BACKGROUND ART Delivery trucks having rear wheel drive with an engine mounted in the front of the vehicle generally require a load floor height of approximately thirty inches. The load floor height cannot be made lower according to conventional designs due to the chassis design, frame rails, rear suspension and drivetrain including the rear axle, differential and brakes that must be covered by the load floor.

Many advantages may be achieved by reducing the height of the load floor for a delivery vehicle, including better ingress and egress from the rear cargo door. If a ramp is used to move heavy items into and out of the truck, the angle of inclination of the ramp or length of the ramp may be reduced making it easier to load and unload the vehicle.

Generally, delivery trucks have a load floor that is of fixed height.

It would be desirable to provide a limited range of adjustment of load floor height generally to lower the load floor further or to allow for raising the load floor to make it easier to load the vehicle from a truck dock.

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. Patent No.

4,362,221 and U. S. Patent No. 4,343,375. Each patent discloses 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 According to one aspect of the present invention, a low load floor is mounted on a truck frame and extends over a differential and an axle with the load floor being mounted at a level that is lower than a top portion of the wheel hubs.

An engine and a transmission are mounted on the front end of the frame. A differential and axle are mounted toward the rear end of the frame and are operatively connected to the engine through the transmission. A pair of front wheels are attached to the front end of the frame and at least two wheels are attached toward the rear end of the frame. The rear wheels may be either tandem or single wheels and include wheel hubs that receive driving torque from the axle.

According to another aspect of the invention, an air spring suspension system is provided between the rear wheels and the frame that supports the frame on the rear wheels at a normal height during driving. A control system is provided for controlling the supply of air to the air spring suspension system. The control system permits the frame of the truck and its load floor to be raised or lowered by raising and lowering the level of the air spring suspension system. The control system permits raising and lowering of the load floor by as much as three inches relative to the normal height of the load floor. The front wheels of the vehicle are provided with a trailing arm spring suspension that is not raised or lowered when the air spring suspension system is adjusted.

The present invention also 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.

BRIEF DESCRIPTION OF DRAWINGS FIGURE 1 is a fragmentary perspective view of a bus having a rear axle drive and suspension system made according to the present invention.

FIGURE 2 is a side elevation view of a bus having the rear axle drive and suspension system made according to the present invention.

FIGURE 3 is a fragmentary perspective view of the rear axle drive and suspension system made according to the present invention.

FIGURE 4 is a plan view of the rear axle drive and suspension system made according to the present invention.

FIGURE 5 is a fragmentary perspective view of a portion of the rear axle drive and suspension system for a bus made in accordance with the present invention.

FIGURE 6 is a fragmentary plan view of an alternative embodiment of a rear axle drive and suspension system for a truck having a front end mounted engine.

FIGURE 7 is a perspective view of a portion of the rear axle drive and suspension for a truck having a front end mounted engine.

FIGURE 8 is a front elevation view of the drive axle connection between the differential and geared hub made in accordance with the present invention.

FIGURE 9 is a rear perspective view of the low load floor truck of the present invention side-by-side with a conventional normal load floor truck.

FIGURE 10 is a side elevation view of the low load floor truck of the present invention.

FIGURE 11 is a front elevation view of a left-hand side drive version of the low load floor truck of the present invention.

FIGURE 12 is a front elevation view of a right-hand side drive version of the low load floor truck of the present invention.

FIGURE 13 is a top plan view of the low load floor vehicle of the present invention.

FIGURE 14 is a control diagram for the air spring control system of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Referring now to FIGS. 1 and 2, a vehicle 10, for example a bus, is shown to include a vehicle frame 12 to which an engine 14 and transmission 16 are secured. A drive shaft 18 powered by the engine 14 through the transmission 16 extends from the transmission 16 to a differential 20. In this embodiment, the drive shaft may be less than 12 inches long and may comprise a spline shaft and constant velocity joints as will be more specifically described below. Differential 20 is of a conventional design including a ring gear and pinion gear (not shown) having a gear reduction ratio, for example, of about 3: 1.

A carriage frame 28 supports right and left wheel sets 30 and 30'that may be either tandem wheels or single wheels depending upon the weight and load requirements of the vehicle. Right and left front air springs 32 and 32'and rear air springs 34 and 34'are preferably secured to the upper surface of the carriage frame 28 and to the vehicle frame 12 so that the air springs support the vehicle on the carriage frame 28 and wheel sets 30,30'.

Referring now to FIGS. 3,4 and 5, the structure of the carriage frame 28 and its associated components are described in greater detail. Right and left rear air springs 34 and 34'are secured between the carriage frame 28 and the vehicle frame 12. Right and left geared hubs 36 and 36'are secured to the carriage frame 28. Geared hubs 36 and 36'preferably provide, for example, about a 2: 1 gear reduction for the rotational input received from the right and left half shafts 38,38' and provide driving output to the wheel sets 30,30'. Axis A is the rotational axis of the half shafts 26 and 26'and axis B is the rotational axis of the wheel sets 30, 30'.

The transmission 16 is connected by a spline shaft connector 48 of the drive shaft 18 to the differential 20. The transmission 16 extends partially through a fire wall 40. The drive shaft also may include constant velocity joints, or U-joints, 50,50'.

The carriage frame 28 includes a front rail 42 and a rear rail 44 that are interconnected by right and left side rails 46 and 46'. Air spring housings 52 are secured to the vehicle frame on their upper ends and are connected to front and rear air springs 32,32', 34,34'that are in turn connected to opposite sides of the front and rear rails 42 and 44.

Right and left air brakes 54 and 54'are provided on the differential output shafts 55,55'. The air brakes 54 and 54'are reduced in size due to the fact that the brake action is subject to gear reduction in the geared hubs 36,36'.

Referring now to FIGS. 3 and 5, right and left sides of the vehicle are each provided with an upper torque rod 56,56'and lower torque rods 58,58'. The torque rods are secured between the vehicle frame 12 and right and left side rails 46, 46'. Transverse torque rod 60 is secured between vehicle frame 12 and front rail 42. The torque rods 56,58 and 60 are preferably connected by a bar pin bracket 62 to the vehicle frame 12 to permit adjustment of the torque rods. The bar pin 63 bracket 62 can be adjusted by simply placing a shim between the bar pin 63 and bracket 62 and the frame 12 or by placing washers between the bar pin 63 and

bracket 62. Shock absorbers (not shown) extend between the vehicle frame 12 and carriage frame 28 in a conventional manner.

Referring now to FIGS. 6 and 7, alternative embodiment of the present invention is shown as applied to a truck 70 having a front end mounted engine 72. The engine 72 is operatively connected to a transmission 74 that are both secured to the frame 76 of the vehicle. A drive shaft 78 connects the transmission 74 to a differential 80. Differential 80 is also secured to the frame 76 of the truck 70.

Air brakes 82,82'are provided on the right and left sides of the differential 80. Half shafts 84 and 84'are also provided on right and left sides of the differential 80.

A carriage frame 86 supports geared hubs 88,88'that interconnect the half shafts 84,84'to wheel sets 90,90'. The geared hubs 88,88'and wheel sets 90,90'are supported on the carriage frame 86. Air springs 92 are retained by air spring brackets 94 at four corners of the carriage frame 86. The air springs 92 support the frame 76 of the truck 70 on the carriage frame 86.

A transverse torque rod 96 interconnects the rear portion of the carriage frame 86 to the vehicle frame 76. As illustrated in FIG. 7, an upper torque rod 98 connects another portion of the carriage frame 86 to the vehicle frame 76.

Referring now to FIG. 8, the axle assembly extending between the differential 80 and geared hubs 88 is described in greater detail. While this description is provided for the embodiment of FIGS. 6 and 7, the construction of the axle half shaft for the embodiment of FIGS. 1-5 is essentially identical in all material respects. The differential 80 has an output shaft 102 to which the air brake 82 is assembled. The output shaft 102 is connected by a constant velocity joint 104, or U-joint, to the half shaft 84. Half shaft 84 provides rotational input about axis C to the geared hub 88 about axis B that in turn provides an output to the wheel hub 106

that is adapted to receive a wheel set similar to the wheel set 90 shown in the embodiment of FIGS. 1-5.

Referring now to Figure 9, a side-by-side comparison of the truck 112 of the present invention having a low load floor 114 is shown juxtaposed to a prior art truck 116 having a normal load floor 118. The normal load floor 118 is typically approximately thirty inches above the ground, while the low load floor 114 of the present invention can be as low as seventeen inches off the ground in its normal position.

Referring now to Figures 10-13, the truck 112 has a frame 122 on which is mounted a body 124. An engine 126 and transmission 128 are mounted on the front end 130 of the frame 122. The transmission 128 drives a driveshaft 132 that provides torque to the differential 134. The differential 134 drives right and left axles 136 and 138. The differential 134 and right and left axles 136,138 are mounted toward the rear end 140 of the truck 112. The front end of the truck is supported on front wheels 146, while the rear end of the truck is supported on rear wheels 148. Rear wheels 148 may be either tandem or single wheels. The rear wheels 148 are mounted on a carriage frame 150 that supports the rear end of the frame 122 by means of air springs 152. The front wheels 146 also include a trailing arm spring suspension 156 that may either include leaf, coil or air springs.

The rear wheels 148 have hubs 154. The load floor is normally at a level that is below a top portion of the hubs 154.

Referring specifically to Figure 13, a ramp 158 may be provided in the rear of the vehicle to facilitate ingress and egress from a rear cargo door 160.

Referring now to Figure 14, an air spring control system 164 is shown schematically. The air spring control system includes a valve 166 that is operated by solenoid 168. Air supply tubing 170 supplies air from a compressor 172 to the air springs 152. A control panel 174 is provided to permit raising or lowering the rear end 140 of the frame 122 by simply increasing or decreasing the amount of air

supplied to the air springs. The load floor may be lowered by approximately three inches from the normal driving height by releasing air from the air springs 152.

Conversely, the air springs 152 may be provided with an increased volume of air to raise the load floor 114 three inches above the normal operating height, if desired.

The air supply for the air spring control system 164 is provided by an air compressor that is either powered by the vehicle battery 176 or may be accessory driven by the engine.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.