JPS61169361A - Brake control device of 4-wheel-drive vehicle - Google Patents

Abstract

PURPOSE:To prevent a concurrent lock of four wheels by releasing the directly- connected front and rear wheel drive when the slip factor becomes a predetermined value or more and operating a wheel lock preventive device while braking under the directly-connected front and rear shaft drive. CONSTITUTION:Modulators 31, 31', 32, 32' controlling the brake pressure are provided at the wheel straight line position of a front wheel side brake pipe 27 and a rear wheel side brake pipe 28. A brake pressure controlling means 33 generates brake pressure control signals P1, P2 to control the brake pressure of front and rear wheels 11, 12 to satisfy an equation (Vc-Vt)X100/Vc=about 10-20%, where Vc is an absolute car speed, and Vt is a wheel speed. A wheel lock preventive device is constituted with the brake pressure controlling means and modulators. The brake controlling means 34 feeds a slip factor signal (s) and a operation start signal (d) to the brake pressure controlling means 33 via signals (v), alpha from a car speed sensor 36 and a deceleration sensor 37.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a braking control device for a four-wheel drive vehicle, and particularly to a technique for improving braking performance during braking in a four-wheel drive directly connected state.

(Prior art) As a conventional four-wheel drive vehicle, for example, "Automotive Engineering VA1
．． 33 No. 84 (published by Railway Japan Co., Ltd. on August 1, 1981), pages 56 to 62 are known.

This 4-wheel drive vehicle is a full-time 4-wheel drive vehicle equipped with a center differential (hereinafter referred to as center differential), and this 4-wheel drive vehicle is
As described on page 1, wheel lock prevention device @ (An
ti Block System (abbreviated as ABS) is equipped as an option.

In addition, the wheel opening/double prevention device is based on the vehicle speed (Vc) and the vehicle e-
The brake pressure of the front wheels, rear wheels, or front and rear wheels is controlled so that the ratio of wheel speed (Vt) This is a device that prevents locking.

In general, when the drive of a four-wheel drive vehicle is directly connected, sufficient braking torque is applied to each wheel, making it possible to brake the vehicle without causing premature locking of the wheels. It is possible.

However, even with 4-wheel drive vehicles, those with a center differential as mentioned above can separate the front and rear wheel drive systems, and in this state, just like a 2-wheel drive vehicle, when braking, the rear wheels are activated first. Wheel lock prevention device (
An anti-skid device (also called an anti-skid device) was used to unlock the center differential.

Note that it is difficult to use a wheel lock prevention device when the center differential is locked, that is, when the front and rear wheel drive systems are directly connected, for the reasons described below.

First, when the front and rear wheels are directly connected, each wheel is connected to the engine drive system, so the inertia during braking becomes extremely large, and the engine brake is stronger than the traction that tries to rotate each wheel. When it is large, all four wheels will lock, making control by the wheel lock prevention device impossible.

Figure 5 shows the control characteristics. Even with the same wheel lock prevention device, when the front and rear wheel drive systems are directly connected (graph A), the wheel speed ( vt
), resulting in long stopping distances, instability, and poor riding comfort.

Second, tight corner braking that occurs during a turn cannot be controlled by the wheel lock prevention device, so even if the wheel lock prevention device attempts to control a braking force that is less than the tight corner braking force, it is impossible.

Note that the center differential is provided for the purpose of preventing tight corner braking due to the difference in rotation between the front and rear wheels when turning.

(Problems to be Solved by the Invention) However, in such conventional four-wheel drive vehicles, wheel lock protection devices are not used when the front and rear wheel drive systems are directly connected. Therefore, although it does not lead to early locking in the drive directly connected state,
Eventually, all four wheels would lock up at the same time, making the vehicle's behavior extremely unstable and making steering impossible, creating a dangerous situation.

