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By LEO SIMPSON Released on to the Australian market only a few months ago, the Holden VN Commodore represents another stage in the integration of electronics into automobiles. It is a large car with a big motor but electronics enables it to give a high level of performance with improved fuel economy. It must come as a surprise to many people to learn that the new VN Commodore has the biggest six cylinder motor ever fitted into a Holden. It is a whopping 3.8 litre V6. As you might expect, it offers sparkling performance but it is lighter and more compact than previous Commodore engines and 4 SILICON CHIP gives better fuel economy. The reason it does give better fuel economy is because of electronics, in the engine management system and in the ignition system. General Motors has certainly had its ups and downs in recent years in the Australian market. Some years ago, rather than spend the money to develop an improved engine, the company committed itself to using the Nissan 3-litre fuel injected engine. This was featured in the VL Commodore. Unfortunately, the relative movements of the Australian and Japanese currencies then made that engine far too expensive. Holden's new 3.8 litre V6 motor does not have a distributor or conventional ignition coil. Instead, it uses Direct Fire Ignition, a system with no moving parts. Three double-ended coils, mounted on a module at the front of the engine, fire the six plugs directly. General Motors then had to find a cheaper engine but one with at least equivalent performance to the Nissan unit. Fortunately, they were able to use one employed in the compact American Buick. This 3.8 litre V6 unit had originally been cut down from a larger VB and in its first version had been a rough running engine. This was because the angle between the cylinder banks was 90° whereas 60° is the ideal angle for a V6. This rough running was one of the reasons that General Motors had not originally adopted it for Australia. Fortunately, a later model of the engine incorporated a balance shaft, similar to that first used on the Mitsubishi Sigma 4-cylinder engine, and this led to very smooth running. The engine is now being assembled in Australia, from American parts, although the inlet and exhaust manifolds are made here. Engine installation The engine bay of the new Holden Commodore is notably clean and uncluttered. This makes a pleasant change from the "chock a block" installations on most modern cars with their complex plumbing, multiple belt drives for all the accessories and a huge air cleaner hiding it all. Since the V6 engine is so short, it sits well back in the engine bay, which incidentally leads to improv- DECEM BER 1988 5 -- +12v------. CONTROL CIRCUIT CAPACITOR POINTS+ .,. Fig.1: a conventional transistor switched ignition system uses one coil and a distributor. The plugs are negatively polarised to lower the required firing voltage. The arrows show electron current flow. ed weight distribution in the car. Apart from its more compact size though, there are several reasons why the V6 looks less complicated and cluttered than engines in other modern cars. First, it uses direct fuel injection into each inlet port so instead of a complicated multibarrel carburettor there is a simple throttle body (containing a large butterfly valve linked to the accelerator pedal). The throttle body is linked via a large diameter duct to the aircleaner which sits on the righthand side of the engine bay. Second, it uses a long "serpentine" belt to drive the accessories rather than the multiple belts used in other cars. The one long belt drives the water pump, alternator, power steering pump and airconditioning compressor. The radiator fan is electrically driven and controlled by the engine A Hall Effect sensor and magnet system generates timing pulses from these toothed wheels mounted behind the harmonic balancer. 