Higher Value Engineering than Resolvers! TMR Angle Sensors as Advanced Solution for E-Motor
As environmental awareness grows and the realization of a sustainable society becomes increasingly important, the mobility market is witnessing an active movement towards “EV adoption," aiming to transition from gasoline-powered to electric-powered motor vehicles. In order to realize higher performance electric vehicles (EVs) and electric motorcycle, next-generation electric motor technology that balances factors such as high efficiency, high reliability, compactness, light weight, and cost performance at a high level is required.
In this article, we make a comparison of angle sensor technologies
responsible for detecting rotational angles in traction electric motor (hereafter referred to as e-motor) control and explain how our TMR angle sensors enhance your design.
Motor control technologies required in electric mobility
E-motor, serving as a power unit, plays a crucial role in the proliferation of electric mobility and is required to balance efficiency and performance.
Highly efficient e-motor reduce energy consumption and extend battery life. This enables long-distance travel on a single charge, improving user convenience. Low noise and vibration characteristics also provide a comfortable ride and minimize operating noise and vibration.
Angle sensor technologies required in e-motor
Angle sensors as rotary angle detector of e-motor assist the accuracy and efficiency of vehicle control systems, requiring the following elements:
Highly accurate angle measurement: Angle sensors must function reliably and accurately even under extreme vibration and temperature changes ranging from -40°C to 150°C. This allows the vehicle's motor control system to operate accurately, ensuring safety and efficient operation with minimal power loss.
Low power consumption: It helps to reduce overall power consumption of the vehicle and extend driving distance. It contributes to energy efficiency and is essential in battery-powered vehicles where power resources are limited.
Compactness and lightness: It enhances the design freedom and overall efficiency. This allows for more flexibility in e-motor design and better use of space.
Redundancy: In case one angle sensor fails, double or quadruple redundancy may be required to keep the motor functioning.
Cost efficiency: The suitable price for mass production is also one of the key factor in the highly price competitive electric mobility market.
Challenges in angle sensors
Resolvers and inductive angle sensors are currently mainstream, but they have several challenges.
Firstly, the high cost is one of the significant problems of resolvers. The complexity of the design and the difficulty in manufacturing these sensors, along with high material costs, lead to an overall increase in expenses. Furthermore, the fee of encoder licenses used in conjunction with the sensors and the expenses included in the R/D converter are also additional burden. Resolver and inductive sensors are not scaling in system cost well as they always need a full set of components.
The next issue is the size. Resolvers require a high-inertia metal target during rotation and take up space due to the use of coil systems. Inductive sensors consist of three or more coils on PCB and a metal plate attached to the shaft to cover them, limiting further miniaturization. The large number of components also poses a disadvantage from the perspective of failure rate.
Magnetic sensors are also used as alternative solutions, but they face challenges in magnetic noise resistance. They react to the strength and direction of magnetic fields, so external magnetic noise can interfere and make accurate detection difficult without shielding.
These challenges prevent the evolution of angle sensor technology and require a new approach.
TMR angle sensors as solution and comparison with other sensors
TMR* angle sensors are the optimal solution to solve these challenges. They are a type of magnetic sensors that detect the direction of a magnet's magnetic field, allowing for high-precision detection of rotation angles and enabling efficient control.
*TMR: Tunnel Magneto Resistance
Please take a look at the differences from the conventional angle sensors.
| Resolver | Inductive | TMR Sensor (On-axis) | TMR Sensor (Off-axis) | |
|---|---|---|---|---|
|
|
|
|
|
| Detection Method | Electromagnetic Induction | Electromagnetic Induction | TMR Effect | |
| Cost | High (RDC IC & Excitation circuit necessary) |
Medium | Low (System BOM, Imprementation) |
|
| Size & Weight | Large & Heavy | Medium | Small & Light | |
| Stray Field Immunity (SFI) Robustness | Good | Good | ・Intrincically robust with multiple sensors (Sensor arrays) ・ Reduction with magnetic shielding |
|
| Accuracy | High | Good but inferior | High | |
| Power Consumption | High | High | Low | |
| Redundancy | Significant cost impact | Possible | Possible | |
| Layout Flexibility | Off-axis only | Off-axis only | ・On-axis and Off-axis possible ・Very simple design changes to adapt to application needs |
|
The benefits of TMR angle sensors are as follows:
- Cost: System cost is very low due to small circuits and low requirements for signal conditioning and signal processing.
- Size & Weight: It maintains an advantage of compactness and lightness even with a magnet besides the IC. (Resolvers require excitation coils and output coils on the stator side and electromagnetic steel plates on the rotor side, which increase size and weight.)
- Stray Field Immunity Robustness: Although angle detection is influenced by external magnetic fields, using multiple sensors and performing correction calculations can improve resistance to such disturbances.
- Accuracy: Even when you use the sensor in off-axis placement, accuracy can be enhanced by using multiple ICs.
- Power Consumption: No current application is needed beyond the IC. (Resolvers require current for excitation and output coils, leading to higher power consumption.)
- Redundancy: Redundancy can be easily achieved by using multiple ICs.
Features and benefits of TDK's TMR angle sensors
TDK's TMR angle sensors boost top-class angle accuracy in the magnetic sensor industry and offer a compact lineup specialized for automotive applications. Compared to other magnetic sensor solutions, they exhibit extremely stable output characteristics over a wide temperature range, eliminating the need for temperature correction processing and contributing to simplified system design.
Achieving high accuracy with angle precision below 0.15°: They achieve an accuracy of ±0.15 degrees in analog output and ±0.05 degrees in digital output, allowing for the observation of absolute values over 360 degrees immediately after installation. This high controllability reduces energy loss due to noise and vibration caused by phase shifts.
Compact packages contributing to the miniaturization, weight reduction, and cost reduction of the entire system: They achieve the the compactness such as TSSOP-8 (6.4 x 3.0mm) and QFN16 (3.0 x 3.0mm). The target magnets are also very small and lightweight, making them easy to integrate even in space-constrained environments, thereby increasing design flexibility and enabling efficient product development.
ASIL compliant redundancy: They provide stable performance over a temperature range of 40 to 150°C. With analog and digital output products suitable for redundant design, they are ideal for traction motors requiring ultra-high-speed rotation. They also support dual MCUs, with separated electrical domains, supporting operation during failures and ensuring high motor operability.
Unique method of external magnetic field noise cancellation: We propose a method to suppress external magnetic field noise signals using multiple sensors and consult you on magnetic shielding methods. The samples of evaluation boards are available as development support, which is highly useful for engineers.
Building on these evaluated features, we have maintained a track record of mass-producing automotive-grade products since 2014.
Product lineup
TDK offers a diverse product lineup ranging from analog output to digital output.
[Note] Supported standards
Functional Safety: ISO 26262 (TAD214x supports ASIL-B, and TAD4140 supports ASIL-D at the system level)
Reliability: AEC-Q100 Grade 0, MSL1
Assembly: AOI (Wettable Flank)
Summary
In this article, we addressed the challenges and solutions of angle sensors that support the high performance and efficiency of e-motors. TMR angle sensors are not only highly accurate but also cost-effective, playing a crucial role in the proliferation of electric mobility. Additionally, our sensors are produced using 100% renewable energy-derived electricity, contributing to the realization of a sustainable society from the production side. There are also product lineups that were not introduced in this article, so please feel free to contact us through the contact form below for further details.
If you have any questions about the products or requests for samples or evaluation boards, please contact us via the "Contact Form" below.
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