Claims:1. An electro-hydraulic hitch draft control system (120), for controlling the working depth of an implement coupled to work vehicle, as a function of hitch position based on soil property, comprising of : an electronic control unit (ECU) (121), for receiving input signals from plurality of sources and processing the received input signals; a plurality of sensors (122a,122b), wherein said sensors are in communication with the said ECU (121); a hydraulic manifold valve block (123), operatively coupled to the said ECU (121); a hydraulic system (124) driven by engine (125), is in fluid communication with the said hydraulic manifold valve (123) for providing fluid flow/pressure to the said hydraulic manifold valve (123); a ram cylinder (126), fluidly coupled to the said hydraulic manifold valve (123), wherein said hydraulic manifold valve block (123) controls the flow of fluid to and/or from the said ram cylinder (126); and a hitch system (127) operatively coupled to the said ram cylinder (126), wherein said hitch system (127) is operated by means of the said ram cylinder (126).

2. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, wherein said sensor is a position sensor.

3. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, wherein said sensor is an angle sensor (122a).

4. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, wherein said sensor is a draft sensor (122b).

5. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, wherein said hydraulic manifold valve block (123) includes a lift control valve (128) and a low control valve (129).

6. An electro-hydraulic hitch draft control system (120), as claimed in claim 1 & 5, wherein said hydraulic manifold valve (123) is a electro - hydraulic valve.
7. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, 5 & 6, wherein said hydraulic manifold valve (123) is a proportional flow control valve.

8. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, wherein said hydraulic system (124) includes a hydraulic pump (133), a fluid suction line (134) and a fluid sump (135).

9. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, wherein said hydraulic fluid is hydraulic transmission oil.

10. An electro-hydraulic hitch draft control system (120), as claimed in claim 1, wherein said hitch system (127) is a three point hitch linkage.

11. A method for electro-hydraulically controlling the working depth of an implement coupled to the work vehicle by adaptively modulating the hitch draft control as a function of hitch position, comprising steps of:

a. establishing the set draft (139) in ECU (121);;
b. establishing the set hitch position (138) with respect to the set draft (139) in ECU (121), , wherein said set hitch position (138) and set draft (139) is used as reference signal;
c. detecting the actual hitch position of the hitch system by means of a position sensor;
d. detecting the actual draft force of the hitch system by means of a draft sensor (122b);
e. transmitting the detected signals to the electronic control unit (121), wherein said ECU (121) processes the soil type based on the detected signals and the reference signal;
f. calibrating the real hitch position based on the detected soil property, wherein said real hitch position is calibrated in ECU (121) with a tolerance band according to the detected soil property for achieving the set draft (139);
g. transmitting the calibrated hitch position as controlled actuation signals to the said hydraulic manifold valve block (123) via the ECU (121);
h. energizing/de-energizing the hydraulic manifold valve block (123) based on the received actuation signal; and
i. actuating the said hitch system (127) based on the received actuation signal from ECU (121), wherein said actuation includes lifting/lowering the said hitch system (127) by energizing/de-energizing the hydraulic manifold valve block (123).

12. The method for electro-hydraulically controlling the working depth of an implement coupled to the work vehicle, as claimed claim 11, wherein said position sensor is an angle sensor (122a).

13. The method for electro-hydraulically controlling the working depth of an implement coupled to the work vehicle, as claimed claim 11, wherein said hydraulic manifold valve block (123) includes a lift control valve (128) and a low control valve (129).

14. The method for electro-hydraulically controlling the working depth of an implement coupled to the work vehicle, as claimed claim 11 & 13, wherein said hydraulic manifold valve (123) is energizing/de-energizing by supply/draining of the hydraulic fluid flow into/from the ram cylinder (126) based on the received actuation signals from the ECU (121).

15. The method for electro-hydraulically controlling the working depth of an implement coupled to the work vehicle, as claimed claim 11,13 & 14, wherein said hydraulic manifold valve block (123) receives the hydraulic fluid flow from the said engine driven hydraulic system (124).

