Vehicle driving control device and method

Details Vehicle driving control device and method Vehicle driving control device and method

2002-02-01

2004-01-20

Pang, Roger (Department: 3681)

Interrelated power delivery controls, including engine control

Transmission control

Engine controlled by transmission

C477S181000

Reexamination Certificate

active

06679807

ABSTRACT:

CROSS REFERENCES TO RELATED APPLICATIONS
This application relates to and incorporates herein by reference Japanese patent application no. 2001-27182 filed on Feb. 2, 2001.
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle driving control device for controlling the driving conditions of a vehicle by control of the engine, or control of both the engine and a braking device, independently of the controls performed by the driver.
A conventional control device performs so-called adaptive cruise control (hereafter, simply ACC), an example of which is disclosed in unexamined Japanese application (JP-A) No.7-47862. The conventional control device controls a trailing vehicle to follow a leading vehicle while keeping a safe distance between the vehicles. The control device computes a first target vehicle speed, which is the speed that is required to follow the leading vehicle. Then a target engine torque, which is the torque necessary to maintain the target vehicle speed, is computed for generating a torque command representing the target engine torque for directing the driving speed of the vehicle to the target vehicle speed.
To compute the target engine torque from the target vehicle speed according to the above-described control device, the basic torque of the engine is computed based on the current running resistance of the vehicle (rolling resistance, air resistance, acceleration resistance, and hill-climbing resistance, which is based on vehicle weight and road gradient), the gear ratio of the power train (the gear ratio of the transmission and differential gears), and the torque ratio of a torque converter. Furthermore, a correction of engine torque (correction torque) is computed from the deviation between the target vehicle speed and the actual vehicle speed. Then, the basic torque is corrected by the correction torque.
In the case of the conventional control device, therefore, the actual torque transmission characteristics of the torque converter will not be reflected in the target engine torque, which is the final control target. Also, it is impossible to set an optimum target engine torque for achieving the target vehicle speed during a transition period during which the engine speed is being greatly changed by the engine torque control and there is significant slippage in the torque converter.
The conventional control device uses an instantaneous value of the torque ratio to represent the characteristics of the torque converter when computing the basic torque of the engine. When the torque converter is locked by a lockup device and the engine is running at a steady speed or when the torque converter is in a relatively stable state because of low slippage, a nearly proper basic torque is obtained. However, during a transition period when the engine speed substantially varies or when the torque converter slips significantly, the characteristics of the torque converter cannot be reflected in the basic torque requirement, and it is impossible to optimally set the target engine torque.
Furthermore, in the conventional control device, the target vehicle speed is determined as the target of the ACC control, and the engine torque is set based on the target vehicle speed in performing engine control. Therefore, if an optimum target engine torque for achieving the target vehicle speed could be set, the acceleration of the vehicle resulting from the engine control would disturb the driver and other passengers. That is, according to the laws of motion, torque and acceleration (and deceleration) are proportional, and the target engine torque and the acceleration (and deceleration) of the vehicle correlate. However, in the conventional control device, since the target engine torque is based on the target vehicle speed, which is an integral value of the acceleration (and deceleration) of the vehicle, it is impossible to set a target engine torque that results in comfortable levels of acceleration. For example, when the target vehicle speed is increased in response to acceleration of the leading vehicle, the trailing vehicle will be abruptly accelerated during a transition period until the target vehicle speed is reached, which creates discomfort for the vehicle occupants. Since it takes time to accelerate the vehicle, the behavior of the vehicle will disturb the occupants.
SUMMARY OF THE INVENTION
In view of the above-described problems inherent in known control devices, it is an object of this invention to provide a driving control device that is capable of accelerating and decelerating a vehicle while giving the vehicle occupants a feeling of smooth operation and to optimize the vehicle driving torque of the engine even during a transition period when the engine speed greatly varies and when the slippage of the torque converter is increasing.
To accomplish this object, a target tire operating torque computing means computes the target tire operating torque necessary to operate the vehicle at a predetermined running state on the basis of an input from a sensor that detects the running condition of the vehicle. Then, a driving resistance estimating means estimates the driving resistance of the vehicle on the basis of an input from the sensor.
Then, target turbine torque computing means computes the target turbine torque of the torque converter on the basis of the target tire operating torque, the computed driving resistance, and the gear ratio of the power transmission train. A target engine operating condition computing means computes the target engine torque and the target engine speed by a rule of control set in accordance with the state of the lockup clutch on the basis of the computed turbine torque and the turbine speed of the torque converter.
The engine control means controls the engine in accordance with the result of a computation by the target engine control target computing means so that the engine torque and the engine speed will be directed to the target engine torque and the target engine speed.
In the driving control device of the invention, the target tire operating torque of the vehicle, which is proportional to the acceleration of the vehicle and not proportional to the target vehicle speed, is a control target for controlling the vehicle, and the target engine torque and the target engine speed are set on the basis of the target tire operating torque and the driving resistance. The term acceleration refers to acceleration or deceleration herein.
The target tire operating torque computing means easily sets the target tire operating torque such that the acceleration of the vehicle will not disturb the vehicle occupants. Therefore, the target tire operating torque computing means is a control target setting means.
If the target vehicle speed is set as a control target, as in the conventional driving control device, acceleration of the vehicle occurs when the target vehicle speed is changed. These parameters are not proportional. Therefore, to produce acceleration of the vehicle such that the vehicle occupants will feel no abnormality at a preset target vehicle speed, it is necessary to sample the optimum realizable acceleration of the vehicle and to precisely set, according to each vehicle driving condition, the operation characteristics of a target vehicle speed setting means on the basis of the sampling.
On the other hand, the acceleration &agr; of the vehicle, the tire operating force Ftire [N] occurring at the vehicle tires, and the driving resistance Fload [N] (air resistance, tire rolling resistance, resistance due to the road gradient, and the like), which are applied to the vehicle during running, the mass of the vehicle M
1
[kg], and an equivalent mass M
2
[kg] for the inertia of rotating members of the vehicle, as shown in FIG.
1
(
a
), can be expressed by the following equation (1) of vehicle motion.
(
M
1
+
M
2
)·&agr;=
Ftire+Fload
  (1)
From this equation, the acceleration &agr; of the vehicle is proportional to the sum of the tire operating force Ftire, occurring at

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