JPS59184025A - Four-wheel-drive vehicle - Google Patents

Abstract

PURPOSE:To make it possible to simultaneously brake and stop all four wheels upon a vehicle being rapidly braked, so that the braking function is enhanced, by providing a differential function inhibiting means for operating a front and rear wheel differential control means in a differential function inhibiting direction when the braking force of the vehicle exceeds a predetermined value. CONSTITUTION:When a vehicle on running is rapidly braked in such a condition that a front and rear wheel differential control means 26 is not operated in a differential function inhibiting direction, braking force exceeds a predetermined value. A brake force detecting means 35 detects this braking force, and simultaneously, a fron and rear wheel differential control detecting means 31 detects such a condition that the control means 26 does not operate in the differential function inhibiting direction. When output signals from the detecting meand 35, 31 are delivered to an electronic control circuit 32, the circuit 32 delivers a signal to a solenoid 23 so that the control means 26 is operated in the differential function inhibiting direction. With this arrangment, a spool 27a in a valve 27 moves downward to increase the hydraulic pressure in an oil chamber 29a, and therefore, a multiple-disc clutch 29 is frictionally engaged. Then, the control means 26 is operated in the differential function inhibiting direction, and therefore, the differential function of a front and rear operating mechanism 7 is inhibited. Accordingly, all wheels are braked and stopped, simultaneously, thereby excellent braking function may be exhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides that when the front and rear wheel differential control means is not operating in the direction of inhibiting the differential function, when the braking force of the vehicle exceeds a predetermined value, the front and rear wheel differential control means automatically activates the front and rear wheel differential control means. The present invention relates to a four-wheel drive vehicle that operates in the direction of inhibiting the differential function to improve braking performance when braking the vehicle.

Generally, a two-wheel drive vehicle has two wheels that generate driving friction force.
Since there are only wheels, the power to climb a slope is weak, and if one of the two drive wheels gets into muddy off-road (outside the road), the differential device on the left and right axles will not be able to generate any driving force, and furthermore, the wheel It has drawbacks such as not being able to overcome obstacles higher than the radius. Four-wheel drive vehicles have been conventionally used to overcome the drawbacks of two-wheel drive vehicles. However, although four-wheel drive vehicles can solve the above drawbacks, as shown in Fig. 1, the steering angle θ of the steering wheels increases, resulting in a difference in the turning radius between the front wheels and the rear wheels (
R-r) increases, a large difference also occurs between the rotation speed of the front wheels (more precisely, the average rotation speed since the left and right wheels differ) and the rotation speed of the rear wheels. In this case, if you try to forcefully steer the vehicle, a very large torque will be generated at both ends of the propeller shaft and axle shaft that transmit rotation to the front and rear wheels, making the steering wheel less responsive, or This causes the front wheels and rear wheels to slip in opposite directions, causing a tendency to understeer (a phenomenon in which the turning radius becomes larger than the one that should be obtained due to the steering angle), and also brakes the vehicle's running. Frictional force that causes the engine to stop or stall (referred to as tight corner braking) occurs on the tires. In order to solve this situation, there are four-wheel drive vehicles that are equipped with a front-rear wheel differential mechanism between the front wheels and the rear wheels.

Now, if even one of the four wheels in the front and rear gets into the mud, the differential mechanism between the left and right wheels and the front and rear wheel differential mechanism work together, and as a result, all of the wheels that got into the mud get stuck. Otherwise, most of the driving force is supplied and the wheel spins, causing all the other three wheels to lose driving force, making it difficult for the vehicle to proceed.

To solve this situation, four-wheel drive vehicles equipped with front and rear differential mechanisms are equipped with front and rear differential control means (lock amplifiers) that can control the differential function of the front and rear differential mechanisms. mechanism or non-slip differential mechanism). In other words, according to such a front and rear wheel differential control means, even if one of the front wheels and the rear wheels gets into mud, etc., it is possible to prevent the front wheel or the rear wheel from moving out of the mud by controlling the front and rear wheels in a direction that blocks the differential function of the front and rear wheel differential mechanism. It becomes possible to transmit the driving torque to the other wheel which has a high frictional force. In addition, in a four-wheel drive vehicle equipped with such front and rear wheel differential control means, when the means is operating in the direction of blocking the differential function, the front wheels and rear wheels are integrated via the drive system. rotate. For this reason, when the vehicle suddenly brakes, either the front wheels or the rear wheels will not brake to a stop first (the front and rear wheels can brake to a stop at the same time, and the braking performance of the vehicle is extremely high. An example of a four-wheel drive vehicle equipped with such a front and rear wheel differential mechanism and front and rear wheel differential control means is disclosed in Japanese Patent Laid-Open No. 114727/1983.

