Torque control device for continuously variable transmission

Abstract

A torque control device is provided to prevent slipping of a belt of a belt type continuously variable transmission. The torque control device calculates a positive input torque inputted from an engine to a primary pulley, and calculates a negative input torque inputted from a drive wheel to the primary pulley based on the positive input torque and a speed ratio of a continuously variable section. The torque control device then restricts an output torque from the engine so that the total torque can be lower than or equal to the torque capacity of the belt when the vehicle is in a running state in which the negative input torque is likely to occur and the total torque which is the sum of the positive input torque and the negative input torque exceeds the torque capacity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of this original disclosure:

FIG. 1 is a simplified schematic view of a vehicle equipped with a belt type continuously variable transmission in accordance with a first embodiment of the present invention;

FIG. 2 is a graph for explaining slipping of the belt of the belt type continuously variable transmission;

FIG. 3 is another graph for explaining slipping of the belt of the belt type continuously variable transmission;

FIG. 4 is a graph for explaining a method of setting the positive input torque that has been determined taking into account a negative input torque;

FIG. 5 is a map used to calculate the positive input torque based on the rotational speed of the a primary pulley and a speed ratio of a continuously variable section; and

FIG. 6 is a flow chart showing the control operations executed by the control unit in order to control the output torque of the engine.

Claims

1. A torque control device comprising: a speed ratio calculation section configured to calculate a speed ratio between a primary pulley and a secondary pulley of a belt type continuously variable transmission;a running state determination section configured to determine if a vehicle running state exists in which a negative input torque will be likely to be inputted to the primary pulley from a drive wheel side;a positive input torque calculation section configured to calculate a positive input torque that is inputted to the primary pulley from an engine;a negative input torque calculation section configured to calculate a negative input torque based on the speed ratio and the positive input torque that were calculated;a torque capacity calculation section configured to calculate a maximum torque capacity of the belt type continuously variable transmission;a torque comparison section configured to compare the maximum torque capacity to a total torque which is a sum of the positive input torque and the negative input torque; anda torque control section configured to restrict an output torque of the engine so that the total torque becomes lower than or equal to the maximum torque capacity when the total torque exceeds the maximum torque capacity upon determining the vehicle running state existing in which the negative input torque will likely be inputted to the primary pulley from the drive wheel.

2. The torque control device as recited in claim 1, wherein the torque control section is further configured to calculate an upper limit value of the positive input torque at which the maximum torque capacity is equal to the total torque when a predetermined speed ratio is established in the continuously variable transmission, andthe torque control section is further configured to control the output torque of the engine so that the positive input torque is maintained at the upper limit value when the total torque is greater than or equal to the maximum torque capacity.

3. The torque control device as recited in claim 1, wherein the torque control section is further configured to calculate a difference between the total torque and the maximum torque capacity when the total torque exceeds the maximum torque capacity, andthe torque control section is further configured to restrict the output torque of the engine depending on the difference that was calculated so that the total torque is equal to the maximum torque capacity.

4. The torque control device as recited in claim 1, wherein the running state determination section is further configured to determine an off-road running state as the vehicle running state.

5. The torque control device as recited in claim 1, wherein the negative input torque calculation section is further configured to calculate the negative input torque from the positive input torque and the speed ratio using a map establishing a relationship between the positive input torque, the negative input torque and the total torque.

6. A torque control device comprising: speed ratio calculation means for calculating a speed ratio between a primary pulley and a secondary pulley of a belt type continuously variable transmission;running state determination section configured to determine if a vehicle running state exists in which a negative input torque will be likely to be inputted to the primary pulley from a drive wheel;positive input torque calculation means for calculating a positive input torque that is inputted to the primary pulley from an engine;negative input torque calculation means for calculating a negative input torque based on the speed ratio and the positive input torque that were calculated;torque capacity calculation means for calculating a maximum torque capacity of the belt type continuously variable transmission;torque comparison means for comparing the maximum torque capacity to a total torque which is a sum of the positive input torque and the negative input torque; andtorque control means for restricting an output torque of the engine so that the total torque becomes lower than or equal to the maximum torque capacity when the total torque exceeds the maximum torque capacity upon determining the vehicle running state existing in which the negative input torque will likely be inputted to the primary pulley from the drive wheel.