WO2018061037A1

WO2018061037A1 - Articulated front-axle for two-wheel driven tractors.

Info

Publication number: WO2018061037A1
Application number: PCT/IN2017/050442
Authority: WO
Inventors: Bhanuprakash S. A.; Nilaventhan I.; Ananth M. CEPHAS; Velavan R. SENGOTTU R.; Pankaj PAWAR
Original assignee: Mahindra & Mahindra Ltd.
Priority date: 2016-09-30
Filing date: 2017-09-30
Publication date: 2018-04-05

Abstract

An articulated super-steering axle assembly (100) for two-wheel driven tractors, comprising: steering axle (110) with 4-bar linkage mechanism; articulating link (104) with radial ball joints; articulation joint (120) fitted at steering axle center (125) and with articulation cross (121) partially enclosing axle (110); unbalanced hydraulic cylinder (102) fitted between bracket (123) and outer wheel (134); tie rod (130) connected between RH and LH knuckle arms (112, 122); pivoting mechanisms (147, 148) fitted on axle's forward and rear face; a cushioning mechanism (106, 109) fitted above the axle; wherein the articulating link is disposed on axle's forward face and tie rod is disposed on axle's rear face at a lower level than the articulating link, for combinedly facilitating oscillation or swiveling of axle with wheels about the tractor's longitudinal axis and articulating them about the vertical axis disposed perpendicular to longitudinal axis and passing through center of articulation cross and axle, to impart additional turning of outer wheel w.r.t. inner wheel to eliminate tractor's dragging.

Description

ARTICULATED FRONT-AXLE FOR TWO-WHEEL DRIVEN TRACTORS FIELD OF THE INVENTION

[0001 ] The present invention relates to tractor wheels turning mechanisms. In particular, the present invention relates to the steering mechanism of two- wheel driven tractors. More particularly, the present invention relates to articulated front-axle for two-wheel driven tractors to achieve shorter turning radius in fragmented small sized farmlands.

BACKGROUND OF THE INVENTION

[0002] A major drawback in Indian agricultural sector is its prevailing small sized farmlands, which are being fragmented further due to growing population. This increasing trend of segmentation of lands creates a demand for machines, e.g. tractors which can increase the farm productivity in such fragmented lands and reduce the farming costs. Thus, the mechanization of such small farmlands is growing slowly and tractors are increasingly being used for agricultural activities, such as tillage of orchards and vine-yards and for potato farming applications. The existing four-wheel and two-wheel driven tractors have a limitation in maximum angle of steered wheels due to axle swing and interference issues and thus the tractor operator needs to take a larger turning radius while turning back at the end of the field, which leads to higher headland loss. Moreover, while negotiating the headland by such larger turning radius, the operator requires more time and more difficulties are faced while turning in tight corners. Furthermore, the operator often tends to apply individual brakes for turning at the end of the farmland, i.e. headland to achieve a shorter turning radius, which also damages the crops standing in that area, thus increasing the crop-losses in these headland areas as well as which causing serious land deterioration.

PRIOR ART

[0003] The prior art document US5046577A (Figure 3b) discloses a steering mechanism for improving the turning radius of a tractor, wherein the wheels are turned relative to the steering axle simultaneous with a pivotal movement of the steering axle relative to the chassis of the tractor. A connecting link interconnects the pivot mechanism pivotally supporting the steering axle relative to the chassis with the steering mechanism such that a manipulation of the steering mechanism to turn the wheels affects a pivotal movement of the steering axle in the same direction in which the wheels are being turned. The pivot mechanism allows for pivotal movement of the steering axle about longitudinally extending horizontal axis in addition to the pivotal movement of the steering axle about a generally vertical axis relative to the chassis. A lost motion linkage interconnecting the pivot mechanism and the steering axle accommodates the differences in arcuate movements due to the pivot mechanism and the steering axle pivotally moving about longitudinally spaced pivot centers.

DISADVANTAGES WITH THE PRIOR ART

[0004] Following are the main disadvantages associated with the tractor disclosed in the above prior-art document:

• Axle pivoted to chassis with offset position (away from the transverse center line connecting the front wheels) and uses a fixed axle.

• Axle transversely oscillating relative to the chassis with respect to aforesaid offset pivotal axis.

• Includes a 6-Bar steering mechanism to achieve the axle translation having a "Bell-Crank" link and a lost motion linkage.

• One of the Steerable wheels becomes closer to the chassis center line than the other side steerable wheel for a turn.

• Axle lateral shift is not symmetric w.r.t to the pivot axis for LH and RH turn, which results in different turning circle radii.

• Steering performance characteristics differs for both side of turns.

• Requires higher number of linkages, thus leading to a higher linkage loss and also necessitates more components for achieving the super steering configuration. With this axle, it is not possible to convert it to a conventional fixed axle. [0005] In addition, the existing tractors require a higher turning radius while maneuvering in tight corners of smaller farmlands, thus leading to headland losses. The time for turning the corners of changing furrows is more and difficult. There are crops losses as well as land deterioration due to individual brake application by the operator for turning in tight corners.

OBJECTS OF THE INVENTION

[0006] Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

[0007] An object of the present invention is to provide an articulated front-axle for two-wheel driven tractors for improving productivity in small sized farmlands.

