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ELECTROMCS '111f. BIG CAT By LEO SIMPSON Prestige cars used to a be relatively cheap in Australia but they are now again truly prestige. Cars such as the Jaguar cost more than the average price of a threebedroom home in many Australian cities. With that sort of price you expect something more than just good paintwork, plush upholstery and a powerful engine. With the Jaguar, you get a car with an astonishing amount of electronics as well as all the normal attributes of a high-performance luxury saloon. Jaguar owners are not technofreaks. So Jaguar had to incorporate all the new technology into the XJ40 without making it too obvious to the driver or the passengers. In fact, if you went for a short ride in the XJ40 you could easily miss out on the subtle evidence that a lot of electronics is at work. Take the braking system for example. To the casual driver, the Jaguar's brakes are perfectly con- ventional and not at all unusual. But under the skin, they incorporate anti-skid which means a lot of control circuitry. In addition, the XJ40 is the only domestic car in the world (that we know of) to use a high pressure hydraulic servo system rather than the conventional vacuum-assisted brakes found on all other cars. And the braking system has all sorts of monitoring to tell whether the system is working up to par: low brake fluid, low brake pressure, handbrake on, pad wear and so on. The new Jaguar X/40 hos been selling in Australia for about a year now, but very few people know just how much electronics it employs. 6 SILICON CHIP Fuel bleed return Air temperature sensor Ignition coil Ignition power stage 1.....11--- ---------------------------....J Fuel used and diagnostics input to VCM Fig.1: the engine management system. Timing information comes from a toothed-wheel pickup on the crankshaft. Or take the suspension. On the Sovereign and Daimler models, the rear suspension has automatic selflevelling, controlled by electronics. Or the air-conditioning. It is totally electronically controlled. There are no mechanical linkages, flap valves or whatever. The system controls the temperature and humidity, with differential settings for both the driver and passengers, front and rear. And it senses the effect of sunshine in determining whether more cold air is needed. Even if you lift the bonnet, there is no great evidence of electronics at work. Sure, there is a thumping big six cylinder double overhead cam 24-valve [four valves per cylinder) engine with fuel injection and electronic ignition but superficially, the electronics are fairly low key. So where is all the electronics? All told, there are no less than seven different microprocessor controlled systems in the Jaguar. They are used for the following functions, some of which we have already noted: (a) engine management; [b) instrument panel and trip computer; [c) air conditioning; [d) anti-lock braking; [e) cruise control; [f) suspension levelling [where fitted); and [g) central processor. In addition there are other electronic modules to control such functions as central door locking, courtesy light switching, and bulb failure warning. Just touching on the courtesy light switching for a moment: if one of the doors is left open for more than two minutes the interior cabin lights and door ("puddle") lights are turned off to conserve the battery. [Jaguar calls them "puddle" lights because they let you see puddles when getting out of the car in: the dark). Engine management The engine management system was developed and made by Lucas to Jaguar requirements. It uses one microprocessor to control both the spark timing and the duration of fuel injection for each cylinder firing. As well, it maintains a constant engine idle speed regardless of whether various accessory pumps are being driven or not. Fig.1 shows the engine management system in schematic form. The distributor is simply a rotating switch which delivers the high voltage output of the ignition coil to the respective spark plugs. There is no .vacuum advance diaphragm, centrifugal advance weights, points or variable reluctance pickup to control the current through the ignition coil. Instead, timing information comes from a toothed-wheel pickup on the crankshaft, adjacent to the fan pulley. It has 60 equally spaced slots with three teeth missing, at intervals 120° apart. The microprocessor recognises the short term changes in frequency associated with the missing teeth and uses this · to provide the necessary timing information for fuel injection and ignition. There are six solenoid controlled fuel injectors, one for each cylinder inlet port. These are not controlled individually but are operated together by the microprocessor. Both the ignition timing and that of fuel injection are varied in response to a number of parameters, including the temperature of the engine, the air-flow into the manifold, throttle position and the lamda sensor, which monitors exhaust emissions [actually monitoring oxygen Gontent). The engine temperature is FEBRUARY1988 7 + ++ + + + ++ + + + ++ + + ++ + + + 5 ++ ++ + ♦ ♦ + E .., 4 ++ ++ + + ++ .; > ·;; 0- 3 ++ ++ + + ++ -£ + + + + + + + + + + + + + + .., u 8 ++ ♦♦ ♦ 7 +♦ ++ ♦ • 6 ++ ~ Detonation critical zones Typical full throttle advance requirement >, u ~ 0 ... ,: ·.; B 00 C :~ _. . fu advance cha~acteristic Mechamcal centn ga1 C .g ·a ~ Areas of compromise with conventional mechanical systems ~ !! 