JP3456227B2 - Differential limit torque control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential limiting torque control device for electronically controlling a differential limiting torque between left and right driving wheels based on left and right driving wheel speed difference information. 2. Description of the Related Art Conventionally, as a differential limiting torque control device, for example, one disclosed in Japanese Patent Application Laid-Open No. 1-215628 is known. [0003] In the conventional source described above, the differential limiting torque component given as a larger value as the turning radius is larger and the lateral acceleration is larger, and the differential based on the left and right driving wheel slip amount (difference between left and right driving wheel speed values) detected by a sensor. An apparatus for calculating a target differential limiting torque based on the sum of the limiting torque components and performing control for obtaining the target differential limiting torque is shown. However, in the above-described conventional differential limiting torque control device for a left-right driving wheel speed difference, the differential is controlled in proportion to the occurrence of the right-left driving wheel speed difference by sensor detection. Since the limited torque is applied, when turning at a tight corner due to full steering extremely low speed, a difference in left and right drive wheel speed occurs due to the difference between the inner and outer wheels of the turning trajectory, and the differential limiting torque is applied, so that the brake is applied. The turning phenomenon makes it difficult to turn. [0005] Therefore, the left-right drive wheel speed difference control is mainly for securing traction at the time of starting the left / right split μ road or exiting the stack. In such a case, the right-left drive wheel speed difference is generated at the same time. Focusing on the fact that there is a large difference between the front and rear wheel rotation speeds, but a small difference between the front and rear wheel rotation speeds even though there is a left and right drive wheel speed difference during tight corner turning, the front and rear wheel rotation speed difference is less than a predetermined value. In the case of, the above-mentioned problem is solved by setting the differential limiting torque corresponding to the left and right driving wheel speed difference to zero and applying the differential limiting torque corresponding to the left and right driving wheel speed difference only when the front and rear wheel rotational speed difference exceeds a predetermined value. There is a plan. However, when a four-wheel summer tire is mounted on the rear wheel side to perform a tight corner turning on a low μ road such as a snowy road, the rear wheel side, which is a driving wheel, tends to be slightly slippery. A rotation speed difference occurs, and even if the front and rear wheel rotation speed difference condition is added, the differential limiting torque corresponding to the left and right drive wheel speed difference will be applied, and the steering characteristic becomes a strong understeer characteristic, and the traveling locus becomes outside. Swell. To solve this problem, the threshold value of the front and rear wheel rotational speed difference condition is simply raised to reduce the low μ
There is also a plan to prevent the differential limiting torque corresponding to the left and right drive wheel speed difference from being applied even during tight corner turning on a road, but in this case, the difference between the left and right drive wheel speed difference Even when the dynamic limiting torque is required, the generation of the torque is delayed, and the traction performance requirement, which is the purpose of the differential limiting torque corresponding to the difference between the left and right driving wheel speeds, cannot be achieved. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a differential control method for electronically controlling a differential limiting torque between left and right driving wheels based on left and right driving wheel speed difference information. An object of the present invention is to provide a dynamic limiting torque control device capable of securing turning performance during tight corner turning including low-mu road tight corner turning by attaching a chain, while ensuring traction performance when starting on a right / left split μ road. In order to achieve the above object, a differential limiting torque control device according to the present invention is provided between left and right driving wheels as shown in the claim correspondence diagram of FIG. Differential limiting torque applying means a for applying a differential limiting torque according to the control command, left and right driving wheel speed difference detecting means b for detecting left and right driving wheel speed differences, and front and rear for detecting front and rear wheel rotation speed differences A wheel rotation speed difference detecting unit c, a differential limiting torque determining unit d for determining a differential limiting torque according to the detected value of the left and right driving wheel speed difference, a front and rear wheel rotation speed difference is equal to or more than a predetermined value, and
