Claims:We claim:

1. A Power Shuttle Transmission (PST) Control Valve for the tractor transmission; the PST Control valve comprises:

• a priority valve,
• an inching valve,
• a directional control valve,
• a pressure modulation valve, and
• a relief valve,

wherein the valves are configured within the PST control valve body and the priority valve and inching valve are integrally configured by having a stepped sleeve configuration to make a compact PST valve.

2. Power Shuttle Transmission Control Valve as claimed in claim 1, wherein the modulation valve and relief valve are made separate for application at different pressure setting whenever required by the tractor operator.

3. Power Shuttle Transmission Control Valve as claimed in claim 1, wherein the diameter of the 1st step or the step to be inserted in the PST valve bore first is configured to be the least diameter of the stepped sleeve.

4. Power Shuttle Transmission Control Valve as claimed in claim 3, wherein the first O-ring is placed in a groove provided at a point disposed just after the 1st cross hole adjacent the first step.

5. Power Shuttle Transmission Control Valve as claimed in claim 3, wherein the first bore diameter d1 is configured as per the O-ring standard.

6. Power Shuttle Transmission Control Valve as claimed in claim 5, wherein the second bore diameter d2 is configured based the outer diameter of O-ring placed at the first bore diameter d1.

7. Power Shuttle Transmission Control Valve as claimed in claim 6, wherein the second bore diameter d2 is calculated by the formula:

D2 min = d1 + 2 × O-ring cross-section + min 0.5 mm (on diameter)

8. Power Shuttle Transmission Control Valve as claimed in claim 7, wherein the second O-ring is selected after obtaining the minimum value of bore diameter D2.

9. Power Shuttle Transmission Control Valve as claimed in claim 7, wherein the second step diameter d2 is configured as per the O-ring standard.

10. A method for forward or reverse (F/R) shuttling of a tractor, wherein the method includes the steps of:

• Supplying oil from the inlet of the priority valve to divide the input oil flow,

• Feeding the priority valve oil flow into the PST valve system to follow less restricted path and bypassing the remaining oil,

• Opening the inching valve or keeping the Directional Control (DC) valve in a Neutral position to lead the oil flow to the oil tank freely without any restriction, or

• Closing the inching valve is closed and bringing the Directional Control (DC) valve in a Forward or Reverse position by leading the oil flow first to the clutch plate by means of more restriction offered by all other paths,

• Pressing the modulation and relief valves to open due to the oil flow, when the passage is closed,

• Opening the Relief Valve (RV) fully to lead the oil flow along the path of the relief valve on exceeding the modulation time (time to reach RV setting pressure),

• Pressing the inching pedal for inching function to move the inching spool moves towards tank port, and

• Reducing the pressure by opening the tank port to starts disengaging the clutch in parallel.
11. Method as claimed in claim 14, wherein the stepped sleeve is placed inside the valve body or manifold bore with O-rings across different ports to avoid cross-connection.

Dated: this 25th day of August, 2016. SANJAY KESHARWANI
APPLICANT’S PATENT AGENT , Description:FIELD OF INVENTION

The present invention relates to a hydraulic clutch for transmission in tractors. In particular, the present invention relates to a power shuttle transmission (PST) system. More particularly, the present invention relates to a power shuttle transmission control valve system for forward-reverse (F-R) shifting or shuttling a tractor.

