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From the US Patent Office, this appears to be for the Murano's CVT. http://www.uspto.gov/patft/index.html
United States Patent 6,220,985
Okahara April 24, 2001
United States Patent 6,220,985
Okahara April 24, 2001
FIELD OF THE INVENTION
This invention relates to speed control of a stepless automatic transmission.
BACKGROUND OF THE INVENTION
A transmission system for a vehicle using a combination of a fluid transmission such as a torque converter or fluid coupling, and a stepless transmission which transmits the output torque of the fluid transmission via a V-belt or variable pulley to a vehicle drive shaft after changing the speed in a stepless manner, is disclosed in Tokkai Sho 61-105353 published by the Japanese Patent Office in 1986. A speed change ratio of this stepless transmission is controlled by a controller, and generally varies according to a throttle opening and vehicle speed which represent the acceleration requirement of the driver. Regarding vehicle speed, the higher the vehicle speed, the more the transmission shifts up, i.e., the more the speed change ratio is reduced.
However in some cases, for example when the vehicle start abruptly or when the vehicle starts and accelerates on a road surface which is of a low frictional coefficient, this type of controller may vary the speed change ratio very rapidly when the vehicle skids. As a result, the V-belt or variable pulley may slip, shocks may occur, the driver may experience a feeling of unpleasantness and the controller may suffer wear. This is due to the fact that in general, the vehicle speed is detected from the rotation speed of the drive system, e.g. the drive shaft. In other words, when the drive wheels slip, the speed change controller determines that the vehicle speed has increased, and therefore shifts up. Subsequently, when the drive wheels regain their grip on the road and stop slipping, the controller determines that there has been a sudden drop in vehicle speed. It therefore performs a rapid shift-down and the speed change ratio sharply increases. This causes frictional parts such as belts in the controller to slip, and a shock is produced.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to prevent a rapid change of speed change ratio when drive wheels slip.
It is a further object of this invention to change over between speed change control when the drive wheels slip and normal speed change control with appropriate timing.
In order to achieve the above objects, this invention provides a speed change ratio controller for use with a stepless automatic transmission which transmits a torque of an engine to drive wheels of a vehicle at an arbitrary speed change ratio. The controller comprises a mechanism for detecting a travel speed of the vehicle, a mechanism for controlling the transmission such that the speed change ratio decreases the more the travel speed increases, a mechanism for detecting slip of the drive wheels, and a mechanism for suppressing decrease of a speed change ratio of the transmission by the control mechanism when the slip is detected.
It is also preferable that the controller further comprises a mechanism for detecting an engine rotation speed, and a mechanism for stopping suppression of the speed change by the suppressing mechanism when the rotation speed exceeds a predetermined value.
It is also preferable that the controller further comprises a mechanism for detecting an engine throttle opening, and a mechanism for stopping suppression of decrease of the speed change ratio by the suppressing mechanism when the throttle opening is decreasing.
It is also preferable that the controller further comprises a mechanism for detecting an engine throttle opening, a timer mechanism for measuring an elapsed time from when the throttle opening starts to decrease, and a mechanism for stopping suppression of decrease of the speed change ratio by the suppressing mechanism when the elapsed time exceeds a predetermined value.
It is also preferable that the controller further comprises a mechanism for determining whether or not the travel speed has increased, and a mechanism for stopping suppression of decrease of the speed change ratio by the suppressing mechanism when the travel speed has increased again after the suppression.
In this case, it is further preferable that the controller further comprises a mechanism for gradually changing a speed change ratio to a speed change ratio which is given by the controlling mechanism when the suppression has stopped.
It is also preferable that the slip condition detecting mechanism comprises a mechanism for detecting a rotation speed of the drive wheels, a mechanism for detecting a rotation speed of non-drive wheels of the vehicle, and a mechanism for determining that slip has occurred when a difference between the rotation speeds of the drive wheels and non-drive wheels is greater than a predetermined value.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.