Der When the left and right drive wheel speed difference is equal to or greater than a predetermined value, to set the differential limiting torque determined in accordance with the left and right drive wheel speed difference detection value as the target differential limiting torque, the left and right drive wheel speed difference is greater than a predetermined value
However, when the front and rear wheel rotational speed difference is less than a predetermined value, a target differential limiting torque setting means e for setting a target differential limiting torque according to the left and right driving wheel speed difference to zero; And a differential limiting torque control means f for outputting a control command to obtain the differential limiting torque applying means a. When the vehicle is running, the left and right driving wheel speed difference detecting means b detects the left and right driving wheel speed difference, and the front and rear wheel rotating speed difference detecting means c detects the front and rear wheel rotating speed difference. When the difference between the front and rear wheel rotational speeds is equal to or greater than a predetermined value and the difference between the left and right driving wheel speeds is equal to or greater than a predetermined value, the target differential limiting torque setting means e responds to the detected value of the left / right driving wheel speed difference. differential limiting torque determined by the differential limiting torque determiner d Te is set as the target differential limiting torque, left
The right drive wheel speed difference is greater than or equal to a predetermined value, but the front and rear wheel rotational speed difference
Is less than a predetermined value, the target differential limiting torque according to the difference between the left and right driving wheel speeds is set to zero, and the differential limiting torque control means f outputs a control command for obtaining the target differential limiting torque. The output is output to the torque applying means a, and the differential limiting torque is applied between the left and right driving wheels. Therefore, for example, when the vehicle is started on the left and right split μ roads, the drive wheel on the low μ road side generates a large drive slip by one wheel, so that the front and rear wheel rotational speed difference is equal to or more than a predetermined value and the left and right drive wheel speed difference is increased. Is greater than or equal to a predetermined value, and a differential limiting torque is applied between the left and right driving wheels based on the occurrence of the difference between the left and right driving wheel speeds. And high traction performance is exhibited. Further, for example, when turning a tight corner at a full turning extremely low speed, the difference between the left and right driving wheel speeds becomes a predetermined value or more due to the difference between the running trajectories of the inner and outer wheels. The dynamic limiting torque is set to zero, which suppresses the tight corner braking phenomenon.In addition, when running on a tight μ corner on a low μ road with a chain attached, the drive wheels with the chain tend to slip slightly, so the front and rear wheel rotation speed is reduced. The difference may be more than the specified value,
Because the road is a road and the difference between the left and right drive wheel speeds caused by the difference between the running trajectories of the inner and outer wheels is small, the differential limiting torque is set to zero, and the steering characteristic becomes strong understeer as in the case where the differential limiting torque is applied, The problem that the running locus bulges outward is prevented. Embodiments of the present invention will be described below with reference to the drawings. First, the configuration will be described. FIG. 2 is an overall system diagram of a rear-wheel drive vehicle to which the differential limiting torque control device according to the embodiment of the present invention is applied. In FIG. 2, 1 is an engine, 2 is a transmission, 3 is a propeller shaft, 4 is an electrically controlled limited slip differential (hereinafter abbreviated as an electrically controlled LSD), 5, 6 are rear wheels, and 7, 8 are front wheels. It is. The electric control LSD 4 has a built-in differential limiting clutch 10 for generating a differential limiting torque between the left and right rear wheels 5 and 6 according to the clutch control pressure applied from the hydraulic unit 9. The hydraulic unit 9 includes a hydraulic source 11 and an LS