BACKGROUND OF THE INVENTION

Power shuttle feature replaces mechanical transmission gearbox normally used for shifting a tractor in a forward-reverse (F-R) direction (shuttling). So, a Power Shuttle Transmission (PST) valve performs this Forward-Reverse Shifting operation by means of a hydraulically actuated wet clutch to control the F-R clutches. PST valve performs this not by any clutch pedal operation, but by engaging and disengaging the hydraulic clutch. A power shuttle control valve facilitates an instantaneous F-R control for changing the direction of forward-reverse motion of a tractor. PST valve offers enhanced service life in comparison to the conventional double cone synchro shuttle (synchronizer) operated by a hand lever. The major differentiating features of the PST valve over the conventional synchro shuttle are summarized below:

S. No. Geared version Power Transmission version
1 Synchro Shuttle Hydraulic wet clutch pack
2 Mechanically operated Clutch pack hydraulically actuated by control valve
3 No Positive-neutral lock Positive-neutral lock
4 Mechanical clutch Direct drive through damper, no mechanical clutch

PST valve provides a smoother control and increased productivity in loader operations because of substantial savings in time required for F-R gear shifting operation. It also reduces the complexity of the conventional gear shifter systems based on the fork-detent-rail system. Thus, F-R shifting arrangement including a PST control valve results in an improved reliability of tractor’s transmission system.
PRIOR ART

US 6212966 B1 discloses a power shuttle transmission in a control system, the transmission comprises a first clutch pack engagement of which drives a transmission output in a first direction, and a second clutch pack engagement of which drives the transmission output in a second direction, and means to engage and disengage the first and/or second clutch pack, the control system comprising control means to initiate and complete engagement and/or disengagement cycles of the first and/or second clutch pack, and wherein the control system comprises adjustment means for actuation by an operator of the transmission to adjust the said engagement/disengagement cycle.

DISADVANTAGES WITH THE PRIOR ART

However, the following are the disadvantages with the existing power shuttle transmission valves discussed above:

Power Shuttle Transmission (PST) valve (e.g. configured with Inching valve and detent) has a combined modulation and relief valve. It also includes different designs for all other components and valve body. It has a simple design, separate modulation, a combined Priority Valve-Inching valve and Direction Control (DC) valve, Relief valve each and particularly a common sleeve design for Priority and Inching valve.

Existing sleeve is configured straight and therefore, several problems are faced during the assembly and dismantling thereof. It is quite difficult to assemble a plurality of O-rings on the straight sleeve. During assembly, if required, the straight sleeve in the mating part is required to be forced by hammering. After assembling the sleeve, most of the O-ring is noticed to have been damaged (cut into several pieces) due to the presence of cross holes in the mating part of the sleeve.

In order to completely eliminate these problems, the PST valve configured according to the present invention includes a stepped sleeve having a simpler design is developed according to the present invention.
This stepped sleeve eliminates damage to the ‘O’-rings while mounting them in the grooves therefor. This PST valve has a completely different layout and separate modulation and relief valve. However, it is also compatible even for the existing clutch pack.

OBJECTS OF THE INVENTION

Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

An object of the present invention is to provide a simple design of the power shuttle transmission (PST) valve for tractor shuttling.

Another object of the present invention is to provide an economical power shuttle transmission (PST) valve for tractor shuttling.

Yet another object of the present invention is to provide a power shuttle transmission (PST) valve for tractor shuttling, which substantially reduces the Forward-Reverse gear shifting time.

A still further object of the present invention is to provide a power shuttle transmission (PST) valve, which increases the productivity during shuttling of a front-end loader tractor application.

A yet further object of the present invention is to provide a power shuttle transmission (PST) valve, which simplifies manufacturing thereof.

Another important object of the present invention is to provide a power shuttle transmission (PST) valve, which increases reliability of overall PST valve system.

These and other objects and advantages of the present invention will become more apparent from the following description, when read with the accompanying figures of drawing, which are however not intended to limit the scope of the present invention in any way.
DESCRIPTION OF THE INVENTION

Power Shuttle Transmission (PST) control valve is a control valve for power shuttle transmission developed and manufactured in-house by the present applicant. This is a combination of five different valves.

Since in existing straight sleeve design, O-rings cannot be assembled easily on the sleeve OD and also O-ring got damage at the time of assembling sleeve in the mating part due to the presence of multiple cross holes. Further, the coarser bore sizes lead to the leakage path, thereby causing a pressure drop.

