TECHNICAL FIFXD
The subject matter described herein, in general, relates to hydraulic valves and in particular, relates to spool valves.

BACKGROUND

Hydraulic valves, such as a spool valves, function as flow regulating devices in a hydraulic circuit. Spool valves are employed in a variety of applications including hydraulic circuits for utility vehicles such as tractors. Typically, a hydraulic circuit, as used in the utility vehicles, includes various valves such as control valves, check valves, lowering valves, etc., for regulating the fluid flow. The fluid flow is regulated to perform various functions such as operating a pump or lifting and lowering an implement attached to the utility vehicle.

Conventionally, a lowering valve implemented in the hydraulic circuits is a spool valve. In a lowering operation of the hydraulic circuit, fluid from a hydraulic actuator, such as a single or double acting cylinder, is discharged to a reservoir through the lowering valve. The rate of discharge of the fluid from the lowering valve controls the rate of lowering of the implement. However, the quantity of fluid discharged from the lowering valve is generally constant and therefore, different rates of lowering of the implement can not be achieved. For example, if the lowering valve is designed to have a fast rate of discharge of the fluid, then the hydraulic circuit may be unable to achieve a short vertical drop of the implement, which may result in abrupt lowering of the implement. On the other hand, if the lowering valve is designed to have a slow rate of discharge of the fluid, the lowering operation may become time consuming.

On the other hand, in a lifting operation of the hydraulic circuit, the fluid flow across the lowering valve is blocked so that there is no discharge of the fluid from the hydraulic actuator to the reservoir. In a neutral operation also, fluid flow in the lowering valve is blocked to minimize vertical drop of the implement and keep the implement at a selected position. However, fluid leakages across various valves, especially the lowering valves, add to the vertical drop of the implement in the neutral operation and the lifting operation.

SUMMARY
The subject matter described herein relates to a hydraulic valve assembly. The hydraulic valve assembly includes a hydraulic valve having a spool disposed inside a sleeve. The spool is capable of moving axially inside the sleeve to control fluid flow between an inlet passage and an outlet passage of the hydraulic valve. The spool includes a first land having a tapered surface, a first end also having a tapered surface, and a second land. A first fluid channel is formed between the first land and the second land. A second fluid channel is formed between the first land and the first end.

The two fluid channels help in achieving zero leakage across the hydraulic valve. Further, due to the tapered surfaces of the first land and the first end, two different fluid discharge rates can be achieved.

These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The above and other features, aspects and advantages of the subject matter will be better understood with regard to the following description, appended claims, and accompanying drawings where:
Fig. la illustrates a longitudinal cross sectional view of a hydraulic valve assembly, according to an embodiment of the present subject matter.
Fig. lb illustrates a cross sectional view of the hydraulic valve assembly of Fig. la along a section plane X-X', according to an embodiment of the present subject matter.
Fig. 2 illustrates an exemplary spool of the hydraulic valve assembly of Fig. la, according to an embodiment of the present subject matter.

Fig. 3 illustrates a cross-sectional view of a hydraulic valve of Fig. la in a first position, according to an embodiment of the present subject matter.
Fig. 4 illustrates a cross sectional view of the hydraulic valve of Fig. la in a second position, according to an embodiment of the present subject matter.
Fig. 5 illustrates a cross sectional view of the hydraulic valve of Fig. la in a third position, according to an embodiment of the present subject matter.
Fig. 6 illustrates an exemplary hydraulic circuit implementing the hydraulic valve assembly of Fig. la, according to an embodiment of the present subject matter.

DETAILED DESCRIPTION

The subject matter described herein relates to a hydraulic valve used in a hydraulic circuit of a utility vehicle, such as, a tractor. The hydraulic valve includes a spool axially and slidably disposed inside a sleeve. The hydraulic valve also includes a first fluid channel and a second fluid channel. The first fluid channel is formed between a first land and a second land of the spool. The second fluid channel is formed between the first land and a first end of the spool. In one embodiment, the first land and the first end are tapered.

Further, the hydraulic valve is a two way-three position valve. The hydraulic valve includes an inlet passage and an outlet passage corresponding to the two ways of the hydraulic valve. The three positions of the valve correspond to a first position, a second position, and a third position. In the first position, the inlet passage is closed and the two fluid channels arrest the fluid, thereby preventing fluid seepage. Thus, provision of such fluid channels help in achieving zero leakage in the hydraulic valve.

