TECHNICAL FIELD

The present subject matter, in general, relates to a hydraulic system and, in particular, relates to a hydraulic valve assembly of the hydraulic system.

BACKGROUND

Usage of heavy vehicles, such as tractors, is prominent in the field of agriculture. Agricultural tractors are used to mount and drive various farm machinery for accomplishing a number of tasks related to agricultural work such as plowing fields and harvesting crops. Typically, farm machinery, such as a plow, is mounted on a rear end of an agricultural tractor via a link mechanism hitched thereto at three points.

The farm machinery is driven by a hydraulic actuator, which is in the form of a single-acting or double-acting hydraulic cylinder. The hydraulic actuator is controlled by a hydraulic system, which generally includes hydraulic pumps and a system of valves. Generally, the hydraulic system includes a directional control valve for a main hydraulic actuator and a secondary directional control valve for an auxiliary hydraulic actuator. Each control valve is connected in series with a hydraulic pump to pump a hydraulic fluid.

Flow rates of one or more hydraulic pumps and capacities of the hydraulic actuator(s) and control valves are determined to set a lifting speed and a lowering speed of the farm machinery attached to the hydraulic actuator(s) within a given range. If the flow rate of a particular hydraulic pump needed to control a given hydraulic actuator driving the farm machinery lies within an acceptable range, the operation executes with ease. However, leakage of the hydraulic fluid from any of the directional control valves in the hydraulic system varies the overall flow rate.

Fluid leakage may happen due to malfunctioning of the valves or wrong selection of the type of valves in the hydraulic system. Leakage of fluid may drastically reduce fluid pressure within the hydraulic system* thereby hindering the lifting/lowering operations performed by the tractor.

In addition, inappropriate flow regulation of the hydraulic fluid is also quite prominent in such hydraulic systems. Inappropriate flow regulation may be attributed to employment of certain types of valves in hydraulic systems of these heavy vehicles. If the pressure of the hydraulic fluid upstream of an hydraulic actuator is not properly regulated by the associated hydraulic valve, then the implement or machinery connected to the hydraulic valve system tends to undergo jerks. Jerks are mainly evident when the implement undergoes either a lifting or a lowering operation. The occurrence of jerks adversely affects both response time and load control of the hydraulic system. Hence, the overall functioning of the hydraulic system and the attached farm machinery tends to become inefficient in due course of time.

Moreover, the overall assembly of the hydraulic valves in a conventional hydraulic system for use in these heavy vehicles is complex, thereby incurring a substantially high production cost. In addition, the replacement of faulty components in such complex valve assemblies is a time consuming and cost-ineffective task.

SUMMARY

The present subject matter relates to a hydraulic valve assembly for a hydraulic system. The hydraulic system may be employed to control operations of an implement or equipment connected to a hydraulic actuator of the hydraulic system.

The hydraulic valve assembly includes a counterbalance valve hydraulically connected to the hydraulic actuator to receive a hydraulic fluid from the hydraulic actuator. In addition, a lowering control valve is hydraulically connected to the counterbalance valve to receive the hydraulic fluid at a regulated pressure from the counterbalance valve. A directional control valve is coupled to the lowering control valve to actuate the lowering control valve. The directional control valve also facilitates routing of the hydraulic fluid within the hydraulic circuit.

The hydraulic valve assembly implemented in the hydraulic system of the present subject matter facilitates jerk-free lifting and lowering of the implement or equipment connected to the hydraulic actuator. Accordingly, an enhanced control can be achieved over the connected implement or equipment and the response time of the overall hydraulic system can also be improved upon.

These and other features, aspects, and advantages of the present subject matter will be 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. 1 is a front view representation of an exemplary configuration of hydraulic valves in an exemplary hydraulic system, in accordance with an embodiment of the present subject matter.

Fig, 2 is a rear view representation of the exemplary configuration of the hydraulic system of Fig. 1, in accordance with an embodiment of the present subject matter.
Fig, 3 is an exemplary circuit diagram representation of a hydraulic valve assembly in the hydraulic system of Fig. 1, in accordance with an embodiment of the present subject matter.

