Part 2: Motors and Air-Moving Devices
Pumping Technology into New Products

by Jill Russell, Assistant Editor

To differentiate their products and present customized options to consumers, appliance producers are developing dishwashers using the latest motor technology.

OEMs and suppliers agree that the use of d.c. motors helps bring intelligence and efficiency to appliance applications while increasing the performance level of the product. Two appliance makers have recently integrated the technology into their dishwashers—one using a brushless permanent magnet d.c. (PM-BLDC) motor the other choosing a high-voltage permanent d.c. (PMDC) motor, each providing consumers distinct features.

Johnson Electric’s high-voltage PMDC motor provided Electrolux with a solution that was more cost effective than traditional induction and synchronous motors typically used in dishwasher applications.

With the help of motor supplier Johnson Electric, Electrolux was able to produce a dishwasher that provided increased washing pressure, versatility regarding power and speed, and energy efficiency.

Appliance maker Arçelik (Istanbul, Turkey) recently started using a variable-speed, PM-BLDC motor in its dishwashers after using the technology in its washing machines for several years. According to a paper by Songül Bayraktar, mechanical engineer, and Orhan Diril, R&D specialist and electrical engineer, the most evident benefits in using the variable-speed control in the dishwasher were improvements in consumption values, cleaning performance, and the operating noise level.

Another appliance maker is achieving similar results. With the help of motor supplier Johnson Electric (Hong Kong, China), Swedish appliance maker Electrolux enhanced its dishwasher performance by creating an entirely new motor, stepping away from traditionally used induction motors. Engineers from both Johnson Electric and Electrolux decided that in order to meet consumer needs, the new motor had to feature variable-speed, high torque speeds, and greater efficiency. The answer, according to Johnson Electric, was a high-voltage PMDC motor.

Optimizing Performance Features

Both Arçelik and Johnson Electric say the use of a d.c. motor is innovative in dishwasher applications and provides several options and features to consumers. “PM-BLDC motors provide variable wash pressures or flow rates,” Ms. Bayraktar and Mr. Diril write in their paper. “Adjusting spray pressures regarding the requirements of the washing step allows for water conservation. Together with the high-energy efficiency of the motor and the possibility of reducing wash power at certain wash steps, considerable reduction in energy consumption is obtained.”

Turkish appliance maker Arçelik has integrated a variable-speed drive system with a PM-BLDC motor into its dishwashers, which the company was previously using in its washing machines.

Johnson Electric used a program to replace induction and synchronous motors with a high-voltage PMDC motor to create a versatile water pump in Electrolux’s Frigidaire brand of dishwashers. This, according to the supplier, made the new dishwasher versatile and efficient. “The design allows some washes to be completed in 50 percent less time than the normal cycle,” T. George Walkden, director of New Accounts Development for Appliances of Johnson Electric explains. “Because of the ability of the motor to provide more washing power, in some applications, the design allows some washes to be completed in four cycles instead of five, thereby reducing the need for an extra cycle in addition to using less water and less electricity.”

Both Arçelik and Johnson Electric say cleaning performance has also improved with the use of PMDC motors. This is achieved with changeable spray forces. According to the companies, the ideal cleaning performance can successfully remove food and debris from plates and tableware, while at the same time, gently cleaning more delicate glassware.

In Arçelik’s new dishwasher, glasses are washed with low jet pressures to prevent scratches, while pots and pans are cleaned with high jet pressures to remove harder soils. According to Ms. Bayraktar and Mr. Diril, the variable-speed pump motor combined with an alternating spray system allows the unit to wash crystals and pans in the same program.

Johnson Electric adds that typically, dishwashers have a water pressure limit, and pots and pans do not get completely cleaned. However, in Electrolux’s dishwasher, the variable-speed motor helps to clean even the dirtiest objects. “A speed-controlled motor/pump adds a new dimension to the washing cycle,” Mr. Walkden says. “By controlling the power of the water jets, as well as temperature and duration, the machine could be made suitable for all loads, from the most delicate bone china to the toughest cooking pans.”

Both Arçelik and Electrolux say their dishwashers achieve quiet operation with the use of the PMDC motors. Arçelik’s dishwasher features several operating modes, including a “night” option that reportedly reduces splash and motor noises without increasing the cycle time. “The motor has no hum at 50 to 60 Hz so the noise level of the machine decreases,” Ms. Bayraktar and Mr. Diril say in their paper. The “fast” option, they add, “increases the mechanical effects and, therefore, shortens the soil removing time and decreases the program duration with an increase in energy consumption.”

