D353 INDUSTRIAL & MARINE ENGINES Caterpillar


MG-521 Systems Operation

Usage:



Operation


CROSS SECTION OF MARINE GEAR
1. Drive spider. 2. Front clutch. 3. Bearing. 4. Front drive gear. 5. Rear drive pinion. 6. Rear clutch. 7. Clutch shaft. 8. Selector valve assembly. 9. Pump. 10. Countershaft. 11. Drive ring. 12. Reverse driven gear. 13. Reverse shaft. 14. Reverse driven pinion. 15. Countershaft gear. 16. Flange.

The marine reverse and reduction gear is attached to the engine flywheel housing and is coupled to the engine flywheel. Full power is transferred from the engine through the reverse and reduction gear in either a forward or reverse rotation at a reduced speed to the propeller shaft.

The diesel engine transmits power to drive ring (11), to drive spider (1), and clutch shaft (7). Since the drive ring is secured to the engine flywheel, these parts rotate in the same direction as the engine at all times.

Separate, hydraulically actuated clutches operate the forward and reverse drives. Selector valve (8) directs flow of oil to either of the clutches for forward or reverse operation. The valve is operated by the lever which can be manually or remotely controlled.

When a right hand propeller is used with the marine gear installation, front clutch (2) will control reverse motion and rear clutch (6) will control forward motion. With a left hand propeller, front clutch (2) will control forward motion and rear clutch (5) will control reverse motion. The companion flange on the propeller shaft connects to coupling flange (16).

Oil pressure for both the lubrication and the hydraulic systems in the marine gear is supplied by oil pump (9) which is attached to the rear of the oil manifold and driven by clutch shaft (7). The pump draws its oil from the sump in the marine gear housing.

Clutch shaft (7) rotates on bearings within the housing. Drive spider (1) and clutch shaft (7) rotate when the engine is running and in the same direction as the engine. Oil pump (9), driven by the clutch shaft, operates when the engine is running.

The selector valve lever controls the rotation of countershaft gear (15), countershaft (10) and coupling flange (16). This control is accomplished by shifting the selector lever into front clutch drive, rear clutch drive, or neutral.


MARINE GEAR DRIVE (SCHEMATIC)
A. Rotation of rear clutch and countershaft when engaged in rear clutch drive position. B. Rotation of front clutch and countershaft when engaged in front clutch drive position. 1. Drive spider. 2. Front clutch. 6. Rear clutch. 7. Clutch shaft. 10. Countershaft. 13. Reverse shaft. 15. Countershaft gear.

The oil manifold and pipe assembly distribute oil from the selector valve to the lubricating system, the oil cooling system for the clutches, and provides actuating oil for the front and rear clutch.

Lubrication And Hydraulic System

Lubrication And Hydraulic System


OIL FLOW IN THE MARINE GEAR (SIDE VIEW)
1. Pipe assembly. 2. Pressure relief piston. 3. Manifold. 4. Front clutch actuating oil passage. 5. Pipe assembly oil passage. 6. Cooling and lubricating oil passage. 7. Front cylinder hub. 8. Chamber. 9. Passage. 10. Groove on sleeve. 11. Rear clutch actuating oil passage. 12. Groove on sleeve. 13. Groove. 14. Hole in shaft and inner tube. 15. Passage. 16. Groove. 17. Hole. 18. Hole in shaft. 19. Tube. 20. Passage. 21. Hub. 22. Hole in sleeve. 23. Passage in sleeve. 24. Sleeve. 25. Chamber. A. Selector valve. B. Oil pump.

The oil pump (B), driven by the clutch shaft, delivers a constant volume of oil at any given engine speed. The oil is drawn from the sump through a strainer to the pump and then to the oil filter, oil cooler, and the selector valve through a series of connecting hoses. The oil flow direction through the manifold (3) and marine gear is controlled by the selector valve (A) which is operated by the selector valve lever. The function of the selector valve, aside from directing the oil flow, is to act as an automatically adjusted relief valve, dumping excess oil according to the pressure build-up required. The purpose is to afford a time delay in the change from neutral pressure to operating pressure.


OIL FLOW IN THE MARINE GEAR (REAR VIEW)
3. Manifold. 4. Front clutch actuating oil passage. 5. Pipe assembly oil passage. 6. Cooling and lubricating oil passage. 11. Rear clutch actuating oil passage. 24. Sleeve. 26. Line from oil cooler. 27. Line to oil cooler. A. Selector valve. B. Oil pump.