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

This solution will be explained using the conceptual diagram of the claim shown in FIG. 1. A clutch 1 that directly connects or separates a front wheel drive system and a rear wheel drive system, a wheel lock prevention device 2 during braking,
In a four-wheel drive vehicle equipped with a four-wheel drive vehicle, a clutch that detects the slip rate of the wheels during braking in a state in which the front and rear wheels are directly connected by engagement of the clutch l, and releases the engagement of the clutch l when the slip rate exceeds a predetermined value. A release signal ■, an operation start signal ■ that starts the operation of the wheel lock prevention device 2,
A control means 3 for outputting is provided.

(Function) Therefore, in the braking control device for a four-wheel drive vehicle of the present invention, by employing the above-mentioned means, when the slip rate of the wheels exceeds a predetermined value during braking in a state in which the front and rear wheels are directly connected, In response to a signal from the control means 3, the clutch 1 is automatically disengaged to separate the drive, and the wheel lock prevention device 2 is started to operate.

This makes it possible to prevent the four axes from locking during braking when the front and rear wheels are directly connected.

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

In describing this embodiment, a brake 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 and 3 will be explained.

The drive transmission system for the front wheels 11.11' and the rear wheels 12.12' includes an engine 13, a transmission 14. Drive output shaft 15, rear wheel side drive shaft 16.
Rear differential 17, rear drive shaft 1
8. Transfer clutch 19, front wheel drive shaft 20, front wheel drive shaft 21. It is equipped with a front drive shaft 22, and the driving force from the transmission l4 is directly transmitted to the rear wheel drive shaft 16, but the driving force is transmitted to the front wheel drive shaft 20 via a transfer clutch 19. Ru.

The transfer clutch 19 is a clutch that switches between two-wheel drive and four-wheel drive, and the actuator 2
When the clutch is released in step 3, the vehicle enters a rear-wheel drive state, and the drive systems for the front and rear wheels are also disconnected, and when the clutch is engaged, the vehicle becomes a four-wheel drive state, and the drive systems for the front and rear wheels are also mechanically directly connected.

The braking system for the front wheels 11.11' and rear wheels 12.12' is as follows:
As shown in FIG. 2, a brake pedal 24, a master back 25, a mask cylinder 26, a front brake pipe 2
7. Rear wheel side brake pipe 28, brake cylinder 29
．． 29', 30.30'.

Incidentally, modulators 31.31' and 32.32' for controlling brake pressure are provided at positions immediately in front of each of the front wheel brake pipe 27 and the rear wheel brake pipe 28, respectively.

33 is a braking pressure control means, which controls the front and rear wheels 11.11' so that the absolute vehicle speed (V (slip ratio) is in the range of 105 to 205 (the friction coefficient is maximum).

12. Brake pressure control signals (Pi), (Pi)', (P2), (P
2) In the embodiment, the necessary slip rate as an input signal is manually input as a slip rate signal ■ from the brake control means 34, which will be described later, and the slip rate calculation in the brake pressure control means 33 is omitted. There is.

Note that this braking pressure control means 33 and modulators 31 and 31
', 32.32' constitute the wheel lock prevention device of the embodiment.

Reference numeral 34 denotes a braking control means, which controls when braking in a state in which the front and rear wheels are directly connected by engaging the transfer clutch 19.
Calculates the slip rate of the wheels, and when the slip rate exceeds a predetermined value, outputs a clutch release signal (■) that disengages the transfer clutch 19 and an operation start signal (@) that starts the operation of the braking pressure control means 33. It is something to do.

This braking control means 34 includes input sensors such as a brake switch 35, a vehicle speed sensor 36, a deceleration sensor 37, and wheel speed sensors 38, 38', and 39.39'.
Brake activation signal■.

A vehicle speed signal ■, a deceleration signal @, and a wheel speed signal [phase] are input.