And a D control valve 12. The hydraulic unit 9 and the differential limiting clutch 10 correspond to differential limiting torque applying means a. The LSD control valve 12 operates in accordance with a control current ILSD from the active LSD controller 13 to generate a clutch control pressure for the differential limiting clutch 10. The active LSD controller 13 includes a left front wheel rotation speed NFL from a left front wheel rotation sensor 14 and
Right front wheel rotation speed NFR from right front wheel rotation sensor 15, left rear wheel rotation speed NRL from left rear wheel rotation sensor 16, right rear wheel rotation speed NRR from right rear wheel rotation sensor 17, and lateral acceleration sensor 18 , A longitudinal acceleration XG from the longitudinal acceleration sensor 19, an accelerator opening ACC from the accelerator opening sensor 20, a switch signal BS from the brake switch 21, and an ABS operation signal AS from the ABS controller 22. Is entered. Next, the operation will be described. [Differential Limiting Torque Control Operation Processing] FIG. 3 is a flowchart showing the flow of the differential limiting torque control operation processing performed by the active LSD controller 13, and each step will be described below. In step 30, the left front wheel speed NFL, the right front wheel speed NFR, the left rear wheel speed NRL, and the right rear wheel speed NRR
And the lateral acceleration YG are read. In step 31, the left front wheel speed NFL, the right front wheel speed NFR, the left rear wheel speed NRL, and the right rear wheel speed NRR
From the front left wheel speed VFL, front right wheel speed VFR and rear left wheel speed V
RL and right rear wheel speed VRR are calculated. In step 32, the vehicle speed VF is obtained by selecting the smaller one of the left front wheel speed VFL and the right front wheel speed VFR, and the difference between the left and right rear wheel speeds ΔVRR is determined by the left rear wheel speed VRL and the right rear wheel speed VRR. (Equivalent to the left and right drive wheel speed difference detection means b), and the front and rear wheel rotation speed difference ΔVFR is calculated from the difference between the rear wheel speed average value VRA and the front wheel speed average value VFA (front and rear wheel rotation speed). (Corresponds to speed difference detecting means c)). In step 33, the front and rear wheel rotational speed difference ΔV
It is determined whether FR is greater than or equal to a set value α, and whether left and right rear wheel speed difference ΔVRR is greater than or equal to a set value β. Here, the set value α is, for example, α = 2.5
km / h, and the set value β is given, for example, at β = 5 km / h. In step 34, when the tight corner countermeasure start condition (ΔVFR ≧ α and ΔVRR ≧ β) in step 33 is satisfied, the split μ road flag SPμF is set to SPμF =
Set to 1. In step 35, the front and rear wheel rotational speed difference ΔV
It is determined whether FR is less than the set value α. In step 36, when the tight corner countermeasure end condition (ΔVFR <α) in step 35 is satisfied, the split μ road flag SPμF is reset to SPμF = 0. In step 37, the sign of the split μ road flag SPμF is determined, and when it is determined that SPμF = 1, the routine proceeds to step 38, where the differential limiting torque TΔV corresponding to the left and right rear wheel speed difference is TΔV = C When set by ΔVRR and it is determined that SPμF = 0, the routine proceeds to step 39, where the differential limiting torque T corresponding to the left and right rear wheel speed difference is set.
ΔV is set to TΔV = 0. Here, C of TΔV = C · ΔVRR is a control gain of the differential limiting torque TΔV corresponding to the left and right rear wheel speed difference with respect to the left and right rear wheel speed difference ΔVRR. For example, as shown in FIG. Therefore, the control gain C is changed to C1 and C2, and a small constant C2 is used in the high speed range to achieve stability due to ease of correction steering compared to the constant C1 in the low speed range.
