supply to 3. These first and second control maps M1
and M2 are determined based on the characteristic diagrams shown in FIGS. 1 and 2, and the vertical axis represents the control current i.
, the horizontal axis indicates the rotational speed difference Δ9. The first control map M1 is for straight-ahead driving, and has a plurality of control lines It that move toward the larger rotational speed difference side as the vehicle speed increases.
, I12,is. On the other hand, the second control map M2 is for steering, and includes a plurality of control lines 14 and I that move toward the larger rotational speed difference side as the steering angle increases.
15.16.

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

The control unit 14 receives a vehicle speed signal Sv, a steering angle signal Sα, and a rotational speed difference signal SΔ0 from each sensor 15, 16, 17.
is input, and then it is determined from the steering angle signal Sα whether it is a straight-ahead state or a steered state, and when the state is a straight-ahead state, the first control map M1 is inputted.
, and the second control map M2 is read out when the vehicle is in the steering state. First, to explain the control when the vehicle is traveling straight, the first control map M1 is set according to the vehicle speed signal Sv.
An appropriate control line L 1 , L 2 or p3 is selected from among them, and the control current i is determined by comparing the rotational speed difference signal SΔ0 with this control line. This control current i is supplied to the hydraulic control valve 13, and this hydraulic control valve 13 operates according to the control current i.
Hydraulic oil with a pressure P proportional to the current i is supplied to the clutch 5. The clutch 5 is engaged at a pressure corresponding to the pressure PI3 of the hydraulic oil, and a torque Trjl proportional to the engagement pressure is applied to the clutch 5.
The signal is transmitted to the rear propeller shaft 6.

On the other hand, in the steering state, an appropriate control line 14.15 or β6 is selected from the second control map according to the steering angle signal Sα, and the rotational speed difference signal SΔ is compared with this control line to control the control current i. is determined, and the same control as above is performed thereafter.

As a result of the above, the rotational speed difference Δ. Knowing this, the torque distribution ratio U of the rear wheels can be maintained constant. In addition, the rear wheel torque distribution setting 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 driving conditions of the vehicle.

Furthermore, although the above control has been described using a control map to determine the control current, it may also be determined by calculation.

Next, in the present invention, a plurality of control modes for the torque distribution ratio are set depending on the driving condition, and the control mode corresponding to the driving condition is selected and control is performed according to the selected control mode. , this will be explained below.

FIG. 7 shows the above-mentioned normal running mode, braking mode, low slip mode, low speed running mode, and high speed small steering angle running mode.

In Fig. 7, when the brake is ON, it is in braking mode,
To T-〇 Characteristics are made to have a high slope and a strong coupling state is established, and the 10th
．． (See characteristic 163, 2 in Figure 11), when the accelerator is turned on, the normal driving mode is set. Also, vehicle speed ■≦V, n
(■ mlr+ is the minimum speed at which stable driving is possible), it is a low speed driving mode, and the characteristics are set to T- to the characteristics at the minimum speed at which stable driving is possible. ), when vehicle speed V > Vffit, the normal driving mode is selected. Also, vehicle speed■≧predetermined vehicle speed■.

and steering angle α≦predetermined steering angle α. If so, it is a high speed small steering angle mode, and the torque T=maximum torque T□8, which is a direct transmission (see Figures 17A, 17B, and 17C), and V<VF or α. If the value is α, the normal driving mode is selected. In addition,
In the normal running mode mentioned above, the rotational speed difference △. If ≦predetermined rotational speed difference △no, the torque T is set to 0 due to the low slip mode and transmission is prevented (No. 12.13).
(see figure), △,. Ku△. In this case, since the vehicle is in a high slip state, the above-mentioned normal torque distribution ratio control is performed. In addition, in each of the above-mentioned modes, the braking mode is given the highest priority. In addition, in FIG. 7, each mode can be selected not only according to the above-mentioned conditions, but also by manual operation.

Each of the above modes, namely the braking mode, low slip mode, low speed running mode, and high speed small steering angle running mode, will be explained in detail below.

Braking mode 4th vI! A brake switch 18 that displays the operation of the brake device and outputs a brake signal S is connected to the control unit 14 of J, and when the control unit 14 receives the brake signal Sb from the brake switch 18, it outputs the brake signal Sb. 10. Third and fourth control maps M, , M, in Figure 11
Accordingly, the current t is controlled based on the control lines 1b1 and Ab2. Control lines lb1 and Ab□ of this map M3 and M4
In this case, the current 1 is controlled to be much larger than in normal control, and therefore the pressure p of the hydraulic oil generated by the hydraulic control valve 13 is also large. Thus,
Although the clutch 5 is not fully engaged, it is in a partially engaged state, whereby the rear wheels 10 are locked slightly later than the front wheels 8, providing a desirable braking state and improving stability during braking. .

Low slip mode 5th and 6th control maps M5 and M6 of low slip mode
are shown in Figure 12.13, and each control line p3, β
2.j! 3, '4, As, j2a, rotational speed difference △. to the predetermined value no+ , △n02 , △, , o
3. It is set so that control current 1 is output only when △1104 , △, , o5, △, , 86 or more, and the hydraulic oil pressure is such that the transmission torque of clutch 5 becomes unstable. The current i is not generated.

The control unit 14 then controls the rotational speed difference. is above△
no1 %△n02 s△h03 %△re04-△h0
51△,,. When it is smaller than 8, the current i is not supplied, and therefore, in this case, the front wheels are driven, and the control becomes stable.

Low-speed driving mode In the first control map M7 in FIG. 14, in the case of low-speed driving, the slope of the control characteristic becomes large as shown by the broken line control characteristic β', and the control characteristic 1 having such a large slope If control is performed according to
This causes a change in the new rotational speed difference, which tends to cause unstable vibration.

