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L6B
Design Article: Integrated Electrical System Integrated Electrical System Although traditional automotive electrical systems may appear relatively simple to those with an electrical or electronic background, many owners of kit cars have cited the installation of electrical wiring as the single most difficult and confusing part of an otherwise enjoyable project. With this in mind, the L6B has adopted a modular approach which integrates many of the distributed components into three preassembled and tested modules, the Relay and Interface Unit, the Display and Switch Unit, and the Instrumentation and Logic Unit. These modules are interconnected by multiconductor cables to enable the builder to complete over a hundred electrical connections (and have them all connected correctly) by simply plugging a few cables into their respective sockets.
Relay and Interface Unit The Relay and Interface Unit (RIU) is a single printed circuit board populated by relays, fuses and terminals. To simplify the final assembly, distributed electrical loads (lights, cooling fans, windshield wiper etc.), regardless of how they are controlled, and distributed sensors (water temperature, oil pressure, wheelspeed etc.) are all wired directly to the RIU. Making these connections requires only that each of the colour coded wires be plugged onto its respective numbered terminal on the RIU. From this point on, all signal and power routing is controlled by printed circuits and preassembled multiconductor cables. Instrumentation and Logic Unit This unit (ILU) integrates four major operating functions: (a) controls the organic light emitting diode display (OLED) to present the information traditionally provided by discrete analog gauges, (b) accepts switch inputs from the Display and Switch Unit (DSU) which is mounted on the steering wheel, provides the logic required to implement the functions initiated by those switches, and controls light emitting diodes (LEDs) on the DSU to indicate operating conditions, (c) accepts switch inputs from the instrument panel, provides the logic required to implement the functions which are initiated by those switches, monitors sensory input and controls advisory LEDs on the instrument panel and (d) gathers sensory input and stores data for subsequent transfer to a Personal Computer (PC) for analysis (known as data logging). Data is stored in a USB flash drive for easy compatibility with standard PCs and easy transfer of the data - just unplug the USB drive from the ILU and plug it into your computer! The data can be analyzed off-line on PC using an array of sophisticated software programs to perform functions such as 3D racetrack mapping (including elevation changes and corner bank angle), virtual wind tunnel, virtual dynamometer, and software for engine or suspension tuning. We expect to offer this sort of software to our customers but do not expect to include every one of these programs in the kit. Display & Switch Unit This unit (DSU) did not exist when the first version of this article was written. After installation, it is an integral part of the steering wheel assembly. It incorporates eight switches, eight LEDs and the 128x64 pixel 16-grayscale OLED with 2000:1 contrast ratio. It provides all indicators except for the Master Caution Light and Shift Light, both of which are mounted on the instrument panel behind the steering wheel. The eight switches are: LEFT & RIGHT turn (both switches activated together = emergency flashers), BEAM (for toggling between low- and high-beam), radio PTT (for control of 2-way communications or entertainment system), SET (to set speed for overspeed indication, discussed later), WIPER, WASHER and HORN. Indicator LEDs are: Left & Right flasher (green), LF, RF, LR, RR traction indication (red/green) discussed later), Overspeed (yellow), High beam On indicator (blue). The drawing below shows the layout of the steering wheel mounted DSU. You can see photos in the photo gallery.
Instrumentation Display The Instrumentation Display, implemented using the aforementioned OLED, has been moved to its final location on the steering wheel. The previous design used a Liquid Crystal Display (LCD) which was to be mounted on the instrument panel and viewed through the upper opening in the steering wheel. That location was not ideal, since some drivers whose eye level winds up above or below the average could potentially have part of the display blocked from view by the steering wheel. Secondly, the LCD requires a powerful back-light to enable night time viewing. In contrast, the OLED is a light emitter, not a light blocker like an LCD. Night time viewing is ideal with an OLED. Day time viewing is rendered acceptable thanks to the well-shaded cockpit and angle of the display. The absence of a back-light makes the design more elegant, more power efficient, and eliminates the need for an additional power converter required solely for the backlight. Thirdly, the response time of OLED is much faster than LCD. If those three reasons were not enough, there is a fourth - cost. The OLED permitted the deletion of a high-current switch-mode power supply and the OLED itself is half the cost of the LCD that it replaces, hence, there were four great reasons to move to OLED from LCD. The figure below shows a typical display configuration in street (upper) and racing (lower) modes. The actual colour of pixels is a shade of yellow. The lettering shown is basically all inverted - black is really white, background is black. Display intensity is automatically controlled using an ambient light sensor. You can adjust the light intensity of the display and also the ambient light intensity at which the display will dim; both of these are set in calibration mode. This automatic dimming function applies to all LED's as well.
