Automobile Electrical and Electronic Systems ( PDFDrive )

Engine performance Charging systems 147 The powertrain control modules (PCMs) usually con- account the mechanical to electrical energy conver- trol engine idle speed in two ways. The main method sion efficiency of the alternator, the result is a signif- is throttle control, using either a stepper motor or an icant torque load on the engine. If the set point air bypass valve. This is a good method but can be (regulated voltage) is reduced during hard acceler- relatively slow to react. Changes in ignition timing ation, the 0 to 60 time can be increased by as much are also used and this results in a good level of con- as 0.4 s (Figure 6.42). trol. However, there may be emission implications. Fault conditions One of the main causes of idle instability is the torque load that the alternator places on the engine. As well as communicating the load status of the Because a PCM control system is ‘aware’ of the alter- alternator to the PCM, the regulator can also provide nator load, it calculates the corresponding torque diagnostic information. In general the following load and sets the idle speed accordingly. Overall the fault situations can be communicated: idle can be set at a lower value thus reducing fuel consumption and emissions. Equally, when required, G No communication between regulator and PCM. the PCM can increase idle speed to increase alterna- G No alternator output due to mechanical fault (drive tor output and prevent battery drain. This would be likely to occur after a cold start, in the dark, when the belt for example). screen is frosted over. In these conditions it is likely G Loss of electrical connection to the alternator. that, because the driver would switch on lights, inter- G System over or under voltage due to short or open ior heaters and screen heaters, there would be an increased electrical load. In addition to the normal circuit field driver. electrical load (fuel, ignition, etc.), the battery would G Failure of rotor or stator windings. also create a high demand after a cold start. The PCM G Failure of a diode. can ensure that it sets an idle speed which results in sufficient alternator output to prevent battery drain. The PCM can initiate appropriate action in response to these failure conditions, for example, to allow fail- A dynamic adjustment to the set voltage point is safe operation or at least illuminate the warning light! also possible. This may be used during starting to Suitable test equipment can be used to aid diagnos- reduce load on the battery. It can also be used during tic work. transient engine loads or, in other words, during accel- eration. An alternator producing 70 A at 14 V is put- Network protocols – CAN and LIN ting out about 1 kW of power (P ϭ VI). Taking into The PWM communication system is proving to be very effective. However, a second system is already establishing itself as an industry standard. The system is known as local interconnect network (LIN). This is a protocol that allows communication between intelligent actuators and sensors. It is, in effect, a cut down version of the controller area network (CAN) protocol and is used where large bandwidth is not necessary. LIN enabled regulators are not yet in pro- duction but the protocol is starting to be used for body systems such as door locks and seat movement. Figure 6.42 Cutaway view of a modern alternator (Source: Summary Bosch Press) Smart or intelligent charging systems are here now, and are here to stay. The ability of the alternator regulator and engine control systems to communicate means new possibilities, increased efficiency and improved performance. New diagnostic equipment may be necessary but new diagnostic techniques certainly are required. However, remember that PWM signals can be exam- ined on a scope or even a duty cycle meter. And, if the voltage you measure across the battery is less than 13 V, it is probably not recharging – unless of course you are measuring it during a 0 to 60 acceleration test!

148 Automobile electrical and electronic systems 1. A only 2. B only 6.8 Self-assessment 3. Both A and B 4. Neither A nor B 6.8.1 Questions The three auxiliary diodes in a nine-diode alterna- 1. State the ideal charging voltage for a 12 V (nomi- tor provide direct current for the: nal) battery. 1. vehicle auxiliary circuits 2. initial excitation of the rotor 2. Describe the operation of an alternator with refer- 3. rotor field during charging ence to a rotating ‘permanent magnet’. 4. warning light simulator 3. Make a clearly labelled sketch to show a typical The purpose of the regulator in the charging system external alternator circuit. of a vehicle is to control: 1. engine speed 4. Explain how and why the output voltage of an 2. fuel consumption alternator is regulated. 3. generator input 4. generator output 5. Describe the differences between a star-wound and a delta-wound stator. The function of the zener diode in the electronic control unit of an alternator is to act as a: 6. Explain why connecting two extra diodes to the 1. current amplifier centre of a star-wound stator can increase the 2. voltage amplifier output of an alternator. 3. voltage switch 4. current switch 7. Draw a typical characteristic curve for an alterna- tor. Label each part with an explanation of its The charging voltage of an engine running at purpose. approximately 3000 rev/min should be: 1. 12.6 volts 8. Describe briefly how a rectifier works. 2. 14.2 volts 9. Explain the difference between a battery-sensed 3. 3 volts above battery voltage 4. the same as battery voltage and a machine-sensed alternator. 10. List five charging system faults and the associ- Rotor windings are connected and supplied by: 1. soldered connections ated symptoms. 2. crimped connections 3. adhesive bonding 6.8.2 Assignment 4. brushes and slip rings Investigate and test the operation of a charging sys- An alternator has been dismantled and the rotor tem on a vehicle. Produce a report in the standard slip rings are blackened with carbon deposits. format (as set out in Advanced Automotive Fault Technician A says clean them with a soft cloth and Diagnosis, Tom Denton (2000), Arnold). alcohol. Technician B says the rotor must be replaced. Who is right? Make recommendations on how the system could 1. A only be improved. 2. B only 3. Both A and B 6.8.3 Multiple choice questions 4. Neither A nor B The purpose of a rectifier in an alternator is to: When fitting a new rectifier pack it is usual to: 1. change AC to DC voltage 1. remove the stator winding 2. control alternator output current 2. replace the regulator 3. change DC to AC voltage 3. connect the battery lead 4. control alternator output voltage 4. unsolder the connections ‘Star’ and ‘Delta’ are types of: 1. rotor winding 2. stator winding 3. field winding 4. regulator winding Technician A says an alternator rotor uses semi conductor components to rectify the direct current to alternating current. Technician B says a stator winding for a light vehicle alternator will usually be connected in a ‘star’ formation. Who is right?

