Electronic Design

Sensors To Transform Vehicles Into Electronic Cocoons

There are about 30 to 40 sensors in today's average economical model, but that figure could more than double in a few years.

While electronics have pervaded almost every aspect of the automobile, the electronic content is only about 8% to 20%. But that scenario is changing rather rapidly. Around the globe, manufacturers of passenger cars and other transportation vehicles are realizing that electronics is the wave of the future. Acting on that knowledge, they're pursuing the technology aggressively. Mechanical and electromechanical methods are giving way to electrical and electronic technologies. Novel vehicle architectures are under development to make electrical and electronic systems part and parcel of the design from the start, not just an afterthought.

The design of the future car is undergoing radical changes as it evolves to become an environment of its own. All of this translates into exploding opportunities for electronics and semiconductor vendors. Experts believe that the value of electronics in vehicles is destined to reach beyond 40% in the near future, and sensors and actuators will capture a major share of that development. As safety and protection take precedence in future models, electronic sensing will dramatically penetrate every aspect of the automobile.

"Sensors will continue to populate automotive systems as new applications are developed," says marketing consultant Roger Grace, president of sensor marketing firm Roger Grace Associates. "They will be used in every imaginable section of the automobile, from safety to vehicle diagnostics and monitoring. Presently on average, about 30 to 40 sensors of all types are utilized in an economical car. But that number will surge much higher in just a few years."

Grace predicts that sensor usage in average automobiles will rise by about 20% to 25% every year. At that rate, there will be roughly 75 to 80 sensors in every economical model in three years. Of course, there are exceptions in some luxury models, where the electronic content is already high and destined to be higher. For example, the BMW750 model already employs nearly 120 sensors.

There's an increasing trend toward the use of silicon microelectromechanical systems (MEMS) and microsystem technologies (MST). While MEMS/MST have played a role in automotive engine control as manifold absolute-pressure (MAP) sensors since 1979, the real boost arrived in the early '90s with the first deployment of the silicon accelerometer in airbag crash applications. Since then, the use of MEMS devices in the automotive sector has more than doubled.

In both entirely new applications and in the replacement of traditional electromechanical technologies, MEMS remain poised for growth in the automotive arena as the technology matures and production costs are cut. Its share of the automotive market is expected to surge at over 16% annually for the next couple of years, predicts a market report developed jointly by Roger Grace Associates and Brussels, Belgium-based Nexus.

A Fast-Growing Segment
The study estimates the worldwide MEMS automotive market at $1.26 billion this year, but it's projected to grow to $2.35 billion by 2004. The study indicates that the major growth for automotive sensors will occur in the areas of the accelerometer, pressure, position, humidity, and distance sensors needed in a myriad of applications that range from safety to vehicle diagnostics and monitoring. Plus, MEMS/MST are well suited to fill many of these old and new applications, according to the study.

From adaptive cruise control to smart airbags to collision avoidance, semiconductor sensors are expected to dramatically enhance the safety of vehicle occupants and other road users. The use of tire pressure and temperature monitors, for example, should prevent crashes resulting from under-inflated or overheated tires. Recent accidents due to such failures have fueled tremendous interest in this area of sensor technology.

For safer journeys, rear-view mirrors will become video screens that continually scan the view behind the driver by using cameras, sensors, and radar. Smart thermal infrared (IR) sensors will provide climate control, person detection, and air-quality control inside the vehicle. Additionally, carbon monoxide sensors will activate air vents, open windows, and shut down engines upon sensing the poisonous gas.

The list goes on, because so many more sensing elements stand in line, ready for deployment. For instance, intelligent Hall-effect-based magnetosensors are being explored to possibly replace mechanical induction coils and enhance the stability of the car during the next few years. Night-vision sensors based on IR technology will provide sight where human eyes cannot see. IR imaging and other optical vision systems that implement CCD cameras are under development to supply traffic information around a vehicle to enhance the safety of a vehicle's driver and its occupants even more. Although some features like night-vision sensors, or IR imaging, and smart airbags have already appeared in select luxury models, the effort is to lower the cost of these systems and install them in economy models.

