Downloaded from SAE International by University of New South Wales, Tuesday, September 18, 2018650626 Truck Retarder — Design and Development W. S. Nagel Eaton Manufacturing Co. RETARDER USAGE in general highway trucks is increasing and their function is generally understood. Simply stated, a retarder function is to do some, or all, of the steady-state braking associated with hill descent. In mountainous terrain the hill descending portion of the foundation brake job causes far more wear than stopping. This is evident from the vast difference of lining life in trucks operating in moun­ tainous terrains as compared with those operating in flat country. A truly useful retarder would do almost all the steady- state braking, leaving the foundation brakes to do the stop­ ping. The ultimate benefit of a retarder could be realized if the foundation brakes were made lighter and less expen­ sive. This can be done if they are required only to produce a certain stopping torque and not required to store large quantities of heat energy. The Fuller project was aimed at developing a retarder unit that would do most of the steady-state braking for the large on-highway trucks and off-on-highway trucks. These are primarily 5 axle units with about 75,000 lb GVW. The technical requirements will be illustrated for such a truck. BASIC RETARDER REQUIREMENTS The basic requirement for a retarder arises from the fact that the typical foundation brake is capable of absorbing only 15-20 hp continuously. Ignoring the front axle brakes (which are not significant in the overall problem) gives the truck a continuous foundation brake absorbing capacity of 160 hp. This figure is low because brakes cannot dissipate heat at a rate greater than 20 hp, and is in contrast to the enormous power they have for a brief time, which may reach 1500 hp per brake. For trucks operating in mountainous country, only 5% or less of hills are straight enough for high speeds. Truckers are fond of talking about hills of great length and grade, but dividing the elevation change by the road length often gives less than the commonly related figures. Descending hills with 75,000 lb GCW at 50 mph on a 5% grade develops 500 hp. Since 210 hp is used in air and tire friction, then if the truck has a 260 hp diesel engine, 60 hp will be absorbed by normal engine braking. This leaves 230 to be done by the brakes and retarder (Fig. 1). If the descent were made at 50 mph, using foundation brakes, the brakes would be overheated within 1-1/2 min- . utes (or about 1-1/4 miles) and within 1/2 minute after this period they would be faded. RETARDER POWER AND WEIGHT A retarder that was capable of producing 200 net hp at the flywheel would add about 230 or 240 hp at the wheels when drive line efficiency was added. Under these condi­ tions, no foundation brakes would be needed and the hill de­ scent could be made with the retarder only. Hills steeper than 5% grade can be descended slower using the retarder only, or at the same speed when using a small amount of foundation braking. With the limit of 5% grade on new in- ABSTRACT This paper describes the Fuller truck retarder and some of its development problems. The equipment is designed as a braking device for large on-highway trucks operating in mountainous terrains with steep descent grades. Since such braking accounts for most of brake lining wear, the retarder will considerably reduce cost of relining and down­ time. Up to 5% grades the retarder effects 100% of the brak­ ing; on steeper grades it contributes the major portion. Since new highway restrictions limit grades to 5%, it may be ex­ pected that the retarder will drastically cut costs in this area. Downloaded from SAE International by University of New South Wales, Tuesday, September 18, 20182 terstate system roads, foundation brakes need not be used in hill descent on such highways. A 200 flywheel hp is anideal figure, from the