(<C1). Steps 33 to 39 correspond to the differential limiting torque determining means d and the target differential limiting torque setting means e. In step 40, it is determined whether the vehicle speed VF is equal to or higher than the set vehicle speed x. Here, the set vehicle speed x is, for example, x
= 5 km / h. In step 41, a peak hold flag PHF indicating whether or not the peak hold control is being performed is set to PHF =
Set to 0. In step 42, it is determined whether or not the peak hold flag PHF is PHF = 0. In step 43, it is determined whether the left and right rear wheel speed difference ΔVRR is equal to or greater than the set left and right rear wheel speed difference y. Here, as the set left and right rear wheel speed difference y, a large value which occurs only at the time of stacking, such as y = 5 km / h, is given. In step 44, the peak hold flag PHF is set to PHF = 1 (during peak hold control). In step 45, each wheel speed VFL of the four wheels
It is determined whether VFR, VRL, and VRR are all zero. In step 46, it is determined whether or not the operation has continued for 1 second or more. In step 47, a filtering process is performed on the differential limiting torque TΔV corresponding to the difference between the left and right rear wheel speeds to obtain a differential limiting torque filter value TF. In this filter processing, the differential limiting torque TΔV corresponding to the right and left rear wheel speed difference one control cycle before is stored, and
This is performed by applying a limiter so that the difference between the left and right rear wheel speed difference-corresponding differential limiting torque TΔV does not exceed a predetermined value on both the increasing side and the decreasing side. In step 48, the differential limiting torque filter value TF obtained in step 37 is set as the target differential limiting torque T ^* . In step 49, it is determined whether the differential limiting torque TΔV corresponding to the difference between the left and right rear wheel speeds is equal to or greater than the differential limiting torque maximum value Tmax. In addition, the differential limiting torque maximum value Tmax
Has an initial value of Tmax = 0, and is reset to Tmax = 0 when the control is switched from the peak hold control to the normal control. In step 50, the differential limiting torque TΔV corresponding to the difference between the left and right rear wheel speeds that satisfies TΔV ≧ Tmax is set as the differential limiting torque maximum value Tmax. In step 51, the maximum differential limiting torque Tmax obtained in step 50 is set to the target differential limiting torque Tmax.
Set as ^* . At step 52, the control current ILSD for obtaining the target differential limiting torque T ^* set at step 48 or 51 is output to the LSD control valve 12 (corresponding to the differential limiting torque control means f). [Left / Right Split μ Road Start] When the left / right split μ road starts, one of the drive wheels on the low μ road generates a large drive slip, and the front and rear wheel rotational speed difference ΔV
The condition that FR is equal to or greater than the set value α and the difference between the left and right rear wheel speeds ΔVRR is equal to or greater than the predetermined value β is satisfied, and in the flowchart of FIG.
→ Step 37 → Step 38, in which the differential limiting torque is applied between the left and right rear wheels 5 and 6 based on the occurrence of the left and right rear wheel speed difference ΔVRR. Therefore, by applying the differential limiting torque between the left and right rear wheels 5, 6, the engine driving torque to the rear wheels on the high μ road side is increased, and high traction performance is exhibited. [Tight corner turning at full steering extremely low speed] During tight corner turning at full steering extremely low speed, the left and right rear wheel speed difference ΔVRR exceeds the set value β due to the difference in the running trajectory of the inner and outer wheels. Since the occurrence of the wheel rotation speed difference ΔVFR is small, the flow chart shown in FIG. 3 is used to execute step 33 → step 35 → step 36 → step 37 → step 39.
In step 39, the differential limiting torque between the left and right rear wheels 5 and 6 is set to zero regardless of the occurrence of the left and right rear wheel speed difference ΔVRR. Therefore, the occurrence of the tight corner braking phenomenon, such as the case where the differential limiting torque is applied based on the occurrence of the difference between the left and right rear wheel speeds ΔVRR at the time of turning the tight corner at a full turning extremely low speed, can be suppressed. [During Low-μ Road Tight Corner Turning with Chain Attached] During low-μ road tight corner turning with a chain attached, the front and rear wheel rotational speed difference ΔVFR becomes a set value α because the drive wheel with the chain is slightly slippery. In some cases, the left and right rear wheel speed difference ΔVRR generated by the difference between the running trajectories of the inner and outer wheels is small,
In the flowchart of FIG.