16. The method for electro-hydraulically controlling the working depth of an implement coupled to the work vehicle, as claimed claim 11 & 15, wherein said hydraulic system (124) includes a hydraulic pump (133), a fluid suction line (134) and a fluid sump (135).
, Description:HITCH DRAFT CONTROL SYSTEM AND METHOD THEREOF
FILED OF THE INVENTION
The present invention generally relates to draft control system, in particular the present invention is related to electro-hydraulic hitch draft control system of agricultural implement as a function of hitch position.
BACKGROUND OF THE INVENTION
Generally agricultural work vehicles such as tractors are used to tow and move implements through agricultural land performing one or more functions, such as ploughing, planting or seeding, fertilizing, and harvesting in a field. Such implements are commonly connected to tractor by means of a hitch, usually a three-point hitch comprising of lower links to connect the implement and a top link interpose between the tractor frame and the implement. The hitch movement including raising and lowering of the implement with respect to ground are moved by an actuating cylinder positioned between the tractor frame and the lift arms. There exists several control arrangements to regulate the position or elevation of implements. Conventional control system senses the position of the hitch and compares this position to a set operator value. Based on the compared value, control system generates control signals to operate the valve which controls the flow of hydraulic fluid to and from the actuator cylinder configured to vertically move the hitch, to the desired elevation.
Various types of hitch control systems for work vehicles have been proposed based on the need to regulate the elevation of the hitch, which also serves to regulate the position of the implement attached to the hitch assembly during operation. Typically, an operator manually operates a device in the tractor cab to raise or lower the implement accordingly. When the operator finishes manipulating the device, the implement remains in the set position by the operator, however will not maintain the desired depth of engagement or draft load as the implement move across the ground. Changes in field contour or soil hardness causes the depth of engagement and/or the draft load to change. To maintain the implement in a desired position to achieve a consistent draft load or depth of engagement, the operator must periodically check rearward and observe the implement. Introduction of hydro-mechanical hitch control systems replaced the manual operation which relatively had a simple command lever control with which operator became more comfortable. However, when such a control system is operated to raise or lower a hitch with the implement above the ground, the required high gain or sensitivity may cause rapid and abrupt hitch movement which results in undesirable vibration and stress on the linkages and hydraulic components. Other depth-sensing devices include ultrasonic sensors mounted on the implement frame for detecting the height of the frame above the ground. However, these devices are quite sensitive and are adversely affected by trash flow or local soil irregularities.
Recently, hitch control utilizing electronics and/or microprocessors has been applied to hitch mounted implements, these electronic draft control (EDC) systems eliminate the need of manual operator for hitch modulation. The EDC control system allows the adjustment of engagement depth so that a constant draft load is applied to the tractor for its smooth operation. Such control systems typically rely on one or more measuring devices to sense the draft loads applied to the hitch by the implement and/or the implement position, and then accordingly adjust the implement position. In general, electronic hitch control systems operate in one of two modes, "position control" and "draft control" modes. In position control mode the height of the hitch linkage is directly determined by means of a sensor to sense the linkage position. In draft control mode, the hitch is either lifted or lowered so as to achieve the set draft. This is achieved by utilising an electronic signal from a force sensor. In this process set draft is achieved irrespective of hitch position and so the working depth of hitch varies significantly. This is prominent when ploughing or operating soil conditions is heterogeneous, because set draft will be achieved at different hitch position when the soil resistance varies. This phenomenon invariably alters the ploughing depth of the hitch which is one of prime parameter for effective ploughed land which ensures uniform plant germination and effective fertilizer utilization. As soil moisture and soil consistency change, tool penetration can vary over a substantial range for a given set draft.