However, in such four-wheel drive vehicles, variations in braking force during vehicle braking are unrelated to the operation of the front and rear wheel differential control means, so this means cannot be operated in the direction of blocking the differential function. There are cases where the vehicle is suddenly braked, and in that case, there is a problem in that the above-mentioned excellent braking characteristics of the vehicle cannot be utilized. Furthermore, it is difficult for the occupant to operate the two-wheel/four-wheel switching means each time the vehicle is suddenly braked, which poses a problem in terms of operability.

This invention was made by focusing on such conventional problems, and provides a four-wheel drive vehicle having a front and rear wheel differential mechanism and a front and rear wheel differential control means. The above-mentioned problem is solved by comprising a dynamic control detection means and a differential blocking means that controls the front and rear wheel differential control means to operate in the differential function blocking direction when the braking force of the vehicle exceeds a predetermined value. The purpose is to

The present invention will be explained below based on the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention. First, to explain the configuration, in Fig. 2, l is the vehicle body, and 2
is an engine supported by this vehicle body l. A transmission 3 and an auxiliary transmission 4 are connected to the engine 2.

A high/low (two-speed) switching device 5, which constitutes a part of the sub-transmission 4, is connected to the shift ta3. A front and rear wheel differential mechanism 7 forming a part of the transmission 4 is connected. The front and rear wheel differential mechanism 7 includes a differential case 7a, a pinion shaft 7b fixed to the differential case 7a, and two differential pinions 7c rotatably supported by the pinion shaft 7b.
and two side gears 7d that are always in mesh with two differential pinions 7c. One end of a rear wheel propeller shaft 13 is connected to one side gear 7d, and a rear left and right wheel differential mechanism 14 is connected to the other end of the rear axle propeller shaft 3. Rear wheel axle shafts 15a, 1 are provided on both sides of the rear left and right wheel differential mechanism 14.
The left and right rear wheels @16a, 16b are connected via the rear wheel 5b, and the left and right rear wheels 16a, 16b are connected by the rear left and right wheel differential mechanism 14.
16b can absorb the difference in rotational speed. A first chain wheel 18 is connected to the other side gear 7d on the same axis, and the first chain wheel [8] is connected to a second chain wheel 20 via a chain heel 9. One end of a front wheel propeller shaft 21 is connected to the axle of the second chain wheel 20, and a front left and right wheel differential mechanism 22 is connected to the other end of the front wheel propeller shaft 21. Left and right front wheels 25a and 25b are connected to both sides of the front left and right wheel differential mechanism 22 via front wheel axles 24a and 24b. 25b can absorb the difference in rotation speed. Differential case 7a of front and rear wheel differential mechanism 7 and first chain wheel 1
Front and rear wheel differential control means 26 is interposed between the front and rear wheels 8.

This front and rear wheel differential control means 26, as shown in FIG.
A front and rear wheel differential control valve 27 connected to a hydraulic system including a vehicle transmission 3, etc., and a spool 27a of this valve 27.
Iron core 23a that can move this spool 27a in contact with
The solenoid 23 housed in the axis and the oil chamber 29a that receives the hydraulic pressure to operate it are the front and rear wheel differential control valves 27.
Hydraulic multi-disc clutch 29 connected to the boat (entrance/exit)
It has The hydraulic child plate clutch 29 includes a pair of clutch plates 29b and 29c, one of which is attached to the differential case 7d, and the other is attached to the first clutch plate.
It is connected to a chain wheel 18.