Fig. 4a is a diagrammatic representation of a control flow within the hydraulic system to trigger or activate the flow of a hydraulic fluid in the hydraulic valve assembly, in accordance with an embodiment of the present subject matter.

Fig. 4b is a diagrammatic representation of a control flow within the hydraulic valve assembly to implement a lifting mode of operation of the hydraulic system, in accordance with an embodiment of the present subject matter.

Fig. 4c is a diagrammatic representation of a control flow within the hydraulic valve assembly to implement a neutral mode of operation of the hydraulic system, in accordance with an embodiment of the present subject matter.

Fig, 4d is a diagrammatic representation of a control flow within the hydraulic valve assembly to implement a lowering mode of operation of the hydraulic system, in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION

The disclosed subject matter relates lo a hydraulic valve assembly employed in a hydraulic system of a utility vehicle, such as a tractor, to operate an implement connected to the vehicle. A hydraulic actuator of the hydraulics system drives the implement, such as an equipment like a plough, pump etc., mounted thereon. The drive of the implement by the hydraulic actuator generally includes lifting or lowering the implement.

The hydraulic valve assembly for controlling the hydraulic actuator includes a number of valves to facilitate and regulate the flow of a hydraulic fluid throughout the hydraulic system under various operating conditions. The hydraulic valve assembly is interchangeably referred to as hydraulic control circuit, hereinafter.

In one embodiment, the hydraulic control circuit includes a clutch independent gear pump, which is powered by an internal combustion engine of the utility vehicle. The clutch independent gear pump pumps the hydraulic fluid from a reservoir or tank and accelerates the hydraulic fluid to a directional control valve. The directional control valve is the main control valve in the hydraulic control circuit and accordingly directs or routes the fluid flow to different sections or sub-circuits of the hydraulic valve assembly.

Specifically, the directional control valve is a manually operable valve and allows a user lo switch between a lifting mode, a neutral mode, and a lowering mode of operation and operate the hydraulic control circuit, and thereby the hydraulic system, in one of selected the modes. Based upon the mode selected, the directional control valve routes the flow of the hydraulic fluid.
The hydraulic control circuit switched in the lifting mode functionally accomplishes the lifting operation of the implement connected to a hydraulic actuator of the hydraulic system. For this purpose, the hydraulic actuator is operably connected at the end of the hydraulic control circuit. During the lifting mode of operation, the directional control valve directs the flow of the hydraulic fluid to a feathering valve through a throttle check valve. As known in the existing art, the throttle check valve includes an inbuilt throttle valve and an inbuilt check valve.

The feathering valve receives the hydraulic fluid from the check valve of the throttle check valve. The feathering valve facilitates a constant flow rate of the hydraulic fluid in the hydraulic control circuit during the lifting mode of operation, irrespective of a pressure differential across the feathering valve. The hydraulic fluid flow reaches the hydraulic actuator from the feathering valve through the throttle valve present inside the throttle check valve. The throttle check valve accelerates the hydraulic fluid flow towards the hydraulic actuator. Accordingly, a combined action of the feathering valve and the throttle check valve prevents occurrences of jerks and overshooting of the implement during the lifting mode of operation.

To accomplish the lowering of the implement connected to the hydraulic actuator, the hydraulic control circuit can be switched to a lowering mode of operation. When the implement is operated in this mode, the directional control valve activates the lowering control valve to operate. The lowering valve in turn activates a counterbalance valve to receive the hydraulic fluid from the hydraulic actuator. The counterbalance valve is a pressure reducing valve and therefore reduces the pressure of the hydraulic fluid downstream of the counterbalance valve. Accordingly, the hydraulic fluid reaches the lowering valve from the counterbalance valve at a reduced pressure. It may be understood that the counterbalance valve facilitates jerk-free lowering of the implement connected to the hydraulic actuator.

