For a long time, the automotive industry has been dominated by mechanical and hydraulic engineering. From suspension and cooling systems to engines and control systems, the vast majority of vehicle systems utilize mechanical and hydraulic control and operation. However, this situation is now changing: driven by the trends of automotive intelligence, electrification, and emission regulations, automotive designers are revolutionizing the automotive field by transforming mechanical-hydraulic systems into electromechanical systems. The automotive industry is placing increasing emphasis on the development of next-generation "X-by-Wire" systems, which can provide superior support for emerging automotive functions compared to traditional mechanical-hydraulic systems. This article introduces the core key technologies of automotive by-wire systems and related solutions launched by Melexis.
Automotive design is moving towards electrification and intelligence
Although automotive design has traditionally been dominated by mechanical control, with the development trends of automotive electrification and intelligence, electronic components are being extensively incorporated into automotive design systems. Although electronic components have been introduced into automobiles since the 1930s, they were mainly used in engine starters, lighting, and optional radios, and the overall mechanical characteristics of automobiles did not change. However, in recent decades, the application scope of electronic systems in automobiles has continued to expand. Numerous mechanical pumps and vacuum control systems have been replaced by solenoids, solid-state relays, and piezoceramics.
On the other hand, electronic sensors and displays have long replaced mechanical feedback systems, such as mechanical gauges. Nevertheless, in core functions such as steering and braking, mechanical and hydraulic systems still dominate, with electronic components playing only a supporting role. This transformation aims to enhance functionality and safety, improve precision, simplify integration, reduce overall system complexity, and decrease emissions and energy consumption.
By-wire systems represent another major shift in automotive control systems. By-wire systems replace traditional mechanical linkages with electronic control mechanisms. This marks a significant change in automotive design and operation, where basic functions such as throttle, braking, and steering no longer rely on physical connections like steering columns, cables, or hydraulic lines. Instead, sensors, electric actuators, and control units manage these functions.
Taking throttle-by-wire as an example, it uses position sensors to measure the accelerator pedal position and transmits signals to the engine control unit (ECU) for electronic power adjustment, thereby replacing the mechanical connection between the accelerator pedal and the throttle valve. Although the lack of a mechanical connection may raise concerns for some, this concept has been successfully validated.
By-wire systems offer many advantages in control, efficiency, safety features, etc.
By-wire systems offer numerous advantages, including finer control, higher efficiency, enhanced safety features, and compatibility with emerging technologies like autonomous driving. However, they also face a series of unique challenges, such as ensuring reliability and meeting advanced integration and redundancy requirements. Although by-wire operation is already common in automobiles, with electronic control used in throttle, engine, and some transmission systems, the transformation of two main vehicle systems has been relatively slow: braking and steering systems. However, this situation is changing rapidly.
Brake-by-wire systems use sensors to monitor brake pedal position or pressure and control the braking force by driving electro-hydraulic or electromechanical brake actuators (brake calipers). Brake-by-wire systems enable seamless integration of Advanced Driver-Assistance Systems (ADAS) and autonomous driving functions, while also promoting regenerative braking in Electric Vehicles (EVs). This function allows the vehicle's powertrain motor to generate a braking force, reversing the current flow to recharges the battery pack during deceleration.
Steer-by-wire systems completely remove the mechanical steering column that directly links the steering wheel to the wheels. Instead, the system relies on electronic sensors to identify steering inputs and communicate them to the actuators that drive the wheels. Compared to traditional mechanical steering systems, steer-by-wire systems offer many advantages. They simplify the integration of advanced functions (such as lane keeping assistance, collision avoidance, variable steering ratios, and autonomous driving capabilities), while alleviating certain packaging constraints and making the application of in-wheel motors possible (which is difficult to achieve to a typical steering rack). Furthermore, by eliminating the need for a physical steering column, steer-by-wire systems open up new paths for innovative vehicle design, expanding interior space and design possibilities.
"Dry" braking and steering systems eliminate associated emissions and maintenance needs
On the other hand, because hydraulic systems are susceptible to fluid contamination and leakage, they require regular maintenance and fluid replacement to ensure safe operation. The application of brake-by-wire and steer-by-wire systems combined with purely electromechanical actuators can completely eliminate hydraulic assistance. This represents a new paradigm in the automotive industry, enabling "dry" braking and steering systems, reducing the amount of fluid in the vehicle, thereby eliminating associated emissions and maintenance needs.
Brake-by-wire technology enables faster application and release of braking torque. Combined with precise speed sensors and automotive intelligence systems, it can minimize brake and tire wear emissions in several ways: maximizing the use of regenerative braking, optimizing braking torque to minimize tire wear, and completely avoiding concurrent use of the throttle and brakes.
In safety-critical systems, electronic components must meet several key technical requirements. These components need to possess inherent accuracy, reliability, and the ability to withstand harsh conditions in vehicles, such as vibration, temperature fluctuations, and electromagnetic interference (EMI). Sensors must also be easy to integrate and able to work collaboratively with other types of sensors, as heterogeneous redundancy has become a core element of the functional safety architecture for by-wire systems to ensure fail-safe operation.
