Japanese companies have been involved in emissions scandals, and Japanese media revealed how to test car fuel efficiency

Recently, according to media reports, after Mitsubishi Motors, Suzuki was also found to have used a fuel efficiency test method that did not comply with Japanese government regulations. How is the fuel efficiency of a car tested?

How is the fuel efficiency test carried out?

According to a report by the Nihon Keizai Shimbun on May 23, the Traffic Safety and Environment Research Institute under the Ministry of Land, Infrastructure, Transport and Tourism of Japan conducted a test on a rolling platform. In order to get closer to the actual road conditions, the "driving resistance value" that takes into account air resistance and tire friction is input into the control device of the rolling platform to increase the load on the car. The larger the resistance value, the lower the fuel efficiency, and the smaller the resistance value, the higher the fuel efficiency. The resistance value is declared by the company itself.

Details of the test method

In the context of international unification of measurement methods, Japan began to implement the European common "coasting method" for measurement in 1991. The coasting method refers to calculating the resistance value by measuring the time required for the car to drop to 10 kilometers per hour when it is driving in neutral.

The reason why Suzuki and Mitsubishi Motors do not adopt the coasting method

Mitsubishi Motors has been using the U.S. "high-speed coasting method" since 1978 and has not changed since 1991. The high-speed coasting method is to measure the speed of the car when it is driving in neutral gear, and then calculate the resistance value. The test time is very short, but Mitsubishi Motors has not explained why it has been using this method.

The degree of error

Suzuki said that the error was within the prescribed range, while Mitsubishi Motors said that except for the four light vehicles that tampered with the resistance values, the data of other models were not much different. However, the two companies continued to use the method knowing that it was not in compliance with the law, and they should bear great responsibility.

Why didn’t Japan’s Ministry of Land, Infrastructure, Transport and Tourism discover it?

The Ministry of Land, Infrastructure, Transport and Tourism used to trust the data reported by manufacturers during the review, but this trust no longer exists. The Ministry of Land, Infrastructure, Transport and Tourism believes that there are problems with the current system of "manufacturer self-reporting" and is currently discussing adjustments, such as government inspectors participating in some data measurements or requiring manufacturers to provide data certification materials.

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