JPS6268135A - Driving force distribution controller for 4-wheel-drive vehicle - Google Patents

Abstract

PURPOSE:To improve the acceleration performance by setting such control characteristic that the clutch fastening force for the driving-force distribution control increases in accordance with the front and rear wheel revolution speed difference and controlling the clutch fastening force by using the control characteristic having the larger control constant as the acceleration state shows sharp acceleration. CONSTITUTION:The captioned apparatus has a variable torque clutch 3 in the driving-force transmission system for rear wheels 1 and 2, and said clutch 3 is operation-controlled by an actuator 4 controlled by a control means 6 on the basis of the input signals supplied from an input sensor 5. In this case, a front and rear wheel revolution speed difference sensor 501 and an accelera tion state sensor 502 are provided as input sensors 5. The control means 6 sets such control characteristic that the clutch fastening force increases corre sponding to the front and rear wheel revolution speed difference. Further, the clutch fastening force is controlled on the basis of the control characteristic having the larger control constant as the acceleration state detected by an acceleration state sensor 502 shows sharp acceleration.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a driving force distribution control device for a four-wheel drive vehicle that controls the distribution of driving force to front and rear wheels according to predetermined control conditions.

(Prior Art) As a conventional driving force distribution control device for a four-wheel drive vehicle, a device as described in, for example, Japanese Unexamined Patent Publication No. 56-26636 is known.

This conventional device is configured to transmit power directly to one of the front and rear wheels in a transmission, and also to the other of the front and rear wheels via a hydraulic transfer clutch, and the clutch is usually slidable by a spring. The clutch is in a half-engaged state, and if a slip occurs between the front and rear wheels, the piston is suppressed to achieve a fully integrated engagement state, and control is performed in two stages. Ta.

Therefore, in the conventional device, when the slip between the front and rear wheels is below a predetermined value, the transfer clutch is in a half-clutch engaged state, and the drive force distribution state (two-wheel drive ), and if the slip between the front and rear wheels exceeds a predetermined value,
The transfer clutch was fully engaged and the vehicle was in full four-wheel drive.

(Problems to be Solved by the Invention) However, in such a conventional driving force distribution control device, it is difficult to switch from a two-wheel drive state to a four-wheel drive state after a predetermined slip ratio.
Because the drive force distribution was switched in an 0N-OFF manner to the wheel drive state, in the direct four-wheel drive state, the turning characteristics tended to have strong understeer, and in the two-wheel drive state, the wheels slipped when starting suddenly. Furthermore, there was a problem in that it could lead to a spin when turning.

On the other hand, the applicant of the present application previously filed an application with the content that the best driving force distribution can be obtained according to the rotational speed difference between the front and rear wheels, with the aim of solving the above-mentioned problems. (Japanese Patent Application No. 59-276048) However, although the proportional constant of the control characteristic that controls the clutch engagement force of the variable torque clutch is varied by manual switching, road surface friction coefficient, etc., it is proportional regardless of the acceleration state of the vehicle. Since the constant was set, when the control characteristic was set to a small proportional constant that indicates a drive force distribution similar to that of two-wheel drive, sudden starts tend to cause wheel slip, and sudden acceleration turns are likely to occur. In addition, when the control characteristic is set to a large proportional constant that indicates a drive force distribution close to that of four-wheel drive, if a slow acceleration turn is performed, the turning characteristic tends to have a strong tendency to understeer. This left the problem that it would become

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above-mentioned problems, and in order to achieve this purpose, the present invention employs the following solving means. did.

The solution of the present invention will be explained with reference to the claim conceptual diagram shown in FIG. 4 and an input signal from the input sensor 5, a control signal for controlling the clutch engagement force of the variable torque clutch 3 is transmitted to the actuator 4.
In the driving force distribution control device for a four-wheel drive vehicle, which includes a control means 6 for outputting an output to
02, the control means 6 is configured to set a control characteristic in which the clutch engagement force increases in accordance with the difference in front and rear wheel rotational speeds, and the control constant is increased as the acceleration state by the acceleration state sensor 502 indicates a sudden acceleration. The clutch engagement force is controlled based on the characteristics.

