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APPLICATION OF DIRECTIONAL CONTROL

VALVE IN AUTOMATIC TRANSMISSION

GUIDED BY,SRI . U.PRAKASH(ASSOCIATE PROFESSOR MECHANICAL DEPARTMENT)

SUBMITTED BY,DENY M THOMAS121U7

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INTRODUCTION

Directional control valves

• As the name implies directional control valves are used to control the direction of flow in a hydraulic circuit. They are used to extend, retract, position or reciprocate hydraulic cylinder and other components for linear motion.

• Valves contains ports that are external openings for fluid to enter and leave via connecting pipelines

• The number of ports on a directional control valve (DCV ) is usually identified by the term “ way”. For example, a valve with four ports is named as four-way valve

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Classification of Directional control valves

1. According to type of construction : • Poppet valves • Spool valves2. According to number of working ports : • Two- way valves • Three – way valves • Four- way valves.3. According to number of Switching position: • Two – position • Three – position4. According to Actuating mechanism: • Manual actuation • Mechanical actuation • Solenoid ( Electrical ) actuation • Hydraulic ( Pilot ) actuation • Pneumatic actuation

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Poppet valves

Directional poppet valves consists of a housing bore in which one or more suitably formed seating elements ( moveable ) in the form of balls, cones are situated. When the operating pressure increases the valve becomes more tightly seated in this design. The main advantage of poppet valves are;

• No Leakage as it provides absolute sealing.• Long useful life, as there are no leakage of oil flows.• May be used with even the highest pressures, as no hydraulic sticking (pressure dependent deformation ) and leakages occurs in the valve. The disadvantages of these valves are;• Large pressure losses due to short strokes• Pressure collapse during switching phase due to negative overlap ( connection of pump, actuator and tank at the same time ).

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spool valves

• The spool valve consists of a spool which is a cylindrical member that has large- diameter lands machined to slide in a very close- fitting bore of the valve body.

• The degree of sealing depends on the size of the gap, the viscosity of the fluid and

especially on the level of pressure.

• The amount of leakage is primarily dependent on the gap between spool and housing. Hence as the operating pressure increases the gap must be reduced or

the length of overlap increased. The radial clearance is usually less than 20 μ.

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DCV FLOW PATH TERMINOLOGY

Valve Type Valve Use

2 way On or off functions for fluid supply

3 way Single acting cylinders & uni-directional motors

4 way Double acting cylinders, bi-directional motors

5 way Pneumatic systems with dual air pressure

The above description refer to the total number of directions in which a fluid can travel through a directional control valve

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DCV FLOW PATH TERMINOLOGY

• 2 POSITION

• 3 POSITION

• 4 POSITION The positions refer to which direction the fluid happens to going when a valve is shifted

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DCV SCHEMATIC SYMBOLS

The basic valve symbol is a blank envelope.DCV ‘S have atleast two envelops which corresponds with 2 position valve. A 3 position valve will have three envelope and so forth.

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Arrows are added to indicate a direction that fluid can travel through the valve in that position. Each arrow crossing represents two ports . The above example indicates four ports.

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3 way valve 2 way valve

The little ‘T’ Emblem represents blocked port

The arrow indicate one inlet port and one outlet port

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4 WAY 3 POSITION DCV

The cutaway diagram shows how a spool can connect and disconnect passages

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WORKING

• If spool is shifted to right ,port A is connected to the port which is being fed by the pump,port P. At the same time port B IS connected to the tank port T.

•The fluid from the port P flows through the port A and tank T receives the fluid from port B

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•If the spool is shifted to left ,the spool connects port P with port B , and port A withport T which gives a reversal of the previous flow path

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DCV OPERATORS

•An operator is a device that physically moves a spool or poppet.

•Manual operators such as the push button,handlever,and foot pedal use human power for actuation.

•Mechanical operators use a machine component to contact a roller or ball bearing.

•Pilot operators use a fluid to move the spool.

•A solenoid uses electro-mechanical force to move a spool or poppet.

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SOLENOID OPERATION

•A solenoid is an electrical-mechanical device that takes electrical energy and produces a linear force in the direction of valve spool.

