Pressure sensor for automatic and air-conditioning systems

Bosch SMP137 marks entry into the integrated medium-pressure sensor market 70 bar maximum pressure and high media resistance

· Quality sensor for hydraulic pressure

· Hermetic metal housing with high media resistance

· Easy installation without “2nd Level Package“

The Bosch SMP13x model series is the first time the company has offered integrated medium-pressure sensors for the automotive sector. These are sensors for pressure in the 10 to 100 bar range. The product range of the globally operating automotive supplier previously included sensors for the low-pressure range up to 10 bar and high-pressure sensors for 140 to well over 2,000 bar. The first SMP137 model measures up to 70 bar and meets very high quality standards. It also offers a full range of special design features, such as the hermetically sealed metal housing, the high bursting strength of the measuring membrane, the 150 °C maximum ambient temperature, and the EMC capacitors integrated in the sensor, which protect against uncontrolled interference. As the sensor is aligned and encapsulated in a housing ex-works, it can be directly installed in control units, without the usual need for packaging in a “2nd Level Package.” This saves on space and costs.

The SMP137’s primary area of application is in automatic transmissions. With a response time of less than a millisecond, it very precisely measures the pressure for activating a clutch. Pressure measuring in air-conditioning systems is a further area of application. The SMP137 has so far been available in sample item numbers – it will be available in large quantities from the fourth quarter of 2011. The SMP132 model for 22 bar maximum pressure will then follow in 2012.

New housing – pressure-resistant and easy to install
The disc-shaped housing of the SMP137 is approximately 19 millimeters in diameter, with an installation height of just under 10 millimeters. The new SMP13x series housing can withstand pressures of more than 100 bar. Another benefit: the electrical connections and the hydraulic connection are arranged on opposing housing surfaces – an important requirement for quick and easy installation.

Fed in at the sensor’s hydraulic connection, the hydraulic fluid presses against the monocrystalline measuring membrane. This membrane bends under pressure, while also sealing the sensor interior against the hydraulic fluid. Neither the sensor element attached to the rear of the membrane, nor the bond wires, nor the integrated electronics come into contact with the hydraulic fluid. The sensor therefore has a very high media resistance and a long service life.

The sensor element consists of a measuring bridge with piezoresistors, produced in MEMS technology. The level of the electric bridge signal changes proportionally to the bend of the membrane. This signal is processed by an analog ASIC integrated on same chip on which the membrane is located; it is then routed to the outside via the sensor’s electrical connections.

Bosch – globally leading manufacturer of MEMS sensors
Bosch has many years of experience in the development and production of hermetically packaged pressure sensors. More than 50 million of these sensors with TO-8 housings have been produced since production began in 1993. Bosch played a crucial role in the development of MEMS technology (microelectromechanical systems), which is used to produce tiny sensor elements. In total, the company has so far produced more than one billion sensors in MEMS technology – more than 220 million last year alone. This makes Bosch the world’s leading provider of MEMS sensors. The company’s portfolio includes pressure, acceleration, and yaw-rate sensors for numerous applications in the automotive industry and consumer electronics.

Jochen Volm,
Phone: +49 7121 35-6651

The Bosch Group is a leading global supplier of technology and services. In the areas of automotive and industrial technology, consumer goods, and building technology, some 275,000 associates generated sales of 38.2 billion euros in fiscal 2009. The Bosch Group comprises Robert Bosch GmbH and its more than 300 subsidiaries and regional companies in over 60 countries. If its sales and service partners are included, then Bosch is represented in roughly 150 countries. This worldwide development, manufacturing, and sales network is the foundation for growth. Each year, Bosch spends more than 3.5 billion euros for research and development, and applies for some 3,800 patents worldwide. With all its products and services, Bosch enhances the quality of life by providing solutions which are both innovative and beneficial.

The company was set up in Stuttgart in 1886 by Robert Bosch (1861-1942) as “Workshop for Precision Mechanics and Electrical Engineering.” The special ownership structure of Robert Bosch GmbH guarantees the entrepreneurial freedom of the Bosch Group, making it possible for the company to plan over the long term and to undertake significant up-front investments in the safeguarding of its future. Ninety-two percent of the share capital of Robert Bosch GmbH is held by Robert Bosch Stiftung GmbH, a charitable foundation. The majority of voting rights are held by Robert Bosch Industrietreuhand KG, an industrial trust. The entrepreneurial ownership functions are carried out by the trust. The remaining shares are held by the Bosch family and by Robert Bosch GmbH.

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PI7071 – November 2010