The elevation and azimuth mechanical drives are part of the launcher drive system (LDS) and are run electrically and hydraulically. Other parts include the hydraulic power supply, the servomotor, valve assemblies, and related electronics components. The related electronics components, the LDS contactors, give the LLM movement.
The azimuth mechanical drive includes the speed reducer and the geared bearing. The elevation mechanical drive includes the transmission/brake angle drive unit, propshafts, and actuators.
If the drive systems fail, the crew will not be able to position the cage manually to fire the rockets. The MLRS repairers you supervise are responsible for isolating malfunctions in the system in forward areas as members of direct support contact teams.
LDS Electrical and Hydraulic System Parts
LDS Electric Motor. The LDS motor is a 12.1 hp, ±18-28 VDC motor, rated 4,000 rpm at ±21 VDC. Steady-state power consumption is 12 kW. The motor drives the hydraulic pump to provide pressure to the azimuth and elevation servo valves. The motor is controlled by the LDS contactor and limit switch system.
LDS Contactor. The contactor is a large power relay with contacts that can carry the high-current demands of the LDS electric motor (1,650-amp surges). The contactor is actuated by the FCS-generated command, LDS ON CMD, from the FCU. The limit switch system can interrupt current to the contactor.
Limit Switch System. The LDS limit switch system is made up of single-pole switches connected in series with the LDS contactor circuit. They interrupt LDS power if the FCS fails to control LLM movement. The switches can be actuated mechanically if the LLM moves into positions that would cause damage to any MLRS system mechanical or electrical component.
Azimuth and Elevation Servo Valves. These are electrically operated valves controlled by command signs from the FCS. They direct hydraulic pressure to the azimuth and elevation servo motors.
Elevation Pressure Regulator. This is a solenoid-operated valve that reduces pressure to the elevation servo valve during the last 35 mils of down movement during stow. It prevents damage to mechanical actuators and is controlled by FCS command signals.
Azimuth Freewheel Solenoid. This is another solenoid-operated valve that removes hydraulic operating pressure from the azimuth servo valve for the last 35 mils of down movement during stow to prevent damage to the cage centering probe. It is also controlled by FCS commands.
Azimuth and Elevation Resolvers. The azimuth and elevation resolver are position indicator devices used during stow and reload to provide servo loop closure to the FCS. The resolver shafts are coupled by gear train to the LLM's azimuth and elevation mechanical axes. They are adjusted when they are installed on the carrier cab and bed and are 0 mils when the LLM is stowed. The FCS supplies an AC, 400-Hz, 18-V signal on the resolver S1 and S3 terminals. This voltage is induced on the R1 to R4 windings and is determinate in phase and amplitude to the direction and amount of movement of the resolver shaft. The resolver position output from R1 to R4 windings is convened to digital position data by an R/D converter and is supplied to the FCS as servo loop feedback. The resolvers are also used to back up the SRP/PDS position signals to the FCS during firing. The two position signals are compared and, if they do not match within ±5 mils, generate a fault message.
Cage Transport Latch Actuator. This is an electric motor-driven screw jack used to lock and unlock the transport latch, which secures the cage for travel. It is controlled by command signals from the FCS.
Boom Controller. This is a hand-held remote switch box used to control LLM and boom and hoist movement during reloading and maintenance.
Hydraulic Heat Exchanger. This is a simple oil-cooler device that uses a fan-cooled radiator through which the return hydraulic fluid is routed. The heat exchanger fan circuit is connected with the LDS electric motor in parallel and runs whenever the LDS motor is on.
LDS Electrical and Hydraulic System Operation
Prefire. During tactical fire mission operations, after the crew has moved the SPLL to the designated firing point and has parked within the proper azimuth and slope limits, the fire control panel displays a prompt, when parked press INIT. After INIT is pressed, the prompt, to continue mission press LCHR lay, is displayed. When the launcher lay key is pressed, the fire control system initiates the necessary commands to unlock the LLM cage and move it to the firing azimuth and elevation.
The fire control unit issues a cage unlock command to the PDB. This command provides a return for the cage unlock (K4) relay in the PDB. The +24 VDC goes from the positive bus of the PDB to the transport latch actuator retract circuit via PDB connector J3, pins R and J. Return is via PDB connector J3, pins T and H. When the actuator completes its travel, a limit switch in the actuator opens the retract circuit and closes the LDS relay +24 VDC connection from the actuator limit switch to the LDS on relay X1 pole via pin N of the PDB J3 connector The cage unlock signal is also routed to the FCS via PDB connector J1, pin 72, to the FCU as a signal that the cage is unlocked.
The FCU then issues an LDS on command to the PDB to provide a return for the LDS on relay K2. When PDB K2 closes, +24 VDC is provided to the X2 anode pole of the LDS contactor relay via PDB connector J4, pin 23, and the limit switch circuitry.
