JP3937121B2 - Differential limiting device for vehicle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a differential limiting device for a vehicle that limits differential between front and rear wheels and between left and right wheels of a vehicle.
[0002]
[Related background]
In a full-time four-wheel drive vehicle that has been widely put into practical use in recent years, a so-called tight corner braking phenomenon is prevented by allowing a center differential to cause a rotation difference between front and rear wheels that occurs when the vehicle turns. This type of center differential may be equipped with a differential limiting device consisting of a hydraulic multi-plate clutch. The hydraulic multi-plate clutch applies a restraining torque to the center differential to limit the differential state, thereby distributing torque between the front and rear wheels. To adjust the running characteristics (for example, turning ability and running stability) arbitrarily.
[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 the driver is suddenly steered, the restraint torque is corrected to decrease when the steering angular velocity is greater than or equal to a predetermined value, based on the viewpoint that the turning performance of the vehicle should be improved and the posture changed quickly. There is one that ensures the turning ability of the vehicle.
[0004]
[Problems to be solved by the invention]
However, the steering angular velocity increases due to sudden steering in a very short time in the initial stage of steering, and in the differential limiting device described above, the restraint torque is only corrected to decrease by switching the correction value only during that period. Therefore, depending on the responsiveness of the hydraulic circuit for restraint torque control, the actual restraint torque may hardly change even if correction is performed. As a result, the restraint torque control is not reflected in the behavior of the vehicle, and sufficient turning I could not expect to secure the sex.
[0005]
It is an object of the present invention to change a restraining torque over an appropriate period according to a steering state and reliably reflect it in the behavior of the vehicle, thereby enabling the vehicle differential limit to always realize optimum driving characteristics. To provide an apparatus.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, differential means for distributing the driving force from the engine to each drive wheel while allowing the differential to be distributed, and a differential torque by applying a restraining torque to the differential means. a differential limiting means capable restriction, on the basis of the longitudinal acceleration and the steering angular velocity of the vehicle and control means for controlling the restraining torque of the differential limiting means, control means, an increase in the speed reduction side of the longitudinal acceleration The target value of the restraint torque calculated to increase the restraint torque is corrected so that the restraint torque decreases as the steering angular speed increases to control the restraint torque, and the response of the correction is reduced to the restraint torque. The increase correction side is set lower than the correction side.
[0007]
Therefore, when the vehicle decelerates, for the purpose of stabilizing the vehicle posture, the target value of the restraint torque is set to increase the restraint torque as the longitudinal acceleration increases toward the deceleration side, and steering is performed during this deceleration. For the purpose of ensuring the turning ability of the vehicle at the time of sudden steering, the target value is corrected so that the constraint torque decreases as the steering angular velocity increases, and the constraint torque is controlled based on this target value. Although the steering angular velocity increases in a very short time at the beginning of steering, the low response is applied on the increase correction side compared to the decrease correction side of the constraint torque. is gradually increased correction become Rukoto. As a result, the restraint torque is maintained in a reduced state for a longer time with respect to the increase period of the steering angular velocity, and the change in the restraint torque at this time is reliably reflected in the behavior of the vehicle .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is embodied in a differential limiting device for limiting the differential of a center differential (hereinafter referred to as a center differential) will be described.
FIG. 1 is an overall configuration diagram showing a vehicle operation limiting device of this embodiment, and 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 disposed on an axle of a front wheel 3F of a vehicle together with a front differential (hereinafter referred to as front differential) 2, and the rotation of the engine 4 is a manual transmission 5 Is input to the ring gear 6 on the outer periphery of the center differential 1. The center differential 1 has a general configuration in which a pair of side gears 8a and 8b are engaged 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 8a, 8a, Torque is distributed at a ratio of 50:50 while allowing a rotation difference to 8b.
[0009]
One side gear 8a of the center differential 1 is connected to the outer casing 9 of the front differential 2, and a ring gear 10 provided on the outer periphery of the outer casing 9 is rear differential (hereinafter referred to as rear differential) via a pinion gear 11 and a propeller shaft 12. 13 is connected. When the outer casing 9 rotates together with the one side gear 8a, the rotation is transmitted to the rear differential 13 through the ring gear 10, the pinion gear 11, and the propeller shaft 12, and the left and right rear wheels 3R are driven to rotate through the drive shaft 14. At the same time, a left-right rotational difference is allowed by a differential mechanism (not shown) built in the rear differential 13.
