JPH05180325A - Automatic transmission control device of four wheel drive vehicle - Google Patents

Abstract

PURPOSE:To regulate the automatic speed change of an automatic transmission when a vehicle is detected to be unstable by detecting rationally whether a vehicle is unstable or not. CONSTITUTION:In controlling torque distribution to the front and the rear wheel by means of a center differential clutch, a comparison is made between a target yaw rate and an actual yaw rate which are determined by the vehicle speed and the steering angle, and the joint force of the center differential clutch is to be controlled by depending upon at least this comparison. Thereupon, judgment is made as to whether or not the joint force of the clutch is stronger than the specified value and by recognizing that the vehicle is unstable when it is found stronger, the speed change of the automatic transmission is to be regulated. Thus, the vehicle can be prevented from becoming further unstable because the practice of automatic speed change, accompanied by a sudden change of the driving force when the vehicle is unstable, is regulated. Moreover, the required driving force can be obtained surely when the vehicle is not unstable because the automatic speed change is practiced as specified even during turn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle in which control of a friction engagement means for changing a torque distribution ratio to front and rear wheels in a four-wheel drive vehicle and control of an automatic transmission are integrally considered. The present invention relates to a control device for an automatic transmission.

[0002]

2. Description of the Related Art Conventionally, a frictional engagement means such as a driving force distribution clutch (or a differential limiting clutch: hereinafter referred to as a center differential clutch) in a transfer device (or a differential device) of a four-wheel drive vehicle is used. A technique is known in which the fastening force is controlled and the torque distribution ratio to the front and rear wheels can be arbitrarily controlled.

For example, in Japanese Unexamined Patent Publication No. Sho 62-198522, the engagement force of the center differential clutch is controlled so that the actual yaw rate detected by the sensor system follows the target yaw rate determined from the vehicle speed and the steering angle. A technique for ensuring stability during turning is disclosed.

This is because the conventional switching from two-wheel drive to four-wheel drive or from four-wheel drive to two-wheel drive has been performed based on the difference in the rotational speeds of the front and rear wheels. If this is done, the vehicle driving force and the steering characteristics will change accordingly, and the turning stability will be markedly reduced.

According to this technique, the torque distribution rate to the front and rear wheels is always adjusted so that the actual yaw rate always matches the target yaw rate determined from the vehicle speed and the steering angle at that time, regardless of the road surface condition and the running condition. Is controlled, it is said that it is possible to realize high turning performance without sudden changes in spin and steering characteristics during turning.

[0006]

However, while the driving situation of the vehicle changes momentarily according to the driver's intention and traffic situation, the clutch pressure control of the center differential clutch is a control factor at that time. For example, "What is the relative rotation of the front and rear wheels ...?"
? , The duty ratio for generating the clutch pressure is first determined, and the solenoid or the like is driven depending on the duty ratio, and as a result, the pilot pressure generated from the solenoid or the like changes. Since the change in the pilot pressure changes the clutch pressure of the center differential clutch, there is a problem that a control delay occurs when the operating state of the vehicle changes suddenly.

As is well known, when the gain is increased to eliminate the control delay, hunting is likely to occur this time, so that the gain cannot be increased easily.

By the way, the automatic transmission in the automatic transmission instantaneously changes the driving force of the vehicle due to the difference in the engine torque before and after the transmission and the difference in the gear ratio, and is the largest factor causing the above-mentioned control delay. ..

In the conventional control, the control of the clutch pressure of the center differential clutch and the control of the shift point of the automatic transmission are basically independent from each other, and therefore, it is possible to cope with the deterioration of the turning performance due to the control delay. It was the actual situation that was not done in particular.

As a related technique, a technique has conventionally been proposed in which automatic shifting of an automatic transmission is prohibited during turning.

However, since this technique uniquely determines the turning time based on the steering angle and the like, the shift may be prohibited even in a traveling state where there is no problem even if the automatic shift is executed. However, there is a problem that the actual traveling state does not always match the regulation of the shift control, and an appropriate driving force may not be obtained at an appropriate time. In addition, as a matter of course, there is a problem that it does not function except when turning.