[0008] Another object of the present invention is to provide an articulated front-axle for two-wheel driven tractors for preventing crop-losses and land deterioration.

[0009] Still another object of the present invention is to provide an articulated front-axle for two-wheel driven tractors to simply and quicken the farming activities, particularly in small-sized farmlands.

[0010] Yet another object of the present invention is to provide an articulated front-axle for two-wheel driven tractors, which improves maneuverability in tight corners of fields.

[001 1 ] A still further object of the present invention is to provide an articulated front-axle for two-wheel driven tractors, which facilitates simultaneous auto- braking of the wheels.

[0012] These and other objects and advantages of the present invention will become more apparent from the following description, when read with the accompanying figures of drawing, which are however not intended to limit the scope of the present invention in any way. STATEMENT OF THE INVENTION

[0013] In accordance with the present invention, there is provided an articulated super-steering axle assembly (100) for two-wheel driven tractors, wherein the articulated super-steering axle assembly comprises:

• a steering axle equipped with a 4-bar linkage mechanism;

• an articulating link, preferably a rod-like body configured with a respective radial ball joint at either end thereof;

• an articulation joint assembly fitted at center of axle and assembled through a partially open articulation cross for enclosing the axle;

• a hydraulic cylinder connected between a bracket fitted on axle adjacent the open portion of articulation joint cross, and center of knuckle arm of the outer wheel;

• a tie rod connected between RH knuckle arm and LH knuckle arm of the respective steering linkages of axle; and

• a respective integrated pivoting mechanism fitted on the forward and rear faces of axle, and a cushioning mechanism placed above the upper face of axle; wherein the articulating link is disposed forward of axle and tie rod is disposed rearward of the axle for combinedly facilitating the articulation of axle assembly with wheels about a vertical axis Y-Y disposed perpendicular to the tractor's longitudinal axis X-X and passing through center of articulation cross and axle, and for oscillating or swinging them about the longitudinal axis to impart a predefined additional turning of axle assembly along with front wheels to steer the tractor to a maximum steering angle either on tractor's LH side or RH side to eliminate tractor's dragging.

[0014] Preferably, the connection of articulating link with the articulation cross is disposed above the connection of hydraulic cylinder with the steering linkage of the outer wheel, for imparting a predefined additional turning angle to the axle with front wheels to steer to maximum steering angle on either side thereof to eliminate tractor dragging. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0015] The present invention will be briefly described with reference to the accompanying drawings, wherein:

[0016] Figure 1 shows a tractor being used for farming activities, such as tillage for making furrows in a small-sized field.

[0017] Figure 2 shows a comparative turn circle radius required to be followed in a field for performing farming activities by using existing tractors and the tractor equipped with articulated axle configured according to the present invention.

[0018] Figure 3a shows a typical kinematics of a conventional 6-Bar chain configuration of mechanical linkage system to achieve axle turning in the field for performing farming activities.

[0019] Figure 3b shows a tractor disclosed in the prior-art and having a conventional 6-Bar chain configuration of mechanical linkage system to achieve axle turning in the field for performing farming activities.

[0020] Figure 4a shows the steering geometry in terms of vehicle dynamics as applicable to the inner (left) and outer (right) wheels, while taking a turn or turning side about the turning radius.

[0021 ] Figure 4b shows the characteristics of the wheel while rolling on ground and on taking a turn or turning side.

[0022] Figure 5a shows typical Ackerman steering geometry for tractor's front axle.

[0023] Figure 5b shows a typical line diagram for steering movement depicting the tractor's front axle in the left-side steered position thereof.

[0024] Figure 5c shows a typical line diagram for steering movement depicting the tractor's conventional front axle in left and right-most position respectively.

[0025] Figure 6a shows the steering geometry for a pivoting or articulating super steering axle configured in accordance with the present invention left- turned to overcome vehicle dragging problem. [0026] Figure 6b shows a detailed schematic view of the front axle and straight steering axles of the super steering axle depicted in Figure 6a before turning.

[0027] Figure 6c shows a detailed schematic view of the articulated super steering axle depicted in Figure 6a.

[0028] Figure 7a shows 4-bar links with one link on ground arranged for a pivoting or articulating super steering axle configured according to the present invention.

[0029] Figure 7b shows a conventional 6-bar linkage (see Figures 3a, 3b) with all the links in the front and having a changed bell crank lever shape provided for a pivoting or articulating super steering axle configured in accordance with the present invention.

[0030] Figure 8a shows a perspective view from top of the front articulating super steering axle equipped with an articulation joint fitted thereon and configured according to the present invention and based on a 4-bar linkage of Fig. 7a.

[0031 ] Figure 8b shows the partially dismantled detailed perspective view of the steering axle of Figure 8a without wheels and articulation link.

[0032] Figure 8c shows a detailed perspective view of the articulation joint of the bell crank lever of the steering axle depicted in Figure 8a.

[0033] Figure 8d shows an exploded perspective view of the front articulating super steering axle of Figure 8a.

[0034] Figure 8e shows a detailed perspective view of the articulation link of the front articulating super steering axle of Figure 8a.

[0035] Figure 8f shows top view of the super steering axle depicted in Fig. 8a.

[0036] Figure 9 shows the friction acting on wheel tyres, while taking a turn.