Accordingly, a stepped sleeve is configured in accordance with the present invention having an improved mating bore thereof. In this stepped sleeve configuration, the assembly of O-rings is very easy, because only one O-ring is to be fitted in every step or diameter and the sleeve design is such that no O-ring can damage at the time of assembly and dismantling of the sleeve. This is particularly advantageous for sleeves facing more than one cross-hole. This stepped sleeve configuration is useful for achieving a constant pressure in the hydraulic system wherever the bore accuracy is an important criterion. So, stepped sleeves are placed inside the valve body or manifold bore with O-rings placed across different ports to avoid any cross connection thereof. These stepped sleeves also offer a flexibility in handling while machining for maintaining a smaller inventory.

Stepped sleeve requires less assembly time, which increases the productivity. This stepped sleeve configuration is also advantageous for making PST control valves error-free or to comply with desired implementation of Poke Yoke to reduce parts per minute (PPM) in the overall tractor manufacturing activity.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a Power Shuttle Transmission (PST) Control Valve for the tractor transmission; the PST Control valve comprises:
• a priority valve,
• an inching valve,
• a directional control valve,
• a pressure modulation valve, and
• a relief valve,

wherein the valves are configured within the PST control valve body and the priority valve and inching valve are integrally configured by having a stepped sleeve configuration to make a compact PST valve body.

Typically, the modulation valve and relief valve are made separate for application at different pressure setting whenever required by the tractor operator.

Typically, the diameter of the 1st step or the step to be inserted in the PST valve bore first is configured to be the least diameter of the stepped sleeve.

Typically, the first O-ring is placed in a groove provided at a point disposed just after the 1st cross hole adjacent the first step.

Typically, the first bore diameter d1 is configured as per the O-ring standard.

Typically, the second bore diameter d2 is configured based the outer diameter of O-ring placed at the first bore diameter d1.

Typically, the second bore diameter d2 is calculated by the formula:

D2 min = d1 + 2 × O-ring cross-section + min 0.5 mm (on diameter)

Typically, the second O-ring is selected after obtaining the minimum value of bore diameter D2.

Typically, the second step diameter d2 is configured as per the O-ring standard.

In accordance with the present invention, there is also provided a method for forward or reverse (F/R) shuttling of a tractor, wherein the method includes the steps of:
• Supplying oil from the inlet of the priority valve to divide the input oil flow,

• Feeding the priority valve oil flow into the PST valve system to follow less restricted path and bypassing the remaining oil,

• Opening the inching valve or keeping the Directional Control (DC) valve in a Neutral position to lead the oil flow to the oil tank freely without any restriction, or

• Closing the inching valve is closed and bringing the Directional Control (DC) valve in a Forward or Reverse position by leading the oil flow first to the clutch plate by means of more restriction offered by all other paths,

• Pressing the modulation and relief valves to open due to the oil flow, when the passage is closed,

• Opening the Relief Valve (RV) fully to lead the oil flow along the path of the relief valve on exceeding the modulation time (time to reach RV setting pressure),

• Pressing the inching pedal for inching function to move the inching spool moves towards tank port, and

• Reducing the pressure by opening the tank port to starts disengaging the clutch in parallel.

Typically, the stepped sleeve is placed inside the valve body or manifold bore with O-rings across different ports to avoid cross-connection.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be briefly described with reference to the accompanying drawings, wherein:

Figure 1 shows a schematic diagram of hydraulic circuit in which the PST valve configured in accordance with the present invention is connected.

Figure 2a shows the detailed front-view of a PST valve shown in Fig.1.
Figure 2b shows a rear-view of the PST valve shown in Fig.1.

Figure 2c shows a side-view of the PST valve shown in Fig.1.

Figure 2d shows the cross-sectional view of the PST valve shown in Fig.1 and depicts constructional features and oil-flow to build hydraulic pressure therein.

Figure 3 shows a cross-sectional view of a priority valve in a PST valve in Fig.1.

