Hino Motors develops Japan’s first Vehicle Stability Control (VSC) system for large tractors

Hino Motors, Ltd. (Hino) has developed Japan’s first1) Vehicle Stability Control (VSC)2) system capable of improving the overall vehicle operation stability of large semi-tractors. The system preliminary detects indications of forms of vehicle instability common to large tractors - such as rolling, jack-knifing3) and drift-out4) - and responds by warning the driver, reducing engine output and applying the brakes in order to regain proper stability.

The relevant permits and approvals for the Japanese market have already been obtained from the Ministry of Land, Infrastructure and Transport, and the system will be launched in Japan in the near future.5)

Large tractors play a key role in the distribution of goods, and are often used to pull large trailer loads. Driving a large tractor with a trailer requires a special endorsed license and advanced driving skills. The tractor and trailer are coupled together with a single pin, which means that the driver is not always aware of the trailer orientation, particularly when the trailer is leaning to one side. For this reason, rolling is one of the most common types of accidents with large tractors.

Hino has been developing control systems to prevent these phenomena for many years. The Roll Stability Assist system, which improves stability when driving with coupled loads, has been fitted as standard equipment to all large tractors produced for the domestic marketplace since November 2003, and has contributed to a reduction in the incidence of rolling accidents.

The new “VSC” system represents a further extension of the “Roll Stability Assist” system, providing control over a greater range of common instability phenomena such as “jack-knifing” and “drift-out” on icy roads. The VSC system operates in conjunction with ABS (Antilock Brake System) on both the tractor and the trailer to provide superior vehicle control even on slippery surfaces such as icy roads.

Hino, the self-styled “Safety Frontrunner”, is dedicated to the goal of eliminating traffic accident fatalities involving commercial vehicles. Hino remains committed to the development of practical and viable safety technology and systems for its vehicles.

1) The Japan’s first vehicle stability control system for large tractors to gain approval from the Ministry of Land, Infrastructure and Transport.
2) The Toyota Group (Toyota Motor Corporation, Daihatsu Motor Co., Ltd. and Hino Motors, Ltd.) has declared the VSC (Vehicle Stability Control) system to be a key technology for reducing traffic accidents.
3) When the tractor and trailer bend at an angle; often caused by wheel ruts on slippery surfaces.
4) When the front wheels lose their grip on a slippery surface and the vehicle is unable to follow the curve.
5) VSC-equipped vehicles will be produced for the domestic market only.
Features of VSC

The VSC analyses information from a range of sensors, including steering angle, horizontal acceleration, yaw rate, vehicle travel speed and wheel speed. If instability is detected, the system controls the vehicle as follows.

1) Roll control	When roll instability is detected, the alarm sounds to warn the driver. If the system does not detect any improvement, it then reduces engine power and applies the tractor and/or trailer brakes to reduce speed until stable driving operation is restored.
2) Jack-knifing and drift-out control	When jack-knifing or drift-out instability is detected, the system sounds the alarm and then reduces the engine power. The brakes are applied to selected wheels on the tractor and to all wheels on the trailer until stable driving operation is restored.

A key requirement of the tractor VSC system is that actions designed to restore stability should not inadvertently lead to other forms of instability. Tractor and trailer combinations differ fundamentally from a passenger vehicle in that the driver is less aware of the status of the trailer. The VSC system works in combination with the trailer ABS control to provide stability control on road surfaces with very low μ (coefficient of friction) such as icy roads.

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