[0037] Figure 10 shows the torque required to turn the wheels for changing side or turning on a radius. [0038] Figure 11a shows the steering wheel axle as seen from the bottom of the tractor in its normal (straight driving) condition thereof.

[0039] Figure 11 b shows the steering wheel axle as seen from the bottom of the tractor after taking a left-hand turn.

[0040] Figure 11 c shows detailed cross-sectional view of articulation joint of Fig. 8a.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0041 ] In the following, the articulated front-axle for two-wheel driven tractors for improving productivity in small sized farmlands configured in accordance with the present invention will be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the present invention in any way.

[0042] Figure 1 shows a tractor being used for farming activities, such as tillage for making furrows F in an agricultural field AF. The tractor is in position T1 after making a furrow F and the tractor operator is required to turn around along a turning circle having a larger turning radius T to change direction for tilling the next furrow from position T2. This leads to loss of headland HL1 , which also increase time of operation as well as loss of substantial area out of the total tillage area, particularly in agricultural fields in a country like India, which are often fragmented and small in size. Moreover, application of individual brakes by the tractor operator to turn around the tractor also damages crops and deteriorates such small agricultural fields.

[0043] Figure 2 shows a comparative turn circle radii TC1 and TC2 required to be followed in a field for performing farming activities by using an existing tractor T_a and the tractor Ti equipped with the pivoted or articulated super steering axle configured in accordance with the present invention respectively. Here, the loss of headland is HL2 by tractor Ti is substantially less than the headland loss HL1 by tractor T_a.

[0044] Figure 3a shows a typical kinematics of a prototype 1 0 consisting of a conventional 6-Bar chain configuration of mechanical linkage system L1 -L6 to achieve axle turning in the field for performing farming activities. It includes a front axle FA connected to first ends 1 1 , 14 of the knuckle arms L1 , L2 disposed on either side thereof. The other end 18 of the first knuckle arm L1 is connected to the first end 21 of the steering cylinder SC via a link L3 and the second knuckle arm L2 is connected at the center 15 thereof to the other end 22 of the steering cylinder SC. The other end of the second knuckle arm L2 is connected at 16 to the first end of a tie rod L5, the other end 17 of which is connected to the first end of a bell crank lever 20 through a pivot joint fixed on the chassis. The other end of the bell crank lever 20 is connected to the first end 12 of an actuating link L6, the other end of which is connected to the front axle FA at point 13. The front axle FA is connected at the center 23 thereof to another pivot point 30 fixed on the chassis. Here, the axle turning angle is about 20° and the turn circle radius (TCR) is about 3m. This 6-bar mechanical linkage 10 is actuated as follows:

[0045] The rotation 1 of front axle FA through pivoted bell crank lever 20 is actuated via input received from knuckle arm L2. This in turn results in translation 2 of tie rod L5, which in turn causes rotation 3 of bell crank lever 20 and thus leads to translation 4 of the actuating link L6 to finally rotate the front axle FA towards right in this figure. However, the problem faced during actual field trials with above prototype was substantial dragging of vehicle while turning full circle, so a smaller turn circle radius (TCR) could not be not achieved without applying brakes. Further, tie rod touched ground while making 12-13" deep trenches or furrows during performing ploughing operations, because the existing ground clearance was just 10.5" or 270 mm. Therefore, it was felt that smaller TCR and good steering geometry would probably address this problem of vehicle dragging and the improved layout should address the packaging constraints to eliminate the steering linkages touching the ground while doing ploughing up to 12" depth of cut.

[0046] It was further learned from the teachings of Mr. Giorgio Bordini, a pioneer in this field and great innovator that vehicle dragging problem is not because of the problematic steering geometry, but due to vehicle dynamics or the relationship between inner wheel angle v/s rolling resistance. Further, using brakes while turning side, produces a counter force to overcome the drag force, which results in true rolling.

[0047] Moreover, the over steering effect is observed while turning the outer wheel more than usual to achieve 100% geometry, because the outer wheel is loaded more than inner wheel while turning side. The smaller inner wheel angle with brake application resulted in inside dragging, particularly in potato planting operation, so a higher inner angle is a desirable condition. While designing the tractor kinematics, it was also suggested to keep the caster angle in the range of 5-6°, the camber angle 2-3°, kingpin inclination 7.5-8° for a regular tractor and 5-6° for narrow tractors.

