Motion Control Advances Move Transportation Forward
By Spencer Chin, Senior Editor

Driven by the need for greater fuel efficiency and concern over greenhouse emissions, automobiles, trucks, and buses are demanding more efficient motors and motion control systems to run functions such as steering and braking. Motion control manufacturers are responding with motors able to generate higher torque in a smaller envelope, in turn allowing vehicles to reduce weight and operate with greater fuel efficiency. To help achieve these goals, manufacturers are turning to advanced drive systems that recover otherwise wasted energy to cut gasoline consumption. They are also employing advanced software algorithms to optimize motor performance parameters, and using intelligent sensors in vehicles to correct for performance deviations that could adversely affect operator control and safety.

Midwest Motion Components’ MMP-TM55-12V-GP52-059 gearmotors use planetary gears to boost operating efficiency.

Light weight is a key driver in many vehicle applications, according to Randy Cordes, President of gearmotor supplier Midwest Motion Components, Watertown, MN. “A common denominator seems to the need to limit physical size and weight. Despite the fact that the application duty’s requirements are typically intermittent, the successful solution must possess high peak torque capacities, while maintaining compact size and light weight. So, efficiencies become imperative, with regard to both motor and gearhead efficiency.”

According to Cordes, Midwest Motion employs lightweight, planetary gears in its motors, such as the MMP-TM55-12V-GP52-059, which achieve operating efficiencies as high as 80 to 90 percent. By contrast, motors with spur, worm, or other gearset designs produce efficiencies as low as 35 to 40 percent.

Reducing weight in a vehicle motion control system cannot come at the expense of environmental ruggedness, according to Russ Strobach, Global Target Market Manager for the Parker Automation Group of Parker Hannifin, Cleveland, OH. “Removing nitrous oxide is a key requirement in diesel engines; unfortunately this adds weight. And, vehicle engine components must be environmentally rugged, able to withstand temperatures down to -40 deg F.

Motion components in vehicles must often operate for long, continuous periods. “A city transit bus typlifies this environment,” said Keith Hallenback, Sales Manager for Ametek Motors, Paoli, PA. “In general, these vehicles go 18 hours a day, 365 days a year. Not many systems are taxed like that. That combined with extreme environments - salt, dirt, grease, extreme temperature, high pressure washers. Vehicle electronics have to be properly cooled, and sealed against high-pressure washes and caustic degreasers.”

Besides environmental concerns, vehicles are also subject to harsh electrical conditions. Hallenback noted that vehicle electrical systems, which typically operate on 27Vdc, must ensure short-term transients as high as 80 to 100 V. “Electrical loads on a bus are getting higher, so efficiency and startup current are often strictly mandated. One of our customers mandates a soft-start feature through pulse width modulation.”

Ametek’s Dura-Tek motor, for transportation applications, integrates drive electronics and includes intelligent onboard control.

Hybrid Vehicles
Advances in motor technology are most evident in power trains used in the growing number of hybrid vehicles, which combine a gasoline engine with an electric motor. A regenerative braking system recovers lost energy help power the vehicle.
Hybrid-electric cars like the Toyota Prius and the proliferating number of hybrid-electric buses are the most visible examples of these technologies, but other vehicles requiring high start-and-stop applications are going to hybrid drives as well. Parker Hannifin has refined a hybrid drive for refuse trucks based on its Proprietary Drive Unit. The system has an onboard controller that coordinates pumps, hydrostatic motors, and accumulators to power the vehicle when in hydrostatic mode during start-and-stop operation when collecting refuse. Accumulated energy from the vehicle’s braking system is stored and is used to power the truck each time it accelerates. The PDU transfers from hydrostatic drive to mechanical drive as the truck reaches highway speed.

According to Parker, the hybrid drive system has achieved fuel savings of 30 to 50% during testing and field trials of refuse collection cycles.

Motion control component suppliers are improving the design of their parts in other ways to reduce weight and cut size. One is magnetics. “The use of high-energy, rare earth magnet materials is instrumental in providing a high-torque to size/weight ratio in dc motor/gearmotor assemblies,” said Midwest Motion’s Cordes. “The ability to provide various motor windings also helps, especially where limitations exist on the amount of current available to the motor.”

Rare earth motors has benefitted race cars used by Newman/Haas/Lanigan Racing – the race car team the late actor Paul Newman was active in. The team’s racing cars use rare earth, brush-type dc motors, from Maxon Precision Motors, Fall River, MA, in weight jacker assemblies that help raise and lower the cars’ rear ends. The rare earth magnets help maximize motor torque in a small frame size – considered key to aiding racing performance. The motor-driven weight jackers enable race car drivers to make adjustments without removing their hands from the steering wheel.

To cut space needs, motor control component suppliers are increasingly integrating and modularizing functions, enabling the OEM to have a complete control solution. For instance, Parker developing a module for a bus kneeling system that controls the actuators that lower buses, motor coaches, and RVs for easy access. The module houses four pneumatic valves that inflate and exhaust air bags mounted on the vehicle axis. Parker’s standard 22mm, grommet-style P2F Series mobile solenoids actuate the valves.

The modules are also favored by transit agencies wishing to minimize the number of vendors they must deal with. “Transit agencies want one solution that fully integrates the drive, brushless motor, pump, fan, blower, and compressor,” said Hallenback. “Value-added assembly is essential to the transportation market.  If you all do is a brushless motor or drive, you can’t participate in this market.”

One of Ametek’s integrated products is its Dura-Tek motor, designed for high duty cycle transportation equipment applications. It features integrated drive electronics and intelligent onboard control, including protection from overcurrent, locked rotors, reverse polarity, transient overvoltages, and overtemperatures. The brushless dc motor generates continuous torque from 19.7 to 55 oz-in. and speeds from 2,927 to 4,400 rpm.

Sensor Advances
Sensors are playing a greater role in vehicle motion control systems. Incorporating intelligence into sensors is a key component in advanced vehicle control systems. “Many of today’s transportation applications require sensors with a higher degree of accuracy, stability, and durability,” said John Pindroch, Business Development Manager for encoder supplier BEI Duncan Electronics, Irvine, CA. “The higher degree of accuracy and stability enables the OEM to design and consistently produce a final product with improved response. An example would be a steering angle sensor with improved accuracy and stability on a steer-by-wire system.”

Pindroch added, “Smart sensors are one of the single most important improvements to the motion control industry. These sensors are improving the OEM’s ability to make huge strides in the reliability and cost of implementing motion control in vehicles. Smart sensors can pre-process measurements, communicate digitally over a data bus, control their sensing elements, make decisions on the information they are gathering, and maintain, monitor, and allow changes to their calibration and configuration settings.”