IN THIS SECTION, YOU WILL FIND THE FOLLOWING SUBSECTIONS:
THE STARTER SYSTEM
SAFETY INTERLOCK SWITCHES
SOLENOID SHIFT STARTER
OUTBOARD ENGINE STARTING SYSTEMS
SAFETY CONTROL SWITCHES AND SENSORS
ELECTROMAGNETISM IN MOTORS
Even though controller, like any component, can fail, it ends up being one last devices tested. Before you investigate controller, eliminate all other components attached to it as causes problem. If engine won’t start, test all devices attached to controller that need to be functioning for controller to release power to starter solenoid. Only after these tests would you focus on controller itself. Following is a list of possible alternatives to malfunctioning controller when problem involves engine that won’t start:
1)Corroded or broken wires and connectors
2)A defective fusible link for supplying power to all engine devices
3)A blown controller safety fuse
4)A defective starter switch that’s keeping controller from receiving a +12 volt signal
5)A poor ground connection through the PTO safety switch
6)A poor ground connection through seat safety switch
If you narrow cause problem down to controller, may have to replace controller unit. Always consult engine manufacturer’s and equipment manufacturer’s service manuals for information specific to your machine and problem with it you’re investigating.
THE STARTER SYSTEM
There are several different types of starter systems used in outdoor power equipment. The purpose of a starter system is to get the crankshaft turning. When the crankshaft turns, it turns the flywheel or rotor that contain the main components of the ignition system (remember that a spinning motion is required to move the magnets in a magneto ignition system in order to produce the voltage needed to fire the spark plug). At the same time, the turning crankshaft starts the piston moving up and down, and so the four stages of engine operation begin.
One of the simplest starter systems is the rope rewind starter. To use this starter, you pull a rope with a handle to start the engine. When the engine starts, you release the rope, and it rewinds by spring action back into the starter mechanism. Rope rewind starters are often used on small lawn mowers, chain saws, weed cutters, and so on.
When the starter rope is pulled, the starter pulley turns. The movement of the pulley engages the crankshaft. This causes the crankshaft to rotate with the pulley. The inside end of the recoil spring is attached to the pulley. When the rope is pulled, the recoil spring is wound tight. When the rope is released, the spring will uncoil and pull the rope back into the starter housing. Note that the rewind action of the rope always occurs, whether or not the engine actually starts.
Different starter systems use different methods to engage the crankshaft. In one of the most common systems, components called pawls or dogs are used to engage the crankshaft. In this type of system, when the starter rope is pulled, the pawls move outward from the pulley and engage the crankshaft. When the rope is released and is completely rewound, the small spring attached to the pawls pulls them back inward to disengage them from the crankshaft.
On larger equipment, electric starters are often used to get the crankshaft turning. An electric starter is simply a small DC motor that has a movable gear on its output shaft. This type of starter system is generally activated by turning a key, or by turning a key and pushing a button. When electricity from a battery reaches the starter motor, the starter motor turns. The starter gear pushes outward and mates with gear teeth on the flywheel. Since the diameter of the flywheel is much larger than the diameter of the starter gear, the engine will rotate at a fairly low speed. Through the gearing arrangement, the motor’s torque is greatly multiplied, allowing a small motor to rotate the crankshaft of a much larger engine. When the engine’s crankshaft starts turning, the starter gear disengages from the flywheel. Once the key or push button is released, the starter motor stops rotating.
SAFETY INTERLOCK SWITCHES
Safety interlock switch is special electronic switch used on outdoor power equipment to protect operator from injury. Safety interlock may prevent engine from starting in unsafe mode, stop engine or blade when operator lets go of handle, or stop engine or blade when operator rises out of seat (in riding mowers). Most newer mowers have safety bar located near top of handle. Bar must be held against handle as you pull starter cord in order for engine to start. If you let go of handle, engine will automatically stop. Bar is attached to cable that connects to brake assembly. If you let go of bar, brake assembly stops crankshaft from revolving. Brake assembly contains a switch that grounds ignition module when brake engaged.
Garden tractors and riding mowers often have safety interlock switches located under operator’s seat. If operator rises from seat, safety switch closes and grounds out ignition module, stopping engine.
On garden tractors, some switches won’t allow engine to start unless transmission in neutral, person is sitting in seat, blade is disengaged, etc. Safety switches must be in their open contact state to allow engine to start. However, once the engine has started, the switches are closed as the transmission is shifted into gear or the blade is engaged under the deck. The safety interlock module allows the engine to run with these switches closed.
The electronic safety interlock module operates by sensing and monitoring the voltage from the ignition coil. If no voltage is present, the engine isn’t running. However, once the engine starts and the ignition coil produces a voltage, the deck switch and the neutral switch are bypassed by the safety interlock module. Ignition switch and safety seat switch still in coil circuit. Closing either will cause engine to stop.