(Function) Therefore, in the driving force distribution control device for a four-wheel drive vehicle of the present invention, by using the above-mentioned means, the driving force distribution changes smoothly according to the difference in rotational speed of the front and rear wheels, and the steering characteristics are improved. There is no sudden change, and during sudden acceleration, clutch engagement force is controlled based on control characteristics with a large control constant, resulting in drive force distribution control similar to four-wheel drive, reducing wheel slip during sudden starts and spin during sudden acceleration turns. In addition, during slow acceleration, the clutch engagement force is controlled based on the control characteristics with a small control constant, resulting in drive force distribution control similar to that of two-wheel drive, reducing the tendency for understeer during turns during slow acceleration. Driving force distribution control can be performed according to the state.

(Example) Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In describing this embodiment, a driving force distribution control system for a four-wheel drive vehicle based on rear wheel drive will be taken as an example.

First, the configuration of the embodiment shown in FIGS. 2 to 6 will be explained.

10 is a driving force distribution device, as shown in FIG.
Drive input shaft 11. Transmission 12, input shaft 13
．． Rear wheel side drive shaft 14. Multi-plate friction clutch 15. Oil pump 16. Pressure oil discharge pipe 17, oil suction v18. Reserve tank 19. Gear train 20. A front wheel side drive shaft 21 is provided.

The drive input shaft 11 is a shaft to which the driving force that has passed through the engine and the clutch is input.

The transmission 12 changes the speed of the rotational driving force from the drive input shaft 11 according to a selected gear position by a shift operation, and in this embodiment, two parallel shafts are provided with teeth of different gear ratios. A type with a trunnion is used.

The input shaft 13 is a shaft for inputting the rotational driving force from the transmission 12 to the multi-disc friction clutch 15 as a transfer.

The rear wheel drive shaft 14 is coaxially and directly connected to the input shaft 13, and the rotational driving force from the input shaft 13 is directly transmitted thereto.

- The multi-disc friction clutch 15 can change the driving force transmitted to the front wheels by means of clutch engagement pressure. A friction brake (15b) engaged with the clutch drum L5a in the rotational direction, and the input shaft 1
Clutch hub 15c rotatably supported on the outer periphery of 3.
, a friction disk 15d engaged in the rotational direction with the clutch hub 15c, a clutch piston 15e provided at one end of the friction plate 15b and the friction disk 15d arranged alternately, and the clutch piston 15e and the friction disk 15d. A cylinder chamber 15f formed between the clutch drum 15a and the clutch drum 15a.

The oil pump 16 is a pump that sucks oil in the reserve tank 19 through an oil suction pipe 18, pressurizes it, and supplies it to a pressure oil discharge pipe 17, which is communicated with the cylinder chamber 15f. When pressurized oil is supplied from the oil pump 16, a clutch engagement pressure P is applied to the clutch piston 15e to press the friction plate 15b and the friction disc 15d into contact with each other, thereby transmitting the driving force from the input shaft 13 to the front wheels. let

The gear train 20 includes a first gear 20a provided on the clutch hub 15C, a second gear 20c provided on the intermediate shaft 20b, and a third gear 20d provided on the front wheel drive shaft 21. This is a means for transmitting the driving force to the front wheels by engaging the multi-disc friction clutch 15.

1. The front wheel drive shaft 21 is a shaft that transmits rotational driving force to the front wheels of the vehicle.

Incidentally, FIG. 3 shows a specific example of the transfer, in which the multi-disc friction clutch 15 is installed in the transfer case 22.
It houses gears, shafts, etc.

In Figure 3, 15g is the dish plate, 23 is the return spring, and 24 is the i'17 control oil-filled cover.

25 is a control pressure oil passage, 26 is a rear wheel side output shaft, 27 is a lubricating oil passage, and 28 is a speedometer pinion.

29 is an oil seal, 30 is a bearing, 31 is a needle bearing, 32 is a thrust bearing, and 33 is a joint 7 flange.

Reference numeral 40 denotes a driving force distribution control device, which includes a front wheel rotation sensor 41 as an input sensor. Rear wheel side rotation sensor 42. An accelerator opening sensor 43 is provided, a control unit 45 is provided as a controller, and a help solenoid 46 is provided as an actuator. It is equipped with an electromagnetic proportional control relief valve 479 and a branch drain pipe 48.