Additionally, the spool can be moved axially inside the sleeve to vary the fluid discharge from the outlet passage. In one embodiment, disengagement of the first end with a tapered surface of the sleeve creates a clearance, which serves as the outlet passage. The second fluid channel opens into the outlet passage. In the second position of the hydraulic valve, the axial movement of the spool is such that the outlet passage is partially open. In the third position, the axial movement of the spool is such that the outlet passage is completely open.

For the purpose of explanation, the hydraulic valve of the present subject matter has been described with respect to a lowering valve of the hydraulic circuit employed in the utility vehicles; however, it would be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. The hydraulic valve as described herein can be used in variety of applications, for example, in tractor hydraulic systems, construction equipments, loaders, etc.

Fig. la illustrates a longitudinal cross-sectional view of a hydraulic valve assembly 100, and Fig. lb illustrates a cross sectional view of the hydraulic valve assembly 100 along a section plane X-X', according to an embodiment of the present subject matter. The hydraulic valve assembly 100 includes a hydraulic valve 105 having a spool 110 capable of sliding in an axial direction inside a sleeve 115. The spool 110 and the sleeve 115 may be housed inside a valve body 120.

The spool 110 includes a plurality of lands, such as a first land 125 and a second land 130. The first land 125 has a tapered surface and the first land 125 may be provided substantially at a centre of a length of the spool 110. However, the first land 125 can also be provided at any other position as per the requirement. A first fluid channel 135 is formed in a neck region of the spool 110 between the first land 125 and the second land 130. A second fluid channel 140 is formed between the first land 125 and a first end 145. The second land 130 may be provided in proximity to a second end 150. The second land 130 may includes a notch 155 to reduce friction between the spool 110 and the sleeve 115. The notch 155 may be a cylindrical notch and based on the requirements, the second land 130 may include more than one notch.

In one embodiment, the sleeve 115 is provided with an inlet passage 157 for intake of fluid into the hydraulic valve 105. A first groove 160 is provided around the sleeve 115 and is in hydraulic connection with a fluid conduit 162. The fluid conduit 162 may be hydraulically connected to a hydraulic actuator of a hydraulic circuit. A plurality of ducts 165-1, 165-2,...165-n, collectively referred to as ducts 165, are circumferentially positioned on the first groove 160. In one embodiment, the ducts 165 are four in number and are positioned are positioned symmetrically with respect to each other around the first fluid channel 135. However, the number and positioning of the openings may be varied based on the requirements. The ducts 165 open into the first fluid channel 135 and the fluid from the first groove 160 enters the first fluid channel 135. In other words, the first groove 160 receives fluid from the fluid conduit 162 and the received fluid flows into the first fluid channel 135 through the ducts 165. The ducts 165 and the first groove 160 constitute the inlet passage 157. An outlet passage 170, which is for discharging fluid from the hydraulic valve 105, is formed between the first end 145 and a sleeve end 172 of the sleeve 115.

The first end 145 has a tapered surface and an axial movement of the spool 110 engages or disengages the first end 145 with the sleeve end 172, which is also tapered. Such engagement or disengagement closes or opens the second fluid channel 140 into the outlet passage 170. In one embodiment, the hydraulic valve 105 is a two-way, three position valve or 2/3 valve. The two ways of the hydraulic valve 105 correspond to the inlet passage 157 and the outlet passage 170 and the three positions of the hydraulic valve 105 correspond to a first position, a second position, and a third position, which are explained in detail with reference to Fig. 4, Fig. 5, and Fig. 6. The spool 110 moves axially in the sleeve 115 to select one of the three positions of the hydraulic valve 105.

In one implementation, the hydraulic valve 105 is a pressure compensated valve. In said implementation, the first end 145 is connected to a spring 175, such as, a compression spring, while a second end 150 protruding out of the sleeve 115 is connected to a coupler assembly 185. The second end 150 may be connected to a pin coupler 180 of the coupler assembly 185. In the first position of the hydraulic valve 105, a force exerted on the pin coupler 180 is counter balanced by the force of the spring 175, and the outlet passage 170 is substantially closed. In the second position and the third position, the force exerted on the pin coupler 180 is greater than the force of the spring 175, and thus the first end 145 disengages with the sleeve end 172 to open the second fluid channel 140 into the outlet passage 170. Owing to such a feature, the hydraulic valve 105 functions as a check valve. Further, the tapered surfaces of the first land 125 and the first end 145, allow for variable opening of the two fluid channels 135 and 140 thereby achieving variable fluid discharge rate as against conventional hydraulic valves. Thus, the hydraulic valve 105 may also function as a directional control valve.

