Title of Invention

AN IMPROVED HYDRO-MECHANICAL HITCH CONTROL VALVE IN A HYDRAULIC SYSTEM OF AN AGRICULTURAL TRACTOR.

Abstract

An improved hydro-mechanical hitch control valve in a hydraulic control system of an agricultural tractor for controlling lifting and lowering of atleast a primary working implement (45) associated with the tractor, the hydraulic system comprising an oil pump (15) which receives oil from a transmission housing of the tractor via a suction strainer (40) and a filter (41), and a response valve assembly (39) for receiving pressurized oil from the oil pump (15) for supply to the hydro-mechanical hitch control valve, the lifting control of the implement (45) being exercised via a control means comprising a cylinder (42) and a piston (44), the cylinder (42) receiving pressurized oil from the hydro-mechanical hitch control valve, the hydro-mechanical hitch control valve comprising a main control valve body and a load holding valve body, the main control valve body comprises a main spool valve (1), a proportional flow control valve (16), an unloading valve (12), and a back pressure valve, the load holding valve body (19) comprises a bad holding valve sleeve (31), a load holding valve poppet (32), a load holding valve piston (33), and a load holding valve spring (34), the main spool valve (1) having a plurality of land portions (11, 13, 14, 17, 20), and in that a series of holes being configured in the third land portion (17) so that oil flow transmitting from the main spool valve (1) to the cylinder (42) in respect of oil pressure, flow-rate and flow direction is proportionally controlled to cause a corresponding reciprocal movement of piston (43) in the cylinder (42) thereby effecting the lifting and lowering control of atleast the primary working implement (45). [FIGURE 3 & 4]

