JP2002087103A - Limited slip differential for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a limited slip differential for a vehicle which can always realize an optimum running characteristic, by changing a forced torque over an adequate period in accordance with a steering condition to be surely reflected in the behavior of the vehicle. SOLUTION: A correction coefficient K3 is set to reduce according to increasing of a steering angular velocity Dθs at rapid steering time, deceleration corresponding forced torque Tb is corrected to a reducing side by this correction coefficient K3, a turning round quality of a vehicle is ensured. This time correction coefficient K3 is made to pass through a filter 97 with responsiveness in an increasing side remarkably lower than the reducing side. An increasing period of the steering angular velocity Dθs by rapid steering is very short, but by moderating an increase in the correction coefficient K3 through the filter 97, a reducing period of the deceleration corresponding forced torque Tb is extended relating to the increasing period of the steering angular velocity Dθs, this reduction of the deceleration corresponding forced torque Tb is surely reflected in the behavior of the vehicle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential limiting device for a vehicle for limiting a differential between front and rear wheels and between left and right wheels of a vehicle.

[0002]

2. Related Background Art In a full-time four-wheel drive vehicle that has been widely put into practical use in recent years, a center differential allows a rotation difference between front and rear wheels generated when the vehicle turns to prevent a so-called tight corner braking phenomenon. I have. In some cases, this type of center differential is provided with a differential limiting device comprising a hydraulic multi-plate clutch. The differential state is restricted by applying a restraining torque to the center differential by the hydraulic multi-plate clutch, thereby distributing the torque between the front and rear wheels. The running characteristics (e.g., turning performance and running stability) can be arbitrarily changed by adjusting.

[0003] In order to achieve optimum running characteristics according to the driving state of the vehicle, the restraining torque is set based on various parameters. For example, when sudden steering by the driver is performed, the restraining torque is reduced and corrected when the steering angular velocity is equal to or more than a predetermined value, based on the viewpoint that the turning performance of the vehicle should be improved and the attitude should be changed quickly. In some cases, the turning performance of a vehicle is ensured.

[0004]

However, the increase in the steering angular velocity due to sudden steering is only for a very short time at the beginning of steering, and in the differential limiting device described above, the restraint torque is reduced by switching the correction value only during that time. It is just done.
Therefore, depending on the responsiveness of the hydraulic circuit of the restraint torque control, the actual restraint torque may hardly change even if the correction is performed. As a result, the restraint torque control is not reflected in the behavior of the vehicle, resulting in a sufficient turning. I couldn't expect to secure sex.

An object of the present invention is to change the restraining torque over an appropriate period according to the steering state and to surely reflect the restraining torque on the behavior of the vehicle, so that the optimum running characteristics can always be realized. It is to provide a differential limiting device.

[0006]

In order to achieve the above object, according to the present invention, there is provided a differential means for distributing a driving force from an engine to each driving wheel while allowing a differential, and a constraint torque applied to the differential means. Differential limiting means capable of acting to limit the differential, and control means for controlling the restraining torque of the differential limiting means based on the steering angular velocity, and the responsiveness of the control means is reduced on the reducing torque side. On the other hand, the increasing side was set lower.

Therefore, for the purpose of ensuring turning performance of the vehicle at the time of sudden steering, for example, the restraining torque of the differential limiting means is controlled to decrease as the steering angular velocity increases. The steering angular velocity increases only for a very short period of time at the beginning of steering, but since the responsiveness is low when the restraint torque increases compared to when the restraint torque decreases, the restraint torque rapidly decreases and then gradually increases. Become. As a result, the restraint torque is maintained in a reduced state for a longer time during the increase period of the steering angular velocity, and the change in the restraint torque at this time is surely reflected in the behavior of the vehicle.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a differential limiting device for limiting a differential of a center differential (hereinafter, referred to as a center differential) will be described. FIG.
Is an overall configuration diagram showing the vehicle operation restriction device of the present embodiment,
FIG. 2 is a partially enlarged view showing details of a center differential and a front differential. As shown in these figures, a center differential 1 as a differential means is a front differential (hereinafter, referred to as a front differential).
It is disposed on the axle of the front wheel 3F of the vehicle together with a front differential 2 so that the rotation of the engine 4 is input to a ring gear 6 on the outer periphery of the center differential 1 via a manual transmission 5. The center differential 1 has a general configuration in which a pair of side gears 8a and 8b are meshed with a pinion gear 7. When the ring gear 6 is rotationally driven by the engine 4, the pinion gear 7 rotates integrally, and the left and right side gears 8 rotate.
The torque is distributed at a ratio of 50:50 while allowing a rotation difference between a and 8b.