Fig 1 is a front view representation of an exemplary configuration of hydraulic valves in an exemplary hydraulic system 100, in accordance with an embodiment of the present subject matter. As shown in Fig 1, the front view representation of the hydraulic system 100 shows an arrangement of a lowering control valve 105, a feathering valve 110, a counterbalance valve 115, and an unloader valve 120. A pin coupler plate 130 acts as a joining means for effectively supporting the hydraulic system 100,

The hydraulic system 100 is operable under three modes of operation including lifting, lowering, and neutral. The different components of the hydraulic system 100 work in tandem to achieve these three modes of operation. Based on the mode of operation selected during work, the hydraulic system 100 acts in a lifting mode or a lowering mode or a neutral mode of operation. For the purpose of explanation, the components that are involved in the lifting operation may be considered to form a sub-system within the hydraulic system 100 and may be referred to as a lifting system of the present hydraulic system 100, Likewise, the components involved in the neutral and lowering modes of operation may constitute a neutral system and a lowering system, respectively.

The feathering valve 110, together with a throttle check valve (not shown in the figure), operates during the lifting mode of operation of the hydraulic system 100. The feathering valve 110 maintains a constant flow rate of a hydraulic fluid directed to a hydraulic actuator (shown in Fig 3) to facilitate a constant speed of lift of an implement connected to the hydraulic actuator. In addition, the operation of the feathering valve 110 remains unaffected by the variations in pressure across the feathering valve 110. Furthermore, the throttle check valve (shown in Fig 3) facilitates a controlled acceleration of the flow of the hydraulic fluid towards the hydraulic actuator in the hydraulic system 100.

In the lowering mode of operation, the operations of the lowering control valve 105 and the counterbalance valve 115 together facilitate the lowering of the implement connected to the hydraulic system 100. In this mode, the lowering control valve 105 actuates the counterbalance valve 115 to receive the hydraulic fluid from the hydraulic actuator. The counterbalance valve 115 allows the hydraulic fluid from the hydraulic actuator to flow across if the pressure of the hydraulic fluid downstream of the counterbalance valve 115 is less than a calibrated pressure value of the counterbalance valve 115. This prevents abrupt lowering of the implement. The lowering control valve 105 receives the hydraulic fluid from the counterbalance valve 115 and directs the hydraulic fluid to a reservoir (shown in Fig 3). If fast or slow lowering of the implement is required, the lowering control valve 105 would accordingly vary the rate of flow of the hydraulic fluid toward the reservoir.

During the neutral and lowering modes of operation of the hydraulic system 100, any incoming hydraulic fluid flow from a hydraulic fluid pump (shown in Fig 3) is directed to the reservoir via the unloader valve 120. Specifically, the unloader valve 120 receives the hydraulic fluid from the directional control valve 205 (shown in Fig. 2) and directs the hydraulic fluid flow to the reservoir at a low pressure.

Fig. 2 is a rear view representation of the exemplary configuration of the hydraulic system 100 of Fig. 1, in accordance with an embodiment of the present subject matter. In the present embodiment, the hydraulic system 100 includes the directional control valve 205, an isolation valve 210, a safety valve 215, and a relief valve 220, all being interconnected to each other. The directional control valve 205, the isolation valve 210, and the relief valve 220 functionally contribute in all the aforementioned modes of operation, i.e., lifting, lowering and neutral, as exhibited by the hydraulic system 100. The isolation valve 210 normally remains open and thereby permits the hydraulic fluid to flow across it in normal conditions, i.e., in one of the aforementioned modes of operation. During maintenance or testing of the hydraulic system 100, the isolation valve 210 is shut or closed. The closure of the isolation valve 210 isolates the hydraulic actuator from rest of the hydraulic system 100, thereby facilitating detection of a fault.

As mentioned before, the directional control valve 205 of the present hydraulic system 100 directs the flow of the hydraulic fluid to the various valves according to the operational requirements. Specifically, the directional control valve 205 is a manually operated valve and allows a user to switch the directional control valve 205 to initiate one of the modes of operation.
The relief valve 220 facilitates in maintaining pressure of the hydraulic fluid upstream of the directional control valve 205 below a threshold pressure value. If the hydraulic fluid pressure value upstream of the directional control valve 205 exceeds the threshold value, the relief valve 220 gets opened and a certain volume of the hydraulic fluid is bypassed to the reservoir (not shown in the figure). The remaining volume of the hydraulic fluid, thereby having an appropriate pressure value, is allowed to reach upstream of the directional control valve 205. However, if the pressure of the hydraulic fluid upstream of the directional control valve 205 is below the threshold value, then the relief valve 220 remains closed and the entire volume of the hydraulic fluid is directed towards the directional control valve 205.

