Crane tech shrunk to fit

The straddle carrier sector produced an estimated 400-500 units in 2008 but crashed to less than half that level in 2009. With terminal infrastructure projects put on ice, large-scale orders for straddles have disappeared and operators of existing fleets are sweating those assets, rather than investing in new machines. At least one manufacturer is understood to have stopped producing straddles and the remaining ones must vie for business with the two dominant players, Cargotec-owned Kalmar and Terex-owned Noell. What an interesting time, then, for Liebherr Container Cranes to enter the straddle sector. But current market conditions make no difference, according to Pat OÕLeary, MD of the Killarney, Ireland-based firm. "It would be a concern if we were a weak company, but weÕre not and our philosophy is to build it and put it out there," he explains.

Of course, Liebherr has not rushed into the market during the recession; it has spent more than two years developing and trialling its designs, including two development prototypes that have been in full operation in Belfast Container Terminal. It has now unveiled the new SC 440S straddle carrier its third machine which it says is based on a new design concept working Òfrom the crane downwards".

"Traditionally straddles grew from the mobile industry like reachstackers and toploaders," says O’Leary. "The advantage of the Liebherr machine is that it has integrated crane technology. It is designed differently Ð structurally, electrically, mechanically."

This follows the pattern of Liebherr’s earlier entry into the RTG sector, when it ’shrank’ STS gantry technology to produce its yard cranes. This time it has shrunk its RTG technology to produce a straddle carrier.

Like its RTGs, admits O’Leary, the straddle will cost a little more than its competitors, but he argues that terminals will benefit from less maintenance, lower total cost of ownership, increased efficiency and reliability, as well as better driver comfort.

The SC 440S is a one-over-three unit with two driven wheels in the centre and two idle wheels on the outside, offering a small turning circle with four individually turned axles. An electronic Òdrive-by-wireÓ system allows electronically adjustable steering sensitivity. Shock relief valves are included on each hydraulic cylinder for impact protection with continuous automatic wheel alignment correction, expected to offer greatly reduce tyre wear.

Like Liebherr’s STS cranes, the straddleÕs steel structure is made from S355 high-tensile steel throughout. Strong box sections are constructed from I-beams for the legs, allowing minimal portal bracing and providing the driver with maximum visibility. All the flange joints are bolted high friction grip joints.

Each of the sill beams has an integrated 750-litre fuel tank and a flow tank is positioned within the genset on top on the straddle, allowing it to use fuel from either sill beam equally to top-up the flow tank.

The straddle is equipped with a stage IIIA-compliant 12.3-litre Volvo Penta engine, though the company says it would also consider Scania engines for future production. CAN-bus communications is used throughout the straddle, expect for spreader communication, where ASI-bus was chosen due to its stability and because the spreader is a high impact zone.

Oil filling and drain lines have been run to ground level, so smaller ports without big maintenance sheds will find it simple to change oil.

"As with all of our cranes, the brain is Liebherr PLC and all of the switchgear is designed and built by Liebherr," explains Paul Bolger, the company’s product manager mobile.

"There are four individual drives for travel and one drive for the hoist. We share the drive DC link power between two of the travel drives and the hoist, which allows the machine to regenerate energy when lowering the hoist to the travel drives, so you can accelerate away as you are lowering. In the same way, when you are braking, if you are hoisting at the same time, you can transfer power from the brake to the hoist. This makes it as energy efficient as possible."

Liebherr has eliminated hydraulic lines on the legs and on top of the straddle. Compared with other straddles, which use hydraulic pumps up high mounted to the engine, the company has placed an electrical motor on each sill beam, an identical tank on each side operating all the hydraulics. "We would say this is a completely new concept in straddle carrier hydraulics," says Bolger. "The key reasons for this are maintenance and performance. It allows us to have a dramatic reduction in the number of connections and hoses that we have."

The drive-by-wire steering also means there are no hydraulics in the driverÕs cabin.

"You do see drive-by-wire steering on other strads," says Bolger, "but not on the hydrodynamic or hydrostatic machines. We believe we are the only ones on the market that has drive-by-wire steering and braking."

The travel drive arrangement uses AC frequency inverter drives, with one per motor. This is designed to allow fine inching control for maximum manoeuvrability at slow speed for positioning and high acceleration. The current one-over-three unit is limited to 25km/hr while the one-over-two unit will be limited to 30km/hr. "With the AC arrangement, we can regenerate quite a lot of power during braking back to the hoist," says Bolger. "Each motor is 60kW. It’s quite a short drive shaft we’ve lifted them off the sill beams so it gives the optimum angle for the drive shaft for maximum life and minimum maintenance."

Tyre wear is expected to be greatly reduced due to the four axle arrangement. The prototype units have, so far, exceeded 8,000 hours of operation, says Bolger, who points out that tyres and engines are two of the biggest maintenance issues for straddle carriers. "All cylinders are controlled hydraulically from within the unit itself by proportional valves, which control the amount of oil you put to the cylinder based on the input from the steering wheel," he continues. "The steering wheel gives you two things: your position and how fast you move it.

"One of the advantages of having the system down below is that there are no big hoses going up to the pump on top Ð short hoses, fast response time, accurate feedback."

O’Leary says that this arrangement is a more expensive way to do it but it means better performance and reliability. "That’s what customers want; to engineer out the maintenance," he explains.

The straddle carrier’s travel brakes comprise up to 30% brake regeneration from the electrical system and the remaining 70% from hydraulic wet disk brakes Ð a combination that Liebherr says means less heat and less wear. Oil for the wet disk brake is circulated from the centralised system.

"The brake combination has a good smooth feel and is totally programmable to what the driver is used to and to give him the best performance," says Bolger.

O’Leary adds: "The regenerative braking is frictionless braking coming from the motor, reversing the torque. All of the slow speed positioning is electrical, so thereÕs no friction and no heat being generated."

The hoist speed is 26 metres/min empty and 18 metres/min fully laden. Again, crane technology, rather than mobile technology, is the basis of the hoist arrangement.

"The [hoist] brake arrangement is Bubenzer at the moment, very similar to what we use on the RTGs and STS cranes," says Bolger. "It’s outside and accessible for maintenance, which is the most important point, for adjustment and brake pad change in years to come."

The hoist arrangement uses 24mm rope with a simple reeving layout. "It has two pulleys up high, others directly from the drum onto the pulley frame attached to the spreader," he adds. "So it’s a minimal number of components, greater reliability, less maintenance and well proven technology from cranes."

Liebherr has chosen the Elme single-lift electro-hydraulic spreader. The lift capacity is 40.6 tonnes under the spreader, capable of lifting any size container. An integrated power pack is used for spreader hydraulic functions, integrated with the steering system to minimise power usage and to minimise maintenance. "The telescoping cylinders are mounted on the outside, again for maintenance," continues Bolger. "As it extends, you don’t rely on the hydraulic cylinders. There are locking pins. If you telescope out to 40ft and take an impact, the locking pins take it, rather than impacting the cylinders."

The skew and side-shift features allow it to fully side-shift side-to-side plus/minus 290mm for positioning on a truck or stack. For maximum manoeuvrability, both ends can skew together or separately.

A button on the driver’s joystick is used for auto centre, auto slowdown and auto landing of the spreader.

Built by Brieda, the cabins have large curved windows for maximum visibility.

An interactive information display, touch screen and joystick control are intended to make all operations simple. A twistlock panel shows if a container deposit has been made and whether the twistlocks are open or closed. A stability warning panel alerts the driver if cornering too fast. Added pre-set auto height positions are included.