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TORQUE-MOTORS as Actuators in Intake and Exhaust System

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Torque Motors

Ever increasing demands for greater environmental acceptability and less fuel consumption of vehicles as well as constantly new performance and comfort features are determining the development of the automotive industry today. As a result, the need for controls is increasing continuously. Efficient actuators are a prerequisite for precisecontrol. For such application fields, the Sonceboz Group has developed a the torque motor which sets itself apart owing to a particularly high torque, extreme compactness and optimal controllability for emission control applications.

Torque Motors as Actuators

in the Intake System

Torque Motors

1 Introduction

The Sonceboz Group develops, produces and markets innovative electromagnetic motors and drives as well as mechatronic systems. More than 25 million items are produced in series annually by the mother company Sonceboz. This market is growing because the number of electrically adjustable elements in vehicles is increasing constantly.

Besides stepper motors, torque motors have become a major sales item within the last few years. MMT developed the technical basis for this drive. MMT in Besançon, France, is 100 % part of the Sonceboz group. The research centre, with over 40 employees consisting mainly of engineers, generates most of its sales through license businesses and has above 200 patents altogether.

2 New Range of Functions for Electronic Drives in Vehicles

The market for the company from French Switzerland is continually growing, driven by the increased efforts of the automotive industry in the field of emission control. The standards in force are increasingly reducing the permissible emission of soot, CO2, NOx and HC compounds. The Euro 6 standards, that is expected to come into effect as from 2014, are forcing the automotive industry to use various control systems when dealing with fuel, air and exhaust fumes.

Additionally, given the steady increase of oil prices and the drive towards reducing CO2 emissions, there are increased efforts to minimize consumption. Components that are increasingly gaining importance for fast and precise solutions are electromagnetic drives. Such drives are also finding their place in comfort and safety solutions. As a result, over 160 electro-motors are used today in a vehicle of the premium class. Nevertheless, the environmental solutions are used in vehicles of any size.

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Torque Motors

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3.2 The Operating PrincipleIn the torque motor, the rotor (5-6) in Figure 1 moves over a sector of 75°. The interaction between the rotor magnet (5) and the stator electromagnet (1-3) produces a torque, the direction of which depends on the current polarity fed into the electromagnet. Hence, any position can be controlled by regulating the current, the rotor (5-6) stops in the position in which the drive torque and the sum of the resisting torques, e.g. air pressure or spring, of the application compensate.

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3 The Torque Motor

A special task is the positioning of valves and flaps, particularly in the area of air supply and exhaust removal. These components must often work under very harsh conditions and have to meet high standards of performance, reliability, force density and precision. Sonceboz developed the torque motor for such tasks and has been producing more than 15 million units since the year 2000. Several million are produced every year.

3.1 Advantages of the Torque Motor

The high torque vs. mass ratio optimizes weight and size. The peak to nominal torque ratio high and the torque output can be maximized for short time periods.•Since the torque runs proportional to the current, the regulation can take place by means of simple and conventional methods. •Very low detent torque makes it possible to use a minimized return spring and thereby to reduce the holding current.•The design as a direct drive provides for high reliability and service life. •The use of permanent magnets in the rotor and the possible integration of a contactless sensor enable a totally brushless solution. •The possible integration of drive and controller electronics enables a compact, intelligent drive system.

Figure 1 : Construction of the motor

Torque Motors

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3

4

5

6

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This is balanced by means of an axial ball bearing (4), Figure 1, that is the one of two sources of friction loss in the entire drive since no current has to be transferred to the rotor thanks to the arrangement of the coils on the stator. This minimizes the wear and potential for electromagnetic interference fields. The parallel force moves the rotor into the position where permanent magnet and electromagnet poles attract each other. This is a linear force in the simplified model, Eq.(1) :

Eq. (1)

In the actual rotary application, the torque is the product of force and average radius of the permanent magnet.

The working range in this linear model corresponds to the width of the ferromagnetic pole on the stator (3a) and is slightly less than the overall pole width.

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3.2.1 Operating Principle in the Linear Model

This working principle can be described by means of a linear model, Figure 2, in which the ferromagnetic stator made of iron, for example, has a row of three poles (3) protruding vertically from the base plate (1) like three teeth with an E-shape. A coil (2) is wound around the centre pole (3a).

Opposite this compound structure, comprising a coil and ferromagnetic poles, and separated by a thin air gap (E) is a permanent magnet (5) fixed to a ferromagnetic yoke (6). A force field results from the interaction between the fields produced by the permanent magnet and the electromagnet. Magnetic fields always interact towards a resulting state in which the field lines of both fields run in the same direction. The shortest way through the air is also physically preferred so that the field lines concentrate where the air gap is the smallest. In this way, the field is concentrated in the ferromagnetic alloy as much as possible. This interaction corresponding to the attraction between magnetic North and South poles at the rotor and stator consists of perpendicular and parallel component. The perpendicular force results from the attraction between the stator and rotors in order to minimize the air gap.

Figure 2 : Functionality in the linear model

Torque Motors

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Eq. (2) shows the direct proportionality between the control current and torque. The remanence of the permanent magnet is particularly important here (5). By calling on rare earth magnets, i.e. high magnetic energy density alloys, the performance of the torque motor can be maximized for given product dimensions and weight. This remains true as long as magnetic saturation is not reached, which in turn depends on the section and magnetic properties of the ferromagnetic parts. The magnetic saturation defines the range in which the torque no longer increases linearly with the current. In nominal operation, the torque remains constant over the operating angle, Figure 4.

