D353 INDUSTRIAL & MARINE ENGINES Caterpillar


7231 Marine Transmission Systems Operation

Usage:



Operation

The marine transmission is fastened directly to the engine flywheel housing. Full power flows from the engine through the transmission in either a forward or reverse direction to the propeller shaft.

Hydraulically activated clutches, one directly in front of the other, operate the forward and reverse drives. Selection of either forward or reverse drive is done by a control valve. The valve is operated by a lever which can be manually or remotely controlled.

A gear-type of pump, at the rear of the marine transmission sends oil under pressure to activate the clutches. It also sends oil to the bearings in the transmission for lubrication.

The clutch front section engages the three gear drive in the marine transmission which turns the propeller shaft in the same direction as the engine. The clutch rear section engages the two gear drive in the transmission which turns the propeller shaft in the opposite direction of the engine.

The direction of flywheel rotation for a standard engine is counterclockwise, when looking at the flywheel end of the engine. The clutch rear section is engaged to get forward motion with a right hand propeller.


MARINE TRANSMISSION SCHEMATIC (Clutch Rear Section Engaged)
1. Clutch rear section. 2. Clutch front section.

NOTE: In the information that follows, the clutch rear section is given the name "forward clutch", and the clutch front section is given the name "reverse clutch".

Power Flow


POWER FLOW COMPONENTS
1. Oil pump. 2. Ring gear. 3. Reverse shaft. 4. Transfer gear. 5. Forward shaft. 6. Transfer gear. 7. Forward clutch. 8. Reverse clutch. 9. Spider. 10. Output shaft. 11. Rubber blocks. 12. Output flange. 13. Planet gears. 14. Sun gear and shaft. 15. Reverse gear. 16. Countershaft. 17. Forward gear.

Power Flow Forward Drive

Power flow in the FORWARD position is as follows: The power from the engine comes from the flywheel to the rubber blocks, which are fastened to the spider. The power moves from the spider to forward clutch (7) and is sent through the clutch discs and plates to forward shaft (5). The forward shaft turns transfer gear (6), which is held to the forward shaft by a key. Power goes from the transfer gear to forward gear (17). The forward gear is held to countershaft (16) by a key. The forward gear turns the countershaft. Splines connect sun gear and shaft (14) to the inside of the countershaft. The countershaft turns the sun gear and shaft. The sun gear turns planet gears (13) around stationary ring gear (2). The movement of the planet gears turn the output shaft. Splines connect the output shaft to output flange (12). The output shaft turns the output flange. The output flange sends the power to the propeller shaft.


FORWARD DRIVE SCHEMATIC
2. Ring gear. 5. Forward shaft. 6. Transfer gear. 7. Forward clutch. 12. Output flange. 13. Planet gears. 14. Sun gear and shaft. 16. Countershaft. 17. Forward gear.

Power Flow Reverse Drive


REVERSE DRIVE SCHEMATIC
2. Ring gear. 3. Reverse shaft. 4. Transfer gear. 8. Reverse clutch. 12. Output flange. 13. Planet gears. 14. Sun gear and shaft. 15. Reverse gear. 16. Countershaft. 18. Idler gear.

Power flow in the REVERSE position is similar to the FORWARD position. Power comes from the engine flywheel through the rubber blocks and spider to reverse clutch (8). Power goes through the clutch discs and plates to reverse shaft (3). The reverse shaft is on the inside of the forward shaft. The reverse shaft turns transfer gear (4), which is held to the reverse shaft by a key. The transfer gear turns idler gear (18). The idler gear changes the direction of rotation and turns reverse gear (15). The reverse gear is held to countershaft (16) by a key. The reverse gear turns the countershaft. The power goes to the propeller shaft in same manner as in the FORWARD position only in the opposite direction.

Hydraulic System

Oil pump (1) sends a supply of hydraulic oil to the control valve. The control valve positions, FORWARD and REVERSE, send the oil under pressure to engage either the forward clutch or the reverse clutch. With the control valve in the FORWARD position, the hydraulic oil moves through the oil passage around the tube in the hollow center of shaft (3). The oil through the shaft flows through passage (7), in the spider assembly, and passage (8), in the clutch ring, to dump valve (11).


MARINE TRANSMISSION CUTAWAY
1. Oil pump. 2. Tube assembly (hydraulic oil passage to reverse clutch). 3. Shaft (hydraulic oil passage, around tube, to forward clutch). 4. Dump valve (for reverse clutch). 5. Reverse clutch. 6. Hydraulic oil passage in spider assembly (to reverse clutch dump valve). 7. Hydraulic oil passage through spider assembly. 8. Hydraulic oil passage through clutch ring (to forward clutch dump valve). 9. Forward clutch. 10. Engaging piston for forward clutch. 11. Dump valve (forward clutch).