By adjusting the magnitude of the current flowing through the solenoid, the iron core 23a is moved, and as this iron core 23a moves, the spout (527a) that it comes into contact with is moved to improve the oil flow of the front and rear wheel differential control valve 27. Adjust. If a high oil pressure is applied to the oil chamber 29a, the hydraulic multi-disc clutch 29 will be frictionally engaged, if the oil pressure in the oil chamber 29a is low, the hydraulic multi-disc clutch 29 will slip, and if the oil chamber 29a is drained, the hydraulic multi-disc clutch 29 will be engaged. The frictional engagement is released. 28 has front wheels 25 at both ends serving as steering wheels.
a, 25b, and is a steering means driven by a steering wheel (not shown). Reference numeral 31 indicates front and rear wheel differential control detection, which measures the oil pressure in the oil chamber 29a of the hydraulic multi-disc clutch 29 and detects the operation of the front and rear wheel differential control means 26, that is, the presence or absence of frictional engagement of the hydraulic multi-disc clutch 29. It is a means. 35 is a braking force detection means for detecting the braking force of the vehicle, which is provided on the vehicle body 1 and includes a brake pedal (not shown).

That is, a strain gauge is attached to the brake pedal, and an electronic circuit calculates and detects the braking force during braking of the vehicle from the amount of deflection of the brake pedal. 32 is an electronic control circuit that can input signals from the braking force detection means 35 and the front and rear wheel differential control detection means 31 and output a signal to the solenoid 23 based on the signal results. This electronic control circuit 32 constitutes a part of differential blocking means that controls the front and rear wheel differential control means 26 to operate in the differential function blocking direction.

Next, the effect will be explained. Currently, the vehicle is being operated without operating the front and rear wheel differential control means 26 in the differential blocking direction, and as shown in FIG. becomes larger, the front wheels 25a, 25
The turning radius (R,
r), which causes a large difference (R-r) in front wheel 2.
A large difference also occurs between the respective average rotational speeds of the wheels 5a, 25b and the rear wheels 16a, 16b. This difference in average rotational speed is absorbed by the operation of the front and rear wheel differential mechanism 7, and the vehicle can turn smoothly while being steered at a large steering angle θ. In this way, the vehicle continues to run without operating the front and rear wheel differential control means 26 in the differential prevention direction,
When a vehicle is suddenly braked for some reason, the braking force of the vehicle becomes greater than a predetermined value. At this time, the braking force detection means 35 detects that the braking force of the vehicle has exceeded a predetermined value. At the same time, the front and rear wheel differential control detection means 31 detects that the front and rear wheel differential control means 26 is not operating in the differential function inhibiting direction. Therefore, when the detection signals outputted by the braking force detection means 35 and the front and rear wheel differential control detection means 31 are input to the electronic control circuit 32, the electronic control circuit 32 controls the front and rear wheel differential control as shown in FIG. A signal is output to the solenoid 23 to operate the control means 26 in the direction of inhibiting the differential function. The current supply to the solenoid 23 gradually increases in response to a signal from the electronic control circuit 32, and the spool 27a of the front and rear wheel differential control valve 27 moves downward in the figure, thereby increasing the oil chamber 29.
When the oil pressure at a increases, the hydraulic multi-disc clutch 29 is frictionally engaged, the front and rear wheel differential control means 26 is operated in the direction of blocking differential, and the differential function of the front and rear wheel differential mechanism 7 is blocked. As a result,
Front wheels 25a, 25'b and rear wheels IEia, 16b
Because the front wheels 25a, 25b and the rear wheels 1 rotate integrally through the drive system, when the vehicle suddenly brakes, the front wheels 25a, 25b and the rear wheels 1
All of the wheels 25a, 25b, 16a, and 16b are braked to a stop at the same time without any one of the wheels 6a and 16b being braked to a stop first, and extremely excellent braking performance can be exhibited. Further, for the occupant, there is no need to operate the front and rear wheel differential control means 26 in the differential prevention direction every time the vehicle is suddenly braked, so that the operability of the four-wheel drive vehicle can be improved.

In the above embodiment, the vehicle braking force is detected from the amount of deflection of the brake pedal, but the braking force may be detected by other means as long as the vehicle braking force can be detected, such as by detecting the hydraulic pressure of the brake mask cylinder. It may also be a means for detecting.

FIG. 5 shows another embodiment.

In addition to the braking force detection means 35 and the front and rear wheel differential control detection means 31 provided in the previous embodiment, this embodiment also includes a friction coefficient detection means for detecting the friction coefficient between the tire of the wheel and the road surface. This is an additional feature. As the coefficient of friction between the tires and the road surface decreases, the braking friction force of the vehicle also decreases, resulting in poor braking efficiency. Therefore, when the coefficient of friction becomes low, the deceleration of the vehicle is set to a lower predetermined value accordingly, and when the deceleration exceeds the predetermined value, the front and rear wheel differential control means 26 is operated in the direction of inhibiting the differential function. There is a need. In this way, the braking efficiency of the vehicle is improved. In FIG. 5, reference numeral 3o denotes a steering angle detecting means that is provided on the vehicle body l near the steering means 28 and detects the state in which the steering means 28 moves and detects the steering angle of the steered wheels. Reference numeral 4o denotes a vehicle speed detection means that is provided in the vehicle body 1 near the output shaft 5a of the high/low switching device 5 and detects the rotational speed of the output shaft 5a to detect the speed of the vehicle.

