JPH0362571B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applied to a part-time four-wheel drive vehicle which normally has two-wheel drive using one of the front and rear wheels, but which runs in four-wheel drive when necessary. , regarding a switching control device that automatically switches to four-wheel drive when a slip occurs in the drive wheels during two-wheel drive driving, and specifically corrects the judgment of slip occurrence and the accompanying switching according to the vehicle speed and load condition. Regarding.

[Conventional technology and issues]

Generally, if you want to obtain a large driving force with 4-wheel drive,
Particularly remarkable performance can be demonstrated when driving on low-friction surfaces such as off-road, frozen, and snowy roads. Therefore, part-time 4-wheel drive vehicle 2,
In the automatic switching of four-wheel drive, in the case of wanting to obtain the above-mentioned former large driving force, there is a conventional method of switching to four-wheel drive at the first or reverse shift position of the low gear, as disclosed in Utility Model Publication No. 48-8821, for example. It has been proposed in the official gazette.

By the way, switching to four-wheel drive when wanting to obtain such a large driving force can be done appropriately at the discretion of the driver, and even if the switching is delayed, the performance of two-wheel drive is maintained. It doesn't pose much of a problem, and there is little need to force automation.

On the other hand, the driver only knows whether tire slip has occurred on a low-friction road surface from abnormalities in steering wheel operation caused by the slip, and if the driver switches to 4-wheel drive at this time, it is already too late and the 4-wheel drive vehicle The vehicle may become inoperable without being able to demonstrate its performance. Therefore, when switching to four-wheel drive in response to the occurrence of such a slip, it is necessary to accurately judge and switch to four-wheel drive at the initial stage of the occurrence of the slip, and from this reason, the switch can be made automatically without waiting for the driver's judgment. That becomes very important.

Here, wheel slip can be detected by the rotational speed difference between the front and rear wheels in two-wheel drive or the rotational angular velocity of the driving wheels. proposed an invention that automatically switches to four-wheel drive using the rotational angular velocity of the drive wheels for slip detection. Such a rotational angular velocity occurs when a sudden start or acceleration occurs, and in order to prevent it from being erroneously determined to have occurred at this time, a reference value is set in advance to serve as a reference for the determination. The presence or absence of actual slippage is determined by comparison with the value, and this reference value is uniquely determined to be a value greater than the rotational angular velocity in the case of a sudden start with the maximum driving force. Only.

By the way, in actual driving, as shown in Fig. 5, the maximum driving force curve of the full load against the vehicle speed through each gear stage is as shown in a, and as the load decreases, the driving force curve changes to b, c, and d. It becomes like this. Here, if the driving force is large, the detected value of the angular acceleration when the driving wheels rotate is large, so it may be incorrectly judged that the criterion value for determining whether or not slipping has occurred should also be increased. If it is small, the detected value of the angular velocity is small, and unless the judgment reference value is also made small, problems such as inaccurate judgment or slow judgment will occur.For this reason, the judgment reference value is corrected in accordance with the driving force. There is a need to. In this case, the driving force decreases as the vehicle speed increases, as shown in Figure 5, and similarly decreases as the load decreases, making it impossible to accurately determine either the vehicle speed or the load. In the end, both of them are 2
Since it can be determined dimensionally, the reference value for determining the presence or absence of slip must also be corrected in relation to these vehicle speed loads.

In view of these circumstances, the present invention focuses on the relationship between the driving force curve depending on vehicle speed and load, and at the same time decreases the reference value for determining whether or not a slip occurs as the vehicle speed increases. This is a switching control system for four-wheel drive vehicles that can be set to reduce slippage accordingly, and can accurately determine the initial stage of slippage with constant accuracy at each drive force when vehicle speed and load change. The purpose is to provide.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a four-wheel drive vehicle that directly transmits power to one of the front and rear wheels and, if necessary, also transmits power to the other of the front and rear wheels by engaging a transfer clutch. , the rotational angular acceleration is calculated based on rotational fluctuations of the drive wheels, and the rotational angular acceleration is compared with a reference value that is set to decrease as the vehicle speed increases and as the load decreases. However, when the rotational angular acceleration is greater than a reference value, it is determined that a two-wheel drive slip has occurred, and the system is configured to automatically switch to four-wheel drive.

〔Example〕

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings.