Therefore it would be a great advantage to provide a constant working depth of ground engagement implement by electro-hydraulically controlling the hitch draft load as a function of hitch position irrespective of different soil conditions, weight of the implement and the set hitch draft force.
US Patent document 3653446 discloses an agricultural tractor having a draft and position responsive hitch control for maintaining an implement at a constant working depth in spite of varying working conditions.
US Patent document 3674095 relates to a servo-control system for an agricultural tractor for operating the valve means of a hydraulic lift to regulate the position of the associated implement according to (a) load or draft, (b) depth or position and (c) a combination or "mixture" of (a) and (b).
However in the above prior-art documents the draft and hitch control are achieved by a combination of hydraulic valves, linkages and joints without implementation of any electronic sensors and/or circuit.
US patent document 4979092 provides a hitch control system comprising of a draft force sensor, a hitch position sensor, an operator command lever, an upper hitch position limit setter, a mixer setter, a drop rate setter and a control unit which generates control signals as a function thereof. The control system includes a first (load) control mode wherein the hitch is controlled as a linear function primarily of sensed draft force and a second control mode wherein the hitch is controlled purely as a non-linear function of sensed hitch position.
US patent document 4809785 relates to an agricultural working vehicle with electro-hydraulic control system for regulating lifting mechanism actuatable by a hydraulic motor, comprising of a plurality of sensors including a position sensor forming an actual value position signal, a force sensor forming an actual value force sensor, and an additional sensor forming an actual value slippage signal dependent on slippage of the driven wheel. Regulation of lifting of the implement coupled to the working vehicle is based on the received modulated output signal.
US patent document 5899279 provides a tractor electronic linkage control system comprising of electronic draft force and linkage position sensors. An electronic control unit derives draft and position error signals and continually compares them to determine whether the system is to operate in draft control mode, where the draft error signal governs linkage movement, or position control mode, where the position error signal governs linkage movement.
US patent application 20080257569 discloses an electronic draft control system for trailed ground-engaging implement of an agricultural tractor that monitors implement height using sensors located on the tractor or sensors coupled to an on-board control communication system and adjusts the implement position in relation to the ground based on draft load, implement height, and tractor wheel-slip to maintain a more accurate, consistent draft load on the tractor while maintaining the implement engaged with the ground.
None of the above cited prior-art documents address the hitch draft control with respect to the soil condition/property. All of the cited prior-art documents teaches draft control using either only hitch draft signal from draft sensor or using hitch position signal or a mix control, which uses a combination of position and draft signals. But none of the prior-art teaches about maintaining a constant ploughing depth and adaptively controlling the hitch draft as a function of hitch position with respect to soil conditions.
The present invention provides a hitch draft control system as a function of hitch position for controlling the working depth of an implement coupled to the agricultural tractor operated with electronic sensing and hydraulic control system. The present invention provides a uniform ploughing depth of a tractor coupled implement irrespective of different soil conditions, implement weight and set hitch draft force. Further the control correction of the present invention is calculated as a function of soil property to avoid system overshoot and delay characteristics. Further the present invention can be used as a retrofit in existing electro-hydraulic hitch control system without the need of any additional sensors, valves and accessories, which provides a cost competitive and better featured product.
OBJECTIVES OF THE INVENTION
The main object of the present invention is to provide a control system for hitch draft control as a function of hitch position.
Another object of the present invention is to provide a hitch draft control system for controlling the working depth of an implement coupled to the agricultural tractor.
Another object of the present invention is to provide an electro-hydraulic hitch control system which enables a constant working depth of a tractor coupled implement when operated in pure draft control mode.