A vertical load detection means 41 is provided on the vehicle body 1 near the front wheels 25a, which are steering wheels, and roughly detects the force applied in the vertical direction to the contact surface between the tires of the front wheels 25a and the road surface. Reference numeral 42 denotes a steering force detection means that is provided as a part of the steering means 28 and detects a steering force generated by being driven by a steering link wheel (not shown). 33 is a friction coefficient calculation which inputs signals from the steering angle detection means 30, vehicle speed detection means 40, vertical load detection means 41 and steering force detection means 42, and calculates the friction coefficient between the tires and the road surface based on the signal results. It is a device. The reason why the friction coefficient can be calculated from these signal results is as follows. The formula for determining the moment M around the king pin axis when the vehicle is running is as shown below.

M=Nsinζsinφe (r +Rw sinζ
cosφe)+SRwsinζsinψe cosζ+
5Xscosζ + Nfrcosζ (Automotive Engineering Handbook, page 8-16, bottom right corner, Automotive Technology Extra Line) In this formula, M is the moment around the kingpin axis, so it is a value that can be found if the steering force is known, and N is the value that can be found if the steering force is known. 25a, the vertical load applied to the contact surface with the tire, r is the scrub radius, Rw is the effective radius of the tire, and S is the force acting in the horizontal direction perpendicular to the tire traveling direction on the contact surface between the road surface and the tire (side force). This S
is obtained from the formula 5=Nf'5 (fs is the sideslip friction coefficient). Since this fs is a value that changes depending on the vehicle speed, S can be approximately estimated from the detection results of the vertical load detection means 41 and the vehicle speed detection means 40. Xs is T
It is expressed in sat/s, and Tsat is the self-lining torque and is determined based on the vehicle type and the steering angle of the steered wheels 25a. Therefore, Xs can be roughly estimated if the vehicle type, steering angle, vehicle speed, and vertical load between the steered wheels and the road surface are determined. f is the coefficient of friction between the tires of the steering wheels 25a and the road surface.

Further, ζ is an angle determined by the kingpin inclination angle δ and the caster angle β as shown in the following equation, that is, an angle that is naturally determined depending on the vehicle type.

tan2ζ=ta'n''δ+tan2βφe is the steering angle of the steering wheel 25a. Therefore, M, N, φe,
S and Xs are estimated by detecting the steering force, the load applied in the vertical direction to the contact surface between the steering wheel 25a and the road surface, the steering angle of the steering wheel 25a, and the vehicle speed, (specification), and the f deviation remains as an unknown quantity. Therefore, the friction coefficient calculation device 33 includes the steering angle detection means 30, the vehicle speed detection means 40,
By inputting the output signals of the detected values detected by the vertical load detecting means 41 and the steering force detecting means 42, the friction coefficient f can be approximately calculated. Then, the calculation result is output to the electronic control circuit 32 as a signal. Therefore, the steering angle detection means 30, the vehicle speed detection means 40, the vertical load detection means 41, the steering force detection means 42, and the friction coefficient calculation device 33 collectively constitute a friction coefficient detection means. When a signal is input from the friction coefficient calculating device 33 to the electronic side 1ali circuit 32, the electronic control circuit 32 calculates and stores a predetermined value of the vehicle braking force according to the value of the friction coefficient. In other words, when the coefficient of friction is low, the predetermined value of braking force is also low (
do. Signals are input from the braking force detecting means 35 and the front and rear wheel differential control detecting means 31 to the electronic control circuit 32, and when the braking force of the vehicle exceeds the stored predetermined value and the front and rear wheel differential control means 26 is When the front and rear wheel differential control means 26 is not operating in the differential function blocking direction, the electronic control circuit 32 outputs a signal to the solenoid 23 of the front and rear wheel differential control means 26 to operate the front and rear wheel differential control means 26 in the differential function blocking direction. It looks like this. As described above, according to this embodiment, even when the coefficient of friction between the tires and the road surface is low, the braking efficiency of the vehicle can be improved and excellent braking performance can be exhibited.

