October 2008 Electric Power Steering (EPS) with GMR-Based Angular and Linear Hall Sensor Application Note V 0.1 Sensors Edition 2008-10-23 Published by Infineon Technologies AG 81726 München, Germany © 2007 Infineon Technologies AG All Rights Reserved. Legal Disclaimer The information given in this document shall in no event be regarded as a guarantee of conditions or characteristics. With respect to any examples or hints given herein, any typical values stated herein and/or any information regarding the application of the device, Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind, including without limitation, warranties of non-infringement of intellectual property rights of any third party. Information For further information on technology, delivery terms and conditions and prices, please contact the nearest Infineon Technologies Office (www.infineon.com). Warnings Due to technical requirements, components may contain dangerous substances. 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Electric Power Steering Electric Power Steering (EPS) with GMR-Based Angular and Linear Hall Sensor Revision History: 2008-10-23, V 0.1 Previous Version: Page Subjects (major changes since last revision) We Listen to Your Comments Any information within this document that you feel is wrong, unclear or missing at all? Your feedback will help us to continously improve the quality of this document. Please send your proposal (including a reference to this document) to: [email protected] Application Note 3 V 0.1, 2008-10-23 Electric Power Steering Table of Contents Table of Contents Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1 1.1 Electric Power Steering with GMR-based Angular Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 2.1 EPS Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 EPS Electric Control Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3 3.1 3.1.1 3.1.2 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 Infineon Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Infineon Angle Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 TLE5011 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 TLE5012 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Infineon’s Linear Hall Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 TLE4990 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 TLE4997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 TLE4998P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 TLE4998S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 TLE4998C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4 Rotor Position Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Steering-Angle Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6 Torque Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Application Note 4 V 0.1, 2008-10-23 Electric Power Steering List of Figures List of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 EPS Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 EPS Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 EPS Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Possible setup for rotor position detection (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Possible setup for rotor position detection (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Additional angle error vs. motor-speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Excitation signal of one coil vs. rotor position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Possible Setup for Steering-Angle Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Torsion Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Torque Sensor - Rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Torque Sensor - Stator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Torque sensor - Concentrator with Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Application Note 5 V 0.1, 2008-10-23 Electric Power Steering List of Figures Application Note 6 V 0.1, 2008-10-23 Electric Power Steering Electric Power Steering with GMR-based Angular Sensors 1 Electric Power Steering with GMR-based Angular Sensors 1.1 Introduction Power steering is a system for reducing the steering effort on cars by using an external power source to assist in turning the wheels. Electro Hydraulic Power Steering (EHPS) is an advanced system that uses conventional hydraulic power steering with an electric motor-driven hydraulic pump. Electric Power Steering (EPS) is the latest system in which the electric motor (“E-motor”) is attached directly to the steering gearbox without a hydraulic system. Sensors detect the motion of the steering column and a processor module applies assistive power via an electric motor. This