y ENGINE USED IS-TPE 331(turboprop engine) y ENGINE TYPE-single shaft turboprop with internal
gear box y COMPRESSOR TYPE-2-stage centrifugal compressor y TURBINE TYPE-3-stage axial turbine
y We have noticed the Garrett engine is pre-maturely
withdrawn for torque fluctuation from the air force and navy bases y We have noticed the engine is not able to perform to expected level at the engine test bed after overhaul assembly shop and sent back to assembly shop at RTS mainly due to torque sensor
y Torque sensor
- Katy schmeisser, weiler(DE); Stefan hauzenberger, wangen(DE); Fred bassett, scheidess(DE);Pub date: Dec 3, 2009 Publication: United States patent application publication
y In hal we mainly focused on torque sensor working in
the garrett engine and problems related to it.y We tested a torque sensor at optimum working
condition and as per our deduction and detailed testing there weren t any snags. y The test we performed on the torque sensor was the rig test.
The engine in this case is the power producer, creating a
twisting moment at the propeller shaft. The propeller shaft is connected to a Dynamometer . This is a load measuring device in the test cell Torque is the twisting force between the power producer and the resistance of the load. This is equally true in the aircraft when the dynamometer is replaced with a propeller. The propeller is a load absorption device. The torque is usually measured in Newton-meter(N-m)
The gas generator shaft transmits its high speed, low torque to the gearbox by means of torsion shaft. The torsion shaft is splined inside the main shaft at the rear end. It extends the center of the main shat is splined to the high pinion gear. The high speed pinion gear and torsion shaft rotate at the same speed as the gas generator. The torsion shaft is designed to accept the twisting load and spring back to normal when the load is removed.
The heavy gear on the left in this picture represents the load being applied to the propeller and the gearbox. As that loading is being applied to the propeller and the Gear box. As that loading is being driven by the gas generator the torsion shaft would be twisted.
The torque sensor is a mechanical device inside the gear box that engages with the gears on the main shaft and high speed pinion. The device measures the twist being applied to the torsion shaft and converts it to a corresponding oil pressure signal that is used in torque indicating system.
y Under normal condition when the engine is producing
power to drive the compressor and the propeller to get thrust, the torque produced is a positive torquey The torque is generated due to wind milling or due to
rotation of the propeller when engine power is cut off in mid air is known as negative torque.
y The following depict the causes leading to snags in y y y y
Garrett engine. The most occurring causes are NTS-Negative torque sensor SFC-Specific fuel consumption Low oil pressure and gear box vibration
The function of NTS system is to limit the torque the
engine absorb from the propeller during windmill and thereby prevent high propeller drag conditions. The NTS system effects a movement of the propeller blades automatically towards their feathered position (should the engine suddenly lose power while in flight) and precisely modulates the propeller-blade pitch angle during a propeller-wind milled engine air start. The torque sensor assembly is internally located. The torque-sensor function in the NTS system is to hydraulically actuate the propeller feathering valve when too much negative torque is applied to the engine.
Negative torque which occurs when the engine suddenly looses powering flight must be restricted to a very low value so that the drag which occurs during wind milling will not cause loss of the aircraft. On the other hand some wind milling capability is necessary so that the propeller can be used to start the engine in flight should the need arise. The value of permitted negative torque is about 20 HP, this is high enough for air starts but not to high as to cause excessive drag should the plot fail to actuate the feather lever following a power failure in flight. NTS regulates feather valve and torque sensors from the negative torque sensing system. When the negative torque occurs, the pilot valve in the torque sensor will move to the left to block the oil passage at the left of the pilot valve. This will allow oil to be dumped from the propeller piston permitting the feather spring to drive the propeller forward gather. The minimum NTS oil pressure necessary for operation of the feathering valve is about 32 psi.