7 Starting systems 7.1 Requirements of the Typical starting limit temperatures are Ϫ18 ° C starting system to Ϫ25 ° C for passenger cars and Ϫ15 ° C to Ϫ20 ° C for trucks and buses. Figures from starter manufactur- 7.1.1 Engine starting ers are normally quoted at both ϩ20 ° C and Ϫ20 ° C. requirements Figure 7.1 Starting system as part of the complete electrical An internal combustion engine requires the fol- system lowing criteria in order to start and continue running. Figure 7.2 Starter torque and engine cranking torque G Combustible mixture. G Compression stroke. G A form of ignition. G The minimum starting speed (about 100 rev/min). In order to produce the first three of these, the min- imum starting speed must be achieved. This is where the electric starter comes in. The ability to reach this minimum speed is again dependent on a number of factors. G Rated voltage of the starting system. G Lowest possible temperature at which it must still be possible to start the engine. This is known as the starting limit temperature. G Engine cranking resistance. In other words the torque required to crank the engine at its starting limit temperature (including the initial stalled torque). G Battery characteristics. G Voltage drop between the battery and the starter. G Starter-to-ring gear ratio. G Characteristics of the starter. G Minimum cranking speed of the engine at the starting limit temperature. It is not possible to view the starter as an isolated component within the vehicle electrical system, as Figure 7.1 shows. The battery in particular is of prime importance. Another particularly important consideration in relation to engine starting requirements is the starting limit temperature. Figure 7.2 shows how, as tempera- ture decreases, starter torque also decreases and the torque required to crank the engine to its minimum speed increases.

150 Automobile electrical and electronic systems capacity at Ϫ20 ° C, is connected to the starter by a cable with a resistance of 1 m⍀. These criteria will 7.1.2 Starting system design ensure the starter is able to operate even under the most adverse conditions. The actual output of the The starting system of any vehicle must meet a starter can now be measured under typical operat- number of criteria in excess of the eight listed ing conditions. The rated power of the motor corre- above. sponds to the power drawn from the battery less copper losses (due to the resistance of the circuit), G Long service life and maintenance free. iron losses (due to eddy currents being induced in G Continuous readiness to operate. the iron parts of the motor) and friction losses. G Robust, such as to withstand starting forces, Figure 7.4 shows an equivalent circuit for a vibration, corrosion and temperature cycles. starter and battery. This indicates how the starter G Lowest possible size and weight. output is very much determined by line resistance and battery internal resistance. The lower the total Figure 7.3 shows the starting system general layout. resistance, the higher the output from the starter. It is important to determine the minimum cranking speed for the particular engine. This varies consid- There are two other considerations when design- erably with the design and type of engine. Some ing a starting system. The location of the starter on typical values are given in Table 7.1 for a tempera- the engine is usually pre-determined, but the pos- ture of Ϫ20 ° C. ition of the battery must be considered. Other con- straints may determine this, but if the battery is closer The rated voltage of the system for passenger to the starter the cables will be shorter. A longer run cars is, almost without exception, 12 V. Trucks and will mean cables with a greater cross-section are buses are generally 24 V as this allows the use of needed to ensure a low resistance. Depending on the half the current that would be required with a 12 V intended use of the vehicle, special sealing arrange- system to produce the same power. It will also con- ments on the starter may be necessary to prevent siderably reduce the voltage drop in the wiring, as the ingress of contaminants. Starters are available the length of wires used on commercial vehicles is designed with this in mind. This may be appropriate often greater than passenger cars. for off-road vehicles. The rated output of a starter motor can be 7.1.3 Choosing a starter motor determined on a test bench. A battery of maximum capacity for the starter, which has a 20% drop in As a guide, the starter motor must meet all the criteria previously discussed. Referring back to Figure 7.2 (the data showing engine cranking torque compared with minimum cranking speed) will determine the torque required from the starter. Manufacturers of starter motors provide data in the form of characteristic curves. These are discussed in more detail in the next section. The data will Figure 7.3 Starter system general layout Table 7.1 Typical minimum cranking speeds Engine Minimum cranking speed (rev/min) Reciprocating spark ignition 60–90 Figure 7.4 Equivalent circuit for a starter system Rotary spark ignition 150–180 Diesel with glow plugs 60–140 Diesel without glow plugs 100–200