First, in FIG. 1, the transmission system of an example of a four-wheel drive vehicle to which the present invention is applied will be explained.
is a crankshaft from the engine, this crankshaft 1 is connected to a turbine shaft 3 via a torque converter 2, and the turbine shaft 3 connects an automatic transmission 4.
Transmission is configured. The automatic transmission 4 includes a planetary gear 5, clutches 6 and 7 that selectively input the power of the turbine shaft 3 to the input elements of the gear 5, a one-way clutch 8 that selectively locks each element of the gear 5, a brake 9, and a brake. The gear band 10 is equipped with a band 10, and the power that has been changed in speed from the automatic transmission 4 is taken out forward by an output shaft 11, and is transmitted to the shaft 1 by a reduction drive and driven gears 12, 13.
6 can be conveyed.

Further, a front wheel final reduction device 14 is disposed at a lower portion between the torque converter 2 and the automatic transmission 4, and a drive pinion formed at one end of a shaft 16 integral with the gear 13 is connected to a crown gear 15 of this device 14. 17 mesh with each other to perform two-wheel drive driving using the front wheels.

The other shaft 16 is extended rearward by a transfer drive shaft 18 and connected to a transfer drive and driven gears 20 and 21 of a transfer device 19 mounted at the rear of the automatic transmission 4. This gear 21 is connected to a rear drive shaft 23 via a transfer clutch 22 consisting of a hydraulic clutch for switching two and four wheel drives, and is further connected from the rear drive shaft 23 via a propeller shaft 24 to a final reduction gear for the final wheel 25. Transmission is configured. In this way, when the clutch 22 is released by draining oil, power transmission to the rear wheels is cut off, and when the clutch 22 is engaged by refueling, power is further transmitted to the rear wheels, resulting in a four-wheel drive state.

Next, the hydraulic control system for the clutch 22 will be explained. An oil pump 26, which is a hydraulic pressure source for the automatic transmission 4, is connected to the clutch 22 through an oil passage 28 having a switching valve 27. Switching valve 2
7 has an inlet port 29 on the oil pump 26 side, an outlet port 30 on the clutch 22 side, and a drain port 31, and is configured to move the spool 34 depending on whether the solenoid 32 is energized or not and the action of the return spring 33. There is. Therefore, when the solenoid 32 is de-energized, the inlet port 29 is closed as shown in the figure, and the outlet port 30 is closed to the drain port 31.
By communicating with the clutch 22, the clutch 22 is released by draining oil, and when the solenoid 32 is energized, the spool 3
4 moves to the left side and the drain port 31 closes,
The clutch 22 is supplied with oil and engaged through communication between the inlet and outlet ports 30 and 29, thereby performing the above-mentioned switching between two- and four-wheel drive.

To explain the electric control system in FIG. 2, a manual changeover switch 36 is provided at a select lever (not shown) of the automatic transmission 4, and this switch 36 is connected in series to the solenoid 32 of the changeover valve 27 and the battery 37. It is connected to. Further, in order to automatically switch when a slip occurs regardless of the operation of the switch 36 for switching between two and four wheel drives, an automatic switching switch 38 is connected in parallel to the switch 36.

Next, the outline of the control system that determines whether or not a slip has occurred will be explained with reference to Fig. 2.
In the transmission system shown in the figure, the driving wheels during two-wheel drive are the front wheels, so the front wheel rotation sensor 40 is installed on the front wheel side of the transfer clutch 22, for example, using the transfer driven gear 21.
The angular acceleration detection circuit 41 calculates the rotational angular acceleration of the front wheel based on the pulse from the rotation sensor 40, and this value is input to the comparator 42. Also,
The vehicle speed is determined by a vehicle speed detection circuit 43 such as a counter,
On the other hand, the detected value of, for example, the throttle valve opening sensor 44 for detecting the load is transferred to the A/D converter 45.
The reference value of the front wheel rotational angular acceleration reference value setting circuit 46 is corrected using this value and the vehicle speed, and is input to the comparator 42, where it is determined whether or not slip has actually occurred. In this way, if the rotational angular acceleration calculated based on the signal from the rotation sensor 40 is larger than the reference value set corresponding to each driving force based on the vehicle speed and load,
It is determined that a slip has occurred, and the comparator 42
An output signal is output from the switch 38 to turn on the switch 38. Note that the reference numeral 47 is a clock pulse generation circuit;
Using this clock frequency, a fixed time (t seconds) is set, and vehicle speed and angular acceleration are calculated, and A/D conversion and comparison are performed for each clock.