[0048] Figure 3b shows a tractor disclosed in the prior-art and having a conventional 6-Bar chain configuration of mechanical linkage system to achieve axle turning in the field for performing farming activities. It includes steerable wheels (19) connected in a pivoting manner to the transversely opposed ends of axle (18) by a pivot axis commonly referred as King pin (24). Each Steerable wheel (19) is provided with fixed steering arm (27) extending outwardly there from and pivotable therewith. The steering mechanism (20) further includes a hydraulic cylinder (14) mounted to either gear housing (22) or steering axle (18). The hydraulic cylinder is provided with a cylinder rod (26) extending transversely from the body of cylinder (25) in opposing transverse directions. A steering link (28) interconnects each respective end f the cylinder rod (26) with a corresponding steering arm (27), such that the extension of the cylinder rod (26) in either transverse direction will affect the pivoting of the steerable wheels (19) via connections of cylinder rod (26) to the steering arms (27) through steering links (28). The Pivot mechanism (31 ) also includes a bell-crank (40) affixed to the first vertical pivot (36) to be rotatable about the pivot axis defined by the pivot (36). Then lost motion linkage (45) pivotally connected to bell-crank (40) at the third vertical pivot (42) and includes transversely extending opposing arms (46) pivotally connected to transversely spaced brackets (47) defines a transverse horizontal axis (49). However, this 6-bar linkage configuration for the articulation of the front axle has the same difficulties as discussed above. [0049] Figure 4a shows the steering geometry in terms of vehicle dynamics as applicable to the inner (left) and outer (right) wheels, while taking a turn or turning side about the turning radius RA. It shows vehicle width T on ground or track, wheel base WB, steering angles a and β, rolling resistance RL and RR and wheel push PL and PR of the inner and outer wheels respectively. The center of gravity CG of the vehicle is disposed between the front (steering) wheel and the rear wheels.

[0050] Figure 4b shows the characteristics of the wheel while rolling on ground and on taking a turn or turning side. The wheel of radius r is rolling on ground and making a wheel foot-print of depth d. The resultant F of the rolling resistance R of the wheel W and vertical weight component VF acts at an angle Θ with respect to the vertical weight component VF.

[0051 ] Figure 5a shows a typical Ackerman steering geometry for a tractor's front axle 40 with reference to its rear axle 50. The axle 40 of turnable front wheels 41 , 42 and axle 50 of the fixed rear wheels 51 , 52 are arranged as radii of circles with a common center point C (Fig. 5b). In contrast to the earlier known "turntable" steering, in which both front wheels were turned around a common pivot, each wheel 41 , 42 shown gains its own pivot close to its own hub 61 , 62 here. A linkage between these hubs 61 , 62 pivots the two wheels 41 , 42 together. By configuring a careful arrangement of the linkage dimensions the Ackermann geometry could be optimized to achieve the best steering performance. This was achieved by making the linkage the length of the track rod 60 (the moving link between the hubs 61 , 62) shorter than that of the front axle 40, so that the steering arms 63, 64 of the hubs 61 , 62 "toe out". On turning the steering, the wheels 41 , 42 also turned according to Ackermann geometry, with inner wheel 41 turning more than outer wheel 42.

[0052] Figure 5b shows a typical line diagram for steering movement depicting the tractor's front axle in the left-most position thereof. The track rod 60 is moved rightwards with respect to the longitudinal axis X-X of the vehicle. In this position, the steering arm 63 makes a smaller angle θι with respect to the axis of the left wheel 41 than the angle Θ2 made by the steering arm 64 with respect to the axis of the right wheel 42 (Fig. 5c). This lateral movement of the track rod 60 is accomplished by means of the steering cylinder mounted on the front axle by means of the steering cylinder mounting arrangement discussed below. The geometric arrangement of linkages in the steering of a vehicle avoids the requirement of tracing out the circles of different radii R1 , R2 on the inside and outside while turning around a curve and so the tyres do not need to slip sideways. Since the rear wheels 51 , 52 are fixed, this center point C is kept be on a line extended from the rear axle 50. Intersecting the axes of the front wheels 41 , 42 on this line requires that the inside front wheel 41 turns by a greater angle δ than the angle So turned by the outside wheel 42 while being steered. This arrangement enhances controllability by compensating for the road surface variations applied to the end of a long lever arm and also substantially reduces the fore-and-aft travel of the steered wheels 41 , 42 on the front axle.

[0053] Figure 5c shows a typical line diagram for steering movement depicting the tractor's front axle in the left and right-most thereof respectively. The track rod 60 is moved leftwards with respect to the longitudinal axis X-X (Fig. 5b) of the vehicle. In this position, the steering arm 63 makes a smaller angle θι with respect to the axis of the left wheel 41 than the angle Θ2 made by the steering arm 64 with respect to the axis of the right wheel 42. Similarly, when the track rod 60 is moved rightwards with respect to the longitudinal axis X-X of the vehicle (Fig. 5b), the steering arm 63 makes a greater angle Θ1 with respect to the axis of the left wheel 41 than the angle Θ2 made by the steering arm 64 with respect to the axis of the right wheel 42. The following equation applies to conventional steering geometry:

R = I/ Sine δ₀;

R = (Cot δι I Cos $o).l + w; and

Y = mX+C

Wherein,

a. R Turning radius,

b. όΌ = Outer steering angle, 0) = Inner steering angle, c. / = Wheel base, w = Track-width. [0054] Figure 6a shows the geometry for the straight rear axle and the pivoting or articulating super steering axle configured in accordance with the present invention turned towards left for auto-braking to overcome the wheel dragging problem of the vehicles. The following equation applies to this super steering's geometry:

w' + w - b

/ + a

w' + b

Cot = ;

I- a

w' 2[b.l + a.w']

(l₊ a) ( a) - (l - a)

Sin *¾

[0055] Figure 6b shows a detailed schematic view of the steering axle linkages of the super steering axle depicted in Figure 6a:

2 tan0 = w/l.

[0056] Figure 6c shows a detailed schematic view of the front axle and straight steering axle of the super steering axle depicted in Figure 6a before and after turning leftwards.

w/2 = c + b = r; b = r- c = r (1 - CosQ); r = w/2; c = r.CosQ); b = r (1 - cosO) = w.(1-cosQ)/2. a = r.SinQ = w.SinQ/2.

