Gear selection in mid-range cars

Article By : Hannes Birk, Sigmund Zaruba

The authors show how TLE493D-W1B6 sensor provides precise and energy-efficient 3D magnetic field detection in mid-range cars.

« Previously: 3D measurement of magnetic fields for gear selectors
 

A magnetic 3D sensor is very useful in detecting the position of the gear selector in an automobile as the existing ‘state-of-the-art’ solution, which uses at least six Hall switches, can be replaced by a single 3D sensor. Because the TLE493D-W1B6 has the same case dimensions as modern Hall switches, a great deal of space, as well as money, can be saved.

Using a gear selector for a current mid-range car as an example, here we will evaluate how the 3D sensor provides an alternative to the current solution.

Figure 4: Gear selector realized with six Hall switches (left) and a single 3D magnetic sensor (right). See larger version of the figure here.
 

Figure 4 (left) shows six gear selector positions on a circular arc at intervals of about 6 °. The original gear selector is detected by means of a Hall switch in each of the six selector positions. These six Hall switches can be replaced by a single TLE493D-W1B6 3D sensor (Figure 4 right).

For a robust magnetic design, the following parameters should be used:

• Magnet shape: Cuboid shaped (7 x 5 x 3 mm)
• Magnet material: NdFeB
• Remanence: 1 T
• Sensor: TLE493D-W1B6
• Air gap between sensor and magnet: 4mm
• Magnetization: Axial
• Lever arm: 1.3cm
• Swept angle: 0 … 30°
• Six positions result in a resolution of 6° per position

The parameters above allow linear behavior between the mechanically deflected angle and the calculated spherical angle Theta (Ɵ). The spherical angle is calculated from the sensor’s x, y, and z components (Figure 5). This allows the angle to be determined unambiguously, which in turn enables an unambiguous determination of the selector position. An application note is available here.

Figure 5: Unambiguous position determination with a 3D magnetic sensor.
 

Functional safety

The TLE493D-W1B6 is also equipped with test functions that make possible malfunction detection during operation, allowing the complete sensor signal chain to be assessed at any time. The test delivers a defined value that the microcontroller can compare with the expected value. If the expected value is obtained, the master does not need to initiate further measures. Test times are significantly lower than 1 ms.

Alert function

A further intelligent feature of the TLE493D-W1B6 is the magnetic field alert. For all three magnetic field directions, a corridor can be determined in milliTeslas for magnetic field strength. The magnetic field is cyclically measured in the set mode and compared with this corridor. If the measured magnetic field value remains within the corridor in all three directions, the sensor suppresses the interrupt signal. If the measured magnetic field value exceeds the upper corridor value or falls below the lower one, the sensor initiates an interrupt and wakes up the microcontroller (Figure 6). When the master (microcontroller) becomes active, it reads out the magnetic field values from the registers. The corridor can be set for all three axes at any time and independently of each other. This allows the thresholds to be adjusted in reaction to changes in mechanical positions.

Figure 6: Magnetic field corridor (top) for the magnetic field alert function.
 

Using the magnetic field alert means that the entire microcontroller system can be set to sleep mode, with the sensor only waking the microcontroller and the connected systems when the magnetic position indication changes. This enables the development of systems that save a great deal of energy, but are nevertheless capable of reacting quickly to a change in position.

Summary

The TLE493D-W1B6 sensor provides precise and energy-efficient 3D magnetic field detection for various applications. Flexible operating modes offer dedicated and scalable system designs with a wide measurement range for precise position determination and very low power consumption. The integrated magnetic field alert can wake up the microcontroller systems in order to inform them of a change in position.

About the authors

Hannes Birk studied electrical engineering at the Constance University of Applied Sciences, Germany and earned an MBA from the TiasNimbas Business School, Netherlands. He is responsible for 3D magnetic sensors and linear Hall sensors at the Automotive Division of Infineon Technologies in Neubiberg, near Munich, Germany.
 

Sigmund Zaruba studied physical engineering in Munich, Germany. He has been with Infineon Technologies for 15 years as an application engineer and is currently responsible for 3D magnetic sensors and Hall switches at the Automotive Division of Infineon Technologies, Neubiberg near Munich, Germany.

This article was sponsored by Infineon Technologies.