The present invention has been made in view of such a conventional problem, and realizes a realization by organically combining the control of the center differential clutch and the shift control of the automatic transmission in a four-wheel drive vehicle. Provided is a control device for an automatic transmission of a four-wheel drive vehicle capable of performing automatic transmission control that matches the vehicle condition,
It is a solution to the above problems.

[0013]

The present invention has a frictional engagement means (center differential clutch) for controlling the torque distribution ratio to the front and rear wheels, as shown in FIG. Four wheels configured to control the torque distribution ratio from the automatic transmission to the front and rear wheels by controlling the engagement force of the friction engagement means depending on the relationship between the target yaw rate and the actual yaw rate determined from the above. In a control device for an automatic transmission of a drive vehicle, a means for electronically controlling a shift stage of the automatic transmission according to a predetermined shift pattern based on a traveling state of the vehicle, and a fastening force of the friction engagement means. By means for determining whether or not is greater than or equal to a predetermined value, and means for restricting the shift of the automatic transmission when it is determined that the fastening force of the friction engagement means is greater than a predetermined value. Is a solution to the above problems. .

[0014]

According to the present invention, the control of the clutch pressure of the center differential clutch, which controls the distribution ratio of the driving force, is controlled depending on the relationship between the target yaw rate and the actual yaw rate determined from the vehicle speed, the steering angle and the like. And on that,
Whether or not the vehicle is unstable to the extent that automatic shifting should be restricted at this point in time is determined by checking whether or not the engagement force of the center differential clutch at that time is equal to or greater than a predetermined value.

Whether the engagement force of the center differential clutch is equal to or greater than a predetermined value can be easily determined by, for example, confirming whether a command value for a solenoid for controlling the center differential clutch is greater than or equal to a predetermined value. .. The engagement force of the center differential clutch generally tends to increase as the vehicle becomes unstable. Therefore, by confirming this engagement force, the degree of instability of the vehicle can be estimated.

For example, when the road surface condition is good and the four wheels are firmly gripping the ground, an actual yaw rate that is equal to the target yaw rate determined by the vehicle speed, the steering angle, etc. is generated. The clutch pressure is adjusted to the lower side. However, if a specific wheel loses grip on the road surface and starts slipping, the vehicle's driving force will be lost due to the slip and the actual yaw rate will deviate from the target yaw rate when the differential is allowed. The control shifts to the direction in which the differential between the front and rear wheels is limited to recover, that is, the direction in which the engagement force of the center differential clutch is increased.

In the present invention, paying attention to such a qualitative tendency, the degree of instability of the vehicle at the present time is estimated by the engagement force of the center differential clutch, and only when it is estimated that the vehicle is unstable. The shift control of the automatic transmission is regulated to prevent it from becoming more unstable, and to prevent the automatic shift from being prohibited more than necessary.When there is no problem, the automatic shift can surely increase the driving force. It is something that can be obtained.

In the present invention, it is essential to control the center differential clutch depending on the relationship between the target yaw rate and the actual yaw rate. However, controlling the center differential clutch only based on this relationship means that Don't ask. For example, in addition to this relationship, the rotational speed difference between the front and rear wheels ΔN
You are free to make it depend on fr as well.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 2 is a skeleton diagram showing an embodiment of a four-wheel drive system for a vehicle to which the present invention is applied.

In the figure, reference numeral 10 is an engine, 20 is an automatic transmission, 30 is a planetary gear type center differential device, 40 is a rear propeller shaft, 50 is a chain, 60 is a front propeller shaft, 70 is a front differential, and 80 is a front differential. Front drive shaft,
Reference numeral 90 is a center differential clutch (friction engagement means for changing the torque distribution ratio), and 100 is a control device (computer).

The engine 10 is vertically installed at the front of the vehicle. The output of the engine 10 is the automatic transmission 20.
Be transmitted to.

The automatic transmission 20 comprises a fluid type torque converter 21 and an auxiliary transmission section 22. Auxiliary transmission unit 2
2 electronically switches the solenoid valve in the hydraulic control device in accordance with a predetermined shift map based on the vehicle speed V and the throttle opening θ taken into the control device 100, whereby four forward gears and one reverse gear are provided. It has a well-known configuration for automatically changing the gear position of. However, in the present embodiment, the automatic shift based on the map is restricted when a predetermined condition is satisfied by a control flow described later.