The LDS limit switches are connected in a series-parallel combination, with the +24 VDC routed to the LDS contactor relay from the PDB K2 relay. The limit switch system interrupts LDS power if the LLM moves into azimuth or elevation angles that would damage the SPLL mechanical components. Movement of the LLM is controlled by software in the FCS. The limit switch system functions only if the FCS fails to control the LLM.
There are four azimuth limit switches. Three of these are in the azimuth position transducer assembly (they have limits of 73°, 106°, and 196°). The remaining azimuth limit switch (1.25°) is on the turret and is actuated by a cam on the base assembly.
There are also four elevation limit switches. Two, 15° and 27°, are mounted on the right rear hinge point of the turret and are operated by cams on the cage. The other two are right and left 62.2° switches and are inside the elevation (ballscrew actuators).
From the stowed position, the 1.25° azimuth limit switch limits azimuth movement until the cage has been elevated to at least 15°. This is to allow clearance between the front of the cage and the carrier cab and engine components. When the cage has been traversed to 73°, the 15° minimum elevation limit is bypassed. After 106°
in azimuth has been reached, elevation is limited to a maximum of 27° to prevent interference between the rear of the cage and the carrier's components. The 196° azimuth switch prevents azimuth movement past that point to protect the electrical cables that interface the base with the turret and cage. The ballscrew actuator 62.2° limit switches keep the actuators from extending to the mechanical limits that damage the actuator.
The return for the K2 relay is by the PDB connector J4, pin 24. When the contactor relay closes, +24 VDC from the batteries pass through the resistor contacts to the LDS motor for 50 msec only, because there's a time delay device in the relay. This delay allows the rest of the circuit to initiate. The resistor circuit is necessary to limit surge current to 1,650 amp. When the time delay is over, the battery-direct contacts route battery current directly to the motor through the M terminal. The LDS motor then runs, driving the hydraulic pump that, in turn, creates operating pressure levels after about 1 sec. Afterwards, the FCS reviews the built-in test (BIT) for LDS.
The LDS built-in test equipment (BITE) is six sensor switches installed in the hydraulic power supply components. They monitor: hydraulic pump
pressure, reservoir fluid level, hydraulic fluid temperature, hydraulic fluid filter cleanliness, and the electric motor brush temperature. The sixth sensor is installed in the elevation valve module to monitor elevation hydraulic pressure when the LLM is stowed.
Abnormal LDS conditions actuate the sensor switches and provide a malfunction display on the gunner's fire control panel. All prefire activity stops until the malfunction is fixed.
If the BIT finds nothing wrong, the FCS will issue an elevation signal from the FCU to the elevation servo valve through the PDB connector J1; pins 46, 47, 48, and 56; and through PDB connector J4; pins 3, 4, 25, and 26. The signal will be software controlled to elevate the LLM to 310 mils (±8 mils). During this initial elevation, the LLM reference angle comes from the azimuth and elevation resolvers, and the azimuth position is maintained at 0 mils (±2.5 mils). Once elevation has been achieved, the FCS commands azimuth movement of the LLM to the firing azimuth through PDB connector J1; pins 49, 50, 51, and 52; and connector J4; pins 27, 28, 29, and 30; to the azimuth servo valve. The FCS then commands the LLM to the firing elevation through a reiteration if it has not already been achieved. During the final firing alignment, the LLM angle reference is supplied by the SRP/PDS. If an arm command is not issued to the crew and acted upon within 10 sec after the aim point has been reached, the FCS shuts the LDS down by removing the LDS on command. When an arm command is issued and the arm switch set to arm, the LDS is powered up and remains active until all selected rockets are fired.
Fire. During firing the FCS monitors the LLM's position, using SRP reference signals. It also issues appropriate azimuth and elevation commands to the servo valves in order to maintain the aim point.
Postfire. After firing is completed, the FCP prompts the operator to stow the LLM. When the stow button is pressed, the FCS issues the appropriate servo valve signals to, first, position the LLM to 310 mils (±8 mils) in elevation and, second, to 0 mils azimuth (±2.5 mils). This angle reference comes from the azimuth and elevation resolvers during stow, and it is backed up by the SRP. After it gets to the proper azimuth, the FCS lowers the LLM with commands to the elevation servo valve.
When the LLM reaches 35 mils (±5 mils), the FCS issues a hydraulic regulator and bypass command from the FCU to PDB connector J1, pin 54. This closes the PDB relay K1, supplying +24 V to the freewheel solenoid and +24 V to the elevation regulator solenoid on PDB J4 connector, pins 1 and 14. Return is by J4, pins 2 and 15.
When the azimuth freewheel solenoid energizes, hydraulic pressure to the azimuth motor through the servo valve is removed, allowing the LLM to freewheel in azimuth as the LLM centering probe enters the centering socket.
When the elevation pressure regulator solenoid energizes, hydraulic pressure to the elevation servo motor slows the rate of depression and reduces mechanical load on the cage ball screw actuators.