2 ++ ++ ·;;; 3"' Static setting limited by starting and/or idle quality requirement + + ♦♦ + + + + + ++ + ++ ++ + + +♦ + + + + + ++ + 5 6 -0 I 0 monitored by an NTC [negative temperature coefficient) thermistor situated in the water jacket of the engine. Air flow into the manifold is monitored by a heated sensor wire in the venturi between the air cleaner and the throttle body. Actually, the hot wire sensor is mounted in a bypass port off the main venturi so that, in the event of an engine backfire through the manifold, the sensor is not blown apart. Throttle position is measured by a potentiometer coupled to the accelerator linkage. Separate microswitches are also mounted on the throttle body to detect the idle and full load settings. Road speed is also monitored, as noted later. Conventional engines with distributors having vacuum and centrifugal advance on the ignition have a lot of compromises on the ignition timing. And rarely is the timing consistent from engine to engine. With the digital system used on the Jaguar, the ignition timing can be precisely optimised to take care of a very wide range of engine operating conditions. For example, when the engine is under heavy load and above 3000 RPM, the ignition is retarded by 3 ° for every"10°C rise above 30° of the inlet air temperature. This was found necessary due to the tendency of the engine to "ping" when the air temperature was around 45 to 50°C [that's 113-122° on the Fahrenheit scale). Those temperatures are common in summer in central Australia. 8 SILICON CHIP 3 4 Engine speed r/min x 1000 Engine speed Fig.2: ignition timing versus speed map. The digital system gives precise control of timing. 2 Fig.3: the load versus speed map is used to derive ignition timing and fuelling control. The air mass flow signal from the hot wire sensor is converted by the processor into a measurement of mass flow per engine cycle. This information is then used to derive the ignition timing and fuelling control. Fig.2 and Fig.3 show the igntion timing versus speed map and the load versus speed map, respectively. Fuel cut-off As with a number of other current cars with electronic fuel injection, the Jaguar XJ40 cuts off fuel when the engine is on a trailing throttle (overrun) above a certain RPM. This gives a worthwhile increase in fuel economy and also helps to reduce unwanted exhaust emissions. In the Jaguar, fuel injection ceases when the throttle is closed, for engine speeds above 1100 RPM, provided that deceleration started from a hove 1500 RPM. This hysteresis is built in to avoid cycling in and out of fuel cut-off when decelerating down to rest. This means that the engine speed has to rise a hove 1500 RPM before fuel cut-off will again occur on a trailing throttle. A refinement of the system has been added to the XJ40, to stop drive line oscillations which can occur when fuel injection restarts in response to opening the throttle. This would normally cause a sudden increase in engine power. To soften this transition, the ignition timing is momentarily retarded and the fuel mixture is weakened slight ly, to reduce the power output. Idle speed control Many modern cars have quite a high idle speed because they have to cope with the load of automatic transmission in Drive, airconditioning, the alternator and other accessories. On the Jaguar for example, there are additional engine-powered pumps for the braking system, air-injection and power steering. If the idle speed was set high enough to cope with all these loads simultaneously, as does happen, the engine would race when the loads were removed. To avoid this, the engine management system uses a stepper motor to control a valve in a throttle bypass port. This system operates to control the idle speed only when the throttle is closed, the fuel system is not cut off and the road speed is under Bkm/h. The idle speed varies depending on whether the engine is cold or hot. At other times the stepper motor continually adjusts the idle setting depending on whether the transmission is in Drive or Neutral and the air-conditioning compressor is clutched in or not. This provides a nominal idle setting at all times so that when the engine does actually come back to idle speed, the control system has a minimum of correction to do. The closed loop idle speed in Drive when the engine has warmed up is below 600 RPM which is a low figure for cars these days. The engine management- processor also provides fuel informn- tion to the trip computer via an interface. The fuel signals are dependent on the injector pulse duration and frequency. The output is equivalent to 50,000 pulses per Imperial gallon. Self-diagnostics and limp home All cars with electronic engine management have a "limp-home" feature in the event of a fault developing in the system. The Jaguar is no exception to this and has comprehensive programming to deal with the failure of each sensor in the system. Anti-lock