FIELD OF INVENTION
This invention relates to a tractor hydraulic lift and in particular to distributor Valve of hydraulic lift assembly.
BACKGROUND OF INVENTION
The distributor valve is an important part of the Hydraulic Lift and required to perform the following functions:
To receive inputs from control levers as set by the operator or through respective mechanisms of position and/or draft control passed on from the sensing system.
On the basis of these inputs, pressure oil flow is directed to meet the needs of tractor hydraulics or external hydraulics.
Various stages of distribution of oil supplied to the cylinder of hydraulic lift are as under:
- Lifting: In this stage entire oil quantity is delivered to the hydraulic lift cylinder.
- Neutral: In this stage oil trapped in the Lift cylinder is retained & oil supply from the pump is directed to tank.
- Damped Dropping: In this stage oil trapped in the lift cylinder is released to the tank through restricted opening. Oil supply from the pump is also diverted to the tank.

- Dropping: In this stage, oil trapped in the lift cylinder is released to the
tank from full opening. Oil supply from the pump is also diverted to the
tank.
Distribution possibilities of oil supply to external circuit are as under:
- Full supply to external circuit.
- Supply to both external as well as internal hydraulic circuit.
Distributor valve as per prior art does not meet positional accuracy requirements of new innovative implements. These new generation of implements require better placement accuracies.
The proposed invention would enable better placement accuracy and make it possible to use implements requiring better placement accuracies.
OBJECTS OF THE INVENTION
The primary object of the present invention is to provide a tractor hydraulic lift, which increases the spool travel for the Lifting stage, by modifying land of the spool.
Another object of the present invention is to provide a tractor hydraulic lift, which brings in proportionality, by introducing a profile adjacent to the spool land.
Still another object of the present invention is to provide a tractor hydraulic lift, which generates variable flow area in part open condition of the unloader valve.

STATEMENT OF INVENTION
According to this invention, there is provided a tractor hydraulic lift comprising of improved spool land to obtain increased travel of the spool for the lifting stage, introduction of profile in the step adjacent to the land of the spool and an improved unloader valve to divert regulated flow to tank.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: -
Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein:
Fig 1 shows sectional view of the Distributor valve, indicating
arrangement of the spool, unloader valve 85 check valve.
Fig 2 shows a sectional view of the distributor valve indicating Unloader
valve & Check valve.
Fig 3 shows a schematic view indicating functioning of the existing
design in Lifting stage.
Fig 4 shows a sectional view of the distributor valve, with modified spool
as per invention.
Fig 5 shows a sectional view indicating arrangement of modified unloader
valve.
Fig 6 shows a schematic view showing functioning of the distributor with
the incorporation of the present invention.
DETAIL DESCRIPTION OF THE INVENTION WITH REFERENCE TO
THE ACCOMPANYING DRAWIGNS:

According to this invention, there is provided a tractor hydraulic lift comprising of improved spool land to obtain increased travel of the spool for the lifting stage, introduction of profile in the step adjacent to the land of the spool and an improved unloader valve to divert regulated flow to tank.
The profile enables generation of pressure variation across the unloader valve of the Distributor valve, depending on the position of the spool during the lifting phase. This profile causes flow opening with varying area with the spool movement.
According to other aspect of the present invention, unloader valve is modified to divert regulated flow to tank depending upon the pressure input from the spool. Oil released to the hydraulic lift cylinder is made dependent on this pressure enabling its regulation 8B hence control on lift cylinder piston movement.
The pressure controls the unloader valve spool opening 8B releases a proportional amount of oil to tank. Thus, flow to the Hydraulic Lift cylinder is regulated , enabling control of lift cylinder piston movement.
The feature of proportionality is missing in case of arrangement in Distributor valve as per prior art. Pressure signal would completely close the unloader valve 8B all the oil would be diverted to the lift cylinder resulting in a larger value of displacement.
Reference may be made to fig. 1, wherein Section of the distributor valve shows spool (1) in Lifting Stage. In this stage, oil from pump enters

through port (a), which is directed to gallery (12) through gallery (11). Opening (4) adjacent to the land (3) on spool (1) transfers the oil from gallery (11) to gallery (12).
Gallery (12) is connected to annular space (17) around the sleeve (5) of the unloader valve (Fig 2). Pressure oil in the annular space (17) passes through opening (7) and presses the sleeve (6) , which in turn applies pressure on ball (8) and prevents it from opening.
Oil blockage due to closed ball (8) forces the pressure oil through opening (10) and opens the ball (18) of check valve (2) and goes to port (b), which is connected to the hydraulic lift cylinder.
Length of the opening (4) on the spool is very small and gets closed with movement of the spool in the direction of arrow (16), at which the Neutral stage starts.
Movement of spool thus in direction opposite to the arrow (16) from Neutral stage is very small and diverts all the oil to Hydraulic Lift cylinder, resulting in larger movement of the Lift cylinder piston.
The oil flow details are shown in Fig 3. Oil supply coming from port (a) is released to gallery (19) through opened check valve (2). This in turn goes to Lift cylinder (20) and causes its piston to move.
Reference may be made to fig. 4, 5& 6, wherein the profile (21) is provided on the spool and opening (4) due to land (3) is increased by relocating the land. The profile (21) causes the area of opening to vary

when spool (1) is moved in a direction opposite to arrow (16) from the Neutral to Lifting stage. Reduced area due to partial opening reduces the pressure in Galley (12). This reduced pressure is transferred to gallery (17) and through passage (7), reduces force on Sleeve (6). Ball (8) of the unloader valve in new arrangement is replaced by Spool (22) with a special profile (23). Profile of seat (9) is also modified to match with that of spool (22).
Reduced pressure in Sleeve (6) causes the Spool (22) to lift slightly, generating opening between Spool (22) & Seat (9), through which some oil passes to the tank through opening (15). Thus quantity of oil directed to the Lift cylinder (20) is reduced & correspondingly movement of its piston is controlled.
Fig (6) shows the oil flow. Some oil coming from port (a) is diverted to the tank gallery (15) and hence quantity of oil getting diverted to the Lift Cylinder (20) through gallery (19) is reduced.
ADVANTAGEOUS FEATURES OF THE INVENTION
Modified lands of Spool of Hydraulic Lifts Distributor to get the
increased spool travel in the Lifting Mode.
Addition of a profile adjacent to the modified land for getting
variable opening during spools movement 8s hence
proportionally of flow.
Replacement of spherical ball by a profiled spool in the unloader
valve. This spool causes release of pressure oil to tank based on
pressure difference on the associated sleeve. It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-

WE CLAIM;
1. A tractor hydraulic lift comprising of improved spool land to obtain increased travel of the spool for the lifting stage, introduction of profile in the step adjacent to the land of the spool and an improved unloader valve to divert regulated flow to tank..
2. A tractor hydraulic lift as claimed in claim 1, wherein; the profile enables generation of pressure variation across the unloader valve of the Distributor valve, depending on the position of the spool during the lifting phase, in which the profile causes flow opening with varying area with the spool movement.
3. A tractor hydraulic lift as claimed in claim 1 or 2, wherein the unloader valve is modified to divert regulated flow to tank depending upon the pressure input from the spool.
4. A tractor hydraulic lift as claimed in any of the preceding claims, wherein Ball of the unloader valve is replaced by Spool with a special profile, in which profile of seat is also modified to match with that of spool.
5. A tractor hydraulic lift substantially as herein described with reference to the accompanying drawings.