The safety valve 215 works similar to the relief valve 220, i.e., facilitates maintenance of the pressure of the hydraulic fluid upstream of the hydraulic actuator below a pre-defined pressure value.

Fig. 3 is an exemplary circuit diagram representation of a hydraulic valve assembly 300 in a hydraulic system such as the hydraulic system 100 of Fig. 1, in accordance with an embodiment of the present subject matter.
In one embodiment, the hydraulic valve assembly or hydraulic control circuit 300 includes a hydraulic fluid pump 305 powered by an internal combustion (IC) engine 310.

In one implementation, the hydraulic fluid pump 305 is a clutch independent gear pump. The pump 305 is operably connected to a reservoir 320 through the combination of a suction filter 315a and a suction strainer 315b. Further, the gear pump 305 is hydraulically connected to the directional control valve 205 via the relief valve 220. The gear pump 305 pumps the hydraulic fluid from the reservoir 320 to the directional control valve 205.

The directional control valve 205 is hydraulically connected to the throttle check valve 325 and the unloader valve 120. The throttle check valve 325, in turn, is hydraulically connected the feathering valve 110. In addition, the directional control valve 205 is operably connected to the lowering control valve 105, and thereby switches on/off the lowering control valve 105. The lowering control valve 105 is, in turn, operably and hydraulically connected to the counterbalance valve 115.

The directional control valve 205 is a manually operable valve. In operation, the directional control valve 205 is adapted to route the hydraulic fluid flow to various sub-circuits of the hydraulic control circuit 300. In one embodiment of the present subject matter, the directional control valve 205 is a four-port, three-position valve. The three positions as exhibited by the directional control valve 205 correspond to three modes of operation of the hydraulic control circuit 300, i.e. lowering, lifting, and neutral. It may be understood that the aforementioned modes of operation of the hydraulic control circuit 300 arc similar to the modes of operation of the hydraulic system 100.

The directional control valve 205, the feathering valve 110, the throttle check valve 325, and the check valve 330 operate together during the lifting mode of operation of the hydraulic control circuit 300 and accordingly constitute a system similar to the lifting system of the hydraulic system 100.

Similarly, during the neutral mode of operation, the directional control valve 205 and the unloader valve 120 operate and accordingly constitute the neutral system of the hydraulic system 100. In this neutral system the directional control valve 205 directs the incoming hydraulic fluid to the unloader valve 120. Furthermore, during the lowering mode of operation, the directional control valve 205, the lowering control valve 105, and the counterbalance valve 115 together operate and accordingly constitute the lowering system of the hydraulic system 100. In one embodiment of the present subject matter, the lowering control valve 105 is a two-way, three-position valve. The three positions exhibited by the lowering control valve 105 correspond to fast lowering, slow lowering, and null.

The aforementioned lifting system, neutral system, and the lowering system of the present hydraulic system 100 may be interchangeably referred as the lifting control circuit, the neutral control circuit, and the lowering control circuit, respectively.

Further, the check valve 330 and the counterbalance valve 115 are hydraulically connected to a single acting cylinder 335 via the safety valve 215. The single-acting cylinder 335 is designed to act as the hydraulic actuator for lifting or lowering the implement connected to the actuator. In one embodiment, the connected implement may be a farm tool or machinery such as plow. The single-acting cylinder 335 of the hydraulic control circuit 300 may also be referred to as the hydraulic actuator 335, hereinafter.

