POWER STEERING

Power steering (fig. 3-2) adds the following components to the steering assembly: a hydraulic pump, a fluid reservoir, hoses, lines, and a steering assist unit whether mounted on the linkage or incorporated in the steering gear assembly.

ARTICULATED STEERING

Hydraulic power is used to turn a whole section of a machine on a vertical hinge. This design is called articulated steering and it is controlled by a steering wheel, a hydraulic control valve, and hydraulic cylinders. (See fig. 3-3.) The pivot is midway in the vehicle, so both parts share equally in the pivoting. This action produces the effect of four-wheel coordinated steering, such as the front-and-rear wheels run in each others tracks, backward and forward.

FRONT-AND-REAR STEERING

Wheeled equipment may be designed to steer by angling the front wheels, the rear wheels, and or both the front-and-rear wheels (fig. 3-4). Front-wheel steering is the standard method. The vehicle follows the

Figure 3-2.-Power steering linkage assembly.

Figure 3-3.-Articulated steering assembly.

Figure 3-4.-Front-and-rear steering.

angling of the wheels and the rear wheels do not go outside the path of the front ones, but trail inside. Rear-wheel steering swings the rear wheels outside of the front-wheel tracks. The principal advantage is greater effectiveness in handling off-center loads at either the front or rear and preventing path down a sideslope. This type of steering is used with front-end loaders, as it keeps the weight of the machine squarely behind the bucket on turns and keeps the front tires tracking in the rear while backing away from banks and dump trucks. In new equipment, this design has been replaced by articulation.

In four-wheel steering, the front wheels are turned one way and the rear wheels are turned to the same angle in the opposite direction. The trailing wheel always moves in the same track as the leading wheel whetherthe equipment is moving forward or backward. This design lessens rolling resistance in soft ground, because one set of tires prepares a path for the other set. Additionally, this design provides maximum control of the direction of the load. Also, it enables the equipment to be held on a straight course and permits short turns in proportion to the maximum angle of the wheels.

In crab steering, both sets of wheels are turned in the same direction. If both sets of wheels are turned at the same angle, the machine moves in a straight line at an angle to its centerline. Results can be obtained from either four-wheel steering or crab steering by using different turning angles on independently controlled front-and-rear wheels.

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