braking Antiskid braking systems (ABS) are becoming more common on upmarket cars these days but few people are aware that these entail a microprocessor control system. The ABS fitted to the Jaguar XJ40 is made by Bosch. It consists of four speed sensors, one for each wheel, the microprocessor module which is placed in the boot, and a pump with three electrically controlled valves, which is in the engine compartment. The valves control the pressure applied to the disc calipers. There is one control valve for each of the front wheels while the third valve controls the pressure to the rear disc calipers. The speed sensors consist of a 48-tooth ring on each wheel which is adjacent to a variable reluctance pickup (a permanent magnet with a coil of wire wound around it). The pickup generates a frequency corresponding to the speed of the wheel. The ABS processor works by evaluating the speed signals from each wheel and then calculating the deceleration rates. The processor can then tell whether a particular wheel is slipping more than it should for maximum braking (in other words it detects the onset of a skid). With the onset of skid, the processor opens a valve to reduce the pressure applied to the affected wheel so that it can speed up to the same rate as the other wheels. The ABS then reapplies the pressure by pulsing the brake line to the point where the wheel then achieves This is one of the many microprocessors used in the Jaguar XJ40. They provide such functions as engine management, anti-skid braking, and suspension levelling. ( BULB FRIWIIE ) CIRCUIT FR/LURE PRRK BRRKE ON Fig.4: warning symbols are displayed on the car's dashboard by the vehicle condition monitor (VCM). Each display consists of a graphic symbol combined with a two-line text message. maximum retardation. This cycle is repeated several times a second so that the car is brought to rest quickly and with much greater steering control than would be possible in a conventional system. The important safety aspects of ABS are that not only does it allow heavy braking in slippery conditions, it also allows much better control of the steering while under braking. Fail-safe operation With all that control possible over the brakes they need to be absolutely failsaf e. To do this, the control system goes through a series of checks when the vehicle is first started and as it moves off and passes . through the speed of 5.75km/h. The first set of tests includes a check to see that the battery voltage is above 10 volts (it would have to be above this value for the engine to have started). Then, as the vehicle moves off, the control valves are turned on for 20 milliseconds and the current through them is checked. FEBRUARY1988 9 variable reluctance sensor working from a toothed wheel on the back axle which generates 4887 pulses per kilometre (7870 pulses per mile). This signal is variously processed and fed to the engine management processor, cruise control, the analog speedometer, the large seven-segment digital speedometer and the odometer (which has non-volatile memory). The tachometer is a conventional electronic instrument, driven by pulses derived from the primary of the ignition coil. The meters for fuel level, coolant temperature, oil pressure and battery condition are all vacuum fluorescent bargraph displays, with variable colour coding to distingguish normal and dangerous conditions. Vehicle condition monitor A computer-controlled diagnostics system is used to track down any faults that may develop. It plugs into a number of connectors around the vehicle. The control pump is also checked in the same way. This checks for short and open circuits. The processor also checks that the signal frequencies from the wheel sensors do not suddenly change (eg, from loss of signal or amplitude). In all cases of a fault being detected, an alarm is displayed on the instrument panel and the system deenergises the control valves so that the car is left with normal braking. Cruise control The Jaguar's cruise control is designed and partly made by Rella of Germany who also supply the majority of relays on the car. The system uses a vacuum actuator on the throttle linkage and an electric vacuum pump with electronically 10 SILICON CHIP controlled regulator and dump valves to control the engine speed. The system operates completely separately to the engine management system and is effectively in parallel with it. Instrument panel At first sight the instruments are conventional circular analog for the speedometer and tachometer but the remainder aredefinitely all electronic. Even the first two instruments are not completely conventional although they are based on moving coil meters with about 240° rotation. Both meters are back lit (variable) and their pointers are illuminated by optical fibres. The speedometer is driven from a A particular feature of the Jaguar's instrument panel is the VCM or vehicle condition monitor. This is a dot matrix vacuum fluorescent display (32 x 32 dot) combined with a 14 segment 2 x 10 character alphanumeric display positioned next to the tachometer. It displays any vehicle faults with graphic symbols and text. The VCM effectively eliminates the