Interrelated power delivery controls – including engine control – Plural engines – Electric engine
Reexamination Certificate
2001-07-16
2003-06-10
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Plural engines
Electric engine
C477S015000, C701S022000, C701S053000, C701S093000, C180S065230, C180S065310
Reexamination Certificate
active
06575870
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a driving force control system for a front-and-rear wheel drive vehicle of a type which drives front wheels and rear wheels independently by first and second prime movers, respectively.
2. Description of the Prior Art
Conventionally, a driving force control system of the above-mentioned kind was proposed e.g. by Japanese Patent Publication (Kokai) No. 2000-79833. The front-and-rear wheel drive vehicle has front wheels thereof driven by an engine and rear wheels thereof driven by a motor. A battery as a drive source for the motor can be charged by recovering running energy of the vehicle. Further, in the driving force control system, on condition that the remaining charge of the battery is equal to or smaller than a predetermined value, and when a driver's operation for accelerating the vehicle has been carried out e.g. by stepping on an accelerator pedal, the gear ratio of a continuously variable transmission is changed toward a higher gear ratio side by a predetermined amount. As a result, a surplus torque is generated, and the battery is charged by a regenerative braking torque corresponding to the surplus torque. This battery charge is continued until the remaining charge of the battery reaches the predetermined value. According to the proposed driving force control system, the charging of the battery is carried out not only during deceleration of the vehicle, but also at other times as described above, whereby the remaining charge of the battery is prevented from becoming insufficient.
However, in the above conventional driving force control system, when the remaining charge of the battery is equal to or smaller than the predetermined value, recharge traveling of the vehicle is carried out unconditionally in response to operation of the accelerator pedal so as to preserve a required amount of remaining charge. This means that despite the fact that a high driving force is desired by the driver who is demanding acceleration of the vehicle, part of the output of the engine is consumed as a regenerative braking torque for charging the battery, which increases load on the engine, thereby causing degradation of fuel economy. Further, the change gear ratio of the continuously variable transmission is changed toward the higher gear ratio side due to the recharge traveling, which can cause a downshift unexpected by the driver. This downshift degrades drivability while giving an uncomfortable feeling to the driver. In addition, since the charging of the battery is simply carried out until the remaining charge reaches the predetermined value, in some operating condition of the vehicle, sudden generation and loss of the regenerative braking torque can occur at the start and end of the recharge traveling, causing torque changes. This also leads to degradation of drivability.
In the above situation, the rear wheels receive the regenerative braking torque acting in a decelerating direction, whereas the front wheels receive a drive torque from the engine, which acts in an accelerating direction. As a result, the front wheels and the rear wheels are driven in respective opposite directions, and at the same time, the torque acting on the front wheels is increased by the amount of the regenerative braking torque acting on the rear wheels. Therefore, e.g. during running of the vehicle on a low friction road, the difference in rotational speed between the front wheels and the rear wheels is increased, whereby slippage of the rear wheels can be also increased, throwing lateral forces acting on the respective front-and-rear wheels out of balance, which makes the behavior of the vehicle unstable.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide a driving force control system for a front-and-rear wheel drive vehicle, which is capable of charging a battery properly and easily depending on a traveling condition of the vehicle and in response to the intention of the driver, thereby improving fuel economy and drivability of the vehicle.
It is a second object of the invention to provide a driving force control system for a front-and-rear wheel drive vehicle, which is capable of limiting the difference in rotational speed between front wheels and rear wheels, which is produced during a recharge mode for charging a drive source of a second prime mover with driving energy, within a proper range dependent on a state of a road surface and a traveling condition of the vehicle, thereby ensuring traveling stability of the vehicle.
To attain the above first and second objects, the present invention provides a driving force control system for a front-and-rear wheel drive vehicle that is driven while switching between a drive mode for driving first drive wheels as one pair of respective pairs of front drive wheels and rear drive wheels by a first prime mover and driving second drive wheels as another pair of the respective pairs by a second prime mover, and a recharge mode for recovering running energy of the vehicle to thereby charge a drive source of the second prime mover with the running energy recovered as driving energy.
The driving force control system according to the invention is characterized by comprising:
parameter detecting means for detecting a parameter indicative of a driving condition of the vehicle;
traveling condition-determining means for determining a traveling condition of the vehicle based on the parameter;
driving energy charge execution-determining means for determining, based on the traveling condition of the vehicle and a state of charge of the driving energy in the drive source, whether or not charging of the drive source with the driving energy is to be executed; and
energy charge-executing means for executing the charging of the drive source with the driving energy.
According to the driving force control system of the invention, it is determined, based on the traveling condition of the vehicle and the state of charge of the driving energy in the drive source, whether or not charging of the drive source with the driving energy is to be executed. This makes it possible to improve performance of the vehicle, that is, enhance fuel economy and drivability of the vehicle can be enhanced, and ensure traveling stability of the same.
Preferably, to attain the first object, the parameter detecting means includes accelerator pedal opening-detecting means for detecting an accelerator pedal opening, and vehicle speed-detecting means for detecting a vehicle speed, the traveling condition-determining determining means including desired driving force-calculating means for calculating a desired driving force based on the detected accelerator pedal opening and the detected vehicle speed, reference driving force-storing means for storing a reference driving force which is set, based on a driving force of the vehicle required for cruising, to a larger value than the driving force, and driving force comparison means for performing a comparison between the desired driving force and the reference driving force, and the driving energy charge execution-determining means including driving energy charge-permitting means for permitting the charging of the drive source with the driving energy when the driving force comparison means determines that the desired driving force is smaller than the reference driving force.
According to this driving force control system, the reference driving force is set, based on the driving force of the vehicle required for the cruising, to a predetermined value which is larger than the driving force, and when it is determined that the desired driving force is smaller than the reference driving force, the charging of the drive source of the second prime mover with the driving energy by recovery of the running energy of the vehicle is permitted, whereby execution of the recharge mode is started. Thus, in a cruising condition of the vehicle, the drive source of the second prime mover is charged with the driving energy when the desired driving force becomes smaller than the re
Fukuda Toshihiko
Kitano Kazuhiko
Nakasako Tooru
Uchiyama Naoki
Yamamoto Akihiro
Estremsky Sherry
Lewis Tisha D.
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