BRUSHLESS MOTORS AUTOMOTIVE APPLICATIONS
Motors are everywhere In-vehicle systems become increasingly more electromechanical from powered seat adjustment, electric window, power steering, HVAC fans, pumps, etc. In many of these systems one or even multiple motors are used as actuators. Various types of motors are in use, but specifically 3-phase brushless DC (BLDC) motors are gaining popularity as they provide important advantages: – Improved speed vs. torque characteristics – High dynamic response – High efficiency – Extended speed ranges – Long operation life BLDC m Automotive interiors still use brushed motors despite the obvious advantages of brushless, primarily because in current market there is a price premium for brushless motors.
The other option is Piezo Motors, but these are primarily designed for micro motion and not torque and thus in most cases not ideal for most automotive applications.
There are substantial advantages to brushless and when evaluated over an entire system the cost penalty could be a save.
Advantages of Brushless over brushed motors:
- Noise reduction.
- Very low vibration
- Reduced EMC concerns.
- Size & weight reduction.
- Features add through speed control.
- Reliability and quality.
- Integration of gear mechanism.
- Higher efficiency.
Basuic design requirements are capabity to operate through enviromental extremes of -40C to 85C with operating voltage from 8v to 16v – nominal voltage 13.2v.
Below is basic Bill of Material comparison between brushed and brushless:
From an economic point of view, a brushless DC motor should always be cheaper than a DC motor if designed for the same specification since it basically is a brushed DC motor without the brushes.
What make it more expensive are two facts.
- A brushless DC motor needs a controller
- A controller needs feedback from a sensor (usually hall or MR sensors)
To make brushless DC motors more economically viable, there are few solutions:
Centralize control and use a bus system: Cars have lots of electronics anyway and to add elements that allow the control of multiple motors throughout the car would not add a lot to the manufacturing cost of the electronics for the car. It would be almost unrecognizable. This can only be done by the system integrator who assures that the motors are compliant with his control scheme.
Use self-sensing coil technology instead of additional sensors:
- Depending on the motor manufacturing technology, sometimes it may just be easier and cheaper to use hall sensors, but today you can actually use the motor coils themselves to detect rotor position by back-EMF detection and therefore get rid of the sensors.
http://www.atmel.com/images/doc8012.pdf.
http://cache.freescale.com/files/product/doc/AN1914.pdf
- The sensor less control has the additional advantage of needing fewer connections. Additionally, you can use every BLDC motor also as a sensor. When there is more resistance to the movement you are trying to perform, the controller must increase the current to get the job done. This current increase is equivalent to the resistance the motor encounters. This way you can get force feedback by a simple current measurement. This could serve to replace pressure and other sensors that would otherwise be used in such cases.
Advantages over brushed motors:
- Quieter: spins at higher speed inaudible to humans.
- Reliability: no brushes that can break.
- Higher efficiency: no added resistance to current flow from brushes and lower electromagnetic emissions.
- Built-in electronics: smooth control over operating range, diagnostics, and configuration.
There is also a Sensor-Less Motor Alternative – No Hall Sensor, Only 3 wires (PWM) and Memory Position from number of rotor spins. Refer http://dare-auto.us/.
Dare Auto using Brushless Motor Technology developed solution for Automotive Powered Retractable Running Board with following Advantages:
- New feature – Wireless interface only needs battery & ground wires.
- New feature – Normal and express dual speed
- New feature – Obstacle detection
- Running change – Self-Contained
- 2x longer life
- 40% lower power consumption suitable for electric vehicles
- 8dB Quieter (~ 3 sones)
- Retrofits in the existing space with fewer wires
BLDC SLOTLESS MOTORS
Motor’s compact structure and low cogging allows slotless BLDC motors to achieve smoother operation at both high and low speeds, more accurate control, higher efficiency, and higher power density.
- Extremely quick response and high acceleration
- Quiet Operation
- High power density
- Wide speed range (up to 50,000 rpm)
- Long life
- Various winding options and customizations
- Modular design for better customization
A typical brushless BLDC motor is constructed using a stator with “slots”; a copper wire is then wound around these slots. Although this technology works well, it has an inherent problem with cogging (or drag torque), which presents a challenge in applications needing fast response, fast acceleration, and smooth operation.
To combat these issues, LIN Engineering has removed the slots from the motor. Instead of slots, we are using a unique process of winding the copper wire without the need of them. This drastically reduces cogging and improves the motor’s ability to respond, accelerate quickly, and operate smoothly. Slotless BLDC motors are also quieter and provide more power with a smaller frame size than their slotted counterparts.
Refer: LIN ENGINEERING SLOTLESS MOTORS
Below is another example of Dare-Auto Voltage Brushless Motor for Automotive Engine Cooling Fan. Key features are
- Motor Size: Stator diameter: 77mm / Motor Length: 86mm
- Rated voltage: 300V
- Motor Pole: 6; Motor Slot: 9; Y connection
- Rated Torque: 1Nm.