Full Text

FIELD OF THE INVENTION This invention relates to an improved hydro-mechanical hitch control valve in a hydraulic control system of an agricultural tractor. This control valve is used for controlling lifting and lowering of atleast a primary working implement as well as controlling the depth and draft force associated with the tractor while operating in the agricultural field using soil engaging implements. BACKGROUND OF THE INVENTION (PRIOR ART) The use of hydro-mechanical hitch control valve is known and it comprises a main spool valve, an unloading valve and a back pressure valve. It gives inferior field performance as compared to 'improved hydro-mechanical hitch control valve' as disclosed in the present application. It is known to use an on-off type flow control via the control valve during the lift operation of the primary implement. Sliding spool type of hydro-mechanical hitch control valve is widely used. However, the disadvantage associated with such known valves is that some leakage of oil through spool valve in neutral condition is unavoidable while holding the load. The leakage further increases during the life cycle because of wear of moving components taking place. OBJECTS OF THE INVENTION Therefore the main object of the present invention is to propose a hydro-mechanical hitch control valve for agricultural tractors, which ensures good quality of agricultural fieldwork. Another object of the present invention is to propose a hydro-mechanical hitch control valve for agricultural tractors, which controls depth of implement and draft force accurately and in the most effective way. Yet another object of the present invention is to propose a hydro-mechanical hitch control valve for agricultural tractors whereby flow during lifting is controlled proportional to stroke of main spool valve. Still another object of the present invention is to propose a hydro-mechanical hitch control valve for agricultural tractors, which will ensure that leakage in neutral condition is negligible. Accordingly, there is provided an improved hydro-mechanical hitch control valve in a hydraulic control system of an agricultural tractor for controlling lifting and lowering of atleast a primary working implement associated with the tractor, the hydraulic system comprising an oil pump which receives oil from a transmission housing of the tractor via a suction strainer and a filter, and a response valve assembly for receiving pressurized oil from the oil pump for supply to the hydro-mechanical hitch control valve, the lifting control of the implement being exercised via a control means comprising a cylinder and a piston, the cylinder receiving pressurized oil from the hydro-mechanical hitch control valve, the hydro-mechanical hitch control valve comprising a main control valve body and a load holding valve body, the main control valve body comprises a main spool valve, a proportional flow control valve, an unloading valve, and a back pressure valve, the load holding valve body comprises a load holding valve sleeve, a load holding valve poppet, a load holding valve piston, and a load holding valve spring, characterized in that the main spool valve having a plurality of land portions, and in that a series of holes being configured in the third land portion so that oil flow transmitting from the main spool valve to the cylinder in respect of oil pressure, flow-rate and flow direction is proportionally controlled to cause a corresponding reciprocal movement of the cylinder thereby effecting the lifting and lowering control of atleast the primary working implement. An improved hydro-mechanical hitch control valve to be used in a lift unit hydraulic control system of an agricultural tractor according to a preferred embodiment is herein described and illustrated in the accompanying drawings wherein: Fig. 1 shows the sectional view of the conventional valve. Fig.2 shows isometric view of hydro-mechanical hitch control valve of the present invention. Fig. 3 shows sectional view of the valve of the present invention Fig.4 shows the sectional view of the load holding and; Fig. 5 shows plan view of hydro lift control unit. Referring to the drawings particularly fig. 1 the hydro-mechanical hitch control valve known in the prior art has a main spool valve 1 adapted to be connected to body 2 of the hitch control valve and unloading valve 3 is disposed within the body 2 above the main spool valve 1. A back pressure valve 4 is provided towards the upper end of the body 2. Passages 5 and 6 are provided in the upper portion of the body 2 for supplying oil from the pump and oil from the cylinder via response valve to the unloading valve 3. A first land 7 is provided with the main spool valve 1 to control the drain of oil from the unloading valve. Similarly, a second land portion 8 is provided with the main spool valve to control the oil supply to the unloading valve such that to operate the hydro-mechanical hitch control valve. These features of a hydro-mechanical hitch control valve are as such known in the prior art and do not constitute the inventive features of the present invention. Specifically, according to the present invention the construction of the main control valve body has been improved such that to avoid the disadvantages associated with the conventional hitch control valve. According to the present invention and as shown in fig. 3 of the specification the hitch control valve has a spin loaded main spool valve 1 provided in the lower portion of the valve body 2 of the device. The main spool valve has a body spool valve 9, a bush spool valve 10. The main spool valve 1 has a first land portion 11 to control the drain of oil from the unloading valve 12 during its reciprocating movement. A second land 13 is provided to control the oil supply to the unloading valve during reciprocating movement of the second land portion. A third land poriton 14 is provided with the main spool valve 1 and controls the oil flow to cylinder 15 with the help of the proportional flow control valve 16. A fourth land portion 17 is provided to control the oil supply from the pump 18 to the load holding valve 19 (fig.5) during its reciprocating movement in the bush spool valve 10. A