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Ergonomic Design, Improved Operation, and Increased Lifting Capability are Key Elements in the Latest Model of Hydraulic Forklifts.

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Mechanical Engineering 121(03), 60-63 (Mar 01, 1999) (4 pages) doi:10.1115/1.1999-MAR-3

This article describes that ergonomic design, improved operation, and increased lifting capability are key elements in the latest models of hydraulic forklifts. More supportive seats and touch-sensitive hydraulic controls are among the ergonomic innovations that Mitsubishi engineered into its latest generation of forklifts. Mitsubishi forklift engines are equipped with hardened steel valve inserts and automatic valves to extend their reliability throughout the length of their performance life. The Mitsubishi designers worked on improving the operator's ability to see through the forklift truck's mast, the structure that carries the forks, by repositioning the hydraulic cylinders and the multiplying chain. Outdoor forklift trucks, also known as rough terrain lift trucks, have been undergoing a change as well. These vehicles offload pallets of bricks, concrete blocks, insulation, and lumber delivered to construction sites. An operator mounts the Manitransit forklift on the rear of a trailer by inserting its forks into the truck's sleeves so that it can be transported to and from unloading sites. The forklifts give drivers full visibility because the telescopic boom needs no mast that might obstruct the view over the forks and load. The boom is mounted low on the truck to ensure a clear field of vision.

Hydraulic Forklifts are used just about any place where something heavy has to go from here to there. They are a staple in factories and warehouses, where they transport everything from automotive engines to rolls of paper. Models designed for outdoor use haul loads ranging from concrete blocks on construction sites to sacks of feed on poultry farms.

All these vehicles depend on the tradition al strengths of hydraulic power: smooth, precise movement delivered by a compact machine.

When you describe them, most of them sound pretty much alike. Indoor forklifts, for instance, typically use a liquid propane or gasoline-burning engine, mounted in a rugged steel frame. The truck is equipped with two front driving wheels, and two rear steering wheels. The forks in front are used to engage the load for transport. A hydraulic pump activated by the truck's engine powers the hydraulic cylinders that move the forks.

Engineers install a Counterweight in the back of the truck-a cast-iron weight equal to the forklift capacity-to balance the vehicle when it is bearing a load.

So what can a forklift manufacturer do? After all, to prosper in any field, a marketer has to distinguish its line of products. To hone their competitive edge in the materials equipment handling market, manufacturers are designing vehicles that are easier to operate, can lift heavier loads, and can reach farther for them.

For example, in October 1998, Mitsubishi Fork lift America Inc. of Houston introduced two series of forklift trucks for indoor applications, and touted their enhanced driver comfort and increased lifting capacity. K-D Manitou Inc. of Waco, Texas, introduced its Manitransit TMT Series forklifts in February 1998 as a design to simplify and extend forklift reach for outdoor cargo offloading.

Mitsubishi Forklift Trucks estimates that it supplies approximately 20 percent of the counterbalanced forklift truck market in the United States and Canada. One of Mitsubishi Forklift Trucks' new series is designated FGC15K through 30K; the forklifts handle loads of 3,000 to 6,000 lbs. The other series, FGC35K through 70K, lift between 7,000 and 15,500 lbs.

More supportive seats and touch-sensitive hydraulic controls are among the ergonomic innovations that Mitsubishi engineered into its latest generation of forklifts.

Grahic Jump LocationMore supportive seats and touch-sensitive hydraulic controls are among the ergonomic innovations that Mitsubishi engineered into its latest generation of forklifts.

Operator comfort and holding the line on cost were the two prime drivers of the smaller forklift truck family, according to Mike Burdick, mechanical engineer and general manager of the product development, design, and testing department for Mitsubishi Forklift Trucks. Bottling, electronics, food, and automotive parts manufacturers are among the major industrial sectors that use the 3,000- to 6,000-lb. forklifts.

"Finding out what our forklift customers want is the biggest challenge in designing new models," Burdick said. "Our goal is to add features that customers want at a price they can afford."