- Rated RPM: 2800
- Maximum efficiency: 86.5%
- Motor Performance Curves:
Brushless Gearmotors for Automotive Interiors
Gearmotors is a pairing of gear reducer and ac or dc electrical motor. The gear and the motors are combined into one unit.
A gearmotor delivers high torque at low horsepower or low speed. The speed specifications for these motors are normal speed and stall-speed torque. These motors use gears, typically assembled as a gearbox, to reduce speed, which makes more torque available. Gearmotors are most often used in applications that need a lot of force to move heavy objects. Advantages are many as they can simplify design and implementation by eliminating the step of separately designing and integrating the motors with the gears, thus reducing engineering costs. Precision gearheads paired with motors can meet high torque requirements. Another benefit of gearmotors is that having the right combination of motor and gearing can prolong design life and allow for optimum power management and use. They also eliminate the need for couplings and eliminate any potential alignment problems.
Advances in gearmotor technology include the use of new specialty materials, coatings and bearings, and improved gear tooth designs that are optimized for noise reduction, increase in strength and improved life, all of which allows for improved performance in smaller packages. More after the jump. Gearmotors can be simply a motor with a simple gear attached or as complex as incorporating bevel gears with a 90-degree hollow-shaft output. Refer https://www.designworldonline.com/gearmotors-classroom.
Gearboxes are designed to be quiet, but some are quieter than others. In some cases, metallic gears produce more noise than non-metallic gears, and helical gears tend to be quieter than spur gears. The noise from a gearbox is affected by the number of gear stages it has, the load on it and armature, or rotor, input speed. Some smaller parallel shaft and planetary gearboxes use a Nylon-type first stage gear to reduce noise and vibration. Worm gears are generally quieter than spur or helical gear reducers because they operate on a sliding action. Because the worm and gear teeth are under crushing rather than cantilever loads, and more teeth are usually in contact, worm gears have higher resistance to shock loads than spur or helical gearing. Refer https://www.motioncontroltips.com/5-design-considerations-gearmotor-application/
Micro Fans & Blowers for In-Car Venting: The Pelonis (www.pelonistechnologies.com) K5331-37 Series brushless blower is the one Design HMI is looking at for in car venting of potentially toxic fumes.
- Operates at voltages 12V & 24V
- Ball bearings to keep motor noise below 55 dBs’
- 5 CFM to 16.4 CFM
- Operating temperature: -10ºC ~ +70ºC so needs work for automotive interior temperatures which during transportation on hot days can be 115C.
Pelonis Technologies’ innovative Micro Fans and Blowers by using Axial Air-Gap Technology has developed Micro Fans and Blowers are smaller and more energy efficient than traditional blowers and have almost no power loss at higher temperatures. Automotive HMI Applications would be LED lighting, Displays, Micro Fuel Cells, Portable air-quality monitoring devices, Ventilation and defrosting and others.
Some of the largest micro fans available are about 30 millimeters wide, or about the length of a paper clip. The smallest micro fans may be about 15 millimeters wide, smaller than the face of a dime. Micro fans that use axial air gap technology, on the other hand, are not only much more compact, they are also more energy efficient. Additionally, they offer a longer operating life, and easily retain all their power, even at high temperatures.
There are several key differences between axial air gap technology and radial air gap technology. An air gap is the space between the rotor and the magnets in a motor. Whereas the flux in axial flux motors runs parallel to the output shaft, along the axis of the shaft, the flux in radial flux motors runs in and out from the center of the shaft, on the radius (perpendicular to the shaft).
Axial air gap motors differ from enclosed motors in that they are very short in length but relatively larger in diameter. Axial air gaps run on the same plane as the rotors. Typically called “flat” or “pancake” motors, these models are an ideal solution for manufacturers requiring compact motors in large batches. Axial flux designs are highly sought after for two main reasons. First, they have a higher torque due to their wide air gap area. They also have shorter flux paths, meaning they have fewer magnetic losses, which, in turn, result in higher torque and efficiency.
Refer https://news.thomasnet.com/featured/axial-air-gap-cooling-with-micro-fans
Also, you may want to upload paper on analytical model of axial air gap induction motors with solid rotors that includes the two-dimensional current distribution in the rotor.
Click https://ieeexplore.ieee.org/document/4252299/ for more information.
Per Pelonis the Axial Air Gap Technology fans are designed for Lower Profile / Energy efficient with power savings 20%~40% / No silicon steel stack resulting in no current loss / Lower startup voltage (< 2.5V) / Ingress Protection: IP57/IP58 No power loss at high temperatures / Highly modularized production process.
For more information on contact Pelonis Technologies at www.pelonistechnologies.com.
