Semi-trailer truck

#This invention relates to semi-trailer trucks and, more particularly, to over-the-road semi-trailer trucks for hauling heavier loads.

#To ensure proper load distribution for safety reasons and to minimize road damage, government regulations establish maximum weight per axle for over-the-road semi-trailer trucks and require minimum spacing between certain axles. For example, present federal regulations require that single axles bearing up to a maximum of 20,000 pounds must be at least ten feet apart. For semi-trailer trucks rated for a maximum gross load of 80,000 pounds, both the tractor and semi-trailer usually have tandem axles spaced about four feet apart. The maximum gross weight imposed on the front steering axle of the trailer is 13,000 and 20,000 for any other axle. The normal weight distribution for a gross load of 80,000 pounds is 12,000 pounds on the tractor front axle, 34,000 pounds on the tractor tandem axles and 34,000 pounds on the semi-trailer tandem axles.

#The wheels on the semi-trailer tandem axles are not steerable and the turning axis of the semi-trailer is at the midpoint of one axle or at a location between the axles. Consequently, when a corner or curve is being negotiated, the wheels on the or both axles are dragged sideways, causing the tires to be scuffed. This also imposes a torque on the semi-trailer support frame members which require these members to be beefed up and can cause premature fatigue. If the semi-trailer axles are spaced at least ten feet apart so that each individual axle can bear a maximum of 20,000 pounds, this problem is compounded.

#FIG. 1 is a side elevational view of a semi-trailer truck including a tractor having a single drive axle and a semi-trailer having a stationary axle assembly and a raisable, self-steering axle assembly shown with the self-steering axle assembly in the operating position.

#FIG. 2 is an enlarged, fragmentary side elevational view, partially diagrammatic, of the stationary axle assembly.

#FIG. 3 is an enlarged, fragmentary side elevational view of the self-steering axle assembly shown in the operating position.

#Illustrated in FIG. 1 is a semi-trailer truck 10 including a cab or tractor 12 having a chassis 14 supported for travel over the ground by front steering wheels 16 and rear drive wheels 18 driven by a drive shaft (not shown) in the usual manner. The semi-trailer truck 10 also includes a semi-trailer 20 which has a pair of frame members 22 supported for travel by a conventional stationary axle assembly 24 including wheels 26 and a self-steering axle assembly 28 including wheels 30 and rearwardly spaced from the stationary axle assembly 24. Both the stationary and the self-steering axle assemblies preferably have a gross load rating of at least 20,000 pounds. The semi-trailer 20 is connected to the tractor by a conventional swivel mount or so-called fifth wheel 32 which provides a generally vertical swivel axis about which the tractor 12 and the semi-trailer 20 pivots relative to each other during turning.

#Referring to FIG. 2, the stationary axle assembly 24 includes a transversely extending axle member 36 which is supported from the semi-trailer frame members 22 by a pair of conventional air bags or springs 38 (one shown). The air springs 38 are airtight, bellows-like rubber units and the interiors are connected to a source of compressed air through a suitable air supply which pressurizes the air springs 38. A wheel or a pair of wheels 26 (one shown) is rotatably mounted on each of the opposite end portions of the axle member 36.

#While the self-steering axle assembly 28 can be fixably supported on the semi-trailer frame members 22, in the specific construction illustrated, it is arranged for pivotal movement between an operating position and a retracted position.