He said the company had gleaned information from dealers and customers in surveys and during training that guided the development of the new forklifts. "We form partnerships with suppliers, and keep a sharp eye on manufacturing processes to keep the costs down," Burdick said.

The Mitsubishi designers worked on improving the operator's ability to see through the forklift truck's mast, the structure that carries the forks, by repositioning the hydraulic cylinders and the multiplying chain. "We also narrowed and deepened the cross section of the uprights that form the structure and spaced them wider to further improve the operator's field of vision," said Burdick.

Mitsubishi Forklift Trucks developed new seats with better bolsters on the side than previously used to support the driver laterally, and to provide better lumbar support. Because carrying a load often blocks a driver's forward vision, the forklift is frequently driven in reverse. To that end, the seat is contoured so that an operator can steady himself by gripping the seatback while facing the rear of the vehicle. Touch-sensitive hydraulic controls were mounted on the engine cowl for the driver's comfort.

Forklift operation frequently requires the operator to dismount to read load tags, mark a load, and the like, so an open step was cut into the side of the new forklift to make it easier for the operator to get on and off. Previous models had no such step and were harder to enter and leave.

"We added a tilt steering column like a car so that the truck can better accommodate different-sized operators more comfortably," noted Burdick.

A convenience tray that can hold a beverage cup, pencils or markers to do paperwork, and a plastic clip to hold papers in place is located to the right of the driver. "We had these trays injection molded, which is expensive to tool, but keeps the cost of the piece part low," Burdick explained.

Mitsubishi forklift engines are equipped with hardened steel valve inserts and automatic valves to extend their reliability throughout the length of their performance life.

Grahic Jump LocationMitsubishi forklift engines are equipped with hardened steel valve inserts and automatic valves to extend their reliability throughout the length of their performance life.

In addition to ergonomics, the new forklift trucks were also designed with an eye toward performance and efficiency. Models FGC15K through 25K, which lift 3,000 to 5,000 lbs., are equipped with Mitsubishi Heavy Industries' 46-horsepower, 2.0-liter 4G63 engine. The FGC20K through 30K models, which lift 4,000- and 5,000-lb. loads, use the 2.4-liter, 57-hp MHI 4G64 engine. All the trucks are equipped with a balanced crankshaft that is supported by five main bearings to enhance smoothness and durability. The engines' semispherical combustion chamber and cross-flow valve ports make them more fuel efficient, while hardened steel valve inserts and automatic valve lash adjusters extend reliability over the life of the engine.

Gear-type hydraulic pumps, protected in the truck chassis, power the forks and the steering system. The hydraulic control valve contains an integral flow divider to provide priority flow to the steering system in order to maintain precise steering control. Mitsubishi Heavy Industries also designed the power shift transmission and drive axle. It matched the torque converter and axle ratios to the engine torque and horsepower curves to optimize overall powertrain performance and reliability.

A heavy-duty steer axle protects the steering cylinder from debris. Tapered roller bearings support cast-iron steer knuckles contained in the axle housing.

In the case of its newly introduced 7,000- to 15,500- lb.-capacity forklifts, Mitsubishi's goal was to modernize a 10-year-old design. This included improving the appearance, performance, and durability of the vehicles, as well as enhancing operator comfort while maintaining affordability of the trucks, which serve the lumber and paper industries. In the former application, the trucks are equipped with forks to move wood products. The forks are replaced with clamps so that the trucks can lift multiton rolls of paper.

The Mitsubishi engineers borrowed some of the ergonomic features of its smaller forklift trucks for the larger models, including improved mast visibility, an open step, a supportive, contoured operator's seat, and a tilt steering column.

A major difference between the new Mitsubishi large lift trucks and their predecessors is that their capacity was raised to 15,500 lbs., from the 12,000 for past models.

Company engineers increased the capacity of the new trucks by lengthening their wheelbase from the 62 inches of the smaller models to 70 inch es, and widening wheel diameters from 22 inches to 28. They also added a two-speed transmission in the 13,500- to 15,500-lb. models, which feature automatic shifting.