show the torque, speed, power and current con- Starting systems 151 sumption of the starter at ϩ20 ° C and Ϫ20 ° C. The power rating of the motor is quoted as the maximum of 16 Nm. This is working on the assumption that output at Ϫ20 ° C using the recommended battery. stalled torque is generally three to four times the cranking torque. Figure 7.5 shows how the required power output of the starter relates to the engine size. Torque is converted to power as follows: As a very general guide the stalled (locked) starter P ϭ T␻ torque required per litre of engine capacity at the starting limit temperature is as shown in Table 7.2. where P ϭ power, T ϭ torque and ␻ ϭ angular velocity. A greater torque is required for engines with a lower number of cylinders due to the greater piston ␻ ϭ 2␲n displacement per cylinder. This will determine the 60 peak torque values. The other main factor is com- pression ratio. where n ϭ rev/min. In this example, the power developed at To illustrate the link between torque and power, we can assume that, under the worst conditions 1000 rev/min with a torque of 16 Nm (at the starter) (Ϫ20 ° C), a four-cylinder 2-litre engine requires is about 1680 W. Referring back to Figure 7.5, the 480 Nm to overcome static friction and 160 Nm to ideal choice would appear to be the starter marked (e). maintain the minimum cranking speed of 100 rev/ min. With a starter pinion-to-ring gear ratio of 10 : 1, The recommended battery would be 55 Ah and the motor must therefore, be able to produce a max- 255 A cold start performance. imum stalled torque of 48 Nm and a driving torque 7.2 Starter motors and circuits 7.2.1 Starting system circuits In comparison with most other circuits on the modern vehicle, the starter circuit is very simple. The prob- lem to be overcome, however, is that of volt drop in the main supply wires. The starter is usually operated by a spring-loaded key switch, and the same switch also controls the ignition and accessories. The supply from the key switch, via a relay in many cases, causes the starter solenoid to operate, and this in turn, by a set of contacts, controls the heavy current. In some cases an extra terminal on the starter solen- oid provides an output when cranking, which is usually used to bypass a dropping resistor on the ignition or fuel pump circuits. The basic circuit for the starting system is shown in Figure 7.6. Figure 7.5 Power output of the starter compared with engine size Table 7.2 Torque required for various engine sizes Figure 7.6 Basic starting circuit Engine cylinders Torque per litre [Nm] 2 12.5 4 8.0 6 6.5 8 6.0 12 5.5

152 Automobile electrical and electronic systems created by heavy duty series windings wound around soft iron pole shoes. Due to improvements The problem of volt drop in the main supply cir- in magnet technology, permanent magnet fields cuit is due to the high current required by the starter, allowing a smaller and lighter construction are particularly under adverse starting conditions such replacing wire-wound fields. The strength of the as very low temperatures. magnetic field created around the conductors in the armature is determined by the value of the current A typical cranking current for a light vehicle flowing. The principle of a DC motor is shown in engine is of the order of 150 A, but this may peak in Figure 7.7. excess of 500 A to provide the initial stalled torque. It is generally accepted that a maximum volt drop Most starter designs use a four-pole four-brush of only 0.5 V should be allowed between the battery system. Using four field poles concentrates the and the starter when operating. An Ohm’s law cal- magnetic field in four areas as shown in Figure 7.8. culation indicates that the maximum allowed circuit The magnetism is created in one of three ways, per- resistance is 2.5 m⍀ when using a 12 V supply. This manent magnets, series field windings or series– is a worst case situation and lower resistance values parallel field windings. are used in most applications. The choice of suit- able conductors is therefore very important. Figure 7.9 shows the circuits of the two methods where field windings are used. The series–parallel 7.2.2 Principle of operation fields can be constructed with a lower resistance, thereby increasing the current and hence torque of The simple definition of any motor is a machine to convert electrical energy into mechanical energy. Figure 7.8 Four-pole magnetic field The starter motor is no exception. When current flows through a conductor placed in a magnetic field, a force is created acting on the conductor relative to the field. The magnitude of this force is proportional to the field strength, the length of the conductor in the field and the current flowing in the conductor. In any DC motor, the single conductor is of no practical use and so the conductor is shaped into a loop or many loops to form the armature. A many- segment commutator allows contact via brushes to the supply current. The force on the conductor is created due to the interaction of the main magnetic field and the field created around the conductor. In a light vehi- cle starter motor, the main field was traditionally Figure 7.7 Interaction of two mag- netic fields results in rotation when a commutator is used to reverse the supply each half turn

the motor. Four brushes are used to carry the heavy Starting systems 153 current. The brushes are made of a mixture of cop- per and carbon, as is the case for most motor or gen- motors tend to use wave winding as this technique erator brushes. Starter brushes have a higher copper gives the most appropriate torque and speed char- content to minimize electrical losses. Figure 7.10 acteristic for a four-pole system. shows some typical field coils with brushes attached. The field windings on the right are known A starter must also have some method of as wave wound. engaging with, and release from, the vehicle’s fly- wheel ring gear. In the case of light vehicle starters, The armature consists of a segmented copper this is achieved either by an inertia-type engage- commutator and heavy duty copper windings. The ment or a pre-engagement method. These are both windings on a motor armature can, broadly speaking, discussed further in subsequent sections. be wound in two ways. These are known as lap winding and wave winding. Figure 7.11 shows the 7.2.3 DC motor characteristics difference between these two methods. Starter It is possible to design a motor with characteristics that are most suitable for a particular task. For a comparison between the main types of DC motor, the speed–torque characteristics are shown in Figure 7.9 Starter internal circuits Figure 7.11 Typical lap and wave wound armature circuits Figure 7.10 Typical field coils and brushes

