FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
& The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Draft force sensing device for a work vehicle
APPLICANT
Mahindra & Mahindra Ltd., Gateway Building, Apollo Bunder, Mumbai 400 001, Maharashtra,
India, an Indian company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to
be performed:

FIELD OF THE INVENTION
[0001] The present invention generally relates to work vehicles and more particularly to,
draft force sensing devices that sense the applied draft load on work vehicles.
DESCRIPTION OF THE BACKGROUND ART
[0002] Generally, work vehicles or off-road vehicles, for example tractors, movers, earth
movers, etc., have working implements attached on a rear end of the work vehicles. Specifically, the working implements are operably coupled to a three point linkage/hitch that is further operably connected to a hydraulic actuating system of the work vehicle. Whenever the work vehicle along with the implement operates on a work field, a continuous draft load is exerted by the working implements on the work vehicle. This may happen due to obstructions such as stones, rocks, uneven ground level, hard soil, etc., come in the way of the work implements, or due to variation in depth of the soil from place to place due to ground undulation.
[0003] Work vehicles measure the draft load through draft responsive units that are
installed generally between the hitch and the hydraulic actuation system. The draft responsive unit senses the quantum of the draft load applied on the work vehicle and transmits this sensing to the hydraulic actuation system through. Generally, the transmission of the draft load happens through mechanical means, which depending on the quantum of the applied draft load, lifts the implement from the ground. Once the implement is released from the obstructions, the hydraulic actuation system accordingly drops the working implement on the ground. The necessary penetration of the working implement within the ground could be adjusted through PC/DC levers provided on the working vehicle.

[0004] Typically, the hitch that is connected between the working implement and the
hydraulic actuation system has a top link and a pair of bottom links. The working implement is connected to the bottom link whereas the top link is connected to the draft responsive unit made up of mechanical linkages having an elastic member that is connected to the top link of the hitch. The draft responsive unit senses the quantum of the applied draft load exerted by the working implement and further transfers the draft load signals in accordance with the quantum of the applied draft load to the hydraulic system. The hydraulic system, which comprises of a combination of mechanical linkages and components operably connected with each other, actuates the hitch and therefore the working implements.
[0005] Accurate sensing of the applied draft load and quick response time in which the
draft load signal is transmitted to the hydraulic actuating system for the working implements to be lifted and/or released is imperative and key in work vehicle field operations. Even a slight delay in sensing and responding may result in partial or complete stalling of the work vehicle in the midst of the field operation. Further, the weight transfer and/or wheel slippage may also occur that could further lead to the alteration in the configuration of the working implement mounted onto the work vehicle. Besides these, chances that working implement may get damage are also very high. Though the above noted draft responsive units or mechanical draft sensors offer ruggedness and durability in field operations, however such sensing devices also have major limitations such as in-accuracy in transmission of the draft load signals and poor response timings by which the signals are transmitted to the hydraulic systems thereby resulting in delayed lifting or releasing of the working implements. Such limitations are mainly caused by the hysteresis or load loss which happens due to the relative movement of the interconnected mechanical components and linkages of the draft responsive units. Additionally, serviceability

and maintenance becomes a time consuming and tedious task since the draft sensing units are directly attached to the hydraulic actuations system.
[0006] In order to avoid above problems encountered by the mechanical sensing devices,
electro-mechanical sensing devices in the form of Torsion/Coil springs, strain gauges, EM (electro-magneto) resistors are nowadays used, however they come with their own problems. One of the major problems being calibration of spring based sensors, which requires skills and time do so. Then damage of strain gauges primarily because of shear load damage is also a concern. Though, the EM based resistors provide some relief towards in addressing some of the noted limitations, but they are very costly.
[0007] Thus, it is necessary to develop a draft force sensing devices that could address
some of the above noted limitations yet be able to accurately sense the draft load and transmit the output signal to hydraulic actuation system without any deviation and in a quick response time. Further, the draft sensing devices should be easily serviceable, have low-cost and reliable.
SUMMARY OF THE INVENTION
(0008] Disclosed herein is a draft force sensing device for sensing a draft load applied on
a work vehicle by an implement that is connectable to a three point hitch, the three point hitch operatively connected to a hydraulic system arranged in an electrical communication with a controller, the controller suitably disposed within the work vehicle and electrically connected with the draft force sensing device for receiving electrical signals generated in response to the applied draft load, and accordingly allowing the hydraulic system to lift and release the three point hitch, the draft force sensing device including a sensing rod insertable within a holding bracket of the hydraulic system and connectable to an end of a top link of the three point hitch, the top link transmits the draft load exerted thereupon by the implement to the sensing rod in a

