Motor vehicles – Having four wheels driven – With differential means for driving two wheel sets at...
Reexamination Certificate
2003-08-07
2004-11-02
Hurley, Kevin (Department: 3611)
Motor vehicles
Having four wheels driven
With differential means for driving two wheel sets at...
C701S069000
Reexamination Certificate
active
06810983
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control apparatus for a four wheel drive vehicle having a differential limiting mechanism on at least either one of a front wheel or a rear wheel side and in which a transfer clutch freely engageable and disengageable is provided between the front and rear wheel sides for changing driving wheels.
2. Related Art
In general, it is known that a tight corner braking phenomenon easily happens to be generated by a differential limiting torque in implementing a differential limiting control according to a difference in wheel speeds between left and right wheels unless a target differential speed between the left and right wheels is set in consideration of the difference in a trace of the respective wheels when steering.
On the other hand, for example, JP-A-2001-71776 discloses the differential limiting of a center differential according to the front and rear wheel differential.
In adopting the differential limiting control of the center differential like the aforementioned related art on a vehicle equipped with a mechanical differential limiting mechanism on either one of front or rear wheel side for the purpose of sporty running, a mechanical differential limiting control between the left and right wheels interferes with the differential limiting control of the center differential. Then an unnecessary control is implemented at the center differential, whereby there may occur a risk that the mechanical differential limiting mechanism does not sufficiently actuate or an unexpected braking phenomenon is generated.
Namely, in a condition where a slippage of the inside wheel while turning is restrained by the mechanical differential limiting control between the left and right wheels, where by the speeds of the turning inner and outside wheels become identical. An excessive driving torque of the inside wheel is shifted to the outside wheel, whereby there is generated a yaw moment at a front portion of the vehicle toward a turning direction, which is desirable for a sporty running. However, in this case, this condition is the regarded as the slippage of the inside wheel and the differential limiting control of the center differential, the torque distribution to the front and rear axles changes vehicle behaviors, this leading to the risk that the tight corner braking phenomenon is generated.
SUMMARY OF THE INVENTION
The present invention was made in view of the situations, and an object thereof is to provide a control apparatus for a four wheel drive vehicle having a differential limiting mechanism on at least either one of a front wheel side or a rear wheel side which can not only prevent unnecessary spins of a inside wheel while turning by the differential limiting mechanism between left and right wheels when a sporty running is being performed but also avoid a tight corner braking phenomenon which would occur when the vehicle is steered largely at a low speed.
With a view to attaining the object, according to a first aspect of the present invention, there is provided a control apparatus for a four wheel drive vehicle having differential limiting unit on at least either one of a front wheel or the rear wheel side, the control apparatus having the turning condition determining unit for determining the turning condition of a vehicle, a left and right inside wheel actual differential speed calculating unit for calculating an actual left and right wheel differential speed according to a turning state of the vehicle, a target differential speed setting unit for setting a target left and right wheel differential speed at the differential limiting unit, a differential limiting torque calculating unit for setting a differential limiting torque based on an information at the differential limiting unit at 0, an inside wheel speed falls below an outside wheel speed by a preset threshold value in the turning state and for calculating a differential limiting torque based on the information at the differential limiting unit based on the target left and right wheel differential speed and the actual left and right wheel differential speed when the inside wheel speed exceeds an outside wheel speed by the preset threshold value in the turning state, and a front and rear wheel differential limiting torque setting unit for setting a front and rear wheel differential limiting torque based on a differential limiting torque based on the information which is calculated at the differential limiting torque calculating unit.
In addition, according to a second aspect of the present invention, there is provided a control apparatus for the four wheel drive vehicle as set forth in the first aspect of the present invention, wherein the threshold value used at the differential limiting torque calculating unit to compare the inside wheel speed with the outside wheel speed at 0 of the turning state.
Furthermore, according to a third aspect of the present invention, there is provided the control apparatus for the four wheel drive vehicle as set forth in the first or second aspect of the present invention, wherein in the event that the turning state determining unit determines the turning state of the vehicle substantially as a straight running condition, the actual actual left and right wheel differential speed calculating unit regards an actual left and right wheel differential speed at the differential limiting unit as an absolute value of a left and right wheel differential speed. The differential limiting torque calculating unit calculates a differential limiting torque based on the information at the differential limiting unit and the absolute value of the left and right wheel differential speed.
In addition, according to a fourth aspect of the present invention, there is provided the control apparatus for the four wheel drive vehicle as set forth in any of the first to third aspects of the present invention, wherein the turning state determining unit determines a turning state of the vehicle from at least one of a lateral acceleration, a yaw rate or a steering angle.
Furthermore, according to a fifth aspect of the present invention, there is provided the control apparatus for the four wheel drive vehicle as set forth in the fourth aspect of the present invention, wherein the turning state determining unit determines that the vehicle is in substantially a straight running state when an absolute value of at least one of the lateral acceleration, the yaw rate or the steering angle is smaller than a predetermined value.
According to a sixth aspect of the present invention, there is provided the control method for the four wheel drive vehicle having the differential limiting unit on at least either one of the front wheel or the rear wheel side, the control method having steps of: determining the turning state of the vehicle; calculating the actual left and right wheel differential speed at the differential limiting unit according to the turning state of the vehicle; setting the target left and right wheel differential speed at the differential limiting unit; setting a differential limiting torque based on the information at 0 of the differential limiting unit, in the event that at the differential limiting unit, an inside wheel speed falls below that of the outside wheel speed by the preset threshold value in the turning state; calculating the differential limiting torque based on the information at the differential limiting unit based on the target left and right wheel differential speed and the actual left and right wheel differential speed, in the event that the inside wheel speed exceeds the outside wheel speed by the preset threshold value in the turning state; and setting the front and rear wheel differential limiting torque based on the differential limiting torque based on the information at the differential limiting unit which is calculated at the previous step.
According to a seventh aspect of the present invention, there is provided the control method as set forth in the sixth aspect, wherein the threshold value used to com
Fuji Jukogyo Kabushiki Kaisha
Hurley Kevin
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