In FIG. 3, to explain the case where the above-mentioned process is performed by an actual microcomputer, the pulse from the front wheel rotation sensor 40 is sent to the counter 48 for a certain period of time (t
seconds) is counted to calculate the vehicle speed V ₁ , and this value is
It is written to register 50 of RAM 49,
Other registers 51 of RAM 49 contain the previous vehicle speed V ₀
is written. Further, the value of the load R detected by the throttle valve opening sensor 44 and converted into a digital value by the A/D converter 45 is written in the register 52 of the RAM 49.

On the other hand, a two-dimensional table map of reference values set based on vehicle speed and load is stored in advance in the ROM 53, similar to the relationship between the driving force curve depending on vehicle speed and load shown in _FIG . The reference value α on the table map determined by is read out and written into the register 54. After that, the CPU (central processing unit 55) subtracts the vehicle speed V ₁ and V ₀ to calculate the front wheel rotational angular acceleration, which is the change in vehicle speed over a certain period of time (t seconds), and compares this with a reference value α to determine the angle of rotation. If the acceleration is larger than the reference value, it is determined that a slip has occurred, and if it is smaller, the vehicle speed is determined.
V ₁ is written to register 51 for next determination. Thereafter, such actions are repeated, and the flowchart in this case is as shown in FIG. The program is stored in the ROM 53, and the CPU sequentially executes the program.

Since the present invention is configured in this way, the switch 36 is turned off and the solenoid 32 of the switching valve 27 is in a de-energized state, and the transfer clutch 22 is released by drained oil and the transfer clutch is operated only by the front wheels.
When wheel drive is performed, the rotational angular acceleration of the front wheel is calculated based on pulses from the rotation sensor 40 on the front wheel side. On the other hand, a reference value for determining whether slip has occurred is determined by correcting each drive force using vehicle speed and load, and this value is compared with the rotational angular acceleration of the front wheels calculated based on the pulses of the rotation sensor 40. Ru. Therefore, corresponding to the fact that the driving force differs depending on the load at each vehicle speed, the same conditions apply whether both the driving force and the slip occurrence are large, and conversely, the driving force and the slip occurrence are small. It is determined whether or not a slip has occurred.

When it is determined that a slip has occurred, the slip 38 shown in Fig. 2 is turned on and the solenoid 32 is energized, automatically switching to four-wheel drive and preventing wheel slip on low-friction road surfaces. It is avoided.

In addition to the rotational acceleration of the above-described embodiment, slip detection can also be performed using the rotational speed difference between the front and rear wheels, and it goes without saying that correction can be made based on the vehicle speed and load in that case as well.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the driving force is determined by both the vehicle speed and the load, and the reference value for determining the presence or absence of slip is determined according to the fact that the degree of slip occurrence differs depending on each driving force. Since it is corrected and made variable, and judgment is always made with a constant precision for each drive force, problems such as incorrect judgment or delay in judgment are prevented, and when a slip occurs, accurate judgment is made at the initial stage and 4-wheel drive is activated. It can be automatically switched to

[Brief explanation of drawings]

Fig. 1 is a skeleton diagram showing an example of the transmission system and hydraulic circuit of a four-wheel drive vehicle to which the present invention is applied;
3 is a block diagram showing an embodiment of the apparatus according to the present invention, FIG. 3 is a block diagram for microcomputer processing, FIG. 4 is a flowchart, and FIG. 5 is a diagram showing a driving force performance curve. 4... Automatic transmission, 14... Front wheel final reduction gear,
22...Transfer clutch, 25...Final wheel final reduction gear, 27...2, 4-wheel drive switching valve, 3
2... Solenoid, 38... Automatic switching switch, 40... Rotation sensor, 41... Angular acceleration detection circuit, 42... Comparator, 43... Vehicle speed detection circuit,
44...Throttle valve opening sensor, 46...Reference value setting circuit.

Claims (1)

[Claims] 1 Power is directly transmitted to one of the front and rear wheels, and the front and rear wheels are transmitted as necessary by engaging the transfer clutch.
In a four-wheel drive vehicle that also transmits power to the other rear wheel, the rotational angular acceleration is calculated based on rotational fluctuations of the drive wheel, and the rotational angular acceleration decreases as the vehicle speed increases, and as the load decreases. When the rotational angular acceleration is larger than the reference value, it is determined that slipping has occurred during two-wheel drive, and the system automatically switches to four-wheel drive. 4 characterized by having done
Switching control device for wheel drive vehicles.