Usage:
General
This marine transmission has forward, neutral and reverse positions obtained by means of the control valve. When these positions are selected, the control valve directs high pressure oil through internal passages to operate the clutches.
Hydraulic System
Oil is pumped through the system by the gear-type pump. The oil is taken from the sump through the strainer by the pump and discharged through the heat exchanger and to the combination control and pressure regulating valve. The oil enters the pressure regulating area of the valve where main pressure is regulated by cascading excess oil into the lube circuit. Lube oil is distributed through fixed controlled orifices to lubricate bearings and cool the clutches.
In neutral, the inlet ports to the clutches are blocked, the clutches are disengaged, and the area behind the clutch pistons is open to sump. Oil is distributed through the lubrication system.
When the control valve is shifted to engage either clutch, the control valve directs main pressure to engage the selected clutch pack. Oil is also directed through a port in the control valve stem to a fixed orifice in the orifice plate causing a controlled flow of oil to unseat the rate-of-rise piston and move it to seat on a shoulder in the rate-of-rise piston bore compressing the pressure regulator springs. This progressively increases the clutch engaging pressure causing the clutches to engage at a controlled rate. Overage oil becomes lube oil. The control valve allows only one clutch to be engaged at a time, and the oil from the disengaged clutch is dumped to sump. When a clutch is disengaged, any pressure head existing behind the clutch apply piston is relieved to sump through the control valve. This allows the return springs to move the clutch piston to the disengaged position to prevent clutch drag.
Control Valve Assembly
General
The control valve assembly contains passages and ports for the transmission and direction of pressurized oil within the hydraulic system. The pressure rate-of-rise piston within the control valve assembly provides a rapid, yet smooth, pressure rise for the hydraulic system during clutch engagement.
Control valve-neutral (fig. 3-1 & 3-2)
Oil enters the control valve body through passage A and fills chamber B. The oil causes the high pressure regulator piston to partially compress the piston springs against the rate-of-rise piston. This pressurizes the oil in chamber B. This pressure varies with engine speed.
The movement of the high pressure regulator piston against the springs exposes port C in the valve body. Ports C/D direct overage oil to lubrication and clutch cooling system. Passage E (which is the engaging outlet to the reverse clutch) and Passage F (which is the engaging outlet to the forward clutch) are interconnected by slot K in the control valve stem when in the neutral position. The slot is aligned with a drilled hole and cored cavity in the front face of the valve body. The drilled hole and cored cavity are aligned with drilled holes that pass through the manifold and the main housing to sump. Therefore, passages E and F are at atmospheric pressure at this time. Also, port J is at atmospheric pressure since it interconnects with slot K. The area between the pistons and around the springs is vented to the sump and main housing. This area is at atmospheric pressure at all times permitting the return to sump of any leakage oil past the pistons.
Figure 3-1 : Control valve-neutral - Sectional view.
Figure 3-2 : Control valve - Neutral - Cutaway View.
Control valve-forward (fig. 3-3 & 3-4).
When a shift to the forward position is desired, the control valve lever is moved away from pump side position. The shift causes the control valve stem to rotate and assume the position indicated in figures 3-3 and 3-4. The pressurized oil in chamber B is directed through passages F and H. Passage F is aligned with a drilled hole and a channel in the manifold directing main pressure to the forward clutch. Pressurized oil from port H travels through passage I and enters chamber L through an orifice in the orifice plate. The orifice in this plate meters the oil for a steady, smooth pressure rise in chamber L. As chamber L fills with oil, the rate-of-rise piston moves against the piston springs until the piston is stopped by a shoulder in the valve body. This causes the pressure in chamber B to rise to clutch engaging pressure. When in forward, passage E remains at atmospheric pressure since slot K remains open to sump.
When a shift is made from forward to neutral, the valve stem is rotated to the position illustred by figures 3-1 and 3-2. Under these conditions, passages E, F are connected to sump by slot K. Passage I is also connected to sump by port J in the valve stem. Since passage F is connected to slot K, oil drains rapidly from the forward clutch to sump. Since passage I is now at atmospheric pressure, the oil pressure in chamber L unseats the steel ball against the compression spring, permitting a rapid oil drain from chamber L to sump and allowing the rate-of-rise piston to move back against the orifice plate. The forward clutch is now disengaged and main system pressure reduced to neutral pressure.
Figure 3-3 : Control valve - Forward - Sectional view.
Figure 3-4 : Control Valve - Forward - Cutaway View.
Control valve-reverse (fig. 3-5 & 3-6).
When a shift to the reverse position is desired, the control valve lever is moved to pump side direction. The shift causes the control valve stem to rotate and assume the position indicated in figures 3-5 and 3-6. The pressurized oil in chamber B is directed through passages H and E. Passage E is aligned with a drilled hole and a channel in the manifold directing main pressure to the reverse clutch. Pressurized oil from port G travels through passage I and enters chamber L through an orifice in the orifice plate.
The orifice in the plate meters the oil for a steady, smooth pressure rise in chamber L. As chamber L fills with oil, the rate-of-rise piston moves against the piston springs until the piston is stopped by a shoulder in the valve body. This causes the pressure in chamber B to rise to clutch engaging pressure.