Figure 4 shows a cross-sectional view of the inching valve of PST valve in Fig.1.

Figure 5a shows the first cross-sectional view of direction control (DC) valve of PST valve of Fig.1 at a neutral position.

Figure 5b shows the second cross-sectional view of DC valve of PST valve of Fig.1 at a forward position.

Figure 5c shows the third cross-sectional view of DC valve of PST valve of Fig.1 at a reverse position.

Figure 6 shows an exploded view of the direction control valve of Figs. 5a to 5c.

Figure 7 shows hydraulic circuit diagram of the PST valve of Figure 2d.

Figure 8 shows a conventional straight sleeve requiring an O-ring for sealing.

Figure 9a shows a stepped sleeve configured in accordance with the present invention for completely eliminating O-ring damage in the PST valve.

Figure 9b shows a cross-sectional view of the bore for stepped sleeve of Fig.9a.

Figure 10a shows a stepped sleeve 102 of Fig. 9a.

Figure 10b shows a cross-sectional view of bore of stepped sleeve of Fig. 10a.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following, the power shuttle transmission (PST) valve system configured in accordance with the present invention will be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the present invention in any way.

Figure 1 shows a schematic diagram of an entire hydraulic system of a tractor’s power shuttle transmission (PST) valve 10 configured in accordance with the present invention, depicting various essential features thereof. The system includes a gear pump 20 connected via a line L1 to a hydrostatic steering unit (HSU) 30 disposed under the steering 40 and discharging to left and right cylinder ports (not shown) via lines LL and LR respectively. HSU 30 is also connected via another line L3 to a PTO valve 50, which in turn is connected via a line L4 to a PST valve 10. PTO valve 10 is connected via a line L6 to an accumulator 60 and other two lines L7 and L8 are leading from it to PTO clutch 70 and PTO clutch lubricating points 72 respectively. PTO valve 50 in turn is connected to PST clutch 10 via lines L9 and L10 for forward and reverse operation respectively. PST valve 10 also includes a lubrication line L11 leading to PST clutch 80.

Figure 2a shows the detailed front-view of a PST valve shown 10 in Fig.1. It depicts a pressure checking port 12 and F/R pressure checking ports 14, 16.

Figure 2b shows a rear-view of the PST valve 10 shown in Fig.1. It depicts the forward port 13, reverse port 15, neutral tank port 17, 18, relief valve tank port 132, inching valve port 152, inlet port 22 and lubrication outlet 24.

Figure 2c shows a side-view of the PST valve 10 shown in Fig.1 and depicts the checking port 12 disposed substantially at the center thereof.

Figure 2d shows the cross-sectional view of the PST valve shown in Fig.1 and depicts constructional features and oil-flow to build hydraulic pressure therein. PST valve 10 includes a directional control (DC) valve 110, a pressure modulation valve 120, a relief valve 130, a priority valve 140 and an inching valve 150, all housed in body of PST valve 10. This PST valve 10 is a combination of five different valves, in which priority valve 140 and inching valve 150 have a single common sleeve 102 to make it more compact. The modulation valve 120 and relief valve 130 are made separate to be beneficial for application at different pressure setting in future. Four cross holes 144, 145, 146 and 148 are also indicated here. Cross hole 144 (6 nos.) are provided for oil inlet flow, cross hole 145 (6 nos.) for lubrication oil flow, cross hole 146 (4 nos.) for main oil flow in the oil gallery and cross hole 147 (6 nos.) to the inching valve tank port respectively. Three (3) oil grooves Og are also configured outside the sleeve 102 as shown.

Figure 3 shows a cross-sectional view of a priority valve in a PST valve of Fig.3. It shows the controlled fixed flow 142, inlet oil flow through oil inlet port via cross hole 144, through lubrication oil port via cross hole 145, oil flow from main oil gallery via cross-hole 146 towards DC valve 110, via cross hole 147 to inching valve tank port and excess oil flow 148 for providing a consistent feeling to the tractor operator.