Still another objective of the present invention is to provide a hitch draft control system for enabling a constant working depth of an implement coupled to agricultural tractor irrespective of different soil conditions, implement weight and set hitch draft force.
Still another objective of the present invention is to provide a method for controlling the working depth of an implement coupled to the work vehicle by adaptively modulating the hitch draft control as a function of hitch position.
Yet another objective of the present invention is to provide a hitch draft control system as a function of soil property to avoid system overshoot and delay characteristics.
Final objective of the present invention is to provide a cost competitive hitch draft control system as a retrofit to the existing electro-hydraulic hitch control system eliminating the need of additional sensors, valves and accessories.
SUMMARY OF THE INVENTION
The present invention provides an electro-hydraulic hitch draft control system (120) as a function of hitch position based on soil property, for controlling the working depth of an implement coupled to work vehicle, comprising of : an electronic control unit (ECU) (121); a plurality of sensors (122a, 122b) ; a hydraulic manifold valve block (123), wherein said hydraulic manifold valve block includes a lift control valve (128) and low control valve (129); a engine driven hydraulic system (124) ; a ram cylinder (126), fluidly coupled to the said hydraulic manifold valve (123), wherein said hydraulic manifold valve controls the fluid flow through/from the said ram cylinder (126); and a hitch system (127) operatively coupled to the said ram cylinder (126), wherein said hitch system (127) is operated by means of the said ram cylinder (126). The Electronic control unit (ECU) (121) receives continuous signals with respect to the height of the hitch position and the magnitude of force signal/draft force from the said plurality of sensors (122a,122b). The set draft force (139) and the hitch position (138) with respect to the set draft is stored as reference signals in the ECU (121). The ECU (121) processes the soil type based on the received signals and the stored reference signals, which then calibrates the real hitch position based on the detected soil property for achieving the set draft (139). The calibrated real hitch position is transmitted as a actuator signal to energize/de-energize the said hydraulic manifold valve block(123), which actuates the hitch system (127) to lift or lower the coupled implement by supply/draining a fluid flow into/from the said ram cylinder (126). Supply and draining of hydraulic fluid flow into/from the ram cylinder (126) is controlled by the hydraulic manifold valve (123) via ECU (121), wherein said hydraulic manifold valve (123) receives the hydraulic fluid flow from the said engine driven hydraulic system (124), wherein said hydraulic system includes a hydraulic pump (133), fluid suction line (134) and a fluid sump (135). The electro-hydraulic hitch draft control system present invention provides a constant working depth of the implement irrespective of different soil conditions, implement weight and set hitch draft force. The control correction in pure draft mode is calculated as a function of soil property to avoid system overshoot and delay characteristics. Further the present invention can be used as a retrofit to the existing electro-hydraulic hitch control system eliminating the need of any additional sensors, valves and accessories, which provides a cost competitive and a better featured product.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the tractor coupled with the working implement and the direction of draft force exerted on the working implement.
Figure 2 represents the system architecture of the electro-hydraulic hitch draft control system according to the present invention.
Figure 3 illustrates the schematic hydraulic layout of the electro-hydraulic hitch draft control system of the present invention.
Figure 4 shows working depth profile of the coupled implement with respect to the soil property in pure draft control mode in both existing hitch control system and the hitch draft control system of the present invention.
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
The present invention as embodied by a “Hitch draft control system and method thereof " succinctly fulfils the above-mentioned need(s) in the art. The present invention has objective(s) arising as a result of the above-mentioned need(s), said objective(s) being enumerated below. In as much as the objective(s) of the present invention are enumerated, it will be obvious to a person skilled in the art that, the enumerated objective(s) are not exhaustive of the present invention in its entirety, and are enclosed solely for the purpose of illustration. Further, the present invention encloses within its scope and purview, any structural alternative(s) and/or any functional equivalent(s) even though, such structural alternative(s) and/or any functional equivalent(s) are not mentioned explicitly herein or elsewhere, in the present disclosure. The present invention therefore encompasses also, any improvisation(s)/modification(s) applied to the structural alternative(s)/functional alternative(s) within its scope and purview. The present invention may be embodied in other specific form(s) without departing from the spirit or essential attributes thereof.