In-vehicle electronics systems that can recognize drivers and automatically adapt the settings for temperature, seat position, and radio stations are in progress. In short, sensor technologies and related electronics are on the move to "wrap" all around an automobile and provide complete safety, security, protection, and comfort to its occupants.

Smart airbags tailored for different types of crashes and occupant position, with improvements in side-impact protection, will begin to appear over the next few years. While earlier airbags were designed to react bluntly during a crash, causing bodily injuries and even deaths, the newer smart systems are being constructed to control the deployment of airbags based on precrash information. Consequently, passive occupant-detection systems (PODS) were developed to optimize restraint protection relevant to infants, young children, and small adults, as well as their proximity to an airbag.

To Deploy Or Not
Toward that goal, Delphi Automotive Systems has developed a commercial PODS based on weight-sensing techniques. Complying with the FMVSS 208 U.S. Federal Motor Vehicles Safety Standard, the Delphi seat-based sensor determines whether to suppress or allow passenger airbag deployment based on the passenger's weight, or suppress the system entirely if the seat is empty. Delphi's PODS technology will be introduced as a critical component of an advanced airbag system in 2001 Jaguar XK sports cars and four models of Ford and Lincoln-Mercury cars.

This move fits requirements mandated by the U.S. government. Beginning in 2004, for example, 35% of every car manufacturer's fleet of vehicles sold in the U.S. must be equipped with advanced airbag systems. That number increases to nearly 100% by 2006, according to a paper given by Delphi at the last year's Convergence2000 Conference in Detroit.

A Weight-Sensing System
The Delphi PODS technology consists of a bladder-weight sensing technology mounted under the passenger seat cushion (Fig. 1). Using a sophisticated occupant classification algorithm and extensive signal processing, it allows the vehicle airbag controller to variably deploy or suppress the passenger airbag. The system consists of a silicone fluid-filled bladder-weight system, a pressure sensor mounted under the seat cushion, and an electronics control unit for sensor data processing.

While Delphi has taken the bladder route, others are applying force-sensing resistor techniques and silicon strain-gauge sensors to develop PODS solutions for their respective OEMs. Siemens Automation Corp. is applying 100 resistive pressure-point sensors to create a sensor mat, which is placed under the seat cushion. This force-sensing resistor array generates a pixelated image or footprint of the passenger or an object sitting on this sensor mat. Implemented in Siemens' occupant-classification system, this technique evaluates the footprint to determine the size of the occupant. Siemens plans to advance this occupant-sensing method with weight-based sensing.

Using silicon micromachined strain gauges supplied by BF Goodrich, GageTek Co. is developing torsional-sensing load cells that detect occupant weight and position for airbag deployment. In this scheme, a load cell is placed on each corner of the seat to sense the weight and position of the passenger. By calculating the centroid of forces at the corners of the seat, GageTek's technique reduces airbag deployment force for children, small adults, and out-of-position occupants. Still to be completed is the algorithm for the reduction of airbag deployment now under development. Also, the torsional sensing system is presently being evaluated by seat suppliers and auto makers.

Meanwhile, Ford Motor Co. is tapping Analog Devices' micromachined silicon accelerometer sensors in its advanced personal safety system. The system detects the severity of a crash and in response deploys a two-stage airbag system to reduce injuries from inflating airbags.

Visteon Automotive Systems has already developed one such advanced safety system using ADI accelerometers for use in Ford Taurus 2000 models. Efforts are under way to extend this to other cars. In this application, the accelerometers, located in the passenger compartment, sense the G force of an impact and produce a signal that's proportional to the force. At the same time, a satellite sensor module in the front detects crash severity. Other sensors in this advanced safety system measure the distance from the driver to the steering wheel and other variables of the occupant in the passenger seat.