Electrolux says that reducing the noise level of its product was traditionally a challenge because all motors using a.c. power will create a “hum” due to the harmonics and base supply frequency. “The use of a large capacitor to smooth the rectified current succeeded in damping out most of this low-frequency hum in the PMDC motor,” Mr. Walkden says. Since the motor used in Electrolux’s application contains brushes, the supplier said it matched the geometry and material of the brush to the geometry and surface finishes of the commutator. This, combined with the capacitor, helped reduce the overall noise levels and also increased motor reliability as it reduced brush wear.

In addition to the “mix wash” mode, Arçelik’s dishwasher, also features a “night” option that is said to reduce the overall noise of the cleaning cycle. A “fast” option is said to shorten the cleaning time while increasing energy consumption.

The Technology Behind the Performance

The use of PM motors is also said to help increase the energy efficiency of the appliance. “Permanent magnet motors do not consume electrical power to excite a magnetic field, so there are no excitation losses resulting in a substantial increase of efficiency,” according to the paper by Ms. Bayraktar and Mr. Diril. “Compared with conventional motors, PM motors yield higher torque or output power per volume unit, have a better dynamic performance, and are better controlled.”

According to Ms. Bayraktar and Mr. Diril, in a variable-speed drive, the main requirement is to regulate the speed with an electronic control system over a wide range. Arçelik says its dishwasher employs an additional electronic control system with speed feedback for a precise control loop. In addition, the variable-speed drive system can be adapted to regulate the speed of the dishwasher pumps by using the PM-BLDC motor. In the drive system, a power converter is deployed as an interface between power supply and motor. According to the paper authors, the power converter can be considered two parts—the power electronic converter and the control electronics.

“ The power converter ensures the phase windings to be driven in proper sequence by appropriate currents,” Ms. Bayraktar and Mr. Diril state. “Timing of the sequence must be determined according to rotor position. To achieve this, accurate rotor position information is needed that may be provided either directly by a sensor (magnet or optical) coupled to the rotor or indirectly without sensors by evaluating electrical parameters such as current and voltages.” Ms. Bayraktar and Mr. Diril also believe that using a sensorless control is more advantageous, as there are no additional costs and the part’s reliability is increased, as no connecting cables are used as with control electronics.

However, the authors say that with a sensorless control, hardware and software for the rotor position estimation can become more complex, especially under loads when special measures are needed to ensure smooth rotor propellation. Through the use of a cost-effective microcontroller with the electronic unit, Arçelik says it has developed a system that produces information regarding the rotor position.

Another benefit of using its PM-BLDC motor, according to Ms. Bayraktar and Mr. Diril of Arçelik, is its contribution to the safety system of the machine. “Some abnormal conditions are detected via a drive system,” the engineers write. “From this aspect, the motor serves as one of the safety sensors of the appliance.”

For Electrolux, its motor produced greater efficiency in terms of percentages of output to input power. “Unlike many induction motors or synchronous motors, the high-voltage PMDC motors can boast efficiencies reaching 80 percent to 90 percent of output power to input power,” explains Mr. Walkden.

Electrolux and Johnson Electric say they also have achieved higher efficiencies in addition to achieving other features and benefits in its dishwasher. Electrolux said it wanted a motor solution that was capable of a high-starting torque to overcome the static friction of seals. According to Johnson Electric, a high-voltage PMDC motor design develops its greatest torque at stall or start-up and could produce more than enough torque to drive the pumps through full start-up resistance.

Also, the supplier says its motor achieves higher working speeds. “Unlike induction and synchronous motors whose speed is determined by the supply frequency (60 Hz in the U.S. and 50 Hz in Europe), the PM motor can be designed to have relatively high no-load and working-load speeds,” Mr. Walkden explains. Johnson Electric also says its high-voltage PMDC motor achieves higher ratios of output power to volume and weight, consequently increasing the performance of the product at a better cost. “The need for less material combined with the economy of scale created by a mass-producer yields a cost-effective motor,” Mr. Walkden says. “The total cost of a high-voltage PMDC motor with rectifiers is lower cost than an induction or synchronous motor with controls.”