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#1
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"Real time" fuel consumption measurement
Given ever higher price for gas it would be nice to be
able to monitor ones driving habbits to get the best MPG posible. In a EFI engine the fuel consumption is based on the on time for the injector(s). Has anyone seen any DIYS circuits for intergrating the injector duty cycle. I have been playing with a laptop PC versio, but it isn't too healthy to be watching a LCD while driving. I am hoping to find a way to reduce this info to a single analog meter so that all you have to do is maximise or minimisethe needle position. Terry |
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#2
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It is called a vacuum gauge and was done back in the 50's.
The higher vacuum you maintain, in theory, the better your mileage. When you press the accelerator your vacuum drops and that means you are using more gas. > wrote in message oups.com... > Given ever higher price for gas it would be nice to be > able to monitor ones driving habbits to get the best MPG > posible. > > In a EFI engine the fuel consumption is based on the on > time for the injector(s). Has anyone seen any DIYS circuits > for intergrating the injector duty cycle. > > I have been playing with a laptop PC versio, but it isn't > too healthy to be watching a LCD while driving. > > I am hoping to find a way to reduce this info to a single > analog meter so that all you have to do is maximise or > minimisethe needle position. > > Terry > |
#3
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"halo2 guy" wrote > It is called a vacuum gauge and was done back in the 50's. > > The higher vacuum you maintain, in theory, the better your mileage. When > you press the accelerator your vacuum drops and that means you are using > more gas. Yeah, I had one in the early 70's for my '70 Chevy Nova - thanks for reminding of those days! Howard |
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#5
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Driving the car in way that'll maximize on ecnomy requires a standard
tranny. Otherwise, you're at the mercey of the automatic. The posted city consumption for my car is 7.8L/100km, but if I put my mind to it, I can get 6.5L/100km. However, I'm not able to shave anything off the highway mileage which is 5.8L/100. Pars 98 Civic Hatch > wrote in message oups.com... > Given ever higher price for gas it would be nice to be > able to monitor ones driving habbits to get the best MPG > posible. > > In a EFI engine the fuel consumption is based on the on > time for the injector(s). Has anyone seen any DIYS circuits > for intergrating the injector duty cycle. > > I have been playing with a laptop PC versio, but it isn't > too healthy to be watching a LCD while driving. > > I am hoping to find a way to reduce this info to a single > analog meter so that all you have to do is maximise or > minimisethe needle position. > > Terry > |
#7
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wrote: > > Given ever higher price for gas it would be nice to be > able to monitor ones driving habbits to get the best MPG > posible. > > In a EFI engine the fuel consumption is based on the on > time for the injector(s). Has anyone seen any DIYS circuits > for intergrating the injector duty cycle. > > I have been playing with a laptop PC versio, but it isn't > too healthy to be watching a LCD while driving. > > I am hoping to find a way to reduce this info to a single > analog meter so that all you have to do is maximise or > minimisethe needle position. > > Terry This could be a fun project. I would start with a circuit like the one below. Point A hooks to the switched side of one of the injectors, point B to a high impedance voltmeter. Power supply to the 74HC14 should be a regulated +5V supply, I am old fashioned and like the LM317 adjustable voltage regulator for that purpose. The 180k / 100k resistors do several things: 1. Voltage divider that converts the 14V / 0V swing at the input to a 5V / 0V swing for the 74HC14 2. Ensures that the circuit is a high impedance load on the ECU. 3. Provides high enough impedance at the input to the 74HC14 that voltage spikes are effectively clamped by the protection diodes in the 74HC14. The three inverters (with Schmitt trigger inputs) shape the potentially ugly signal at the injector into a nice square wave with a 0 - 5V swing. The 74HC14s are nice in that if they are supplied with 5V, the high output voltage at moderate loads is very close to 5V. The 100 k resistor and 10 uF cap form a low pass filter with -3dB point around 0.16 Hz. This is a difficult trade-off. At idle you will still see quite a bit of wiggle on your meter, and the response time is on the order of 7 second. If you want faster response, you will get more wiggle at idle. You could add more poles to the filter to get a better compromise between response time and reading stability. I would imagine that the duty cycle on the injectors is quite low, so you might have to add an op-amp for gain between point B and your meter. That will also allow you to add a gain adjust for calibration as well as allow you to implement a more sofisticated filter. Remember to ground the input of the three unused inverters. 74HC14 180k |\ |\ |\ 100k A ---\/\/\/---------| >0----| >o----| >o----\/\/\/--------- B | |/ |/ |/ | | ===== 10uF |---\/\/\/--- | 100k | | V V Now, if you like microcontrollers, you could hook the output of the last inverter to the timer / counter input of your favorite controller (If you still want to use the analog low-pass filter you probably would want to use the second inverter rather than the third for your microcontroller). Then you could time the pulses and calculate the duty cycle that way. This will allow you to adjust your filtering to the engine RPM so that you get a rock steady output regardless of RPM and at the same time get quick response time on your meter. A further experiment would be to use one resistive divider and one inverter for each injector. Then use four diodes to OR the output of the 4 inverters together, and follow it with two more inverters. Then you would get less wiggle on the meter at low RPM, or you could bump up the cutoff frequency on the RC filter for quicker response. The possibilities are endless... Note: My 1:42 am engineering output is prone to errors. Use at your own risk! -- ================================================== ===== A very modest collection of Honda tech info can be found at: http://www.geocities.com/ng_randolph |
#8
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