The vehicle speed sensor 36 is a drive shaft rotation detection means, etc., and detects the drive shaft rotation speed (Vco), but since wheel slip is not considered at all, the deceleration sensor 37 is used. Since an approximate value of the absolute vehicle speed (VC) cannot be calculated unless the vehicle deceleration (α) is detected, two sensors 36 and 37 are provided in the embodiment to detect the vehicle speed (VcO) and the deceleration (α). ing.

Further, in the embodiment, the brake pressure control means 33 and the brake control means 34 are housed in a control unit 40 using a microcomputer.

Next, a block diagram of the brake control means 34 shown in FIG. 3 will be explained.

This braking control means 34 includes an A-D conversion circuit 341, a clock circuit 342, a RAM 343, a ROM 344, and a CPU.
345, a clutch release signal generation circuit 346, and an operation start signal generation circuit 347, each of which will be specifically described below.

The A-D conversion circuit 341 uses the CPU 345 to calculate a vehicle speed signal ■, a deceleration signal @, and a wheel speed signal ■ based on analog signals input from the vehicle speed sensor 36, deceleration sensor 37, wheel speed sensor 38, and so on. This is a circuit that converts signals into digital signals that can be processed.

Note that if the input signal is a pulse signal, a count circuit is used instead of the A-D conversion circuit 341.

The clock circuit 342 provides time instructions and
This is a circuit for performing arithmetic processing and data reading in H.345 at predetermined intervals.

The RAM 343 (random, access, memory) is a memory that can be written to and read from, and temporarily stores signals input while the CPU 345 is performing arithmetic processing.

The above ROM344 (read, only, memory) is
This ROM 344 is a read-only memory, and this ROM 344 stores in advance a predetermined slip ratio in the form of a numerical value, which is necessary when comparing slip ratios.After the actual slip ratio is calculated, the comparison Therefore, this set slip rate is read out.

The CPU 345 (central, processing, unit) is a central processing unit that performs arithmetic processing.
U345 reads data from the RAM 343 and ROM 344, calculates the slip ratio, etc., and outputs the resulting signals to the clutch release signal generation circuit 346 and the operation start signal generation circuit 347, and also outputs the results to the brake pressure control means 3.
3, a slip rate signal ■ is output.

The clutch release signal generation circuit 346 is a circuit that receives a result signal indicating that the slip ratio has reached a predetermined value or more from the CPU 345 and outputs a clutch release signal (■) to the actuator 23 used for clutch connection/disconnection of the transfer clutch 19. It is.

The operation start signal generation circuit 347 inputs a result signal indicating that the slip ratio has reached a predetermined value or more from the CPU 345, and
This circuit outputs an operation start signal @ to the braking pressure control means 33.

Next, the operation of the embodiment will be explained.

In describing the operation of the embodiment, a flowchart showing the flow of operations in the CPU 345 of the brake control means 34 shown in FIG. 4 will be described below.

First, in step 100, the brake operation signal (2), vehicle speed signal (2), deceleration signal @, and wheel speed signal (phase)) are read.

In the next step 101, it is determined whether or not a brake operation is being performed by depressing the brake pedal 24, depending on whether or not the brake operation signal ■ is input. If the brake operation is being performed, the next Proceeding to step 102, if the brake is not being operated, the transfer clutch 19 is connected (step 103), and the wheel lock prevention device is stopped (step 104).

The operations in steps 103 and 104 are performed when the brake is not being operated, the transfer clutch 19 is in the released state, and the wheel lock prevention device is in the operating state.

In step 102, the vehicle speed (Vco) is determined by the vehicle speed signal ■.
Then, the absolute vehicle speed (V c) is calculated based on the deceleration (α) caused by the deceleration signal @.

Furthermore, the calculation formula for absolute vehicle speed (Vc) is as follows: Vc=Vco
-fadt.

In step 105, the slip ratio (S) is calculated from the absolute vehicle speed (Vc) calculated in step 102 and the wheel speed (Vt) based on the wheel speed signal Co., Ltd.

becomes.