One side gear 8a of the center differential 1 is connected to an outer casing 9 of the front differential 2, and a ring gear 10 provided on the outer periphery of the outer casing 9 is connected via a pinion gear 11 and a propeller shaft 12 to a rear differential. 13 (referred to as a rear differential). When the outer casing 9 rotates together with one of the side gears 8a, the rotation is transmitted via the ring gear 10, the pinion gear 11, and the propeller shaft 12 to the rear differential 1.
3, and the right and left rear wheels 3R are rotationally driven via the drive shaft 14, and a differential mechanism (not shown) incorporated in the rear differential 13 allows a left and right rotational difference.

The other side gear 8b of the center differential 1 is
A pair of planetary gears 16 connected to an inner casing 15 housed in the outer casing 9 and supported in the inner casing 15 mesh with sun gears 18 formed at inner ends of left and right drive shafts 17, respectively. I have. When the inner casing 15 rotates together with the other side gear 8b, the rotation is
6, transmitted to the drive shaft 17 via the sun gear 18, the left and right front wheels 3F are driven to rotate, and the rotation difference between the left and right is allowed as the planetary gear 16 rotates.

A hydraulic multi-plate clutch 19 is provided between the outer casing 9 and the inner casing 15 of the front differential 2 as a differential limiting means. Occurs, and the relative rotation of the casings 9 and 15 is regulated. When the hydraulic multi-disc clutch 19 is completely disengaged (restraint torque 0), the casings 9 and 15 are held in a free state without being restricted in rotation, and the front wheels 3F are arranged at a ratio of 50:50 as described above.
When the hydraulic multi-plate clutch 19 is fully engaged (maximum restraining torque), torque is distributed to the rear wheel 3R and the rear wheel 3R.
The rotation of both casings 9, 15 is held in a locked state, and at this time, torque is distributed at a ratio according to the ground load of the front and rear wheels 3F, 3R. Then, according to the adjustment of the restraint torque, the running characteristics of the vehicle change as described later. The hydraulic multi-plate clutch 19 is used for the hydraulic unit 2
When the hydraulic oil is supplied from 0, the hydraulic oil is operated, and the supply state of the hydraulic oil is controlled by the solenoid valve 21, whereby the engagement state of the hydraulic multi-plate clutch 19 is adjusted, and an arbitrary restraining torque is realized. .

On the other hand, a 4WD ECU (Electronic Control Unit) 31 as control means is installed together with an engine / transmission ECU, an ABS ECU and the like (not shown) in the cabin of the vehicle. Similarly to the ECU of the first embodiment, an input / output device (not shown) and a storage device (ROM, RAM
Etc.), a central processing unit (CPU), a timer counter and the like. On the input side of the 4WD ECU 31, a longitudinal acceleration sensor 33 for detecting a longitudinal acceleration Gx acting on the vehicle, a steering angle sensor 37 for detecting a steering angle θs, and a driver having a high μ road surface (for example, pavement) Road),
A mode changeover switch 38 for selecting three kinds of road surface conditions, that is, a medium μ road surface (for example, an unpaved road) and a low μ road surface (for example, a frozen road) is connected. 4WD ECU 31
The solenoid valve 21 is connected to the output side of the solenoid valve.

Next, a description will be given of a procedure for setting the restrictive torque applied to the differential limiting control of the center differential 1, particularly the differential limiting control, which is executed by the ECU 31 of the vehicle differential limiting device configured as described above. FIG. 3 is a block diagram systematically showing the procedure for setting the restraining torque executed by the ECU. As shown in the figure, the constraint torque setting procedure includes a front / rear difference rotation constraint torque setting unit 41, a front / rear G proportional constraint torque setting unit 42 for calculating a constraint torque from different parameters according to the driving state of the vehicle, The torque setting unit 43 and the deceleration-response constraint torque setting unit 44, and the constraint torques Tv, Tx, Ta, and Tb set by the setting units 41 to 44, respectively.
And a final restraint torque setting section 45 for setting a final restraint torque Tfinal.