In addition to the directional control valve 205, the relief valve 220, the safety valve 215, and the isolation valve 210 in the hydraulic control circuit 300 operate in all the three modes of operation. In one embodiment of the present subject matter, the hydraulic valves hydraulically connected to the reservoir 320 of the hydraulic control circuit 300 include the unloader valve 120, the relief valve 220, the directional control valve 205, the feathering valve 110, the safety valve 215, the counterbalance valve 115, and the lowering control valve 105.

All of the aforementioned elements of the hydraulic control circuit 300 are operably interconnected with each other by means known in the art. The functionality achieved by the operation of all the aforementioned components, in tandem with each other, can be understood with respect to the description of Figs. 4a-d,

Fig. 4a is a diagrammatic representation of a control flow within the hydraulic system 100 to trigger the flow of hydraulic fluid in the hydraulic valve assembly 300, in accordance with an embodiment of the present subject matter.

In one embodiment, the reservoir 320 acts as a storage tank for the hydraulic fluid. The hydraulic fluid is extracted from the reservoir 320 by the hydraulic fluid pump 305. The suction filter 315a and the suction strainer 315b together facilitate filtering of the hydraulic fluid as the hydraulic fluid flows from the reservoir 320 towards the pump 305. Further, the pump 305 provides the hydraulic fluid to the directional control valve 205.

At block 410, the flow of the hydraulic fluid starts from the gear driven pump 305. The pump 305 accelerates the flow of the hydraulic fluid towards the directional control valve 205.

At block 415, the pressure of the hydraulic fluid upstream of the directional control valve 205 is evaluated. If the pressure of the hydraulic fluid is above a threshold value, then at block 420, a relief valve 220 opens to bypass a particular volume of the hydraulic fluid to the reservoir 320 through the relief valve 220.

This operation of the relief valve 220 facilitates maintenance of the pressure of the hydraulic fluid upstream of the directional control valve 205 at a level confirming to the prescribed safety standards. However, if the pressure of the hydraulic fluid upstream of the directional control valve is determined below the threshold value, then the relief valve 220 remains closed.

At block 425, a remainder volume of the hydraulic fluid out of the block 415 is transmitted to the directional control valve 205. In case (he relief valve 220 remains closed at block 415, then the entire volume of the hydraulic fluid from the block 410 reaches the directional control valve 205.

The directional control valve 205 may be operated in three modes, namely lifting, neutral and lowering modes. Such operations of the directional control valve 205 switch the hydraulic control circuit 300, and thereby the hydraulic system 100, operates in any one of the modes of operation of the hydraulic control circuit 300.

As explained before, only a certain number of hydraulic valves out of the total number of hydraulic valves present in the hydraulic control circuit 300 operate at any instant. Moreover, the operation of these valves depends upon the selection of a particular mode of operation. Accordingly, in one embodiment, the hydraulic control circuit 300 may have different sub-circuits such as the lifting control circuit, the neutral circuit, and the lowering control circuit, as already mentioned earlier, to carry out a particular operation. The three modes of operation of the hydraulic control circuit 300 are explained below in detail.

Fig. 4b is a diagrammatic representation of the control flow within the hydraulic valve assembly 300 to implement a lifting mode of operation of the hydraulic system 100, in accordance with an embodiment of the present subject matter.

At block 430, the directional control valve 205 is switched into the lifting mode of operation by an operator of the hydraulic system 100. The switching of the directional control valve 205 into the lifting mode automatically opens an in-built check valve of the throttle check valve 325. As known in the existing art. a throttle check valve is a combination of a check valve and a throttle valve. Accordingly, the throttle check valve 325 permits a free flow of the hydraulic fluid in one direction while maintaining a throttled or accelerated flow of the hydraulic fluid in another direction.

As per the aforementioned description, at block 450, the hydraulic fluid proceeds towards the throttle check valve 325 from the directional control valve 205, from where it further travels to the feathering valve 110.

At block 455, the hydraulic fluid is received by the feathering valve 110 from the throttle check valve 325. In one embodiment, the feathering valve 110 is a pressure compensated flow control valve, which assists in maintaining a constant flow rate of the hydraulic fluid in the hydraulic valve assembly 300 irrespective of the implement connected to the hydraulic actuator 335. Specifically, the feathering valve 110 keeps the flow rate of the hydraulic fluid independent of a pressure differential across the feathering valve 110. In another embodiment of the present subject matter, the feathering valve 110 may be calibrated to yield a particular flow rate of the hydraulic fluid.