[0010]
The other side gear 8 b of the center differential 1 is connected to an inner casing 15 housed in the outer casing 9, and a pair of planetary gears 16 supported in the inner casing 15 are formed at the inner ends of the left and right drive shafts 17. Are engaged with the sun gears 18 respectively. When the inner casing 15 rotates together with the other side gear 8b, the rotation is transmitted to the drive shaft 17 via the planetary gear 16 and the sun gear 18, and the left and right front wheels 3F are driven to rotate, and as the planetary gear 16 rotates, A rotation difference of is allowed.
[0011]
A hydraulic multi-plate clutch 19 as a differential limiting means is provided between the outer casing 9 and the inner casing 15 of the front differential 2, and a restraining torque is generated according to the engaged state of the hydraulic multi-plate clutch 19. Thus, the relative rotation of the casings 9 and 15 is restricted. When the hydraulic multi-plate clutch 19 is fully released (restraint torque is 0), the casings 9 and 15 are held in a free state without being restricted in rotation. Torque is distributed to the rear wheel 3R side. On the other hand, when the hydraulic multi-plate clutch 19 is completely engaged (restraint torque is maximum), the casings 9 and 15 are restricted in rotation and held in a locked state. Torque distribution is performed at a ratio according to the ground contact load of the front and rear wheels 3F, 3R. Then, according to such adjustment of the restraining torque, the running characteristics of the vehicle change as will be described later. The hydraulic multi-plate clutch 19 operates by receiving hydraulic oil supplied from the hydraulic unit 20, and the engagement state of the hydraulic multi-plate clutch 19 is adjusted by controlling the supply state of the hydraulic oil by the solenoid valve 21. Arbitrary restraint torque is realized.
[0012]
On the other hand, a 4WD ECU (electronic control unit) 31 as a control means is installed in the interior of the vehicle together with an unillustrated engine / transmission ECU, ABS ECU, etc., and this 4WD ECU 31 is connected to other ECUs. Similarly, an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs and control maps, a central processing unit (CPU), a timer counter, and the like are provided. On the input side of the 4WD ECU 31 are 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). A mode changeover switch 38 is connected to select three types of road surface conditions: road), medium μ road surface (for example, unpaved road), and low μ road surface (for example, frozen road). The solenoid valve 21 is connected to the output side of the 4WD ECU 31.
[0013]
Next, a description will be given of the setting procedure of the restraint torque applied to the differential limiting control of the center differential 1, particularly the differential limiting control, executed by the ECU 31 of the vehicle differential limiting device configured as described above.
FIG. 3 is a block diagram systematically showing the setting procedure of the restraining torque executed by the ECU. As shown in the figure, this restricting torque setting procedure includes a front-rear differential rotation restricting torque setting unit 41, a front-rear G proportional restricting torque setting unit 42, an acceleration corresponding restriction that calculate the restricting torque from different parameters according to the driving state of the vehicle. The final restraint torque setting for setting the final restraint torque Tfinal from the restraint torques Tv, Tx, Ta, and Tb set by the torque setting unit 43, the deceleration-corresponding restraint torque setting unit 44, and the respective setters 41 to 44. Part 45.
[0014]
The setting of the restraining torques Tv, Tx, Ta, and Tb by the restraining torque setting units 41 to 44 is based on the following points. The front / rear difference rotational restraint torque setting unit 41 calculates the front / rear difference rotational restraint torque Tv based on the rotational difference between the front and rear wheels for the purpose of realizing the behavior of the vehicle in accordance with the driver's will during turning. The front / rear G proportional restraint torque setting unit 42 is intended to prevent hunting that occurs in the front / rear difference rotational restraint torque Tv based on the rotational difference between the front and rear wheels on a low μ road surface or the like. The front-rear G restraining torque Tx is calculated based on Gx. The acceleration-corresponding restraint torque setting unit 43 is provided for the purpose of preventing the initial slip of the rear wheel 3R when the transmission torque is expected to increase suddenly, such as when suddenly starting from a stopped state. Based on the state, the acceleration corresponding restraint torque Ta is calculated. The deceleration-corresponding restraint torque setting unit 44 calculates a deceleration-responding restraint torque Tb based on the deceleration state of the vehicle for the purpose of ensuring the stability of the vehicle posture during sudden deceleration.