When the cage is fully down, a cage down switch on the probe completes a signal circuit to the FCS by PDB connector J1, pins 70 and 71, telling the FCS that the cage is down. The FCS releases the unlock command on PDB connector J1, pin 53, to the PDB K4 relay and supplies ±24 VDC to the transport latch actuator extend circuit engaging the transport latch. When
the latch has fully engaged, a limit switch in the actuator opens, stopping actuator movement and sending a cage lock signal to the FCS by PDB connector J1, pin 73.
It is important to note that, during the stow sequence, as the actuator moves from the fully retracted position, the +24 VDC going to the LDS on relay K2 is lost. As the cage unlock signal is lost on PDB connector J3, pin N, a supplemental +24 VDC is provided by the LDS relay power command to K3 during stow at 12 mils (±2 mils) to maintain LDS power until the FCS gets a cage down and lock indication from the transport lock actuator and the cage down switch on PDB connector J1; pins 70, 71, and 73. Once this signal sequence is received, the FCS removes the LDS relay power command, and the LDS contactor relay opens, stopping the motor. Finally, an LLM-stowed message is displayed on the fire control panel so the operator knows the LLM is stowed.
Reload. The functional sequence for reloading the LLM begins when the MLRS gunner selects a reload position.
Initially, the FCS controls the LLM automatically, as described during the discussion of LLM FCS control (in this lesson and an earlier lesson). When the LLM has been positioned, the FCS enables the BC by supplying +24 VDC to the BC J1 connector, pins 21 and 15, from the FCU through PDB connectors J1 and J3. The +24 VDC circuit to pin 21 illuminates the enable lamp on the BC showing that the controller is enabled. Operators who want to move the LLM in azimuth or elevation press the appropriate switch: LLM Up, LLM Dn, LLM CW or LLM CCW. Once pressed, the switch sends a signal from the BC to the FCS by the PDB J3 and J1 connectors and the FCU J52 connector. The FCS issues an LDS on command along with the appropriate azimuth or elevation servo valve command, and the LLM moves. Once the LLM is at the desired position, the operator releases the switch and the FCS servo valve command is removed. The FCS maintains the LDS on command for 10 sec. If no further LLM commands come in from the BC in that time, the FCS removes the LDS on command.
When reload is complete, the FCS operator presses the stow button on the fire control panel, and the FCS automatically stows the LLM as previously described. It also automatically disables the BC. All angle reference angles during reload come from the azimuth and elevation resolvers.
Troubleshooting and Repair of Drives
With the preceding information and TM 9-1425-646-30-1, you should be able to tell if the MLRS repairers you supervise can determine the exact symptom or malfunction properly as follows:
1. Find the symptom on the list.
2. Identify the malfunction number in the symptom index that most closely describes the fault in the system.
3. If the fault is displayed as a message on the FCP, compare description of conditions (given in parentheses) to actual condition of the equipment.
4. Perform troubleshooting procedures called for on the page given in the symptom index.
To do their work, repairers you supervise use table 3-2, TM 9-1425-646-30-1; multimeters; breakout boxes; limit switch test cables; and DS/GS tool kits. Repairers can refer to electrical schematic diagrams and a hydraulic schematic diagram on unusual or extremely difficult fault isolation problems. These diagrams can also be used to reinforce the troubleshooting logic used in table 3-2. They are in appendix C, TM 9-1425-646-30-1, which is not necessary for completing this subcourse.
Use of Breakout Boxes
Depending on the malfunction symptom that is used for troubleshooting or the unusual or extremely difficult problems that require the use of schematics, the breakout boxes are extremely useful in helping to determine what you need to do to repair the malfunction. They were introduced in lesson 2.
MLRS breakout boxes (figure 4-1) connect cable assemblies and electronic LRUs to bring individual data lines to test points. Then voltages, resistances, and continuities can be measured. The multimeter, breakout boxes, and the limit switch test cable are used for electrical checks during launcher drive system troubleshooting.
Tools from the DS/GS tool kit are needed for moving the LLM manually and for accessing certain test points.
To use the breakout boxes, there are several things that must be done correctly or the breakout boxes will not be functional. The correct procedures for connecting the boxes follow:
1. Disconnect W1P2 from FCP J1 and W1P1 from FCP J2.
2. Connect W1P1 and W1P2 to keyed connectors on FCP breakout box.
3. Connect FCP breakout box keyed connectors to FCP J1 and J2.
4. Secure breakout box so you won't damage it.
5. Install power distribution box breakout box.
6. Disconnect W43P1, W75P1, W26P1, W76P1, W27P1, W23P1, W25P1, and W24P1 from the power distribution box.
7. Connect the eight connectors to keyed connectors on the PDB breakout boxes.
8. Connect the eight PDB breakout box connectors to keyed power distribution box connectors. Secure breakout box so it won't get damaged.