The front wheel rotation sensor 41 and the rear wheel rotation sensor 42 are provided in the middle of the front wheel drive shaft 21 and the rear wheel drive shaft 14, respectively, and include, for example, a rotary plate fixed to the shaft,
The cylindrical rotation sensors 41 and 42 are installed using rotation sensors such as phototubes and photoelectric elements placed in the holes of the rotary plate.
Rotation signals (nf) and (nr) corresponding to the rotation of the shaft are output from.

The accelerator opening sensor 43 detects the degree of depression of the accelerator, and generates an accelerator opening degree signal (
This is a sensor that outputs a) and is used as a means to detect an acceleration state.

The control unit 45 includes the rotation sensor 41
, 42 and the accelerator opening signal (a) from the accelerator opening sensor 43,
From among a plurality of preset control characteristics with different proportional constants (control constants), a control characteristic corresponding to the accelerator opening degree A at that time is selected each time the control is started, and the control characteristic and the front and rear wheel rotational speed difference ΔN are selected. It outputs a control signal (C) based on the above to the valve solenoid 46, and as shown in FIG.
53, ROM 454, CPU 455, and output circuit 456.

The above control characteristics are expressed as a function of the torque transmitted to the front wheels ΔT and the rotational speed difference ΔN (ΔN=Nr-Nf) as shown in the following equation, and by changing the proportionality constant K, multiple controls can be performed. Characteristics are set.

ΔT=−func (ΔN) K; The proportional constant input circuit 451 is a circuit that converts input signals input from each input sensor 41, 42, 43 into a signal that can be processed by the CPU 455.

The clock circuit 452 gives time instructions and
This is a circuit for performing the arithmetic processing in 455 at predetermined time intervals.

The RAM 453 (random access memory) is a memory that can be written to and read from, and input signals input while the CPU 455 is performing calculation processing and information necessary for the calculation processing are temporarily stored in the RAM 453. This is a circuit that stores information.

The ROM 454 (read-only memory) is a read-only memory, and as shown in the map shown in Fig. 5, the ROM 454 has a map that shows the relationship between the rotational speed difference ΔN and the torque transmitted to the front wheels ΔT. Multiple control characteristics C+, C with different constants CKI, 2, 3)
2. C3 is stored in advance in the form of a table,
One control characteristic is selected based on the accelerator opening degree A, and a table lookup is performed based on the rotational speed difference ΔN calculated by the CPU 455.

The control characteristics of the rotational speed difference ΔN and the transmission torque ΔT are as follows:
The characteristic is based on the slope of the proportional relationship up to a predetermined rotational speed difference, but the slope suddenly rises in the middle, increasing the rate of increase of the transmitted torque ΔT relative to the rotational speed difference ΔN, and is a characteristic that prevents clutch slippage. .

The CPU 455 (central processing unit) is a central processing unit that performs arithmetic processing.
In U455, calculation of rotational speed difference ΔN between front and rear wheels and RA
Performs reading from M453 and ROM454,
The resulting signal is output to output circuit 456.

The output circuit 456 is a circuit that outputs a control signal (C) according to a result signal from the CPU 455 to the valve solenoid 46, which is an actuator.

The valve solenoid 46 is an actuator that drives an electromagnetic proportional control relief pulp 47 provided in the middle of a branch drain pipe 48 that branches from the pressure oil discharge pipe 17 to the reserve tank 19, and opens and closes the relief valve 47. The clutch engagement pressure P is set according to the control signal (C).

Note that the clutch engagement pressure P is expressed by the following formula.

P=ΔT/ (p・s・2n−Rm) μ: Friction coefficient of clutch plate S: Pressure acting surface on piston a n: Number of friction disks Rm: Torque transmission effective radius of friction disk Therefore, clutch engagement pressure When P is increased, the transmitted torque ΔT also increases proportionally.

Next, the operation of the embodiment will be explained.

First, the flow of the driving force distribution control operation in the embodiment will be explained with reference to the flowchart shown in FIG.