direction perpendicular to a longitudinal axis of the sensing rod, one of the ends of the sensing rod having a seating space for positioning a PCB circuit that is electrically connected to the controller, the sensing rod including, a first mating member having a first elongated body that has a first planar surface, the first planar surface including a closed loop groove formed thereon defining a sensor receiving zone, the sensor receiving zone receiving a substantially thin film sensor connectable to the PCB circuit, and a second mating member having a second elongated body that has a second planar surface, the second planar surface including a protruding boundary formed thereon, the protruding boundary positively fits within the closed loop groove formed on the first planar surface when the first and second mating members are joined.
[0009] In some embodiments, the sensor receiving zone of the first mating member
includes an opening that extends within the body of the first elongated member to be exposed on one of the ends of the sensing rod having the PCB circuit positioned thereon, and wherein a connecting wire of the thin film sensor extends through the opening to be electrically connected with the PCB circuit.
[0010] In some embodiments, a sealing device is positioned within the closed loop
groove of the first mating member, the sealing device provides a tight sealing between the first and second mating members when joined together.
[0011] In some embodiments, the first and second elongated bodies are formed to have
conforming semi-circular shape, and wherein the sensing rod is formed to have a cylindrical shape having smooth outer peripheral surface when the first and second mating members are joined together.
A BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above-mentioned and other features and advantages of the various
embodiments of the invention, and the manner of attaining them, will become more apparent and will be better understood by reference to the accompanying drawings, wherein:
[0013] FIG. 1 is a perspective view of a tractor having a draft force sensing device
operably connected between a hydraulic system and a three point hitch according to an embodiment of the present invention;
[0014] FIG. 2 is a perspective view of the draft force sensing device of FIG. 1 coupled
with a top link of the three point hitch according to an embodiment of the present invention;
[0015] FIG. 3 is a front perspective exploded view of the draft force sensing device of
FIG. 2 illustrating constructional features thereof; and
[0016] FIG. 4 is a bottom perspective view of the draft force sensing device of FIG. 2.
DETAIILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] FIGS. 1 and 2 shows a rear side of a tractor 100, an example of a work vehicle,
illustrating connection between a partially shown hydraulic system 101 and a three point hitch 102 that is operatively connected to the hydraulic system 101, according to an embodiment of the present invention. The hydraulic system 1 includes a top link 104 and a pair of bottom links 106 that is pivotally connected to the hydraulic system 101. A working implement (not shown) is generally connected to the three point hitch 102. One of the ends 108 of the top link 104 is connected to a draft force sensing device 110 that is suitably attached to a housing 112 of the hydraulic system 101. The draft force sensing device 110 senses the applied draft force by the implement on the three point hitch 102 when the work vehicle is operating on fields. The draft force sensing device 110 generates an output signal corresponding to the quantum of the applied

draft load and electrically communicates the signal to a controller (not shown). The controller may be suitably positioned within the hydraulic system 101. Depending upon the output signal, the controller actuates the hydraulic system 101 to necessary lifting/releasing actions on the three point hitch 102. Releasing or lifting of the hydraulic system 101 accordingly allows the implement to be released or lifted from the ground. It is to be understood that the draft force sensing device 110 may also be suitably incorporated on the connecting points between the pair of bottom links and the implements and electrically connected with the controller. A skilled person in the art would understand that such modifications should be considered to be within the scope of the present invention.
[0018] Preferably, the draft force sensing device 110 is insertable within a holding
bracket 114 of the hydraulic system 101 and rotatably coupled with the top link 104 of the hydraulic system 101 in a manner shown in FIG. 2. The pair of bottom links 106 of the hydraulic system 101 is suitably connected with the housing 112 of the hydraulic system 101. The two bottom links 106 are responsible used for pulling the implement and for adjusting the depth of the implement on a particular nature of working ground. The top link 104 is used for holding the implement in stable position, thereby maintaining the implement on a level plane, when the work vehicle is in operation. The two bottom links 106 are equipped with ball joints to allow flexibility.
[0019] FIG. 3 shows an exploded view of the draft force sensing device 110 that is
primarily constructed of a first mating member 116 and a second mating member 118 couplable together by fastening means, for example, screws (not shown) to form a sensing rod. Preferably, the first and second mating members when joined result in a cylindrical shape that has smooth outer peripheral surface. The draft force sensing device 110 extends between a first end 120 and