Throughout this specification, the use of the word "comprise" and variations such as "comprises" and "comprising" may imply the inclusion of an element or elements not specifically recited.
The present invention provides an electro-hydraulic hitch draft control system (120) as a function of hitch position based on soil property, for controlling the working depth of an implement coupled to work vehicle, comprises of : an electronic control unit (ECU) (121), for receiving input signals from plurality of sources and processing the received input signals; a plurality of sensors (122a,122b), said sensors are in communication with the said ECU (121); a hydraulic manifold valve block (123), operatively coupled to the said ECU (121); a hydraulic system (124) driven by engine (125), is in fluid communication with the said hydraulic manifold valve block (123) for providing fluid flow/pressure to the said hydraulic manifold valve (123); a ram cylinder (126), fluidly coupled to the said hydraulic manifold valve block (123), wherein said hydraulic manifold valve block controls the flow of fluid to the said ram cylinder (126); and a hitch system (127) operatively coupled to the said ram cylinder (126), wherein said hitch system (127) is operated by means of the said ram cylinder (126).
In the preferred embodiment, wherein said plurality of sensors (122a, 122b) is selected from an angle sensor and/or draft sensor, wherein said draft sensor is a transducer.
In the preferred embodiment, wherein said hydraulic manifold valve block (123) includes a lift control valve (128) and a low control valve (129), wherein said hydraulic manifold valve (123) is a electro - hydraulic valve, wherein said hydraulic manifold valve (123) is a proportional flow control valve.
In the preferred embodiment, wherein said hitch system (127) is a three point hitch linkage, wherein said hitch linkage is operatively coupled to the implement.
In the preferred embodiment of the present invention, wherein said hydraulic fluid is hydraulic transmission oil.
Agricultural work vehicles such as a tractor is mechanically connected to the implement by means of a hitch system which is a three point linkage, which is further disposed to lift and lower with respect to the tractor. Lifting and lowering of three point linkage and implement system is done through hydraulic actuator. Three point linkages include a rocker shaft that is rotationally couple to the tractor to permit rotational movement with respect to tractor. Two rocker arms are coupled to rocker shaft which extends inwardly/outwardly. The free ends of rocker arms are pivotally coupled to the upper end of lifting links (130) to lift lowering links. The lower end of lifting links is pivotally connected to centre of lower link (131) where one end is coupled to the rear axle and the other one is free end of lower links thus forming two free ends of lower link for implement attachment. A hydraulic actuator is pivotally coupled to rocker shaft, thus extending the piston of hydraulic actuator caused three point linkages to lift with respect to tractor. Three point linkages also include a top link (132) coupled to tractor and other side is free end to lifting and lowering implement with respect to tractor.
Tractor coupled implement as shown in fig.1, when involved in field operations like ploughing experiences a draft force (143) exerted in the direction opposite to the vehicle travel direction (144). Generally agricultural tractors are connected with various types of implements like MB plough, disc harrow, tiller etc. based on the soil property and cultivation crop. Hence draft force exerted on the implement also vary based on the said parameters. Therefore operator is allowed to set the draft force to maintain the working depth of hitch depending on the operational conditions. This is called as set draft. The Electronic control unit (ECU) (121) receives continuous signals regarding the height of the hitch position from the said angle sensor (122a) and the magnitude of force signal/draft force exerted on the hitch from the said draft sensor (122b). When the measured actual draft force varies from the said set draft value which is stored in the ECU (121), the ECU provides the controlled actuator signal as flow either to lift or lower the said hitch system (127) by supply/draining a fluid flow into the said ram cylinder (126). Supply and draining of hydraulic fluid flow into/from the ram cylinder (126) is controlled by the hydraulic manifold valve block (123) via ECU (121), wherein said hydraulic manifold valve (123) receives the hydraulic fluid flow from the said engine driven hydraulic system (124), wherein said hydraulic system includes a hydraulic pump (133), fluid suction line (134) and a fluid sump (135).