[0015]
Each of the above-mentioned restraint torques Tv, Tx, Ta, Tb is input to the final restraint torque setting unit 45, and the maximum value selection unit 101 of the final restraint torque setting unit 45 performs the front-rear differential rotation restraint torque Tv and the front-back differential proportional restraint torque Tx. The larger side is selected. When control hunting occurs in the front / rear differential rotation restraint torque Tv due to the four-wheel slip, the front / rear G proportional restraint torque Tx is appropriately selected, and as a result, the output value of the maximum value selection unit 101 is stabilized. This suppresses the influence of hunting.
[0016]
The selected restraint torques Tv and Tx are added to the acceleration restraint torque Ta and the deceleration restraint torque Tb in the addition processing unit 102 to obtain the final restraint torque Tfinal. This final restraining torque Tfinal is input to the limiter 103, limited to the maximum restraining torque that can be realized by the hydraulic multi-plate clutch 19 of the center differential 1, and then input to the addition processing unit 104. Further, the final restraining torque Tfinal that has passed through the high-pass filter 105 is also input to the addition processing unit 104, and after both are added, the limiter 106 limits the maximum restraining torque again and outputs it as the final restraining torque Tfinal. The high-pass filter 105 reduces the response delay when the solenoid valve 21 is driven and controlled based on the final restraining torque Tfinal by performing a surge addition when the final restraining torque Tfinal suddenly changes.
[0017]
Based on the final constraint torque Tfinal set in this way, the actual constraint torque of the center differential 1 is controlled. That is, the duty ratio corresponding to the final restraining 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 engagement state of the hydraulic multi-plate clutch 19 is adjusted, and the restraint torque is controlled to the final restraint torque Tfinal.
[0018]
On the other hand, FIG. 4 is a block diagram showing a detailed setting procedure of the restraining torque of the deceleration-corresponding restraining torque setting unit. Hereinafter, the setting process of the deceleration-responding restraining torque setting unit 44 will be described with reference to FIG.
The longitudinal torque Gx detected by the longitudinal acceleration sensor 33 and the operation status of the mode changeover switch 38 are input to the restraint torque calculation unit 91 of the deceleration-corresponding restraint torque setting unit 44, and from three preset maps. A map corresponding to the road surface condition is selected. Based on the selected map, the deceleration-corresponding restraint torque Tb is calculated from the longitudinal acceleration Gx.
[0019]
As shown in the figure, in any map, as the longitudinal acceleration Gx increases to the negative side (deceleration side), the deceleration-corresponding restraint torque Tb is set to increase, thereby stabilizing the vehicle posture during deceleration. Figured. In addition, each map is set such that, for the same longitudinal acceleration Gx, the map corresponding to the high μ road surface calculates a larger deceleration-corresponding binding torque Tb. With this setting, a higher restraining torque is set on a high μ road surface where the front wheel load during braking is high and it is difficult to simultaneously lock the four wheels, thereby improving the braking force.
[0020]
Further, the steering angle θs detected by the steering angle sensor 37, the operation state of the mode changeover switch 38, and the estimated vehicle speed VB calculated by the estimated vehicle speed calculation unit 54 are input to the K2 calculation unit 92. . The estimated vehicle speed VB represents the vehicle speed VB after a predetermined time t. For example, the second smallest 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 It is calculated by correcting with the longitudinal acceleration Gx (meaning the subsequent change in vehicle speed). In the K2 calculation unit 92, a map corresponding to the road surface condition is selected from three preset maps, and a correction coefficient K2 is calculated from the steering angle θs and the estimated vehicle speed VB based on the map. The calculated correction coefficient K2 is input to the multiplication processing unit 94 via the C / S correction unit 93, and the multiplication processing unit 94 multiplies the deceleration corresponding restraining torque Tb by the correction coefficient K2. Although not shown, the correction coefficient K2 is set within a range of 0 to 1.0, and is set to decrease as the steering angle .theta.s increases, for example, and thereby the deceleration-corresponding restraint torque Tb is corrected to decrease to ensure the turnability. Is planned.