Engineers added a heavier counterweight and bigger hydraulic cylinders to handle the larger loads. Pressurized, self-centering gears and bushings in the hydraulic pump maintain the requisite clearance to provide volumetric efficiency.

The steel truck frame is a box construction to provide rigidity while minimizing stress. Engineers equipped the trucks with a V-shaped rear brace to support the steering axle and protect the radiator, hydraulic pump, and hydraulic lines. Mitsubishi integrated tilt cylinder mounts in the forklift truck frames to lessen the impact of shock loads-for example, from running into something-by distributing them over a larger surface.

Mitsubishi engineers altered the design of the larger forklift truck frames so that they could be manufactured at the company's own Houston factory. This facility turned out 7,000 forklift trucks in 1993, before a major expansion (begun the following year and completed in 1998) raised output to more than 20,000 trucks per year.

"We had previously contracted out the building of our large forklift frames to another company," Burdick said. "Machining was required after these frames were welded together. Because the frames are so large, machining after welding was expensive. Our new design frames are welded together by robot and are designed so components can be bolted on without further machining."

A General Motors 4.3-liter V6 engine gives the FGC35K and FGC70K forklifts 92.5 hp and 2,220 lbs.-ft. of torque for their more than seven-ton loads. The gasoline-fueled models are equipped with an electronic governorth at improves performance in the high-rpm ranges when the driver is lifting or traveling quickly.

Mitsubishi engineers repositioned the hydraulic cylinders and the multiplying chain to improve the operator's field of vision while driving the new FGC15K through FGC30K forklifts. They can handle loads of up to 6,000 lbs.

Grahic Jump LocationMitsubishi engineers repositioned the hydraulic cylinders and the multiplying chain to improve the operator's field of vision while driving the new FGC15K through FGC30K forklifts. They can handle loads of up to 6,000 lbs.

Manitou engineers extended the range of their Manitransit telescopic forklifts so that they could reach pallets stacked on the opposite side of a trailer.

Grahic Jump LocationManitou engineers extended the range of their Manitransit telescopic forklifts so that they could reach pallets stacked on the opposite side of a trailer.

Outdoor forklift trucks, also known as rough terrain lift trucks, have been undergoing a change as well. These vehicles offload pallets of bricks, concrete blocks, insulation, and lumber delivered to construction sites. In addition, they handle sod for landscapers, animal feed for farmers, seed for plant nurseries, and wrecked cars for fire departments.

K-D Manitou Inc. introduced its Manitransit Truck Mounted Telescopic (TMT) Series of truck-mounted telescopic forklifts in February 1998, aimed at reducing the costs of truck offloading. K-D Manitou, which was known as K-D Manufacturing Co. before it was acquired in 1986 by Manitou B. F. of Ancenis, France. The French firm has been manufacturing rough terrain lift vehicles since 1953, and ships its products to more than 85 countries.

The Manitransit TMT trucks combine a conventional forklift with a crane to provide freedom of movement and reduce overall handling costs. Mounting a permanent crane on a truck generally requires expensive modifications; the crane can complicate handling and reduce deck area. The crane is restricted to offloading in the immediate vicinity of the truck. In addition, cranes are relatively slow, and it is difficult to uncouple cranes from the truck.

Manitou designed its Manitransit forklifts to mount on the end of a freight truck's trailer for transport to the offloading site. The forklift is removed to offload and remounted when the job is completed.

To mount the forklift rig onto the trailer, the lift operator inserts the forks into the trailer truck's sleeves and uses the Manitransit's own forklift to raise its wheels off the ground. The driver straps the forklift to the truck and connects its running lights to the trailer via a cable.

When unloading pallets, the operator drives the Manitransit forklift to face the trailer's wheels, then uses the telescopic boom and sideshift to insert the forks into the pallet sleeves to raise the pallet and then deliver it to its destination.

The forklifts can reach forward 44 or 55 inches, depending on the model, to reach pallets stacked on the opposite side of the trailer away from the lift truck.