6 SILICON CHIP Fig.2: this diagram shows one of the three coils in Holden's Direct Fire Ignition. Each coil simultaneously fires two plugs, one with positive polarisation, one with negative polarisation. management system which we'll talk about later. Third and perhaps of most interest to readers of SILICON CHIP, the usual ignition coil and distributor is not present on the V6 engine. Instead, it uses a new computer controlled ignition system with no moving parts at all. General Motors call it "Direct Fire Ignition" (DFI} and it is made by their AC Delco division. Direct Fire Ignition Commodores have had solid state ignition systems since 1980 while more recent models such as the VK and VL had electronic spark timing (EST) via sensors mounted on the flywheel. However, they still employed a more or less conventional ignition coil and HT distributor. In the new model with V6 engine, all that has gone out the window and is replaced by a system which is housed in one module adjacent to the alternator. All six spark plug leads plug into this module. Its workings are quite different to conventional transistor switched ignition systems. Inside the module are three double-ended ignition coils, each driving two spark plugs. Each pair of spark plugs is fired simultaneously by its associated coil which means that while one plug fires at just before TDC (top dead centre) for the power stroke another plug fires at just before TDC for the exhaust stroke. This brings up a number of in- teresting points. In a conventional ignition system, as shown in Fig.1, the spark plug is polarised so that its centre electrode is negative with respect to the outer core. In this way, the voltage needed to fire it is reduced by 30 % compared to the alternative connection whereby the centre electrode is positive. Spark plugs in series This situation cannot be obtained in the Commodore V6 though, because of the double-ended ignition coils. The circuit configuration is as shown in Fig.2. Effectively, the coil secondary is connected in series with the two spark plugs. One plug is fired with the "correct" negative polarisation as in a conventional system while the other plug has positive polarisation of the centre electrode. In practice, this makes no difference to the reliability of the ignition since the coil has more than enough secondary voltage to fire both spark plugs. Open circuit voltage is more than 40,000 volts. The only real consequence of the differing polarisation for each pair of spark plugs is that after a long period of use, those plugs with negative polarisation will have erosion of the centre electrode while those with positive polarisation will have erosion of the outer electrode. Even this is of no importance since General Motors recommend that the spark plugs be replaced after 15,000 kilometres. After this period of use they will have negligible wear but the additives in lead vance or centrifugal advance system. All the engine timing information comes from the main electronic control module (ECM) which performs all the engine management functions. However, the ECM still requires basic timing information to derive the spark timing. On previous Commodores with electronic spark timing, this information was derived from a sensor driven by magnets on the flywheel. On the V6 motor, timing pulses are produced from a double Hall Effect sensor which monitors concentric toothed rings on the harmonic balancer (at the front of the engine). The outer ring has 18 equally spaced teeth while the inner ring has three "windows" of differing length at 120° intervals. The electronic control module determines the crankshaft position by measuring the number of voltage transi tions from the sensor on the 18-tooth ring during the period the other sensor "sees" a window on the inner ring. This crankshaft position information is fed from the DFI module to the ECM which then provides precise timing of the three ignition coils. 0 The electronic control module (ECM) uses surface mount custom microprocessor and co-processor ICs. The specially programmed EPROM module to suit it to the V6 engine is mounted on a socket at the bottom. Engine management Electronic instruments are used in the Commodore Calais. This is the back of the instrument panel showing the flexible printed wiring and three sockets for connection to the harness. free petrol (to replace the lubrication effects of lead tetra-ethyl) eventually cause contamination of the ceramic insulator which encloses the centre electrode. This contamination will lead to plug misfiring, hence the recommendation to replace plugs at 15,000km intervals. Claimed advantages of the AC Delco Direct Fire Ignition include no moving parts, less maintenance, no mechanical load on the engine, elimination of mechanical timing adjustments, more coil down time between sparks, and more time available to allow the ignition coils to saturate. As in previous Holden Commodores, there is no vacuum ad- Having explained how the double