[0021]
Further, the C / S correction unit 93 determines whether or not the current steering state is counter steer. This counter steer determination is made based on, for example, the steering direction estimated from the steering angle θs and the lateral acceleration of the vehicle detected by a lateral acceleration sensor or the like, and when both coincide, non-counter steer (CSH = 0) ), And it is determined as counter steer (CSH = 1) if they do not match. The C / S correction unit 93 replaces the correction coefficient K2 with 1 only when the determination result of the C / S determination unit 60 is counter steer (CSH = 1). Therefore, when the correction coefficient K2 set based on the steering angle θs becomes inappropriate due to the counter steer, correction based on this is prohibited.
[0022]
On the other hand, the steering angle θs from the steering angle sensor 37 is time-differentiated by the differentiation processing unit 95 and converted into the steering angular velocity Dθs, and this steering angular velocity Dθs is input to the K3 calculating unit 96 together with the operation state of the mode changeover switch 38. . In the K3 calculation unit 96, a map corresponding to the road surface condition is selected from three types of preset maps, and the correction coefficient K3 is calculated from the steering angular velocity Dθs based on the map. The calculated correction coefficient K3 is input to the multiplication processing unit 99 via the filter 97 and the C / S correction unit 98, and the multiplication processing unit 99 multiplies the deceleration corresponding restriction torque Tb by the correction coefficient K3, and responds to the deceleration after multiplication. The restraint torque Tb is output to the above-described final restraint torque setting unit 45 and applied to the calculation of the final restraint torque Tfinal.
[0023]
The correction coefficient K3 is set within the range of 0 to 1.0. In any map, the correction coefficient K3 is set to decrease as the steering angular speed Dθs increases in an area where the steering angular speed Dθs is equal to or greater than a predetermined value. The As a result, when the steering angular velocity Dθs increases with sudden steering, the correction coefficient K3 is set to the decreasing side and the deceleration-corresponding restraint torque Tb is corrected to decrease, and as a result, the turning ability is ensured. Further, the map of the low μ road surface is set so that the correction coefficient K3 is maintained at the maximum value (1.0) up to a higher steering angular velocity Dθs, and as a result, a decrease in the deceleration-restraining torque Tb due to sudden steering is suppressed. Thus, running stability is ensured. In this example, the same map is applied regardless of the steering direction (cutting side and returning side), but a map having different characteristics may be applied depending on the steering direction.
[0024]
The C / S correction unit 98 replaces the correction coefficient K3 set in this way with 1 only when the counter steer (CSH = 1) is set. Therefore, when the correction coefficient K3 set based on the steering angular velocity Dθs becomes inappropriate due to the counter steer, correction based on this is prohibited.
The characteristics of the filter 97 are set, for example, to 0.5 Hz on the increase side and 8 Hz on the decrease side, and the response on the increase side is greatly reduced compared to the response on the decrease side. Therefore, 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 quickly decreases the output with high responsiveness. The torque Tb is also quickly reduced. On the other hand, when the steering angular velocity Dθs is reduced immediately thereafter, the output of the filter 97 is slow because the response of the filter 97 is low even if the input correction coefficient K3 is increased. Without increasing, the deceleration-restraining torque Tb also increases gradually.
[0025]
That is, the steering angular velocity Dθs increases due to sudden steering for a very short time in the initial stage of steering, but the deceleration-restraint restraint torque Tb is maintained in a decreasing state for a longer time with respect to the increase period of the steering angular velocity Dθs. Will be. Then, since the actual restraining torque of the center differential 1 is reduced over the reduction period of the restraining torque Tb corresponding to deceleration, the behavior of the vehicle surely changes in the direction of improving the turning ability. Needless to say, the appropriate reduction period of the restraining torque varies depending on various conditions such as the responsiveness of the hydraulic unit 20 and the turning performance of the vehicle. Therefore, the characteristics of the filter 97 take these conditions into consideration. It can be changed arbitrarily.
[0026]
As described above, according to the vehicle differential limiting device of the present embodiment, the deceleration-corresponding restraint torque Tb is decreased over an appropriate period according to the steering state. It is possible to reliably reflect the behavior of the vehicle, so that it is possible to always ensure optimum running characteristics while ensuring sufficient turning ability during sudden steering.
