DESC:FIELD OF THE INVENTION
The present invention relates generally to couple a semitrailer to a prime mover, particularly to an improved fifth wheel coupling mechanism to reduce off-tracking without largely affecting the load distribution among the axles of the prime mover.

BACKGROUND OF THE INVENTION
Over the years, commercial vehicles, especially prime mover-semitrailer combinations have become larger and longer. With the increasing demand for their accessibility in remote locations, these vehicles face the problem of off-tracking, which is the ensuing difference in path radii between the front and rear axles of a vehicle as it manoeuvres a turn. Apart from steering the rear axle of the semitrailer, one of the feasible ways of mitigating off-tracking is to shift the fifth wheel coupling rearwards. However, this is limited by the distribution of the semitrailer’s load between the two axles of the prime mover; any rearward shift of the fifth wheel coupling results in the reduction of the total static load on the prime mover’s front axle and hence available traction. This may in turn lead to directional instability of the vehicle.

In recent years, civil design engineers have been considering the turning profile of various vehicle combinations while designing highway intersections, roundabouts and parking lots. This is due to the fact that improper designs could cause accidents; large off tracking of vehicles could be one of the reasons. Off-tracking becomes very significant when large vehicles undertake a turning manoeuvre. The analysis of the movement and loci of various parts of a vehicle when it negotiates a curve is collectively termed as swept path analysis and off-tracking is one of the parameters most engineers focus on. A lot of study has been carried out to formulate mathematical expression for off-tracking. Also, there is plenty of literature in modelling the off-tracking and to reduce it. Though rear axle steering and addition of more articulation joints are well accepted solutions, they are associated with certain drawbacks.

Besides steering the semitrailer rear axle and increasing articulation joints, one could think of shifting the fifth wheel coupling behind the prime mover’s rear axle, though stability issues have to be looked into. In order to maintain proper traction between wheels and ground, load distribution between the prime mover’s axles has to be taken care of, thereby imposing a constraint of load transfer point being positioned in front of the prime mover’s rear axle.

WO1984000936A1 discloses one such arrangement. The connecting arrangement has first and second connectors connectible to the tractor and to the trailer respectively. In one embodiment, a drawbar D' constitutes the connecting arrangement, the drawbar having a beam (15), the first connector at one end of the beam, and a third connector at the other end of the beam. The third connector is attached to a weight transfer hitch W attached to the tractor. In another embodiment, the connecting arrangement is used to connect the tractor and trailer of an articulated semi-trailer. In this case, the first connector is a fifth wheel (30) and the second connector is a king pin (40). The fifth wheel (30) is fixed to the end of an arm (33) pivotally mounted on the chassis (36) of the tractor. The king pin is fixed to the front of the trailer. In both embodiments means (such as a hydraulic ram 17 or 37) is provided for moving the first connector laterally with respect to the central longitudinal axis of the tractor.

WO1984000936A1 has a complex arrangement and requires lot of constructional modifications to the prime mover- semitrailer combination. A drawbar constitutes the connecting arrangement, the drawbar having the first connector at one end thereof, the other end of the drawbar being provided with a third connector for attachment to a weight transfer hitch attached to the tractor. A hydraulic ram controls the lateral movement of the trailer for both right-hand and left-hand turns. The ram is pivotally attached to the beam and pivotally attachable to a connection point on the trailer.

Hence there is a need for a mechanism to reduce off-tracking without affecting the load distribution among the axles of the prime mover.

OBJECTS OF THE INVENTION
It is yet another object of the invention to disclose a coupling mechanism for a prime mover and trailer.

It is an object of the invention to disclose a mechanism to reduce off-tracking without largely affecting the load distribution among the axles.

It is yet another object of the invention to provide a method of coupling to reduce off-tracking without largely affecting the load distribution among the axles.