Many types outdoor power equipment use electric start. Main component in system is starter itself. All electric starters use electric motor to turn over engine. Most starter systems use gear arrangement that meshes with teeth on outside of flywheel.
Starter motor works in manner directly opposite generator. In generator, group of coils rotated within magnetic field to create electricity. In motor, electricity used to create magnetic field around coils wire on rotor or armature. These magnetic fields oppose fields of starter, cause armature to turn. In generator, electricity created through rotation. In motor, electricity used to produce rotation.
Motors and generators close in design and components. On some equipment, generator and starter motor same device. When engine to be started, solenoid relay places battery voltage on armature of starter generator. Field windings, similar to stator windings, energized through voltage regulator. After engine starts, starter generator rotates due to belt drive connected to engine. Once start switch in circuit opened, starter generator has armature connected to voltage regulator and battery for charging.
More common starter is permanent magnet DC motor. This the same type motor used in cordless power tools like drills, saws, and sanders. Permanent magnet DC motor doesn’t use stator windings. Windings replaced by high quality ceramic magnets glued to motor’s case. Armature of motor resembles generator armature; there’s a series wires connected to a copper commutator. These coils connected through commutator by two or four carbon graphite brushes to 12 volts DC when motor energized to start engine.
Electricity creates magnetic field around poles on which coils wound. These magnetic fields oppose magnetic fields of permanent magnets, causing armature to turn.
Second major component starter system is starter drive. One of most common is Bendix drive. Starter assembly a separate complete unit. Electric connection to starter made by means threaded stud and nuts at lower left of assembly. Consider exploded view of starter assembly. Bottom section or commutator end cap has bushing that supports armature.End cap also holds carbon brushes and brush springs. Starter frame or case holds permanent magnets. Case should never be struck by hammer, etc. because magnets can be weakened or dislodged.
Center section of starter is armature. On output section of armature is set machined splines. Splines are grooves machined in spiral formation up the shaft. On spline sits drive pinion, a gear that meshes with gear teeth on outside edge of flywheel when starter motor energized.
The anti drift spring used to keep drive pinion away from flywheel when starter not energized. Other components include end cap, spacers, and stop nut. Drive end cap also contains bearing to support armature.
When electric motor energized, armature begins to turn. Centrifugal force created by rotation causes drive pinion to be pushed up splines to compress anti drift spring. By this time, drive pinion has engaged with teeth on flywheel, rotation of armature through drive pinion causing engine to rotate.
As long as speed engine same as speed drive pinion, pinion remains engaged with flywheel. Once engine starts, flywheel turns more quickly than pinion and armature. To prevent damage to starter, pinion pushed back down spline, away from flywheel by faster speed of flywheel. By this time, operator usually released start button or key to deenergize starter.
SOLENOID SHIFT STARTER
Previous starter used splines of Bendix drive to cause pinion to engage flywheel. Second type starter uses solenoid to shift pinion into engagement with flywheel. Consider typical solenoid shift electric starter. Similar to previous starter in that uses four brushes on armature and permanent magnets on case of starter.
Device used to energize windings of starter and force drive pinion into flywheel is solenoid. Consider side view of solenoid assembly. Solenoid coil is main component. When coil energized, plunger pulled to left and into coil. When plunger pulls backward, shorting bar pressed against two electric contacts. This causes battery voltage to be applied to brushes of starter. Both shorting bar and contacts must have sufficient current capacity, since motor draws great deal of current from battery. Wire that attaches from battery to terminal of starter of larger diameter, higher ampere rating than other wires on equipment.
Second thing that occurs when plunger pulled backwards is drive lever pushes pinion forward on shaft of armature, into contact with flywheel. Armature shaft also splined, splines cause drive pinion to rotate into mesh with gear teeth on flywheel. This prevents direct impact of drive pinion tooth against flywheel tooth.
Small electric starters used even on weed trimmers. Starters used on small two and four stroke equipment contain same basic components as larger starters. May encounter small starter that uses small plastic gear or small drive belt with cogs to drive pinion gear.
OUTBOARD ENGINE STARTING SYSTEMS
Type starting system used on outboard depends on size of engine. Single cylinder outboards and small multicylinder usually equipped with recoil starters. One type recoil operates such that when handle pulled, a nylon pinion gear slides up and engages the teeth in flywheel edge. Once engine starts, the pinion automatically disengages from flywheel.
Larger outboard engines may use automotive type electrical system with key switch, lead acid battery, starter motor, solenoid, and alternator type charging system. An outboard engine electric start will also typically contain prevent start switch that prevents engine from starting unless the gear selector set in neutral. The electrical system in larger outboard may also include an electronically operated hydraulic pump to run power trim and tilt system, plus necessary wiring and controls for the pump. In outboard engine electrical system, a junction box may be used to hold the electrical connections between engine and battery. Junction box is mounted in protected location away from fuel tank, the battery, and floor of boat (to protect it from water damage).