The oil manifold (3) contains four main passages which direct oil from the selector valve to the marine gear. One passage (6) directs oil from the selector valve to cool and lubricate the clutches. The passage (11) directs high pressure oil from the selector valve to engage the rear clutch, and passage (4) directs high pressure oil to the front clutch. A passage (5) for lubricating oil is connected to a pipe assembly (1) located inside the marine gear. Oil flow through an orifice in the pressure relief piston (2) in the pipe assembly, and is metered out in streams through small holes located in the pipe assembly to lubricate the gears and bearings. The pressure relief piston relieves excessive pressures in the cooling and lubricating system by opening a dump hole in the pipe assembly when the pressure exceeds 20 psi (140 kPa) in the system.

Cooling and lubricating oil to the clutches flows through passage (6) in the manifold to the chamber (25) formed at the end of the clutch shaft. The oil to the front clutch flows out of this chamber into tube (19), out through the hole (14) in the tube and shaft, around the groove (16) on the shaft, and into two grooves (13) located in the inner bore of the clutch inner hub. The oil flows from the grooves into the chamber (8), formed by the clutch pinion and the inner hub, and through drilled holes (17) in the inner hub and into the clutch plates. The sintered bronzed plates have concentric lubrication grooves that allow oil flow whether the clutches are engaged or disengaged. The oil flows around the outer periphery of the clutch cylinder and returns to the sump. The cooling oil to the rear clutch flows through two drilled passages (23) in the sleeve and into two grooves in the inner hub, and into the clutch plates in the same manner as oil flows to the front clutch.

When the front clutch is engaged, high pressure oil from the selector valve flows through the passage (4) in the manifold to a groove (10) in the sleeve (24), and through two drilled holes (22), one through each side of the sleeve. The oil flows into the clutch shaft through a passage (20), formed by the bore of the shaft and the tube (19). At the front clutch, the oil flows to the front clutch cylinder hub (7) by the means of two drilled holes (18) in the clutch shaft and two passages (15) in the clutch inner hub. The oil flows from the hub into the clutch cylinder to engage the clutch.

To engage the rear clutch, pressure oil from the selector valve flows through the passage (11) in the manifold to a groove (12) on the sleeve. Oil, from the groove, passes through two drilled passages through the sleeve, on each side, and into two passages (9) in the rear clutch cylinder hub (21), and into the clutch cylinder to engage the clutch.

NOTE: Regardless of whether the selector valve lever is in the neutral, front clutch or rear clutch drive positions, an ample volume of pressure-reduced oil is released at the pressure regulator piston in the selector valve. This oil flows through the selector valve lubricating oil outlet. This oil provides lubrication for the gears and bearings, and also cools the clutches.

An oil filter bypass valve allows oil flow to the marine gear should the filter element become clogged or restricted.

Actuating Oil In The Clutches

The construction of the front and rear clutches are identical with the exception of three lock-up bolts in the rear clutch. In the front clutch, three hollow head screws plug these bolt holes. The clutch cylinder contains clutch plates (9) and piston (8). Pressure oil enters chamber (7) and forces the piston against the plates. This engages the clutch to transmit the power through the clutch from the clutch shaft to the countershaft.

The clutch cylinder contains two passages (6), one opposite the other, which leads to the outer diameter of the cylinder. There is a cavity in dump valve cover (5) that directs oil in the passage to the top of the dump valve piston (3).


CROSS SECTION OF CLUTCH
1. Hole for rear clutch actuating oil. 2. Spring. 3. Piston. 4. Spacer. 5. Cover. 6. Actuating oil passage. 7. Chamber. 8. Piston. 9. Clutch plates. 10. Hole for front clutch actuating oil.

The high pressure oil enters the clutch cylinder through holes (10) on the front clutch, which mate with holes in the shaft, and through holes (1) in the rear clutch when the selector valve is placed in the appropriate drive position. In the rear clutch, hole (1) mates with holes in the sleeve on the end of the shaft.


END VIEW OF CLUTCH
1. Holes for rear clutch actuating oil. 2. Spring. 3. Piston. 4. Spacer. 5. Cover. 6. Actuating oil passage. 10. Hole for front clutch actuating oil. 11. Dump port. 12. Dump port.