Figure 4 shows a cross-sectional view of the inching valve 150 in a PST valve 10. Inching valve 150 includes a tank port 152, an inching spool 154, an inching plunger 156 and two spring 157 and 158. The inching valve 150 is used by the tractor operator for frequent stopping by using an inching pedal.

Figure 5a shows a first cross-sectional view of the direction control valve 110 in a PST valve 10 of Fig.3. Two tanks 112 are provided with a DC spool 114 moveable to and from therein. A DC spool plug 113 is provided at one longitudinal end (LHS in this figure) of the DC valve 110. DC spool plug 116 and a DC spool bellow 118 are provided the other longitudinal end (RHS in this figure) of the DC valve 110. Here, the DC valve is in its neutral position 115, in which all ports are connected.

Figure 5b shows a second cross-sectional view of the direction control valve 110 in a PST valve 10 of Fig.3. Here, DC valve 110 is in its forward position, in which pressure line 117 is connected to the forward port for changing into a forward motion of the tractor.
Figure 5c shows a third cross-sectional view of the direction control valve in a PST valve 10 of Fig.3. Here, DC valve is in its reverse position, in which pressure line 119 is connected to the reverse port for changing into a reversed motion of the tractor.

Figure 6 shows an exploded view of the direction control valve 110 of Figure 5a. It includes a plug 113 for DC valve, a directional control (DC) spool 114, a plug 116 for DC spool, a bellow 118 for DC spool and detent springs 122 inside the plugs 124 for detent ball holder, detent balls 125 and Dowty washers 126.

Figure 7 shows hydraulic circuit diagram of a PST valve 10 of Figures 1 and 3. The hydraulic system of the power shuttle transmission (PST) includes a forward 212 and a reverse clutch 214 each connected to a directional control valve 110 via a forward clutch pressure checking port 213 and reverse clutch pressure check port 215 respectively. PST valve 10 includes a directional control (DC) valve 110, a pressure modulation valve 120, a relief valve 130, a priority valve 140 and an inching valve 150. The pressure modulation valve 120 and relief valve 130 are connected to each other and also to a pressure check port 217. Similarly, the priority valve 140 and inching valve 150 are connected to each other as well as to another pressure check port 219. The hydraulic fluid is pumped by a pump 218 to the priority valve 140, which includes a lubricant flow line 220 and is also connected to another lubricant flow check port 221.

Figure 8 shows a conventional straight sleeve 02 requiring a plurality of O-rings fitted in the circumferential grooves provided therein for sealing purposes.

Figure 9a shows a stepped sleeve 102 configured in accordance with the present invention for completely eliminating O-ring damage during assembly of the sleeve in PST valve 10. Stepped sleeve 102 is configured according to the present invention to avoid earlier observed O-ring damages due to shearing or cutting-off during assembly in the existing PST valves. Here, four cross holes 144, 145, 146 and 147 are provided. Cross hole 144 allows inlet flow of the PST valve and the direction of this inlet oil flow is from the valve body to the inside of the sleeve 102. Cross hole 145 facilitates bypass flow for lubrication for oil flow from the sleeve interior to the valve body. Cross hole 146 allows a priority flow or main flow to the relief valve, modulation valve and DC valve and the oil flows from the sleeve 102 to the valve body. Cross hole 147 connects the main oil flow to the tank / tank port, when inching valve opens or inching spool moves towards right side (in this figure). Here, the oil flows from inside the sleeve to the valve body.

Figure 9b shows a cross-sectional view of bore 106 for the stepped valve 102 of Figure 9a.

Figure 10a shows a stepped sleeve 102 of Fig. 9a having three ‘O’ rings in four grooves provided on the stepped sleeve. Here, the layout is completely different and has separate modulation and relief valve. Since there are four cross holes here, diameter d1 of the 1st step or the step to be inserted in the bore first should be the least diameter. The first O-ring is placed in a groove provided at point a disposed just after the 1st cross hole. The second O-ring is placed in another groove provided at point b disposed just after 2nd cross hole and adjacent the next step’s higher diameter d2. This process is followed for the remaining cross holes in the mating bore.

