An all-terrain truck-mounted forklift boasts many hydraulically powered features that give a big boost to productivity. One such feature is its reach mechanism, which can engage a load placed on the far side of a truck bed.
The HST also incorporates a traction control system that can be engaged when the lift truck is operated under conditions that prevent the tires from getting good traction. The operator activates the traction control system through a switch, which routes hydraulic fluid through a flow divider-combiner. With the system activated, the divider-combiner valve routes hydraulic fluid equally to both wheels. This prevents the wheel with lower traction from spinning—often referred to as positraction.
Using the HST simplifies the design by providing not only propulsion, but braking as well. This eliminates the need for the many braking components that would otherwise be necessary if the vehicle used a mechanical drive. A spring-applied/pressure-released brake holds the lift truck in place when it is parked. A switch on the parking brake is wired to the engine’s electrical circuit to keep the engine from starting unless the brake is applied.
Rotary Actuator Simplifies Steering
Steering is accomplished though a third wheel mounted in the center-rear of the vehicle. (As an option, this wheel incorporates an axial-piston motor to provide 3-wheel drive.) This rotary actuator uses a piston-and-helix configuration to generate high torque through a full 180° rotation. The rotary actuator offers several advantages over a conventional steering cylinder and linkage setup. The rotary actuator:
• eliminates mechanical linkages and the maintenance associated with them
• exhibits constant steering effort throughout the full range of steering
• needs no periodic adjustment for wear
• achieves longer life
• is more compact
• provides more precise steering control
In addition to these benefits of using rotary actuators, the lift truck takes advantage of the rotary actuator’s pivot-style mounting. This mounting design incorporates integral bearings and a heavy-duty shaft and flange assembly, making it a self-contained steering actuator and wheel mount. Installation simply involves connecting the wheel assembly at the bottom, bolting the top flange of the actuator to the underside of the vehicle frame, and connecting the hydraulic lines.
An engineer for the lift truck manufacturer pointed out that precise steering control is important because designers wanted the vehicle to be easy to use. This is one reason why they decided against using a skid-steer drive arrangement. With skid-steer, steering is accomplished by varying the speed of the wheels on the left or right side of the vehicle.
In fact, rotating wheels forward on one side of the vehicle and in reverse on the other side allows the vehicle to turn on its own center. But because most operators would be accustomed to operating a conventional forklift truck, designers wanted their vehicle to have the steering feel of a conventional forklift. With the rear wheel positioned perpendicular to the front wheels, the Trailer Mate exhibits a turning radius of only 114 in., or 93 in. for the optional 3-wheel-drive model.
Far-Reaching Versatility
One of the most useful features of the lift truck is its reach mechanism. Essentially, this is a horizontally mounted scissors jack powered by a pair of hydraulic cylinders that extends the forks forward up to 48 in. This allows the vehicle to unload a truck entirely from one side of its cargo bed. Not only does this increase productivity, but it also improves safety because operators don’t have to venture out onto the traffic side of a truck to unload it. Also, if an operator needs to reach a loaded pallet that lies behind another one, he or she can extend the forks forward and above the obstacle to gain access to the load without having to move the pallet that’s in the way.