The hydraulic system of the TrailerMate TM50 is powered by a 46-hp (@2700 rpm) diesel engine driving a Sauer-Sundstrand Series 40 pump for the hydrostatic transmission (HST). A tandem-mounted gear pump provides flow for steering, the mast assembly, and stabilizers. In the HST circuit, the variable-displacement, axial-piston pump delivers up to 46 cc/rev (2.8 in.3/rev) and has a maximum pressure rating of 350 bar (5000 psi). Output flow from the pump is routed to a parallel circuit feeding a pair of 35 cc/rev (2.14 in.3/rev) fixed-displacement, axial-piston motors (which also are part of the Series 40). Each motor is connected through a splined shaft to a Torque-Hub planetary wheel drive from Fairfield Mfg. to drive the front wheels.

The HST also incorporates a traction control system that can be engaged when the TrailerMate 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.

Using the HST simplifies the design providing not only propulsion, but braking as well. This eliminates the need for the many braking components that would be necessary if the TrailerMate used a mechanical drive. A spring-applied/pressure-released brake holds the TrailerMate 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.) Supplied by Helac Corp., 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 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, and

* provides more precise steering control.

In addition to these benefits of using rotary actuators in general, the TrailerMate takes advantage of what Helac calls a pivot-style mounting. This actuator 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.

Rusty Shinn, lead engineer at Eagle-Picher, pointed out precise steering control is important, because designers wanted the TrailerMate 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 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 the TrailerMate 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 TrailerMate is its Pantograph 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 TrailerMate to unload a truck entirely from one side of a truck's cargo bed. Not only does this increase productivity, but it 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 is in the way.

The TrailerMate is also designed for ease of maintenance, especially the hydraulic system. All hydraulic connections use O-ring face seal fittings to prevent leakage and simplify removal and replacement of components. To ensure reliability, the hydraulic system incorporates 2-µm filters in the HST circuit, which uses a piston pump and motors, and 10 µm filtration for other circuits, which use the more-forgiving gear pump. In addition, all maintenance checks can be performed from the right-hand side of the vehicle.