New Sensing Technologies in Automotive Applications

Automotive designers are continually demanding devices that offer higher performance and greater flexibility than traditional position sensing technologies. These devices must also be versatile and adaptable to a wide range of applications. This demand requires the integration of the best design elements of traditional contact and non-contact sensor technologies into devices.

As today's vehicles utilize more and more electronics and control systems, engineers face increasing challenges in integrating these electronic devices into the vehicle. This is especially true for sensors and other feedback (parameter) circuits used to ensure vehicle safety, reduce fuel consumption, and reduce emissions.

Electronic system designers are constantly challenged to improve system resolution and signal quality in order to keep pace with processors that handle higher speeds and I/O functions. Mechanical flexibility, environmental stability, and signal integrity are key design features for any sensing technology used in today's automotive environment.

One of the requirements for electronic devices is the operating temperature range they can withstand. From a cold ambient temperature of -40 degrees Celsius to over +150 degrees Celsius in the engine compartment, sensors and related electronics are facing the extreme temperature limits that current materials can withstand. Further applications, such as variable turbochargers, push this temperature limit even higher, possibly beyond +180 degrees. This requires sensor designers to develop materials and packages that can meet these requirements.

At the same time, the sensor must be able to accept a variety of mechanical configurations required by the overall system. Traditional sensing devices such as potentiometers and Hall effect devices (technology) can be packaged in either linear or ring packages. Both technologies have their advantages - potentiometers are low cost, mature technology, and mechanically flexible, while Hall effect devices have low wear and good signal quality - the specific choice depends on the application requirements of the system. More advanced technologies such as inductive sensors take advantage of the advantages of both sensors to achieve more robust sensing systems.

Potentiometer technology has a high degree of design flexibility in meeting linear or ring applications. Due to the design characteristics of the potentiometer, it provides an output signal that is proportional to the input voltage. However, the technology is somewhat limited by the characteristics of its analog output signal. Although this signal can be converted to a digital format, this conversion requires additional electronic components, which increases the cost of the sensor. Moreover, the converted signal is not a true high-resolution digital format. As more and more high-speed networks and communication buses are being used in automobiles, the need for an AD converter for each potentiometer can be a disadvantage. Potentiometers are also a contact sensing technology that is susceptible to wear due to long-term operation and vibration. When the wear of the potentiometer becomes very obvious, it will cause excessive noise in the signal. This will become a problem in the direct feedback control loop.

Figure 1: Traditional sensing technologies including potentiometers and Hall-effect devices

Hall effect sensors typically generate an analog signal, and the device communicates with the vehicle system using an ASIC that converts the analog signal directly to a digital signal. Because Hall technology measures changes in Gaussian magnetic flux, it requires a very sophisticated support system to maintain its integrity. This limits the mechanical packaging flexibility of such devices to a certain extent. This support system also increases the cost of the sensor to a certain extent. On the positive side, Hall effect sensors are non-contact technology, so they do not degrade due to wear like potentiometers. Generally, these sensors have a relatively short travel distance to control the Gaussian magnetic field that affects the Hall effect sensor. Typically, Hall effect sensors are designed for less than 180 degrees of rotation or less than 25 mm of linear movement.

Recently, some progress has been made in the development of new inductive sensing technology that takes advantage of the advantages of both potentiometer and Hall effect technologies. The device consists of a non-contact sensing system consisting of two printed circuit boards, with the core of the signal generation and sensing. The device, called Autopad, generates inductive coupling between the two circuit boards, which is measured and converted by the on-board ASIC.

Unlike Hall sensors, Autopad sensors allow for misalignment in the X, Y, and Z axes, thus eliminating the need for rigid mounting systems. In addition, the ASIC makes it a true digital sensor, generating a 12-bit PWM signal that can communicate directly with a high-speed controller. The signal can also be converted back to analog format if necessary. OPTEK's Autopad can also be implemented in a variety of physical configurations, including rotational and linear. Rotational designs can be used for systems with angular misalignment up to 360 degrees. Linear sensors allow for misalignment of 20 to 200 mm or even more.

As the automotive industry evolves, design engineers continue to demand devices with higher performance and flexibility. Although traditional sensing technologies have their advantages, the development of inductive sensing technology provides solutions to the various technical challenges and needs of today's demanding automotive electronics . The design flexibility of this sensing technology makes it a reliable and more cost-effective solution for many automotive applications.

Figure 2: Autopad sensing technology from TT electronics OPTEK Technology