This content is excerpted from Sensor Technology Alert and Newsletter, a sensor intelligence service published by the Technical Insights unit of Frost & Sullivan.
Magnetic field sensors are widely used to provide information about rotational speed or position in diverse automotive applications, such as wheel speed sensing (used in conjunction with antilock braking systems [ABS]), engine management (for example, camshaft or crankshaft ignition timing), transmission speed sensing, as well as, for example, seat position sensing, seat belt sensors, electric power steering, transmission range sensors, transfer case position or speed sensors.
Variable reluctance (VR) sensors, which use a magnet and coil, represent an older magnetic sensing technology that has, historically, been used in volume for automotive wheel speed sensing as well as in such high-volume automotive applications as engine and transmission speed sensing. The VR sensor is a passive sensor, which does not require an input current. Active sensors use an input current to generate a digital signal.
The VR sensor, which cannot adequately provide a zero-speed signal and provides a poor signal at low speeds, has been experiencing threats and encroachments from noncontact, active Hall effect or anisotropic magnetoresistive (AMR) magnetic sensing technologies, which are capable of providing a zero-speed signal and are readily integrated into smart electronics.
The VR sensor has limitations, for example, in camshaft position or angle sensing for ignition timing (the moment at which to fire a spark in each cylinder). Other automotive applications where the sensor's ability to provide a zero-speed signal can be advantageous include car navigation and ABS applications.
Hall effect sensors utilize the Lorenz force in semiconductor materials. When a voltage is applied across a semiconductor material, charge carriers will begin to flow. If a magnetic field is, simultaneously, applied perpendicular to the semiconductor sheet, the current carriers are deflected to one side by the Lorenz force. A charge accumulates along the side until the resulting electrical field produces a force on the charged particle that is sufficient to counteract the Lorenz force. The voltage across the sheet perpendicular to the applied voltage is called the Hall voltage.
A common type of sensor that uses the Hall effect (or Lorenz force) is the Hall sensor, which mostly uses n-type silicon as the semiconductor material. Hall integrated circuits (ICs) can be made cost-effectively in high volumes by merging the silicon Hall element with standard bipolar IC fabrication and assembly techniques.
AMR sensors (also known as MR sensors) use thin-film permalloy resistors whose resistance changes in the presence of an external magnetic field. AMR sensors are well-suited for detecting low-magnetic fields (that are within the Earth's field) and can offer certain benefits for specific speed and position or angle sensing applications.
The AMR sensor provides a larger output signal than the Hall effect sensor, leading to a superior signal-to-noise ratio and allowing a larger air gap between the sensor and the magnet or target at comparable target field strength. However, anisotropic magnetoresistive sensors have had a somewhat higher sensor element cost than Hall effect sensors, although they use ferrite magnets rather than the more expensive samarium cobalt magnets. Moreover, in the past, AMR sensors have reportedly been susceptible to false triggering due to stray magnetic fields, and have been vulnerable to electromagnetic and radio frequency interference.
Siemens VDO has significantly extended its position and opportunities in the North American automotive speed and position sensors arena by acquiring the automotive-related assets (sensor and solenoid products used in automotive, off-road, heavy duty truck, or marine applications) of American Electronic Components Inc. (AEC, Elkhart, IN) in early December 2005.
Siemens VDO acquired the aforementioned assets of AEC from The Riverside Co., which had purchased AEC from Dana Corporation in 2002. The acquisition affords Siemens VDO access to AEC facilities that comprise about 152,000 sq. ft. of operational space and 294 employees. In FY 2004, AEC generated approximately $40 million in revenues. 2005 revenues are reportedly relatively similar to those of 2004. In fiscal 2005, sensors accounted for about 82% of AEC's revenues. The acquisition of AEC has approximately doubled the annual sales of the company's North American Sensors Division to nearly $100 million. Siemens VDO's sensors division has global sales of over $500 million.
By late summer of 2006, Siemens VDO's sensors division would have relocated its North American headquarters from Newport News, VA to the former AEC location in Elkhart, IN in order to better serve its customers, who are mostly in the midwest.
Bret Sauerwein, general manager of Siemens VDO sensors division, told Sensor Technology that the acquisition of certain assets of AEC significantly compliments and extends the sensors division's product portfolio and broadens the sensor division's customer base in such areas as commercial vehicles and heavy-duty vehicles. He also noted that AEC has a very talented engineering and management staff, and has the capability to efficiently design and produce highly engineered position and speed sensors.
