The post explains a simple method of converting a wasted spark type ignition system in an automobile, into an enhanced, sequential spark, 6 cylinder engine type ignition system.
The idea was requested by Mr. Brenton, as given below:
I was looking through the car and motorcycle section but couldn't find what I was looking for. I'm hoping you might be interested in looking at my project.
My car has a straight 6 cylinder EFI engine with firing order 1-5-3-6-2-4 (Ford Australia). The ignition setup is a wasted spark type with coils 1 and 6 paired, 2 with 5 and 3 with 4.
I am looking for a circuit that can receive the ignition pulse from the ECU and alternate it between 1 and 6, 5 and 2, 3 and 4.
That way you can have separate coil drivers and full sequential ignition. On power up, the system resets, a counter monitors odd and even number pulses, maybe some software will be involved I imagine.
With 3 separate circuits, 1 for each output pulse from the ecu, 1, 5 and 3 always get the first pulse on the odd count and 6, 2 and 4 get the second pulse on the even count. Then the circuit just alternates until you cut the ignition.
I hope you find this project idea interesting and worthy of your time and effort to post a solution on your website.
My Reply: I'll try to design the specified circuit for you, however since I am not an auto expert, I am curious to know how your existing system is a wasted spark type, while the new odd/even idea will help to improve it?
Nevertheless, the new idea can be implemented using ordinary IC 4017 counter divider ICs, according to me, without a software.
Mr. Brenton: I intend to supercharge the engine once the ignition is upgraded with more powerful, individual coils. You are correct, there is no advantage introducing a sequential ignition system on a standard engine.
The three pulses fired from the ECU are in sequence, the timing of which is calculated by the ECU based on engine speed, intake air temp, throttle position etc.
How the Circuit needs to Work
This circuit doesn't need to worry about the working of the ECU. All it needs to do is route the pulse between a pair of terminals to the same terminal first time, then alternate between them.
I'll just put three identical circuits on the one board, one independent circuit per output from the ECU.
What happens is when you first crank over the engine, the ecu waits for a signal from the crankshaft trigger wheel sensor.
Then it waits for a signal from the camshaft position sensor. Once the ECU receives both those signals, it knows where top dead center of cylinder 1 is on the compression stroke.
It then sends out the first pulse as it is programmed to do to fire up the engine and the other pulses follow in sequence.
I’m pleased to hear you think there is a simple solution and I am very grateful that you consider this project worthy of your time.
Please consider the attached sketch for the detailed info.
The processor circuit for converting the wasted spark ignition to the enhanced sequential type ignition is shown in the following diagram.
In the diagram points A and B are supposed to be connected to the trigger inputs of the appropriate CDI units, for firing the relevant combustion engines.
The working of the circuit may be understood with the help of the following points:
1) As soon as the circuit is powered from the 12V battery, the IC 4017 is reset through C1.
2) Pin3 of the IC now becomes high, and T2 gets into the standby condition with its base biased with the pin3 voltage. But T2 cannot conduct as yet due to the absence of a voltage on its collector pin.
3) When the first ECU pulse arrives at the base of T4, it is turned ON, and T4 grounds pin14 of the IC. But the IC does not respond to this since it is designed to respond only to positive pulses at pin14 and not to negative pulses.
4) However, during the time T4 conducts, T1 is also turned ON, due to its base getting the negative bias via D1, R2, T4. In the process T1 transfers the + 12V to the collector of T2, until the voltage is transferred to its emitter, and to point A
5) Next, the ECU pulse switches OFF, causing T4 to switch OFF, which instantly causes a positive pulse to generate at pin14 via R1.
6) At this point, the IC 4017 responds and causes the logic high from pin3 to jump to pin2.
7) Now, pin2 gets into the standby mode, waiting for the next pulse from the ECU.
8) When the next ECU pulse arrives, the above procedure repeats, until the ECU pulse turns OFF, which in turn causes the logic high from pin2 of the IC to jump to pin4. Simultaneously, the point B is also fired via the emitter of T3.
9) The moment the logic high reaches pin4, the IC gets instantly reset, causing the logic high to return to pin3.
10) The circuit now reaches its earlier position waiting for the next repetition.
We will Need 3 of these Circuits
In the above explained wasted spark to sequential spark ignition converter design, only one example is discussed. We will need 3 such circuit modules to be configured with the appropriate outputs from the ECU, for implementing the proposed enhanced, and highly efficient 6 cylinder engine sequential system.
The design of the wasted spark switching circuit displayed above seems to have a serous flaw. The emitter leads of the T2, T3 emitter-followers, would be always ON in response to the HIGH logic from the relevant IC 4017 pinouts, rendering the working of the unit completely useless.
The issue can be corrected by incorporating AND gates across the IC 4017 outputs as shown in the following diagram.
Here we have employed the IC 4081 quad AND gate IC for the switching. Only two AND gates are used out of the 4 gates, the remaining two are not used and appropriately terminated to the ground line.
As an example, if we observe the inputs 1 and 2, we find that 1 is connected to the 4017 output, while the pin2 is connected to T1 collector. The output of this gate is pin3, which is always at logic zero. It will not switch ON or turn HIGH, unless and until, both the input 1 and 2 become high, which can only happen when the T1 switches ON in response to the ECU trigger. The same working can be expected across the input pins 6 and 5, and its output 4.
Feedback from Mr Brenton:
It's been a while since I last contacted you and I hope you and your family are well and safe.
I continued to experiment with the circuit depicted in 'wasted spark2' because it wasn't doing what I wanted. Output A would go high immediately upon powering the circuit. I didn't want this. I wanted output A to wait for the signal from the ECU before going high momentarily to fire the ignition coil. So I finally decided to connect BC557 to the ECU signal line instead of directly to 12V and SUCCESS!
My prototype circuit started working exactly as I wanted.
Due to COVID I have put my project on hold but I am so happy I have a working prototype and I owe it all to you Swagatam. I can't thank you enough.
The final working prototype of the wasted spark ignition circuit, as suggested by Mr. Brenton can be seen below:
Additional Specifications Provided by Mr. Brenton
- The circuit must lose power if the engine stalls.
- Usually, there is only one big positive terminal on the back of an alternator for power cables to connect to.
- There needs to be a heavy gauge wire connecting this terminal to the battery so that the battery is being charged by the alternator whilst the engine is running.
- When the engine stops, the circuit must lose power and therefore some careful consideration must be given to placement of diodes to control the flow of current.