DUMP VALVE
12. Plunger (removed from body).

The pressure oil in dump valve passage (14) moves plunger (12) toward the clutch. Plunger (12) was held away from the clutch by centrifugal force caused by clutch rotation. The down position of plunger (12) lets the pressure oil flow through valve passage (13), which goes directly to engaging piston (10) of the forward clutch. The pressure oil moves and holds piston (10) against the plates of the forward clutch and the clutch is engaged.


DUMP VALVE OPERATION (Clutch Engaged Position)
12. Plunger. 13. Passage (to clutch piston). 14. Inlet passage.

With the control valve in the REVERSE position, the hydraulic oil moves through tube assembly (2), through hydraulic passage (6) in the spider assembly which goes to the dump valve (4) for the reverse clutch. The dump valve sends the pressure oil to the piston for the reverse clutch, which engages the reverse clutch. Dump valve (4) is same as dump valve (11) and operates in the same way to engage or release the clutch.


DUMP VALVE OPERATION (Clutch Not Engaged)
12. Plunger. 13. Passage (to clutch piston). 15. Outlet passage.

When the control valve is moved to NEUTRAL position, oil is not sent to a clutch. With no oil pressure to hold plunger (12) toward the clutch, the centrifugal force caused by clutch rotation moves plunger (12) out. This opens oil passage (13) to a clutch piston and to outlet passage (15). As the oil from the piston goes through the outlet passage, springs in piston and cylinder assembly move the piston away from the clutch plates and the clutch releases.

Control Valve in Neutral


CONTROL VALVE (Neutral Position)
1. Control valve body. 2. Directional spool valve. 3. Springs. 4. Port to oil cooler. 5. Oil inlet port. 6. Relief valve. 7. Check valve.

The control valve is fastened at the rear of the marine transmission. This valve sends and controls the flow of oil to the transmission. The pressure control section of the valve gives automatic control of the pressure, with a slight delay effect to give a smooth flow of power as it goes from NEUTRAL to either FORWARD or REVERSE.

With the engine running and the directional valve (2) in the NEUTRAL position, the oil flow through the control valve is as follows:

Oil flows from the filter to inlet port (5), around the stem of relief valve (6) and through a passage to the NEUTRAL chamber of directional spool (2). The oil is stopped at the directional spool. The oil pressure in the control valve goes up and opens check valve (7). The oil fills the chamber below the relief valve. When the oil pressure in the chamber is higher than the pressure of springs (3), relief valve (6) opens. The oil flows out through port (4) to the oil cooler.

Control Valve in Forward Position

With the engine running and directional valve (6) in the forward position, the oil flow through control valve body (1) is as follows:

Oil from the filter flows to inlet port (14), around the stem of relief valve (16) and through a passage to directional spool valve (6). The oil flows around the spool valve and out port (9) to the forward clutch. The oil also moves ball check valve (11) against its seat and goes on to main check valve (5). The oil moves check valve (5) against stop (3). The oil flows through small holes in the four plugs in the bore of the check valve, through orifice (4) and through small holes drilled in stop (3) to the end of load piston (2). The force of the oil on load piston (2) puts springs (10) in compression until the force of the load piston and the relief valve force are in balance. Relief valve (16) controls the maximum pressure needed to engage a clutch. Orifice (4) of check valve (5) gives a gradual increase in pressure so the clutch will be engaged smoothly. As oil goes in to the clutch cavity, the oil pressure increases behind load piston (2) and moves it down. When the pressure is enough to engage the clutch, the relief valve moves up. The oil not needed to keep the clutch engaged flows through port (12) to the oil cooler.


OIL FLOW IN THE FORWARD POSITION
1. Control valve body. 2. Load piston. 3. Stop. 4. Orifice. 5. Check valve. 6. Directional spool valve. 7. Port to sump. 8. Port to sump. 9. Port to forward clutch. 10. Springs. 11. Ball check valve. 12. Port to oil cooler. 13. Port to reverse clutch. 14. Oil inlet port. 15. Port to sump. 16. Relief valve.

Any leakage of oil by directional spool valve (6) goes to the case through ports (7) and (15).

When the directional spool valve is moved to NEUTRAL, oil in the forward clutch drains through the dump valve to the case. The oil behind check valve (5) goes to case through port (7). Since the oil pressure on the bottom of check valve (5) is less than the oil pressure on top of the check valve, the pressure oil on top of the load piston moves the check valve open and the oil flows out port (7) to the case.