SUMMARY OF THE INVENTION
To meet the objects of the invention, it is disclosed herein a fifth wheel coupling mechanism for coupling a prime mover and a semitrailer comprising of a roller mechanism and a cylindrical joint on either side of the rear axle of the prime mover.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 shows the 3D model of the prime mover semitrailer with an embodiment of the invention.
FIG 2 shows 3D model of the chassis of the prime mover -semitrailer with an embodiment of the invention.
FIG.3 is the zoom view of an embodiment of the invention.
FIG.4 shows 3D model of the chassis of the prime mover with an embodiment of the invention.
FIG.5 shows 3D model of the chassis of the semitrailer with an embodiment of the invention.
FIG.6 shows the bottom view of 3D model of the prime mover semitrailer with an embodiment of the invention
FIG.7(a). is the geometrical representation of prime mover-semitrailer (top view) with conventional fifth wheel coupling (CFWC)
FIG.7(b). is the geometrical representation of prime mover-semitrailer (top view) with split fifth wheel coupling (SFWC)
FIG.8(a) is the representation of Heading angle of prime mover’s wheelbase.
FIG.8(b) represents Turning geometry of prime mover-semitrailer with SFWC.
FIG.9(a) is the graphical representation of Variation of maximum off-tracking with respect to the kingpin offset, maintaining overall length of the vehicle constant.
FIG.9(b) is the graphical representation of Maximum off-tracking of prime mover semitrailer with CFWC and SFWC at different turning radii.
FIG.10(a) shows the trajectory of the various points of interest on the prime mover-semitrailer with CFWC; turning radius = 600 inches; angle swept = 900°
FIG.10(b) shows the trajectory of the various points of interest on the prime mover-semitrailer with SFWC; turning radius = 600 inches; angle swept = 900°
FIG.11 shows the graphical representation of Transient off-tracking curves for CFWC and SFWC models at turning radius of 600 inches.

DETAILED DESCRIPTION OF THE INVENTION
The invention and its various embodiments are better understood by reading the description along with the accompanying drawings which appear herein for the purpose of illustration only and do not limit the invention in any way.

SPLIT WHEEL FIFTH COUPLING (SFWC)
The basic idea behind SFWC is splitting the functions of a fifth wheel coupling. The functions of a SFWC are:
• Load transfer from semitrailer to prime mover’s chassis
• Transmission of longitudinal and lateral forces between prime mover and the semitrailer
• Imparting articulation, roll and pitch limits (allowing the limited independent motion of semitrailer without transmitting the direct force to the prime mover)

The coupling mechanism of the invention comprises of two sub-mechanisms: a roller mechanism and cylindrical joint.

Referring to FIGs.2-6, the fifth wheel coupling mechanism for coupling a prime mover and a semitrailer comprises of a roller mechanism (10) and a cylindrical joint (20) on either side of the rear axle of the prime mover. The roller mechanism (10) comprises of a roller-track combination, where one or more rollers (1), rotatable around their axis, are fixed to the chassis (24) of the prime mover and a track (2) fixed beneath the chassis of the semitrailer (22) across the width of the semitrailer. The rollers (1) roll over the track disposed above while articulating. (1). Alternatively, the rollers (1) rotatable around their axis, may also be fixed to the chassis (22) of the semitrailer and track (2) on the chassis (24) of the prime mover. The track (2) is in the shape of an arc.

The cylindrical joint (20) comprises of a kingpin (3) rigidly mounted below the chassis (22) of the semitrailer and a cylindrical mating part (4) rigidly fixed to chassis (24) of the prime mover and adapted to engageably receive the kingpin (3). Alternatively, the kingpin may also be rigidly fixed on the chassis (24) of the prime mover and the cylindrical mating part rigidly mounted below the chassis of the semitrailer.

In one or more variations of the embodiments of the invention, a suspension system could be provided to each of the rollers so as to reduce any jolt/jerk during the operation.

Landing gears (not shown in the figures) are mounted to the semitrailer at appropriate distance from the kingpin such that it does not intersect with any part of the prime mover during its operation within the set range of articulation angle.

A spring system could be attached to the inner pivoted ring of cylindrical joint to maintain the default orientation as horizontal. Similar spring system could be attached to the outer pivoted ring of cylindrical joint too to maintain the default orientation as horizontal. This will help while engaging the semitrailer with the prime mover.