allows varying amounts of assistance depending on driving conditions. With electronic systems becoming more and more common in cars, EPS is the future power steering system that they will use. Unlike its conventional counterpart, EPS is active only during the actual steering process. It also eliminates maintenance on steering hydraulics and cuts fuel consumption by as much as 0.4 l/100 km. 2 EPS Systems Different EPS systems are in use (see Figure 1). Column Type Pinion Type Dual Pinion Type APA Rack Type Source: IQPC Advanced Steering Systems, ZF Lenksysteme, Dr.G.Ruck, May 2006 Figure 1 EPS Systems Which EPS type will be used depends on the steering rack force (see Figure 2). The column drive is used for small and lower mid-sized cars. The motor is located in the passenger compartment. Its advantage is its better performance at reduced temperatures, and sealing. The pinion drive is used for mid-sized cars, and the dual pinion drive is used for upper mid-sized cars. Both of these drives are located in the engine compartment. Another possibility is the rack drive. This type is appropriate for large vehicles such as Sports Utility Vehicles (SUVs) and trucks. Application Note 7 V 0.1, 2008-10-23 Electric Power Steering EPS Systems Steering Rack Segments Force [N] Car SUV/Trucks Upper Segment Upper Middle Segment Middle Segment Lower Middle Segment Small Car Mini 15000 14000 13000 12000 11000 10500 10000 9500 9000 8500 8000 7500 7000 6500 Column Pinion Dual Pinion APA - Rack With advanced steering technology Servolectric with 12V Source: IQPC Advanced Steering Systems, ZF Lenksysteme, Dr.G.Ruck, May 2006 EPSc high … Figure 2 EPS Application 2.1 EPS Electric Control Unit Each EPS Electric Control Unit (ECU) handles the data from different sensors. The sensors send information about the steering torque, driving speed, and the steering angle. Figure 3 is an example of a block diagram of an EPS ECU. Using this information from the sensors, the ECU calculates the necessary steering assist and controls the 3-Phase Driver. +12VRail 2x TLE5011/12 XC866/8 Torque Sensor Torque TLE5011 TLE4998 Differential Hall IC Speed Tracker TLE4250/51 8-Bit Microcontroller XC866 (optinal) Steering Angle Sensor Interface 8-Bit Microcontroller SupplyICs TLE 6361 TLE 6389 TLE4941/42 Fail Safe 16-/32-Bit Microcontroller 3-Phase Driver IC TLE 7183F TLE 7189F TLE 718X Steering Angle Sensor Electric Power Steering ECU Rotor Position TLE5011/12 Current Sense (Shunt Substitute ) 2xTLE4990/98 XC2364 Master CAN/LIN Transceiver TLE6251DS/G, OptiMOS-T 40V IBP180N04S3 -02 IBP180N04S3 -H2 x6 Rotor Position TLE6258,6285G HS-CAN-Bus Figure 3 EPS Block Diagram Application Note 8 V 0.1, 2008-10-23 Electric Power Steering Infineon Sensors 3 Infineon Sensors 3.1 Infineon Angle Sensors Infineon offers some angle sensors based on GMR technology. This section gives a short overview of Infineon’s angle-sensor portfolio. For more detailed information, please refer to the products’ individual datasheets. 3.1.1 TLE5011 The TLE5011 is a 360° angle sensor that detects the orientation of a magnetic field. This is achieved by measuring sine and cosine angle components with monolithic integrated GMR elements. The data communications are accomplished with a bi-directional SSC Interface that is SPI compatible. The sine and cosine values can be read out. These signals can be processed digitally to calculate the angle orientation of the external applied magnetic field. This calculation can be easily done by using a COordinate Rotation DIgital Computer (CORDIC) algorithm. It is also possible to connect more than one TLE5011 to one SSC Interface of a microcontroller for redundancy or any other reason. In this case the synchronization of the connected TLE5011 is done by a broadcast command. Each connected TLE5011 can be addressed by a dedicated chip-select pin. 3.1.2 TLE5012 The TLE5012 is also a 360° angle sensor. Compared to the TLE5011, this sensor calculates the absolute angle on chip with an implemented CORDIC. This angle value and additional register values can be read out with a bidirectional SSC Interface that is SPI-compatible. A Pulse-Width-Modulation (PWM) protocol and an Incremental Interface are also implemented. An angle error smaller than 1.0° will be achieved over temperature and lifetime using an internal autocalibration algorithm. This autocalibration is only helpful in applications with an angle range more than 360°. The sensor calculates the calibration parameters and updates the new parameters within a timeslot or within the following angle range. A revolution counter is also implemented within the TLE5012. This counter counts every full rotation. It is a 9-bit signed value, so ±256 revolutions could be measured. 3.2 Infineon’s Linear Hall Sensors Infineon offers a variety of linear Hall sensors with different programming, package and interface options. This section is a general overview of our sensor portfolio. For more detailed information, please refer to the datasheets for each product. Table 1 Overview of Infineon’s linear Hall sensors Product Programming Package Interface TLE4990 Fuses PG-SSO-4-1 Analog TLE4997 EEPROM PG-SSO-3-10 Analog TLE4998P EEPROM PG-SSO-3-10 PG-SSO-4-1 PWM TLE4998S EEPROM PG-SSO-3-10 PG-SSO-4-1 Digital, SENT TLE4998C EEPROM PG-SSO-3-10 PG-SSO-4-1 Digital SPC Application Note 9 V 0.1, 2008-10-23 Electric Power Steering Infineon Sensors 3.2.1 TLE4990 The TLE4990 is Infineon's basic linear Hall sensor with analog signal processing and fuse programmability. The sensor is end-of-line programmable, meaning that its gain and sensitivity can be set in a two-point calibration in the module. Due to its thin PG-SSO-4-1 package, it fits in small air gaps. The TLE4990 has been field-proven over the last few years and is well established for automotive applications such as gas-pedal position sensing. 3.2.2 TLE4997 The TLE4997 has been designed to improve on some of the shortcomings of an analog compensation scheme as the one used in the TLE4990 and most competing products, including offset and sensitivity drifts over temperature, range of the programmable parameters, and accuracy. The signal processing in the TLE4997 is entirely shifted to the digital domain, making the influence of the programmed parameters completely deterministic. Temperature effects of the Hall probe can readily be compensated for by pre-calibration in Infineon's fabrication. The TLE4997 is also the first sensor on the market that offers independent, programmable parameters for both first- and secondorder temperature coefficients of the application sensitivity. The TLE4997 has an analog, ratiometric output and can be used as a robust replacement for potentiometers. It comes in a small 3-pin PG-SSO-3-10 package and is therefore suited for use in the limited space inside magnetic circuits. 3.2.3 TLE4998P The TLE4998 family is the successor of the TLE4997, providing innovations on the interface side. The signal processing concept is based on the TLE4997 design, offering high-precision analog-to-digital signal conversion and a deterministic digital signal processing. The TLE4998P features a PWM interface in which the duty cycle carries the Hall signal information. It offers 12-bit resolution on the output, and combined with accurate detection on the microcontroller side, is more accurate than an analog interface. 3.2.4 TLE4998S The TLE4998S is equivalent to the TLE4998P except for the interface, which is implemented as SAE's1) Single Edge Nibble Transmission (SENT) standard. SENT offers a low-cost alternative to CAN and LIN, but still incorporates a coded digital signal transmission with a Cyclic Redundancy Check (CRC) to check the validity of a transmission. Apart from an industry-leading 16-bit Hall value, the transmitted SENT frame includes 8-bit temperature information and 4-bit sensor status information. The status information finally allows for a massive improvement of overall system safety. 3.2.5 TLE4998C The TLE4998C features a Short PWM Code (SPC) protocol, which is an extension to the standard SENT protocol and therefore has all the advantages already present in the TLE4998S such as high resolution, status, temperature, and CRC information. The sensor does not, however, send out the measured values indefinitely, but only after being triggered by the ECU. This functionality permits synchronized transmission of data. The protocol makes it possible to select one of four sensors, which are connected to a single bus line. 1) SAE: Society of Automotive Engineers Application Note 10 V 0.1, 2008-10-23 Electric Power Steering Rotor Position Sensor 4 Rotor Position Sensor The rotor position is very important for correct commutation of the motor, independent of the motor type (Permanent Magnet Synchronous Motor (PMSM); Brush Less Direct Current (BLDC); Asynchronous Motor (ASM)). For detection of rotor position, a TLE5011 or TLE5012 could be used as depicted in Figure 4 a.Figure 5. Pinion Gear EC-Motor Magnet Sensor Figure 4 Possible setup for rotor position detection (1) EC-Motor Pinion Gear Magnet Sensor Figure 5 Possible setup for rotor position detection (2) The angle information tells the system which coil has to be excited next. The angle detection has to be done very fast. Depending on the number of poles used and the rotation speed, an additional error has to be considered for the electrical commutation, which