Additionally, in the first position, the provision of two fluid channels 135 and 140 reduces the leakage of fluid in the hydraulic valve 105. To further prevent fluid seepage, the valve body 120, the sleeve 115, and the spool 110 may employ a plurality of O-ring seals 190 such as a first O-ring 190-1, a second O-ring 190-2,... and so on.

The O-ring seals 190 may be used in conjunction with back up seals to prevent fluid seepage. The first O-ring seal 190-1 is provided in proximity to the second land 130 and prevents fluid seepage from the first fluid channel 135 towards the second end 150. The second O-ring seal 190-2 is provided on the sleeve 115 to seal the fluid path between the sleeve 115 and the valve body 120.

Fig. 2 illustrates the spool 110 of Fig. la, according to an embodiment of the present subject matter. As aforementioned, the first land 125 and the first end 145 are tapered to achieve different discharge rates of the fluid. The tapered surfaces of the first land 125 and the first end 145 converge in a direction of increasing pressure. In one embodiment, the tapered surface of the first end 145 is at an angle of about 44° to 46° to a longitudinal axis of the spool 110, while the tapered surface of the first land 125 is at an angle of about 14 to 16°. The spool 110 has two extensions, namely a first extension 205, which is at the first end 145 for mounting of the spring 175, and a second extension 210, which is at the second end 150 to connect to the pin coupler 180.

A second groove 215 formed between the second end 150 and the second land 130 is provided with the first O-ring 190-1 to prevent fluid leakage from the second end 150. For the purpose, the second groove 215 may also be provided with a back-up seal. The notch 155 provided on the second land 130 functions as a conventional balancing groove. The notch 155 allows the fluid to flow circumferentially around the second land 130, thereby balancing the pressure around the spool 110 and reducing friction between spool 110 and the sleeve 115.

Fig. 3 illustrates an exemplary hydraulic valve, such as the hydraulic valve 105 of Fig. la. in a first position, according to an embodiment of the present subject matter. In the first position, the spring 175 is in an unloaded state and the forces on either ends of the spool 110 are balanced. As a result, a centering of the spool 110 is achieved and a positive overlap is established between the first land 125 and the sleeve 115. The positive overlap ensures sealing of the first fluid channel 135 so that fluid seepage into the second fluid channel 140 is negligible or zero. Thus, the fluid coming from the inlet passage 157 is arrested in the first fluid channel 135.

Further, in the first position, the first end 145 engages with the sleeve end 172 and a metal-to-metal contact is established therebetween. Owing to the metal-to-metal contact, the outlet passage 170, and hence the second fluid channel 140, is substantially closed and fluid leaking from the first fluid channel 135 is arrested in the second fluid channel 140. Additionally, the sealing of the outlet passage 170 due to the metal-to-metal contact of the first end 145 and the sleeve end 172 prevents fluid seepage from the second fluid channel 140 into the outlet passage 170. In this way, the two fluid channels 135 and 140 reduce the leakage of fluid across the hydraulic valve in the first position. In addition, the first O-ring seal 190-1 blocks any potential leaching path of the fluid from the first fluid channel 135 to the second end 150 of the spool 110. Further, the O-ring seals 190 provided on the sleeve 115 and the valve body 120 help in achieving zero leakage across the hydraulic valve 105. As a result, the lowering of the implement is brought to a complete halt.

Fig, 4 illustrates the hydraulic valve 105 of Fig. la in the second position, according to an embodiment of the present subject matter. Upon selection of the second position, a force is exerted on the pin coupler 180 by operation of an associated hydraulic circuit. The force exerted on the pin coupler 180 achieves the selection of the second position by moving the spool 110 in a direction of compression of the spring 175, as indicated by an arrow 405. The force positions the spool 110 inside the sleeve 115 such that a limited clearance is created between the first land 125 and the sleeve 115. The limited clearance created partially opens the first fluid channel 135. Owing to the limited clearance, a restricted amount of fluid is discharged from the first fluid channel 135 into the second fluid channel 140.

