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Standards including SAE J2716 (SENT) are helping Mahle engineers reduce wiring for sensors.

Powertrain sensors add functions, help reduce wiring

Sensors have become central elements in powertrains as designers add functions from stop-start to double clutches. More stringent fuel efficiency and emissions requirements are driving many changes in sensor technologies as well as in cabling and standards.

Collecting analog information such as pressure and temperature for digital control units is critical for engineers attempting to meet tightening regulations. More precise sensors help engines burn fuel more efficiently and let transmissions add gears. They’re also central components needed to add stop-start functionality to automatic transmissions. That’s more of a challenge than with manual transmissions where drivers select the correct gears.

“Improved sensing makes the process smoother because it’s very precise,” said Anil Sondur, Vice President of Tata Elxsi. “Gear-neutral sensing is one technique that’s improved upon some of the original [stop-start] systems, which were not smooth all the time. Gear-neutral sensing aims to avoid stalling that can occur when the transmission goes from one gear to another using powerful sensors to help get everything to a particular gear position.”

Market researchers predict solid increases in the number of sensors used in powertrains. In internal combustion engines, IHS Technology predicts that sensor shipments will hit 1.34 billion units in 2019, up from roughly 1 billion last year. That 3.6% compound growth rate is slightly higher than the expected growth in vehicle sales.

Sensors are essential in the evolution of transmissions. Adding gears and making smooth shifts requires high accuracy for moving components. Sensor pricing is one of the factors that determines what strategies transmission designers use.

“Double clutches used in high-end vehicles [require] more sophisticated control techniques, looking at pressure with closed-loop pressure controllers,” said Joe Funyak, Transmission Lead at Infineon. “They’re accurate but more expensive. Pressure sensors are very costly; you need one for each gear. But in an expensive car, another $100 is not a big deal.”

Adding precision can increase the volume of data, which is soaring as more sensors are added. Many design teams are adding intelligence, from 8- to 32-bit microprocessors, to sensors to reduce bandwidth requirements and offload processing task from the host.

As more of these intelligent sensors come into play, communication technologies are changing. Digital architectures are letting developers eliminate wires and improve communications capabilities.

“Sensors with the SAE’s SENT (Single Edge Nibble Transmission) standard are starting to appear in volumes, letting us move away from analog signals,” said William Davidson, Manager of Powertrain Calibration and Controls at Mahle Powertrain. “SENT communications are more robust with better quality and we can eliminate a wire. SENT also provides better diagnostics.”

Eliminating wires is only one aspect of the evolution of sensors. Many observers feel that design teams will increasingly standardize on components to reduce complexity while gaining the benefits of higher volumes.

“There can be as many as 44 sensors on an engine,” said Pat Hunter, Automotive Systems Marketing Manager at Texas Instruments. “As OEMs go to more complex controls on the engine, they’ll add more sensors. If they standardize on sensors, they can get costs down and reliability up.”

These changes are being matched by advances in sensor elements. Some suppliers are shifting to new types of magnetic sensors in powertrains because they are contactless.

“In contrast to Hall-sensor based systems, anisotropic magneto resistance (AMR) sensor-based systems offer very high accuracy, excellent linearity, and they are independent of magnet drifts and shifts over entire lifetime,” said Klaus Reinmuth, Senior Director Segment Marketing Automotive & Transportation at NXP Semiconductors. “In the context of drivetrain systems, they are a perfect fit for all kind of throttle and exhaust gas recirculation applications. Redundancy and functional safety requirements are covered by a dual sensor system in a one package approach.”

Some suppliers are adding new features as they also push to improve performance. Speed sensors, ancillary yet important powertrain components, are adding features to help designers build effective human machine interfaces.

“Speed sensors are becoming more accurate, jitter is being reduced,” said James Sterling, Manager of Integrated Sensors at Infineon. “Vibration suppression is a new feature, with some used on speedometers so that when the sensor sees oscillation, it doesn’t send a false signal to the controller.”

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