multitude of warning lights found in most modern cars and adds a great deal of monitoring which would otherwise just not be possible. Fig.4 illustrates some of the variety of faults which can be displayed on the VCM. Note that each display consists of a graphic symbol combined with a two-line text message. A secondary function of the VCM is to act as a display for the trip computer. This is a facility found in many modern cars and cm the Jaguar it provides the readouts of functions such as: average speed of journey, average fuel consumption, range on current fuel, and fuel used so far. The trip computer's function switches are arranged on a small panel just to the right of the steering wheel housing and integrated with those for the cruise control. Central processor Since the Jaguar has so many microprocessor-controlled systems, the company was very concerned 12 V Power to load microprocessor Fig.5 (above): the XJ40 employs a common + 12V line to all electrical accessories which are switched on by transistors in rewsponse to a microprocessor signal. The vehicle condition monitor (VCM) at left displays vehicle faults with graphic symbols and text. about overall reliability. The possibility of bad connections, susceptibility to voltage spikes and EMI (electromagnetic interference) is a nightmare for designers of automotive electrical systems. After a lot of research, Jaguar adopted a signal wire earth switching system for the electrical system. This employs a common + 12V line to all electrical accessories which are then turned on by transistors in response to a microprocessor signal. The normal convention of using the car body for all negative return currents has been abandoned. The respective microprocessors respond to switches, operated by the driver, which cause only very small currents to flow in the common earth return line. Since all the control switches now only handle very small currents, the normal automotive style switches with their wiping contacts are no longer suitable. Such switches rapidly become unreliable when switching small currents. Instead, all switches in the Jaguar are effectively sealed membrane switches (as used in most computer keyboards) with noble metal contacts. The switches have a toggle mechanism to give a positive toggle action. The relays , connectors and harness all had to be completely redesigned to give a much higher order of reliability than has previously been obtained. The whole car electrical system is designed to operate over the ex- treme temperature range of - 40 to + 85°C. In addition, the vehicle was developed to be proof against electromagnetic interference at levels of: 25 volts/metre for noncritical items; 50 volts/metre for moderately critical items; and 200 volts/metre on critical items These very high levels of interference apply for signal frequencies all the way up to one Gigahertz (one thousand Megahertz). Reverse polarity and voltage surge protection is provided for all microprocessors and logic units with automatic resetting in the unlikely event of a microprocessor crash. By the way, the central processor not only provides the timing for all system functions but also controls such things as the flash rate of the traffic indicators, the timing of the heated seats (these can be heated to 30°C in a short time in even the coldest climates), the rear window heating, the windscreen and headlamp washers and so on. A central locking switch locks all doors, the boot and the sunroof, and raises all the windows in a rapid sequence. Repairing the system Clearly, no automotive electrician, no matter how well trained, could hope to diagnose and repair such a complex electrical system. It has over 100 multiway plugs and sockets and countless relays and switches. To aid the finding and repair of faults, Jaguar has developed a computer controlled diagnostics system in conjunction with GenRad of the USA. This can be plugged into a number of connectors around the vehicle and will lead the automotive electrician through a series of tests to discover the fault. How else would you do it? Interestingly, Jaguar staff in Australia have played a large part in the rigorous program of testing of pre-production models before the car was released. To the north of Sydney and around Cobar (NSW), about two million miles of testing have been run up on Jaguars to ensure they could withstand the extremes of dust heat and rough roads. For extremes of cold, testing was done in Canada during the winter months where temperatures down to - 45°C were regularly experienced. Driving the big Cat Well, as part of this report, we couldn't let an opportunity to drive these advanced cars go by. On a visit to the Jaguar facility at Liverpool in Sydney we had a chance for a short drive and we can report that the Jaguar drives exactly as you would expect a large high performance saloon to do. It is fast, quiet and handles extremely well although it does not have the neck-snapping acceleration of high performance cars qf a decade ago. And certainly the electronic aspects are never obtrusive. They work. They probably represent a glimpse of the future for the cars we'll be driving in years to come. FEBRUARY1988 11