FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
IMPROVEMENTS IN AND RELATING TO DRAFT SENSING MECHANISM OF TRACTOR


2. APPLICANT
MAHINDRA & MAHINDRA LTD.
1, GATEWAY BUILDING, APOLLO BUNDER, MUMBAI - 400001. AN INDIAN COMPANY.

The following specification describes the invention.


Field of the Invention
The present invention relates to hydraulic power lifting mechanism having application in the field of off-road vehicles and farm machineries such as tractors, and more particularly, to a draft sensing means and construction thereof.
Background of the Invention
Generally, farm machineries such as tractor and vehicles that work in farm land are provided with an arrangement such as three point linkage to attach earth-working implement(s), in the rear end of the vehicle, which is linked to the hydraulic power lifting mechanism. When these vehicles operates with earth working implement, chances are very often that it comes across many obstructions such as stone, rocks, hard soil and the implement gets stuck up with the mentioned obstructions. Also the depth of soil may vary due to ground undulation, further, weight transfer and/or wheel slip may cause the change in the pull of the implement on the tractor. Hence, it is necessary to control the implement so as to avoid variations in depth (its insertion in soil) or to avoid any damage to the implement..
The conventional practice of sensing the draft force generated by implement is done by providing a draft responsive unit in between the implement and hydraulic actuation system, having a spring member connected with top link to sense the draft and linkages for transferring the sensed force to the hydraulic system. But, providing a linkage for transferring force may lead to delay in response time and adversely affecting accuracy of draft force because of multiple number of links and relative movement there between. Also, serviceability and maintenance becomes a time consuming and tedious task since the


draft sensing unit is directly linked/attached with entire hydraulic system. Some of the inventions in this regard are being described hereunder as prior art:
GB Patent 1036774 discloses a lifting mechanism for tractor-drawn earth-working implements having a drag responsive unit that comprises a support member to which a bearing member is pivoted; the bearing member rests, through a curved leaf spring, resiliency against the housing and receives the end of the upper link via a bore provided therein. A lever is firmly connected to the bearing member to transfer the force to mechanical linkages provided inside the housing. The above invention consists of more number of relatively moving parts which may greatly affect accuracy of sensing draft force, also with need of more efforts and time for service and maintenance related activities.
GB Patent 876258 discloses a hydraulic power lift system comprising a draft responsive unit which further consists of a casing supporting a transverse pivot for a bell crank lever having an upper forwardly extending arm co-acting with a vertically disposed draft load reaction spring, a downwardly extending arm provided with a projection in contact with a sliding member and a pivotal connection adapted to receive top link of three point linkage at the lower end thereof. According to this invention, it is quite difficult to predict the component of actual draft force to design draft responsive unit, more particularly, spring member due to continual proportionate variations of compression force exerted on top link by implement and the corresponding position of the bell crank lever compared with proposed invention. Further, it comprises more number of movable parts that leads to configurational intricacy, also owing to relative motion of parts

it is vulnerable to friction thereby bringing in increasing inaccuracy in the system over time, which further leads to frequent maintenance and time consuming service work.
EP Patent 0693250 discloses draft force sensing arrangement, preferably, for sensing draft force by connecting to top link. It comprises a back plate directly mounted on tractor and provided with a bore to receive an electrical draft force sensing pin, further acting as a support for mounting spur which is used to connect the top link. The construction is made of casting and requires machining with appropriate tolerance(s) to make the intended invention effective and requires high amount of material due to lack of compactness in size. Also it needs control unit because of the electrical sensing pin which further leads to design complexity and high costs and further necessitates need/use of additional electrical power other than hydraulic power.
US Patent 4425970 discloses tractor draft sensing apparatus including a draft link, further including sensing means, a mounting member and restraining means which are all commonly interconnected with the tractor by means of support plate. It also includes a sensing arm connected to the mounting member and having a portion disposed adjacent to the restraining means and engaged by the sensor, the sensing means detecting variations of horizontal draft forces transmitted by lower draft link. Sensing of the draft force getting generated vertically is not possible due to the construction of the said invention and further thereto, lower draft link is the sensing device sensing force from the implement and not the top link. Also the sensing means which is used here is in the form of electro-mechanical transducer which in turn further requires control unit and additional


electrical power apart from hydraulic power. Serviceability and maintenance is also a complex and tedious activity here because of more number of parts and complex design, further to that, consumes more time due to interconnected assembly of system with tractor.
Hence, to overcome the aforementioned disadvantages, it is necessary for farming industry to develop a system with low-cost, easily serviceable and more reliable draft sensing means that can sense draft force exerted by implement on top link and thereupon send signal to hydraulic system to lift the implement automatically, without needing intervention of the operator, and lower it down when draft force diminishes.
Summary of the Invention
The present invention overcomes the shortcomings associated with the prior art and achieves other advantages not realized by the background art.
The main object of the present invention is to provide a draft sensing means for transferring draft force to the hydraulic power lift system with high accuracy by minimizing relatively-moving components between them.
Another object of the invention is to avoid frictional movements amongst the relatively moving components, thereby improving system response and reliability