All relevant values can be displayed in either English or metric units, selectable in calibration mode. Fuel level is given in percent. Temperatures (radiator, engine and gearbox) are displayed in Fahrenheit or Celsius. Oil pressure is displayed in psi or kPa. Battery voltage is shown in Volts. The totalizing and trip odometer readouts can also be displayed in miles or kilometers, basically, the speeds and distances are either in km or mi, you can't mix and match individual readings - we didn't see much point in allowing that. Tachometer only displays in RPM. In the street version, distance to empty fuel is shown as is time and date. In the racing version, time is displayed which can be useful since there are generally time limits for practice and qualifying sessions. Of particular interest is the bottom line which shows your lap number, time for that lap, and which lap you must come in for a pit stop based on fuel (shown is your current lap is lap #200 (that's a long race!), time for lap 200 is 13:39.59 (that's a really long lap!) and advises to Pit in 100 laps for fuel, shown as P100). Obviously those examples are all rather extreme - it demonstrates that there is plenty of room on the display to accommodate anything reasonable. Unlike many integrated digital displays, all the monitored parameters are displayed all the time with one exception: important messages are displayed in place of the bottom line when necessary. Warning Displays A large yellow Light (this may be an LED or an incandescent lamp bulb, to be determined) located on the instrument panel is used to signal an out of limit condition such as low oil pressure or high temperature. When illuminated, the applicable indication on the Instrumentation Display will highlight the appropriate parameter. A large red Light (LED or lamp bulb), also located on the instrument panel, is used to signal that you have reached the desired gear shift engine speed. This desired engine RPM can be set when the ILU is in calibration mode. To eliminate the need for the driver to continually monitor the speedometer, a bright yellow light emitting diode, located in the driver’s peripheral vision (i.e. on the DSU), will begin to flash if the speed exceeds a preset value. Two green LEDs on the DSU provide an indication of turn signal operation. A blue LED on the DSU is used to indicate when high beam headlights are ON. Logic and Control Functions As can be seen in the above drawings, pushbutton switches, to access electrical functions required most often while driving, are mounted on the steering wheel. Logic required to control the headlights, turn signals, windshield wiper etc. in response to inputs from the steering wheel switches, instrument panel switches and the various sensors, is provided by the microprocessor and is configured by the built-in software, including the personalized adjustments you have made in calibration mode. Electrical functions required only at startup or infrequently while driving are controlled by a bank of rocker switches. Headlights are selected by a three position Off/On/Auto switch on the instrument panel. In the Auto position, the low beam headlights are automatically switched on when the engine is running and the handbrake is released. In normal daylight, when they are used as daytime running lights, the lights are powered through a series resistor, slightly reducing their intensity and significantly increasing their operating life. As the ambient light diminishes, the resistor is automatically bypassed to restore the lights to full brilliance. Traction Monitor A rectangular grouping of four bicolour LEDs mounted on the DSU, each representing a specific wheel, provide traction status. If a wheel loses traction and spins, its LED will illuminate green. If a wheel locks up, its LED will illuminate red. Data Logger The data logger functions any time you have a USB memory device plugged into the ILU. If you do not view the data it is eventually over-written by new data. Some time-critical data is stored every 5 milliseconds. Although you will see some very expensive after-market data loggers with 2ms sampling capability, there is no good reason to sample data that frequently. In our view, even a 5ms sample period is overkill. The data logger stores some less time-sensitive data every 10ms and the remainder once every second. Stored data includes elapsed lifetime run time, instantaneous engine shaft speed, instantaneous wheel speed for all four wheels, wheel distance traveled for all four wheels, 3-axis accelerometer reading (forward, lateral, down), traction control info, warning flag, lap marker, fuel flow time accumulation, air-to-fuel ratio, wheel vertical displacements for all four wheels, fuel level, radiator temperature, oil temperature, oil pressure, gearbox temperature, steering wheel switch activations, ambient light sensor and battery voltage. Over 70 hours of continuous data storage is provided in the L6B kit. As if that isn't enough for any application, you can expand it by using a higher capacity USB drive. Engine Control Unit The Engine Control Unit (ECU) is an integral part of the Electronic Fuel Injector (EFI) system. It is provided with the EFI system if you chose to use an EFI-based engine (we expect most L6B builders will). The ECU and associated EFI system are entirely separate from the remainder of the electrical system, described above. The ECU controls the spark advance, fuel injector pulsing, fuel pump operation, etc., all to provide the ideal air to fuel ratio (AFR) and spark to the engine cylinders for whatever operating conditions exist. There will be more discussion on this in the future article on engines. The ECU is not included in the L6B kit since it is closely associated with the engine selection.
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