Fig. 2 illustrates the schematic layout of the electro-hydraulic hitch draft control system of the present invention, where the said hydraulic manifold valve block (123) comprising of lift control valve (128) and a low control valve (129), is in communication with the hydraulic system (124) and the said hitch system (127). The hydraulic system (124) comprising of a hydraulic pump (133), fluid suction line (134) and a fluid sump (135) supplies flow/pressure to the said hydraulic manifold block (123) by suction of hydraulic fluid from the fluid sump (135) via suction line filter (134). The system safety pressure is maintained through a system relief valve (136) which is designed in the system based on the maximum hitch carrying capacity of the tractor. Hydraulic manifold valve block (123) comprising of lift (128) and low control valve (129) is operated based on the control actuation signals received from the ECU (121). When lift control valve (128) is energized via Electronic control unit, flow from hydraulic pump (133) passes to the said ram cylinder (126) through the lift control valve (128) and the implement attached to the said hitch system (127) is lifted. Similarly when low control valve (129) is energized via ECU (121), hydraulic flow/pressure from the said ram cylinder (126) is drained to the tank (137) through the said low control valve (129), which constitutes in lowering the implement.
When agricultural work vehicles such as tractor coupled with implement is operated in pure draft control mode, hitch is either lifted or lowered so as to achieve the set draft. In this process set draft is achieved irrespective of hitch position and so the working depth of hitch varies significantly. This is prominent when ploughing or operating soil conditions is heterogeneous, because set draft will be achieved at different hitch position when the soil resistance varies. This phenomenon invariably alters the ploughing depth of the hitch which is one of prime parameter for effective ploughed land.
In an embodiment of the present invention, when the work vehicle coupled with implement is operated in draft control mode, the said ECU (121) continuously receives the signals regarding the hitch position and draft force from the said angle sensor (122a) and draft sensor (122b) respectively. Hitch position (138) at which the set draft (139) is achieved is stored in the ECU, which is used as reference signal, wherein said reference hitch position for a set draft modulates with respect to the changing land profile. Based on the measured hitch position signal and set draft, soil type is predicted. With the known factor of soil property, a tolerance band for hitch position for achieving the set draft is devised. When the controller identifies the referenced soil type as hard type or medium type, hitch will not be lowered when the soil property transitioned from hard to medium soil. This eliminates the variation in ploughing depth of the implement. This also maintains a constant engine speed which is the prime advantage of pure draft control mode.
A method for electro-hydraulically controlling the working depth of an implement coupled to the work vehicle by adaptively modulating the hitch draft control as a function of hitch position, comprising steps of:
a) establishing the set draft (139) in the ECU (121);
b) establishing the set hitch position (138) with respect to the set draft (139) in the ECU (121), wherein said set draft (139) and set hitch position (138) is used as reference signals;
c) detecting the actual hitch position of the hitch system (127) by means of an angle sensor (122a);
d) detecting the actual draft force of the hitch system by means of a draft sensor (122b);
e) transmitting the detected signals to the electronic control unit (121), wherein said ECU (121) processes the soil type based on the detected signals and the reference signal;
f) calibrating the real hitch position based on the detected soil property, wherein said real hitch position is calibrated in ECU (121) with a tolerance band according to the detected soil property for achieving the set draft (139);
g) transmitting the calibrated hitch position as controlled actuation signals to the said hydraulic manifold valve block (123) via the ECU (121);
h) energizing/de-energizing the hydraulic manifold valve block (123) based on the received actuation signal from the ECU (121); and
i) actuating the said hitch system (127) based on the received actuation signal from ECU (121), wherein said actuation includes lifting/lowering the said hitch system (127) by energizing/de-energizing the hydraulic manifold valve block (123).