Further, due to the axial movement of the spool 110, the first end 145 disengages with the sleeve end 172 such that a limited clearance is created therebetween. The limited clearance created between the first end 145 and the sleeve end 172 partially opens the outlet passage 170, and the fluid from the second fluid channel 140 is discharged through the outlet passage 170. In the second position, the partial opening of the outlet passage 170 restricts the amount of fluid discharged from the hydraulic valve 105.

Hence, the two fluid channels 135 and 140, which were sealed in the first position, open up in the second position owing to the clearances created. Consequently, the fluid flows in the direction of the arrow 405 and is accordingly routed from the first fluid channel 135 into the second fluid channel 140 from where the fluid is discharged out of the hydraulic valve 105 through the outlet passage 170.

Fig. 5 illustrates the hydraulic valve 105 of Fig. la in the third position, according to an embodiment of the present subject matter. In the third position, the force on the pin coupler 180 shifts the spool 110 further in the direction of the arrow 405 such that the clearance created between the first land 125 and the sleeve 115 is maximized. In addition, the first end 145 disengages with the sleeve end 172 such that the clearance thus created is maximized. Due to this, the two fluid channels 135 and 140 completely open up and a relatively large amount of fluid flows out of the outlet passage 170 of the sleeve 115. The fluid can now discharge through the outlet passage 170 at a faster rate as compared to the rate of discharge of the fluid in the second position.

As aforementioned, due to the axial movement of the spool 110 in the direction of the arrow 405, limited clearances are created in the second position and further movements of the spool 110 in the same direction provide increasingly larger clearances in the third position. Therefore, due to the tapered surfaces of the first land 125 and the first end 145, two different discharge rates of the fluid are achieved.

In order to bring back the hydraulic valve 105 to the first position, the force on the pin coupler 180 is released and the spool 110 is moved in a direction of release of the spring 175, as indicated by an arrow 505. As a result, the clearances created between the first land 125 and the sleeve 115, and between the first end 145 and the sleeve end 172 are sealed. In the absence of any external force, the spring 175 always tends to return back to its set position, thereby ensuring a centering of the spool 110. The centering of the spool 110 ensures that the positive overlap between the first land 125 and the sleeve 115 is maintained in the first position. As mentioned previously, the positive overlap of the first land 125 and the sleeve 115 aids in minimizing the fluid seepage across the hydraulic valve 105.

Fig. 6 illustrates an exemplary hydraulic circuit 600 implementing the hydraulic valve assembly 100 of Fig. la, according to an embodiment of the present subject matter. The hydraulic circuit 600 may be employed in a utility vehicle, such as a tractor. The hydraulic circuit 600 is controllably coupled to an implement (not shown in the figures), connected to the utility vehicle, to control various operations associated with the implement, such as lifting or lowering of the implement. The utility vehicle may also include a power take off unit to drive the implement.

In one embodiment, the hydraulic circuit 600 employs the hydraulic valve 105 as a lowering valve and regulates a volume of fluid being discharged from the lowering valve 105 to control the lowering of the implement. In said embodiment, the inlet passage 157 may be hydraulically connected to a hydraulic actuator (not shown in the figures) such a single acting or a double acting cylinder, and the outlet passage 170 may be hydraulically connected to a reservoir (not shown in the figures) such as a fluid tank.
The hydraulic circuit 600 includes a control valve 605 operably coupled to the hydraulic valve 105. In one implementation, the control valve 605 is a spool valve and includes a main spool 610. The main spool 610 can be connected to the pin coupler 180 though a coupler plate 615. The coupler assembly 185 includes the coupler plate 615 and a locking screw 620 for firmly connecting the coupler plate 615 to the pin coupler 180 and the main spool 610. In one implementation, levers such as position control levers and draft control levers provided on the utility vehicle actuate the main spool 610. Thus, the linear movement of the main spool 610 may be controlled through the levers. The levers may actuate the main spool 610 through an actuating means (not shown in the figures) including linkage levers and cam mechanism. In said implementation, the flow of fluid from the hydraulic valve 105 is allowed or blocked when a corresponding position of the control valve 605 is selected.

