4 Wheel Steering

Topics: Steering, Power steering, Hydraulic machinery Pages: 6 (2091 words) Published: January 19, 2013
Introduction To Power Steering Systems - Night School
Power Steering Systems An Introduction To Classic Truck Steering Systems, Part 2 From the February, 2010 issue of Classic Trucks
By Moses Ludel

| The Saginaw rotary valve steering... read full captionThe Saginaw rotary valve steering gear is an integral, streamlined design introduced in 1959. By the end of the '60s, all GM cars and light trucks offered this gear. Ford, I-H, Dodge, and Jeep outsourced rotary valve gears as well. Saginaw's recirculating ball-and-rack piston engineering has become a worldwide standard.By 1951, many American vehicles required power steering. Gemmer's Hydraguide system, the first power steering system used on an American car, was Chrysler's answer to the massive front end weight created by the new hemi V-8. Other manufacturers quickly followed.Two power steering designs emerged. Linkage assist steering and the integral power steering gear-each use a constant flow, positive displacement hydraulic pump. The pump, belt-driven by the engine, pressurizes and circulates power steering fluid.Linkage assist steering consists of a hydraulic control valve attached to one end of the drag link or centerlink. The valve receives input signals from the steering wheel and steering gear. Left or right steering causes the valve to react, opening ports to move hydraulic fluid into a hydraulic ram. The ram attaches to the steering linkage. Fluid directed to one side of the ram's piston or the other determines which direction the power assist will apply.This apparatus is a Saginaw... read full captionThis apparatus is a Saginaw offset integral steering gear. Introduced in 1952 GM luxury models, the design preceded Saginaw's inline gear. Like the Gemmer Hydraguide, the offset was essentially a manual steering gear with a parallel power assist cylinder and rack drive. The unit was too large for light truck, ladder frame use.The linkage assist system is the easiest to adapt. Some truck manufacturers made power assist kits available for dealer installation. The kits worked with the existing manual steer gear and included a drag link and control valve assembly, the hydraulic power ram, a power steering pump with brackets, and the pressure and return hoses.Linkage power steering makes use of the manual steering gear. On a beam axle model, the control valve attaches to the drag link. The power cylinder's ram end attaches to the tie rod. An anchor bracket supports the cylinder end. For independent front suspension like the '60-66 GM trucks, the control valve attaches to the centerlink at the pitman arm end. Apply pressure is controlled by the valve settings and pump input pressure.The significant downside to linkage power steering is its vulnerability to damage. The power ram and hoses are continually exposed to the elements, road obstacles and debris.Saginaw's inline integral... read full captionSaginaw's inline integral steering gear came online in 1956. A compact unit, the inline became a GMC light truck option. Despite use on luxury GM cars and the GMC trucks, there were weaknesses in the design. GM phased out the inline within four years of its introduction. The better inline features carry forth to the rotary valve steering gear.Integral Power Steering Gears Modern light trucks use integral power steering. Integral power gears include the control valve, apply piston, and gear system. The assembly mounts to the frame at the same location as a manual steering gear. A pitman arm delivers power from the gear to the steering linkage in the same manner as a manual steering gear.Light truck power steering came directly from automotive applications. The earliest integral automotive designs were contraptions, a complex melding of manual gear technology and power pistons. Fortunately, Gemmer's Hydraguide and Saginaw's offset applications never made the light truck option list. These designs were cumbersome, taxed horsepower and ate up engine bay space-undesirable...
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