ESP sensor measures yaw rate and acceleration

MUNICH, Germany — Bosch Automotive Electronics claims that its SMI540 is the world's first micromechanical inertial measurement unit for vehicle dynamics control in low-cost SOIC16w housing. The unit opens up new development possibilities for the ESP electronic stability program.

The 3-D sensor simultaneously monitors three of a vehicle's movement axes — two acceleration or inclination axes (ax, ay), and one axis of rotation (Oz). Until now, at least two separate sensors were required for this. The SMI540 has a digital serial peripheral interface (SPI) with two standard protocols. Thanks to a constant internal self-test of the yaw-rate sensor element, this interface meets the highest operating safety standards, the vendor promises.

Samples of the new sensor are available. The sensor is set to go into large-scale series production from the second quarter of 2010. Bosch also plans to launch the SMG540, a version of the sensor that contains only the yaw sensor element.

Two of SMI540's three sensor signals provide information that is relevant for the ESP system: the yaw rate and lateral acceleration. The remaining third sensor signal is not generally used by ESP. It measures a vehicle's acceleration or inclination in the direction of travel. Developers can use the information this sensor delivers for other applications, such as the hill hold function or for fuel-saving functions in cars with automatic transmissions (N control). The car automatically shifts into the fuel-saving "N" gear, provided that — and this is where the inclination sensor comes into play — the car is on level ground and cannot begin to move by itself.

The SMI540 serves conventional ESP concepts as with a separate sensor device in the vehicle interior as well as new, more cost-effective approaches. As an example, the Bosch ABplus airbag concept no longer contains the sensor device for ESP control. In this case, the inertial sensor is now integrated directly into the airbag control unit. These are ideal conditions for the SMI540, with its small SOIC16w housing (10.3 x 10.3 x 2.65 millimeters) and multiaxial sensors

The sensor is also suited to the alternative concept of a central domain control unit (DCU). This unit integrates several of a vehicle's sensor functions and forwards measurements for safety and comfort and well as driver information to the relevant on-board electronics.