The articulation is achieved by the cylindrical joint (20) with 2 degrees of freedom (DOF): rotation about z-axis, i.e., yaw motion and translational motion along positive z-axis, i.e., bounce. The cylindrical joint only offers reaction forces in the x-y plane of the vehicle and all vertical forces are taken care of by the roller mechanism shown. The weight of the semitrailer is distributed between its axle and the roller mechanism according to their respective distances from the semitrailer’s centre of gravity (CG). The need for a roller mechanism is to enable load transfer even when the vehicle is articulating. The roller rolls on the track provided on the semitrailer’s chassis during articulation. In order to prevent the roller from rolling out of the prime mover’s chassis during a sharp turn, the maximum articulation angle is limited by the width of the semitrailer and the distance between the axis of the cylindrical joint and the roller contact point. Further a stopper mechanism could be attached to the arc shaped track so that the rollers don't come off the track in the event of jack-knifing. The number of such rollers can be increased to widen the limits of the articulation angle. Also, another set of arc shaped track and the mating roller mechanisms could be attached at a different radius to make sure that lateral load imbalance of prime mover does not occur during turning manoeuvre with articulation angles close to 900. When the prime mover and semitrailer pass over a vertically uneven road surface, there is a difference in pitch and roll angles between the prime mover and the semitrailer. The roller stays in contact with the track mounted on the semitrailer’s chassis and this movement has to be accommodated by the cylindrical joint. A simple cylindrical joint with the cylindrical mating part which is rigidly fixed to the chassis of the prime mover or semitrailer, would not allow any relative motion between these two units in pitch and roll direction. Hence the cylindrical mating part (4) is provided with two additional DOF: rotation about local x and y axes, with appropriate limits. To obtain the two additional DOF, the cylindrical mating part (4) has an outer ring (6) which is swivably attached to the chassis of the prime mover and an inner ring (5) swivably attached to the outer ring (6) as shown in FIGs.1-6.

Kinematic analysis is a primary step to analyse the steering geometry of a ground vehicle. Once it is found by kinematic analysis that there is significant advantage in terms of reduced off-tracking by implementing SFWC model, further study can be done considering the dynamic effects. In the kinematic analysis, one can find out the trajectory of different points on the vehicle and the zero-speed off-tracking, wherein the mass of the vehicle and the forces acting on it are not considered.
METHODOLOGY
The kinematic analysis of the prime mover-semitrailer with the proposed concept of SFWC is performed and the results are compared with those of the conventional fifth wheel coupling (CFWC) model, assuming that the overall length of the vehicle remains the same, as represented in FIGs. 7(a) and 7(b). FIG. 7a corresponds to the prime mover-semitrailer with CFWC, whereas FIG. 7b corresponds to that of SFWC.

Points A, C, and D represent the centres of semitrailer axle, prime mover’s rear axle, and prime mover’s front axle respectively. Point B refers to the location of fifth wheel coupling in FIG.7a. Kingpin offset is denoted by KO which is the distance between the articulation point and the prime mover’s rear axle. In FIG.7b, Points X and B' refer to the roller mechanism and the cylindrical joint respectively, which are on either side of the prime mover’s rear axle. Lt and Ls are wheelbases of prime mover and semitrailer respectively.

Off-Tracking Model
For calculating off-tracking, a simple bicycle model is considered, neglecting the width of the vehicle. All reference points lie along the longitudinal axis of the vehicle and turning radius is with respect to the centre of prime mover’s front axle, which is the only steered axle in the model considered, however this invention is not limited to vehicle with single steered axle. Also, the non-steered axle groups are represented by an equivalent axle located at the geometric centre of their original positions. As a simple case, it is assumed that the centre of the prime mover’s front axle is tracing a circle (clockwise), which is divided into a number of uniform intervals of arc length 10 mm. FIG.8a depicts the geometry for computing the trajectory of different points on the vehicle. MN and OP represent the prime mover’s wheelbase at (n-1)th and nth interval respectively. A relationship is established between the coordinates of the prime mover’s front and rear axle centres. A program is developed using MATLAB®, which computes the coordinates of the rear axle centre for each position of the front axle centre. In every subsequent iteration, the front axle is advanced by a small distance resulting in ?? increase in the heading angle of the prime mover’s wheelbase. Again the coordinates of the rear axle are found at this position and this process continues. Since a very small increment is considered in comparison with the dimensions of the vehicle, it is assumed that the rear axle moves in a straight line during each interval.