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3.2.2 Operating Principle in the Motor

In the torque motor, this linear model is wrapped around a vertical axis: On the stator (1-3), four ferromagnetic poles (3) are wound around with coils (2), Figure 1 and Figure 3, in a similar fashion to the linear approach but with each pole wound around in alternating direction. This winding alternation produces a N-S-N-S pole pattern at the electromagnet (or S-N-S-N if the current polarity is inversed). The “curve width” in turn defines the operating angle (typically 70—75°). On the rotor (5—6) there is a permanent magnetic disk (5), which contains 4 poles in a circular changing order (N-S-N-S). It is fitted to the yoke (6), which serves the purpose of the mechanical assembly and of guiding the magnetic flux. This results in Eq. (2) , which defines the torque of the torque motor:

Eq. (2)

The factor of 8 results from the 4 magnetic transitions between the permanent magnet poles (m=4), i. e. the force defined in the linear equation operates four times.

Figure 3 : Cross-section of the motor

Torque Motors

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2 3

456

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The large ratio between nominal and peak torque gives the drive boost capacity. It is also possible to create a bistable actuating drive by adjusting certain parameters of the magnetic circuit so that a current-free residual torque is produced on the respective stroke ends. In a normal design, however, only a very low residual torque is produced in the current-free state with the result among other things, that the force of a return spring can be minimized. Stable and unstable positions are found each 90°, i. e. outside the working range. These positions are either unstable, namely where the torque slope is positive, and permanent magnet and electromagnet fields are in an opposite direction, or they are stable, where the torque slope is negative, and the fields are in the same direction.

Figure 4 :Typical torque vs. angle plots of a torque motor

3.3 Application-specific construction

Simple and precise regulation schemes can be designed, thanks to the linear relationship between torque and current. The actual challenge is the application-specific design of the motor, which apart from the permanent magnet (5) mentioned previously, comprises yoke (6), coil (2), magnetic pole (3), base plate (1) and air gap (E). As a result, specifications such as torque, geometry and mass can be taken into account. MMT laid the foundations for an actuator design by means of an optimized magnetic design. By systematic optimization based on the basic physical principles, it is possible to achieve a high torque density for which the magnetic remanence plays a particularly important role.

Torque Motors

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Motor Type 4236 4246 4256 4276

Angular stroke ° 75 75 75 75

Response time ms < 100 < 100 < 100 < 100

Sensor output signal V 0,5 - 4,5 0,5 - 4,5 0,5 - 4,5 0,5 - 4,5

Operating temperature °C -40 - +150 -40 - +150 -40 - +150 -40 - +150

Torque constant mNm/A 80 120 220 100

Resistance Ω 2,6 2,4 2,1 2,1

Peak torque at 13,5V mNm 360 600 1400 560

Weight g 320 430 640 330

This enables a high torque density of the motor, which makes a gearless compact design possible. This results in the data for the four basic motor series as listed in the Table.

4 Sensor Integration

In order to keep its construction as compact as possible, the motor has an integrated position sensor based on a contactless magnetic principle. In the practical construction, the sensor, Figure 5, comprises a disk permanent magnet (7) attached to the rotor yoke (6), Figure 1 and Figure 3.

Torque Motors

Figure 5 :Construction of the sensor

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Table: Main parameters of the torque motor family

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A Hall-effect-ASIC (9) is mounted on a printed circuit board in the sensor cover. The design is such that the direction of the magnetic induction (or field) of the sensor magnet lies in the plane of the ASIC. It rotates with the rotor, and both planar components are sensed by the Hall-effect-ASIC, and computed to yield the position angle. The sensor therefore converts the position into voltage by means of magnetic induction. The voltage signal is sampled by an A/D converter in the controller, which continuously compares it with the specified position, and drives the torque motor coils by means of a power H-bridge. The controller and drive operate under 12 V. A 5 V voltage is required for the sensor.

5 Applications

The compact and contactless design of the torque motor with an integrated sensor is well suited for use in the emission control systems for instance, which requires exceptional resistance to temperature and vibration as well as a high degree of resistance to o harsh environment. Additionally, the entire motor can also be encapsulated in plastic. This moulded casing encapsulates the coils, helps dissipate heat, protects against the harsh environment and has the function of a bearing for the rotor shaft as well. The production process takes place on fully automatic production lines that guarantee high quality and cost efficiency.

Sonceboz itself designed the special production tools and process for the most part. At the end of this process, each fully encapsulated motor leaves the assembly line and its functions are tested automatically. In the meantime, the number of torque motors produced at the factory in Sonceboz is a million fold. They are used for controlling exhaust gas recirculation valves, throttle flaps and adjustable turbochargers, for example, Figures 6 through 10. The Swiss company is convinced that the systemic advantages of torque motors and the ever-increasing number of electronic drives in automotive and automation engineering indicate that the quantity and market share will continue to grow in the future.

Torque Motors

Torque Motors

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Dr. Marc-Olivier André

Business Unit Manager Engine Controls

marc-olivier.andre@sonceboz.com

Author

Figure 10 :Torque motor with adjus-table turbocharger for passenger carFigure 8 :Torque motor with diesel

throttle for passenger car

Figure 6 :Torque motor with dual poppet for medium-duty

Figure 7 :Torque motor with EGR valve for medium- and heavy-duty

Dr. Richard ARLOT

Asia Marketing Manager

rarlot@movingmagnet.com

Contact JSAE 2009