The setting of the constraint torques Tv, Tx, Ta, Tb by the respective constraint torque setting sections 41 to 44 is based on the following purport. Front / rear difference rotation restraint torque setting unit 4
1 is for realizing the behavior of the vehicle according to the driver's intention at the time of turning, and calculates the front / rear difference rotation restricting torque Tv based on the rotation difference between the front and rear wheels. The front-rear G proportional constraint torque setting unit 42 aims to prevent hunting generated in the front-rear difference rotation constraint torque Tv based on the rotation difference between the front and rear wheels on a low μ road surface or the like. The longitudinal G restraining torque Tx is calculated based on Gx. Acceleration-response restraint torque setting unit 43
The purpose of the present invention is to prevent an initial slip of the rear wheel 3R when the transmission torque is expected to increase suddenly, such as when the vehicle suddenly starts from a stopped state, and to set an acceleration response based on the acceleration state of the vehicle. The torque Ta is calculated. The deceleration-response constraint torque setting unit 44 calculates the deceleration-response constraint torque Tb based on the deceleration state of the vehicle for the purpose of ensuring the stability of the vehicle attitude during sudden deceleration.

The above-described respective constraint torques Tv, Tx, Ta, and Tb are input to the final constraint torque setting unit 45, and the maximum value selection unit 101 of the final constraint torque setting unit 45 determines whether the rotational difference torque Tv is proportional to the longitudinal G proportionality. The side with the larger constraint torque Tx is selected. Front-rear difference rotation restraint torque T due to four-wheel slip
When control hunting occurs in v, the front-rear G proportional constraint torque Tx is appropriately selected, and as a result, the output value of the maximum value selection unit 101 is stabilized, and the effect of hunting is suppressed.

The selected constraint torques Tv and Tx are added to an acceleration-response constraint torque Ta and a deceleration-response constraint torque Tb in an addition processing unit 102 to obtain a final constraint torque Tfinal.
It is said. This final restraining torque Tfinal is the limiter 10
3 and the hydraulic multi-plate clutch 19 of the center differential 1
Is limited to the maximum restraint torque that can be realized by Further, the addition processing unit 104 has a final constraint torque Tfi that has passed through the high-pass filter 105.
nal is also input, and after adding both, limiter 1 again
06, it is limited to the maximum constraint torque, and is output as the final constraint torque Tfinal. The high-pass filter 105 performs a surge-like addition when the final constraint torque Tfinal changes suddenly, thereby reducing a response delay when the solenoid valve 21 is driven and controlled based on the final constraint torque Tfinal.

The actual constraint torque of the center differential 1 is controlled based on the final constraint torque Tfinal set as described above. That is, the duty ratio corresponding to the final constraint torque Tfinal is set from a map (not shown), and the solenoid valve 21 is operated based on the duty ratio to control the hydraulic oil supplied from the hydraulic unit 20 to the hydraulic multi-plate clutch 19. As a result, the hydraulic multi-plate clutch 1
9 is adjusted, and the restraining torque is controlled to the final restraining torque Tfinal.

On the other hand, FIG. 4 is a block diagram showing a detailed procedure for setting the restraining torque by the restraining torque setting unit for deceleration.
Hereinafter, the setting process of the deceleration-response constraint torque setting unit 44 will be described with reference to FIG. The longitudinal acceleration Gx detected by the longitudinal acceleration sensor 33 and the operation status of the mode changeover switch 38 are input to the restraining torque calculating unit 91 of the deceleration-response restraining torque setting unit 44, and the three kinds of preset maps are used. The map corresponding to the road condition is selected. Based on the selected map, the restraining torque Tb corresponding to deceleration is calculated from the longitudinal acceleration Gx.

As shown in the drawings, in each of the maps, the deceleration-response restraining torque Tb is set to increase as the longitudinal acceleration Gx increases to the negative side (deceleration side).
The vehicle posture during deceleration is stabilized. In addition, each map is set such that, for the same longitudinal acceleration Gx, a larger deceleration-response constraint torque Tb is calculated for a map on a high μ road surface. With this setting, on a high μ road surface where the front wheel load during braking is high and it is difficult to lock the four wheels simultaneously, a larger restraining torque is set and the braking force is improved.

The K2 calculator 92 includes a steering angle sensor 3
7, the steering angle θs detected at 7, the mode changeover switch 38
And the estimated vehicle speed VB calculated by the estimated vehicle speed calculation unit 54 are input. The estimated vehicle speed VB indicates the vehicle speed VB after a predetermined time t. For example, the second lowest wheel speed is regarded as the current vehicle speed (the minimum value is excluded because there is a possibility of failure, and the value is calculated as It is calculated by correcting with the longitudinal acceleration Gx (meaning the change of the vehicle speed thereafter). In the K2 calculating section 92, a map corresponding to the road surface condition is selected from three kinds of preset maps, and a correction coefficient K2 is calculated from the steering angle θs and the estimated vehicle speed VB based on the selected map. The calculated correction coefficient K2 is input to the multiplication processing unit 94 via the C / S correction unit 93, and is input to the multiplication processing unit 9
At 4, the deceleration-response constraint torque Tb is multiplied by the correction coefficient K2. Although not shown, the correction coefficient K2 is set in the range of 0 to 1.0, and is set to decrease with an increase in the steering angle θs, for example. Is achieved.