In an embodiment of the present invention, wherein said hydraulic manifold valve (123) is energizing/de-energizing by supplying/draining the hydraulic fluid flow into/from the ram cylinder (126) based on the received actuation signals from the ECU (121), wherein said hydraulic manifold valve (123) receives the hydraulic fluid flow from the said engine driven hydraulic system (124). The hydraulic manifold valve block (123) comprises of lift control valve (128) and low control valve (129) which is operated based on the actuation signals received from the ECU (121).
In an exemplary embodiment of the present invention, the ECU (121) continuously receives real time signals of hitch position and draft force of the hitch system (127) by means of the said angle sensor (122a) and draft sensor (122b). The ECU (121) then processes the soil type based on the detected signals, set draft (139) and set hitch position (138) stored in the memory. The ECU (121) then calibrates the real hitch position based on the detected soil property, for achieving the set draft (139). The calibrated real hitch position along with the tolerance band based on the detected soil property for achieving the set draft is transmitted as actuation signal to the said hydraulic manifold valve block (123). The said hydraulic manifold valve (123) is energized by allowing a modulated amount of hydraulic fluid/oil inflow into the said ram cylinder (126) through the lift control valve (128). When the lift control valve (128) is actuated via Electronic control unit (121), flow from hydraulic system (124) passes to the said ram cylinder (126) through the lift control valve (128) and the implement attached to the said hitch system (127) is lifted, wherein said amount of fluid/oil required for lifting of the implement is modulated as a function of real time hitch position calculated based on the soil property.
In another exemplary embodiment of the present invention, the ECU (121) continuously receives real time signals of hitch position and draft force of the hitch system by means of the said angle sensor (122a) and draft sensor (122b). The ECU (121) then processes the soil type based on the detected signals, set draft (139) and set hitch position (138) stored in the memory. The ECU (121) then calibrates the real hitch position based on the detected soil property, for achieving the set draft (139). The calibrated real hitch position along with the tolerance band based on the detected soil property for achieving the set draft is transmitted as actuation signal to the said hydraulic manifold valve block (123). The said hydraulic manifold valve (123) is de-energized by allowing a modulated amount of hydraulic fluid/oil outflow from the said ram cylinder (126) through the said low control valve (129) to the said tank (137). When the low control valve (129) is actuated via Electronic control unit (121), hydraulic fluid flow from the ram cylinder (126) passes to the tank (137) through the low control valve (129) and the implement attached to the said hitch system (127) is lowered, wherein said amount of fluid/oil required for lowering of the implement is modulated as a function of real time hitch position calculated based on the soil property.
Fig.3 shows working depth profile of the coupled implement with respect to the soil property in pure draft control mode in both existing hitch system and the hitch system of the present invention. The upper portion of Fig. 3 shows the working depth profile based on the draft force in the pure draft control mode of the existing hitch system (A), where the controller modulates the working depth based on the difference between the set draft and the actual draft through an electro-hydraulic control valve. Generally draft force exerted on the implement varies with respect to soil properties, which also leads to changes in the working depth. In hard soil, working depth for achieving the set draft is lesser than the working depth achieved for set draft in soft soil. Considering when the set draft of “x” kg is achieved at “y “inches of working depth in hard soil, the same draft force will be achieved at “y+?y” inches & (y+2?y) inches for medium and soft soil conditions respectively. Thus uniform ploughing depth cannot be achieved with the existing draft control system. The bottom portion of Fig. 3 (B) compares the working depth profile of the present invention (140) with the existing hitch system (141) in the pure draft control mode, where the set draft load of say Fd=”x” kg is established by the operator in pure draft control mode, based on the soil property. When user demands a working depth through a set draft load say ”x” kg , the present hitch draft control system (120) estimates the soil property like hard, medium or soft. Based on the estimated soil property by the ECU(121), position of the hitch system is adaptively modulated to reduce fluctuations in the working depth. Say a depth variation of 2?y is reduced to ?y (140) by the hitch draft control of present invention as against in the existent (141) hitch draft control system.
Thus the electro-hydraulic hitch draft control system for controlling the working depth of an implement coupled to work vehicle of the present invention provides a uniform ploughing depth of a tractor coupled implement irrespective of different soil conditions, implement weight and set hitch draft force. The present invention calculates the working depth as a function of hitch position based on the estimated soil property to avoid system overshoot and delay characteristics. Further the hitch draft control of the present invention can be used as a retrofit in existing electro-hydraulic hitch control system without the need of any additional sensors, valves and accessories, which provides a cost competitive and better featured product.
It will be apparent to a person skilled in the art that the above description is for illustrative purposes only and should not be considered as limiting. Various modifications, additions, alterations, and improvements without deviating from the spirit and the scope of the invention may be made by a person skilled in the art.

LIST OF REFERENCE NUMERALS
121 - Electronic Control Unit (ECU)
122a - Angle sensor
122b - Draft sensor
123 -Hydraulic manifold valve block
124 -Hydraulic system
125 -Engine
126- Ram Cylinder
127 - Hitch System
128- Lift Control Valve
129 - Low control valve
130 - Lifting link
131 - Lower link
132 - Top link
133 - Hydraulic pump
134 - Suction line filter
135 - Oil sump
136 - System Relief valve
137 - Tank
138 - Set Position
139 - Set Draft
A - Working depth profile of the hitch control system based on the draft force
B - Comparison of working depth profile of existing hitch control system with the hitch control system of present invention
140 - Working depth profile of hitch control system of present invention
141 - Working depth profile of the existing hitch control system
143 - Direction of draft force
144 - Vehicle Direction