Development of Driving Force Control Technology of CVT for North American Market

Toyota Motor Corporation developed a continuously variable transmission (CVT), unit K313, to satisfy the rising demand for improved fuel economy. This transmission was installed in the North American market Corolla for the 2014 model year. In this market, the driveability demands for automatic transmissions (AT) are very high. Additionally, the market is dominated by conventional AT with fixed gear ratios, leaving CVTs in the minority. In order to increase the volume and acceptance of CVTs in North America, excellent driveability had to be ensured.

The key driveability advantage of CVTs is the ability to change gear ratio continuously without engaging or disengaging clutches. This allows for smooth driving without any shocks or gaps in drive force; however, it can also feel strange to drivers of conventional AT. To achieve the required driveability performance for the CVT in North America, the following technologies were introduced:

• A new drive force design method was developed to better utilize the continuously variable gear ratio, which results in better, more proportional acceleration feelings for the driver.
• The drain circuit of the primary pulley was designed from an early stage to maximize response.
• New pressure control logic was developed that makes shifting more controllable.
• “Sports Mode” was developed for the S trim, which provides a, more direct feeling.