a second end 122. The first end 120 is a closed end whereas the second end 122 has some openings 124 that extend to a distance towards the first end 120. A peripheral portion of the second end 122 adjacent to the exposed openings 124 has a seating space 126 to securely position electrical components (not shown) such as PCB, amplifier and their related circuitry. Further, a cap (not shown) may also be arranged to cover the second end 122 of the draft force sensing device 110 so that the electrical circuitry is securely retained at the second end 122. The first mating member 116 and the second mating member 118 may be formed of materials that have properties such as hardness, high compressive strength, durability, etc so that the draft force sensing device 110 can sustain any breakage/rupture when the work vehicle is operating on rough terrains, s
[0020] As seen in FIGS. 3 and 4, the first mating member 116 is formed of a first
elongated body 127 that has a first planar surface 128. The first planar surface 128 has a sensor receiving zone 130 that is formed by providing a closed loop groove 132 on the first planar surface 128 through known means (FIG. 3). The second planar surface 133 of the second mating member 118 has a protruding boundary 134 formed to conform the shape of the closed loop groove so that when both the first and the second mating members 116, 118 are joined together they have positive fitting therebetween. As seen in FIGS. 3 and 4, an ultra thin film sensor 136, which is a proprietary of Tekscan Inc., USA, is taken and positioned on the sensor retaining zone 130 of the first mating member 116. As seen in FIG. 3, the sensor retaining zone 130 of the first mating member 116 also has a passage 138 formed therein that first, extends inwards within the planar surface 128 of the first mating member 116 and second, extends towards the second end 122 of the first mating member 116 (FIG. 2) for being exposed. A skilled person in the art would

understand that the passage 138 serves for connecting the ultra thin film sensor 136 with the electrical components positioned on the second end 122 through an electrical wire 140.
[0021] Preferably, the ultra thin film sensor 136 has 0.008 mm of thickness and due to
that the ultra thin film sensor 136 is easily sandwiched between the first and second mating members 116, 118 of the draft force sensing device 110. Further, the shape of the ultra thin film sensor 136 is taken to be circular. It should however be noted that the above thickness and shape is not critical for performance of the invention and limiting rather it is just illustrative. Various other modifications in the thickness or shape of the film should be considered to be within the scope of the present invention. Such modifications would obviously be considered within the realm of the present invention.
[0022] As shown in FIGS. 3 and 4, a sealing device 142 such as a gasket or the like
element is preferably positioned within the closed loop grooves 132. The shape of the sealing device 142 conforms the shape and dimensions as that of the grooves 132 so that the sealing device 142 could be comfortably positioned therein. The benefit of using the sealing device 142 between the first mating member 116 and the second mating member 118 is complete isolation of the ultra thin film sensor 136 from the outside environment. Such a requirement is extremely necessary because work vehicles such as a tractor, earth movers, etc., operate mostly in rough conditions and subjected to heavy dust, muddy waters. Complete isolation of the ultra thin film sensor 136 from such severe environmental exposure allows longer durability and also prevents any potential malfunction of the ultra thin film sensor 136.
[0023] Reference is now given to the working of the various embodiments of the present
invention in the following description. In one embodiment of the present invention, the draft force sensing device 110, the constructional features of which are described above, is taken and

connected with the top link 104 of the hydraulic system 101. During operation on work fields, the implement attached to the hydraulic system 101 exerts the draft load the hydraulic system 101 of the work vehicle. An arm (not shown) of the implement that is connected to the top link 104 allows the draft load to be transmitted to the top link 104 of the three point hitch 102. The draft load experienced by the top link 104 is further transmitted to the draft force sensing device 110 connected to the top link 104. In principle, the draft force sensing device 110 is a transducer that converts physical force into a measurable electrical output. The draft force sensing device 110 acts as a force sensing resistor in an electrical circuit. When the draft force sensing device 110 is unloaded, its resistance is very high, however when the draft force is applied to the draft force sensing device 110, the resistance decreases thereby resulting in a signal output. It is to be noted that this resistance measurement can be adjusted so as to increase or decrease the sensitivity of the draft force sensing device 110.
[0024] The electrical output of the draft force sensing device 110 is received by electrical
circuitry positioned on the second end 122 of the draft force sensing device 110 to trigger appropriate output signals. The electrical output generally relate to detection and measurement of a relative change in draft force or applied load, detection and measurement of the rate of change in force, and/or identification of force thresholds. The output signals are subjected to further processing by the amplification circuit and the processed, measurable electrical output signals coming out from the amplification circuit is received by a controller suitably positioned within the hydraulic system 101. Preferably, the electrical circuitry and the controller are connected through wire harness. However, other electrical connections therebetween should also be considered to be within the scope of the present invention.

