3起动系-汽车电器设备(英文版)

Chapter 3 The Starting System1. Operation and purposeThe battery sends current to the starting motor when the driver turns the ignition switch to START. This causes a pinion gear in the starting motor to mesh with teeth on the ring gear around the engine flywheel.The starting motor then rotates the engine crankshaft for starting,2. DC electric motorBasic principle of DC electric motorWhen current from the battery flows through the loops of motor rotor, a strong magnetic field is produced around the loops. This magnetic field opposes the magnetic field of the stationaryIt consists of :2.2.1Magnetic polesIt consists of : (magnetic)pole shoesmagnetic field windings (or stationary field windings)Usually there are 2 couples of magnetic poles ( or 4 poles). Heavy-duty motors have 3 couples of magnetic poles (or 6 poles).2.2.2 ArmatureIt consists of : laminated core (or lamination core)armature windings (or armature loops or armature conductors)The wiring connection of magnetic field windings and armature windings is often adopted in series connection. These are two basic ways of connection.21— magnetic field windings ; 2—armature windings2.2.3 Commutator assemblyIt consists of : commutator (on armature shaft)electric brushes , brush holders and springsCharacteristics of DC electric motor2.3.1 Properties of DC electric motor(1) Great starting torque.(2) High speed at low load and low speed at high load. This property ensures reliable startingof engine.2.3.2 Characteristic curves of DC electric motorDefinition:Characteristic curves of DC electric motor describe the relations of torque M, speed n, and power P with electric current I , or M=f(I), n=f(I), P=(I).I 0 racing 2max II max locked I(1) When just starting, n=0, I is max(lock current), M is max.for starting.(2) When no load existing, n is max., I is min., M is min.(3) At the middle point 2maxI , P is max.Parameters selecting of starting motor2.4.1 Power selecting9550n M Q Q P ≥(KW) n Q ―Min. engine-starting speed. for gasoline engine,50~70rpm. for diesel engine, 100~200rpm M Q ―S tarting resistant torque: including friction, compression lossand accessory mechanism lossTherefore, through testing ,the essential power for starting motor is :For gasoline engine: P=(0.18~0.22)L (KW) L ―E ngine displacementFor diesel engine: P=(0.74~1.1)L (KW) L ―E ngine displacement2.4.2 Gear ratio selectingZ Z n n S F F S i ==n s ―M otor speed ;n F ―C rankshaft speed for starting,n F =n QZ F ―T ooth number of ring gear of flywheelZ s ―T ooth number of drive pinion of motorWe can obtain the motor speed through matching with the Max.P from the characteristic curves. In fact, practical gear ratio is smaller than the optimum gear ratio because of Z F design problem. Generally, for gasoline engine, gear ratio is 13~17; for diesel engine, gear ratio is 8~102.4.3 Battery capacity selectingBattery capacity can be decided according to the rating power of starting motor. The empirical formula is:UP C )800~600( C ―battery capacity, Ah P ―rating power of starting motor, KWU ―rating voltage of starting motor, 12V3. Construction and control of starting motor3.1 Types of starting motorThere are two types of starting motors: inertia type and pre-engaged typeThe inertia type is a simple motor that the armature spindle carries an inertia-engaged drive arrangement consisting of a pinion mounted on a screwed sleeve.When the motor is operated, the sudden movement screws the pinion along the sleeve into mesh with the flywheel ring gear,when its movement is arrested by a strong buffer spring. As the engine starts and the driver releases the starter switch, the flywheel spins faster than the motor pinion, forcing it out of mesh.The pre-engaged type are almost always fitted to heavy diesel engines, and can be found on many modern cars. They differ from the inertia drive because the pinion is fully engaged with the flywheel before the starting motor starts to spin. This is achieved by mounting the solenoid switch on top of the motor and connecting it to a lever whose other end engages with the pinion. Activation of the switch draws in the solenoid, which pulls the lever and moves the pinion into mesh with the flywheel ring gear.In the last part of the lever movement the contacts are bridged that link the motor to the battery. Pre-engagement of the pinion greatly reduces the wear on the flywheel ring gear.3.2 Construction and control of starting motor(pre-engaged type)It consists of :(1) DC electric motor(2) Driving mechanismThis includes driving pinion,overrunning clutch,shift lever(or fork),clutch spring,etc.(3) Control equipmentThis includes two ways of control: mechanical control and electromagnetic control.3.2.1 Overrunning clutch(1) Types of overrunning clutchThere are three types: Roller type (most vehicles use)Spring typeFriction disk type(2)Function●Transmit cranking force to the engine flywheel.●Prevent the engine flywheel from driving the starting motor.(3)Construction and operation (roller type for example)It consists of outer shell and pinion, rollers, plungers and springs, cross block.In fact,the overrunning clutch is also called one-way clutch.●When starting engine:The rollers lock outer shell and cross block, outer shell andpinion drive flywheel to rotate.●After starting engine: The flywheel velocity is greater than starting motor velocity.The outer shell begins to rotate with flywheel. This action makes the overrunningclutch slip.3.2.2 Solenoid switch and control operationConstruction:It consists of: plunger(or moveable core), return spring, pull-in or winding, hold-in orControl operation:The solenoid switch has two windings, a pull-in winding(in series connection with the windings of DC electric motor )and a hold-in winding(in parallel connection with the windings of DC electric motor). They work together to pull the plunger in. This combination of windings (resultant magnetic force) provides sufficient magnetic strength to mesh the pinion and close the witch(this switch allows full motor current to flow). After the pinion is meshed and the switch is closed, less magnetism is required to hold the plunger in. Consequently, as the switch closes, the pull-in winding is shorted out, since it is connected between the two solenoid terminals. This makes a full current flow through the motor and the motor rotates at normal speed.4. Operating principle of starting motorOn starting motors with overrunning clutches, a solenoid switch is commonly used to produce the clutch-shifting action. The solenoid contains a pair of winding that are connected to the battery when the starting switch is closed. This produces a magnetic field that pulls a plunger in. The plunger movement causes a shift lever to move the overrunning clutch on the armature shaft. This shifts the overrunning-clutch pinion into mesh with the flywheel teeth. At the same time, the plunger movement forces a heavy switch to connect the starting motor directly to the battery. Now, cranking begins.5. Inspecting the starting motor unitsThis includes inspecting overrunning clutch, commutator, armature windings, magnetic field windings, brush and brush spring, solenoid switch,etc.6. Starting system troublesThere are two basic starting system troubles:(1)The starting motor does not crank the engine.(2)The staring motor cranks slowly, but the engine does not start.6.1Starting motor does not crank the engineThe most likely cause of this condition is a run-down battery. But there could be other causes. Turn on the headlights, and try cranking. There are five possibilities.(1)No cranking, no lightsThis is probably due to a completely dead battery. It could be caused by a bad connection at the battery or starting motor or an open fusible link(which indicates a short or ground in the system.(2)No cranking, but lights go out as you turn the key to START.This usually indicates a bad connection at the battery. It could also be due to a nearly dead(discharged) battery.Try wiggling the battery connections to see if this helps.(3)No cranking, and lights dim only slightly as you try to startThe trouble probably is in the starting motor. The pinion may not be engaging with the flywheel. If the starting-motor armature spins, the overrunning clutch is sleeping.(4)No cranking, and lights dim heavily as you try to startThis is most likely due to a run-down battery. It could be low temperature, too. The battery is much less efficient at low temperatures, and the engine oil is much thicker. This combination could prevent cranking, even though the battery is in fairly good condition. Also, the starting motor or engine could be jammed, or locked.(5)No cranking, and lights stay brightListen to hear if the magnetic solenoid is pulling the plunger in. you can hear this as a loud click. If nothing happens when you try to start , check the solenoid. Connect one end of a jumper wire to the solenoid battery terminal. Connect the other end to the small terminal on the solenoid that is connected to the ignition switch. If nothing happens, the trouble is in the solenoid. If the solenoid and starting motor work with the jumper wire connected, the trouble is in the ignition switch, or the wires connecting them.6.2Engine cranks slowly but does not startIt is very likely due to a run-down battery or defective battery. The battery is unable to spin the starting motor at normal speed. Low temperature could also be a factor here.It is also possible that the driver may have run the battery down trying to start. Some condition in the engine, or the fuel or ignition system, is preventing normal starting. The driver continued to try, however, until the battery ran down.7. Sliding-armature starting motorIt is used for heavy –duty diesel engine in particular.1―main winding 2―auxiliary winding 3―holding winding 4―solenoid switch5―stationary contact-point 6―tumbler bridge 7―release lever 8―locking paw9―return spring 10―release disk 11―armature 12―magnetic pole13―friction-disk clutchIn its rest position , the armature is displaced axially out of the field windings. The pinion is driven from the armature shaft by way of a multi-plate clutch(friction disk type). The starting motor has three field windings: the auxiliary winding, the holding winding(shunt-wound) and themain winding(series-wound). To permit the armature to move axially, it has extra-long bearings and a wide commutator. There is also a return spring, a control relay(or solenoid switch) with tumbler bridge and a locking paw with release disk.Engagement is in two stages. In stage 1, the armature is displaced by the magnetic field of the auxiliary and holding winding, so that the pinion engages with the flywheel ring gear, aided by the armature rotating slowly. In stage 2, the release disk on the commutator raises the release lever to switch on the second stage of the control relay. The main winding is then energized by way of the tumbler bridge in the control relay.A multi-plate clutch is installed between the armature and the pinion. It ensures that the drive is taken up smoothly between armature and pinion after the pinion has engaged with the flywheel ring gear. If the ring gear begins to drive the pinion after the engine has started, the clutch is freed and acts like a freewheel. This prevents dangerous acceleration forces from reaching the armature of the starting motor as the engine speeds up. If a given torque is exceeded at the pinion, the multi-plate clutch interrupts the power flow between armature and ring gear(overload protection). This minimizes loads on the starting motor,pinion and ring gear.8. Gear-reduction starting motorThis starting motor has a gear reduction which increases cranking torque. The shift lever(or fork)is enclosed. When it is actuated by the solenoid, it shifts the overrunning-clutch pinion into mesh with the flywheel. The gear ratio between the armature and flywheel, due to the extra gears(the gear ratio of this gear reduction is about 3~4), is 45 : 1 for example. The armature turns 45 times to turn the flywheel, and the engine crankshaft, once. This provides a high cranking torque for starting.There are three types of gear-reduction mechanism:Internal gearing typeExternal gearing typePlanetary gearing type9. Permanent magnet starting motorThis motor uses permanent magnet instead of magnetic field winding. It has some advantages such as simple construction, small volume and weight. But its power is low and the magnetism is reduced as time goes on.。