Coordinates of the Prime mover’s Front Axle Centre
The prime mover’s front axle centre follows a circular path of radius R and its coordinates are given by
1(a)
1(b)
where, ?n is the angle swept by the prime mover’s front axle centre with respect to the global X-axis, measured in clockwise direction and the subscript refers to the nth interval.

Coordinates of the Prime mover’s Rear Axle Centre
Heading angle of the prime mover’s wheelbase (?) is (2)
Where ?n = Heading angle of the prime mover’s wheelbase at nth interval
?n–1 = Heading angle of the prime mover’s wheelbase at n-1th interval
?? = Increment in the heading angle
From FIG. 8a,
(3)
(4)
(5)
(6)
Further, using Pythagorean relations,
(7)
The above mentioned distances can be written in terms of the coordinates of front and rear axles of the prime mover as
(8a)
(8b)
(8c)
(8d)

In equation (8), subscripts ‘f’ and ‘r’ refer to front and rear axle centres respectively. Summing up all the above relations, the heading angle of the prime mover is given by,
(9)

Coordinates of the prime mover’s rear axle centre are given by
(10a)
(10b)

where, Lt is the wheelbase of the prime mover.

Coordinates of the Articulation Point
(11a)
(11b)
where, subscript ‘a’ refers to the articulation point and KO is the kingpin offset. For the CFWC model, KO is negative and for SFWC model it is positive.

Coordinates of the Semitrailer Axle Centre
To find the coordinates of semitrailer axle centre (Xs,n, Ys,n) the same procedure as for the prime mover is followed, but with corresponding changes with respect to the wheelbase and the coordinates of the leading point, i.e., Lt is to be replaced by Ls and (Xf,n, Yf,n) by (Xa,n, Ya,n) Subscript ‘s’ refers to the semitrailer axle centre.

Off-Tracking
The turning geometry of the prime mover-semitrailer with SFWC taking a turn is illustrated in FIG.8b. As per the definition, off-tracking for a prime mover-semitrailer is the difference in path radii of the prime mover’s front
axle and the semitrailer axle i.e., (R-R1). For calculating off-tracking, loci of axle centres have been considered. The terms d, ? and R1 in the FIG.8 refer to the steering angle, articulation angle and the radius of the curve traced by the semitrailer axle centre respectively. The off-tracking at any interval n is given by,
(12)
where, (Xc, Yc) are the coordinates of centre of the curve

RESULTS
The prime mover-semitrailer used in the current study is based on AASHTO Standard Design Interstate Prime mover-Trailer WB-62, the specifications of which are attached in Appendix A. The results are analysed considering 2 parameters: maximum off-tracking (OTmax) and transient off-tracking. The former is the maximum value of the off-tracking which can be observed when the value reaches the steady state after a certain rotation of the vehicle. The angle swept to reach the steady state off-tracking depends upon the turning radius.

Maximum Off-Tracking (OTmax)
Retaining the overall length of the vehicle constant, the off-tracking reduces almost linearly as the kingpin offset is increased, as is evident from FIG.9a. This implies that the farther the cylindrical joint from the conventional position of the fifth wheel coupling, the smaller the off-tracking value. But this is limited by the movement of the roller on the chassis of the prime mover, owing to the fact that the roller would roll out of the prime mover’s chassis at higher articulation angles. The track width of the vehicle chosen for this study is about 75 inches and the articulation angle at minimum turning radius is about 65°. Hence the Kingpin offset of 32 inches has been chosen to analyse SFWC model; however this can be further increased by adding more rollers, which in turn reduces off-tracking values. The maximum off-tracking values for the CFWC and SFWC models are found for different turning radii and are plotted as shown in FIG.9b. It is clear that both of these models exhibit similar behaviour and that the value of maximum off-tracking decreases exponentially as the turning radius is increased.

