DN Staff

August 25, 1997

12 Min Read
Engineering Productivity Kit - Power Transmission

Compact transmissions bring maneuverability to home mowers

Eden Prairie, MN--Peek beneath the housing of a zero-turn-radius lawnmower and you're likely to find a hydrostatic transmission. It's been that way for years, and it's likely to remain that way for as long as anyone can foresee.

Nevertheless, there's a new twist in the zero-turn-radius lawnmower market. And the chief agent of that change is the seemingly static hydrostatic transmission.

Using a new breed of smaller, simpler, less costly hydrostatic transmissions, engineers are taking zero-turn-radius mowers out of the realm of the professional groundskeeper and into the garages of homeowners. That's good news, especially for homeowners with large lots, because zero-turn-radius mowers can dramatically reduce the time needed to mow expansive lawns. Some users claim they can cut an eight-hour job to a mere four hours using a zero-turn-radius mower. Others say that zero-turn-radius enables them to dispense with special trim mowers for hard-to-reach places, because these mobile mowers can turn on a dime and reach virtually any spot.

"There's always been great interest in these machines among commercial cutters, " notes William Lowe, director of marketing for Snapper, Inc., McDonough, GA. "The reason is that the zero-turn-radius reduces your mowing time because it maneuvers faster."

The most common technique for creating a zero-turn-radius machine is to connect two right-angle transmissions together. The two right-angle transmissions provide both steering and propulsion, and, more importantly, create a machine that can articulate around its own transaxle.

Up until recently, however, this type of power arrangement was too costly for most homeowners to afford. Part of the high cost was attributable to the use of the two right-angle transmissions. But with the introduction of simpler, more compact versions, such as Eaton Hydraulics' Model 778,cost has dropped low enough for homeowners to take advantage of the technology.

Eaton's Model 778 accomplishes all that through integration of its hydraulic pump, motor, and gear train. This integration provides the unit with "plug-and-play" capabilities. "When customers receive it on the assembly line, they attach a linkage and simply bolt it in place," explains William Byrd, Eaton's chief engineer for light duty hydrostatics.

As a result, the assembly time normally required to install three separate components, along with related plumbing, is eliminated. The integrated design fits neatly in a program of "least installed cost" for the customer, Byrd says. In most cases, Eaton engineers believe they can cut the customers' installed cost for the unit by at least 15%.

Key to the success of the Model 778 design is the use of a planetary gear train and a radial pump/motor combination. In comparison to the spur gears often used for such applications, the planetary gear set offers greater compactness that translates to less material use, which lowers cost. And the radial pump uses less components than axial piston pumps, which are also commonly used in hydrostatic transmissions. The overall result: simpler manufacturing and lower cost.

For companies such as Snapper, use of the Model 778 has alleviated much of the conventional assembly line complexity. Used on the Snapper Yard Cruiser, the hydrostatic unit eliminated the need for independent hydraulic motors at the drive wheels. It also eliminated the need to run dedicated hydraulic lines to the wheel motors and to bolt a hydrostatic pump to the mechanical gear box.

As a result, Snapper executives report that they can produce about three times as many mowers in a day as they could using stand-alone components. And the unit's performance "is as good as those of the split systems."

"It's functionally is the same as a large zero-turn-radius transmission," notes Gale Maddy, marketing group leader at Eaton Corp.'s Hydraulics Division."But we're able to package it smaller and scale back the costs to meet the needs of the competitive market."

In addition to the Snapper Yard Cruiser, Eaton's unit has been employed on the EZ Rider mower, made by Ariens Co., Brillion, WI. Most of the 16 or so major manufacturers of lawn equipment, including Toro Co. and Dixon, make zero-turn-radius machines for the home market. By some estimates, manufacture of zero-turn-radius machines has increased 25% in the past two years.

"There's good reason for the popularity," Lowe says. "They're fun to drive, easier to operate, and they take less time. When you combine all those features, you create consumer interest."

SmartMotor focuses on performance, reliability, simplicity

David Benson, Electronic Project Engineer Baldor Electric Company

Fort Smith, AR--The Baldor SmartMotorTM is the first product to integrate an adjustable speed inverter control with an industrial motor in one package. This innovative design represents a standard in Matched PerformanceTM for the drive (motor + control) industry.