In the next step 106, the slip ratio (S) calculated in the step 105 is compared with a predetermined value (i) of the slip ratio stored in advance.
) is smaller than (i) (S≦i), the process proceeds to steps 103 and 104, and if the slip ratio (S) is greater than (i) (Ski), the process proceeds to the next step 107.

Note that the predetermined value (i) of the slip ratio is set to a value that almost causes the wheels to lock.

In the next step 107, the clutch release signal generation circuit 3
A circuit activation start signal is output to 46 to disengage the transfer clutch 19.

Note that, by disengaging and disengaging the transfer clutch 19, the mechanical direct coupling state between the front wheels 11.11' and the rear wheels 12.12' is also disengaged.

In the next step 108, the operation start signal generation circuit 347
A circuit operation start signal is output to the brake pressure control means 33 (wheel lock prevention device).

Incidentally, the CPU 345 also outputs a slip ratio signal (2) necessary for control to the braking pressure control means 33.

Furthermore, the operations in step 107 and step 108 may be performed with a slight time lag or may be performed simultaneously.

The above operation is repeated at every set time by the clock circuit 342.

Therefore, when braking is performed on the four-wheel drive vehicle of the embodiment, braking is performed in a state in which the four wheels are directly connected until the slip ratio of the wheels reaches a predetermined value (i), and when the slip ratio exceeds the predetermined value (i). , braking is automatically performed using the wheel lock prevention device in the two-wheel drive 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, in the example, we have explained a part-time 4-wheel drive vehicle based on rear-wheel drive, but even if it is a front-wheel drive-based or full-time 4-wheel drive vehicle, The invention can be applied.

Further, in the embodiment, a transfer clutch is shown as a clutch that directly connects or separates the drive systems of the front and rear wheels, but a center differential or other clutch may be provided in the middle of the drive system as in the conventional example.

Further, the wheel lock prevention device may be a device or system other than the embodiment.

Yet again. Wheel lock prevention control may be performed by determining the absolute vehicle speed using a radar, etc. In this case, it is possible to detect the vehicle speed more accurately than in the previously described embodiment, and the accuracy of the control is also improved. is possible.

(Effects of the Invention) As explained above, in the braking control device for a four-wheel drive vehicle of the present invention, during braking in a state in which front and rear wheel drives are directly connected,
When the slip ratio exceeds a predetermined value, the front and rear wheel drive direct connection is released and the wheel lock prevention device is activated.

Taking advantage of the braking performance in direct connection to 4-wheel drive, which does not cause early locking until the slip ratio reaches a predetermined value, when the slip ratio exceeds a predetermined value, the wheel lock prevention device is activated to reduce the 4-wheel drive time. This has the effect of being able to prevent locking.

This effect improves vehicle behavior stability during braking.
Steering performance and braking distance can be shortened.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a claim showing a braking control device for a four-wheel drive vehicle according to the present invention, Fig. 2 is an overall diagram showing a braking control device of an embodiment, and Fig. 3 is a block diagram showing a braking control means in the embodiment device. 4 is a flowchart showing the flow of operations in the CPU of the brake control means, and FIG. 5 is a graph showing braking pressure control characteristics when a wheel lock prevention device is used in a conventional four-wheel drive vehicle. be. l... Clutch 2... Wheel lock prevention device 3... Control means ■... Clutch release signal ■... Operation start signal Fig. 1

Claims (1)

[Claims] 1) In a four-wheel drive vehicle equipped with a clutch that directly connects or separates the front wheel drive system and the rear wheel drive system, and a wheel lock prevention device during braking, braking in a state where the front and rear wheel drives are directly connected by engaging the clutch. The control means detects the slip rate of the wheels and outputs a clutch release signal to disengage the clutch and an operation start signal to start the operation of the wheel lock prevention device when the slip rate exceeds a predetermined value. A braking control device for a four-wheel drive vehicle, characterized in that: