Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2003-06-19
2004-11-23
Marc-Coleman, Marthe Y. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C180S197000, C180S244000
Reexamination Certificate
active
06823252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive power distribution control method and device for a four-wheel drive vehicle. It also relates to a four-wheel drive vehicle having the drive power distribution control device.
2. Discussion of the Related Art
Heretofore, there has been known a drive power distribution control device for a four-wheel vehicle, wherein the drive power transmission rate of a drive power transmission device is variably controlled in dependence upon a vehicle speed and an acceleration manipulation amount (e.g., a throttle opening degree in the case of a gasoline engine car) so as to variably control the drive power distribution rate between front and rear wheels. More specifically, a drive power (transmission torque) depending on the vehicle speed and the acceleration manipulation amount is obtained by reference to a predetermined torque characteristic map, and the friction engagement force of an electromagnetic clutch constituting the drive power transmission device for the four-wheel drive vehicle is controlled so that the torque so obtained can be transmitted to the front wheels or the rear wheels. The torque characteristic map is a table map of the type that a transmission torque can be extracted by designating the vehicle speed and the acceleration manipulation amount as parameters and is prepared in advance by experiments using a vehicle model or by a well-know theoretical calculation processing.
However, the foregoing known drive power distribution control device for the four-wheel drive vehicle involves the following problems. For example, in a vehicle with an automatic transmission (hereafter referred to as “AT vehicle”), the vehicle in an idling state with the transmission being selected to D-range is advanced due to a so-called creep phenomenon even when the driver does not make the acceleration manipulation (i.e., stepping-on manipulation of an accel pedal). This is because the drive power of an engine being in the idling state is transmitted to the drive wheels through a torque converter of the AT (automatic transmission).
For the reason mentioned above, even during the creep motion or a low speed traveling, the drive wheels (i.e., the front wheels in a vehicle of the front-drive basis) tend to slip on an excessively small “&mgr;” road (i.e., a slippery road such as an “eisbahn” or the like). For example, where the vehicle stands stopped on an ascending road with the “eisbahn”, the front wheels happen to slip at the moment that the driver shifts to the D-range. In this case, the problem can be solved by increasing the drive power distributed to the driven wheels (e.g., rear wheels) in dependence on the rotational speed difference between the front and rear wheels.
However, it is often the case that the drive power distributed to the driven wheels is to be restrained in order to avoid a tight-corner braking phenomenon which occurs at the time of, for instance, garaging or the like (namely, the phenomenon in which a braking torque is generated against the front wheels due to the difference in the average turning radius between the front and rear wheels in the case for example that much more drive power is distributed to the rear wheels during a turning motion). This does not allow to unconditionally increase the drive power to be distributed to the rear wheels (driven wheels) in dependence on the rotational speed difference between the front and rear wheels. Accordingly, it has been difficult to restrain the front wheels (drive wheels) from slipping at the time of starting on the excessively small “&mgr;” road.
Further, the known four-wheel drive vehicle involves another problem concerning a quick starting which can be done with the engine being kept rotated at a high speed. If the front wheels are brought into connection with the rear wheels at such a quick starting, it often occurs that the passengers suffer a shock (torque shock). Such a torque shock has been verified to be large when the vehicle is started quickly with the drive power output from the engine being maintained at a high power.
In addition, another drive power distribution control device for a four-wheel vehicle of a similar type has also been known as described in Japanese unexamined, published patent application No. 2002-206566. In this known drive power distribution control device, when the drive mode is set in AUTO mode, the opening degree of a throttle valve, a vehicle speed and a rotational difference between the rotational speeds of front and rear wheels are extracted from two torque maps based on signals from sensors and are made reference thereto to extract a first transmission torque depending on the throttle opening degree, a second transmission torque depending on the front-rear rotational difference and first and second gains depending on the vehicle speed. A command transmission torque to be distributed to the rear wheels is calculated by summing up the product of the first transmission torque and the first gain and the product of the second transmission torque and the second gain. And, in the know device, the torque maps are designed so that first and second transmission torques are increased with the respective increases in the throttle opening degree and the front-rear rotational difference, while the first and second gains are decreased with increase in the vehicle speed; i.e., the first and second gains are set larger when the vehicle speed is low.
However, the prior art of the Japanese patent application does not describe how to control the command transmission torque to be distributed to the rear wheels at the starting of the vehicle in connection with the state or manner in which the vehicle is beginning to start, such as for example the state of a road surface on which the vehicle is beginning to start or the manner of beginning to start the vehicle.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an improved torque distribution control device for a four-wheel drive vehicle capable of restraining drive wheels from skidding or slipping at the starting of the vehicle.
Another object of the present invention is to provide a four-wheel drive vehicle having an improved torque distribution control device capable of preventing or restraining a torque shock from being generated even when the vehicle is brought into the four-wheel drive state with an engine being in the state of a high power output.
Still another object of the present invention is to provide an improved torque distribution control device for a four-wheel drive vehicle capable of controlling the drive torque to be transmitted to rear wheels so that the slips or skids of both front and rear wheels can be restrained to the least.
Briefly, according to a general inventive concept of the present invention, there is provided a drive power distribution control method and device for a four-wheel drive vehicle for variably controlling the amount of drive power distributed to a driven wheel axle by variably controlling the power transmission rate of a drive power transmission device based on signals from various sensing means including at least vehicle speed sensing means for detecting the vehicle speed. The drive power distribution control method and device comprises a traveling state judgment step and means for judging whether the vehicle is beginning to start or not and also judging the state or manner in which the vehicle is beginning to start. The drive power distribution control method and device further comprises a transmission torque control step and means operable when it is judged based on a vehicle speed signal that the vehicle is beginning to start, for controlling the drive torque transmitted to the driven wheels in dependence on the state or manner judged by the traveling state judgment step and means.
With this configuration, the starting of the vehicle is discriminated from an ordinary four-wheel drive traveling state, and when it is detected that the vehicle is beginning to start, the drive to
Ito Isao
Murakami Tsuyoshi
Shigeta Ryouhei
Wakao Hisaaki
Yamada Yasushi
Marc-Coleman Marthe Y.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyoda Koki Kabushiki Kaisha
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