When the selector valve is positioned to direct high pressure oil to a clutch (front or rear), the high pressure oil passes through the passages leading to the clutch cylinder. In the cylinder, the oil passes through the passages (6) into the cavity in the cover (5) and onto top of dump valve piston (3), which is held against the spacer (4) by the spring (2). The pressure of the oil overcomes the force of the spring and forces the piston down uncovering the port (B). This allows the high pressure oil to flow into piston chamber (7) and force piston (8) against the clutch plates to engage the clutch.


QUICK DUMP VALVE OPERATION (IN CLUTCH ENGAGED POSITION)
3. Piston. 4. Spacer. 7. Chamber. 8. Piston. 9. Clutch plates. 11. Dump port. 13. Dump port. B. Port.

When the selector valve is moved, the pressure in the system drops, and the force of the spring (2) overcomes the force of the oil in the top cavity forcing the piston up against the spacer (4). The port (B) is opened and allows chamber (7) to be vented through dump port (11). This rapidly relieves all the pressure in chamber (7) and the clutch disengaging springs move the piston (8) away from the clutch plates, disengaging the clutch.

When engaging the clutches, high pressure oil forces the dump valve piston down to compress the spring. Any oil trapped around the dump valve spring (2) between the dump valve piston (3) and the bottom of the spring seat is forced out dump port (13).

Marine Gear And Selector Valve Operation

Power is transmitted from the engine to clutch shaft (5) through drive ring (2) which is attached to the engine flywheel and drive spider (1). Front clutch cylinder (4) and rear clutch cylinder (9) are pressed onto the tapered, keyless clutch shaft. The clutches are hydraulically actuated through positioning selector valve (11) in the appropriate clutch drive positions.

When the selector valve lever is placed in the rear clutch drive position, engine power is transmitted from the clutch shaft through the clutch cylinder and driving plates (8) to the driven plates (10). The driven plates transmit the power to the rear clutch inner hub (7) which is pressed on the splined end of rear clutch pinion (6). Clutch pinion (6) meshes with countershaft gear (15). Coupling flange (17), attached to countershaft (16), transmits the engine power to the propeller shaft.


CROSS SECTION OF MARINE GEAR
1. Spider. 2. Drive ring. 3. Front clutch cylinder. 4. Front clutch gear. 5. Clutch shaft. 6. Rear clutch pinion. 7. Rear clutch inner hub. 8. Driven plate. 9. Rear clutch cylinder. 10. Driving plate. 11. Selector valve. 12. Reverse shaft gear. 13. Reverse shaft. 14. Reverse shaft pinion. 15. Countershaft gear. 16. Countershaft. 17. Flange.


REAR CLUTCH DRIVE (SCHEMATIC)
1. Spider. 5. Clutch shaft. 9. Rear clutch cylinder. 15. Countershaft gear.

With the selector valve lever in the front drive position, the power is transmitted from front clutch cylinder (3) and driving plates to the driven plates. The driven plates drive the inner hub which is splined to front clutch gear (4). The front clutch gear drives idler gear (12) and idler pinion (14) on idler shaft (13). The idler pinion is meshed with countershaft gear (15); therefore, it drives the countershaft and propeller shaft in opposite rotation to that of the rear clutch drive rotation.


FRONT CLUTCH DRIVE (SCHEMATIC)
1. Spider. 3. Clutch cylinder. 4. Clutch gear. 5. Clutch shaft. 12. Idler shaft gear. 13. Idler shaft. 14. Idler shaft pinion. 15. Countershaft gear.

Oil Pump

The gear-type positive displacement oil pump is mounted on the oil manifold. The pump furnishes oil when the engine is running, to cool, lubricate and actuate the marine gear clutches.

The pump is driven by a drive sleeve and the clutch shaft of the marine gear. The clutch shaft rotates, when the diesel engine is running, in one direction only.


NOTICE

If the vessel is to be towed, disconnect or clamp the propeller shaft to prevent rotation. The output shaft must not be allowed to turn when the engine is not running. With the engine stopped, the oil pump is not operating.


Selector Valve

The selector control valve is mounted on the marine gear and directs the flow of oil and also regulates the oil pressure being delivered to the marine gear. The pressure regulating section of the valve furnishes automatic regulation of pressure, with a slight delay effect affording smooth transition from neutral pressure to engaging pressure.