Siemens VDO sensors division's automotive products include, for example, VR and Hall effect speed sensors and Hall and AMR position sensors.
Sauerwein noted that, as a result of the acquisition of AEC, the Siemens VDO sensors division is focusing on becoming a very significant player in the North American automotive speed and position sensor markets. He explained that the sensors division's strength in wheel speed sensing will be complemented by AEC's strength in transmission and engine speed applications as well as in Hall effect-based rotary position sensors.
Siemens VDO, Sauerwein noted, has been strong in AMR position sensors used in vehicles with variable valve timing engines. With the addition of AEC, the Siemens VDO sensors division adds to its portfolio significant production experience with Hall effect position sensors to help round out their position sensor offerings.
AEC's sensor product portfolio includes Hall effect and VR speed sensors for ABS, camshaft, crankshaft, transfer case, and transmission applications. The transmission speed sensor measures the rotational speed of the input and output shafts to control shift points and shift characteristics in an automatic transmission. It also can serve as a vehicle speed sensor for input to the speedometer.
In addition, AEC produces a broad range of noncontact, Hall effect position sensors. Key applications for such rotary position sensors include transmission range sensing (indicating Park, Reverse, Neutral, Drive, and Low for transmissions), transfer case position sensing in four-wheel drive vehicles for monitoring clutch position, chassis ride/height sensing (to determine vehicle height, adjust the air suspension, and provide a constant vehicle ride height), accelerator pedal position in electronic throttle control systems, X-Y position sensing in conjunction with shifting in heavy-duty trucks, and EGR (exhaust gas recirculation) position sensing (measuring the position of the EGR stepper motor). Like Siemens VDO, AEC buys its Hall effect sensor elements and applies its experience in sensor packaging, electronics, engineering, validation and high quality, low-cost production.
Growth opportunities for rotary pedal position sensors are driven by a scenario of increased use of electronic throttle controls. Height sensors have potential opportunities in headlamp leveling systems, especially for vehicles with high-intensity discharge lights. Opportunities for transmission range sensors would be boosted by the proliferation of electronically-controlled transmissions.
Recent innovations from the former AEC include, for example: a flexible design Hall effect cam and crank sensor; Hall effect dual-output transmission speed sensor that can sense speed and direction; Hall effect transmission speed sensor; probe-style, multiuse ABS sensor that can be adapted for after-market applications; and heavy duty pedal position sensors.
Sauerwein explained that Siemens VDO sensor division is focusing on Hall effect rotary position transmission sensors and on transmission modules (consisting of, for example, two speed sensors, a rotary or linear position sensor, temperature sensor, pressure sensor, and possibly a transmission controller). Such transmission modules can allow for easing the transmission supplier's integration task in, for example, newer electronically-controlled transmissions.
The Sensors Division will soon be launching a noncontact, 360-degree rotary position sensor. In addition to magnetic speed and position sensors, the Siemens VDO sensors division provides a wide array of sensors for such parameters as temperature, pressure, mass air flow, manifold absolute pressure, NOx (oxides of nitrogen), knock and fluid level.
Moreover, the sensors division has been developing, primarily for powertrain applications (engine, transmission and transfer case), a noncontact magnetoelastic torque sensor using patented technology licensed from Magna-Lastic Devices Inc., a subsidiary of Methode Electronics Inc. The torque sensing technology, which is purportedly not susceptible to temperature drift, comprises a magnetostatically active element and a magnetic sensor. Siemens also has a version of this technology that can be used in electric power-assisted steering applications.
The sensors division is focused on innovation and is actively working on many advanced development projects, including cylinder pressure sensing, touch sensors for door applications, steering angle sensors, differential pressure sensors, and electronic nose sensors for cabin air quality. They have also developed a prototype of a sensing solution for detecting and monitoring urea for reducing NOx emissions in diesel engines using selective catalyst reduction systems.
According to Frost & Sullivan's North American Automotive Original Equipment Sensors Markets research service (published October 2003), revenues for the North American original equipment market for speed sensors used in engine, transmission, and wheel speed applications are projected to total $299.0 million (representing 128.1 million units) in 2009.