[0057] Figure 7a shows a pivoting or articulating super steering axle in accordance with the present invention for providing sufficient ground clearance while turning and configured as a steering axle linkage 100 with the axle articulation by using a 4-bar mechanism with one link fixed as ground G. This mechanism includes an axle pivot AP along with another link or tie rod 1 L1 on ground G. Tie rod 1 L1 is linked to the knuckle arm 1 L2, which in turn is connected to the front axle FA on the left and right side thereof and fixed via links 1 L3, 1 L4 respectively. The position of the driver is along 'X' direction which is transverse to the vehicle front axle. Here, the tie rod 1 L1 is on one side (front or rear) of the front axle FA and the knuckle arms 1 L2 are on the opposed sides of the front axle FA. This facilitates turning the axle 1 10 about a vertical axis Y-Y which is perpendicular to the tractor longitudinal axis X-X (Fig. 1 1 c) and which passes through the center of the articulation cross and axle (125 in Fig. 8a) as well as oscillating or swinging thee axle 1 10 about a longitudinal axis X-X lying (Fig. 1 1 c) on the plane passing through the tractor longitudinal axis, to impart a predefined additional turning of the axle 1 10 along with front wheels 132, 134 to steer to the maximum steering angle either on LH or RH side of the vehicle to eliminate vehicle dragging. This provides 20° turning of the front axle, which prevents vehicle dragging problem, which was observed with the conventional non-pivoting axle using a 6-bar mechanical linkage (Fig.5b). Here, the principle of 4-bar linkage mechanism is successfully adopted and the arrangement is modified to achieve articulation as well as swing of the steering axle, which is much simpler and involves fewer components that the 6-bar linkage mechanism of the prior art, thus reducing the manufacturing and maintenance costs thereof.

[0058] Figure 7b shows the steering axle linkage 200 with a 6-bar mechanical linkage (see Figures 3a, 3b) with all the links in the front and having a changed bell crank lever shape provided for a pivoting or articulating super steering axle for providing sufficient ground clearance while turning side. This includes a redesigned bell crank lever 2L1 connected to one end of the tie rods 2L2 and 2L3 on either side thereof. The other end of the tie rod 2L2 on the LHS is connected to the front axle via a knuckle arm 2L4. The other end of the tie rod 2L3 on the RHS is fixed to the ground 210. The bell crank lever 2L1 and front axle are fixed on ground 210 via link 2L5 and 2L6 on either side of front axle. However, this 6-bar mechanism is more complex than 4-bar mechanism of Fig. 7a, which is finally used for implementing the pivoting or articulating super steering axle configured according to the present invention. [0059] Figure 8a shows a perspective view from top of the front articulating super steering axle 110 equipped with an articulation joint 120 fitted thereon configured according to the present invention and based on a 4-bar linkage of Figure 7a. The steering wheel is used to turn the axle 110 by means an unbalanced hydraulic cylinder 102 to actuate the steering arm for turning the wheels 132, 134 (not shown). A front axle 110 made in a 3-piece (1 10a, 1 10b, 1 10c) box structure (see Figure 8d) is fitted with the articulation joint 120 on the center box-piece (1 10b) thereof. Accordingly, here the 4-bar linkage mechanism (Fig. 7a) reduces the complexity and enables to package the linkages by providing adequate space for the linkage movement. When the steering wheel (not shown) is turned towards left, the piston rod of RH unbalanced hydraulic cylinder 102 (here disposed on the rear side of front axle 110) pushes RH knuckle arm 112, which rotates about the axis of RH king pin 116 and simultaneously pull the tie rod 130 towards right and exerts a force on LH knuckle arm 122 to be turned about the axis of LH king pin 126, thereby causing the turning of both wheels 132, 134 and front axle 110 towards left in this figure.

[0060] Figure 8b shows the partially dismantled detailed perspective view of the steering axle 110 of Figure 8a without wheels, articulation link 104 and articulation joint 120.

[0061 ] Figure 8c shows a detailed perspective view of the articulation joint 120 of the bell crank lever 2L1 of the steering axle 110 depicted in Figure 8a.

[0062] Figure 8d shows an exploded perspective view of the front articulating super steering axle 110 assembly of Figure 8a.

[0063] Figure 8e shows a detailed perspective view of the articulation link 104 of the front articulating super steering axle 110 assembly of Figure 8a. Articulation link 104 is basically a rod having two radial ball joints provided at each end 127, 127 thereof. One end 127 of link 104 is connected to articulation cross 122 the other end 128 of link is connected to the LH knuckle arm 122 on the axle 110. The uniqueness of this link 104 is by virtue of its connection and position, thus it causes the axle 110 to turn about the vertical axis while the wheels 132, 134 are being steered.