Control Valve in Reverse Position


OIL FLOW IN THE REVERSE POSITION
1. Control valve body. 2. Load piston. 3. Stop. 4. Orifice. 5. Check valve. 6. Directional spool valve. 7. Port to sump. 8. Port to sump. 9. Port to forward clutch. 10. Springs. 11. Ball check valve. 14. Oil inlet port. 15. Port to sump. 16. Relief valve.

With the engine running and directional spool valve (6) in the REVERSE position, the oil flow through control valve body (1) is as follows:

Pressure oil from the filter flows around the stem of relief valve (16) through a passage to directional spool valve (6). The oil flows around the spool valve and out port (13) to the reverse clutch. The oil also moves ball check valve (11) against its seat and goes on to main check valve (5).

The control of oil pressure to engage the reverse clutch is the same as in the FORWARD position, except ball check valve (11) is held on the seat at the opposite end.

Any leakage of oil by directional spool valve (6) goes to the case in the same manner as in the FORWARD position.

Cooling System

The oil cooler for the marine transmission is fastened to the right side of the transmission. Bypass valve (3), which is controlled by oil temperature, controls the flow of oil through oil cooler (5).

Bypass valve (3) is open when the temperature of the oil is below 150°F (65°C). Oil from the control valve, through oil line (6), flows through bypass pipes (4) and through the bypass valve, which is open, into the oil manifold in the marine gear housing.


OIL COOLER GROUP
1. Oil temperature gauge. 2. Sensing switch for oil temperature. 3. Bypass valve. 4. Cooler bypass pipes. 5. Oil cooler. 6. Oil line to control valve.

Bypass valve (3) will start to close when the oil temperature increases to approximately 150°F (65°C). Some of the oil will then flow through oil cooler (5). The bypass valve will be closed completely when the temperature of the oil increases to 160°F (71°C). All of the oil will then flow through oil cooler (5) and into the oil manifold in the marine transmission housing.

Sensing switch (2) for oil temperature is an electric switch. It can be connected to some type of an alarm, which can be put any distance from the marine gear. The sensing switch will close and activate the alarm when the temperature of the oil gets too high.

Lubrication System


LUBRICATION SYSTEM SCHEMATIC
1. Oil filter. 2. Magnetic strainer. 3. Control valve. 4. Oil line to clutches (through top shaft). 5. Top shaft. 6. Idler shaft bearings. 7. Oil manifold (passage in gear housing). 8. Oil pump. 9. Oil line to output thrust bearings. 10. Bearings. 11. Clutch shaft bearings. 12. Output shaft thrust bearings. 13. Sun gear. 14. Planet gears. 15. Countershaft rear bearing. 16. Oil line to sun gear (through sun gear shaft).

The marine transmission takes the same lubricant as the engine. The gear-type oil pump fastened at the rear of the transmission is turned by a hollow shaft which is connected to the spider. The spider is connected to the engine flywheel, and is in rotation whenever the engine is running. The oil pump is also in rotation, and sends oil for lubrication, when the engine is running.

NOTE: Do not let the propeller shaft turn the gears and shafts in the marine transmission when the boat is either pushed or pulled with the engine stopped.

The oil pump gets oil from the case through magnetic strainer (2). All of the oil from the pump goes to oil filter (1) and flows through an oil manifold to control valve (3). When the filter element gets dirty and prevents oil flow, the filter bypass valve will open and send oil to the control valve.

The control valve sends oil to engage either the forward or reverse clutch at 250 psi (1720 kPa). The remainder of the oil at 30 psi (205 kPa) is sent from the control valve to the oil cooler (not shown in the schematic). The oil goes from the oil cooler to oil manifold (7). The oil flows from the oil manifold to bearings (10) through separate oil lines connected to the manifold. Oil line (4) through top shaft (5) is used to send oil to the clutches for lubrication. Idler bearings (6) and countershaft bearing (15) get lubrication from oil thrown from the bottom of transmission case.

Oil line (9) is used to send oil to output shaft thrust bearing (12). The oil goes to planet gears (14) from the thrust bearings.

Oil is sent to sun gear (13) through oil line (16). The oil flows through holes in the sun gear for lubrication of the contact area of the sun gear teeth and the planet gear teeth.

The transfer gears on the top shaft and the idler gear get their lubrication from the reverse and forward gears on the countershaft. The reverse and forward gears run in oil held in separate pan assemblies at the bottom of the marine transmission case.

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