NOTE: The illustrations of the selector valve showing the pipe assembly (5) body as part of the selector valve is for illustration purposes only. The pipe assembly (5) body is actually located in the lubricating oil pipe assembly which goes all the way through the marine gear.


SELECTOR VALVE (Top View and End View)
1. Selector valve lever. 2. Selector valve body. 3. Clutch exhaust to sump. 4. Lubricating oil outlet. 5. Pipe assembly. 6. Pressure regulating piston. 7. Piston relief to sump. 8. Pressure regulating double valve. 9. Pressure rise control piston. 10. Selector valve stem. 11. Inlet from oil filter. 12. Lubrication chamber. 13. Oil passage. 14. Ball check exhaust from pressure rise control piston. 15. Orifice inlet to pressure rise control piston. 16. Oil chamber. 17. Passage to rear clutch. 18. Valve stem passage. 19. Valve stem passage. 20. Passage to front clutch.

Oil Flow In Neutral Position

With the engine running and the selector valve lever (1) in a neutral position, the oil flow through selector valve body (2) is as follows:


OIL FLOW THROUGH THE SELECTOR VALVE IN NEUTRAL
1. Selector valve lever. 2. Selector valve body. 4. Lubricating oil outlet. 5. Pipe assembly. 6. Pressure regulating piston. 8. Pressure regulating double spring. 9. Pressure rise control piston. 11. Inlet from oil cooler. 12. Lubrication chamber.

Oil enters the selector valve at inlet (11) and continues into chamber (12). There is only one path for the oil to follow, since the selector valve stem passages are not aligned with the chamber openings to the clutch cylinders. The open path is to outlet (4) which supplies the pressure relief arrangement in pipe assembly (5) and also opens into the manifold leading to the cooling oil outlets in the clutch hubs.

Since there is no oil pressure against the pressure rise control piston (9), the pressure against the pressure regulating piston (6) and double spring (8) is able to push the piston to a position where it offers enough resistance to the oil flow to develop only 25 to 65 psi (170 to 450 kPa). In this position, the piston also uncovers the opening to outlet (4).

Neutral to Rear Clutch Drive Position

When the selector lever (1) is moved to the rear clutch drive position, oil flow through the selector valve is as follows:


OIL FLOW THROUGH THE SELECTOR VALVE IN THE NEUTRAL TO REAR CLUTCH DRIVE POSITION
1. Selector valve lever. 3. Clutch exhaust to sump. 4. Lubricating oil outlet. 6. Pressure regulating piston. 8. Pressure regulating double spring. 9. Pressure rise control piston. 10. Selector valve stem. 11. Inlet from oil cooler. 12. Lubrication chamber. 13. Passage. 15. Orifice inlet to pressure rise control piston. 16. Oil chamber. 17. To rear clutch. 18. Valve stem passage. 19. Valve stem passage.

In the rear clutch drive position, valve stem passage (18) aligns with passage (17) and valve stem passage (19) aligns with passage (13). Oil flows through inlet passage (11), valve stem passage (18) and out through the rear clutch passage (17). Passage (17) connects with the manifold passage which directs oil to engage the rear clutch.

At the same time oil is flowing through valve stem passage (19) and passage (13) which leads to the orifice (15).

Oil then enters and fills chamber (16), moving the pressure rise control piston (9) forward and compressing double spring (8). This causes higher pressure in chamber (12).

This cycle continues through the selector valve until a steady oil pressure of 120 to 165 psi (830 to 1135 kPa) is maintained in chambers (12) and (16) and passage (13). This keeps a steady pressure to the rear clutch, maintaining an engaged position.

As described in neutral, excess oil being relieved at pressure regulating piston (6) flows through lubricating outlet (4), lubricating the bearings and gears, and also through manifold passages furnishing cooling oil for the engaged clutch and disengaged clutch.

The entire oil flow pattern requires one half to one second to take place.