154 Automobile electrical and electronic systems Figure 7.14 Series wound motor Figure 7.12 Speed and torque characteristics of DC motors Figure 7.15 Compound wound motor Figure 7.13 Shunt wound motor (parallel wound) connected, which is either across the armature or across the armature and series winding. Large starter Figure 7.12. The four main types of motor are motors are often compound wound and can be oper- referred to as shunt wound, series wound, com- ated in two stages. The first stage involves the shunt pound wound and permanent magnet excitation. winding being connected in series with the armature. This unusual connection allows for low meshing In shunt wound motors, the field winding is torque due to the resistance of the shunt winding. connected in parallel with the armature as shown in When the pinion of the starter is fully in mesh with Figure 7.13. Due to the constant excitation of the the ring gear, a set of contacts causes the main supply fields, the speed of this motor remains constant, to be passed through the series winding and armature virtually independent of torque. giving full torque. The shunt winding will now be connected in parallel and will act in such a way as to Series wound motors have the field and arma- limit the maximum speed of the motor. ture connected in series. Because of this method of connection, the armature current passes through the Permanent magnet motors are smaller and sim- fields making it necessary for the field windings to pler compared with the other three discussed. Field consist usually of only a few turns of heavy wire. excitation, as the name suggests, is by permanent When this motor starts under load the high initial magnet. This excitation will remain constant under current, due to low resistance and no back EMF, all operating conditions. Figure 7.16 shows the generates a very strong magnetic field and there- accepted representation for this type of motor. fore high initial torque. This characteristic makes the series wound motor ideal as a starter motor. The characteristics of this type of motor are Figure 7.14 shows the circuit of a series wound motor. broadly similar to the shunt wound motors. However, when one of these types is used as a starter motor, The compound wound motor, as shown in the drop in battery voltage tends to cause the motor Figure 7.15, is a combination of shunt and series to behave in a similar way to a series wound machine. wound motors. Depending on how the field wind- In some cases though, the higher speed and lower ings are connected, the characteristics can vary. torque characteristic are enhanced by using an inter- The usual variation is where the shunt winding is mediate transmission gearbox inside the starter motor.

Starting systems 155 Figure 7.16 Permanent magnet motor Figure 7.18 Inertia type starter Figure 7.17 Starter motor characteristic curves gear only during the starting phase. If the connec- tion remained permanent, the excessive speed at Information on particular starters is provided in which the starter would be driven by the engine the form of characteristic curves. Figure 7.17 shows would destroy the motor almost immediately. the details for a typical light vehicle starter motor. The inertia type of starter motor has been the This graph shows how the speed of the motor technique used for over 80 years, but is now becom- varies with load. Owing to the very high speeds ing redundant. The starter shown in Figure 7.18 is developed under no load conditions, it is possible to the Lucas M35J type. It is a four-pole, four-brush damage this type of motor. Running off load due to machine and was used on small to medium-sized the high centrifugal forces on the armature may cause petrol engined vehicles. It is capable of producing the windings to be destroyed. Note that the max- 9.6 Nm with a current draw of 350 A. The M35J imum power of this motor is developed at mid- uses a face-type commutator and axially aligned range speed but maximum torque is at zero speed. brush gear. The fields are wave wound and are earthed to the starter yoke. 7.3 Types of starter motor The starter engages with the flywheel ring gear 7.3.1 Inertia starters by means of a small pinion. The toothed pinion and a sleeve splined on to the armature shaft are In all standard motor vehicle applications it is threaded such that when the starter is operated, via necessary to connect the starter to the engine ring a remote relay, the armature will cause the sleeve to rotate inside the pinion. The pinion remains still due to its inertia and, because of the screwed sleeve rotating inside it, the pinion is moved to mesh with the ring gear. When the engine fires and runs under its own power, the pinion is driven faster than the armature shaft. This causes the pinion to be screwed back along the sleeve and out of engagement with the flywheel. The main spring acts as a buffer when the pinion first takes up the driving torque and also acts as a buffer when the engine throws the pinion back out of mesh. One of the main problems with this type of starter was the aggressive nature of the engagement. This tended to cause the pinion and ring gear to wear prematurely. In some applications the pinion tended to fall out of mesh when cranking due to the engine almost, but not quite, running. The pinion was also prone to seizure often due to contamination by dust from the clutch. This was often compounded by application of oil to the pinion mechanism, which tended to attract even more dust and thus prevent engagement.

156 Automobile electrical and electronic systems Figure 7.19 Pre-engaged starter The pre-engaged starter motor has largely over- come these problems. 7.3.2 Pre-engaged starters Figure 7.20 Starter circuit Pre-engaged starters are fitted to the majority of winding holds the plunger in position as long as the vehicles in use today. They provide a positive solenoid is supplied from the key switch. engagement with the ring gear, as full power is not applied until the pinion is fully in mesh. They pre- When the engine starts and the key is released, vent premature ejection as the pinion is held into the main supply is removed and the plunger and mesh by the action of a solenoid. A one-way clutch pinion return to their rest positions under spring is incorporated into the pinion to prevent the starter tension. A lost motion spring located on the plunger motor being driven by the engine. One example of ensures that the main contacts open before the pin- a pre-engaged starter in common use is shown in ion is retracted from mesh. Figure 7.19, the Bosch EF starter. During engagement, if the teeth of the pinion hit Figure 7.20 shows the circuit associated with the teeth of the flywheel (tooth to tooth abutment), operating this type of pre-engaged starter. The basic the main contacts are allowed to close due to the operation of the pre-engaged starter is as follows. engagement spring being compressed. This allows When the key switch is operated, a supply is made the motor to rotate under power and the pinion will to terminal 50 on the solenoid. This causes two slip into mesh. windings to be energized, the hold-on winding and the pull-in winding. Note that the pull-in winding is Figure 7.21 shows a sectioned view of a one-way of very low resistance and hence a high current clutch assembly. The torque developed by the starter flows. This winding is connected in series with the is passed through the clutch to the ring gear. The motor circuit and the current flowing will allow purpose of this free-wheeling device is to prevent the motor to rotate slowly to facilitate engagement. At the same time, the magnetism created in the solenoid attracts the plunger and, via an operating lever, pushes the pinion into mesh with the flywheel ring gear. When the pinion is fully in mesh the plunger, at the end of its travel, causes a heavy-duty set of copper contacts to close. These contacts now supply full battery power to the main circuit of the starter motor. When the main contacts are closed, the pull-in winding is effectively switched off due to equal voltage supply on both ends. The hold-on

