Motor vehicles – Transmission mechanism – Gear transmission relationship to frame or axle
Reexamination Certificate
1999-08-06
2001-02-27
Mai, Lanna (Department: 3619)
Motor vehicles
Transmission mechanism
Gear transmission relationship to frame or axle
C180S372000, C180S352000
Reexamination Certificate
active
06193007
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the rear suspension and drive axle of a motor vehicle, and in particular of a bus or delivery truck, that facilitates providing the lowest possible floor height.
BACKGROUND ART
Drive wheels of commercial trucks and busses are generally driven by transverse axles that connect wheels mounted on wheel hubs to a large differential disposed in the center of the vehicle body. The vehicle body includes a rigid frame that is supported on a spring suspension on the axles. Brakes are generally provided adjacent the wheel hubs.
Some of the disadvantages associated with such designs are loading restrictions and high floor heights that are generally required to maintain vertical clearance between the vehicle body, the differential and other parts of the drive axle assembly. Attempts to minimize these problems have included mounting the differential to the vehicle body and using universal joints in the axles. This approach has required complex wheel support structures that lack durability and add cost.
Prior art bus designs generally have relatively high floors that require at least two steps in the doorway for ingress and egress. To make such buses useable by handicapped persons it is normally necessary to add a wheelchair lift.
Prior art commercial truck designs, especially of the type used for package delivery, normally have rear wheel drive with a front end mounted engine. Problems associated with these trucks include a relatively high floor height, vehicle weight, payload weight and space constraints.
Examples of prior art designs are disclosed in U.S. Pat. No. 4,362,221 and U.S. Pat. No. 4,343,375 that each disclose a vehicle drive wheel suspension in which the differential housing is carried by the body and frame structure of the vehicle while the wheels are connected to the differential by live axles having universal joints. Wheel bearings are connected to rigid support members forming part of the laterally opposite ends of the drive axle. The support members are connected by transversely extending rails that require clearance forward and rearward of the differential for vertical movement.
These and other disadvantages and problems associated with prior art designs are addressed by the invention as summarized below.
DISCLOSURE OF INVENTION
The present invention relates to a motor vehicle having an engine and transmission assembled to a frame of the vehicle with the transmission forward or rearward of the engine. The vehicle has a rear drive axle and suspension assembly comprising a differential operatively connected to an output shaft of the transmission to receive rotational force from the engine for driving the vehicle. The differential is directly assembled to the frame and has right and left drive axle output shafts. The output shafts are connected by universal joints to right and left half axles that are connected to geared hubs. The geared hubs are directly assembled to a carriage frame. The differential provides a first level of gear reduction while the geared hubs provide a second level of gear reduction. Right and left wheels or sets of wheels are operatively connected to the right and left geared hubs respectively.
According to another aspect of the invention, the geared hubs are mounted on the vehicle so that the axis of rotation on the drive axles and the axis of rotation of the wheels, or wheel sets, may be oriented with the axis of the drive axles directly above the axis of the wheels or at the same height as the axis of the wheels to permit lowering of the vehicle floor height. The floor height may also be established at a lower level due to the gear reduction provided by the geared hubs that permits the ring and pinion gear of the differential set to be reduced in size due to the reduced need for gear reduction at the differential and allows the use of a smaller differential housing.
According to another aspect of the invention, air disc brakes are provided on the drive axles between the differential and the geared hubs that permit braking forces to be applied prior to the final gear reduction in the geared hubs. This gear reduction at the wheel hubs allows for the use of smaller air disc brakes. The air disc brakes each have a combination brake chamber having an internal spring for providing a parking brake function for the vehicle thereby utilizing the air disc brakes that are used for normal vehicle braking.
According to another aspect of the invention, fore and aft torque rods can be provided between the frame of the vehicle and the carriage frame. The torque rods preferably include a bar pin that connects to a bracket on the frame that is adjustable by inserting shims in the bracket.
These and other aspects of the present invention will be better understood upon reference to the attached drawings and in light of the attached detailed description of the best modes of practicing the invention.
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