One of the first Manitransit TMT forklifts was purchased by Neosho Concrete Products Inc., headquartered in Neosho, Mo. The company makes concrete blocks, and office ads most of them from one of two 10-wheel trucks or one 18-wheel truck, all equipped with cranes.

"We bought the Manitou forklift to service construction jobs where we cannot get around with an 18- wheeler," said Thomas Bowers, maintenance supervisor at Neosho Concrete Products. The Manitransit forklift lets Neosho deposit concrete blocks anywhere on a construction site, far beyond the limits of a crane.

"Because we often park our transport trucks on the side of a road, the Manitransit allows us to offload from the curbside with out interfering with the flow of traffic on the opposite side of the road," said Bowers. He added that the Mani-transit, unlike cranes, is not limited by the presence of overhead power lines, or by existing construction on residential projects that would hamper access by truck.

Manitransit drivers have full visibility because the forklift has no need for a mast that could conceivably obstruct their view over the forks and load, and its boom is mounted low.

Grahic Jump LocationManitransit drivers have full visibility because the forklift has no need for a mast that could conceivably obstruct their view over the forks and load, and its boom is mounted low.

All three Manitransit models, the TMT 320, TMT 332 FI, and TMT 322, share a basic capacity of 5,500 lbs., although their capacity at maximum height differs-4,940 lbs. at 112 inches, 5,115 lbs. at 132 inches, and 5,620 lbs. at 132 inches, respectively.

The forklifts give drivers full visibility because the telescopic boom. needs no mast that might obstruct the view over the forks and load. The boom is mounted low on the truck to ensure a clear field of vision.

Manitou engineers mounted the sideshift integrally between the boom and chassis to enhance the forklift's durability. The sideshift eliminates a carriage attachment that would otherwise be needed and increases the load-bearing area.

The Manitransit designers made the chassis rugged, including engine and cab, by welding it into a single frame. The heavy-duty main pivot pin and the bronze bushings on all the boom's pins increase wear resistance. Fuel and hydraulic oil tanks are fixed to the chassis with metal lugs, allowing them to be removed to facilitate repairs.

The forklifts are powered by a four-cylinder, water-cooled, Lister Petter 40-hp diesel engine. The engineers mounted the engine on blocks to minimize vibration noise, a key consideration when the forklift is used in public spaces. Integrated stabilizers increase the capacity for handling loads up to 5,500 lbs. Manitou hydraulic cylinders are fitted with check valves and the hydraulic hoses are protected by the chassis.

The Manitransit 's hydrostatic transmission system contributes the benefits of fluid drive over mechanical drives, namely, by reducing transmission damage caused by daily wear or negligent operation. There are three braking systems on the forklifts. The driver releases the truck's accelerator pedal to reduce hydraulic flow to the transmission. As a result, braking, inching the forklift, and slow-speed approaches are smoother.

Depressing an inching pedal when approaching a pallet or trailer gradually disconnects the transmission, thereby improving the slow-approach hydraulic functions. In addition, the driver can manually engage a negative disc parking brake to secure the vehicle before leaving it. This brake engages automatically when the engine is turned off.

In contrast to indoor forklifts, the three-wheeled Manitransit vehicles have large Hauler SKS 15-ply tires measuring 31x10 inches, and high ground clearance to handle rough terrain easily. Outriggers on the two front wheels increase stability.

Driver comfort was also a priority in the Manitransit's design. For example, one joystick controls two functions: the raising and lowering of the boom, and its extension and retraction. The forward/reverse lever is located on the steering column, rather than on the accelerator pedal, for easier manual control.

An operator mounts the Manitransit forklift on the rear of a trailer by inserting its forks into the truck's sleeves so that it can be transported to and from unloading sites.

Grahic Jump LocationAn operator mounts the Manitransit forklift on the rear of a trailer by inserting its forks into the truck's sleeves so that it can be transported to and from unloading sites.

Copyright © 1999 by ASME
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