Starting systems 157 Figure 7.21 One-way roller clutch drive pinion the starter being driven at an excessively high speed Permanent magnets provide constant excitation if the pinion is held in mesh after the engine has and it would be reasonable to expect the speed and started. The clutch consists of a driving and driven torque characteristic to be constant. member with several rollers between the two. The rollers are spring loaded and either wedge-lock the However, due to the fall in battery voltage under two members together by being compressed against load and the low resistance of the armature windings, the springs, or free-wheel in the opposite direction. the characteristic is comparable to series wound motors. In some cases, flux concentrating pieces or Many variations of the pre-engaged starter are in interpoles are used between the main magnets. Due common use, but all work on similar lines to the to the warping effect of the magnetic field, this above description. The wound field type of motor tends to make the characteristic curve very similar has now largely been replaced by the permanent to that of the series motor. magnet version. Development by some manufacturers has also 7.3.3 Permanent magnet taken place in the construction of the brushes. starters A copper and graphite mix is used but the brushes are made in two parts allowing a higher copper con- Permanent magnet starters began to appear on pro- tent in the power zone and a higher graphite content duction vehicles in the late 1980s. The two main in the commutation zone. This results in increased advantages of these motors, compared with conven- service life and a reduction in voltage drop, giving tional types, are less weight and smaller size. This improved starter power. Figure 7.23 shows a mod- makes the permanent magnet starter a popular choice ern permanent magnet (PM) starter. by vehicle manufacturers as, due to the lower lines of today’s cars, less space is now available for engine For applications with a higher power require- electrical systems. The reduction in weight provides ment, permanent magnet motors with intermediate a contribution towards reducing fuel consumption. transmission have been developed. These allow the armature to rotate at a higher and more efficient The standard permanent magnet starters cur- speed whilst still providing the torque, due to the rently available are suitable for use on spark igni- gear reduction. Permanent magnet starters with tion engines up to about 2 litre capacity. They are intermediate transmission are available with power rated in the region of 1 kW. A typical example is the outputs of about 1.7 kW and are suitable for spark Lucas Model M78R/M80R shown in Figure 7.22. ignition engines up to about 3 litres, or compression ignition engines up to about 1.6 litres. This form of The principle of operation is similar in most permanent magnet motor can give a weight saving respects to the conventional pre-engaged starter of up to 40%. The principle of operation is again motor. The main difference being the replacement similar to the conventional pre-engaged starter. The of field windings and pole shoes with high quality intermediate transmission, as shown in Figure 7.24, permanent magnets. The reduction in weight is in is of the epicyclic type. the region of 15% and the diameter of the yoke can be reduced by a similar factor. The sun gear is on the armature shaft and the planet carrier drives the pinion. The ring gear or

158 Automobile electrical and electronic systems where A ϭ number of teeth on the annulus, and S ϭ number of teeth on the sun gear. annulus remains stationary and also acts as an inter- mediate bearing. This arrangement of gears gives a The annulus gear in some types is constructed reduction ratio of about 5 : 1. This can be calculated from a high grade polyamide compound with min- by the formula: eral additives to improve strength and wear resist- ance. The sun and planet gears are conventional Ratio = AS steel. This combination of materials gives a quieter S Figure 7.22 Lucas M78R/M80R starter Figure 7.23 Modern permanent magnet starter (Source: Figure 7.24 Starter motor intermediate transmission Bosch Press)

and more efficient operation. Figure 7.25 shows a Starting systems 159 PM starter with intermediate transmission, together with its circuit and operating mechanism. 7.3.4 Heavy vehicle starters Figure 7.25 Pre-engaged starter and details (Bosch) The subject area of this book is primarily the elec- trical equipment on cars. This short section is included for interest, hence further reference should be made to other sources for greater detail about heavy vehicle starters. The types of starter that are available for heavy duty applications are as many and varied as the applications they serve. In general, higher voltages are used, which may be up to 110 V in specialist cases, and two starters may even be running in par- allel for very high power and torque requirements. Large road vehicles are normally 24 V and employ a wide range of starters. In some cases the design is simply a large and heavy duty version of the pre-engaged type discussed earlier. The Delco- Remy 42-MT starter shown in Figure 7.26 is a good example of this type. This starter may also be fitted with a thermal cut-out to prevent overheating dam- age due to excessive cranking. Rated at 8.5 kW, it is capable of producing over 80 Nm torque at 1000 rev/min. Other methods of engaging the pinion include sliding the whole armature or pushing the pinion with a rod through a hollow armature. This type uses a solenoid to push the pinion into mesh via a rod through the centre of the armature. Sliding-armature-type starters work by position- ing the field windings forwards from the main armature body, such that the armature is attracted Figure 7.26 Delco-Remy 42-MT starter