[0025] The controller receives the output signals and assimilates the current draft load
experienced by the work vehicle by the implement with the stored readings, and accordingly triggers the hydraulic system 101 to control and adjust the height levels of the hydraulic system 101 and the implement. It should be understood by a skilled person in the art that the controller before triggering the hydraulic system 101 to adjust the height of the implement also takes into account input from a position sensor (not shown). The position sensors are suitably disposed on the rear side of the tractor 100 to measure position levels of the implement with respect to the work vehicle and operating ground.
[0026] Preferably, such draft force sensing devices 110 find application in work vehicles
having power of up to 90HP. However, with very little modification, incorporation of such draft force sensing devices 110 in work vehicles having power of more than 90HP could be very easily carried out. A skilled person in the art would easily envisage and appreciate the below noted benefit and advantages that such a draft force sensing device 110 brings in with it when used within such work vehicles.
[0027] The draft force sensing device 110 provides superior linearity & accuracy (±3%),
measures higher implement loads, and generates stable electrical output with respect to load area. Adaptability of such draft force sensing device 110 is very high as no modification in the top link 104, bottom links 106, or in any part of the work vehicle is required. On cost part, such ultra thin film sensors 136 have comparatively less cost associated with themselves and therefore, such draft force sensing devices 110 are very cost-effective. For example, the cost of various currently used draft sensing devices 110 are in range of Rs. 10,000- Rs. 20,000, draft force sensing device 110 as described above in various embodiments may be kept around Rs. 2,000 only. This provides significant cost advantage over the existing draft force sensing devices 110.

[0028] It will be apparent to those skilled in the art that various modifications and
variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

We Claim:
l.A draft force sensing device for sensing a draft load applied on a work vehicle by an implement connectable to a three point hitch, the three point hitch operatively connected to a hydraulic system arranged in an electrical communication with a controller disposed therein, the controller being electrically connected with the draft force sensing device for receiving electrical signals generated in response to the applied draft load, and accordingly allowing the hydraulic system to lift and release the three point hitch, the draft force sensing device comprising:
a sensing rod insertable within a holding bracket of the hydraulic system and connectable to an end of a top link of the three point hitch, the top link transmits the draft load exerted thereupon by the implement to the sensing rod in a direction perpendicular to a longitudinal axis of the sensing rod, one of the ends of the sensing rod having a seating space for positioning a PCB circuit that is electrically connected to the controller, the sensing rod including:
a first mating member having a first elongated body that has a first planar surface, the first planar surface including a closed loop, groove formed thereon defining a sensor receiving zone, the sensor receiving zone receiving a substantially thin film sensor connectable to the PCB circuit; and
a second mating member having a second elongated body that has a second planar surface, the second planar surface including a protruding boundary formed thereon, the protruding boundary positively fits within the closed loop groove formed on the first planar surface when the first and second mating members are joined.
2. The draft force sensing device according to claim 1, wherein the sensor receiving zone of the first mating member includes an opening that extends within the body of the first elongated

member to be exposed on one of the ends of the sensing rod having the PCB circuit positioned thereon, and wherein a connecting wire of the thin film sensor extends through the opening to be electrically connected with the PCB circuit.
3. The draft force sensing device according to claim 1, wherein a sealing device is positioned within the closed loop groove of the first mating member, the sealing device is sandwiched between the closed loop groove and the protruding boundary to provide a tight sealing therebetween when the first and second mating members are joined together.
4. The draft force sensing device according to claim 1, wherein the first and second elongated bodies are formed to have a conforming semi-circular shape, and wherein the sensing rod is formed to have a cylindrical shape having smooth outer peripheral surface when the first and second mating members are joined together.

6. The draft force sensing device according to claim 1, wherein a plurality of holes are formed within the first and second elongated bodies and each of the holes match with each other when both the first and second mating members are joined, each of the matching holes receiving a fastening member for providing tight fitting between the first and second mating members.
7. The draft force sensing device according to claim 1, wherein the thickness of the thin film sensor is about 0.008 mm.