[0027]
Further, as described above, the correction coefficient K3 is set steplessly according to the steering angular velocity Dθs according to the map of the K3 calculation unit 96, and the deceleration-responding restraint torque Tb also changes steplessly based on the correction by the correction coefficient K3. . 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 stepwise depending on whether or not the steering angular velocity Dθs exceeds a predetermined value. Corresponding restraint torque Tb is also switched in a step-like manner, causing a sudden change in the behavior of the vehicle. On the other hand, since the behavior of the vehicle changes smoothly when the deceleration-corresponding restraint torque Tb is changed steplessly, the driver can easily understand the behavior change, and the driving operation can be facilitated. can get.
[0028]
This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the differential limiting device for the center differential that allows the differential between the front wheels and the rear wheels is embodied, but for example, the differential limit for the front differential and the rear differential that allows the differential between the left and right wheels. It may be embodied in a device.
In the above embodiment, the front-rear differential rotation restraint torque Tv, the front-rear G proportional restraint torque Tx, the acceleration restraint torque Ta, and the deceleration restraint torque Tb are calculated to set the final restraint torque Tfinal. The constraint torque may be omitted, or a constraint torque calculated from another parameter may be added.
[0029]
Furthermore, in the above embodiment, the filter 97 is provided on the output side of the K3 calculation unit 96, and the increase / decrease state of the correction coefficient K3 is changed by the filter 97, thereby realizing a desired reduction period of the deceleration-corresponding restraint torque Tb. For example, as indicated by a two-dot chain line in FIG. 4, the position of the filter 97 may be changed to the output side of the differentiation processing unit 95, and the increase / decrease state of the steering angular velocity Dθs may be changed by the filter 97. Contrary to the above case, the characteristics of the filter 97 in this case are set so that the response on the decrease side is lower than the response on the increase side. As a result, when the steering angular velocity Dθs increases due to sudden steering, the filter 97 quickly increases the output with high responsiveness, and when the steering angular velocity Dθs immediately thereafter decreases, the output of the filter 97 is low because the responsiveness of the filter 97 is low. As a result, the decrease period of the deceleration-restraining restraint torque Tb is extended with respect to the increase period of the steering angular velocity Dθs, and as a result, sufficient turnability can be ensured as in the above embodiment.
[0030]
On the other hand, in the above embodiment, the filter 97 having different responsiveness on the increase side and the decrease side is used. However, for example, a peak hold filter that holds the maximum value for a predetermined time or a bottom hold filter that holds the minimum value for a predetermined time may be used. Good. Specifically, when the increase / decrease state of the correction coefficient K3 is changed as in the above embodiment, the decrease period of the correction coefficient K3 is extended by the bottom hold filter, and the steering angular velocity Dθs is changed as in the above-described another example. When changing the increase / decrease state, the increase period of the steering angular velocity Dθs may be extended by the peak hold filter. Furthermore, instead of these filters, for example, a gradient limiter with a characteristic that changes the output only when the rate of change on the input side exceeds a predetermined value may be used. The decrease period of the restraining torque Tb can be extended.
[0031]
【The invention's effect】
As described above, according to the differential limiting device for a vehicle of the present invention, the restraint torque is changed over an appropriate period according to the steering state to be surely reflected in the behavior of the vehicle, so that the optimum traveling is always achieved. Characteristics can be realized.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram illustrating 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 setting procedure of restraint torque executed by an ECU.
FIG. 4 is a block diagram showing a detailed procedure for setting a restraint torque of a deceleration-corresponding restraint torque setting unit.
[Explanation of symbols]
1 Center differential (differential means)
3F front wheel (drive wheel)
3R rear wheel (drive wheel)
4 Engine 19 Hydraulic multi-plate clutch (Differential limiting means)
31 ECU (control means)

Claims (1)

Differential means for distributing the driving force from the engine to each driving wheel while allowing a differential;
Differential limiting means capable of limiting the differential by applying a restraining torque to the differential means;
And control means for controlling the restraining torque of the differential limiting means on the basis of the longitudinal acceleration and the steering angular velocity of the vehicle,
The control means corrects the target value of the restraint torque calculated to increase the restraint torque as the longitudinal acceleration increases toward the deceleration side so that the restraint torque decreases as the steering angular velocity increases. And controlling the restraint torque, and setting the responsiveness of the correction to be lower on the increase correction side than on the decrease correction side of the restraint torque.

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