The power that has passed through the automatic transmission is transmitted to the center differential device 30 via the output gear 24.

The center differential device 30 includes a sun gear 31, a planetary pinion 32 that meshes with the sun gear 31, a carrier 33 that rotatably supports the planetary pinion 32 around the sun gear 31, and a ring gear 34 that meshes with the planetary pinion 32. Have.

The power transmitted to the output gear 24 of the automatic transmission 20 is input from the carrier 33 of the center differential device 30, part of which is transmitted to the rear propeller shaft 40 via the ring gear 34, and part of the power is transmitted. Is transmitted to the chain 50 via the sun gear 31.

The power transmitted to the rear propeller shaft 40 side is transmitted to the left and right rear wheels via a rear differential and a rear drive shaft (not shown). On the other hand, the power transmitted to the chain 50 side is transmitted to the left and right front wheels (not shown) via the front propeller shaft 60, the front differential 70, and the front drive shaft 80.

The center differential clutch 90 connects the carrier 33 of the center differential device 30 and the sun gear 31 in a torque transmitting relationship. The center differential clutch 90 has a wet multi-plate clutch and is known per se.

That is, the clutch pressure of the center differential clutch 90 is controlled to an arbitrary value by using the hydraulic pressure regulated to a predetermined value by a linear solenoid (not shown) in response to a command from the control device 100, and as a result, this clutch is controlled. A fastening force (engagement force) corresponding to the pressure is generated.

The torque distribution ratio on the front side and the rear side depending on the magnitude of the engaging force of the center differential clutch 90 is calculated from the tooth number ratio (radius ratio) of the ring gear 34 and the sun gear 31.
The load distribution ratio on the front side and the rear side can be changed.

As described above, the control device 100 takes in various signals indicating the traveling state via the various sensor groups 101, 102, ... And controls the engine 10 and the automatic transmission 20 based on these signals. In addition, the clutch hydraulic pressure Pga of the center differential clutch 90 is controlled.

The signals taken in include the vehicle speed V, the throttle opening θ, the steering angle δ, the front and rear wheel rotation speeds Nf and Nr, the actual yaw rate Y, and the like.

FIG. 3 shows a control flow for obtaining the clutch hydraulic pressure Pga.

FIG. 3 is repeated every prescribed period.

First, at step 202, the vehicle speed V,
The steering angle α is detected. In step 204, the map determined in advance depending on the vehicle speed V and the steering angle α
The target yaw rate Yo is required. In step 206, the actual rotational angular acceleration around the center of gravity of the vehicle, that is, the actual yaw rate Y is detected.

Further, in step 208, the slip amount ΔNfr of the front and rear wheels is obtained based on the information from the rotational speeds Nf and Nr of the front and rear wheels.

In step 210, this slip amount ΔN
From fr to the center differential clutch 90 basic clutch hydraulic pressure BP
ga is calculated from the map.

In step 212, the actual yaw rate Y and the target yaw rate Yo are compared.

The vehicle according to this embodiment is basically designed to show the tendency of over-steering. When the tendency of neutral steering is recognized, that is, when the determination at step 212 is NO, the routine proceeds to step 216, where the basic clutch hydraulic pressure BPga obtained at step 210 is used as it is as the clutch hydraulic pressure Pga, especially for the yaw rate. No related corrections are made.

On the other hand, when it is recognized that the vehicle is excessively over-steered, that is, step 21
If YES is determined in step 2, it is estimated that the vehicle is clearly in an unstable state. Therefore, the process proceeds to step 214, and the basic clutch hydraulic pressure BPga is further increased by ΔP, which is the final clutch hydraulic pressure. Pga.

That is, when the slip amount ΔNfr of the front and rear wheels is large, the basic clutch hydraulic pressure BPga itself is increased and the clutch hydraulic pressure Pga is also increased accordingly. In addition to this, the actual yaw rate Y is greater than the target yaw rate Yo. When it is large, that is, when excessive oversteering is detected, the clutch pressure Pga is further increased.

Next, a control flow for setting a flag for restricting the automatic shift of the automatic transmission based on the clutch hydraulic pressure Pga will be described.

The control flow of FIG. 4 is repeated every prescribed period.

First, at step 302, the value of the instability index KPga of vehicle running is determined depending on the clutch oil pressure Pga. Specifically, this calculation is based on the present clutch oil pressure Pga (i) and the previous instability index KPga (i-1).
A value obtained by subtracting a predetermined value (decreasing side smoothing coefficient) A is compared, and the larger value is determined.

By this process, the clutch hydraulic pressure Pga changes momentarily, while the vehicle running instability index KP.
ga will be directly reflected in the increase of Pga, but will be given a certain anneal in the decrease.

As shown in FIG. 5, this is a measure for determining that "the vehicle is highly unstable for a while" when the vehicle is once unstable.

In this way, the vehicle running instability index K
Once Pga (i) is determined, then steps 304 and 30 are performed.
At 6, measures are taken to cut the upper limit of KPga (i). This is because an excessive KPga (i) attenuation process is performed in step 302, so that an excessive KPga (i)
This is a measure to prevent the vehicle from being mistaken for instability for an unnecessarily long time after the occurrence of (i).

Due to the existence of these steps 304 and 306, for example, as shown in FIG.
Even if ga (i) is calculated, KPga (i) used to determine whether or not the automatic shift is actually restricted has a value as indicated by a thick solid line with B being the upper limit.

At step 308, it is determined whether or not KPga (i) thus processed and calculated is equal to or larger than a predetermined value C. If it is determined that the value is equal to or greater than the predetermined value C, it is understood that the vehicle is unstable to the extent that the automatic transmission 20 must regulate the automatic transmission. Therefore, the process proceeds to step 310 and the flag is set. F is set to 1.

On the other hand, the vehicle running instability index KPga (i)
Is smaller than the predetermined value C, the automatic transmission 20
Since it is understood that the vehicle is not unstable to the extent that the shift of the vehicle must be regulated, the routine proceeds to step 312, where the flag F
Is set to 0.

Next, a control flow for receiving the value of the flag F and actually restricting the automatic shift in the automatic transmission will be described.

FIG. 7 is a control flow executed every prescribed period.

First, in step 402, flag F is set.
Is determined to be 1 or not. If the value of flag F is 0
When, the vehicle is in a stable state (not unstable enough to regulate the automatic transmission of the automatic transmission 20).
Since it has been determined that, the control flow is left as it is. That is, the shift control of the automatic transmission 20 is not particularly limited, and the shift according to a predetermined shift map is executed as usual based on the vehicle speed V and the throttle opening θ.

On the other hand, in step 402, the flag F
When it is determined that the value of is 1, it is determined that the vehicle is unstable. Therefore, it is not appropriate that the driving force suddenly changes in this state. The measures to regulate the

That is, at step 404, it is judged if the current gear is the fourth gear. If the current gear is the fourth gear, the process proceeds to step 407 and the downshift line from the fourth gear to the third gear is 0 (km / h) in all throttle opening regions. ) Is set. That is, by this processing, substantially from the fourth speed stage to the third speed stage.
Downshifts to higher gear are prohibited.

On the other hand, when it is determined that the current gear is not the fourth gear, the routine proceeds to step 406, where it is determined whether the current gear is the third gear.

When it is determined that the vehicle is in the third gear, the routine proceeds to step 408, where the downshift vehicle speed from the third gear to the second gear is set to 0 in all throttle opening regions. , The upshift vehicle speed from the third speed to the fourth speed is changed to a constant value M3 (km / h).

As a result, the downshift from the third speed stage to the second speed stage is substantially prohibited, and the upshift from the third speed stage to the fourth speed stage causes the vehicle speed to exceed a predetermined value M3. It will be held for the first time when it becomes. The upshift vehicle speed is set to M3 because the engine may overrun if the upshift is completely prohibited. Therefore, this M3 is set to a vehicle speed at which overrun does not occur in the third speed.