SAFETY CONTROL SWITCHES AND SENSORS
If switch on equipment designed to function automatically, is probably being used to trigger either safety feature or sensor display.
Safety control switches—before testing electrical safety control switch, examine physical mechanism used to operate switch. Make certain mechanism adjusted correctly. Next check condition wires and their insulation for damage. Often, safety switches located on exterior of equipment. Switches may collect lots moisture and corrosion, so check for signs oxidation. See if battery voltage reaching switch. Check to see if safety switch transfers battery voltage when switch activated. Also use meter to make sure is zero resistance from switch to ground.
Consider typical seat switch which is designed to stop motor when nobody sitting on tractor seat. Can test such a switch by attaching multimeter or ohmmeter to two wires coming from seat switch. Then, sit on seat. Meter should register zero ohms as switch closes and circuit completed. If switch good, check voltage on wires coming from switch and ground. Look for corroded ground connection. Finally, test for continuity across all connections going into controller. Be aware that, depending on safety feature and how it controlled, engineers will select a switch designed to function either by opening or by closing. Only way to be sure which way safety switch designed to function to study electrical schematic.
Sensors—sensor displays are indicators used to illustrate how machine running at given time, indicators such as fuel level or oil pressure gauges. A fuel level indicator, for instance, is a variable resistor triggered by changes in position of float in fuel tank. This type sensor allows whole range of readings based on level fuel at any instant. Sometimes, as in case many oil pressure sensors, sensor may activate on off indicator light when certain conditions met instead of showing variations in pressure level. Pressure sensor would trigger indicator light to come on when oil pressure drops below safe level.
To test circuit of pressure switch sensor, should first disconnect sensor. Then can check to make sure is +12 volts getting through wire that connects to sensor. If wire to sensor is okay, can look elsewhere for cause any problems. First, look up pressure required for sensor’s pressure switch to function. Then start engine and measure oil pressure at engine’s governed rpm. To check oil pressure, would thread a pressure gauge into hole from which had removed sensor. If pressure okay, then problem with sensor’s pressure switch. To check switch, reinstall it and test for continuity and resistance through switch with multimeter. While contacts on sensor switch closed, meter should indicate near perfect continuity or zero resistance. When pressure triggers contacts to open, reading should swing toward infinite resistance.
Another way to check be to bypass sensor to see if gauge or indicator light functioning properly. If oil pressure and indicator light both good, would leave only sensor as source defect.
If sensor’s switch functioning properly, perform continuity test on reinstalled switch by measuring electrical contact to ground. Remember to check for good ground, and to test voltage going to switch before blaming sensor for problems. Then start and run engine up to full throttle to get maximum oil pressure. Once again, test switch to make sure that contacts open. If switch fails to open, replace.
ELECTROMAGNETISM IN MOTORS
Suppose a current carrying conductor placed in magnetic field. Interaction between the magnetic field and moving electrons in conductor causes a physical force to be applied to the conductor. If conductor free to move, force will cause it to move for as long as conductor current and magnetic field are maintained. This called motor action of electromagnetic induction.
Consider a conductor connected to a battery to form a complete circuit. Current already flowing in conductor when it’s placed in magnetic field between two magnets. Reaction between magnetic field and moving electrons causes conductor to move upward.
The motor action of electromagnetic induction is basic property used to operate electric motors. In a motor, the armature is rotating component mounted on a shaft, positioned between motor’s field magnets. Loops of conductor wire called armature windings connected to commutator. Brushes are electrical contacts that slide over surface of commutator as armature rotates. Brushes connected to power source outside motor, usually a battery. Wires called field windings are wound around field magnets. When current flows into these wires, field magnets become electromagnets, produce powerful magnetic field inside the motor. When current applied to the brushes, moves through the brushes into commutator and armature windings. Current flowing through armature windings produces magnetic fields around the windings.
Interaction of these magnetic forces causes armature to spin. Output shaft of armature connected to machine or load.
Larger lawn tractors contain electric motors in starter system. Output shaft of electric motor in such a system connected to gears that engage flywheel. Spinning motion of electric motor’s armature transferred through gears to flywheel and engine crankshaft.
If two conductors placed close together, and current applied to one of them, a voltage will be induced in the other. The energy in “live” conductor will stimulate other conductor to become energized too. This effect called mutual inductance, used to operate transformers. If conductors moved far apart, energy of “live” conductor won’t influence second conductor, and mutual inductance will cease.
Transformer is a device consists of two windings of wire around an iron core. First winding called the primary winding, second winding called the secondary winding. When switch open, no current flows through primary winding.; therefore no magnetic field produced, no voltage induced in secondary winding. When switch closed, current flows through primary winding, producing magnetic field around primary winding. Field spreads outward, cuts across secondary winding, inducing voltage in secondary.