•When solenoid is energized ,the air gap is closed quickly and a force is developed in the direction of the valve spool.

•A spring holds the spool against the solenoid push pin when the solenoid is de-energized.

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DETENTS(OPERATOR)

•Detents are used to hold a valve spool in place.

•They keep the spool from moving due to vibration or possibly from gravity where the valve is placed in an upright position.

•The above fig shows a ball and spring type detent

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SUB PLATE MOUNTED 4 WAY VALVES

•Sub plate or sub base mounting is convenient way of attaching a DCV to a system and reducing the time required to replace it should the need arise.

•The DCV is held into place by four fasteners and a seal is made with O rings. The time savings is in to having to remove pipe connections

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PIGGY-BACK DCV

•Piggy-backing is a term used to describe two valves connected as a Unit where small valve controls the operation of larger valve.

•This arrangement makes used of the powerful force of fluid in order to actuate a largeflow DCV.

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CENTER CONDITIONS• OPEN CENTER

• In open- center circuit, all ports are open to each other in the center position. When the valve is in open center position, the pump flow is directed to the tank at atmospheric pressure.

•At the same time the actuator can be moved freely by applying an external force. Open center valve help to prevent heat buildup.

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CLOSED CENTER

•In closed center DCV all ports are closed to each other. Hencethe actuator connected to ports A and B is hydraulically locked and cannot be moved byan external force .

•This not only waste pump design power but promotes wear and shortens pump life. Also the temperature of oil is raised due to heat buildup in the system. This promotes oil oxidation , viscosity drop, which further raises the wear of parts and increased leakage.

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TANDEM CENTERED

• In the center configuration, the working ports A and B are blocked , and the pumpport P is connected to tank port T.

• The tandem center also results in a locked actuator . However, it also unloads the pump at atmospheric pressure.

•The application of this design may be to hold a cylinder or fluid motor under load.

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FLOATING CENTERED

• In this position the pump port is blocked and the two working ports A and B are connected to tank port T. Since the working ports A and B are connected to tank T, the actuator can be moved freely without any external force and hence the name floating.

•The pump produce flow at the high pressure setting of the pressure relief valve, which builds up heat in the circuit. Hence this center configuration is used only in special case.

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APPLICATION OF CV IN AUTOMATIC TRANSMISSION

•Control valves can also react to changes in pressure.This simple shift valve is held at the end of its bore by spring tension and blocks the fluid under pressure at port A.•The larger differential area at port C is subject to governor pressure and as vehicle road speed increases, the increasing pressure forces the valve to the left and allows fluid to flow across from port A to port B. This can be directed to operate the next clutch or servo and change the transmission to a higher ratio.•As road speed falls and governor pressure diminishes, the spring moves the valve back to cut off the fluid supply and the transmission downshifts.

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APPLICATIONS IN AUTOMOTIVE AREA

• Control valves are applied in each area where hydraulic control and actuation tasks occur.

• In the automotive area, Supply, control and regulating of actuations for automated manual transmissions (AMT), double clutch transmissions (DCT), continuous variable automatic transmissions (CVT) or automatic transmissions (AT).

• Control of automated clutch actuations in hybrid drives.• Control of differential locks.

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C0NCLUSION

• Directional control valve is used to direct the supply of oil to the actuator in a hydraulic system.

• Directional control valves are essentially used for distribution of energy in a fluid power system. They establish the path through which a fluid traverses a given circuit. For example they control the direction of motion of a hydraulic cylinder or motor.

• These valves are used to control the start, stop and change in direction of flow of pressurized fluid.

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REFERENCE

• Jagadheesha T-fluid power control systems-hydraulics control in machine tools(chpter2)

• Maher yahya sallom,Zahurrin samad-MAGNETO-RHEOLOGICAL DIRECTIONAL CONTROL VALVE-Date:21May2011

• V.J Sonavane,T.J Rane,P.C Gawade-DESIGN AND ANALYSIS OF GLOBE VALVE AS CONTROL VALVE USING CFD SOFTTWARE-Date:16 July 2012

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THANK YOU