1) Field of the Invention
This invention relates to vehicle trailing arm air suspension system, more particularly to a driven axle and more relevant to tandem driven axles. Driven axles of trucks carry invariably an input shaft also called pinion shaft to which is connected a propeller shaft to transmit power from engine to the differential assembly from where power is distributed to the wheels. A cardan type universal joint generally joins the propeller shaft and pinion shaft in the driven axle. Angle of pinion shaft is set in a truck to achieve low included angle between the propeller shaft and pinion shaft. Low included angle between the propeller shaft and the pinion shaft will induce low torsional acceleration of the pinion shaft which is desirable. Maintaining the pinion shaft angle around its set design angle in various positions of the axle travel during jounce and rebound is a challenge in a trailing arm air suspension. Change in the pinion angle from its ideal design angle will increase driveline induced vibrations to the suspended mass of the vehicle and also reduce the life of the driveline components including cardan joint. A substantially constant pinion shaft angle maintained around the ideal design angle would result in low cardan joint induced vibrations and longer life of parts in the driveline, including transmission parts.
During vehicle acceleration, deceleration, and braking, the axle is subjected to equal and opposite reactions in response to drive torque and braking torque. Torsional resilience, about the axle lateral axis, is generally incorporated in the suspension systems. In a suspension where the trailing arm is “rigidly” connected to the axle, due to this suspension torsional resilience, the reaction torque on axle changes the pinion shaft angle unless this reaction torque is suitably countered.
2) Description of the Related Art
2.1) Single Driven Axle Suspension:
A typical truck trailing arm air suspension functionally attached to a driven axle has a pair of trailing arm assemblies, comprising pairs of hanger brackets, trailing arms, their attachments to axle and hanger brackets, air springs and shock absorbers. The front end of trailing arm of each assembly is pivotally connected to or longitudinally sliding in hanger brackets. The later is aided by additional tie link between axle and hanger bracket. The middle portion of trailing arm is generally “rigidly” connected to one side of axle housing. The trailing arm generally extends behind the axle where it is connected to an air spring and to a shock absorber. The front portion of trailing arm bears partial suspended weight of the vehicle. The rear portion of the trailing arm bears partial suspended weight through the air spring which is connected to the frame rail. The rigid attachment of the trailing arms to axle combined with pivoted or vertically restrained sliding of the front end of the trailing arm to the hanger bracket, make the suspension inherently reactive to torque induced by traction force and wheel braking torque. Due to the resilience in the suspension system, this reaction changes pinion shaft angle of the driven axle. The effect is more pronounced during vehicle acceleration from stop and during vehicle hard braking. While it is a industry practice to set the pinion angle to its ideal design angle that cancels the joint-working-angle of all the cardan joints in the driveline system, a ‘rigidly axle mounted trailing arm set up’ generally does not maintain the pinion shaft angle during jounce and rebound of axle and during acceleration and braking.
Therefore in a driven axle, it is desirable to have pinion shaft angle closer to its ideal design angle during any condition of power transmission from engine to wheels and wheels to engine and during jounce and rebound motion of axle.
2.2) Tandem Driven Axle Suspension:
Typical trailing arm air suspension of tandem driven axles has two pairs of trailing arm assemblies, each comprising pairs of hanger brackets, trailing arms, their attachments to axle and hanger brackets, air springs and shock absorbers on each axle. The front end of trailing arm of each assembly is pivotally connected to or longitudinally sliding in hanger brackets. The later aided by additional tie link between axle and hanger bracket. The middle portion of trailing arm is generally “rigidly” connected to housing of driven axle. The front portion of trailing arm bears partial suspended weight. Rear portion of trailing arms bear partial suspended weight through air springs. Drive torque is transmitted from front driven axle to rear driven axle through an inter-axle propeller shaft. Output shaft of front driven axle is connected to the inter axle propeller shaft generally by a cardan type universal joint. Other end of inter-axle propeller shaft is connected to the pinion shaft of the rear driven axle generally by another cardan type universal joint. Depending on the geometric configuration of the tandem axles, the pinion shaft angles are set to their ideal design angle to achieve near equal and low included joint angles between the pinion shafts and the inter axle propeller shaft. Angle of the pinion shafts change during drive torque transmission to the pinion shafts of the axles and during vehicle braking due to the torsional resilience (about the axle lateral axis) of the suspension. Angle of the pinion shafts change during jounce and rebound of axles, increasing or decreasing the included joint angles between the pinion shafts and the inter-axle propeller shaft. Both parallel pinion arrangement and broken back arrangement of the pinion shafts are susceptible to change in pinion shaft angle from their ideal design angle. Effect of this change is higher torsional and inertial vibrations emanating from the inter axle shaft joints of both axles causing occupant discomfort and cumulative structural damage to the driveline parts.