If it is determined in step 406 that the gear is not the third speed, the process proceeds to step 410, where it is determined whether the current gear is the second speed. When it is determined that the vehicle is in the second gear, the routine proceeds to step 412, where the downshift vehicle speed from the second gear to the first gear is set to 0 in all throttle opening regions, and the Downshifting from second gear to first gear is prohibited.

When the current gear is the first gear, the gear shift point is not changed.

Next, another embodiment of the present invention will be described.

In the above-described embodiment, the regulation of the automatic shift in the automatic transmission 20 is judged only by the value of the flag F, and the shift is regulated accordingly.
In addition to this, a method of more directly reflecting the instability index KPga (i) of the vehicle running on the regulation of the automatic transmission of the automatic transmission 20 is also considered.

For example, each vehicle speed in the base shift point map is Ns, and each vehicle speed in the execution shift point map is RNs.
In such a case, a control method in which RNs are related by α · KPga (i) · Ns is also conceivable. Here, α is a shift point change coefficient, which is shown in FIG. 8 for each type of shift and for each current shift stage.
It is defined by the map shown in. When such control is performed, it is possible to change the shift point according to the degree of instability of the vehicle, the throttle opening, the vehicle speed, and the current gear stage, and it is possible to further improve the adaptability.

According to the above-described embodiments (both of the two embodiments), the vehicle cannot be accurately operated not only when turning but also when the yaw rate is generated without operating the steering wheel on a low μ road or the like. Since it is determined that the vehicle is in a stable state, it is possible to effectively prevent execution of an automatic shift that causes a sudden change in driving force in such an unstable state.

Further, even when the vehicle is turning, if the four wheels are surely gripping the road surface and the yaw rate as intended is generated, the automatic shifting is not regulated, so that it is necessary as a result. The required driving force can be reliably obtained at any time.

[0066]

As described above, according to the present invention, automatic shifting can be restricted when the vehicle is in an unstable state regardless of whether the vehicle is turning or traveling straight. That is, as a result, it is possible to reliably prevent the vehicle from becoming more and more unstable due to the automatic gear shift that causes a sudden change in the driving force in an unstable state.

Further, when the vehicle is not unstable, a predetermined automatic shift is executed even during turning, so that the required driving force can be secured as a predetermined value.

[Brief description of drawings]

FIG. 1 is a block diagram showing the gist of the present invention.

FIG. 2 is a skeleton diagram showing a configuration of a four-wheel drive vehicle for a vehicle to which the present invention is applied.

FIG. 3 is a control flow for obtaining the clutch pressure of the center differential clutch in the above embodiment.

FIG. 4 is a control flow for determining whether or not to restrict the automatic shift based on the clutch pressure.

FIG. 5 is a diagram showing a relationship between a vehicle running instability index and clutch hydraulic pressure.

FIG. 6 is a diagram showing characteristics when an upper limit value is set for the vehicle instability index.

FIG. 7 is a control flow showing a specific regulation content of the automatic transmission.

FIG. 8 is a diagram showing a shift point change coefficient when changing a shift point map.

[Explanation of symbols]

 10 ... Engine, 20 ... Automatic transmission, 30 ... Center differential device, 40 ... Rear propeller shaft, 50 ... Chain, 60 ... Front propeller shaft, 70 ... Front differential, 80 ... Front drive shaft, 90 ... Center differential clutch, 100 …Control device.

Claims (1)

[Claims] 1. A friction engaging means for controlling a torque distribution rate to front and rear wheels, wherein the friction engaging means is dependent on a relationship between a target yaw rate and an actual yaw rate determined from a vehicle speed, a steering angle and the like. In a controller for an automatic transmission of a four-wheel drive vehicle configured to control the fastening force of the vehicle to control the torque distribution ratio from the automatic transmission to the front and rear wheels, a predetermined value is set based on the running state of the vehicle. Means for electronically controlling the shift stage of the automatic transmission according to a shift pattern, means for judging whether or not the engagement force of the friction engagement means is a predetermined value or more, and the engagement force of the friction engagement means is predetermined. A control device for an automatic transmission of a four-wheel drive vehicle comprising: means for restricting a shift of the automatic transmission when it is determined to be greater than a value.