A pressure compensating mechanism in the feathering valve 110 compensates for a change in the pressure differential value across the feathering valve 100. As known in the existing art, the pressure differential value across any hydraulic valve depends upon the value of load of the implement connected to the hydraulic actuator 335. As the change in the pressure differential value across the feathering valve 110 is sensed by the pressure compensating mechanism, a control mechanism located within the feathering valve 110 varies an outlet opening of the feathering valve 110 to keep the flow rate of the hydraulic fluid flowing across the feathering valve 110 at a constant value.

Further, the hydraulic fluid flow from the outlet of the feathering valve 110 reaches back to the throttle check valve 325, at block 457. When the hydraulic fluid is received by the throttle check valve 325 from the feathering valve 110, the in-built throttle valve of the throttle check valve 325 acts as a passage for the hydraulic fluid to speedily flow past the throttle check valve 325 towards the hydraulic actuator 335. This operation of the throttle check valve 325 is required to minimize energy losses associated with respect to the hydraulic fluid flow towards the hydraulic actuator 335. The throttle check valve 325 accelerates the hydraulic fluid flow emerging from the outlet of the feathering valve 110 and sends the accelerated fluid towards the hydraulic actuator 335. In one embodiment, the in-built throttle valve of the throttle check valve 325 is a non pressure compensated fixed orifice valve.

The combination of the feathering valve 110 and the throttle check valve 325 helps in controlling the flow rate of the hydraulic fluid during lifting of the implement connected to the hydraulic actuator 335. Moreover, any abrupt or exponential rise of the implement is also prevented.

The hydraulic fluid flow is directed from the throttle check valve 325 to the check valve 330, at block 460. The check valve 330 is a spring loaded valve and opens to permit the How of the hydraulic fluid only if the pressure of the fluid flow at the input is greater than a pre-defined pressure value. For the purpose, a spring of the check valve 330 is calibrated or set according to the pre-defined pressure value.

In addition, the check valve 330 propagates the fluid flow in one direction only, which is, according to the present subject matter, towards the hydraulic actuator 335, and blocks the fluid flow in the reverse direction. In this way, the check valve 330 facilitates prevention of an unwanted lowering of the implement by preventing the flow of the hydraulic fluid in a direction opposite to the intended direction under the lifting mode of operation. The hydraulic fluid flow may occur in this opposite direction while lifting a heavy load associated with the implement.

At block 463, the safety valve 215 controls the pressure of the fluid flow in a manner similar to the functionality of the relief valve 220. Accordingly, the safety valve 215 directs either the entire volume or a certain volume of the incoming hydraulic fluid to the hydraulic actuator 335. At block 465, the fluid flow reaches the hydraulic actuator 335 from the safety valve 215.

Fig 4c is a diagrammatic representation of a control flow within the hydraulic valve assembly 300 to implement a neutral mode of operation of the hydraulic system 100, in accordance with an embodiment of the present subject matter.

At block 440, the directional control valve 205 can be switched by the user to the neutral mode of operation. The neutral mode is selected is to put the working of the hydraulic control circuit 300 on hold, thereby forcing the hydraulic actuator 335 to stop functioning and attain a stationary position. Accordingly, the implement connected to the hydraulic actuator 335 is rendered immobile. To achieve the neutral mode of operation, the hydraulic fluid is neither directed towards the hydraulic actuator 335 by the directional control valve 205, nor allowed to escape from the hydraulic actuator 335.

In operation, the hydraulic fluid flow accelerated by the pump 305 towards the directional control valve 205 is diverted by the directional control valve 205 towards the unloader valve 120, at block 470. In one implementation, the unloader valve 120 is a spring loaded valve, thereby having a similar principle of operation as that of the check valve 330.
At block 473, the unloader valve 120 sends the hydraulic fluid to the reservoir 320 at a low pressure,

Fig 4d is a diagrammatic representation of the control flow of the hydraulic fluid in the hydraulic valve assembly 300 to implement a lowering mode of operation of the hydraulic system 100, in accordance with an embodiment of the present subject matter.