The motor is a Baldor TEFC (Totally Enclosed, Fan Cooled), Super-E premium efficient AC induction motor with a specially designed winding and insulation system. A Baldor inverter specifically designed for motor-mounted applications connects on top of the motor.

The Baldor SmartMotor is available in NEMA standard frame sizes, from 1 through 10 hp at 230 or 460V, and in NEMA 1 and NEMA 4 enclosure types. All ratings are UL and cUL approved.

Matched Performance is a commitment by Baldor for motor/control compatibility and to provide tested performance data for the drive (motor + control). Integration of the motor and control into one package takes Matched Performance another step. The parameters necessary for optimum performance in variable torque or constant torque applications and protection of the Baldor SmartMotor are preset in the control. The control protects the motor with a timed current overload (I2t) that is approved by UL so no motor overload sensors are necessary.

With the short distance between the inverter and the motor winding, the amplitude of voltage spikes at the motor terminals is minimized, and the enclosure acts as a shield, eliminating the potential for radiated EMI/RFI noise from the motor leads. Besides the Matched Performance advantage, motor/control integration also provides a simple, cost effective installation and requires no panel space for the control.

The Baldor SmartMotor is not a micro inverter bolted to a motor. Instead, Baldor designed a specific control to withstand the excessive temperatures, vibration, and EMI experienced by the electronics in a motor-mounted application.

Cooling for both the motor and the electronics is provided by a patented method using the fan mounted on the shaft of the motor. The highly integrated IGBT power module uses a DBC (Direct Bond Copper) substrate that is preferred over an Insulated Metal Substrate (IMS) when thermal stress is the dominant design factor, as in this case. The module was designed for motor-mounted applications and withstands the vibrations and extreme thermal stress.

Cylindrical cavities in the electronic housing secure the bus capacitors in place and help remove heat from their cores. With the high temperature-rated capacitors and a dc choke, the lifetime of the inverter is greatly increased in extreme operating conditions. Additional advantages of the dc choke include reduction in input harmonics, improved input power factor, and a 1% minimum line impedance compared to the competition's requirement for 3%.

The Baldor SmartMotor gives the industrial drives market a reliable product with guaranteed performance. Similar to Baldor's wall-mounted controls and motors, the Baldor SmartMotor provides Matched Performance, all in one package. Focusing on reliability of the product, engineers designed a specific control to withstand exposure to vibration and thermal stress, while remaining easy to install and simple to operate. Design validation testing and comparison tests on competitors' units have confirmed that our focus on performance, reliability, and simplicity delivers a superior product for our present and future customers.

Integrated Motor Drive cuts installation costs, saves space

Dave Peiffer, Design Engineer TB Wood's Incorporated

Chambersburg, PA--Wire runs from inverters to motors have increased dramatically with recent changes in industrial plant design. Control panels often are installed hundreds of feet from motors doing the work. This scenario presents a host of power quality problems for the motor, in addition to the heat load introduced when putting an inverter in the control cabinet.

The solution is simple: move the inverter out of the cabinet and onto the motor it drives. But this remedy presents its own challenges. Under the guidelines of NEMA (MG1) specification and the IEC, motor profiles must meet standard dimensions. Mounting the inverter on top of the motor housing, as some manufacturers do, may render the assembly non-compliant. Yet the MG1 specification does offer some flexibility, as it does not define the length of the motor.

The Integrated Motor Drive (IMD) from TB Wood's takes advantage of that opening. It integrates the inverter into the end of the motor.

Inverters generate heat, as does the motor. When the inverter is mounted on top of the motor, cooling can become a problem, especially at continuous low-speed operation when the cooling comes from a shaft-driven fan. The TB Wood's IMD solves this problem by integrating a dc-powered fan into the end of the inverter to provide consistent cooling.

When the IMD is installed in applications requiring control of electromagnetic or radio frequency interference (EMI/RFI), filters can be easily integrated right onto the motor, with a slight increase in size of the power junction box. The IMD can therefore be brought into compliance with the CE mark.

Separating the power from the control also simplifies and allows enhancements to the control of the IMD. A simple swap of the standard input/output (I/O) interface allows use of DeviceNet, Modbus Plus, Interbus S, Profibus, or future network connections.