The flow is → step 36 → step 37 → step 39. In step 39, the differential limiting torque between the left and right rear wheels 5, 6 is set to zero regardless of the occurrence of the left and right rear wheel speed difference ΔVRR. Therefore, as shown in the case where the differential limiting torque is applied at the time of turning on a low μ road tight corner by mounting the chain, the steering characteristic becomes strong understeer,
The problem that the running locus bulges outward is prevented. FIG. 5 shows the results of an experiment conducted by the present inventor. The experimental conditions were as follows: a tight corner on a compacted snowy road (turning radius of 6 to 7 m, close to full steering); four-wheel summer tires + left and right rear wheels With chain attached, accelerator opening 1 /
I ran more than eight. Note that in FIG. 5, the mark “○” indicates that the ladder-type chain is mounted, and the mark “△” in FIG. 5 indicates that the spring chain is mounted. In this experiment, the differential limiting torque control corresponding to the difference between the left and right driving wheel speeds was performed only under the condition of ΔVFR ≧ α (2.5 km / h). Was imparted, resulting in a strong understeer characteristic. That is, the difference between the front and rear wheel rotation speeds ΔVFR was 2.5 km / h, and the maximum reached 10 km / h or more. Therefore, in order to solve the above problem only on the condition of the front and rear wheel rotational speed difference ΔVFR, the set value α is set to 15 km / h.
However, in this case, the time when the differential limiting torque is applied when the vehicle starts on the right or left split μ road is greatly delayed, and it is no longer possible to obtain desired traction performance. On the other hand, ΔVFR ≧ α (2.5 km / h) and ΔVRR ≧ β (5 km / h) were set as AND conditions.
In this case, while the front and rear wheel rotational speed difference condition was kept as it was, the vehicle was in a non-control region when turning on a low μ road tight corner with the chain attached, and a differential limiting torque of zero was achieved. [Escape from Stack] When the vehicle speed is less than the set vehicle speed x when the vehicle escapes from the stack, the flow chart shown in FIG.
→ step 34 → step 35 → step 37 → step 38 → step 40 → step 42 → step 43 →
The flow proceeds from step 44 → step 49 → step 50 → step 51 → step 52, and the maximum differential limiting torque Tmax of the differential limiting torque TΔV corresponding to the left and right rear wheel speed difference is set as the target differential limiting torque T ^*. Differential limiting torque control by peak hold, which is maintained until the vehicle speed reaches x, is performed. Therefore, when one of the right and left rear wheels 5 and 6 is in the stack, the maximum differential limiting torque Tmax based on the occurrence of the left and right rear wheel speed difference ΔVRR starts moving completely, and the vehicle speed is reduced. By maintaining VF until the set vehicle speed x is increased, an increase in engine driving torque to one wheel not in the stack is secured until the vehicle completely escapes from the stack, and high stack escape performance is exhibited. Since the peak hold control is performed under two conditions of the vehicle speed condition of step 40 and the left and right rear wheel speed difference condition of step 43, for example,
When the vehicle starts turning with a small left and right rear wheel speed difference ΔVRR, a large differential limiting torque is not applied by the peak hold, the tight corner braking phenomenon is prevented, and a smooth start is secured. [Abrupt Change in Differential Limiting Torque] If a large difference in differential limiting torque occurs at a tight corner turning exit or at the time of running after exiting the stack, the filter processing in step 47 is effective, and the torque is gradually reduced. By controlling to increase or decrease, a sudden change in vehicle behavior due to a sudden increase or decrease in the differential limiting torque is prevented. Next, the effects will be described. (1) In a differential limiting torque control device for electronically controlling the differential limiting torque between the left and right rear wheels 5 and 6 based on the left and right rear wheel speed difference information, when the front and rear wheel rotational speed difference ΔVFR is equal to or greater than a set value α. The left and right rear wheel speed difference ΔVRR is obtained by two AND conditions that the left and right rear wheel speed difference ΔVRR is equal to or greater than a predetermined value β.