An Integrated System
As automotive safety evolves, vehicle manufacturers worldwide are tapping into newer technologies. With expanded use of microcontrollers, sensors, actuators, high-speed data buses, and X-by-wire technologies, developers are readying an integrated safety system (ISS) that guarantees protection and safety for every moment occupants are in the vehicle.

The ISS approach encompasses a series of interdependent safety states, which are primarily divided into two zones, avoidance and mitigation (Fig. 2). The avoidance zone includes normal driving, warning, and collision-avoidable states. This last state overlaps into the mitigation zone, which also includes the collision-unavoidable and post-collision states.

While the first three states focus on avoiding accidents, the unavoidable state must minimize the impact of the accident and protect the occupants. Toward that end, interest in smart or advanced airbag systems has intensified to provide enhanced occupant protection under a variety of real-world accidents, as well as to minimize the adverse effects caused by airbag deployments.

There are many situations in which an automobile can find itself in the unavoidable state. A rollover is one such state. Delphi engineers are developing sensing techniques to address this unavoidable situation and reduce the risk of injury.

At Delphi, researchers are developing a variety of sensors to comprehend the three-dimensional aspect of a rollover—yaw, roll, and pitch—and to take take appropriate countermeasures to protect passengers from injuries. Using a lateral accelerometer and an angular rate sensor (ARS), also known as a gyroscope or simply a gyro, Delphi is readying a rollover-sensing module (RSM) that can measure vehicle lateral (side-to-side) and angular rotations. By combining the knowledge of ac-celerometer and gyro signals dynamically as the vehicle roll angles change, the RSM can effectively determine the dynamic vehicle roll angle.

Additionally, the researchers have developed a corresponding sensor algorithm that addresses the countermeasure deployment criterion, safety, and robust immunity levels when the vehicle reaches a critical angular threshold. The rollover sensors and associated algorithm offer a high level of immunity to a number of events. These include vibrations and transient shock inputs due to rough road or severe nonrollover events, lateral accelerations and inertial forces associated with vehicle maneuvering, and sensor errors as a result of noise, biases, scale factors, misalignments, and ARS G sensitivities.

Discriminating Between Events
In particular, the ARS is designed to be minimally sensitive to G shocks from rough roads and nonrollover crash events. According to Delphi, this G sensitivity performance is crucial because many rollovers are initiated by a curb-induced tripping force or a side/frontal impact.

When designing this RSM module, the researchers took into account both performance and cost-effectiveness demanded by the automotive marketplace.

Another critical area of automotive application in terms of safety is vehicle dynamic control, which includes the antilock braking system (ABS) and traction control, as well as stability. This area continues to seek better sensors without paying a higher price.

Wheel-speed information from all four of a car's wheels is one aspect that contributes to dynamic control and stability. Consequently, this information must be precise and reliable under all travel conditions. Although variable-reluctance-based induction coils are finding use in this application, they're rapidly being replaced by semiconductor-based magnetosensors that combine precision and advanced performance with cost-effectiveness. Consequently, both semiconductor-derived magnetoresistive (MR) and Hall-effect technologies are being explored for better dynamic control and stability.

Even though MR sensors offer a sensitivity and a signal-to-noise ratio (SNR) that's two to three times higher than the Hall-effect sensors, they're space-consuming. Unlike MR technology, Hall-effect sensors offer integration of both the magnetic Hall plate and the evaluation circuitry on the same monolithic chip. When embedding the Hall probe into a modern mixed-signal IC process, designers can compensate for the low-sensitivity limitation of the Hall-effect sensor by adding intelligent features on-chip, according to a joint paper given by the research-ers of Infineon Technologies AG and Robert Bosch GmbH at the Convergence2000 Conference.

Another advantage of the monolithic Hall-effect sensor is the increased robustness against humidity and EMC, as no interconnect exists between the sensor and the electronic circuit.

For this application, by implementing a submicron biCMOS process, the researchers have jointly developed a differential Hall-effect magnetosensor with built-in digital self-adjustment of thresholds. This ensures minimal phase jitter under changing environmental conditions. With the Hall-effect probes separated by 2.5 mm, this chip detects the motion of ferromagnetic or permanent-magnet wheels by measuring the differential flux density of the magnetic field. To detect this motion, a back-biasing permanent magnet provides the magnetic field.

This IC has been encased in an ultra-thin two-lead ceramic package capable of withstanding −40°C to 170°C operating temperatures. Its accuracy and sensitivity were optimized for an air gap of 2.5 mm. The researchers hope that within the next few years, the Hall-effect approach to wheel-speed measurement will replace the present mechanical induction coils and enhance vehicle stability. They're not the only ones, either. Allegro Microsystems Inc. also supports applying Hall-effect techniques to wheel-speed sensing.

By using indium antimonide (InSb) magnetic Hall sensors coupled with gallium-arsenide (GaAs) HBT signal-processing circuitry, Emcore Corp. is attempting to overcome the limitation of silicon Hall sensors. Compared to silicon Hall sensors, these integrated compound-semiconductor sensors provide higher sensitivity, improved SNR, greater robustness against ESD, no switching noise, and clean signals. That's according to a paper presented by Emcore researchers at last year's Sensors Expo Conference in Detroit. The high InSb mobility leads to high sensitivity and, therefore, a high-voltage output under a magnetic field.

The paper shows that a typical sensitivity of an InSb Hall sensor is 0.14 mV/V/G. Plus, it can operate from −60°C to 200°C, making it suitable for harsh automotive environments. Also, the offset voltage is a low ±0.4 mV/V at a zero magnetic field. The added benefit is the use of GaAs HBTs for signal conditioning. These offer many advantages over silicon ASICs, like high-temperature operation, a high breakdown voltage, and low noise.

Philips Semiconductors is keen on exploiting the benefits of MR technology for automotive use. Implementing MR properties of thin-film permalloy, Philips has developed angle and rotational speed sensors that exhibit a wide operating-frequency range with detection down to zero speed. According to Philips, both the MR sensor and the associated signal-conditioning chip have been housed in a single plastic package, which the maker plans to deliver to select users by 2002. There are other solutions for wheel speed sensing under development too.

MEMS-based angular rate sensors are actively vying for this space as well. BEI Electronics, for instance, has readied a similar sensor that it believes will propel the adoption of these systems into less expensive vehicles in the near future.

Tire Watch
As auto makers and OEMs streamline vehicle safety systems, sensor producers are pushing toward more intelligence for better control and communications. These intelligent sensors are beginning to incorporate features, such as self-calibration, two-way communication, self-diagnostics, and programmability.

Concurrently, auto makers and OEMs are exploring new safety-related areas within an automobile. One such application that garnered tremendous interest last year is tire pressure and temperature monitoring systems. Given recent tire recalls, government safety organizations are expected to push for tire pressure monitoring (TPM) standards immediately. Silicon pressure sensors are aggressively pursuing their way into future automobiles toward these applications.

Thanks to an agreement between TRW Automotive Electronics and French tire manufacturer Michelin, drivers will soon have access to an advanced tire-pressure monitoring technology and a new generation of tire and wheel systems. This combination of smart tires and software will enable motorists to avoid hazardous driving conditions as a result of underinflated tires.

TRW's TireWatch system uses a pressure sensor that's mounted on the tire valve stem to monitor air pressure and temperature inside the tire. The tire transmits the information via a radio signal to a control unit in the vehicle, which provides warning messages to the driver information display. Simultaneously, Michelin has developed an innovative tire/wheel assembly me-thod called the Pax System. This will prevent the tire from coming off the wheel when it goes flat, while providing excellent handling, mobility, and safety in run-flat situations. Together, the two partners are working to combine their complementary strengths and create a single system that will allow car makers to optimize the package for performance, reliability, weight, and cost.

According to TRW, this technology will not only alert drivers about potential problems, but it also will identify the tire involved. Under the agreement, the two will develop improved tire-pressure monitoring systems for both the Pax System and conventional radial tires.