Transient Off-Tracking
FIGs.10a and 10b represent the trajectory of various points of interest on the prime mover-semitrailer with CFWC and SFWC respectively, for a turning radius of 600 inches (slightly more than the minimum centreline turning radius of 492 inches). The origin of the global axis system is the starting point of the prime mover’s front axle centre and vehicle orientation is along global Y-axis with zero articulation angle at this point. It is clear from FIGs.10a and 10b that the semitrailer axle of the SFWC model traces a comparatively larger circle, the trajectory of the prime mover’s front axle centre and initial position being the same in both cases. This implies that for the same turning radius, swept path of the SFWC model is narrower compared to the CFWC model. FIG.11 shows the transient off-tracking curves for both the models at the turning radius of 600 inches and it is evident that there is considerable reduction in off-tracking by implementing SFWC.

Table 1 shows the comparison between CFWC and SFWC models.
Turning radius, inch OTmax, inch % Decrease in OTmax
CFWC model SFWC model
600 380.06 297.29 21.78
700 277.72 229.25 17.45
900 194.11 164.08 15.47
1440 112.65 96.44 14.39
3000 52.42 45.08 13.99
7200 21.68 18.67 13.91
10800 14.44 12.44 13.90
14400 10.83 9.32 13.89

The comparison between CFWC and SFWC models in terms of
maximum off-tracking and percentage decrease in maximum
off-tracking at different turning radii are shown in Table 1. It is evident that with SFWC model, off-tracking can be reduced by up to 21.78% for a turning radius of 600 inches. The percentage decrease in maximum off-tracking shows a decreasing trend with increasing turning radius and it can be inferred that SFWC model is more useful in the cases of sharp turns with space constraints, such as parking lot manoeuvre.

The description describes an exemplary case of single axle semitrailer for the purpose of explanation of the invention alone, it is possible to use the invention in multiple axle semitrailers. Also, the prime mover may have tandem rear axle set.

It will be obvious to a person skilled in the art that with the advance of technology, the basic idea of the invention can be implemented in a plurality of ways. The invention and its embodiments are thus not restricted to the above examples but may vary within the scope of the claims.

Further the above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto. ,CLAIMS:We Claim:

1. A fifth wheel coupling mechanism for coupling a prime mover and a semitrailer comprising of a roller mechanism (10) and a cylindrical joint (20) on either side of the rear axle of the prime mover.

2. A fifth wheel coupling mechanism as claimed in claim 1 wherein, the said roller mechanism (10) comprises of a plurality of rollers (1), rotatable around their axis, fixed to the chassis (24) of the prime mover and a track (2) fixed beneath the chassis (22) of the semitrailer, wherein the rollers (1) roll over the track (2) disposed above while articulating.

3. A fifth wheel coupling mechanism as claimed in claim 1 wherein, the said roller mechanism (10) comprises of a plurality of rollers (1), rotatable around their axis, fixed to the chassis (22) of the semitrailer and a track (2) fixed above the chassis (24) of the prime mover, wherein the rollers (1) roll over the track (2) disposed below while articulating.

4. A fifth wheel coupling mechanism as claimed in claim in any of the preceding claims wherein, the said cylindrical joint (20) comprises of a kingpin (3), a cylindrical mating part (4) adapted to engageably receive the kingpin (3), guide plate to guide the kingpin (3) and a locking mechanism to lock the kingpin (3) in position.

5. A fifth wheel coupling mechanism as claimed in any of the preceding claims where in the said kingpin (3) may be rigidly fixed on the chassis (22) of the semitrailer.

6. A fifth wheel coupling mechanism as claimed in any of the preceding claims where in the said kingpin (3) may be rigidly fixed to chassis (24) of the prime mover.

7. A fifth wheel coupling mechanism as claimed in any of the preceding claims where in the said cylindrical mating part (4) may be rigidly fixed to chassis (24) of the prime mover.

8. A fifth wheel coupling mechanism as claimed in any of the preceding claims where in the said cylindrical mating part (4) may be fixed rigidly on the chassis (22) of the semitrailer

9. A fifth wheel coupling mechanism as claimed in any of the preceding claims wherein the track (2) is in the shape of an arc.

10. A fifth wheel coupling mechanism as claimed in any of the preceding claims wherein the said coupling mechanism may be removably attached on the chassis (22,24) of the semitrailer and prime mover.