Based on the position of the main spool 610, the first position, the second position or the third position is achieved. In operation, when a lifting position or a neutral position of the control valve 605 is selected, the first position of the hydraulic valve 105 is achieved. The lifting position or the neutral position can be selected when an operator wishes to lift an implement connected to the utility vehicle or wishes to hold the implement in a set position. Upon selection of the first position of the hydraulic valve 105, the main spool 610, which is coupled to the spool 110, moves the spool 110 such that the two fluid channels 135 and 140 are sealed and outlet passage 170 of the hydraulic valve 105 is closed. Since, the fluid seepage across the hydraulic valve 105 is minimized, the vertical drop of the implement in the lifting position and the neutral position of the control valve 605 is also minimum.

Further, when a lowering position of the control valve 605 is selected, either the second or the third position of the hydraulic valve 105 is achieved. The lowering position of the control valve 605 is selected to lower the implement. Upon selection of lowering position of the control valve 605, the main spool 610 is moved to push the spool 110 against the spring 175 through the coupler assembly 185 to open the hydraulic valve 105 to drain the fluid into the reservoir. Based on the settings of the levers, the main spool 610 moves the spool 110 to select the second or the third position of the hydraulic valve 105. The second position and the third position of the hydraulic valve 105 correspond to different lowering rates of the implement. Therefore, to vary the flow rate the clearance provided at the two fluid channels 135 and 140 is varied based on a position selected by a user.

In one embodiment, the second position corresponds to a slow lowering rate or to a slow lowering of the implement, while the third position corresponds to a fast lowering rate or to a fast lowering of the implement. In one implementation, the hydraulic valve is designed to achieve the slow lowering in around 3 seconds and a fast lowering in around 1 second for a given drop of the implement. In said embodiment, the load of the implement is around 375 -425 Kilograms (Kg). However, the slow lowering rate and the fast lowering rate may be varied according to requirement of the utility vehicle implementing the same. Thus, when a slow drop of the implement is required, the second position of the hydraulic valve 105 may be selected. On the other hand, when a fast drop is required, the third position may be selected.

As aforementioned, based on the positioning of the main spool 610, the second position or the third position of the hydraulic valve is achieved. In the second position, the axial movement of the spool 110 in the direction A is such that the first fluid channel 135 and the second fluid channel 140 are partially open and therefore the outlet passage 170 is partially open. Consequently, a restricted amount of fluid is discharged into the reservoir. Thus, upon selection of the second position of the hydraulic valve 105, a slow lowering of the implement is achieved.

To achieve fast lowering of the implement, the third position of the hydraulic valve 105 is selected. Successively greater movements of the spool 110 in the direction A further open the first fluid channel 135 and the second fluid channel 140 and in this way, the outlet passage 170 becomes completely open. Thus, in the third position a relatively large volume of fluid is discharged to the reservoir and fast lowering of the implement is achieved.

The present subject matter also proposes a method for varying lowering rate of an implement connected to a utility vehicle. The method is described in conjunction with the concepts introduced in Fig. 1-6. According to an aspect of the present subject matter, upon selection of a position of the control valve 605, a corresponding position of the hydraulic valve 105 is selected. For example, on selection of the lifting position of the control valve 605, the first position of the hydraulic valve is achieved. The described method allows for selectively adjusting the opening of the outlet passage 170, in response to selection of a required lowering rate of the implement.

In one embodiment, a user may select the second position of the hydraulic valve 105 to achieve slow lowering of the implement, while the third position may be selected to achieve fast lowering of the implement. In one embodiment, to open a clearance created at the outlet passage 170 the tapered surface of the first land 125 and the first end 145 disengages with the sleeve 115 to create a clearance that allows for discharge of fluid. In order to vary the fluid discharge rate thereby varying the lowering rate of the implement, the first land 125 and the first end 145 partially or completely open the clearance. Thus, the provision of varying the clearance created at the outlet passage 170 allows for different fluid discharge rates and thus provides for different lowering rates of the implement.