Compared to a conventional braking system, a brake-by-wire system require sensing in more areas and higher redundancy at each point in the system because they lack mechanical backup. To ensure safe operation, several sensing channels are typically deployed, making sensor integration and flexibility key considerations for engineers' designs. System control and feedback are collected through brake pedal position and force sensors, as well as additional sensors installed on the calipers and brake fluid circuits. Given the temperature ranges, vibration, and noise (EMI) challenges in these areas of the vehicle, sensor accuracy and reliability are crucial at every point in the system, necessitating the deployment of redundant high-quality sensors.
In a steer-by-wire system, supplementary sensors are needed to track the rack position and verify that its movement aligns with the demand indicated by the steering angle sensor. Similarly, reliability is paramount, so multiple sensing technologies are deployed to achieve heterogeneous redundant system operation.
Cutting-edge magnetic and inductive sensors for by-wire systems
Melexis has a long-term cooperative relationship with the automotive industry and has long provided various sensing technologies. Its product line includes cutting-edge magnetic and inductive sensors designed specifically for next-generation by-wire systems. Melexis's magnetic sensors, such as the MLX90423, MLX90424, and MLX90427, utilize Melexis's proprietary Triaxis® technology and are designed for advanced automotive brake-by-wire and steer-by-wire applications. Unlike conventional Hall sensors that only detect the magnetic flux density perpendicular to the surface of the Hall element, Triaxis® sensors can detect the three magnetic flux components (XYZ) due to the integrated magnetic concentrator (IMC). This technology enables the sensors to accurately decode the absolute position of any moving magnet, whether it is rotational or linear displacement.
Melexis's Triaxis® sensors, such as the MLX90423 and MLX90427, comply with the ISO 26262 ASIL-C standard and can withstand stray fields up to 5 mT, making them an excellent choice for electric vehicles or systems close to other magnetic sensors. They are also available in TSSOP-16 Dual-Die packaging, providing additional built-in redundancy and supporting the implementation of ASIL-D systems. Products like the MLX90424 integrate two Triaxis® MLX90423 sensors and one MLX92292 low-power latch and switch wake-up sensor in a single package, providing the ultimate sensing solution for brake-by-wire applications.
In addition to the sensing elements, Triaxis® sensors offer a range of key features designed to further simplify the development of advanced by-wire systems. Multiple output modes (Analog, SPI, PWM, and SENT, including the SPC function in chips like MLX90377 and MLX90376) support applications with multi-sensor bus architectures and ensure compatibility with different system configurations, enabling smooth integration into various automotive platforms.
Furthermore, by including a gateway (input pin) in chips like the MLX90372, the sensor can integrate signals from external sources such as pressure sensors, force-sensing resistors, or NTC temperature sensors. This feature enhances integration possibilities, reduces wire count, and simplifies system design.
Moreover, Melexis's inductive sensing chips (such as the MLX90513) are immune to magnetic stray fields (ISO 11452-8), allowing them to be deployed in high electromagnetic interference (EMI) environments and used in combination with magnetic sensors like the MLX90423 or MLX90427. This makes them ideal for the heterogeneous setups required by safety-critical by-wire systems.
The MLX90513 is designed for automotive and industrial applications, leveraging Melexis's over 15 years of experience in inductive sensors. It is a robust interface capable of sensing the absolute position of rotary and linear motion. Inductive sensors work through inductive coupling between a transmitter coil, a target piece, and three receiver coils. When the on-chip LC oscillator generates an electromagnetic field through the transmitter coil, this field induces a voltage in the three receiver coils that is dependent on the angle of the target piece (rotor).
The MLX90513's internal signal processing unit captures and processes these three signals, providing precise position information with a maximum error of ±0.1% of full scale. The receiver coils are positioned relative to each other according to the number of poles on the metal target piece (rotor) above them. Typically, these coils are tracks on a printed circuit board, facilitating simple custom design and elegant integration into brake-by-wire and steer-by-wire systems.
Similar to magnetic sensors, the MLX90513 also complies with the ISO 26262 ASIL-C standard and offers four output modes (SENT/SPC, PWM, and Analog) to accommodate multi-sensor bus setups and promote seamless integration with automotive platforms.
Melexis's sensors offer unparalleled accuracy, a wide operating temperature range (-40°C to 160°C), and excellent immunity to electromagnetic interference and stray magnetic fields, ensuring outstanding performance even in the harshest automotive environments. Beyond technical capabilities, Melexis's solutions simplify complex system design through features such as built-in redundancy (e.g., TSSOP-16 Dual-Die packaging for ASIL-D systems), multiple output modes (Analog, SPI, PWM, SENT, SPC), and the ability to integrate external signals via input pins. This holistic approach enables automotive OEMs and Tier 1s suppliers to simplify development cycles and reduce overall system complexity and cost.
Conclusion
The automotive industry is undergoing profound changes, with steer-by-wire and brake-by-wire technologies becoming the cornerstones of next-generation vehicles. These safety-critical systems offer significant advantages over traditional mechanical and hydraulic setups, enabling enhanced functionality, superior control, and taking important steps towards a more sustainable, cleaner, and smarter mobility future. However, the successful implementation of these advanced systems relies on highly accurate, reliable, and intelligently integrated sensing solutions. The Melexis Triaxis® magnetic sensors and stray-field-immune inductive sensors introduced in this article are designed to meet the stringent requirements of automotive by-wire applications. These high-quality position sensors are not just components; they are key enablers ensuring the safety, performance, and innovative design of future vehicles.