The C / S corrector 93 determines whether the current steering state is counter steer. The determination of the countersteer is made based on, for example, the steering direction estimated from the steering angle θs and the lateral acceleration of the vehicle detected by the lateral acceleration sensor or the like. ), And if they do not match, it is determined that counter steer (CSH = 1). The C / S corrector 93 replaces the correction coefficient K2 with 1 only when the result of the determination by the C / S determiner 60 is counter steer (CSH = 1). Therefore, when the correction coefficient K2 set based on the steering angle θs becomes inappropriate due to countersteering, correction based on this is prohibited.

On the other hand, the steering angle θs from the steering angle sensor 37
Is differentiated with respect to time by a differentiation processing unit 95 and is converted into a steering angular velocity Dθs. The steering angular velocity Dθs is input to the K3 calculation unit 96 together with the operation state of the mode changeover switch 38. In the K3 calculating section 96, a map corresponding to the road surface condition is selected from three kinds of preset maps, and a correction coefficient K3 is calculated from the steering angular velocity Dθs based on the map. The calculated correction coefficient K3 is determined by the filter 97 and the C / S
After being input to the multiplication processing unit 99 via the correction unit 98, the multiplication processing unit 99 multiplies the deceleration-response constraint torque Tb by the correction coefficient K3, and outputs the deceleration-response constraint torque Tb after the multiplication to the final constraint torque setting unit 45 described above. And applied to the calculation of the final constraint torque Tfinal.

The correction coefficient K3 is set within the range of 0 to 1.0. In any of the maps, the steering angular velocity Dθs
Is greater than or equal to a predetermined value, the correction coefficient K3 is set to decrease as the steering angular velocity Dθs increases. As a result, when the steering angular velocity Dθs increases with rapid steering, the correction coefficient K3 is set to the decreasing side, and the deceleration-response restraining torque Tb is corrected to decrease, and as a result, the turning performance is ensured. Also, the correction coefficient K3 is set to be maintained at the maximum value (1.0) up to a higher steering angular velocity Dθs as the map of the road surface becomes lower.
As a result, a decrease in the deceleration-response restraining torque Tb due to sudden steering is suppressed, and traveling stability is ensured. In this example, the same map is applied irrespective of the steering direction (cut side and return side), but a map having different characteristics may be applied according to the steering direction.

The C / S corrector 98 replaces the thus set correction coefficient K3 with 1 only when counter steer (CSH = 1). Therefore, when the correction coefficient K3 set based on the steering angular velocity Dθs becomes inappropriate due to counter steering, the correction based on this is prohibited. The characteristics of the filter 97 are set, for example, to 0.5 Hz on the increasing side and 8 Hz on the decreasing side, so that the response on the increasing side is much lower than the response on the decreasing side. For this reason, when the steering angular velocity Dθs increases due to sudden steering and the correction coefficient K3 input to the filter 97 changes to the decreasing side, the filter 97 rapidly reduces the output with high responsiveness. The torque Tb is also rapidly reduced. On the other hand, when the steering angular velocity Dθs immediately thereafter decreases, the output is only slow because the response of the filter 97 is low even if the input correction coefficient K3 increases. Without increasing, restraining torque T corresponding to deceleration
The increase in b will also be modest.

That is, the steering angular velocity Dθs increases due to sudden steering for a very short time at the beginning of steering, but the deceleration-response restraining torque Tb decreases over a longer period of time during the increase in the steering angular velocity Dθs. It will be kept in a state. Then, the actual restraining torque of the center differential 1 is reduced during the reduction period of the restraining torque Tb corresponding to deceleration, so that the behavior of the vehicle surely changes in a direction to improve the turning performance. Needless to say, the appropriate reduction period of the restraining torque varies depending on various conditions such as the response of the hydraulic unit 20 and the turning performance of the vehicle.
The characteristics of 7 can be arbitrarily changed in consideration of these various conditions.

As described above, according to the vehicle differential limiting device of the present embodiment, the deceleration-response constraint torque Tb is reduced in order to reduce the deceleration-response constraint torque Tb over an appropriate period according to the steering state. Can be reliably reflected in the behavior of the vehicle, so that sufficient turning performance can be ensured at the time of sudden steering and always optimal driving characteristics can be realized.