Figure 10b shows a cross-sectional view of the mating bore of the stepped sleeve of Fig. 10a. Bore diameter D1 is designed depending on the O-ring standard. The bore diameter D2 is decided based the outer diameter of O-ring placed at d1, which is calculated as given below:

D2 min = d1 + 2 × O-ring cross-section + min 0.5 mm (on diameter)

The O-ring in the groove at point b is selected after obtaining the minimum value of bore diameter D2. The step diameter d2 is decided as per O-ring standard.

The bore can be applicable to manifold or valve body which can be solid block machined or casted. It also covers lead-in chamfer or entry chamfer for various valve body bore and mating shaft of hydraulic assembly. The accuracy of bores is very important for achieving a constant pressure in the hydraulic system, as the coarser bore sizes leads to leakage path and therefore causes a pressure drop. Sleeves are placed inside the valve body/manifold bore with O-rings across different ports to avoid cross connection. These sleeves provide a flexibility in handling while machining as well as reduce the inventory thereof. The same process will be followed for designing rest of the diameters of sleeve and bore and selection of O-rings.

WORKING PRINCIPLE OF THE INVENTION

• Oil is fed from the inlet of the priority valve, which divides the input flow.

• Priority oil flow enters PST valve system and remaining oil is bypassed. The priority oil flow tries to follow less restricted path.

• When the inching valve is opened or Directional Control (DC) valve is in a Neutral position, the oil flow follows the path to the oil tank freely without any restriction.

• When the inching valve is closed and Directional Control (DC) valve is in a Forward or Reverse position, oil flow first goes to the clutch plate as all other paths are offer more restriction.
• When the passage is closed, the oil flow presses the modulation and relief valves to open.

• When the modulation time (time to reach RV setting pressure) is exceeded, the Relief Valve (RV) fully opens and the oil flow follows the path of the relief valve.

• When the inching function is required, the operator has to press the inching pedal and with this the inching spool moves towards tank port. With the opening of that tank port the pressure starts falling down and parallel way the clutch starts disengaging.

• Stepped sleeve reduces the assembly time, since pressing of stepped sleeve is easier and requires less effort as compared to straight sleeve.

? Sleeve design is good for mistake-proofing or Poke Yoke to reduce PPM in manufacturing.

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

Power Shuttle Transmission (PST) control valve system configured with stepped sleeve configured in accordance with the present invention has the following technical and economic advantages:

• Hydraulic transmission having less wear.
• Enables F-R movement (shuttling) without any clutch pedal operation.

• Reduced time for shifting F-R gears, thus increases productivity of loader operation.

• Instantaneous and on-the-go F-R control.
• Increases service life of the DC control valve.

• Simplifies PST control system design.

• Enhanced system reliability.

• Positive neutral lock present.

• Contains no mechanical clutch, facilitates direct drive through damper.
• Reduces rejection rate.

• Avoids necessity of making heavy fixtures for handling valve body.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description.

The description provided herein is purely by way of example and illustration. The various features and advantageous details are explained with reference to this non-limiting embodiment in the above description in accordance with the present invention. The descriptions of well-known components and manufacturing and processing techniques are consciously omitted in this specification, so as not to unnecessarily obscure the specification.

It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, the skilled person will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments described herein and can easily make innumerable changes, variations, modifications, alterations and/or integrations in terms of materials and method used to configure, manufacture and assemble various constituents, components, subassemblies, assemblies and in terms of the size, shapes, orientations and interrelationships without departing from the scope and spirit of the present invention. It is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

The numerical values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure unless there is a statement in the specification to the contrary.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.

The use of the expression “a”, “at least” or “at least one” shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention.