ME467 Engine Starting

ME 467 : Automobile Engineering Dr. Md. Ehsan 2015 ME, BUET

STARTING AN AUTOMOBILE Things to check before starting an automobile - (a) Under the bonnet - (i) Lubricating oil level (ii) Coolant level in the radiator (iii) Brake & Clutch fluid level

(iv) Battery terminals (v) Engine Belts

(b) Outside the vehicle - (i) Tyres (running and spare appearance, pressure) (c) Inside the vehicle - (i) Seat belt (ii) Brake Pedals (iii) Hand brake position (iv) Gear lever position (neutral or parking) (v) Mirror positions (rear and side views) (vi) Fuel indicator level (vii) Indicator lights on the dash board when switched on. Once satisfied with initial check we can start the engine by turning a key or pressing a button.

STARTING WITH KEY KEYLESS STARTING


How the engine starts? All internal combustion engines need to be rotated at sufficient speed with the help of external force in order to start. External assistance can come from

(a) Manual Power (eg. small engines irrigation, lawn mower, boat, generator and pushing a vehicle)

(b) Electric Power from energy stored in a battery and an electric motor (most automobiles)

(c) Pneumatic Power Compressed air from a storage tank and pneumatic motor ( Big engines)

(d) Engine Power using another small engine, which itself also needs starting (Very big engines)


The Electric Starting System To start the automobile engine, the crankshaft must turn fast enough for air-fuel mixtur to enter the cylinders. An electric starter or starting motor does this job. It converts electrical energy from the battery into mechanical energy that rotates the crankshaft. The starting system has two separate but related circuits. One is the low-current control circuit. The other is the high-current motor circuit. Both operate on battery voltage. When the driver turns the ignition key to START, the control circuit causes heavy contacts to close in a starter relay or solenoid switch. High current then flows from the battery insulated cable through these contacts to the starting motor. A gear on the starting-motor shaft moves into mesh with the ring gear around the engine flywheel or drive plate. As the starting-motor shaft turns, it spins the crankshaft fast enough to start the engine.

The use of a relay or solenoid shortens the distance that heavy-gauge cable must carry the cranking current and improves passenger safety. The control circuit includes a safety switch. It prevents energizing of the relay or solenoid with the automatic transmission or transaxle in gear. In a vehicle with a manual transmission, the gear must be ensured (by driver) in neutral position before cranking occurs. Typical starting speed is about 200 rpm of cranking and it may draw high current in the order of 150-200 amps for several seconds from a 12 volt automotive storage battery.


CONSTRUCTION OF THE STARTER MOTOR

The starting motor has two basic parts: an armature and a field-frame assembly. The armature is the rotating assembly that includes the main current-carrying conductors. Field windings in the electromagnet starting motor produce a strong magnetic field when battery current flows through them. In the permanent-magnet starting motor strong permanent magnets provide the stationary magnetic field. When current flows, the armature windings and field windings or magnets produce opposing magnetic fields. This forces the armature to rotate and crank the engine. Most automotive starting motors have used electromagnets to produce the magnetic field. More starting motors now have permanent magnets instead. Starting meters are typically engaged with the engine crankshaft through a pinion and a large ring gear mounted on the flywheel. A low gear ratio (15:1 20:1) between the starter motor and the engine enables sufficient torque to be developed to turn the crank shaft.


THE OVER RUNNING CLUTCH

The starting motor has an overrunning clutch that transmits torque in one direction and turns freely in the other direction. When the armature turns, the clutch locks and transmits cranking torque to the ring gear. As soon as the engine starts, it spins the pinion faster than the armature is turning. This unlocks the clutch, allowing the pinion to overrun the armature. This prevents damage to the armature from spinning at high speed.

The overrunning clutch consists of an outer shell and a pinion-and-collar assembly. The outer shell has steel rollers fitted into five notches. The notches are smaller at one end. When the armature and shell begin to rotate, the rollers roll into the smaller ends of the notches. There, they jam between the shell and the pinion collar. This forces the pinion to turn with the sleeve, cranking the engine. When the engine starts, it drives the pinion faster than the shell and armature. The rollers roll back into the larger ends of the notches. This allows the pinion and collar to spin faster than the shell and armature.


GEAR REDUCTION To increase cranking torque, many starting motors have internal gear reduction. This acts in addition to the speed ratio between the motor pinion and the ring gear fitted around the flywheel. Next figure shows an electromagnet starting motor with gear reduction. The small pinion gear on the armature shaft drives the larger gear on the clutch shaft. There are two gear reductions. One is the reduction-gear set inside the starting motor. The other is the reduction between the overrunning-clutch pinion and the ring-gear teeth. The starting motor shown in shown below provides a gear reduction of 45:1. The armature turns 45 times to turn the crankshaft. This provides high cranking torque. Some starter motors use a second type of gear reduction uses a planetary-gear set. It provides a gear reduction of about 4.5 to 1. Total gear reduction between the starting-motor armature and crankshaft is about 70 to 1. Many permanent-magnet starting motors have planetary gears.

PERMANENT-MAGNET STARTING MOTORS Instead of electromagnets, some starting motors use four or six permanent magnets to provide the stationary magnetic field. This allows permanent-magnet starting motors to be smaller and lighter than similar starting motors with field coils. The electrical energy required to crank an engine is the same for both types of starting motors. Both use magnetism to rotate the armature. The difference is in the source of the magnetism. Most permanent-magnet starting motors have gear reduction. Permanent magnets in the starting motor increase its useful life or durability. Failures caused by shorted or grounded field coils are eliminated.


MOVABLE-POLE-SHOE STARTING MOTOR

Instead of a solenoid mounted on the starting motor, some cars have a movable-pole-shoe starting motor. It uses a movable pole shoe to move the over-running clutch shift lever. When no current flows to the starting motor, the return spring forces the shift lever and overrunning clutch back. This raises the movable pole shoe, which is attached to the other end of the shift lever.

The control circuit includes a magnetic switch or relay. When the ignition key is turned to START, contacts close in the relay and current flows to the starting motor. The magnetic field from the field coil around the movable-pole shoe pulls it down. As the shoe moves down, the shift lever pivots. This moves the pinion into mesh with the ring-gear teeth.


ENGAGEMENT OF STARTER MOTOR There are two types of engagement systems used in starter motors

Inertia Engagement System

Pre-Engagement System

The inertia engagement system depends on the natural reluctance (inertia) of a heavy pinion to change its state of motion. The pinion is mounted on a helix which is splined to the starter motor armature. Sudden rotation of the armature rotates the helix but owing to inertia, the pinion remains stationary which causes it to slide along the helix and engage with the flywheel teeth. A lead chamfer is present both on the pinion and the flywheel teeth to aid the initial engagement. When the engine fires the increase in engine speed spins the pinion along the helix and causes it to disengage from the flywheel teeth. The shock at the instance of engagement and disengagement is severe, so a large spring is fitted to act as a cushion. This system is getting less common as pinion wear rate is more.


Figure below shows how the pinion moves into mesh with the ring-gear teeth. The starting-motor solenoid has a plunger that connects by a shift lever to the overrunning clutch. When the driver turns the ignition key to START, current flows to the solenoid. This creates a magnetic field that pulls the plunger in. The attached shift lever pivots and pushes the pinion into mesh with the ring-gear teeth.

At the same time, pinion movement moves the contact plate which closes the contacts in the solenoid switch. This connects the starting motor to the battery so the armature rotates and cranks the engine. The solenoid has two windings, a hold-in winding and a pull-in winding. Their combined magnetic fields force the pinion into mesh with the ring-gear teeth. Then the pull-in winding is disconnected. This reduces the load on the battery. Less magnetism is required to hold the pinion in mesh than to engage


it. In this system the basically the solenoid engages the pinion with the ring gear teeth first and then the motor runs during engagement. During disengagement the motor power supply is disconnected first and the solenoid is disengaged later. This reduces pinion wear and makes the process smoother.

STARTING SYSTEM TROUBLE DIAGNOSTIC CHART

CAUTION: TO PREVENT STARTER DAMAGE, DO NOT CRANK ENGINE FOR MORE THAN 15

SECONDS AND ALLOW 2 MINUTES FOR COOLING BETWEEN CRANKING TESTS.


JUMP STARTING A CAR Jump starting is starting the engine of a vehicle that has a dead battery by using a charged battery, usually in another vehicle. The charged battery is the booster battery. It is dangerous when performed incorrectly. Sparks may cause a battery explosion. In addition, sparks and improper connections may damage electrical and electronic equipment on the vehicle. Follow the jump-starting procedure in the vehicle owners manual. Also, follow the safety cautions for working safely around batteries. In addition, observe the safety cautions below when trying to jump start an engine. This will help reduce the chance of injury and damage.

The jump-starting procedure requires a set of two jumper cables. These are lengths of heavy-gauge insulated cable with spring-loaded clamps on the ends. One cable is black. The other is usually red. Adapters may be needed to attach the clamps to a side-terminal battery. 1. Move the vehicle with the charged battery close to the vehicle with the dead battery. Do not allow

the vehicles to touch each other. 2. Check that the jumper cables are long enough to reach from battery to battery. Do not allow the

jumper-cable clamps to touch the terminals on either battery at this time. 3. Cover the caps of a vent-cap battery with a damp cloth. 4. Set parking brakes in both vehicles. The transmissions or transaxles in both vehicles should be in

PARK (automatic) or NEUTRAL (manual). 5. Turn off all lights, switches, and electrical equipment, except the heater blower motor. Turn it on or

set the air-conditioning controls to DEFROST. This helps prevent voltage surges from damaging the ECM.

6. On some vehicles with an antilock-braking system (ABS), disable the antilock system. This may

require disconnecting the ABS wiring-harness connector, removing the ABS power relay, or removing the ABS fusible link from near the battery positive terminal. The procedure is in the vehicle owners manual and service manual.

7. Connect one end of the red (positive) jumper cable to the positive (+) terminal of the dead battery.

Connect the other end of this jumper cable to the positive terminal of the charged battery. 8. Connect one end of the black (negative) jumper cable to the negative ( ) terminal of the charged

battery.


9. Connect the other end of the black jumper cable to the engine block or a head bolt at least 18 inches [450 mm] away from the dead battery. Do not connect the jumper cable to the negative terminal of the dead battery. This prevents any sparks that occur from causing a battery explosion.

10. Check that the jumper cables are clear of the engine fan and other rotating parts. Start the

engine in the vehicle that has the charged battery. Run this engine at fast idle. Start the engine of the vehicle with the dead battery. Do not crank for longer than 30 seconds. If the engine does not start, wait two minutes for the starting motor to cool. Then try again. Prolonged cranking can overheat and damage the starting motor.

11. Disconnect the black jumper cable from the engine block. Then disconnect the other end of

this cable. Finally, disconnect the red jumper cable. 12. Safely dispose of the damp cloth used to cover the caps of a vent-cap battery. REMOVING AND INSTALLING STARTING MOTOR To remove the starting motor, disconnect the ground cable from the battery. If necessary, raise the vehicle. Remove any braces, shields, or other parts that may be in the way. Disconnect the wires and cable from the starting motor. Support the starting motor so it will not fall on you or on the floor. Then remove the starting-motor mounting bolts. Watch for any shims located between the starting motor and its mounting pad. The shims must be reinstalled with the starting motor. Before installing the starting motor, clean the mounting surfaces on the drive end and on the engine. This ensures good electrical contact. The starting motor is case grounded through this connection. Then install the starting motor and reconnect the wiring and cable. Start the engine. Follow the procedure to restore data to the ECM and volatile memories. Then check for normal cranking speed and starting-system operation. SERVICING STARTING MOTOR Many starting motors require no maintenance between major engine repairs or overhaul. However, brushes, bearings, and bushings wear. The solenoid, overrunning clutch. and other parts can fail. A defective starting motor is removed and repaired, or exchanged for a new or rebuilt unit. Follow the procedure in the vehicle service manual. To disassemble a typical starting motor, remove the solenoid (if used) and the through bolts. Then remove the end frames or housings. Inspect and service the components. Major steps in rebuilding a starting motor include: 1. Replace armature bushings or bearings.

2. Test the armature and field coils (if used).

3. Refinish ("turn down") the commutator.

4. Replace damaged field coils.

5. Replace brushes.

6. Wipe clean or replace overrunning-clutch drive.

7. Replace contacts in solenoid switch.

After completing the tests and inspections, lubricate the shaft splines, bushings, and bearings. Then assemble the starting motor. If required, energize the solenoid and check the pinion clearance. This is the clearance between the pinion and the pinion stop when the pinion is in the fully-engaged position.


PUSH START The most common way to push start a vehicle is to put the manual transmission in second gear typically, switching the ignition to on/run, depressing the clutch, and pushing the vehicle until it is at a speed of 5 to 10 mph (8 to 16 km/h) or more, then quickly releasing the clutch to make the engine rotate and fire, then quickly depressing the clutch so it does not stall. This is done by one person pushing a lightweight automobile, pulling or being pushed by another vehicle or even rolling down a hill. Instructions for Push Start Make sure that the problem is either the battery or the starter motor.

1. Plan to have at least one person sitting in the driver's seat and other person(s) pushing. Mid-size and large cars require two or three people to push, depending on the strength of the people and whether or not the car is parked on an incline.

2. Turn off all accessories (radio, wipers, lamps).

3. Turn the key to the "on" position.

4. Depress the clutch pedal with your foot.

5. Put the transmission in first or second gear.

6. Release the hand brake and the foot brake.

7. Note that the people pushing need to get the car rolling as fast as they can (8-12 km/h or more). This works best down a hill or an incline.

8. Release the clutch pedal while giving the engine a little gas with the gas pedal once the car is moving about as fast as you can run. The engine should start.

Caution: A car with automatic transmission can not be push started.

Be aware that to push start a car you need to have a manual transmission, and trying to push start an automatic vehicle will either fail to start it, or possibly damage the transmission.

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ME467 Engine Starting

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