Hall Effect sensor monitors crankshaft position, we can list the other parameters monitored by the electronic control module. They are listed as follows: • Engine speed; • Manifold absolute pressure; • Manifold air temperature; • Engine coolant temperature; • Throttle position; • Exhaust gas oxygen content; • Battery voltage; • Park neutral switch position; • Vehicle speed; • Air conditioning 'on' or 'off'; • Engine detonation (using a knock sensor); • Cranking signal; • Auto transmission sump temperature; • Auto overdrive clutch 'on' or 'off'. With continuous monitoring of all the above parameters, the ECM controls the ignition system, as already mentioned, as well as the following systems: DECEMBER 1988 7 to 1 by monitoring the signal from an oxygen sensor mounted in the exhaust manifold and then optimising the amount of fuel fed via the solenoid-operated fuel injectors . In electronic terms, the engine management system is therefore a "closed loop" feedback system although at times it does operate in "open loop" mode. This can happen during idle, deceleration and starting. The electronic control module uses a custom microprocessor in conjunction with a a 16-bit coprocessor and 16K of random access memory. The module is the same as fitted to the current Group A Commodore V8, the JD Camira and the LD Astra/Pulsar series. It is customised to suit the V6 engine with a plug-in ROM (read only memory) module which General Motors refer to as a "Mem Cal" unit. Inside the cruise control module: on the left is the stepper motor which operates the throttle valve while at right is the microprocessor and stepper motor drive circuitry. The zirconia element oxygen sensor screws into the stainless steel exhaust manifold to provide feedback signals for the engine management system. It generates an output voltage at temperatures above 360°C. • • • • 8 Fuel system, consisting of the fuel injectors and electric fuel pumps; Idle air control; Auto transmission torque converter clutch; Air conditioner compressor clutch; SILICON CHIP • Radiator fan; • Diagnostics. The major purpose of the electronic control module (ECM) is to control exhaust emissions while maintaining good driveability and fuel economy. The ECM maintains the air/fuel ratio at precisely 14.7 Information sensors We've already talked about the Hall Effect sensor and toothed rings on the harmonic balancer. As well as providing the crankshaft position information for ignition timing, they also provide a measure of engine speed (RPM) for engine control as well as a signal for the tachometer which is an option on some vehicles. Let's now describe some of the other sensors. To obtain a measure of air flow in the inlet manifold, the V6 has a solid state pressure transducer. It also has a temperature sensor which is a negative temperature coefficient thermistor. At low temperatures it has a high resistance (around l00kO at - 40°C} while at high temperatures it has a low resistance (around 700 at 130°C). The throttle position sensor is a potentiometer connected to the butterfly valve on the throttle body. As with most of the sensors in the V6, it is fed with + 5V from the engine control module. The output of the throttle position sensor is zero at idle (when the butterfly valve is completely closed) and it increases to + 4.5 volts at wide open. The detonation sensor detects engine knocking. It is based on a vibration sensor (accelerometer) which puts out a voltage when it <at>HITACHI 20MHz/lmV $830 ExSa!esTax $996 me tax · ■· Wouldn't you pay a bit more for features like this? So good we give the full Spee! 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Call (02) 648 5455 32 Parramatta Rd, Lidcombe 2141 Fax (02)6471545 TelexAA24949 P.O.Box14Lidcombe2141 Melbourne (03) 480 0111 72-74 Chifley Drive, Preston 3072 Adelaide (08) 354 0588 Brisbane (07) 277 4422 Perth (09) 325 9333 Sydney ( BELL ] Bell Test & Measurement The measure of quality A Division of Bell-lRH Ltd (inc in N.S.W.) Prices subject to change without notice 6-inch rectangular. Internal , 8 x 10 div (1 div = 1 cm), Horiz onta l and vertical center lines further marked in 0.2 div increments, mark ing for measurement of rise tl me Trigger Coupling Trigger Slope Calibrator Power Supply Ambient Temperature Dimensions Weight MTBF Accessories Supplied 2 kV. Voltage : 5V o r more. Effect ive bandw idth : DC to 2 MHz. Max . inpu t voltage: 30V (DC+ AC peak }. 