[0064] Figure 8f shows a top view of the front articulating super steering axle 110 depicted in Figure 8a. On turning the steering wheel towards left, the piston rod of RH unbalanced hydraulic cylinder 102 pushes RH knuckle arm 112, which rotates about the axis of RH king pin 116 and simultaneously pull the tie rod 130 towards right and exerts a force on LH knuckle arm 122 to be turned about the axis of LH king pin 126, thereby causing the turning of both wheels 132, 134 towards left in this figure. Since an articulation link 104 is connected to the LH knuckle arm 122 having a separate integrated arm, the anticlockwise turning of LH knuckle arm 122 causes the articulation link 104 to be pushed forward. Since the other end of articulation link 104 is fixed on an articulation cross 122, this force acting along the articulation link 104 causes the super steering axle 110 to rotate about the vertical axis of the articulation cross 122 as a reaction force.

[0065] Figure 9 shows the friction acting on wheel tyres, while taking a turn. Accordingly, calculating friction on rubber tires of the vehicles involves using:

- Independent / dependent surface contact area (Coulomb Friction Model).

- 2-dimensional area of the Radius of Gyration (R_g).

- Parallel Axis Theorem.

- Tire width as diameter of contact surface (Circle).

Rg² = I / A

Iz = Ix + Ar²

[0066] Figure 10 shows the torque required to turn the wheels 132, 134 for changing side or turning on a radius on ground G. King pin 116, 126 are attached to the articulating super steering axle 110 and supports the wheels 132, 134 having a width W and revolving on the wheel hub 136. Here, king pin (steering) torque required to turn the wheels is given by equation:

T = L x μ V(W²/B + K²) kg-mm [0067] Figure 11a shows the steering wheel axle as seen from the bottom of the tractor in its normal (straight driving) condition thereof. The features depicted here are same as shown/described in Figs. 8a, 8b, thus not repeated here.

[0068] Figure 11 b shows the steering wheel axle as seen from the bottom of the tractor while taking a right-hand turn. The features depicted here are same as shown/described in Figs. 8a, 8b, thus not repeated here. A typical steering geometry for condition of SAP includes a wheel base of 2200 mm, track-width of 56" at ground with 7.5 x 16" tyres and 16 mm offset. Accordingly,

King pin inclination = 8°

Caster = 4° Camber = 3°

Inner wheel angle = 50°, Outer wheel angle = 36.58° with 0 = 15.3°

Axle turning angle = 20°.

% Ackerman = 73% and Turning Circle Radius = 2.88 mm.

Ackerman Percentage = (Inner wheel angle - Outer wheel angle) /

Inner wheel angle for 100% Ackerman, wherein Inner wheel angle 100% Ackerman = Tan-1(WB / (WB/Tan(Outer wheel angle)

- Front track)) - Outer wheel angle.

[0069] Figure 11c shows detailed cross-sectional view of articulation joint 120 assembly of Fig. 8a. The articulation joint assembly includes an articulation cross 121 enclosing the center box-piece 110b of the axle 110 and which are connected together by means of a center pin 1402 inserted through a central sleeve 1401. Bushes 1403 and 1404 are placed on top and bottom faces of center box-piece, V-seal retainers 1405, 1406 hold V-seals 1407, 1408; oil/dust seals 1409, 1410; and thrust washers 1411 , 1412 inserted before fixing the articulation cross on center box-piece from its top and bottom side. Further, pillow blocks 147, 148 placed forward (bumper side) and rear (engine side) ends of articulation cross after placing oil/dust seals 1475, 1485. The pillow blocks are hollow to accommodate bushes 1476, 1486 at front and rear ends of articulation cross and articulation joint assembly is closed by placing oil/dust seal 1474, 1484 on outer ends of bushes 1476, 1486 and fixing internal circlips 1477, 1487 for locking both ends thereof. A respective plug 1478, 1488 also closes oil channels 1479, 1489 in articulation cross. Finally, articulation cross 121 is also welded on top face of center box-piece along the length of center box-piece 110b and sleeve assembly is welded around its periphery on top, bottom sides of center box-piece.

WORKING PRINCIPLE OF THE INVENTION

[0070] Articulation cross 121 is a uniquely configured feature of the present invention, which facilitates the oscillation or swiveling of the front axle 1 10 about a longitudinal axis X-X (e.g. Fig. 5b) which coincides with the tractor axis when viewed from top (Fig. 8f). Articulation cross also facilitates the front axle to simultaneously turn or swivel about a vertical axis passing through the center 125, 135 of the front axle, this axis being perpendicular to the tractor axis X-X. Articulation cross has integrated pivots to mount the axle as well as cushioning and pivoting arrangement for smooth turning and swiveling of the axle about said vertical as well as longitudinal axis. The front wheels 132, 134 are pivotably connected to transversely opposed ends of the articulating super steering axle by a respective pivot axis commonly referred as King pin 118, 126. Each Steerable wheel is provided with knuckle arm 112, 122 extending outwardly there from and other end of each knuckle arm is mounted with tie rod 130 to steer the wheels simultaneously.

[0071 ] The articulated steering mechanism further includes a hydraulic cylinder 102 mounted on axle and pivoted to RH knuckle arm 112 to actuate the articulated steering motion of the axle.