Applied torque according to RR, and at other times, the differential limiting torque is set to zero so that differential limiting torque control corresponding to the left and right rear wheel speed difference is ensured, ensuring traction performance when starting on a left / right split μ road While turning on a tight corner including a low-μ road tight corner by chain attachment, it is possible to ensure turning performance. (2) When the vehicle speed VF is equal to or higher than the set vehicle speed x, or when the vehicle speed VF is lower than the set vehicle speed x and the left / right driving wheel speed difference ΔVRR is smaller than the set left / right rear wheel speed difference y, the left and right rear wheels for control are used. When the differential limiting torque TΔV determined according to the speed difference ΔVRR is used as it is as the target differential limiting torque T ^* , when the vehicle body speed VF is lower than the set vehicle speed X and the left and right rear wheel speed difference ΔVRR is equal to or more than the set left / right driving wheel speed difference y. In addition, since the maximum differential value Tmax of the differential limiting torque TΔV determined in accordance with the left and right driving wheel speed difference ΔVRR is maintained as a target differential limiting torque T ^* until the vehicle speed x is reached, a device for performing stack-compatible control is used. While avoiding the tight corner braking phenomenon at the time of starting, a reliable escape can be achieved by peak hold control at the time of stack escape. Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to the embodiment, and even if there are changes and additions without departing from the gist of the invention, the invention is included in the invention. It is. For example, in the embodiment, the example in which the differential limiting torque is applied by the hydraulic multi-plate clutch has been described. However, if the differential limiting torque can be variably controlled by an external control command, the electromagnetic clutch may be used. And so on. As described above, according to the present invention, there is provided a differential limiting torque control device for electronically controlling a differential limiting torque between left and right driving wheels based on left and right driving wheel speed difference information. When the front-rear wheel rotational speed difference is equal to or greater than a predetermined value and the left-right driving wheel speed difference is equal to or greater than a predetermined value, the differential limiting torque determined according to the detected value of the left-right driving wheel speed difference is set as the target differential limiting torque. The difference between the left and right drive wheel speeds is equal to or greater than a predetermined value,
When the rear wheel rotational speed difference is less than the predetermined value, the apparatus is provided with target differential limiting torque setting means for setting the target differential limiting torque according to the left and right driving wheel speed difference to zero, so that the left and right split μ road starts. The effect is that the turning performance can be ensured during tight corner turning including low-μ road tight corner turning by attaching a chain while securing traction performance at the time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram corresponding to claims showing a differential limiting torque control device of the present invention. FIG. 2 is an overall system diagram of a rear wheel drive vehicle to which the differential limiting torque control device of the embodiment is applied. FIG. 3 is a flowchart showing a flow of a differential limiting torque control operation process performed by an active LSD controller of the apparatus of the embodiment. FIG. 4 is a differential limiting torque characteristic diagram corresponding to a difference between left and right rear wheel speeds in the apparatus according to the embodiment. FIG. 5 is a diagram showing a state of occurrence of front and rear wheel rotational speed differences and right and left rear wheel speed differences during low-μ road tight corner turning traveling by mounting a chain in the embodiment device. [Description of Signs] a Differential limiting torque applying means b Left and right driving wheel speed difference detecting means c Front and rear wheel rotational speed difference detecting means d Differential limiting torque determining means e Target differential limiting torque setting means f Differential limiting torque controlling means

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B60K 23/04 B60K 17/34-17/35 F16H 48/00-48/30

Claims (1)

(57) [Claims 1] A differential limiting torque applying means provided between left and right driving wheels for applying a differential limiting torque according to an external control command, and a left and right driving wheel speed. Left and right driving wheel speed difference detecting means for detecting the difference, front and rear wheel rotating speed difference detecting means for detecting the front and rear wheel rotating speed difference, and differential limiting for determining the differential limiting torque according to the detected value of the left and right driving wheel speed difference A torque determining unit that, when the front and rear wheel rotational speed difference is equal to or more than a predetermined value and the left and right drive wheel speed difference is equal to or more than a predetermined value, sets the differential limiting torque determined according to the detected left and right drive wheel speed difference to the target difference; Is set as the dynamic limit torque, and the difference between the left and right drive wheel speeds is
When the rotational speed difference is less than a predetermined value, target differential limiting torque setting means for setting the target differential limiting torque according to the left and right driving wheel speed difference to zero, and a control command for obtaining the target differential limiting torque. And a differential limiting torque control unit that outputs the differential limiting torque to the differential limiting torque applying unit.