When in reverse, passage F remains at atmospheric pressure since slot K remains open to sump. When a shift is made from reverse to neutral, the valve stem is rotated to the position illustrated by figures 3-1 and 3-2. Under these conditions, passages E, F are connected to sump by slot K. Passage I is also connected to sump by port J in the valve stem. Since passage E is connected to slot K, oil drains rapidly from the reverse clutch to sump. Since passage I is now at atmospheric pressure, the oil pressure in chamber L unseats the steel ball against the compression spring permitting a rapid oil drain from chamber L to sump and allowing the pressure rate control piston to move back against the orifice plate. The reverse clutch is now disengaged and main system pressure reduced to neutral pressure.
Figure 3-5 : Control Valve - Reverse - Sectional view.
Figure 3-6 : Control Valve - Reverse - Cutaway View.
Trolling Valve (Optional equipment).
General.
The trolling valve contains passages and ports to work in conjunction with the control valve for the transmission and direction of pressurized oil within the hydraulic system required for trolling. The rate-of-rise piston of the control valve and the cam of the trolling valve work together to provide and maintain pressures within the hydraulic system required for trolling.
NOTE: The 1/16 NPTF plug (see figure 3-2) must be removed to allow pressure in chamber L to be drained to sump through trolling valve device.
Trolling valve - Non-trolling mode.
The trolling valve is in non-trolling mode when the cam/trolling lever is in the detent position.
Figure 3-7 : Trolling valve - Non-trolling mode.
See figures 3-6 and 3-7. The trolling valve, with the cam/trolling lever in the non-trolling position, allows the valve to operate as a standard control valve.
Trolling valve - Forward or reverse.
When the trolling valve is to be used for either forward or reverse the cam trolling lever is moved out of the detent position and into the trolling range. With the cam/trolling lever out of the detent position, the rate-of-rise piston position can be hydraulically adjusted by partially draining chamber L to decrease the compression of the outer, middle, and inner springs against the high pressure regulator piston decreasing the pressure in chamber B of the valve. (See figures 3-4, 3-6 and 3-8). With the cam/trolling lever out of detent, the trolling valve provides manual control by adjustment of trolling lever, at low pressures required for trolling.
Figure 3-8 : Trolling valve - Trolling mode. Forward and Reverse.
NOTE: Be sure to observe and record marine transmission sump oil temperature. If temperature drops below 135° F. during trolling mode operation, it is recommended that a thermostatic bypass valve be installed in the transmission's hydraulic circuit. Consult Twin Disc for appropriate recommendations.
The operator must select the trolling mode with the control valve lever in neutral and set the engine speed at or below the recommended maximum trolling rpm.
| NOTICE |
|---|
Do not operate marine transmission in the trolling mode at engine speeds above the maximum trolling rpm. The maximum engine speed in trolling for the MG 5061SC marine transmissions is 1100 rpm or 40 % of full load engine speed, whichever is smallest. Install the pilot house instruction plate in an area near the trolling valve control head in the pilot house where it may be easily read. Failure to obey this operating limit can result in major damage to marine transmission components, which can cause an unsafe operation condition to occur. Unsafe operating conditions could result in loss of vessel manoeuvering control, vessel damage, and/or loss of property and/or life. |
figure 3-9 Power Flow Diagrams.
Power Flow (See figure 3-9).
Neutral.
When in neutral, the forward and reverse shafts, transfer gears, and steel clutch plates rotate at engine speed. Other parts including the output shaft do not turn.
Forward.
In forward, the same parts are turning that were turning in neutral. When the forward position is selected, hydraulic pressure is applied to the forward clutch piston clamping the friction and steel clutch plates together. The forward input pinion will then rotate at engine speed and direction, because the friction plates are spline-connected to the pinion. Since the forward input pinion is in mesh with the output gear, the output gear and shaft will rotate in anti-engine direction. The reverse input pinion will be back-driven (engine direction) when the unit is in forward.
Reverse.
In reverse, the same parts are turning that were turning in neutral. When the reverse position is selected, hydraulic pressure is applied to the reverse clutch piston clamping the friction and steel plates together. The reverse input pinion will then rotate at engine speed and anti-engine direction, because the friction clutch plates are spline-connected to the input pinion. Since the reverse input pinion is in mesh with the output gear, the output gear and shaft will rotate in engine direction. The forward input pinion will be back-driven (anti-engine direction) when the unit is in reverse.
Back Driving.
All current Twin Disc production marine transmissions can be back-driven (propeller windmilling with dead engine) for the following conditions provided that the vessel speed when back driving the marine transmission does not exceed the normal maximum propulsion speed of the vessel.
Examples :
* Towing to deliver a boat.
* Towing home a boat with engine trouble.
* Sail boat auxiliary.
* Multiple screw vessel with engine(s) shut down.
Selective methods required for Back Driving (any one will suffice).
1. Start the engine and operate the marine transmission in neutral at normal fluid pressures for a minimum of five (5) minutes, doing this once every 8 hours. Maintain the back driven marine transmission's oil level at the full mark on the dipstick.
2. Lock the propeller shaft to prevent rotation.
3. It is possible to add an electric auxiliary oil pump into the lube circuit of many Twin Disc marine transmission models. See the hydraulic system prints dor more details on auxiliary pump specifications for the applicable transmission or contact Twin Disc.
4. In the case of an inoperable engine where pressure lubing the transmission is not possible, plug the dipstick tube and fill the unit with oil; then drain the oil down to full oil level. Repeat this process every 8 hours.