160 Automobile electrical and electronic systems Figure 7.27 Integrated starter alternator damper (Source: Bosch Press) forwards when power is applied. A trip lever mech- anism will then only allow full power when the control will be supported by an ECU. The electronic armature has caused the pinion to mesh. starter incorporates a static relay on a circuit board integrated into the solenoid switch. This will pre- 7.3.5 Integrated starters vent cranking when the engine is running. A device called a ‘dynastart’ was used on a number ‘Smart’ features can be added to improve com- of vehicles from the 1930s through to the 1960s. fort, safety and service life. This device was a combination of the starter and a dynamo. The device, directly mounted on the crank- G Starter torque can be evaluated in real time to shaft, was a compromise and hence not very efficient. tell the precise instant of engine start. The starter can be simultaneously shut off to reduce wear The method is now known as an Integrated and noise generated by the free-wheel phase. Starter Alternator Damper (ISAD). It consists of an electric motor, which functions as a control element G Thermal protection of the starter components between the engine and the transmission, and can allows optimization of the components to save also be used to start the engine and deliver elec- weight and to give short circuit protection. trical power to the batteries and the rest of the vehicle systems. The electric motor replaces the G Electrical protection also reduces damage from mass of the flywheel. misuse or system failure. The motor transfers the drive from the engine G Modulating the solenoid current allows redesign and is also able to act as a damper/vibration absorber of the mechanical parts allowing a softer oper- unit. The damping effect is achieved by a rotation ation and weight reduction. capacitor. A change in relative speed between the rotor and the engine due to the vibration, causes It will even be possible to retrofit this system to one pole of the capacitor to be charged. The effect existing systems. of this is to take the energy from the vibration. 7.3.7 Starter installation Using ISAD to start the engine is virtually noiseless, and cranking speeds of 700 rev/min are Starters are generally mounted in a horizontal pos- possible. Even at Ϫ25 ° C it is still possible to crank ition next to the engine crankcase with the drive at about 400 rev/min. A good feature of this is that a pinion in a position for meshing with the flywheel stop/start function is possible as an economy and or drive plate ring gear. emissions improvement technique. Because of the high speed cranking, the engine will fire up in about The starter can be secured in two ways: either by 0.1–0.5 seconds. flange or cradle mounting. Flange mounting is the most popular technique used on small and medium- The motor can also be used to aid with acceler- sized vehicles and, in some cases, it will incorporate ation of the vehicle. This feature could be used to a further support bracket at the rear of the starter allow a smaller engine to be used or to enhance the to reduce the effect of vibration. Larger vehicle performance of a standard engine. When used in alternator mode, the ISAD can produce up to 2 kW at idle speed. It can supply power at different voltages as both AC and DC. Through the application of intelligent control electronics, the ISAD can be up to 80% efficient. Citroën have used the ISAD system in a Xsara model prototype. The car can produce 150 Nm for up to 30 seconds, which is significantly more than the 135 Nm peak torque of the 1580 cc, 65 kW fuel injected version. Citroën call the system ‘Dynalto’. A 220 V outlet is even provided inside the car to power domestic electrical appliances! 7.3.6 Electronic starter control ‘Valeo’ have developed an electronic switch that can be fitted to its entire range of starters. Starter

Starting systems 161 reliable and longer lasting. It is interesting to note that, assuming average mileage, the modern starter is used about 2000 times a year in city traffic! This level of reliability has been achieved by many years of research and development. Figure 7.28 Flange mounting is used for most light vehicle 7.4 Case studies starter motors 7.4.1 Ford starters are often cradle mounted but again also use the flange mounting method, usually fixed with at The circuit shown in Figure 7.29 is from a vehicle least three large bolts. In both cases the starters fitted with manual or automatic transmission. The must have some kind of pilot, often a ring machined inhibitor circuits will only allow the starter to oper- on the drive end bracket, to ensure correct position- ate when the automatic transmission is in ‘park’ or ing with respect to the ring gear. This will ensure ‘neutral’. Similarly for the manual version, the starter correct gear backlash and a suitable out of mesh will only operate if the clutch pedal is depressed. clearance. Figure 7.28 shows the flange mountings method used for most light vehicle starter motors. The starter relay coil is supplied with the posi- tive connection by the key switch. The earth path is Clearly the main load on the vehicle battery is the connected through the appropriate inhibitor switch. starter and this is reflected in the size of supply cable To prevent starter operation when the engine is run- required. Any cable carrying a current will experi- ning the power control module (EEC V) controls ence power loss known as I2R loss. In order to reduce the final earth path of the relay. this power loss, the current or the resistance must be reduced. In the case of the starter the high current is A resistor fitted across the relay coil reduces the only way of delivering the high torque. This is the back EMF. The starter in current use is a standard reason for using heavy conductors to the starter to pre-engaged, permanent magnet motor. ensure low resistance, thus reducing the volt drop and power loss. The maximum allowed volt drop is 0.5 V 7.4.2 Toyota on a 12 V system and 1 V on a 24 V system. The short circuit (initial) current for a typical car starter is The starter shown in Figure 7.30 has been in use for 500 A and for very heavy applications can be 3000 A. several years but is included because of its unusual design. The drive pinion incorporates the normal Control of the starter system is normally by a clutch assembly but is offset from the armature. spring-loaded key switch. This switch will control Drive to the pinion is via a gear set with a ratio of the current to the starter solenoid, in many cases via about 3 : 1. The idle gear means the pinion rotates in a relay. On vehicles with automatic transmission, the same direction as the armature. an inhibitor switch to prevent the engine being started in gear will also interrupt this circuit. Ball bearings are used on each end of the arma- ture and pinion. The idler gear incorporates a roller Diesel engined vehicles may have a connection bearing. The solenoid acts on the spring and steel between the starter circuit and a circuit to control ball to move the pinion into mesh. The electrical the glow plugs. This may also incorporate a timer operation of the machine is standard. It has four relay. On some vehicles the glow plugs are activated brushes and four field poles. by a switch position just before the start position. 7.4.3 Ford integrated starter- 7.3.8 Summary generator (ISG) The overall principle of starting a vehicle engine Ford has produced a new integrated starter-generator with an electric motor has changed little in over 80 and 42-volt electric system that will be used by an years. Of course, the motors have become far more Explorer over the next few years. The vehicle will achieve breakthrough levels of fuel economy and offer more high-tech comfort and convenience fea- tures. It will use the new higher voltage electrical system that enables several fuel saving functions, including the ability to shut off the engine when the vehicle is stopped and to start it instantly on demand.