Incidentally, the recent Firestone tire controversy has prompted the U.S. Congress to make it mandatory for auto makers to outfit all cars within three years with a warning system that indicates when a tire is significantly underinflated (see "Firestone Recall Fuels Interest In Smart Tires," wall street journal, Nov. 22, 2000, p. 1). Many more developers are jumping on this bandwagon to take advantage of new laws, whereby auto makers and consumers have no choice. Expect to possibly pay more for these new safety features, which will soon be mandatory.

As car makers attempt to surround the vehicle with an electronic cocoon, they're importing sensor technologies that are standard equipment in other transportation systems like aircraft and ships. For object detection and collision warning, they're tapping radar sensing technologies. Recently, Visteon and Raytheon entered into a cooperative deal to develop radar-based sensors for detecting objects in front of and behind a vehicle.

For back-up warning applications, the Maple Consulting Group has readied a programmable microwave sensor that combines FSK modulation and Doppler techniques to warn drivers of possible obstructions in the reverse mode. Because the microwave sensor is programmable at the time of installation, it can be used on many vehicle platforms, asserts Heyward S. Williams, president of Maple Consulting. Programmable parameters include range, priority, velocity, turn-off time, direction of motion, and alarm. The range can be programmed from 0.3 to 10 meters. It implements an autocalibration feature that improves accuracy and avoids human intervention.

The probability of avoiding an accident varies with respect to the distance that the obstacle is located from the sensor, as explained in a paper titled "A Programmable Microwave Back-Up Warning Sensor," presented last year by Williams in the Automotive Sensors & Applications session at Sensors Expo (Fig. 3). Nonetheless, Williams believes that the microwave sensor is commercially viable and can provide detection and warning in 90% to 95% of possible scenarios that could cause a collision. "Any alarm is as good as the driver," Williams notes.

The initial target for this sensor was fleet vehicles where installation procedures can be quickly established. Now, the developers are focusing on OEMs and are hoping to supply them within three years. The microwave back-up warning sensor uses a 10.525-GHz carrier with less than 10 mW of transmit power. To prevent it from interfering with other similar sensors or setting off radar detectors, the microwave sensor is pulsed at a 12% duty cycle.

Similarly, Motorola and MobilEye Vision Technologies Ltd. are collaborating to extend advanced robotic vision technology to the automotive arena. Through this alliance, Motorola will combine its expertise in microcontrollers and DSPs with MobilEye's computerized vision capabilities to develop auto safety features, such as lane-departure warning, collision warning, drowsy-driver detection, and obstacle/pedestrian detection.

There are many more opportunities for sensors in the automotive world. Engine-oil monitoring is on the horizon, where MEMS suppliers and others are diligently exploring the use of sensors to monitor the chemical composition of the oil, as well as its level. The monitor's sensors and signal-conditioning circuitry must be able to withstand the elevated temperatures of the engine and surrounding harsh environment.

Rugged packages are under development, so these sensors and electronics can be embedded in the system. With drivers seeking real-time information on vehicle dynamics, the trend is toward more on-board diagnostics and high-speed data transfers, including the use of the CAN interface (Fig. 4). Such an interface minimizes the need for a wiring harness within an automotive system while making it simpler to add or remove sensors in that environment.

Companies And Organizations Mentioned In This Report
Allegro Microsystems Inc.
(508) 853-5000

American Sensor Technologies
(973) 398-9900

Analog Devices Inc.
(781) 937-1428

Capacitec Inc.
(978) 772-6033

Delphi Automotive Systems
(765) 451-0655

GageTek Co.
(916) 801-7640

Maple Consulting Group
(603) 434-1865

Motorola Automotive and
Industrial Electronics Group
(847) 480-6883

Robert Bosch GmbH
(248) 553-9000

Roger Grace Associates
(415) 436-9101

Siemens Automotive Corp.
(248) 253-1000

TRW Automotive Electronics
(248) 478-7210

Philips Semiconductors
(408) 991-2000

Visteon Automotive Systems
(313) 755-9500

Infineon Technologies
(408) 501-6384

TAGS: Automotive
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