yMatch set testing ySpring rate testing yRig testing
MATCH SET TESTING: we checked the dimensions of parts of the torque sensor. we maintained the dimension within the standard limit because if the torque sensor parts dimension were differed from standard it will be hazardous to the engine . SPRING RATE TESTING: In the test stand of DS 3101726 REV F 12 16 81, the inspector check out the spring rating. Free length = 0.78 inches Loaded length = 0.73 inches Test load = 1.65 08 lbs Spring rating = 28 to 32 lbs /inch In the test load value 1.65 0.08lbs the spring rating must be 28 to 32 lbs /inch
RIG TEST: In the test board we completely checked the total unit of the torque sensor. In this we interchanged the index head position according to the different load conditions and we took the pressure difference. DATUM CONDITION AT DEGREE SETTING : The index head positioning at zero degree known as datum position. In this position torque sensor must be given the oil pressure which may vary between the values. INDEX POSITION AT -2 DEGREE INDEX SETTING : In this position the torque sensor must be given the pressure between 75 psi and 105 psi.
INDEX POSITION AT +2 DEGREE : In this position torque sensor must have the oil pressure less than 18 psi. TAKE OFF CONDITION AT +6 DEGREE : In this section engine produce the power to rotate the compressor and all accessories of the engine. At this position the torque sensor must be given the oil pressure of 21.5 1 psi TAKE OFF CONDITION AT +16 DEGREE SETTING : In this position the engine produce power take off the flight from the ground position. This position torque sensor must be giving the oil pressure Between 59.5 and 64.5 psi.
y Piston and sleeve y Helical gear shaft y Cluster gear y Springs
Part name 1.Piston and sleeve
Function It is a variable oil pr. Metering unit. Helical gear shaft can be moved right and left according to the torque developed in the engine. With the movement of helical gear shaft the oil pr. Is increased or decreased with the help of piston and sleeve. It is driven by the main shaft gear. Helps in converting angular displacement of the high speed torsion shaft w.r.t main shaft into linear movement of the pilot valve.
Failure mode 1. Piston insert not secure in sleeve. Having movement between them. 2. Interior surface of insert and inside sleeve having scratches, nicks, burrs and scoring. 3. Diameter having scorings, burrs, nicks and scratches. 1.Poor copper platting .
Cause of failure 1. Wrong reading of torque sensor. 2. Erratic reading of torque sensor. 3. Erratic reading of torque sensor.
2.Helical gear shaft
2.Bad surface finishing. 3.Sharp edges. 4.Burr on the surface. 5.Worn out surface.
1.Cluster gear does not move freely causing incorrect reading in torque pr. 2.non-linear movement of pilot valve. 3. Gives stiff movement result in incorrect reading. 4. Stiff and non linear movement. 5. Gives loose and non-linear movement.
Part name 3. Cluster gear
Function It is driven by high speed pinion. the helical spline in cluster gear mates with the helical gear shaft and converts the angular displacement into linear movement wit h respect to main shaft gear.
Failure mode 1. Bad surface finish
Effect of failure 1. Unable to give smooth linear movement to the cluster gear over the shaft. 2. Gives stiff movement to the shaft which results in incorrect reading. 3. Give stiff and non linear movement. 1. Wrong indication of torque 2. Erratic torque Pr. reading 3. Non linear movement of piston valve.
2. Sharp edges
3. Burr on surface
The function of the spring is to operate the metering valve inside the torque sensor.
1. Distorted coils of spring. 2. Coil geometry of the spring 3. Dimension/spring rate requirement s are not met.
S.NO 1 2 3 4 5 6 7 8 9
DESCRIPTION 40k NTS trip p at 100% torque Turbine vibration Gearbox vibration TET at 840 SFC at 840 Torque fluctuation Fuel flow Min oil pressure a)At ground idling RPM b)At maximum RPM ITT TET at 840 shp Engine oil temp
MAX.LIMIT 140 lbs 65 psi 0.35 inch/sec 0.50 inch/sec 1855 f 0.605 lb/hr/shp 2% (on both sides) 508 Pph-rep 495 Pph-prod 50 psi 90-115 psi 1693 f(923 c) 1855 f 165 f
10 11 12 13
Max allowable oil leak at 01 cc compressor seal
Thus our project on analysis on torque sensor was completed and as per testing we found out that there weren t any snags in the y Piston and sleeve y Helical gear shaft y Cluster gear y Springs and further concluded that most of the problems are mechanical failure and they can be corrected through thorough inspection and correction.