At block 445, the directional control valve 205 is switched by the user into the lowering mode of operation. As mentioned before, the lowering mode of operation of the hydraulic valve assembly 300 facilitates lowering of the implement connected to the hydraulic actuator 335.

At block 475, the lowering control valve 105 is activated by the directional control valve 205 to initiate the lowering mode of operation.

At block 480, the lowering control valve 105 actuates the counterbalance valve 115 to open, and thereby allow the hydraulic fluid from the hydraulic actuator 335 to flow out of the hydraulic actuator 335. Alternatively, the activation of the counterbalance valve 115 by the lowering control valve 105 may also trigger the departure of the hydraulic fluid from the hydraulic actuator 335.

At block 483, the safety valve 215, implemented as a spring-loaded relief valve, controls the pressure of the hydraulic fluid upstream of the counterbalance valve 115.

At block 485, the hydraulic fluid reaches the counterbalance valve 115 from the hydraulic actuator 335 via the safety valve 215. In one implementation, the counterbalance valve 115 is a pressure reducing valve. Accordingly, a spring of the counterbalance valve 115 is calibrated at a pressure equal to the pressure value of the hydraulic fluid downstream of the counterbalance valve 115. Such an arrangement enables ON state of the counterbalance valve 115 as long as the pressure of the hydraulic fluid downstream of the counterbalance valve 115 is at a value less than the calibrated pressure value of the spring.

In operation, the counterbalance valve 115 is activated by the lowering control valve 105 to permit the flow of hydraulic fluid from the hydraulic actuator 335 to lower the connected implement. Accordingly, the counterbalance valve 115 opens and permits the hydraulic fluid from the hydraulic actuator 335 to flow across, This flow of fluid across the counterbalance valve 115 triggers the lowering of the implement connected to the hydraulic actuator 335.

As the implement also tends to drop under the influence of its own weight, the flow of hydraulic fluid across the counterbalance valve 115 also increases, and thereby the pressure at the outlet or downstream of the counterbalance valve 115 increases. When the pressure of the hydraulic fluid at the outlet of the counterbalance valve 115 increases beyond the calibrated pressure value of the spring of the counterbalance valve 115, a portion of the hydraulic fluid flowing through the counterbalance valve 115 is bypassed to the reservoir 320.

This bypassing of the hydraulic fluid actuates an in-built mechanism in the counterbalance valve 115 to drive a valve element of the counterbalance valve 115 to decrease a passage area of the counterbalance valve 115. Accordingly, the flow of the hydraulic fluid across the counterbalance valve 115 decreases, thereby reducing the pressure of the hydraulic fluid downstream of the counterbalance valve 115. However, when this pressure of the hydraulic fluid decreases considerably below the prescribed pressure value, then the aforesaid in-built mechanism increases the passage area of counterbalance valve 115. In this manner, the counterbalance valve 115 assists not only in providing jerk-free lowering of the implement but also in countering the effect of gravitation induced, abrupt lowering of the implement.
At block 490, the hydraulic fluid moves from the counterbalance valve 115 to the lowering control valve 105. The lowering control valve 105 varies the flow rate of the hydraulic fluid flowing across the lowering control valve 105 to achieve fast or slow lowering of the implement. In one embodiment, the lowering control valve 105 may be a fixed orifice, non-pressure compensated valve.

To vary the flow rate across the lowering control valve 105, a number of associated controls may be located at the directional control valve 205. In one embodiment, the lowering control valve 105 is a double tapered spool-and-sleeve valve. By virtue of this configuration, the operation of the lowering control valve 205 ensures zero leakage of the hydraulic fluid within the present hydraulic control circuit 300. In addition, the lowering control valve 105 may also be deactivated by the directional control valve 205 in accordance with the aforementioned null position of the lowering control valve 105.

