Lift trucks with AC drive technology replacing conventional IC engine models

Jun 08, 2005

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For years the workhorse for industrial and commercial material handling of heavy loads has been the forklift with an internal combustion (IC) power plant.  Accepted as a necessary evil are the noise, emissions and performance limitations of conventional forklifts.  However, one of the most significant trends in the forklift industry is the increased use of electric-powered forklifts.  And, now that an 80-volt, 5000-6000 pound capacity truck is available, the applications arena for electric forklifts is limitless.

Twenty years ago, the ratio of forklift sales in the U.S. was 55 percent IC engine-powered and 45 percent electric-powered; and the electric vehicles were typically used for lighter duty applications.  Today, electric forklift sales are approaching 60 percent of the overall market.  The recent growth can be attributed to several factors, including performance and operational improvements, extended range of vehicle capacities, environmental and OSHA concerns and operating cost benefits.

Performance Enhancements
The general task of all material handling equipment is to move an item from “Point A” to “Point B”.  The advantage held by IC-powered forklifts is power -- the ability to move heavy loads quickly and efficiently over any terrain.  More specifically, they can climb ramps and grades, they can accelerate faster, they reach higher top-end speeds and they can lift loads faster.  Overall, they are regarded as the true workhorse of industry.

Recent advancements in electric forklifts with 48-Volt and now 80-Volt AC motors have generated alot of interest in the forklift market.  AC motors offer several advantages, i.e. high performance, reduced maintenance and improved energy consumption, to mention a few.  However, the load capacity limits for electric trucks have been a drawback.  Operators want the freedom (flexibility) to convey all loads with a single truck. 

In addition to advances in performance, operators are getting more comfortable with electric forklifts, realizing they are significantly more quiet and operate cleaner.  Also, there is less vibration transferred from the engine through the seat, floorboard and steering wheel.  Tests have shown reduced vibration keeps operators alert and less fatigued, especially in operations that require extended periods of forklift use.

Advancements In Detail
Several improvements and enhancements have increased the popularity of electric forklifts.  The switch to AC drive technology versus DC has provided several operational benefits, as well as environmental advantages.  Also, ergonomic controls and digital displays provide a more user-friendly vehicle.

An AC-powered pallet truck still uses a DC battery.  However, an inverter in the truck’s controller converts the DC current to three-phase AC current.  AC power is then delivered to the truck’s motor, controlling the speed and acceleration of the vehicle.  The end-user realizes the following benefits:

  • Higher Performance – AC motors allow for quicker speeds up to 12.5 mph, better acceleration and gradeability, and lift speeds up to 108 fpm.  Operators notice a faster and smoother response when changing from forward to reverse and vice versa.  This improvement in directional changes increases productivity output.
  • Reduced Maintenance – Unlike DC motors, AC motors do not have brushes, controller contactors needed for switching the direction of the motor rotation and motor commutators.  Fewer moving parts translates into reduced maintenance costs.  In addition, the elimination of brushes allows AC motors to be much smaller than comparable DC motors.
  • Improved Energy Consumption – One of the weak points of electric DC powered trucks has been the decrease in performance as the battery loses its charge.  An AC power system offers the control needed to maintain power, even as battery charge runs low -- up to 30 percent less energy consumption when compared to conventional trucks.

Typical AC systems recover battery energy using three forms of “regenerative” braking:  when the accelerator lever is released (coasting), when the brake is applied, and when the directional lever is operated (switch back or plugging).  Essentially, the inertia energy that is created by these actions is converted to electrical energy and returned to the battery, extending overall operating times and operating cycles.

 Industrial truck manufacturers are constantly searching for ways to meet the pending EPA clean-air regulations.  Using California as a model, where the California Air Resources Board (CARB) has set standards for emission limits, new trucks take a new approach to emissions.  Technical advancements for IC engine trucks, such as three-way catalytic converters have been designed to meet the standards.  However, electric trucks with their zero-emission capabilities provide the buyer with the ultimate solution to environmental concerns.

Apart from emissions, the elimination of “fuel” costs can add to acceptance of electric trucks.  For example, an electric forklift may cost $4 in electricity, whereas an IC forklift may need $10 in fuel to accomplish the same amount of work.  The initial costs of an electric truck with battery and charger may be higher, but the overall true operating costs over time will provide significant savings.

Electric vehicles have digital displays providing operators with instant information regarding the status of their vehicle condition.  Speedometer readings, battery discharge gauges, warning messages and multiple-hour meter readings are common on most trucks.  Using built-in analyzers and self-diagnostic capabilities, electrical forklifts with digital displays make troubleshooting quick and easy.
 
Electric Truck Example
A new line of AC-powered 80-volt electric 4-wheel sit-down forklift trucks that provide increased performance and handle loads up to 6,000 pounds are now available.  The vehicles reach travel speeds of 12.4 mph, lift speeds of 108 ft/min and offer a real alternative to combustion trucks, even when using heavy attachments.

The totally enclosed drive axle, which includes motors, gears and multiple disc brakes is completely maintenance-free.  Dust and moisture-protected axle and enclosed AC controllers in combination with super-elastic tires allow the truck to be operated indoors as well as outdoors without any compromise.

The new AC controller enables the truck to stop automatically on any gradient when the accelerator pedal is released.  For safety reasons, travel speed is automatically reduced when driving around curves.  Six-month or 1,000-hour service intervals drastically reduce maintenance cost due to missing contactors and brushes.

Five individually adjustable travel programs are avilable, from highest performance to energy saving.  Also, the AC truck consumes up to 30 percent less energy than conventional electric forklifts.

For more information on AC Travel Drive Trucks contact Jungheinrich Lift Truck Corp., 5701 Eastport Boulevard, Richmond, VA 23231, toll free phone 888-333-2644, phone 804-737-6084, fax 804-737-6316, www.jungheinrich-us.com.

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