Fluid-pressure and analogous brake systems – Speed-controlled – And traction control
Reexamination Certificate
1995-03-28
2002-07-02
Graham, Metthew C. (Department: 3103)
Fluid-pressure and analogous brake systems
Speed-controlled
And traction control
C303S141000, C303S149000, C303S196000, C303S197000, C180S197000
Reexamination Certificate
active
06412886
ABSTRACT:
FIELD OF THE INVENTION
The present application relates to a driving force control apparatus for a vehicle which, when driving wheels of the vehicle slip, reduces the driving force of the driving wheels to suppress slipping. Further, when the slip is suppressed, it restores the reduced driving force to the original value. This thereby prevents the speed variation of the driving wheels (fluctuation of rotational speed of the driving wheels) from vibrating and, in turn, prevents the vehicle body from vibrating.
BACKGROUND OF THE INVENTION
An excessive driving force when the vehicle is traveling on a slippery road such as a snow-laden road tends to cause a slip of the driving wheels. This results in a reduction of gripping force of the tires, acceleration characteristics and drivability. To deal with such a case, a conventional driving force control apparatus or a so-called traction control apparatus has been developed and practically used.
In the traction control apparatus, a slip of the driving wheels is detected (slip detection method will be described later) and, when the slip is considerable, the output of the engine is forcibly and rapidly suppressed to reduce the driving force of the driving wheels (driving force reduction method will be described later). As described above, the slip is suppressed by forcible reduction of the driving force to improve the starting and acceleration characteristics on a slippery road such as a snow-laden road.
When the traction control apparatus is applied to a two-wheel driving (2WD) vehicle, a slip amount DVS has been detected as follows. For a front wheel driving vehicle, for example, first a target driving wheel speed V
OT
(this is in one to one relation to a vehicle body speed V
B
) is calculated based on the rear wheel (driven wheels) speed. Then, speeds of the right and left front wheels (driving wheels) are averaged to determine an average driving wheel speed V
FX
. The target driving wheel speed V
OT
is then subtracted from the average driving wheel speed V
FX
to detect the slip amount.
Further, a control device for reducing the engine output (driving force) to suppress a slip includes the following:
(1) Throttle control (throttle valve of the intake system is closed)
(2) Ignition timing retard control (ignition timing of the ignition plug is retarded)
(3) Fuel control (fuel cutting or fuel injection amount control)
(4) Cylinder number control (operation of a predetermined number among plural cylinders is suspended).
Most of the conventional traction control apparatuses use a combination of the throttle control and the ignition timing retard control. According to the throttle control, the engine output can be controlled smoothly and over a wide range. In an abrupt start or when the road surface condition suddenly changes from a dry road to a frozen road, an abrupt slip occurs. The throttle control is not able to control such an abrupt slip. When an abrupt and excessive slip occurs, the ignition timing retard control is temporarily operated to suppress the abrupt slip with a good response.
In a traction control apparatus using a combination of the throttle control and the ignition timing retard control, setting (control begins to reduce the driving force) and resetting (control ends to restore the driving force) of the both controls are performed as follows.
First, setting and resetting conditions of the ignition timing retard control will be described. In the ignition timing retard control, setting and resetting are made in dependence on the conditions of the slip amount DVS and a slip rate GDVS which is obtained by differentiation of the slip amount DVS. That is, the control is set when both the slip amount DVS and the slip rate GDVS are greater than predetermined values. It is reset when one of the slip amount and the slip rate GDVS is decreased to some extent, and the other is considerably reduced. In practice, these are made as follows, wherein G indicates the gravitational acceleration.
The ignition timing retard control is set when both conditions (1-1) and (1-2) shown below are simultaneously met:
(1-1) Slip amount DVS≧2 [km/h]
(1-2) Slip rate GDVS>0.6 G.
The setting is made when the slip amount DVS and the slip rate GDVS are both greater than the predetermined values.
The ignition timing retard control is reset when both conditions (2-1) and (2-2), or (3-1) and (3-2), shown below are simultaneously met:
(2-1) −0.5 G≧GDVS≧0 G; and
(2-2) DVS<6 [km/h] or
(3-1) GDVS<−0.5 G; and
(3-2) DVS<18 [km/h].
The above (2-1) and (2-2) are conditions where the slip rate GDVS is decreased to some extent and the slip amount DVS is considerably decreased. The above (3-1) and (3-2) are conditions where the slip amount DVS is decreased to some extent and the slip rate GDVS is considerably decreased.
Next, setting and resetting conditions of the throttle control will be described. In the throttle control, the throttle control is set when the slip amount DVS is greater than a preset value. It is reset when the slip amount DVS is smaller than a preset value. The steps are as follows.
Details will be described in the embodiments of the present invention. To achieve slip suppression control by the throttle control, first a reference driving torque T
B
to maintain a vehicle body speed V
B
is calculated, and feedback correction torque T
F
which is a cause of the occurrence of a slip is calculated based on the slip amount DVS. The feedback correction torque is T
F
is determined by PID (proportional, integration, differentiation) calculating the slip amount DVS. Therefore, by subtracting the feedback correction torque T
F
from the engine output torque, the slip amount DVS can be reduced. Then, the feedback correction torque T
F
which is a cause of slip occurrence is subtracted from the reference driving torque T
B
to determine the target driving torque T
O
. This thereby reduces the engine output torque to the target driving torque T
O
. By reducing the engine output to the target driving torque T
O
, that is, by suppressing an excessive torque which is a cause of slip occurrence, slip occurrence is suppressed. As the torque reduction device in this case, the previously described fuel control or cylinder number control can be used instead of the throttle control.
In a vehicle using the traction control apparatus, when traveling, for example, on a split road (a road surface where the frictional coefficient of the road surface is different between the right and left wheel, that is, where one side road surface is the ground and the other side is snow-laden or frozen), a high vehicle body vibration may occur. The vehicle body vibration can be broadly divided into the following two causes.
Initially, a first cause of vehicle body vibration will be described.
When a driving force control apparatus (traction control apparatus) in which the target driving wheel speed V
OT
is decreased from an average driving wheel speed V
OT
to determine the slip amount DVS, and setting and resetting of the ignition timing retard control are made according to the above conditions (1-1), (1-2), (2-1), (2-2), (3-1) and (3-2) is used on a 2WD vehicle, and when the vehicle travels on a split road (a road surface where the frictional coefficient of the road surface contacting the driving wheels differs between the right and left wheel), a high vehicle body vibration may occur.
The cause of occurrence of the high vehicle body vibration will be described with reference to FIG.
6
. When the vehicle travels on a split road, a single-wheel slip condition may occur where only one of the right and left driving wheels slips. In such a single-wheel slip condition, for example, since the left driving wheel slips whereas the right driving wheel does not slip, the average driving wheel speed V
FX
abruptly increases. Thus, the on-board computer outputs a retard command to make the ignition timing retard control. When the ignition timing retard control is made, and the target driving wheel speed V
OT
is made, the ignitio
Abe Yasushi
Ito Yoshihito
Graham Metthew C.
Mitsubishi Jidosha Kogyo Kabushi Kaisha
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