At block 495, the flow of the hydraulic fluid reaches the reservoir 320 from the lowering control valve 105. During the lowering mode of operation of the hydraulic control circuit 300, the incoming fluid flow from the pump 305 is routed by the directional control valve 205 to the reservoir 320 via the unloader valve 220.

The isolation valve 210 facilitates disconnection of the fluid flow from the directional control valve 205 to the hydraulic actuator 335. In such a case, the hydraulic fluid flow that would otherwise reach the hydraulic actuator 335 is available at the output of the isolation valve 210. This available hydraulic fluid flow may be tested to monitor various parameters associated with the fluid flow like flow rate, pressure, etc. Any sort of deviation of these parameters from a standard value helps in determining faults that may be occurring in the hydraulic valve circuit 300. As an example, the isolation valve 210 helps in the determination of leakage in the hydraulic system 100.

In one embodiment, the hydraulic control circuit 300 is implemented in a hydraulic system of an agricultural tractor. The hydraulic control circuit 300 facilitates lifting and lowering of a machinery connected to the hydraulic actuator 335 of the hydraulic system 100 of the agricultural tractor. In addition to this main hydraulic actuator 335, if the hydraulic system 100 of the agricultural tractor has an auxiliary hydraulic actuator attached to the hydraulic control circuit 300, an additional machinery can be connected to the hydraulic system 100 of the agricultural tractor, The auxiliary machinery may include a tipping trailer, a grass cutter, a reversible mould broad flow, etc.

The previously described versions of the subject matter and its equivalent thereof have many advantages, including those which are described below:

The hydraulic system 100 facilitates smooth lifting and lowering of the connected implement. A combination of the feathering valve 110 and the throttle check valve 325 helps in implementing jerk-free lifting of the implement connected to the hydraulic actuator 335 during the lifting operation. Likewise, the counterbalance valve 115 facilitates jerk-free lowering of the implement during the lowering operation. In addition, the present hydraulic system 100 achieves better control over the connected implement. Accordingly, a response time of the hydraulic system 100 gets improved. Moreover, the combination of the throttle check valve 325 and the feathering valve 110 lessens the probability of overshooting of the implement, while the implement undergoes either lifting or lowering.

Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.

I/We Claim:

1. A hydraulic valve assembly 300 for a hydraulic system 100, the hydraulic valve
assembly 300 comprising;

a directional control valve 205;

a counterbalance valve 115 hydraulically connected to a hydraulic actuator 335 to receive a hydraulic fluid from the hydraulic actuator 335; and

a lowering control valve 105 to receive the hydraulic fluid from the counterbalance valve 115 at a regulated pressure, wherein the lowering control valve 105 is operably connected to the directional control valve 205.

2. The hydraulic valve assembly as claimed in claim 1, wherein the lowering control valve 105 actuates the counterbalance valve 115.

3. The hydraulic valve assembly as claimed in claim 1, wherein the hydraulic valve assembly 300 further comprises:

a throttle check valve 325 hydraulically connected to the directional control valve 205 to receive the hydraulic fluid from the directional control valve 205; and

a feathering valve 110 hydraulically connected to the throttle check valve 325, wherein the throttle check valve 325 receives the hydraulic fluid from the feathering valve at a fixed flow rate.

4. The hydraulic valve assembly as claimed in claim 3, wherein the throttle check valve 325 is hydraulically connected to the hydraulic actuator 335 to provide the hydraulic fluid to the hydraulic actuator 335 at a regulated flow rate.

5. The hydraulic valve assembly as claimed in claim 1, wherein the counterbalance valve 115 is a pressure reducing valve.

6. The hydraulic valve assembly as claimed in claim 1, wherein the lowering control valve 105 is a double tapered spool and sleeve valve to vary the flow rate of the hydraulic fluid.

7. A utility vehicle comprising:

an implement; and

a hydraulic system to drive the implement, wherein the hydraulic system comprises the hydraulic valve assembly 300 as claimed in any of the preceding claims.

8. The utility vehicle as claimed in claim 7, wherein the utility vehicle is a tractor.