Therefore, find the minimum speed V m l n that allows stable running, and if the vehicle speed ■≦V m I h,
The control characteristic β when . is fixed, and control is performed according to this fixed control characteristic po to prevent unstable vibration. The flowchart at this time is shown in FIG.
and the low speed vehicle speed V m l□, ■≦V m I
h, the control characteristic is fixed at 1° as a low-speed running mode in step 104, and V > Vm
In the case of ln, normal torque distribution ratio control is performed as a normal driving mode.

High speed small steering angle driving mode When driving at high speed and the steering angle is small, clutch 5
The torque transmission amount is set as the maximum value. To explain this based on the flowchart in FIG. 16, start 200
If the vehicle speed ■≧predetermined vehicle speed ■ is satisfied in step 202, the process proceeds to step 204, and in step 204, the steering angle α is determined.
≦Predetermined steering angle α.

Then, in step 206, the control current j−maximum control current+1naM is set. Note that in step 202, the vehicle speed V
If <Vp, the steering angle α>α is determined in step 204.

If so, the process advances to step 208 and normal torque distribution ratio control is performed. Then, in step 206, if the control current 1 - the maximum control current l m1M , the first
As shown in the graphs in Figures 7A, 1.7B, and 17C, the pressure P of the hydraulic oil to the power transmission means becomes the maximum pressure P□a8, and the rear side torque T becomes the maximum torque T II a 11
becomes. When the rear side torque T-T Ill AM is applied, 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 manner, high-speed straight running performance is stabilized, and the power transmission means is prevented from slipping, thereby reducing loss and improving durability.

As described above, control is performed in the braking mode, low slip mode, low speed driving mode, high speed small steering angle driving mode, or normal driving mode depending on the driving condition, so that driving performance can be improved.

Further, in the above embodiment, the front propeller shaft 4 is always connected to the output shaft 2 of the power plant 1,
A clutch 5 is installed between the rear propeller shaft 6 and the output shaft 2.
Although the explanation has been given on a case in which a second clutch 20 and a gear train 21 are provided between the output shaft 2 and the front propeller shaft 4, this may be reversed. It may also be possible to select the propeller shaft to be directly connected. Note that in this case, it is necessary to provide the second hydraulic control valve 22.

[Brief explanation of the drawing]

FIG. 1 shows the transmission torque Tr and rotational speed difference Δ when the torque distribution ratio is constant and the steering angle is constant. A graph showing the characteristics, FIG. 2, shows the transmitted torque T and -rotational speed difference Δ when the torque distribution ratio is constant and the vehicle speed is constant. Graph showing the characteristics, FIG. 3 is a schematic diagram showing the drive system of a four-wheel drive vehicle, FIG. 4 is a schematic diagram of a transmission torque control device according to an embodiment of the present invention, and FIGS. 5 and 6 are , a first and a second used for transmission torque control in the transmission torque control device, respectively.
The graph showing the control map, Figure 7, shows the normal driving mode,
An explanatory diagram showing a braking mode, a low slip mode, a low speed traveling mode, and a high speed small steering angle traveling mode. FIG. 8 is a schematic diagram of a transmission torque control device according to another embodiment of the present invention. FIG. 9 is a diagram showing a transmission torque control device specific to tires. 10.11 is a graph showing the third and fourth control maps M3 and M4 in braking mode, and FIG. 12.13 is a graph showing the fifth and sixth control maps in low slip mode. 14 is a graph showing the seventh control map M7 of the low-speed driving mode. FIG. 15 is a flowchart that separates the low-speed driving mode and the normal driving mode. FIG. 16 is a graph showing the vehicle speed and steering Control current i” 1 based on the angle
Flowchart showing the flow to make mmM) II, 1st
Figures 7A, 17B, and 17C show the maximum control current,
It is a graph showing maximum pressure and maximum torque. 1... Power plant, 2... Output shaft, 4... Front propeller shaft, 5...
...Clutch, 6...Rear propeller shaft, 13...Hydraulic pressure control valve, 14...
Control unit, 15...Vehicle speed sensor, 16...
... Rudder angle sensor, 17 ... Speed difference sensor, 18 ... Brake switch. Fig. 16 Diagram 11 Fig. 17A Fig. 1 γB Fig. 17C Fig. Rotation speed difference bn Procedural amendment 60, 10.15 Showa year Month Day 1, Incident indication 1985 Patent application No. 191034
No. 2, Title of the invention Transmission torque control device for four-wheel drive vehicles 3, Person making the amendment Relationship to the case Applicant, name (313) Mazda Motor Corporation 4, Agent 5, Date of amendment order Initiator 1, Details In the 6th and 4th lines from the bottom of page 12 of the book, "peroperapa" is corrected to "propeller". 2. The formula % formula % on page 16 of the same book is revised as follows. r,',T,-... (18) J3, The entire page 16 of the same book is modified as follows. To-ichisa To-ゝ)〈
No 2 z,! ￥〆
4, same book, page 19, No. 1
line

Claims (1)

[Claims] At least one of the torque transmission paths that transmits torque from the power plant to the front and rear wheels is provided with a power transmission means that can change the amount of torque transmission, 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 driving state detecting means for detecting a traveling state of the vehicle and an output signal from the detecting means are received, and a front and rear wheel torque distribution ratio is determined based on the output signal from the detecting means. The control means controls the amount of torque transmitted by the power transmission means so that a desired constant distribution ratio is always achieved, and the control means sets a plurality of control modes for the torque distribution ratio depending on the driving condition. a control mode setting means for selecting a control mode corresponding to the driving state based on an output signal from the detection means, and a selection means for controlling according to the selected control mode. Control device.