(a) When the rotational speed difference ΔN between the front and rear wheels is positive When the rotational speed difference ΔN between the front and rear wheels is positive, that is, when the rear wheels are slipping, the flow of control operation is as follows: Step 200 → Step 201 → Step 202 → Step 203 → Step 204 → Step 205 → Step 206, and this operation is repeated.

Note that step 200 is a step for reading the front and rear wheel rotational speeds Nf and Nr, step 201 is a calculation step for the front and rear wheel rotational speed difference ΔN (ΔN=Nr-Nf), and step 202 is a step for calculating whether ΔN is positive or negative. It is a judgment step,
Step 203 is a step of reading the accelerator opening degree A, and step 204 reads the control characteristic C+ according to the accelerator opening degree A.

This is a selection step to select C2 and C3, and step 2
05 is a search step in which the transmission torque ΔT is looked up in a table from the control characteristics selected based on the front and rear wheel rotational speed difference ΔN, and step 206 is a control signal (C) from which the transmission torque ΔT looked up in the table in step 205 is obtained. This is the step to output.

As a specific example, when accelerating by depressing the accelerator pedal, and when the front and rear wheel rotational speed difference ΔN is ΔN+, the selection of the control characteristic becomes C as the accelerator opening degree A increases.
! → C2 → C3, so as shown in Figure 5,
When the accelerator pedal is first depressed and the control characteristic C+ is selected, a control signal (C) that provides the transmission torque ΔT1 is output, and when the accelerator pedal is slightly depressed and the control characteristic C2 is selected. is the transmitted torque Δ
When a control signal (C) that yields T2 is output, and the accelerator pedal is depressed significantly and control characteristic C3 is selected, a control signal (C) that yields transmission torque ΔT3 is output.
) will be output. Moreover, when the accelerator pedal is suddenly depressed, the transmitted torque ΔT changes from ΔT1 → ΔT2 → ΔT3 in a short period of time, and when the vehicle enters the acceleration state, the transmitted torque ΔT to the front wheels increases, resulting in four-wheel drive. The driving force distribution will be close to the state.

Also, during slow acceleration, when the amount of depression on the accelerator pedal is small and there is almost no pedal movement,
Similarly to the above, when the front and rear wheel rotational speed difference ΔN is ΔN1, the accelerator opening A is small and there is almost no change in the accelerator opening A, so control characteristic C+ remains selected, and the control characteristic C+ remains selected. The transmission torque ΔT also remains at ΔT+, which is the smallest torque, and the drive force distribution to the front wheels becomes close to that of the rear wheel drive state where the drive force distribution is small.

(b) When the rotational speed difference ΔN between the front and rear wheels is zero or negative When the rotational speed difference ΔN between the front and rear wheels is zero or negative.

In other words, the flow of control operation when driving straight on a dry road where the tires do not slip is from step 200 to step 20.
1→Step 202→Step 2.7, the control signal (C) is output as zero, and the rear wheel drive state is maintained.

As described above, in the embodiment, the accelerator opening degree A is used as the input information of the acceleration state, and the control characteristic is selected such that the proportionality constant K increases as the accelerator opening degree A increases, so that when the accelerator pedal is depressed, the vehicle When the vehicle enters a sudden acceleration state, the clutch engagement force is controlled based on the large control characteristic of the proportional constant, that is, the drive force distribution control is similar to that of four-wheel drive, which reduces wheel slip during sudden starts and sudden acceleration. It is possible to prevent spin when turning.

Furthermore, when the accelerator pedal is pressed down to a small extent during slow acceleration, the clutch engagement force is controlled based on a small control characteristic of the proportional constant, that is, the drive force distribution control is similar to rear wheel drive. It is possible to reduce the tendency of understeer when turning at slow acceleration.

In this way, by smoothly changing the drive force distribution according to the difference in rotational speed between the front and rear wheels, it is possible to perform drive force distribution control that does not cause sudden changes in steering characteristics, and it is also possible to perform drive force distribution control according to the acceleration state. .

Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention may be modified without departing from the gist of the present invention. included.

For example, although the embodiment shows a four-wheel drive vehicle based on a rear-wheel drive vehicle, it may also be based on a front-wheel drive vehicle. In that case, the rotational speed difference ΔN is Nf −
It may be calculated as Nr.