162 Automobile electrical and electronic systems Figure 7.29 Starter circuit as used by Ford The integrated starter-generator, as its name restarts smoothly and instantly when any demand implies, replaces both the conventional starter and for power is detected. This ‘stop/start’ function alternator in a single electric device. A vehicle provides fuel savings and reduced emissions. equipped with the ISG system could be considered G Regenerative Braking: This feature collects a mild hybrid because it is capable of most of the energy created from braking and uses it to functions of a hybrid electric vehicle. recharge the vehicle’s batteries. This allows items such as the headlights, stereo and climate control There are three functions common to both a full system to continue to operate when the engine hybrid electric vehicle and ISG, or mild hybrid, and shuts off. By greatly reducing the amount of a fourth function unique to a full HEV: electric power that must be generated by the engine, regenerative braking significantly reduces G Start/Stop: When the engine is not needed, such fuel consumption. as at a stoplight, it automatically turns off. It

Starting systems 163 Figure 7.30 Toyota starter motor components Figure 7.31 Engine fitted with an integrated starter generator at start-up and during hard acceleration, providing (Source: Ford) short bursts of added power. Because the ISG system uses a 42-volt battery and the hybrid G Electrical Assist: Internal combustion engines electric vehicle uses a 300-volt battery with a on both types of systems receive assistance from much larger energy capacity, the HEV electrical an electric motor, but in vastly different ways. assist is capable of providing much more power, The electrical assist ISG system helps the engine more frequently and for a longer duration. G Electric Drive: Only full hybrids have the ability to drive in electric-only mode. In the Escape HEV, this means the SUV’s electric motor can drive the vehicle at low speeds (under 30 mph (km)) while the engine is off. The capacity for electric-only drive clearly separates a full hybrid electric vehicle from a mild hybrid vehicle using an ISG system. In addition to the 42-volt battery and integrated starter generator the system is comprised of three major components: a slightly modified V-6 engine, new auto matic transmission and an inverter/motor controller. When restarting, DC power from the battery is processed by the inverter/motor controller and sup- plied as adjustable frequency AC power to the ISG. The frequency of the AC power is controlled to bring the engine up to idle speed in a small fraction of a second. Regenerative braking captures energy normally lost as heat energy during braking. The ISG absorbs power during vehicle deceleration, converts it to DC

164 Automobile electrical and electronic systems Escape HEV ISG 42-Volt SUV Mild Hybrid Full Hybrid 12-Volt Integrated Starter 12-Volt Battery Engine Battery Generator (ISG) Electric Transmission Transmission Motor 300-Volt Battery Pack 42-Volt Figure 7.32 Hybrid electric vehi- Battery Pack cle (HEV) compared to an ISG (Source: Ford) Figure 7.33 42 V Integrated starter generator (ISG) (Source: Ford) 10 kW Electric Machine power and recharges the battery. Electro-hydraulic brakes replace the vacuum booster and micro- (Mounted to Crank) processors control the operation of front and rear brakes to maintain vehicle stability while braking. 42V EPAS 42V Battery Pack The vehicle’s mechanical brakes are coordinated with the ISG, so the difference between mechanical 12-V Battery and regenerative brakes is transparent to the driver. (Down-sized) IMC The ISG also provides added power and perform- ance. The ISG delivers battery power to the wheels (Inverter Motor Controller) to assist the engine during vehicle launch. The ISG is also referred to as an integrated starter alternator Figure 7.34 42 V ISG installation in the SUV (Source: Ford) damper (ISAD) (Ford Motor Company, 2001).1 1Ford Press, 2001. Ford Explorer to Feature Hybrid Electric Technology, Ford Motor Company.

Starting systems 165 Table 7.3 Common symptoms of a charging system malfunction and possible faults Symptom Possible fault Engine does not rotate when trying to start G Battery connection loose or corroded. G Battery discharged or faulty. Starter noisy G Broken, loose or disconnected wiring in the starter or circuit. Starter turns engine slowly G Defective starter switch or automatic gearbox inhibitor switch. G Starter pinion or flywheel ring gear loose. G Earth strap broken, loose or corroded. G Starter pinion or flywheel ring gear loose. G Starter mounting bolts loose. G Starter worn (bearings etc.). G Discharged battery (starter may jump in and out). G Discharged battery (slow rotation). G Battery terminals loose or corroded. G Earth strap or starter supply loose or disconnected. G High resistance in supply or earth circuit. G Internal starter fault. 7.5 Diagnosing starting The idea of these tests is to see if the circuit is sup- system faults plying all the available voltage to the starter. If it is, then the starter is at fault, if not then the circuit is 7.5.1 Introduction at fault. As with all systems, the six stages of fault-finding If the starter is found to be defective then a should be followed. replacement unit is the normal recommendation. Figure 7.35 explains the procedure used by Bosch to 1. Verify the fault. ensure quality exchange units. Repairs are possible 2. Collect further information. but only if the general state of the motor is good. 3. Evaluate the evidence. 4. Carry out further tests in a logical sequence. 7.6 Advanced starting 5. Rectify the problem. system technology 6. Check all systems. 7.6.1 Speed, torque and power The procedure outlined in the next section is related primarily to stage 4 of the process. Table 7.3 lists To understand the forces acting on a starter motor some common symptoms of a charging system let us first consider a single conducting wire in a malfunction together with suggestions for the pos- magnetic field. The force on a single conductor in a sible fault. magnetic field can be calculated by the formula: 7.5.2 Circuit testing procedure F ϭ BIl The process of checking a 12 V starting system where F ϭ force in N, l ϭ length of conductor in operation is as follows (tests 3 to 8 are all carried the field in m, B ϭ magnetic field strength in Wb/m2, out while trying to crank the engine). I ϭ current flowing in the conductor in amps. 1. Battery (at least 70%). Fleming’s left-hand rule will serve to give the 2. Hand and eye checks. direction of the force (the conductor is at 90 ° to the 3. Battery volts (minimum 10 V). field). 4. Solenoid lead (same as battery). 5. Starter voltage (no more than 0.5 V less than This formula may be further developed to calcu- late the stalled torque of a motor with a number of battery). armature windings as follows: 6. Insulated line volt drop (maximum 0.25 V). 7. Solenoid contacts volt drop (almost 0 V). T ϭ BIlrZ 8. Earth line volt drop (maximum 0.25 V). where T ϭ torque in Nm, r ϭ armature radius in m, and Z ϭ number of active armature conductors.