Engaged to Neutral Position

When the selector lever is moved to the neutral position from either rear clutch drive or front clutch drive position, oil flowing into selector valve body (2) through inlet (11) is as follows:


OIL FLOW THROUGH THE SELECTOR VALVE IN THE ENGAGED TO NEUTRAL POSITION
2. Selector valve body. 3. Clutch exhaust to sump. 8. Pressure regulating double spring. 9. Pressure rise control piston. 10. Valve stem. 11. Inlet from oil cooler. 12. Lubrication chamber. 13. Oil passage. 14. Ball check exhaust from pressure rise control piston. 16. Oil chamber. 17. Rear clutch outlet. 20. Front clutch outlet.

Oil flow to the engaged clutch is immediately blocked off.

Since the engaged clutch is no longer receiving a supply of pressure oil, the dump valves located in clutch cylinder open directly to sump. This allows clutch release springs to move the clutch piston away from the clutch plates, disengaging the clutch.

While this oil is being discharged from the disengaged clutch, a noticeable drop in pressure occurs at chambers (16) and (12) and also at passage (13). When this pressure drop occurs, spring (8) pushes piston (9) back. This forces oil in chamber (16) to unseat the ball check valve (14), and the oil flow through passage (13), and the small hole in the valve stem and out the exhaust to sump outlet (3).


NOTICE

In shifting across neutral, a slight delay should be made at the neutral detent, since too rapid shifting would not allow chamber (16) to empty, in which case the delay rise in pressure would not occur and shift would go directly from high pressure in one direction to high pressure in the other direction, resulting in shock loading the affected parts.


Neutral to Front Clutch Drive Position

When the selector valve lever (1) is moved to the front clutch drive position, the oil flow through the selector valve is basically the same as the neutral to rear clutch drive oil flow.

The oil flows from the oil cooler through outlet (11) and through valve stem passage (19) to front clutch outlet (20). At the same time oil flows through valve stem passage (18) to passage (13), through orifice (15) and chamber (16).

Oil flowing out of the front clutch outlet (20) is directed through the manifold passage which leads to the front clutch cylinder, engaging the front clutch.


OIL FLOW THROUGH THE SELECTOR VALVE IN THE NEUTRAL TO FRONT CLUTCH DRIVE POSITION
1. Selector valve lever. 4. Lubricating oil outlet. 5. Pipe assembly. 6. Pressure regulating piston. 8. Pressure regulating double spring. 9. Pressure rise control piston. 11. Inlet from oil cooler. 12. Lubrication chamber. 13. Oil passage. 15. Orifice inlet to pressure rise control piston. 16. Oil chamber. 18. Valve stem passage. 19. Valve stem passage. 20. Front clutch outlet.

Clutch engagement causes a momentary pressure drop in chamber (12). Oil metering through orifice (15) moves piston (9) and springs (8) forward which increases pressure in chamber (12).

This cycle occurs until a steady pressure of 120 to 165 psi (830 to 1135 kPa) is maintained in chambers (12) and (16) and passage (13).

Excess oil is flowing through outlet (4) at all times to cool the engaged and disengaged clutch plates, and also through pipe assembly (5) which lubricates the bearings and gears.

Pipe Assembly

Besides the regulation of the clutch cooling and lubrication oil pressure by the selector valve, the flow of oil is further regulated by pipe assembly (1). The pipe assembly is a combined pressure relief valve and lubrication distributor.


PIPE ASSEMBLY
1. Pipe assembly body. 2. Relief orifice. 3. Pressure regulating spring. 4. Pressure relief piston. 5. Oil passage through piston.

The pressure relief piston (4) is held at a constant pressure by spring (3), and at 20 psi (140 kPa) it is located just in front of a small relief orifice (2) in the pipe assembly housing. Pressure exceeding 20 psi (140 kPa) forces the piston back, exposing the hole and dumps excess oil to sump.

NOTE: The preceding illustration of the selector valve showing the pipe assembly body (1) as part of the selector valve is for illustration purposes only. The pipe assembly body (1) is actually located in the lubricating oil pipe assembly which goes all the way through the marine gear.

The passage (5) in piston (4) allows a small amount of oil to flow through the pipe assembly. This oil is directed through a series of holes to lubricate the gears and bearings.

The front bearing of the marine gear is also lubricated by oil from the pipe assembly. This oil flows through the pipe assembly and a passage in the front of the marine gear housing.

The pressure relief at 20 psi (140 kPa) applies to all the cooling and lubricating oil, since the opening to the cooling and lubricating manifold passages is directly beneath the pipe assembly.

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