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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

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.
 

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Discussion Starter #2
And perhaps related:

United States Patent 5,658,216
Ochiai August 19, 1997

FIELD OF THE INVENTION

This invention relates to a drive force controller for preventing slipping of a drive wheel of a vehicle comprising a continuously variable transmission.

BACKGROUND OF THE INVENTION

A drive force control system or traction control system which prevents a drive wheel from slipping during acceleration of a vehicle and prevents the decline of acceleration performance, suppresses wheel slip for example by decreasing an engine output according to the slip of the drive wheels.

The decrease of engine output may be realized for example by closing a second throttle which is provided in parallel with an intake throttle, by stopping fuel injection to a specific cylinder of the engine, or by retarding the fuel ignition timing of the engine.

In the CVT, a real speed change ratio is found for example from the ratio of the output shaft rotation speed and the input shaft rotation speed of CVT, and speed change control is performed so that the real speed change ratio coincides with a target speed change ratio which is set according to a running state.

However, since the CVT attempts to decrease the speed change ratio when the engine output torque is decreased due to fuel cut, but the response of the CVT is somewhat slower than that of drive force reduction by fuel cut, a hunting, i.e., fluctuation, of the speed change ratio is apt to occur, and the torque transmitted to the drive wheels may also fluctuate. This torque fluctuation causes vibration of the vehicle body.

For example, during acceleration after vehicle startup, the rotation speed of the drive wheels increases suddenly if the drive wheels slip. The output of the engine is therefore correspondingly reduced by performing fuel cut, the drive wheel speed decreases, and the slip converges. The target speed change ratio of the CVT also varies largely relative to the sudden change of drive wheel speed during this time, but as the response of the CVT is lower than that of the engine output variation due to fuel cut, hunting easily occurs while the drive wheel speed is rapidly varying.

Further, although drive force control due to fuel cut is highly responsive, the control resolution is low, and in an engine with a small number of cylinders, the engine output largely varies due to the fuel cut in one cylinder. Therefore, a variation of drive force easily becomes excessive due to fuel cut operation.
 

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Discussion Starter #3
Also:

United States Patent 5,672,137
Adachi , et al. September 30, 1997

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Control apparatus for continuously variable transmission mounted in automotive vehicle


BACKGROUND OF THE INVENTION

The present invention relates to a control apparatus for a continuously variable transmission mounted in an automotive vehicle as an automatic power transmission with a disturbance compensator.

A kind of the continuously variable transmission to be applied to an automatic power transmission of the automotive vehicle includes, for example, a pair of drive pulley and driven pulley whose pulley widths contacted against a V-shaped belt are variably controlled according to the hydraulic pressure and a gear shift ratio of the continuously variable transmission is continuously varied by controlling the pulley width of each pulley. The gear shift ratio is varied in accordance with a predetermined pattern according to a vehicle driving condition such as a vehicle speed, engine revolution speed, and vehicle load, an opening angle of a gear shift ratio control valve associated with each pulley being controlled on the basis of the detected vehicle driving condition.

Japanese Patent Application First Publications No. Heisei 3121358 published on May 23, 1991 and No. Showa 59-217047 published on Dec. 1, 1984 exemplify previously proposed control systems for actuators to control opening angles of gear shift ratio control valves of the continuously variable transmissions, each of which is designed to achieve appropriate gear shift ratio response characteristics according to a predicted vehicle driving condition, in order to improve a vehicular acceleration performance, a fuel consumption, and a comfortability of the vehicle.

However, there arises a problem such that even if each of the control systems described in the above-identified Japanese Patent Application First Publications outputs an appropriate gear shift ratio command value as a target value of each of the control systems, the associated continuously variable transmission does not always indicate a gear shift ratio response as a designer has desired to achieve and a desired control effect cannot be achieved.

Causes that such a problem as described above rises may be considered as follows:

1) A relationship between a hydraulic pressure applied to a gear shift ratio varying mechanism and an actual gear shift ratio of the continuously variable transmission is not always in a proportional relationship.

2) Dynamic characteristics of a gear shift ratio exhibited when a gear shifting operation is carried out from a certain gear shift ratio to another gear shift ratio are not uniform since a flow quantity of working oil is different according to the hydraulic pressure applied to the gear shift ratio varying mechanism.

3) When such a gear shift control valve as having a different characteristic in a direction to which the gear shifting up is carried out and in a direction to which a gear shifting down is carried out is applied to the continuously variable transmission in order to enable the gear shifting operation during, e.g., occurrence of failure in the gear shift ratio varying mechanism, the gear shift ratio response is different depending on the direction of the gear shift ratio (high gear shift ratio or low gear shift ratio). Consequently, a deviation occurs from the target gear shift ratio control characteristic that the designer of the control system is desired to achieve.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an improved control apparatus of a continuously variable transmission mounted in an automotive vehicle which is so designed as to achieve a desired gear shift ratio response that a designer of the control apparatus has desired to achieve without deviation of the gear shift ratio irrespective of dynamic characteristics that the applied continuously variable transmission naturally has and/or variations in operating parameters.

The above-described object can be achieved by providing a control apparatus for an automotive vehicle, comprising:

a) a continuously variable transmission, including a gear shift ratio varying mechanism and whose gear shift ratio is continuously controlled according to an operating variable of said gear shift ratio varying mechanism, said gear shift ratio varying mechanism being so arranged and constructed as to continuously vary the gear shift ratio of the continuously variable transmission according to a gear shift ratio command value;

b) a first sensor which is so arranged and constructed as to detect a vehicle driving condition of the vehicle in which the continuously variable transmission is mounted;

c) a second sensor which is so arranged and constructed as to detect an actual gear shift ratio of the continuously variable transmission; and

d) a control unit having;

e) a target gear shift ratio calculating block for calculating a target gear shift ratio on the basis of the detected vehicle driving condition;

f) a dynamic characteristic estimating block for estimating a predetermined dynamic characteristic for each instantaneous gear shift ratio of the continuously variable transmission;

g) a disturbance compensator which is so arranged and constructed as to calculate a disturbance compensation output as functions of the actual gear shift ratio and of either the gear shift ratio command value or the operating variable of the gear shift ratio varying mechanism;

h) a gear shift ratio control constant calculating block for calculating a control constant of each instantaneous gear shift ratio of the continuously variable transmission so as to achieve a target dynamic characteristic using the estimated dynamic characteristic;

i) a first gear shift ratio command calculating block for calculating a first gear shift ratio command value from the target gear shift ratio, the actual gear shift ratio, and the control constant of the corresponding instantaneous gear shift ratio; and

j) a second gear shift ratio command calculating block for subtracting the disturbance compensation output of the disturbance compensator from the first gear shift ratio command value so as to derive and output the gear shift ratio command value,

and the control apparatus further comprising;

k) a gear shift ratio control block for adjustably controlling the operating variable of the gear shift ratio varying mechanism as the function of the output gear shift ratio command value.
 

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Discussion Starter #4
And there's more...

Needless to say, Nissan through it's subsidiary Jatco, has put a lot of R&D into the CVT the Murano has...

I'd find it hard to go back to a conventional automatic, in any other vehicle!
 

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Jaak, do you know who manufacture lexus rx400hybrid's

cvt? Is it Jatco as well?
 

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Discussion Starter #6
I haven't looked into it, but it's possible... Jatco makes transmissions for a lot of vehicle manufacturers, including Toyota, I think. Lexus, Toyota, same thing. Infiniti, Nissan, same thing.

It's interesting cruising the patent office...
 
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