In typical material handling, a single power bus feeds many IMDs, which are controlled through a network interface, allowing for a clean, low-cost installation. This installation is further simplified via design flexibility: IMD's I/O interface can be mounted in the F3, F2, or F1 positions. The IMD can also be foot-mounted or flange-mounted.

The IMD's two main components are an inverter-duty motor and a totally redesigned XFC inverter. The motor frame sizes range from a 48 to 184T for a power range of 0.5 to 5 hp.

Input power can be single-phase to three-phase, 200-460V, depending on the model. Future releases will feature 115V single-phase and higher-horsepower ranges.

Operating speed range is 20:1, with an overload capacity of 110% continuous, and 150% for 60 seconds of constant torque.

Vibration and other environmental factors may cripple some integrated inverter motors, but the IMD is designed to withstand the same rigorous use to which a motor is normally exposed. To prevent vibration damage, the inverter assembly is filled with epoxy. With the inverter rated at NEMA 12, the entire IMD satisfies the Totally Enclosed Non-Vent (TENV) standard.

The IMD employs the same keypad as other TB Wood's inverter products. The deceptively simple design uses eight buttons and a backlit alphanumeric display to control and monitor commands and operating parameters. Step-through configuring makes set-up and operation straight forward, while sensors and software allow fault determination and data rending.

TB Wood's engineers set out to integrate motor and control in a single, streamlined package that meets or exceeds the standards that designers must consider for industrial applications. By achieving that goal with the IMD, Wood's developed a unique solution that reduces the cost of installation and saves space at the same time--simplifying two challenges that all designers face.

Products to watch

Brushless linear servo motors

The Solution series of brushless linear servomotors is designed for applications requiring smooth motion, high accuracy, quick acceleration, and greater stiffness. Designed by engineers at Airex Corp., Dover, NH, it uses patented technology to produce true unit-to-unit repeatability and zero cogging. A very strong magnetic field is created using high temperature rare earth magnets attached to highly permeable magnetic backiron. The magnet track is designed to maintain high mechanical stiffness while allowing flexibility in mounting.
Airex Corp., Route 108, Dover, NH 03820, FAX: 603-742-0977.

Rollfeed controls and servo drives

High speed precision rollfeed controls and ac servo drives from Indramat are designed to meet the performance needs of metalforming applications. They offer precise, closed-loop, high performance motion control with pre-defined inputs/outputs and diagnostic/status messages in multiple languages. The product line includes compact single-axis control for small rollfeeds, a standard single-axis control with jerk-limiting and S-curve acceleration, and one- or two-axis synchronized rollfeed control with registration, measuring wheel, tool gagging and loop control capabilities.
Indramat, 5150 Prairie Stone Parkway, Hoffman Estates, IL 60192, FAX: 847-645-6201.

Induction motor designed for easy mounting

A new size 34 ac induction motor conforms to NEMA MG 7 frame standards. It allows for easy mounting into customer equipment or drop-in replacement into existing systems. Designed by Eastern Air Devices, the motor features a flange mounting complete with pilot, making it compatible with standard mounting brackets and gearboxes, and allows for precise shaft alignment with other machine components. Shaft dimensions are compatible with a variety of industry standard accessories, such as pulleys, couplings, and gears.
Eastern Air Devices, Inc., 1 Progress Drive, Dover, NH 03820, FAX: 603-742-9080.

Air cylinders simplify mounting

A new line of medium-duty cylinders offers a unique design that allows for equipment to be mounted to four tapped holes at each end of the cylinder. The same four holes can be used to add a detachable mounting, making the cylinder interchangeable with the NFPA medium-duty cylinder standard. Designed by engineers at Advanced Machine & Engineering, the Series CA cylinders are available in bore sizes ranging from 1.5 inches to 12 inches for use with up to 250 psi air. A separate series, known as Series CCA, also offers integral rod clamps.
Advanced Machine & Engineering Co., 2500 Latham St., Rockford, IL 61103-3963, FAX: 815-962-6483.

Did you know...

...motor quality and reliability is the most important factor in selecting a motor/drive supplier, according to a recent Design News survey?

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