fifth land portion 20 is provided to control the drain of the oil from the load holding valve piston 19 to transmission housing of the vehicle. A proportional flow control valve 16 provided above the main spool valve 1 and disposed within the main body 2 of the valve comprises a spool flow control valve 21, a bush control flow 22, spring flow control valve 23. The proportional flow control valve 16 further comprises a first land portion 24 of spool flow control valve 21 to control oil flow to oil cylinder 15 alongwith the third land portion 14 of the main spool valve 1. During the reciprocating movement in the bush flow control valve 22 whenever oil pump 18 is in excess of demand the spool flow control valve 21 moves and excess oil is dumped through opening creative by the movement of first land poriton 24. An unloading valve 12 is provided within the upper portion of the body 2 of the valve the unloading valve 12 comprises a spool unloading valve 25, bush unloading valve 26 and spring unloading valve 27. The unloading valve 12 has a first land portion 28 to transmit the oil to the transmission housing through a back pressure valve 29 (fig.5) during the reciprocating movement in the bush unloading valve 26 by opening or blocking the passages of the exhausting pump. A second land portion 30 is provided with the spool unloading valve 25 to prevent escape of pump oil to transmission housing. The back pressure valve 29 is provided to control the pressure of the oil pump during neutral and lowering position of the equipment alongwith flow restricting orifice. The load holding valve 19 shown in fig. 5 comprises a load holding valve sleeve 31, a load holding valve poppet 32, load holding valve piston 33 and a load holding valve spring 34. A hole 35 is provided in the load holding valve body for supply of oil from the cylinder 15. A passage 36 is provided in the load holding valve body for the supply of oil from the fourth land 17 of the main spool valve 1. A drain passage 37 is provided in the lower portion of the valve body for draining oil to the transmission housing. Another passage 38 is provided in the lower portion of the valve body for the drainage of the oil to the transmission housing. When the oil is supplied to the load holding piston 33 by fourth land 17 of the main spool valve 1 load holding poppet 32 gets lifted from its seat in load holding valve sleeve 31 and oil passes from cylinder 15 to transmission housing through response valve assembly 39 (fig.5). When main spool valve 1 comes to neutral oil lifting of the equipment position the oil from load holding valve piston 33 is drained to the tank and thus shutting of oil flow from cylinderlS to transmission housing. Reference is now made: to fig.5 the oil from the transmission housing of the tractor goes to pump 15 through suction strainer 40 and filter 41. The pressurized oil from pump 15 flows to response valve assembly 39 and from there it flows to hydro-mechanical hitch control valve. Oil at pressure, flow and direction controlled by hydro-mechanical hitch control valve flows to cylinder 42 through check valve 43. The movement of piston 44 in cylinder causes change in position of implement 45. Depending upon oil flow, pressure and direction controlled by hydro-mechanical hitch control valve 46, the implement 45 control takes place. We Claim 1. An improved hydro-mechanical hitch control valve in a hydraulic control system of an agricultural tractor for controlling lifting and lowering of atleast a primary working implement (45) associated with the tractor, the hydraulic system comprising an oil pump (15) which receives oil from a transmission housing of the tractor via a suction strainer (40) and a filter (41), and a response valve assembly (39) for receiving pressurized oil from the oil pump (15) for supply to the hydro-mechanical hitch control valve, the lifting control of the implement (45) being exercised via a control system comprising a cylinder (42) and a piston (44), the cylinder (42) receiving pressurized oil from the hydro-mechanical hitch control valve, the hydro-mechanical hitch control valve comprising a main control valve body and a load holding valve body, the main control valve body comprises a main spool valve (1), a proportional flow control valve (16), an unloading valve (12), and a back pressure valve, the load holding valve body (19) comprises a load holding valve sleeve (31), a load holding valve poppet (32), a load holding valve piston (33), and a load holding valve spring (34), characterized in that the main spool valve (1) having a plurality of land portions (11, 13,14, 17, 20), and in that a series of holes being configured in the third land portion (17) so that oil flow transmitting from the main spool valve (1) to the cylinder (42) in respect of oil pressure, flow-rate and flow direction is proportionally controlled to cause a corresponding reciprocal movement of the cylinder (42) thereby effecting the lifting and lowering control of atleast the primary working implement (45). 2. The valve as claimed in claim 1, wherein the pressurized oil is supplied to the cylinder (42) via a check valve (43). The valve as claimed in claim 1, wherein one of the proportional flow control valve (16) and the load holding valve body (19) is actuated in registration with the actuation of the main spool valve (1) which is actuated by the oil delivered at a pressure and in a flow-controlled manner from the response valve assembly (39) corresponding to the lifting / lowering requirement of the primary working element (45). 3. An improved hydro-mechanical hitch control valve substantially as herein described and illustrated in the accompanying drawings.

Documents:

612-del-2001-abstract.pdf

612-del-2001-claims.pdf

612-del-2001-Correspondence Others-(04-05-2011).pdf

612-del-2001-correspondence-others.pdf

612-del-2001-correspondence-po.pdf

612-del-2001-description (complete).pdf

612-del-2001-drawings.pdf

612-del-2001-form-1.pdf

612-del-2001-Form-15-(04-05-2011).pdf

612-del-2001-form-19.pdf

612-del-2001-form-2.pdf

612-del-2001-form-26.pdf

612-del-2001-form-3.pdf

612-del-2001-form-4.pdf

612-del-2001-form-5.pdf

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