[0072] This mechanism also includes an articulation link 104 connecting between one end of LH knuckle arm 122 and articulation joint 120. This link facilitates the articulation of the articulated super steering axle relative to the articulation joint, particularly w.r.t. a vertical axis Y-Y perpendicular to tractor's longitudinal axis X-X and passing through axle centers 125, 135. Articulation joint assembly is pivotally mounted to the front axle support-chassis along the longitudinal axis X-X to permit the articulation joint assembly including along with axle mounted with front wheels 132, 134 to transversely oscillate or swivel w.r.t longitudinal axis X-X to negotiate ground undulations by eliminating tractor dragging normally seen in the conventional tractor axle. TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

[0073] The pivoting or articulating super steering axle configured in accordance with the present invention for auto-braking to overcome vehicle dragging problem has the following technical and economic advantages:

• Offers a Super steering on 2-Wheel Drive Front-axle as against provided on 4-Wheel Drive Front axle offered by most of the competitors.

• Achieves same steering characteristic for the LHS or RHS turns.

• Axle pivoted to the chassis on the axle-box center (i.e. inline to the transverse center line connecting the front wheels.

• Axle rotates relative to the chassis w.r.t. the abovementioned pivot axis and achieves a symmetrical axle rotation.

• Achieves axle rotation by means of a 4-bar mechanism.

• Act both as conventional fixed axle and articulated super steering axle.

• Same inner wheel angle & Turning Circle Radius for LHS/RHS turns.

• Same steering performance characteristics for LHS or RHS turns.

• Requires less no. of Linkages, so causes lower linkage-losses.

• Reduced no. of components to achieve the super steering configuration.

• Offers a first of its kind feature to enable articulated super steering axle with a 4-bar mechanism facilitated by disconnecting the 4^th link.

[0074] The exemplary embodiments described in this specification are intended merely to provide an understanding of various manners in which this embodiment may be used and to further enable the skilled person in the relevant art to practice this invention.

Although, the embodiments presented in this disclosure have been described in terms of its preferred embodiments, the skilled person in the art would readily recognize that these embodiments can be applied with modifications possible within the spirit and scope of the present invention as described in this specification by making innumerable changes, variations, modifications, alterations and/or integrations in terms of materials and method used to configure, manufacture and assemble various constituents, components, subassemblies and assemblies, in terms of their size, shapes, orientations and interrelationships without departing from the scope and spirit of the present invention.

[0075] The numerical values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure unless there is a statement in the specification to the contrary.

[0076] Throughout this specification, the word "comprise", or variations such as "comprises" or "comprising", shall be understood to imply including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.

[0077] The use of the expression "a", "at least" or "at least one" shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention.

[0078] Also, any reference herein to the terms 'left' or 'right, 'up' or 'down, or 'top' or 'bottom' are used as a matter of mere convenience, and are determined by standing at the rear of the machine facing in its normal direction of travel.

Claims

We claim:

1 . An articulated super-steering axle assembly (100) for two-wheel driven tractors, wherein the articulated super-steering axle assembly comprises:

• a steering axle (1 10) equipped with a 4-bar linkage mechanism;

• an articulation joint assembly (120) fitted at center (125, 135) of axle (1 10) and assembled through a partially open (1 19) articulation cross (121 ) for enclosing the axle (1 10);

• a hydraulic cylinder (102) connected between a bracket (123) fitted on the axle (1 10) adjacent the open portion (1 19) of articulation cross (121 ) and center of knuckle arm (1 12) of the steering linkage of outer wheel (132);

• an articulating link (104), preferably a rod-like body configured with a respective radial ball joint at either end (127, 128) thereof;

• a tie rod (130) connected between right-hand (RH) knuckle arm (1 12) and left-hand (LH) knuckle arm (122) of the respective steering linkages of axle (1 10); and

• a respective integrated pivoting mechanism (147, 148) fitted on the forward and rear faces of the axle (1 10) and cushioning mechanism (107, 109) placed above the upper face of the axle (1 10); wherein the articulating link (104) is disposed forward of the axle (1 10) and tie rod (130) is disposed rearward of the axle (1 10) for combinedly facilitating articulation of the axle (1 10) about a vertical axis (Y-Y) disposed perpendicular to tractor's longitudinal axis X-X and passing through center (125) of the articulation cross (121 ) and axle (1 10), and oscillating or swinging them about longitudinal axis X-X to impart a predefined additional turning of the axle (1 10) along with front wheels (132, 134) to steer the tractor to a maximum steering angle either on tractor's LH side or RH side to eliminate tractor's dragging.

2. Articulated super-steering axle assembly (100) as claimed in claim 1 , wherein the axle (1 10) is configured in a multi-piece box-structure, preferably in a 3-piece box-structure having a center box-piece (1 10b) and a respective box-piece (1 10a, 1 10c) attached into the center box-piece (1 10b) on either side thereof.

3. Articulated super-steering axle assembly (100) as claimed in claim 1 , wherein the articulation joint assembly (120) is fitted at the center box-piece (1 10b) and the hydraulic cylinder (102) is connected between the bracket (123) fitted on the rear face of the center box-piece (1 10b) and RH knuckle arm (1 12) of the steering linkage of outer wheel (134) and the articulation link (104) is connected at its first end (127) to articulation cross (121 ) and connected at its second end (128) to LH knuckle arm (122) of the steering linkage of inner wheel (132).

4. Articulated super-steering axle assembly (100) as claimed in claim 3, wherein the RH knuckle arm is profiled to connect the tie rod (130) at its first end and king pin (1 16) at its second end and comprises an integrated arm (128a) extended from the second end (128) thereof for connecting the second end of the articulation link (104).