166 Automobile electrical and electronic systems Figure 7.35 Quality starter overhaul procedure This will only produce a result for stalled or lock revs/second, Z ϭ number of armature conductors, torque because, when a motor is running, a back c ϭ 2p for lap-wound and 2 for a wave-wound EMF is produced in the armature windings. This machine. opposes the applied voltage and hence reduces the current flowing in the armature winding. In the The formula can be re-written for calculating case of a series wound starter motor, this will also motor speed: reduce the field strength B. The armature current in a motor is given by the equation: n ϭ ce 2 p␾Z Iϭ VϪe R If the constants are removed from this formula it clearly shows the relationship between field flux, where I ϭ armature current in amps, V ϭ applied speed and back EMF, voltage in volts, R ϭ resistance of the armature in ohms, e ϭ total back EMF in volts. nϰ e ␾ From the above it should be noted that, at the instant of applying a voltage to the terminals of a To consider the magnetic flux (␾) it is necessary to motor, the armature current will be at a maximum differentiate between permanent magnet starters since the back EMF is zero. As soon as the speed and those using excitation via windings. Permanent increases so will the back EMF and hence the magnetism remains reasonably constant. The con- armature current will decrease. This is why a starter struction and design of the magnet determine its motor produces ‘maximum torque at zero rev/min’. strength. Flux density can be calculated as follows: For any DC machine the back EMF is given by: B ϭ ␾ (units: T (tesla) or Wb/m2) A e ϭ 2p␾nZ c where A ϭ area of the pole perpendicular to the flux. Pole shoes with windings are more complicated where e ϭ back EMF in volts, p ϭ number of pairs of poles, ␾ ϭ flux per pole in webers, n ϭ speed in as the flux density depends on the material of the pole shoe as well as the coil and the current flowing.

The magneto-motive force (MMF) of a coil is Starting systems 167 determined thus: Figure 7.36 Belt-driven starter-generator concept (Source: MMF ϭ NI Ampere turns Gates) where N ϭ the number of turns on the coil and called I2R losses. Mechanical losses include fric- I ϭ the current flowing in the coil. tion and windage (air) losses. Magnetic field strength H requires the active Using the previous example of a 1 kW starter it length of the coil to be included: can be seen that, at an efficiency of 60%, this motor will require a supply of about 1.7 kW. H ϭ NI l From a nominal 12 V supply and allowing for battery volt drop, a current of the order of 170 A where l ϭ active length of the coil, H ϭ magnetic will be required to achieve the necessary power. field strength. 7.7 New developments in In order to convert this to flux density B, the per- starting systems meability of the pole shoe must be included: 7.7.1 Belt-driven B ϭ H␮0␮r starter-generator where ␮0 ϭ permeability of free space (4 ϫ 10Ϫ7 Henry/metre), and ␮r ϭ relative permeability of Gates, well known as manufacturers of drive belts, the core to free space. are working on a starter-generator concept that is belt driven. This work has been carried out in con- To calculate power consumed is a simple task junction with Visteon. It is known as the Visteon/ using the formula: Gates E-M DRIVE System. It is an electro- mechanical system made up of a high efficiency P ϭ T␻ induction motor, long-life belt-drive system and sophisticated electronic controls. The belt-driven where P ϭ power in watts, T ϭ torque in Nm, and starter-generator replaces the current alternator and ␻ ϭ angular velocity in rad/s. has a similar space requirement. Here is a simple example of the use of this One of the key components of this system, in formula. An engine requires a minimum cranking addition to the starter-generator is a hydraulic ten- speed of 100 rev/min and the required torque to sioner. This must be able to prevent significant achieve this is 9.6 Nm. movement during starting but also control system dynamics during acceleration and deceleration of At a 10 : 1 ring gear to pinion ratio this will the engine. A dual pulley tensioner concept is shown require a 1000 rev/min starter speed (n). To convert below. this to rad/s: The combination of Visteon’s motor design and ␻ ϭ 2␲n Gates’ belt technology has led to the development 60 of a highly robust and economical power manage- ment system. The starter-generator is driven by a This works out to 105 rad/s. P ϭ T␻ 9.6 ϫ 105 ϭ 1000 W or 1 kW 7.6.2 Efficiency Efficiency ϭ Power out/Power in (ϫ100%) The efficiency of most starter motors is of the order of 60%. 1 kW/60% ϭ 1.67 kW (the required input power) The main losses, which cause this, are iron losses, copper losses and mechanical losses. Iron losses are due to hysteresis loss caused by changes in magnetic flux, and also due to induced eddy currents in the iron parts of the motor. Copper losses are caused by the resistance of the windings; sometimes