The previously described versions of the subject matter and its equivalent thereof have many advantages, including those which are described below. The hydraulic valve 105 of the present subject matter includes the first land 125 and the sleeve end 172 to provide two different fluid discharge rates. Such a provision also prevents abrupt dropping of the implement. Further, the two fluid channels 135 and 140 provide negligible or zero leakage across the hydraulic valve 105. Therefore, if the hydraulic valve 105 is used as a lowering valve in a hydraulic circuit such as the hydraulic circuit 600, zero leakage across the hydraulic valve 105 provides substantially zero dropping rates for an implement held at set position. In addition, owing to different fluid discharge rates, slow or fast lowering of the implement can be achieved.

While certain features of the claimed subject matter have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the claimed subject matter.

I/We claim:

1. A hydraulic valve (105) comprising:
a sleeve (115); and
a spool (110) disposed to move axially inside the sleeve (115), wherein the spool (110) has a first end (145) and a second end (150);
characterized in that,

the spool (110) comprises,

a first land (125) having a tapered surface;

a second land (130), wherein the first land (125) and the second land (130) form a first fluid channel (135) therebetween; and

the first end (145) having a tapered surface, wherein the first end (145) and the first land (125) form a second fluid channel (140) therebetween.

2. The hydraulic valve (105) as claimed in claim 1, wherein the hydraulic valve (105) is a two way valve having a first position, a second position, and a third position.

3. The hydraulic valve (105) as claimed in claim 2, wherein the first position corresponds to engagement of the first land (125) with the sleeve (115) to substantially seal the first fluid channel (135) and engagement of the first end (145) with a sleeve end (172) of the sleeve (115) to substantially seal the second fluid channel (140).

4. The hydraulic valve (105) as claimed in claim 2, wherein the second position corresponds to disengagement of the first land (125) with the sleeve (115) to partially open the first fluid channel (135) and disengagement of the first end (145) with a sleeve end (172) of the sleeve (115) to partially open the second fluid channel (140).

5. The hydraulic valve (105) as claimed in claim 2, wherein the third position corresponds to disengagement of the first land (125) with the sleeve (115) to completely openthe first fluid channel (135) and disengagement of the first end (145) with a sleeve end (172) of the sleeve (115) to completely open the second fluid channel (140).

6. The hydraulic valve (105) as claimed in claim 1, wherein the first land (125) is provided substantially at a centre of a length of the spool (110).

7. The hydraulic valve (105) as claimed in claim 1, wherein the second land (130) comprises at least one notch (155).

8. The hydraulic valve (105) as claimed in claim 1, wherein the hydraulic valve (105) is a pressure compensated valve.

9. The hydraulic valve (105) as claimed in claim 1, wherein the tapered surface of the first land (125) and the tapered surface of the first spool end (145) diverge in a direction of the decreasing pressure.

10. The hydraulic valve (105) as claimed in claim 1, wherein the tapered surface of the first end (145) is at an angle of about 44° to 46° to a longitudinal axis of the spool (110).

11. The hydraulic valve (105) as claimed in claim I, wherein the tapered surface of the first land (125) is at an angle of about 14° to 16° to a longitudinal axis of the spool (110)

12. The hydraulic valve (105) as claimed in claim 1, wherein the hydraulic valve (105) is a lowering valve.

13. A hydraulic circuit (600) comprising:

a control valve (605); and

a hydraulic valve (105) as claimed in any of the preceding claims coupled to the control valve (605) by a coupler assembly (185).

14. A utility vehicle comprising:

an implement;

a power take-off unit to drive the implement; and

a hydraulic circuit (600) operatively coupled to the implement to control operations of the implement, wherein the hydraulic circuit (600) comprises a hydraulic valve (105) as claimed in any of the claims 1-12.

15. A method for controlling a fluid discharge rate from an outlet passage of a hydraulic valve to vary a lowering rate of an implement, the method comprising:

selectively adjusting a clearance created at the outlet passage of the hydraulic valve to allow a fluid to flow from the hydraulic valve to a reservoir upon selection of the lowering rate of the implement.

16. The method as claimed in claim 15, further comprising:

completely closing the clearance when the lowering of the implement is brought to a halt;

partially opening the clearance when the lowering rate is slow; and
completely opening the clearance when the lowering rate is fast.

17. The method as claimed in claim 15, wherein the clearance is created due todisengagement of a tapered surface of a first land of a spool of the hydraulic valve with asleeve of the hydraulic valve and disengagement of a tapered surface of a first end of the
spool with a sleeve end of the sleeve. _