Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
2000-08-04
2002-05-14
Zanelli, Michael J. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C701S051000, C701S054000
Reexamination Certificate
active
06389348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for a vehicle having a continuously variable transmission capable of changing a gear ratio continuously and, more particularly, to a control system for controlling a power source and a continuously variable transmission in parallel on the basis of an output demand.
2. Related Art
In the prior art, a continuously variable transmission (i.e., CVT) is known as a vehicular transmission. In short, this continuously variable transmission is a transmission having a function to change the ratio between an input speed and an output speed continuously. At present, there has been practically used a system which is constructed to set the gear ratio properly by continuously changing the radial position of a transmission member on an input side rotary member and the radial position of the transmission member on an output side rotary member. Specifically, there have been practiced the belt type continuously variable transmission and the toroidal type (or traction type) continuously variable transmission.
The former belt type continuously variable transmission is constructed such that an input pulley and an output pulley running over a belt are made of a fixed sheave and a movable sheave which is made movable in the axial direction, respectively, and such that the groove widths of the individual pulleys are changed by moving the movable sheaves of the individual pulleys axially thereby to change the belt winding diameters, i.e., the gear ratios continuously. By applying an axial force according to a demanded transmission torque to the movable sheave in the output side pulley, the tension of the belt is set to one according to the demanded torque. To the movable sheave of the input side pulley, on the other hand, there is applied the axial force for setting the gear ratio which is determined on the basis of an output demand signal based on the depression stroke (or the accelerator opening) of an accelerator pedal, an output demand signal from a cruise control for setting the vehicle speed automatically to a predetermined value, and a running state such as the vehicle speed, thereby to change the groove width of the input side pulley.
Thus according to the continuously variable transmission, the gear ratio can be continuously changed to change the speed of the power source such as an engine freely. In the vehicle mounting the continuously variable transmission thereon, therefore, the gear ratio can be controlled not only to satisfy a demanded driving torque but also to run the power source efficiently, i.e., to reduce the fuel consumption.
One example of this control is disclosed in Japanese Patent Publications Nos. 3-72867 (JP-B-3-72867) and 62-110535 (JP-A-62-110535). In this control, firstly a target driving force is determined from the depression stroke of the accelerator pedal and the vehicle speed. Next, a target power, a throttle opening and a target engine speed corresponding to the target driving force are individually determined, and a target gear ratio of the continuously variable transmission is then determined on the basis of the target engine speed and the vehicle speed. Moreover, the engine is controlled to generate a target torque determined on the basis of the target power and the engine speed, whereas the continuously variable transmission is controlled to set a gear ratio for the most efficient engine speed for achieving the target power.
However, the engine and the continuously variable transmission are different in their responses to the control. Specifically, the engine is enabled to change the torque immediately after the intake air and the fuel supply are increased, but the continuously variable transmission takes a considerable time until the target gear ratio is achieved, because the gear ratio is changed by gradually increasing/decreasing the groove widths of the pulleys by the hydraulic control. In response to the depression stroke of the accelerator pedal, however, the target driving force is changed, and the target power is changed. On the other hand, the engine torque is determined by the calculation of (the target power/the engine speed). If the engine speed is brought in a low state due to a delay in the speed change of the continuously variable transmission, the engine torque, as determined by the calculation of (the target power/the engine speed), abruptly rises, and an acceleration shock may occur. Due to an abrupt change in the torque, on the other hand, a torsional deformation may occur in a power transmission line to cause the longitudinal vibration (or the surging) of the vehicle.
When a torque converter is employed in the starting system of the vehicle having the continuously variable transmission, on the other hand, the driving torque at the start may become excessively high. In the fluid type torque converter, for example, a torque amplifying action occurs in a converter region where the ratio (i.e., the speed ratio) between the input speed and the output speed is smaller than “1”, the torque to be outputted from the torque converter increases. At the start, the output speed is substantially zero so that the torque ratio or the torque amplification factor takes the maximum value. As a result, the aforementioned controls of the power source and the continuously variable transmission might make the driving torque excessive at the start. In this case, an abrupt acceleration feeling might be given to passengers of the vehicle, or the tire slip might be invited when a road surface has a low &mgr; (i.e., friction coefficient) (as on a pressed-snow road, a frozen road or a gravel road). The torque converter as the starting system basically performs the action to augment the starting torque, as described above, so that a similar situation occurs even if the torque converter is not of the fluid type.
In order to eliminate this disadvantage, it is conceivable to perform the so-called “rounding control”, in which the target driving force according to the depression stroke of the accelerator pedal is reached, even if calculated, not instantly but gradually. With the control based on the target value which is corrected in the rounding control or set temporarily, the abrupt change in the torque is avoided to eliminate the shock. However, the rounding control delays the achievement of a final target value by reducing the corrected target value so that the control response is deteriorated. If the gear ratio of the continuously variable transmission is controlled on the basis of the target value by the rounding control, on the other hand, the target value of the gear ratio is gradually changed so that the speed changing rate of the continuously variable transmission cannot be maximized. As a result, the intrinsically inferior shift response becomes worse to cause a problem that the physical discomfort for driving the vehicle becomes more serious.
SUMMARY OF THE INVENTION
A main object of the present invention is to provide a control system capable of improving the responses of an engine and a continuously variable transmission and the power characteristics of the vehicle and capable of controlling the vehicle without any physical discomfort.
For this object, therefore, the control system of the invention is so constructed for controlling the power source and the continuously variable transmission to a target value based on an acceleration demand, as to make either a correction only for the target value of one of the power source and the continuously variable transmission or a correction different from that for the target value of the other.
According to the invention, specifically, there is provided a control system for a vehicle including: a power source; and a continuously variable transmission capable of changing gear ratios continuously, wherein a target driving force is calculated on the basis of an acceleration demand and a vehicle speed, and a target power of the power source is calculated on the basis of the target driving force, so that the continuously var
Ito Yasushi
Kubota Hirofumi
Mashiki Zenichiro
Mitani Shinichi
Takagi Isao
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyota Jidosha & Kabushiki Kaisha
Zanelli Michael J.
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