5. Articulated super-steering axle assembly (100) as claimed in claim 3, wherein the LH knuckle arm (122) is profiled to connect the tie rod (130) at its first end and king pin (126), and connected to the second end of the hydraulic cylinder rod connected in between integrated arm.

6. Articulated super-steering axle assembly (100) as claimed in claim 1 , wherein the hydraulic cylinder (102) is configured as an unbalanced hydraulic cylinder and the unbalance thereof facilitates a sequential actuation of the RH and LH steering arms (1 12, 122) for turning the wheels (132, 134) to eliminate tractor dragging while turning sides or driving the tractor along curved paths.

7. Articulated super-steering axle assembly (100) as claimed in claim 2, wherein the multi-piece box-structure of the axle (1 10) comprises a center box-piece (1 10b) of larger length and cross-section than a respective box- piece (1 10a, 1 10c) of smaller length, cross-section and similar shape, slid inside and snugly attached inside and at either end of center box-piece (1 10b) by means of fasteners (1 1 1 , 1 13) for mounting inner wheel (132) and outer wheel (134) by a respective LH and RH steering linkage on the axle (1 10).

8. Articulated super-steering axle assembly (100) as claimed in claim 1 , wherein the pivoting mechanism comprises a respective front and rear pillow block (147, 148) assembly respectively fitted on the forward end of the articulation cross (121 ) for connection to the steering wheel and on the rear end of the articulation cross (121 ) for connection to inner and outer wheels (132, 134).

9. Articulated super-steering axle assembly (100) as claimed in claim 1 , wherein the cushioning mechanism comprises a respective cushion pads (107, 109), preferably made of composite material of high compressive strength, placed above the upper face of the center box-piece (1 10b) and respectively fitted on either side of the articulation joint assembly (120).

10. Articulated super-steering axle assembly (100) as claimed in claim 1 , wherein the articulation joint assembly (120) comprises:

• an articulation cross (121 ) fitted on the steering axle (1 10) by placing a central sleeve assembly (140) between the upper and lower faces of the articulation cross (121 );

• a center pin (1401 ) inserted into the central sleeve assembly (140) inserted through articulation joint assembly (120) for welding thereon around the periphery on the upper surface of articulation cross (121 );

• a respective welded joint formed around the periphery of the central sleeve (1402) protruding from the upper and lower faces of the center box-piece (1 10b);

• a respective pillow block assembly (147, 148) fitted at the forward (bumper side) face and rearward (engine side) face of the articulation cross (121 ) and provided with a respective channel (1478, 1488) closed by a plug (1479, 1489); wherein the articulation cross (121 ) is partially open (1 19) at the rear lower portion thereof for accommodating the bracket (123) thereon for connecting the first end of the hydraulic cylinder (102) thereto and the connecting rod protruding from the other end of the hydraulic cylinder (102) is connected substantially at middle portion of the knuckle arm (1 12) of the steering linkage of outer wheel (134).

1 1 . Articulated super-steering axle assembly (100) as claimed in claim 10, wherein a respective sealing joint is provided at the outer ends of pillow block assembly (147, 148) fitted on the articulation cross (121 ).

12. Articulated super-steering axle assembly (100) as claimed in claim 1 1 , wherein the sealing joint of pillow block assembly (147, 148) comprises a spacer (1471 , 1481 ) placed after inserting a thrust washer (1472, 1482) on the forward and rear ends of the articulation cross (121 ) and a respective bush (1473, 1483) is inserted between the articulation cross (121 ) and the pillow block (1473, 1483) by placing a respective pair of oil/dust seals (1474, 1475; 1484, 1485) on either side of the bush (1476, 1486); and fixing a respective internal circlip (1477, 1487) on the forward and rear faces of the articulation cross (121 ) for locking pillow block assembly (147, 148) thereon.

13. Articulated super-steering axle assembly (100) as claimed in claim 10, wherein a respective sealing joint is provided at the upper and lower faces of the central sleeve (1402) assembly inserted through the articulation joint assembly (120) and center box-piece (1 10b).

14. Articulated super-steering axle assembly (100) as claimed in claim 13, wherein the sealing joint on the central sleeve (1402) assembly comprises a respective bush (1403, 1404) inserted between the articulation cross (121 ) and central sleeve (1402) and a respective oil/dust seal (1409, 1410) is inserted above and below upper and lower faces of the articulation cross (121 ); and a respective thrust washer (1225, 1466) placed on the upper and lower inner faces of the oil/duct seals (1409, 1410); and a V-seal retainer (1405, 1406) provided on the upper and lower end of the central sleeve (140) assembly for holding a respective V-seal (141 1 , 1412).

15. Articulated super-steering axle assembly (100) as claimed in claim 3, wherein the articulating link (104) is disposed forward of the axle (1 10) and tie rod (130) is disposed rearward of the axle (1 10) and the connection of the articulating link (102) with the articulation cross (121 ) is disposed substantially above the connection of the hydraulic cylinder (104) with the steering linkage of the outer wheel, for imparting a predefined additional turning angle to the axle (1 10) assembly along with front wheels (132, 134) to steer the tractor to a maximum steering angle either on LH side or RH side thereof to eliminate tractor dragging.