Hydraulic Transmission System of BEML Tractor

details of twin turbine torque converter

Description on Structural Detail and Operation

The transmission is of direct mounted type and is bolted directly to the engine flywheel by a flexible disc drive. Provision is made to isolate the necessary drive gears from the flywheel cavity to provide a dry fly wheel housing while maintaining lubrication for the gears.

This transmission provided two forward and two reverse speeds with short drop output. The range clutches are multi disc hydraulic actuated type which compensate wear automatically. Its twin turbine convertor extends the torque multiplication of the converter; in each gear ranges providing broad torque coverage equal to two normal planetary gear ratios and is accomplished automatically and efficiently.

The twin turbine torque converter consists of pump assembly (6) First turbine assembly (3) Second turbine assembly (4) stator (5). The pump assembly is the driving member and is driven at engine speed. First and second turbine assemblies are driven members connected by transfer gears (10) (11) (14) and (15) to the transmission range-gearing Stator (5) is reaction member.

The first and second turbines function either alone or together during operation depending on the load demand and speed of the tractor. The first turbine gear train consists of gears (10 & 11) and second turbine gear train consists of gears (10 & 11) and second turbine gear train consists of gears (14 & 15). The turbine can function either alone or together by means of a free wheel clutch and is engaged to permit both turbines to drive thereby providing maximum input torque to the range gearing.

With the increasing tractor speed and decrease in load demand the second turbine speed exceed that of first turbine and provides all of the torque. The first turbine then freewheels. The free wheel clutch automatically reengages permitting both the turbines to provide necessary torque multiplication, when there is increase in load and the resulting decrease in tractor speed.

Forward, Reverse Gearing and Clutches – The Transmission includes forward and reverse gearing and clutch configuration. The forward and reverse gearing consists of a 6 and a 4 pinion planetary gear set respectively. The planetaries are interconnected and provide speed and torque ratio for the forward and reverse drive of the tractor. The multi disc clutches consists of resin graphite or bronze faced steel, internal splined and external-tanged plain steel clutch alternately assembled. They are hydraulically actuated and spring released.

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High and Low Range clutches Planetary – The high and low range clutches, and a planetary gear set which may be high or low range provide forward and reverse. These components work with either the forward or reverse planetary.

Transmission hydraulic system – The transmission control is meant for selecting various gear ranges through shifting control valve spool in the control valve assy mounted on the transmission. The movement of the control valve spool is done by means of a range selector located on the left of the operator, mounted on a mounting stand through a connecting push pull cable. The various gear ranges are marked on the gating of the range selector. The control valve spool when is fully protruding out from the valve body will correspond to reverse gear range and when is fully inside control valve corresponds to forward range. The Adjustment of push cable is required to be done to provide the above shift pattern.

Throttle control – Throttle control is meant to accelerate the engine speed as required by the operator, this is accomplished by pressing the throttle pedal providing in front of the operator which in turn actuates the fuel injection pump lever through push cable and mechanical linkages. When the force is applied on the foot pedal .The throttle plate which is held against the foot pedal will actuate a bar throttle, housed in bearings on either side, will in turn actuate through throttle link. The push pull cable, when pedal is depressed from low idle position and the full throttle position, the fuel injection pump lever from the idle position, moves 60°to come to full throttle condition. 10. The low idle and high idle is achieved by adjusting the yokes on either side of the cable. “The cable hub is anchored with the help of ‘U’ bolts, shims and nuts on the brackets.

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Hydraulic System

(a) At the control valve assembly, oil flows around the main pressure regulator valve and to the selector valve bore. At the regulator valve, oil flows through a diagonal passage to the left end of the valve. The oil pressure pushes the valve right ward against its spring. This uncovers the port which directs oil to the convertor. When sufficient oil flow to the convertor occurs, main pressure will establish a balance against the force of the main pressure regulator valve spring.

(b) Under certain condition, more oil than the convertor in line can handle must be exhausted to prevent excessive pressure in the system. When this occurs, the main pressure regulator valve moves further rightward to allow oil to flow into the exhaust port (at the left end of the valve) between the two short lands on the valve. Oil flowing into the convertor in line is directed to the torque convertor. A pressure regulator flowing into the convertor in circuit limits the convertor pressure to 80 PSI.

Convertor-Out, Cooler, and Lubrication Circuit – Oil flowing out of the torque convertor is directed in to the oil cooler. From the cooler the oil flows to the transmission lubrication circuit. All oil in excess of that required to maintain lubrication pressure (20 PSI) is exhausted to sump through the lubrication pressure (20 PSI) is exhausted to sump through the lubrication regulator valve.

Manual Selector Valve Circuit

(a) Main pressure oil from orifice B flows into the manual selector valve bore and surrounds the valve in the area of the détente notches. From this main oil flows, regard less of valve position, to another area at the valve. Here it is available for high range and forward clutches and for operation of the trimmer.

(b) Moving the selector valve one notch rightward will leave the low range clutch applied and will change the forward clutch. This is forward 1 st gear. (c) Moving the selector valve a second notch rightward will close off oil to the low range clutch and allow it to exhaust. The forward clutch will remain applied and the high range clutch will be charged. This is second forward gear.

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(d) Moving the selector valve one notch leftward of neutral will charge the reverse clutch while allowing the low range clutch to remain charged. This is reverse 1. If the vehicle is equipped with a reverse warning signal, clutch apply pressure in the reverse circuit actuate the warning device.

(e) Moving the valve of second notch leftward will close off oil to the low range clutch and allow it to exhaust. The reverse clutch will remain applied and high range clutch will be charged. This is reverse 2.

(f) When the selector valve is moved to the high range position (either F2 or R2) oil to fill the high-range clutch must pass through orifices, B and the high range-clutch orifice. This is due to the oil passage immediately to the right of the high range clutch orifice being blocked by the manual selector valve. The high range clutch orifice is smaller than orifice B and restricts the flow of oil to the high range clutch. As a result the high range clutch fills at a slower rate than other clutches and thus provides smoother engagement.

Trimmer Circuit

(a) The trimmer regulates clutch application pressure during initial stages of clutch engagement to obtain smooth operation. Normally full main pressure holds the trimmer plug left ward against it spring and a shoulder in the plug bore. This compresses the main pressure regulator valve spring and gives maximum main pressure.

(b) When any shift is made, oil is required to charge clutch. This oil must flow through orifice B, located below the main pressure regulator valve. The restriction of the oil flow through orifice causes pressure blow the orifice to be reduced. This reduction in pressure allows trimmer plug to move rightwards. Force against main pressure regulator valve spring is reduced and main pressure is reduced.

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