One of the advantages of prior art “rigidly” axle mounted trailing arm air suspensions is their simple construction for the application that the suspensions are intended. Prior art rigidly mounted trailing arm air suspensions are more suitable for low torque engines in the range of 1050 ft.lb to 1650 ft.lb wherein the effect of reactive torque on driven axle is lesser. However, pinion shaft angle change during jounce and rebound still exist in these “rigidly” axle mounted air suspensions.
With higher torque output of current generation engines and higher braking performance demands for similar applications, maintaining the pinion shaft angles close to their ideal design angle during vehicle operation has become more challenging with prior art “rigidly” axle mounted trailing arm air suspensions.
The invention is a vehicle trailing arm air suspension system and more particularly a truck driven-axle air suspension system. One of the preferred embodiment of this invention is based on four bar mechanism, the four bars represented by 1) hanger bracket, 2) trailing arm of preferably spring steel and preferably rectangular cross section, 3) link rod and 4) driven axle housing with its attachments. The invention as applied to a single driven axle comprises a pair of trailing arm assemblies. Each assembly comprises a hanger bracket, a trailing arm and its attachments to hanger bracket and axle, a link rod and its attachments to hanger bracket and axle, an air spring and shock absorber. Front end of the trailing arm is pivotally connected to upper portion of hanger bracket. The hanger bracket is rigidly attached to the frame rail. The middle portion of the trailing arm is “spherically” connected to top of driven-axle by two concentric spherical segments one below and one above the trailing arm. The spherical segments are suitably keyed to the trailing arm to prevent linear relative movements between the segments and the trailing arm. The spherical segments are preferably fastened together on either sides of the trailing arm. The said spherical segments are contained and slide inside matching spherical cavities formed in blocks above and below trailing arm. The said blocks together are rigidly attached to top of the axle by clamping them to the axle preferably using U-shaped bolts. All four spherical surfaces have a common center. Required clearance is maintained between the spherical cavities in the blocks and the spherical segments to allow free sliding of the spherical surfaces of segments on the matching spherical surfaces of blocks. The spherical segments combined with spherical cavities in the blocks form a limited articulation spherical joint. The center of the joint thus formed by the spherical surfaces of segments and blocks act as one of four nodes of four bar mechanism. The pivoted connection of the front end of the trailing arm acts as one of four nodes. The portion of the trailing arm, rear of axle, is connected to the bottom of an air spring and to bottom of a shock absorber. Other end of the air spring and the shock absorber are connected to the main frame rail. One end of the link rod is pivotally connected to the lower portion of hanger bracket and other end is pivotally connected to the lower portion of the axle to form one of the links of four bar mechanism. In operation, the hanger bracket acts as the ‘ground link’ of the four bar mechanism and driven axle, with its connections to trailing arm and link rod, acts as the ‘driven link’ of four bar mechanism. This arrangement of four bar mechanism thus formed is geometrically arranged to achieve the required ideal design angle of the pinion shaft. The lengths of opposite links are preferably maintained equal to achieve substantially constant pinion shaft angle during jounce and rebound motion of axle. This arrangement of four bar mechanism makes the suspension substantially non-reactive to traction force reaction and brake torque reaction on axle. Drive torque and brake torque induced reaction on axle, about axle axis, are substantially countered by the front portion of the trailing arm and the bottom link rod. To control the lateral motion of the axle during jounce and rebound, one end of a tie rod is pivotally or spherically attached to the frame rail and the other end of the tie rod is pivotally or spherically attached to the axle. The vertically resilient front portion of the trailing arm and the air spring in the rear portion of trailing arm act as energy absorption elements of the suspension. Though the preferred embodiment of this invention has a vertically resilient front portion of the trailing arm, it can also be a non-resilient trailing arm. The spherical joint on top of the axle substantially relieves the axle of forces that may otherwise strain the axle if the trailing arm is rigidly attached to axle, more particularly during cross articulation when the wheels on either side of the axle are not in same horizontal plane.
In the drawings:
The invention is capable of supporting high torque engines more suitably in the range of 1650 ft lb. to 2250 ft lb. Based on the structural capacity of the components in the suspension, engine torque capacity can be higher.
When used on a 4×2, 6×4, 8×6 (tridem) wheel configuration of a tractor, the invention can substantially cancel cardan joint working angle as explained in the summary of the invention.
When used on a 6×2 configuration of a truck, the invention can substantially cancel cardan joint working angle on driven axle as explained in the summary of the invention and can be, by suitable mechanism, made to lift the rear non-driven axle when the truck is partially loaded or unloaded to reduce fuel consumption and increase tire life.
Due to substantial cancellation of reaction induced by traction force on the driven axle, the frame raise that is inherent in “rigidly” axle mounted trailing arm air suspension is substantially reduced by this invention.
Due to substantial cancellation of reaction induced by braking force on the driven axle, the frame squat that is inherent in “rigidly” axle mounted trailing arm air suspension is substantially reduced by this invention.
Although the above description relates to specific preferred embodiments as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.
Number | Date | Country | |
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61460105 | Dec 2010 | US |