Automotive emission control systems essentially "breath" the dirty air from the engine to determine the engine's efficiency: fuel and engine efficiency can be determined by the oxygen concentration in the exhaust stream. Oxygen sensors are certainly not new, says Vishy Seetharaman, technical marketing manager for Delphi (Troy, MI; www.delphi.com). However, up to now, these sensors could only report whether the engine was running rich or lean, not how rich or how lean. The Delphi linear oxygen sensor can report the how. This sensor measures the air/fuel ratio of the exhaust gas from diesel and gasoline engines over a wide lambda (rich/lean) range. The five-wire, two-cell sensor combines new geometry (an integrated heater), different material sets (an alumnia/zirconia element), and an optimized membrane thickness to yield fast light-off and closed-loop operation. With such sensors, continues Seetharaman, vehicles can run closer "to the edge," which means getting more out of an automobile engine while reducing emissions even further.
ADAPTIVE CRUISE CONTROL
Adaptive (or active) cruise control (ACC) systems can detect a vehicle ahead, detect both the distance to and the relative speed of that vehicle, and then maintain both the appropriate distance and speed between it and the car ahead. The latest ACC from TRW Automotive (Livonia, MI; www.trwauto.com) uses a 77-GHz radar sensor to detect vehicles up to 200 meters away. This system, which features range precision of 5%, speed measurement precision of 0.12 mph, and a search area of 12 degrees, is in the Volkswagen Phaeton and will be coming out in the new Volkswagen Passat.
But that's highway driving. In Japan, some cars are now being equipped for "low-speed following"; that is, drivers have highway-like cruise control capabilities on city streets, explains Jerry Bricker, vice president and general sales manager for Omron Automotive Electronics, Inc. (Novi, MI; www.omronauto.com). Note the differences here. In highway driving, a two-second gap between vehicles at 60 mph is roughly 150 feet (except, say, in Massachusetts). In city driving, there may be half a car length—six feet—between vehicles traveling under 25 mph.
Omron's new sensor, the Gen3 laser radar (lidar) sensor using Omron's micro lens array technology can handle both long- and short-range sensing. Wave pattern recognition technology in the sensor detects highly reflective light, such as that off vehicles, and poorly reflective light, such as that off pedestrians. The lidar's photodiodes receive and convert the reflected laser light into electrical signals. These signals are analyzed to determine reflectivity and, from that, the type of object ahead. The width of the Gen3 side direction detection is ±15 degrees; vertical direction detection is ±10 degrees.
Lane departure warning (LDW) systems are just beginning to appear in cars. These video systems, explains Glenn Widmann, chief engineer of integrated safety systems at Delphi, use a camera situated behind the rear-view mirror. The camera looks forward and detects lane markers in the road. It then alerts the inattentive or drowsy driver when the car starts to swerve outside its lane. The 2005 Infiniti FX35 and FX45 SUVs and 2006 Infiniti M45 will have LDW systems.
Not surprisingly, automotive applications such as LDW, blind spot detection, and pre-collision warning are pushing video sensing technology. Consider, for instance, the Omron high dynamic range CMOS (HDRC) camera. Currently available as a prototype, this camera has a high dynamic range—over 170 db—and a high sensitivity—minimum 0.001 lux—which makes the system capable of operating in a wide range of conditions, both bright and dark. The HDRC camera does not require an F-stop, shutter control, or an additional light source. It can detect images that are irradiated with near-infrared light outside the range of normal headlights.
Cameras, says Widmann, provide good information about the width and angle to an object; radars provide very good range and velocity information. "Between the two, you can make a determination that an object is a pedestrian, a truck, or a road sign." (Camera-based pattern recognition provides the capability of recognizing objects, such as distinguishing a utility pole from a pedestrian.) Such camera-based systems linked to the vehicle's brakes are of particular interest to car makers in Europe and Japan. In those countries, versus the U.S., people tend to walk more and village streets are narrower and not as well lit. Hence the interest in technologies for pedestrian safety systems. In the future, adds Widmann, these same systems might be able to read the speed limit on road signs and, with the ACC system, adjust the car speed appropriately.