Yet another object of the invention is to provide a draft sensing means with easily serviceable, maintainable, cost effective construction and simple design.
Yet another object of the invention is to provide a draft sensing means of such a kind that the whole sensing means, as such, can be dismantled at any time from hydraulic power lift system without disturbing the initial draft control setting.
Yet another object of the invention is to provide a draft sensing means having a point contact sensing to improve the accuracy of draft force response as well as for easy serviceability of the sensing means.
Yet another object of the invention is to provide a draft sensing means to restrict undesirable deflection of spring member thereby to increase reliability of spring member further to improve the reliability of hydraulic power lift system.
In accordance with the present invention one aspect of draft sensing means comprises:
a spring member which is directly mounted on the hydraulic housing, a stopper and a projection member disposed on the said spring member to make a point contact with a plunger thereby to transfer the draft force to hydraulic power lift system. Thus, when the implement gets stuck up in the ground, it exerts draft load on the top link which further compresses leaf spring so as to transfer said draft load sensation to the hydraulic system by giving linear movement to the plunger proportionally.


Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Brief Description of the Drawings
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the same are described here below in details with reference to the accompanying drawings.
FIG. 1 is an exploded perspective view of the present invention and assembly thereof with tractor hydraulic housing.
FIG. 2 is an illustrative side view of the present invention in mounted position with tractor hydraulic housing.
Detailed Description of Preferred Embodiment
Referring now to drawings and specifically to FIG. 1, shows a draft sensing means 1 according to present invention comprising a leaf spring 2, having a first extended portion 14 and a second extended portion 15 of substantially flat surface along the width thereof, being constructed in such a way to have surfaces of both first extended portion 14 and second extended portion 15 facing each other, as shown in FIG. 1 and 2, to give elasticity to the free end 17 of leaf
3 0 MAR 2009

spring 2. It is understood that the loop 16, first extended portion 14 and second extended portion 15 are made of homogeneous material and make a continuous body to form the said leaf spring 2. The first extended portion 14 is made shorter than the second extended portion 15 along the length of leaf spring 2. Said leaf spring 2 is disposed on tractor hydraulic housing 13 so that the loop comes on the upper side (as shown in FIG. 1) and first extended portion 14 is away from the housing 13. The second extended portion 15 is provided with required number of holes sufficiently above the level of free end 17 for mounting the said leaf spring on the housing 13 using studs 11.
Referring to FIG. 1 and 2, draft sensing means 1 consists of first plate 3 and second plate 19, which are laterally mounted on the first extended portion 14 and provided with pivot holes 10 in each plate 3 and 19 (making a pair of holes), of same size so as to receive a top link pin (not shown) in either of the two (optional) positions. Optionally, more than one pivot holes can be provided to give multiple ranges of draft, which descent from upper pivot holes. According to the present invention, both plates 3 and 19 are made separate for easy replacement of either one cost-effectively in case any one gets damaged; without such arrangement, replacement of the whole top link mounting member would be necessary. Optionally, it is possible to provide an integrated mounting member for top link pin if desired so. The second plate 19 is provided with a lock plate 12 (seen in FIG. 2) to arrest rotational movement of pin inside the hole 10 so that wear of the pin can be minimized, thereby also improvising reliability of the pin. The forward end of first plate 3 is provided with sufficient number of holes to mount a projection member 6, with fasteners such as bolt, in such a way as to make contact with mechanical draft force sensing means, such as plunger (not shown), disposed functionally in hole 7 provided in the housing 13. Optionally, the said projection member 6

can be an integral part of first plate 3 or can be integral part of top link mounting member. In accordance with present invention, intention of sensing the draft force via a point contact is that the draft sensing means 1 can be dismantled at any time without disturbing the initial draft control setting thereby the accuracy of sensing draft force is also improved.
The present invention further consists of a stopper member 4 (ref. FIG. 1) having a slot 8 along the width and provided with mounting holes 9 along the length thereof. The stopper member is mounted over the second extended portion 15 (of the leaf spring 2) further on to the housing 13, longitudinally, so as to receive the free end 17 (of the leaf spring 2) in the backward extreme (shown in FIG. 1) of the slot 8 provided in the stopper member 4. The length of the slot is determined based on the maximum deflection the free end 17 should be allowed to exert towards the tractor body, while transferring the draft force sensation to the hydraulic power lift system. The said stopper member being mounted via fastener such as bolt 5 on the housing 13 to give added support strength to the leaf spring 2 and to restrict the excess deflection of free end 17 thereof, thereby to improve strength and reliability of the draft sensing means and also to make its servicing more convenient and simple by way of enabling easy removal of the stopper member 4 without having to disturb other components of draft sensing means 1.
Operation of the aforementioned construction according to the present invention, with reference to FIG.l and 2, is described hereunder. When implement depth increases, it exerts draft load on the toplink, connected to the plates 3 and 19 via a pin inserted through holes 10, which further presses the first extended portion 14 of the leaf spring 2 towards the tractor body. The projection member 6 attached to the
30 MAR 2009

first plate 3 also moves forward along with deflection of the first extended portion 14 moving the plunger in turn which is always in contact with the projection member 6, to activate the hydraulic system, thereby to cause lifting of the implement. After passing such condition of depth variations, leaf spring 2 returns to its normal form and position due to elasticity, thereby causing similar return movements of the projection member 6 and the plunger so that hydraulic system sensing the same moves the implement back to its initially set position.

Shyam Sunder Iyer Patent Agent
Dated this 30th day of March 2009