Leaf Spring Vehicle Suspension

A rear axle of a vehicle is typically mounted on the frame by a leaf spring whose opposite ends are continually held to the frame by connectors and whose middle portion lies directly over the rear axle. The leaf spring is preferrably constructed so that under quiescent conditions its top is flat. When the spring is "reversely" curved, so that its top surface is convex, the ride is harsh. One way that has been used to avoid reverse bending is to place an air sleeve or air bag between the frame of the vehicle and the axle. However, this has been found to still result in a relatively harsh ride. An air sleeve would appear to be a good mechanism for helping to absorb shock in combination with the length of the leaf spring, but none of the systems known to applicant have produced a very smooth ride.

It may be noted that air sleeves have been proposed in the patent literature for use in conjunction with leaf springs to support one end of the leaf spring, with all of the load transmitted through the front portion of the leaf spring being transmitted through the air sleeve. In two patents of this type, U.S. Pat. No. 3,309,107 by Chieger (FIGS. 5 and 7) and U.S. Pat. No. 3,063,732 by Harbers, air bags or sleeves have been placed at the front of the leaf spring so all shock has been transmitted through the air bags. However, such air bags must be large so they are capable of transmitting large forces, since at least half of the weight supported by the adjacent vehicle tire must be transmitted through the air bag. Also, the air bag then does not avoid reverse spring curvature. An air sleeve assembly which enabled most of the shock to be transmitted through ordinary connectors, with a moderately low capacity air sleeve serving to supplement the leaf spring and prevent reverse curvature of the leaf spring, and which resulted in a very smooth ride, would be of considerable benefit.

In accordance with one embodiment of the present invention, an improvement is provided for a suspension system of the type wherein a portion of a vehicle frame is continually attached to the ends of a leaf spring whose middle is supported on a vehicle axle. The improvement enables most of the weight of the vehicle frame that is carried by a tire, to be carried by the leaf spring while effectively absorbing shocks. The improvement includes an air sleeve device which is coupled between the leaf spring and the vehicle frame to support some of the weight of the vehicle frame on a middle portion of the spring. The air sleeve device lies forward of the axle but rearward of the connector which connects the front end of the spring to the frame. The air sleeve device preferrably lies between 25% and 75% of the distance between the axle and the connector of the front end of the spring.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

FIG. 1 is a perspective view of a vehicle which utilizes the vehicle suspension system of the present invention.

FIG. 2 is a perspective view of a portion of the vehicle of FIG. 1, showing a suspension arrangement therein.

FIG. 3 is a side elevation view of the arrangement of FIG. 2.

FIG. 4 is a sectional view of an air sleeve device of the arrangement of FIG. 3.

FIG. 1 illustrates a vehicle 10 which has front and rear axles 12, 14 that are supported on front and rear wheels 16, 18. As shown in FIG. 2, the axle 14 supports a leaf spring 20 which, in turn supports the chassis or frame 22 of the vehicle. The leaf spring has front and rear ends 24, 26 that are connected through connectors 28, 30 to the frame, and has a middle 32 that is supported directly over the rear axle 14.

The leaf spring 20 includes several leafs of varying length, with the uppermost leaf 20U having ends extending in loops to form the ends of the spring. The connector 28 is attached to the front end 24 of the spring by a bolt 34 that passes through the looped end of the spring, while the front connector itself is attached by several bolts to the vehicle frame. Thus, the front of the spring is continually connected to the vehicle frame, even in the quiescent condition of the vehicle, to continually transfer part of the frame weight to the front end of the spring for transfer to the axle 14. The rear end 26 of the spring is formed by a loop of the top leaf. The rearward end 26 is held by a bolt 36 that passes through it and the upper end of a shackle 38. The lower end of the shackle is pivotally mounted about a lower bolt 40 on a lower rear connector 42 that is bolted to the vehicle frame. A portion of the vehicle frame weight is continually supported through the rear connector 42, the shackle 38, and the rearward end of the spring 26. In this way, the entire length of the leaf spring continually carries part of the weight of the vehicle frame.

In the absence of an air bag or air sleeve 46, the leaf spring can undergo reverse bending, as indicated at 20A in FIG. 3, wherein the upper surface of the leaf spring becomes convex. In that case, the leaf spring cannot absorb shocks as well and the vehicle frame is subjected to large shocks from a road of given uneveness. It is possible to apply an air sleeve at the position 32 which is directly over the axle 14, to slightly depress the middle of the leaf spring to avoid reverse bending. However, applicant has found that this leads to a harsh ride. Applicant has also tried the placing of an air sleeve between the vehicle frame 22 and the rearward portion of the spring which lies between the middle 32 and the rearward end 26. Applicant has found that this also results in a harsh ride. It is believed that this is due to the fact that when a large bump B in the road is encountered, the vehicle axle will move rearwardly as well as upwardly, as in the direction indicated by arrow 48. An air sleeve along the rearward portion of the vehicle will directly transmit much of this shock directly to the frame of the vehicle, thereby resulting in a sudden shock experienced by a rider in the vehicle.

In accordance with the present invention, applicant applies an air sleeve 46 between the vehicle frame 22 and a middle location 50 on the leaf spring which is spaced forward of the axle 14 but spaced rearward of the front end 24 of the spring. The distance 52 of the air sleeve forward of the axle is preferably between 25% and 75% of the total distance 54 between the axis 56 of the axle and the axis 28a about which the front end of the spring is held to the vehicle. Applicant has found in his experiments that when the air sleeve is placed less than about 25% forward of the axle there is not a great difference between that and placing the air sleeve over the axle, and in both cases a harsh ride is experienced. In a similar manner, applicant has found in his experiments that when the air sleeve is placed more than 75% of the distance 54 forward of the axle 14, that there is not a great difference between the riding quality experienced with such an arrangement and the riding quality experienced when no air sleeve is present at all. Thus, the air sleeve should be placed within the area 56 which is between 25% and 75% forward of the axle 14. It is also preferable that a rear region of the spring which lies between the axle 14 and rear connector 36 does not carry a substantial portion (e.g. over 5% or even 21/2%) of the weight transferred through the spring to the axle or which is applied to the spring by the front and rear connectors. This permits shock absorption along the rearward spring portion by deflection of the leaf spring. It is especially desireable that a rear region 59 which extends behind the axle, between 25% and 50% of the length of the rear spring portion, be free of any device that would transfer over 5% of the total weight.

Applicant has found that the ideal placement of the air sleeve is about 38% of the distance 54 forward of the axle 14 (i.e. between 25% and 50% of the distance 54 forward of the axle). For a Class A Chevy chassis, which is used for trucks and vans, the distance 54 if 26 inches, and it is found that the ideal distance 52 forward of the axle should be about 10 inches, although the ideal distance varies between 9 inches and 11 inches, depending on the individual chassis and leaf spring. For a Dodge Class A chassis, wherein the distance 54 is 281/2 inches, the ideal distance 52 is also about 10 inches. For a Ford Class A chassis, the distance 54 is about 28 inches, and the ideal distance 52 is also about 10 inches. Thus, for Class A chassis the ideal distance 52 is about 10 inches and in all cases the ideal distance 52 is about 38% of the total distance 54. For a minivan wherein the distance 54 is about 21 inches, it was found that good results were obtained for a distance 52 of about 7 inches which is about 33% of the total distance 54.

Applicant has utilized a 4 inch diameter air sleeve of the type illustrated in FIG. 4 for Class A chassis. Such an air sleeve 46 contains pressured gas 72 in a chamber 74 that biases its upper and lower ends 76,78 apart. In a typical installation for a moderate size recreation vehicle, the load carried by each end of the axle 14 is about 1000 pounds. This is indicated by the load arrow 60 is FIG. 3. With the air sleeve 46 containing air at 30 psi, the load carried by the air sleeve is as indicated by the arrow 62, and equals about 175 pounds. The load 64 at the rear of the spring is about 425 pounds, while the load 66 at the front of the spring is about 400 pounds. When a bump B is encountered and the middle of the spring 32 flexes upwardly, the entire spring flexes towards a convex configuration indicated at 20A, but more flexing occurs along the rearward portion of the spring because the air sleeve resists some of the flexing that would otherwise be transmitted to the front portion of the spring. It is found that this results in a smoother absorbtion of shock than heretofore.

In a typical installation of an air sleeve 46 of 3 inches to 41/2 inches in diameter in a recreational vehicle weighing about 4000 pounds, air pressure of between 20 and 100 psi is applied to the air sleeve 46, through a hose 70 (FIG. 4) leading to the spring. Of course, another gas could be used instead of air, but the device is still referred to as an air sleeve. A person installs the air sleeve as shown (and another at the opposite side of the rear axle), and applies the minimum pressure of 20 psi to the air sleeve at each side, if his chassis or frame is level. Then the person drives down a familiar section of rough road with a passenger in the rear. After each drive, if the ride is not "bouncy" he adds 5 psi to the air sleeve pressure and tries the vehicle again. When a passenger in the rear notices a bounce in the ride, then after the vehicle is stopped the pressure is reduced by 5 psi. If one side of the vehicle sags, the pressure in the air sleeve on that side is initially increased so it is 10 psi higher than the other side and then adjusted until the chassis is level.

While an air sleeve is generally preferred as the auxilary resilient load transfer device for resiliently transferring a portion of the vehicle frame weight to the front portion of the leaf spring, other resilient devices such as coil springs could be used instead. Air sleeves have the advantage that the air pressure within them can be easily adjusted to vary the preload and the spring rate, to respectively level the vehicle and adjust the stiffness of the ride. Also, the mass of an air sleeve portion that moves with the leaf spring can be less than the moving portion of a coil spring, so better shock absorption can be obtained. A compromise can be resorted to by using both an air sleeve and a coil spring, as in a device wherein the coil spring lies within an air sleeve, such a device being referred to herein as an air sleeve though of a special type. It is possible to use a lower cost coil spring to transfer at least 5% of the weight, by first using an air sleeve or other means to determine the coil spring characteristics that are needed in a particular situation although this can involve extra time and corresponding cost.

Thus, the invention provides an improvement in a vehicle suspension which reduces the shock felt by passengers therein. In a vehicle suspension which includes a leaf spring having front and rear ends that are connected to the vehicle frame to continually support the frame through the front and rear ends of the spring, better absorption of shock is obtained by the use of an air sleeve placed between the middle of the spring where the axle supports it and the front of the spring. The air sleeve is preferably placed at a distance forward of the axle which is between 25% and 75% of the total distance between the axle and the front of the spring, and preferably between 25% and 50% of this distance forward of the axle. Tests have shown that placement of the air sleeve between about 33% and 38% of the distance between the axle and the front end of the spring, forward of the axle, results in best shock absorption. It also permits a relatively small capacity air sleeve to be used which carries less than half of the total load carried by the air sleeve and the front of the spring during quiescent operation of the vehicle, while effectively absorbing shock. While the air sleeve has been tested and used primarily for rear axle suspensions, it could be applied to front axles.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents .