Pressure sensor for automatic transmissions and air-conditioning systems Bosch SMP137 marks entry into the integrated medium-pressure sensor market 70 bar maximum pressure and high media resistance

21st February 2011
ES Admin
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

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