Focus on Electronics

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April 2002
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Denso sensors for common-rail injection

Denso's common-rail pressure sensor is a key component in the development of direct-injection diesel engines.

The direct-injection diesel engine system was developed to solve such problems of conventional diesel engine systems as emissions of particulate matter (PM) and high emissions of NOx. The common-rail pressure sensor, which requires high-pressure resistance to 160 MPa (23,000 psi) and an accuracy of ±1%, is a key part of the system. Researchers from Denso discussed how a new generation of common-rail, high-pressure sensors are structurally simpler to conventional sensors while still meeting the needed performance requirements during the Vehicle Sensors and Actuators technical session at the SAE 2002 World Congress.

Diesel engines have CO₂ emissions of about 67% those of the gasoline engine because the diesel engine offers greater thermal efficiency and lower fuel consumption than other internal-combustion engines. In the direct-injection diesel engine, the common-rail injection system's high-pressure sensor monitors fuel pressure so it can be kept at an optimal value determined by engine speed and load.

The improved sensor features a hermetically sealed structure, a diaphragm for receiving fuel pressure, and a single-crystal silicon, piezoresistive sensor element for converting the pressure into an electrical signal.

A single-crystal silicon piezoresistive element has three times as many gage factors as a thin-film polycrystalline silicon piezoresistive element. The element therefore can be made with three times the sensitivity, an advantage in improving sensor accuracy that led to the selection of a single-crystal to achieve an accuracy level of 1% over the operating temperature range of -30 to +120°C (-22 to +248°F).

During development, stress generated on the metal diaphragm was found to be caused by diaphragm thickness and corner curvature. As a result, a diaphragm thickness of 1.4 mm (0.055 in) and corner radius of 0.9 mm (0.035 in) were chosen to ensure diaphragm stress lower than that of the adhesive layer or low-melting glass, yet higher than the minimum required by the silicon piezoresistive element.

- John Fobian

Next generation Omron pursuits

Omron's passive entry uses a radio frequency-based key fob to unlock a vehicle's door.

Two future products—one relying on an optical device and the other relying on radio frequency-based technology—highlight the wares that were on display at SAE 2002 by Novi, MI-based electronics supplier Omron Automotive Electronics, Inc. Omron's passive entry system, a next-generation version of remote keyless entry that Omron has produced since the 1980s, allows vehicle entry without actually depressing a key fob or putting a key in a door lock.

As the driver carrying the transponder approaches the vehicle, a two-way radio signal prepares the door to open. "When the driver touches the door handle, the car door automatically unlocks. The key part of the technology is how the door handle 'senses' it's being touched," said Jerry Bricker, Vice President & General Sales Manager for Omron.

At the Omron exhibit, show-goers could experience passive entry by using a key fob to unlock a door. The system was also illustrated by a graphical display.

The company also featured new cruise control technology at its booth. Omron's laser radar-based adaptive cruise control, targeted for a 2005 MY vehicle application, is a next-generation iteration of a current co-developed product serving as optional equipment on select 2002 MY vehicles. "It's less than half the size of the current product, so it's easier to package. This next-generation product will be self-aiming technology," said Bricker. A key enabler for the product is the system's internal optics.

- Kami Buchholz

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