5m V/di v to 5V/div in 10 calibrated steps ± 3%. lmV/div, 2mV/d iv ± 5% when using x5 magnifier. Uncalibra ted co nt inuous control between steps 1 : < 2 .5. DC t o 20 MHz 1-3 dB }. DC to 7 MHz (- 3 dB) when using x5 magnifier . 17.5 ns. 50 ns when using x 5 magnifier . 300V {DC+ AC peak) or 500Vp-p AC at 1 kHz AC,GND, DC. 1Ml1 approx. 25 pF. CH1, CH2 {n ormal o r invert). ALT. CHOP , ADD Voltage : appro x . 20mV / div in t o 50!1 Bandwidth : 50 Hz t o 5 MH z (-3 dBi i nto 50!1. CH1 : X -a xi s. CH2 : Y -a xis. 5m V/div to 5V /div. lmV/ div, 2m V/div w hen using x5 magnifier. DC t o 500 k Hz 1- 3 dB ). 3" or less from DC to 50 k Hz . 0 .2 µs/ div t o 0.2s/div in f9 calibrated steps ±3%. 100 ns ± 5% w hen using x10 magnifier (20 ns and 50 ns uncatib rated ). Uncalibrated con ti nuous co ntrol between steps 1 : < 2.5. Automatic {sweep runs in absence of a triggering signa l and for signal below 30 Hz), Norma l {sweep runs when triggered ), TV' V, TV-H. CHl, CH2, V -MODE. Ex ternal, Line. 20 Hz to 2MHz 12 MHz to 20MHz I CH 1 an d CH 2 i 0 .5 di v I 1.5 div I 20mV I E,?C ternal I I 800rnV I AC. + or Square w ave. Vo ltage: 0.5 V ± 3%. Frequency: Approx . 1k Hz Vol t age : 100/ 120/220/240 V ± 10%. Frequency : 50/60 / 400 Hz. Power consumpti on : approx . 30 W. Rated range of use : +10 to 35° C. Limits of operation : 0 to 50° C. Storage and transport : - 20 to 70°C. 310IW) x 130IH) x 370ID) mm. 12.2 X 5. 1 X 14.6 in . Approx. 6 kg/ 13.2 lb. 20 ,000 hours for target value. Two AT-l 0AJ 1.5 pro bes, Fuse , Power cable , Operation manual. I i I the electrical pulse fed to the injectors. This varies between O and 11 milliseconds and happens normally once every crankshaft revolution. Control modes The compact V6 motor sits well back in the engine bay of the new Commodore. It has an uncluttered appearance due to the use of fuel injection and Holden's new Direct Fire Ignition system. detects vibration at around 6kHz with quite a narrow bandwidth of 500Hz. It is screwed into the lower front side of the engine block. If engine knocking (or pinging) is detected, the ECM responds by quickly reducing the ignition advance setting by 8 ° . When detonation stops, the ECM slowly restores the original ignition advance setting. The addition of the knock sensor is quite an improvement on the engine management of previous Commodores which had no way of varying their electronic spark timing if knocking did occur. The exhaust gas sensor is a zirconia element which is screwed into the exhaust manifold on the lefthand side of the engine. When the zirconia element is heated to temperatures above 360°C, it produces a voltage at its tip based on oxygen content, as compared to oxygen in the atmosphere. The vehicle speed is monitored by a 10-tooth wheel on the drive shaft. The toothed wheel is monitored by a Hall Effect sensor and the pulses it delivers are fed not only to the electronic control module but also to the instrument panel where they drive the analog speedometer and odometer. In the 10 SILICON CHIP Calais model, the odometer is based on a non-volatile RAM (ie, a memory which is not lost when battery voltage is removed). Fuel control The fuel system is based on solenoid operated fuel injectors made by Bosch. These are fed with fuel pressurised at between 235 and 320kPa, as regulated by the intake manifold pressure. A high manifold pressure, caused by a wide throttle opening, results in a high fuel pressure. A low manifold pressure, which results when the throttle is closed, gives a lower fuel pressure. In effect, the fuel pressure regulator maintains a constant pressure difference between the fuel line and the inlet manifold. This ensures that the fuel admitted by the injectors does not vary according to manifold vacuum. There are six injectors, located directly in front of each cylinder inlet port. They act as control valves and spray atomised fuel when they are electrically pulsed by the ECM. All six injectors are wired in parallel and so they are pulsed simultaneously. The amount of fuel delivered for each engine revolution is controlled by the length of We have already mentioned the "closed loop" control mode whereby the fuel/air mixture is maintained at the optimum for best working of the catalytic converter. There are times though, when this mode is not wanted, for example, during cranking. At these times the electronic control module works in open loop mode. In the starting mode for example, the ECM ignores the signals from the oxygen sensor and