Lasting the life of a forklift

Marginal Column

Photo: Jungheinrich Moosburg GmbH

Developed especially for tough, heavy-duty service: the new radial piston motors used to drive the wheels.

Magnifier

A tiny detail with a huge effect. Thanks to the projection over the hub and a new seal, no grime can enter the housings in Series 33.

July 2014

 

When building its counterbalance forklifts for heavy-duty work, Jungheinrich has used hydrostatic drives for many years now. Daniel Rösch, of product management at the Jungheinrich Moosburg GmbH, reports on the advantages, challenges and further development of the 4s series.

 
 

We have used hydrostatic drives in our counterbalance forklifts for quite some time. This drive system is interesting especially when total cost of ownership and the vehicle’s ride are important. High performance is essential in transshipping for logistics operations and in the beverage, paper and recycling industries.

Here speed is of the essence and the forklifts never take a break. In two- or three-shift operations, where the forklift frequently reverses, where short paths are involved, and where trucks are unloaded and loaded in parallel, for instance, the advantages of the hydrostatic drive make it the right choice.

It enables precise, and at the same time, powerful acceleration and braking; it is both rugged and easy to service. In addition, depending on the exact application, the hydrostatic drive uses as much as 30 percent less fuel than comparable vehicles equipped with a torque converter. The efficiency, the ride and the working properties are simply better.

Arguments in favor of the new development

Three considerations gave us the impetus to pursue new developments in counterbalance forklifts equipped with hydrostatic drives. Firstly, we wanted to position ourselves as a full-line vendor in every segment. That meant we had to offer the appropriate vehicle for every application. Secondly, users’ expectations for the product had been rising continuously. Thirdly, the restrictions on exhaust emissions had become more stringent all around the world, especially for diesel engines. That is why the decision was made to develop a completely new generation of vehicles to meet these requirements.

We quickly identified Bosch Rexroth as a premium development partner in the hydrostatics sector, since it delivers entire subsystems from a single source, in superb quality, and with a focus on energy efficiency.

Implementing the platform concept

Working with this partner let us implement perfectly our concept for the common platform, on the basis of which three different forklift series were created. The development project with Bosch Rexroth started with the 4s series, which has a payload of from 2.5 to 3.5 tons. It covers about 50 percent of the market’s volume.

We unveiled this series at the end of 2007 and it was followed by the 3s series – with payloads of 1.6 to 2 tons – and the 5s series carrying 4 to 5 tons. Design elements, the body shape and the operator’s cab are identical in all three series, varying only in size. The situation is similar for components in the hydrostatic drive. They all come from one product group and we use them for various series, differing only in their dimensioning.

Forklift operators’ preferences

Once our development department in the Bavarian town of Moosburg had established the basic dimensions, we forwarded these specifications to Bosch Rexroth. In an intense exchange of ideas, we then constructed and tested prototypes incorporating several variations in the pumps and motors at the wheels.

The major challenge was to design the vehicle so that it runs smoothly. To achieve this, it was necessary to harmonize the components in the hydrostatic drive, the work functions, the internal combustion engines, and the controls for each. Especially demanding was fine tuning for the engines, the drive pump and the controls – and this task fell primarily to our software developers at Jungheinrich. Their first job was to analyze the context and the mutual influences of the various systems and the effects on the system and on the ride and working properties. Then it was necessary to draw the proper conclusions.

It is true that a vehicle’s behavior can be tested or simulated on the test bed only to a certain extent. Experienced forklift operators have clear – but sometimes far different – expectations for the vehicle. These can be tested only in actual operation.

To be able to satisfy driver preferences and meet the conditions for use, the operator can select one of five operating modes at the display panel – from gentle starting and stopping to very dynamic responses aimed at high performance. These programs are regulated by the electronic controls. Here the hardware is built by Rexroth, the software is written by us.

The facelift saves up to ten percent

At mid-2014, Jungheinrich marketed a facelift for the 4s series, responding to more stringent exhaust emission regulations. As a vendor of premium equipment, we always aspire to continuously improve our vehicles. As regards the actuators, we had identified great potential for improving energy efficiency.

In addition to the hydrostatic drive, we also employed a working pump by Rexroth in this upgraded version. The change from a constant-discharge pump to a variable-displacement pump made it possible, depending on the particular use, to increase efficiency by up to 20 percent in lifting and hydraulic functions.

When joined by other factors, savings in the system as a whole came to about ten percent. In addition to boosting energy efficiency, we also introduced a new and user-friendly control concept with an improved armrest and individual adjustment options. A new generation of masts, featuring improved visibility, was also used.

Banning dirt

Pursuing the logical next step in the development of the series, Bosch Rexroth, in the course of product maintenance, further refined its radial piston motors especially for this heavy-duty use. The casing for Series 33 now projects over the hub (see the illustration) and is fitted with a new seal. Bits of plastic film or dirt on the floor, stirred up during travel, can now no longer be pulled into the motor at the wheel. Thus we are coming ever closer to our goal of making these costly items last for the entire life of the forklift.

In addition, Rexroth includes in Series 33 separate, mirror-image motors for the right and left sides. The advantage here is that system components like the velocity sensors, for example, are better accessible, both in production and during service work.

Improved TCO

This hydrostatic drive lets us achieve stepless changes in travel, superb precision, and highly responsive driving controls as well as parallel operations with automatic boosting of the engine speed. This is, in fact, the state of the art for this kind of travel drive, but – thanks to improved engineering and by selecting Bosch Rexroth as a supplier when we started development for the current hydrostatic system – we can offer an overall concept that is significantly more coherent.

All in all, we have aligned this counterbalance forklift, with the Rexroth hydrostatic drive, with market demands in regard to the total cost of ownership – at Jungheinrich we call this BestInvest. We have attained this by adopting even tougher components. That lessens service costs and improves vehicle ergonomics and efficiency.


 

Author

 

Daniel Rösch,

VFG product management,

Jungheinrich Moosburg GmbH, Moosburg, Germany