Occupant sensing seeks to determine two things, explains Peter Suh, North America product manager for TRW's Electronics & Restraint Systems: the size and location (especially the head). This is important for disabling an airbag if a small child is in the seat, or to create a more tailored restraint system by deploying the airbag to a different size or pressure.
Several sensor technologies can solve the relatively simple problem of determining the size of the occupant: measure weight (just like a bathroom scale), recognize a pattern (the occupant's posterior on a seat cushion), or measure pressure (ditto). Tracking the occupant's position, a more difficult problem, seems to cry out for video sensing. Also, video sensing leads to other applications. For example, a camera could detect driver drowsiness, says Marc Bolitho, chief engineer, sensor engineering, for TRW Automotive's braking and steering systems. A camera could also detect a child abandoned in the back seat. When necessary, such a child detection system could roll back a sunroof or roll down a window, saving the child from asphyxiation or heat stroke. The system could also call a cell phone.
Much attention has been given to airbag deployment. TRW Automotive promotes using two acceleration sensors for both longitudinal and lateral direction sensing. These detect crashes as well as discriminate between any rough-road and misuse conditions, explains Suh. On the horizon are pressure sensors mounted in vehicle door cavities, thereby improving side impact detection, such as when a vehicle slides into a pole. Acceleration-based sensors mounted in the door pillar could work, but a pole might not squarely hit the door pillar.
Another approach to the same problem uses capacitive film sensors, such as that from Sensor Products LLC (East Hanover, NJ; www.sensorprod.com). These sensors are a sandwich consisting of two polyolefin layers and air in between. Changes in the 70-micron thickness of the sensor from an outside force generates a corresponding voltage. The solid-state, low-mass sensor is well-suited to sensitive and low-pressure applications, explains Carlos Ruiz, Tactilus product manager for Sensor Products. "If you stand on the sensor, it'll detect your heart beat."
VEHICLE STABILITY AND SEAT BELT CONTROL
Recently, General Motors announced that all of its cars and trucks will have vehicle stability control (VSC) by the end of the decade. VSC systems help prevent over- and under-steering. The sensors for this application divide into two categories, explains Bolitho: One measures driver intent; the other, vehicle dynamics.
The VSC output has several spin-off applications. For example, TRW Automotive is applying the VSC signal to what it calls the active control retractor (ACR). "It's a fancy name for motorized seat belt," comments David Williamson, director of TRW's
Systems Engineering. ACR takes the slack out of a seat belt, thereby putting the passenger in the ideal position for airbag deployment if the car's VSC and "brake assist" systems detect a potential crash or a loss in vehicle control. Today, such seat belt systems would use pyrotechnics. The problem with this is, after the pyrotechnics, after the seat belt is tightened, only the dealer can replace the seat belt system. The motorized system obviates that problem.
The VSC feed to the ACR is "one of the first real-world examples of active/passive safety integration," explains Bolitho. This system, called the "Pre-Safe" pre-crash occupant safety system, is in Mercedes-Benz S-Class cars and will soon come out in the new M-Class SUV.
A SNIFF OF THE FUTURE
The Patriot Act and homeland security has done much to sensor development and applications, points out Paul Ainslie, Delphi's director of advanced projects. Some of that same technology can measure chemicals in the interior of the vehicle. For instance, a driver stuck in traffic in one of Boston's Big Dig tunnels might find the diesel exhaust fumes overpowering. Chemical sensors in the car could automatically sense these fumes and try to keep them out by turning on the air conditioner and closing the vehicle's air vents as much as possible. A more intriguing application, continues Ainslie, is the "Holy Grail for a lot of people working on chemical sensors for cars: Actively measure the alcohol level in a driver to determine whether the vehicle should run or not. The federal government would love to have a good, reliable ethanol sensor that could measure a drunk driver's breath." So, too, would car occupants, other drivers, pedestrians, highway departments, insurance companies, and a host of other interested parties both on and off the road.