is depicted in Figure 6. With one pole pair, the electrical 360° (one period) matches the mechanical 360° (one rotation). With a rotor with two pole pairs, the switching in the coils has to be done two times faster. This means the electrical period must be completed within a half rotation (Figure 7). Application Note 11 V 0.1, 2008-10-23 Electric Power Steering Rotor Position Sensor Additional Angle Error vs. Application Speed (Sensor Update Rate = 80µs) 100 Angle Error [°] 10 1 0,1 PP=1 0,01 100 PP=2 1000 PP=3 PP=4 PP=5 10000 100000 Motor-Speed [1/min] Figure 6 Additional angle error vs. motor-speed Excitation Signal of one coil with 1 polpair Excitation Signal of one coil with 2 polpairs Mech. Angle 0° Figure 7 360° 180° Excitation signal of one coil vs. rotor position Application Note 12 V 0.1, 2008-10-23 Electric Power Steering Steering-Angle Sensor 5 Steering-Angle Sensor The steering angle indicates where the driver wants to go. This information is also used by other systems such as the Electronic Stability Program (ESP), Active Front Steering (AFS), Adaptive Front Lighting (AFL), and so forth. The steering-angle sensor unit is mounted on the steering column, mostly within the passenger compartment. It is important to determine an angle value at power-on. This true power-on functionality is achievable by the nonius principle. This is patented by Robert Bosch GmbH; Figure 8 shows an example of how one might build such a steering-angle sensor. Source: 2nd Advanced Steering Conference; Ms. Schiebel; May 2007 Figure 8 Possible Setup for Steering-Angle Sensor This module consists of three gear wheels. One hub gear wheel is mounted on the steering column and represents the steering angle ϕ. The two smaller gear wheels differ by one or more teeth, and there is a magnet in both of them. These magnets, with diametrical magnetization, each rotate above an angle sensor. Due to the different number of teeth, one gear wheel turns faster than the other one. The two measured angle values have the following output characteristics Figure 9: Gear wheel ψ andθ [°] 360° 360° Figure 9 720° 1080° 1420° Absolute measuring rangeφ [°] Output With this principle it is possible to determine an unambiguous steering angle over more than four full turns of the steering wheel. In addition, no standby current is needed. At every startup the sensor knows its position as a result of having both angle values. Application Note 13 V 0.1, 2008-10-23 Electric Power Steering Torque Sensor 6 Torque Sensor The power-steering control unit uses a torque sensor as the main input for determining the amount of steering assistance needed. The steering column is split into two parts: The input shaft, from the steering wheel to the torque sensor; and the output shaft, from the torque sensor to the steering shaft coupler. The input and output shafts are separated by a torsion bar (Figure 10), where the torque sensor is located. The torque sensor measures the shift angle between input and output shaft. One possible torque sensor from Moving Magnet Techologies (MMT) is described below. Please note that this design is covered by a patent1) and should give only an idea how to implement torque sensing with linear Hall sensors. Input Shaft Output Shaft Torsion Bar Figure 10 Torsion Bar The sensor by itself is split into two parts, the rotor and the stator. The rotor, a multipole magnet ring, is mounted on one side of the shaft (Figure 11). Multipole Magnet Ring Figure 11 Torque Sensor - Rotor The stator consists of two parts. They are made of soft ferromagnetic material, and are mounted on the opposite side of the torsion bar (Figure 12). Stator Figure 12 Torque Sensor - Stator 1) US patent 2004-0011138 Application Note 14 V 0.1, 2008-10-23 Electric Power Steering Torque Sensor To detect the shift angle, a stationary fixed concentrator is necessary. This concentrator also contains the linear Hall sensor and is put over the stator (Figure 13). When torsion occurs between input and output shaft, a flux variation is detected by the sensor, which is proportional to the shift angle. This information is processed by the EPS ECU, which controls the EC motor via the 3-Phase Driver IC Sensor (e.g. TLE4998) Fluxconcentrator Stator Figure 13 Torque sensor - Concentrator with Sensor ----------------------------------------------------------------------------------------------------------------------------------------------------Infineon Technologies AG und Infineon Technologies Austria AG leisten keine wie immer gearteten Garantien und übernehmen keine wie immer geartete Gewährleistung für die übermittelte(n) Informatione(n). 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