As explained above, according to the present invention, the vehicle body and
The front and rear wheels are rotatably supported by the vehicle body, and the front and rear differential mechanism is connected to the front and rear wheels, respectively, and absorbs the difference in rotational speed between the front and rear wheels. A four-wheel drive vehicle having a front and rear wheel differential control means capable of limiting or blocking an operational function, a braking force detection means for detecting a braking force of the vehicle, and a front and rear wheel differential control means capable of inhibiting an operational function of the front and rear wheel differential control means. Front and rear wheel differential control detection means for detecting the presence or absence of operation; and a front and rear wheel differential control means that inputs signals from the braking force detection means and the front and rear wheel differential control detection means to ensure that the braking force of the vehicle exceeds a predetermined value. and differential blocking means for controlling the front and rear wheel differential control means to operate in the differential function blocking direction when the front and rear wheel differential control means is not operating in the differential function blocking direction. When the vehicle suddenly brakes, all four wheels can be braked and stopped at the same time, resulting in excellent braking performance. In addition, for the occupants, there is no need to manually operate the front and rear wheel differential control means in the differential blocking direction each time the vehicle suddenly brakes, which has the effect of improving the operability of the four-wheel drive vehicle. can get.

Further, in other embodiments, it is possible to obtain an effect that excellent braking performance can be exhibited even when the coefficient of friction between the tire of the wheel and the road surface is a low value.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a vehicle showing the difference in the turning radius of the front wheels and rear wheels on a road surface when the steering angle of the steering wheel is large, and FIG. 2 is a plan view of a four-wheel drive vehicle according to the present invention. FIG. 3 is a partial cross-sectional schematic diagram showing the front and rear wheel differential control means, FIG. 4 is a block diagram showing the signal system of one embodiment shown in FIG. 2, and FIG. 5 is a diagram showing another example. FIG. 6 is a block diagram showing the signal system of another embodiment shown in FIG. 5. 1-------One vehicle body, 7----One front and rear wheel differential mechanism, 7a------Tifferency middle case, 7b-
---Pinion shaft, 7C---Differential pinion, 7d---
--- Side gear, 16a, 16 b --- Rear wheel, 23 ---
-Solenoid, 25a, 25b ----One front wheel, 26--Front and rear wheel differential control means, 27----One front and rear wheel differential control valve, 29----
- Hydraulic multi-disc clutch, 30 - - Steering angle detection means, 31 - Front and rear wheel differential control detection means, 32 - -
---1 electronic control circuit (differential blocking means), 33---1 friction coefficient calculation device, 35--1 braking force detection means, 40--1 military speed detection means, 41--1- - Vertical load detection means, 42-1 - Steering force detection means. Patent Applicant Nissan Motor Co., Ltd. Representative Patent Attorney Agagun Part

Claims (2)

[Claims] (1) A vehicle body, a front wheel and a rear wheel that are rotatably supported by the vehicle body, and a front and rear wheel differential mechanism that is connected to the front wheels and the rear wheels, respectively, and absorbs the difference in rotational speed between the front wheels and the rear wheels; In a four-wheel drive vehicle having front and rear @□ differential control means capable of limiting or blocking the operating function of the front and rear wheel differential mechanism, a braking force detection means for detecting the braking force of the vehicle, and the front and rear wheel differential control. Front and rear wheel differential control detection means detects whether or not the means operates in the direction of inhibiting the operation function, and signals are input from the braking force detection means and the front and rear wheel differential control detection means to detect the vehicle speed.
j When the power exceeds a predetermined value and the front and rear wheel differential control means is not operating in the direction of inhibiting the differential function, the front and rear wheel differential control means is configured to operate in the direction of inhibiting the differential function. A four-wheel drive vehicle characterized by comprising: differential blocking means for controlling. (2) The four-wheel drive vehicle is provided with a friction coefficient detection means for detecting a friction coefficient between the steered wheels and the road surface, and the differential blocking means receives a signal from the friction coefficient detection means and receives a friction coefficient from the friction coefficient detection means. Claim 1: When the predetermined value of the braking force is low, the predetermined value of the braking force is correspondingly low and the front and rear wheel differential control means is controlled to operate in the direction of inhibiting the differential function. 4 wheel drive vehicle as described.