Further, as described above, the correction coefficient K3 is set steplessly in accordance with the steering angular velocity Dθs according to the map of the K3 calculation section 96, and the deceleration-response restraining torque Tb is also set steplessly based on the correction by the correction coefficient K3. To change. As a method of setting the correction coefficient K3 according to the steering angular velocity Dθs,
It is conceivable to switch the correction coefficient K3 in a step-like manner depending on whether or not the steering angular velocity Dθs exceeds a predetermined value.
In this case, the deceleration-response restraining torque Tb is also switched in a step-like manner, causing a sudden change in the behavior of the vehicle. On the other hand, when the restraining torque Tb corresponding to the deceleration is changed in a stepless manner, the behavior of the vehicle changes smoothly, so that the driver can easily recognize the behavior change and the driving operation can be facilitated. can get.

Although the embodiment has been described above, aspects of the present invention are not limited to this embodiment. For example, in the above-described embodiment, the differential limiting device for the center differential that allows the differential between the front wheel and the rear wheel is embodied. However, for example, the differential limiting device for the front differential and the rear differential that allows the differential between the left and right wheels. It may be embodied in an apparatus. Further, in the above-described embodiment, the final constraint torque Tfinal is set by calculating the longitudinal difference rotational constraint torque Tv, the longitudinal G proportional constraint torque Tx, the acceleration-response constraint torque Ta, and the deceleration-response constraint torque Tb, respectively. May be omitted, or a constraint torque calculated from another parameter may be added.

Further, in the above embodiment, the K3 calculator 96
A filter 97 is provided on the output side, and the decrease / decrease state of the correction coefficient K3 is changed by the filter 97, thereby realizing a desired reduction period of the deceleration correspondence constraint torque Tb. For example, as shown by a two-dot chain line in FIG. , The position of the filter 97 may be changed to the output side of the differential processing unit 95, and the increase / decrease state of the steering angular velocity Dθs may be changed by the filter 97. In this case, the characteristic of the filter 97 is set so that the response on the decreasing side is lower than the response on the increasing side, contrary to the above-described case. As a result, when the steering angular velocity Dθs increases due to rapid steering, the filter 97 quickly increases the output with high responsiveness. When the steering angular velocity Dθs immediately decreases, the output of the filter 97 is low because the responsiveness of the filter 97 is low. As a result, the decreasing period of the deceleration corresponding restraining torque Tb is extended for the increasing period of the steering angular velocity Dθs,
As in the above-described embodiment, sufficient turning performance can be ensured.

On the other hand, in the above-described embodiment, the filters 97 having different responsivenesses on the increasing side and the decreasing side are used. For example, a peak hold filter for holding the maximum value for a predetermined time and a bottom hold filter for holding the minimum value for a predetermined time are used. May be used. Specifically, as in the above embodiment, the correction coefficient K3
When the increase / decrease state of the steering angular velocity Dθs is changed by changing the increase / decrease state of the steering angular velocity Dθs as in the above-described another example, the peak hold filter is used. What is necessary is to extend the increase period of the steering angular velocity Dθs. Further, instead of these filters, for example, a gradient limiter having a characteristic of changing the output only when the rate of change on the input side exceeds a predetermined value may be used. The reduction period of the restraining torque Tb can be extended.

[0031]

As described above, according to the differential limiting device for a vehicle of the present invention, the restraining torque is changed over an appropriate period according to the steering state so as to be surely reflected on the behavior of the vehicle. Optimum running characteristics can always be realized.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a vehicle operation restriction device according to an embodiment.

FIG. 2 is a partially enlarged view showing details of a center differential and a front differential.

FIG. 3 is a block diagram systematically showing a procedure for setting a constraint torque executed by an ECU.

FIG. 4 is a block diagram illustrating a detailed setting procedure of a restraining torque of a restraining torque setting unit for deceleration.

[Explanation of symbols]

 Reference Signs List 1 center differential (differential means) 3F front wheel (drive wheel) 3R rear wheel (drive wheel) 4 engine 19 hydraulic multiple disc clutch (differential limiting means) 31 ECU (control means)

Claims (1)

[Claims] 1. Differential means for distributing a driving force from an engine to each driving wheel while allowing a differential, and differential limiting means capable of restricting the differential by applying a restraining torque to the differential means. Control means for controlling the restraining torque of the differential limiting means based on the steering angular velocity, wherein the responsiveness of the control means is set lower on the increasing side than on the decreasing side of the restraining torque. Vehicle differential limiting device.