Further, in the embodiment, an example of control characteristics based on the proportional relationship between the transmission torque ΔT and the rotational speed difference ΔN is shown, but the relationship is not necessarily limited to that shown in the embodiment. Other control characteristics may also be used.

Furthermore, although an accelerator opening sensor is shown in the embodiment as an acceleration state sensor, a negative pressure sensor provided in the engine intake pipe, a sensor that detects the operation of an accelerator pedal, or the like may be used.

In addition, in the embodiment, an example was shown in which a plurality of control characteristics were stored in advance in the form of a table, and the torque transmitted to the front wheels ΔT was determined by table lookup. Alternatively, the transmission torque ΔT may be determined by calculating the proportionality constant and the rotational speed difference between the front and rear wheels by substituting the proportionality constant and the rotational speed difference between the front and rear wheels into this calculation formula.

In addition, at this time, the proportionality constant is not limited to three types of proportionality constants as in the embodiment, but the value of the accelerator opening may be used as the proportionality constant, or the proportionality constant may be determined from the accelerator opening by a predetermined calculation. Good too.

In addition, in the embodiment, an example was shown in which the accelerator opening degree A, which allows the accelerator opening degree to be known over time, is used as it is as the human power information for the acceleration state jQ that determines the proportionality constant K, but the accelerator opening degree A can be changed over time. The differentiated accelerator opening degree differential value A may be used as the input information of the acceleration state by 1, or the accelerator opening degree A and the accelerator may be used as input information.

In addition, in the case of the accelerator opening differential individual, it is possible to know the rate of change of the accelerator opening, and in the case of αA + β person, it is possible to know the most accurate acceleration state by setting the constants α and β. be.

Further, the clutch engagement pressure control means is not limited to the electromagnetic proportional relief valve of the embodiment, and other means may be used.

Further, the mounting position of the rotation sensor is not limited to the mounting position of the embodiment as long as it is provided in the drive transmission system of the front wheel side and the rear wheel side.

(Effects of the Invention) As explained above, in the driving force distribution control device for a four-wheel drive vehicle of the present invention, the control means has a control characteristic in which the clutch engagement force increases in accordance with the difference in rotational speed between the front and rear wheels. is set, and the clutch engagement force is controlled based on a control characteristic in which the control constant is larger as the acceleration state detected by the acceleration state sensor indicates a sudden acceleration, so the drive force distribution changes smoothly according to the difference in rotational speed between the front and rear wheels. This eliminates sudden changes in steering characteristics, prevents wheel slip during sudden starts and spins during sudden acceleration turns, reduces understeer tendency during slow acceleration turns, and controls drive force distribution according to acceleration conditions. You can get the effect that you can.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a claim showing a driving force distribution control device for a four-wheel drive vehicle according to the present invention, FIG. 2 is an overall view showing a driving force distribution control device of an embodiment, and FIG. 4 is a block diagram showing the control unit of the embodiment device, FIG. 5 is a map showing the control characteristics stored in advance in the control unit of the embodiment JA, and FIG. 6 is the embodiment device. It is a flowchart figure showing the flow of operation in a control unit in . l... Front wheel 2... Rear wheel 3... Tj variable torque clutch 4... Actuator 5... Input sensor 501... Front and rear wheel rotation speed difference sensor 502... Acceleration state sensor 6... ... Control means patent application Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1) A variable torque clutch provided in the middle of the drive power transmission system to the front and rear wheels, an actuator that operates the variable torque clutch, and a variable torque clutch that operates based on an input signal from an input sensor. A driving force distribution control device for a four-wheel drive vehicle, comprising: a control means for outputting a control signal to the actuator to control a clutch engagement force of the four-wheel drive vehicle, wherein the input sensor includes a front and rear wheel rotational speed difference sensor and an acceleration state sensor. a sensor, the control means is configured to set a control characteristic in which the clutch engagement force increases in response to a difference in rotational speed between the front and rear wheels, and the control characteristic has a large control constant as the acceleration state detected by the acceleration state sensor indicates a sudden acceleration. 1. A driving force distribution control device for a four-wheel drive vehicle, characterized in that the clutch engagement force is controlled based on the following.