looks instead at the coolant temperature, to find out how hot or cold the engine is. It then sets the injector pulse width; ie, the length of time the injectors are turned on for each engine revolution. Depending on whether the engine is hot or cold, the injector pulse length will be between 8 and 115 milliseconds. If the engine is accidentally flooded with fuel, it can be started by pushing the accelerator pedal all the way to floor. The ECM then pulses the the injectors for only 8 milliseconds every crankshaft revolution, which has the effect of clearing the excess fuel. The ECM maintains this narrow pulse width as long as the throttle is open more than 98 % and the engine RPM is below 300. Once the engine starts, the ECM remains in the open loop mode until the following conditions are obtained: (1). The oxygen sensor has a varying output, indicating that the exhaust temperature is above 360°C; (2). The coolant temperature is above 44°C. (3). Engine not at idle. In the open loop mode the injector pulse width may well give an air/fuel ratio of more than 14.7 to 1. This can happen, for example, when the engine is cold and needs a richer mixture to drive without stalling. Acceleration mode When high acceleration is called for, the ECM notes the rapid change in throttle setting and in manifold The new Commodore has been completely tested to ensure electromagnetic compatibility for all its electronics. pressure and provides extra fuel by increasing the injector pulse width. If extreme acceleration is called for, the ECM may provide extra injector pulses during each engine revolution. During deceleration, the ECM can cut off the fuel supply completely for short periods, giving improved fuel economy. Fuel cut off occurs when all the following conditions are met: (1). The coolant temperature is above 56°C; (2). Engine speed above 1500 rpm; (3). Vehicle speed above 35km/h; (4). Throttle is closed; (5). Park/neutral input indicates "in gear" (auto transmission only); (6). Manifold pressure less than 20kPa. If fuel cut off is in effect, the fuel will be restored if any one of the following occurs: (1). Engine RPM drops below 1400. (2). Vehicle speed drops below 30km/h. (3). Throttle open at least 1 %. (4). Manifold pressure more than 20kpA. (5 ). Park/neutral input indicates "in gear" (auto transmission only); Fuel can also be cut off to protect the engine against over-revving. It cuts out for engine speeds above 5400 rpm and cuts back in again when engine revs drop below 5000 rpm. Battery voltage correction Another interesting wrinkle to the electronic control module is the battery voltage correction mode. If the battery voltage is low, the ignition system may deliver a weak spark and the injectors may be slower to respond to their short pulses. The ECM compensates for these potential problems by increasing the ignition dwell time, if the voltage is less than 12 volts, and increasing idle RPM and the injector pulse width if the voltage is less than 10 volts. Idle speed is something we haven't touched on yet but the ECM has control over this too, by varying the opening of the electrically controlled "idle air control" which bypasses the throttle valve when it is closed. The idle air control valve moves in steps from 0 to 255, corresponding to an 8-bit control system. Cruise control A trip computer and cruise control are fitted as standard on the Calais model and are an option on other Commodore models. The cruise control offers much the same facilities as those on competitive brands but it is of interest because it does not use inlet manifold vacuum to operate the throttle. Instead, it uses a stepper motor. General Motors cite a number of advantages in using the stepper motor, among them being the fact that the cruise control operation is not affected by changes in engine vacuum. In reality, since the cruise control employs a microprocessor, it is likely that the stepper motor lends itself better to more precise digital control. Driving the Commodore Part of the fun of preparing this report was a short test-drive of the car. Well, naturally the engine starts and runs extremely well and offers really sparkling acceleration. No doubt it will be the bestselling Commodore yet. Now, how can we scrape up the dollars to buy one? Acknowledgement Our thanks to Marc Mcinnes of General Motors Holdens Automotive Ltd and to Jack Stepanien for their assistance in the preparation of this report. '~ DECEMBER1988 11