Industry studies of lift truck accidents have shown that one of the most frequent accidents leading to deadly injuries is tipping. Quite often the accident is caused by high centrifugal forces acting on the load and truck while turning a corner. Following the standards established in Europe, all lift trucks in use today must be fitted with a passive restraint system, such as a seat belt (In December 1998 all new lift trucks were fitted with the restraint system and trucks built before this date were retrofitted). Passive safety features contain the driver within a protective space and have reduced injuries.
However, the philosophy of “prevention instead of protection” has spurned new developments that actively increase safety and reduce the initial risk of tipping to a minimum. For example, Curve Controltechnology, developed by Jungheinrich AG (Hamburg, Germany), with U.S. Subsidiary Jungheinrich Lift Truck Corp. (Richmond, Va.), provides a pro-active safety feature by automatically reducing the risk of tipping when cornering.
Prevention Instead of Protection
“There are two basic principles that can reduce the risk of tipping as lift trucks maneuver around corners: blocking the movement of the pendulum axle, and automatic speed reduction depending on steering angle. Blocking the movement of the pendulum axle is only possible on four-wheel models and since the majority of the lift truck market is three-wheel models, changes to the axle were not a viable solution,” explains Jurgen Butzke, chief of product management for Jungheinrich in Moosburg, Germany. “We began to develop a system that automatically reduces the drive speed as it correlates to initial speed, wheel position and steering angle. The result is a system that assures stability and prevents the tendency of lift trucks to tip over.”
Three key components are the basis for the Curve Control System: 1) a high-performance drive controller, 2) a quick reacting, very fine adjustable three-phase AC drive motor, 3) a continuously working sensing unit that monitors the steering angle. Simply stated, the system quickly and effectively reduces the drive speed when an excessive steering angle is sensed. Curve Control’s development was predicated on the calculation and the practical assessment of the speed graphs for the various vehicles.
Currently the systems are adjusted to enable full forward speed if a wide turn is made. When the steering input is larger than 20 degrees off center, the system will progressively slow the vehicle down until; in some extreme cases a walking pace of approximately 3-4mph is reached. The underlying principal was to enhance safety as far as possible without unnecessarily reducing handling capacity. Preliminary results on the shop floor have shown that a good, safety conscious driver hardly notices the Curve Control System, as he already reduces forward speed before turning, not requiring the system to actively intervene.
Independent University Tests System
As is typical with all new technology, potential customers want documentation of a system’s effectiveness. Jungheinrich asked the Bundeswehr University of Hamburg to test trucks fitted with the Curve Control System. Professor Dr. Rainer Bruns, head of the laboratory for conveyance devices and engineering, conducted various driving tests on one of the most commonly used Jungheinrich trucks, the EFG Four-Wheel Series. Examining the dynamic tilting properties, the University concluded that:
It is virtually impossible to tip the truck over, even with maximum allowable loads.
The only situation where the truck may be tipped is an extreme and sudden steering input (i.e., an sudden extreme steering action followed by an immediate countersteering action). This can only be accomplished when a driver has high driving skills.
The system reduces the load on the rear axle so that the vehicle will swerve instead of tipping over. The Jungheinrich Curve Control System increases the safety of the lift truck.
Safe Driving With Elevated Load
Additional tests performed by the University proved that the system significantly reduces the potential for accidents caused by high centrifugal force. Butzke explains, “We examined the load-based toppling accidents, such as fast driving with an elevated load. The Curve Control System has an added feature that adjusts driving speed as it relates to the lifting height of the load. More specifically, when a load is lifted over 30 in. the drive controller automatically reduces the speed to a maneuvering minimum. This feature also increases safety while stacking and retrieving loads. The Curve Control System assures that the driver does not approach stacking racks or trucks during loading activities at overly high speeds.”
The immediate success of the Curve Control System in Europe convinced Jungheinrich to initially offer it as an option on all electric trucks. Butzke concludes, “Since the original development of Curve Control technology in the late ’90s, we have continually improved and fine-tuned the system, hoping that the lift truck industry would establish standards for this type of ‘active’ safety technology. We are so confident that this system is the best method of providing operator safety that we have implemented the Curve Control System as a standard feature on our complete line of counterbalanced and reach trucks.”
Additional Safety Feature Helps Stability
Another standard feature of trucks designed in Europe is battery positioning. The European standard design places the battery between the front and rear axles, which differs from the U.S. design where the battery is situated slightly over the rear axle. The European design has some significant advantages: the center of gravity is lowered which increases maneuverability and stability; ergonomically the low battery position allows for a lower driver’s seat, and reduced maintenance because all electronic connections and cables and hydraulic houses are above or next to the battery instead of underneath.
“Better stability with a lower center of gravity can be best explained using an automotive analogy, i.e. the handling of a jeep versus a corvette,” explains Jungheinrich’s Jan-Martin Lorenz. “For years it has been documented that jeeps are prone to tipping because of their higher center of gravity, whereas a corvette can corner extremely well due to its lower center of gravity. The same principals apply in the lift truck application.
“The lower battery position allows us to lower the driver’s seat. This facilitates the driver’s ‘climbing’ into and out of the truck. By the end of a worker’s shift he will be less fatigued.”
Battery maintenance is critical to its prolonged service life and this requires the constant monitoring of water level in the battery. Lorenz explains, “On a weekly basis the water level of lift truck batteries should checked and often filled on the spot. The potential for water that now contains acid to spill out onto anything below the battery is very high. Therefore, eliminating the need to run cables or hose under the battery helps reduce some of the typical maintenance issues with U.S. designed trucks.”
“A final maintenance issue, battery ‘change-outs’ has been addressed by our change from DC to AC drive control,” concludes Lorenz. “In 1996 we developed an AC drive technology prolongs battery life per shift and ultimately extends battery life. We currently offer our third generation of AC drive control on a majority of our trucks.”
Safety Belts Still Required
Even though modern lift trucks may have active safety devices such as Curve ControlÒ, they must be fitted with passive safety equipment, like safety belts, an OSHA requirement for all drivers. Butzke states, “Accidents caused by uneven surfaces or slipping of the load can still not be avoided, even with the most modern technology. Therefore, all vehicles must be fitted with duo-sensitive lap belts.” In addition to this standard lap belt, many manufacturers offer an array of alternative restraint systems, as in fully contained driver cabins or door and brace systems.
Jungheinrich has also co-developed an electrically controlled restraint system. The system automatically opens and closes guards beside the driver’s seat in accordance with the parking brake. Butzke adds, “All these options are much more expensive than the standard belt, and many customers will not make the investment. Often it comes down to the belt, which more often than not remains unused because the driver simply doesn’t buckle up. As a result, the customer must make sure that lift truck operators follow current regulations.”
In the U.S., OSHA mandates that lift truck operators complete a driver training course, which they must pass before they can use the vehicles. Further regulations dictate that drivers be re-certified every three years and that their employer be responsible for certification. OSHA fines for non-compliance are extremely harsh.
Source: Jungheinrich Lift Truck Corp.