00:00 |
- As mentioned in the electrical fundamentals section of the course, almost all the actuators we control in an EFI system are inductive to one degree or another.
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00:08 |
One way we can take advantage of this inductance is with pulse width modulation.
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00:13 |
Pulse width modulation is a method of providing a variable amount of power to an actuator.
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00:18 |
Instead of only being able to have the actuator completely off or completely on, we can control it with more precision.
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00:25 |
The way we pulse width modulate an actuator is to apply power to it and then remove it continually very quickly.
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00:33 |
If we do this fast enough, the actuator will no longer be able to determine when it is powered and when it isn't, and we'll just see a lower level of power being supplied overall.
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00:42 |
There are two main variables to consider when using pulse width modulation.
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00:45 |
The first is the switching frequency.
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00:47 |
This is how often we switch the power on and off to the device we're controlling.
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00:52 |
We express this speed as a frequency or number of times per second.
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00:56 |
A great example of pulse width modulation is a boost control solenoid.
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01:01 |
It's typical to pulse width modulate these at a frequency of 20 hertz.
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01:04 |
This means we're switching the power on and off to the device 20 times every second.
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01:09 |
The second variable to consider when pulse width modulating an actuator is the duty cycle.
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01:14 |
This is the ratio of time we spend applying power to an actuator versus the time we spend with the power disconnected.
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01:21 |
If we look at our boost control solenoid example again, we're pulse width modulating a solenoid with a frequency of 20 hertz, or switching it 20 times per second.
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01:31 |
This means every second is broken up into 20 50 millisecond time intervals.
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01:36 |
If we look at just one of these 50 millisecond time intervals, we could choose to have the device powered for 25 milliseconds and then unpowered for the remaining 25 milliseconds.
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01:46 |
This would be a duty cycle of 50% as half the solenoid's time is spent powered and the other half is spent unpowered.
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01:54 |
If we then change the duty cycle to 10%, we would now power the solenoid for five milliseconds, and leave it unpowered for the remaining 45 milliseconds.
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02:04 |
Wiring an actuator for pulse width modulation is usually no different than any other actuator.
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02:09 |
We supply power to the actuator from our power supply circuit and use the ECU output channel as a low side switch to provide the ground connection.
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02:17 |
However you need to ensure the ECU output channel the actuator is connected to is capable of pulse width modulation.
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02:23 |
Your ECU documentation will have this information.
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02:26 |
It's not unusual for multiple ECU output channels to support pulse width modulation but at different switching frequencies.
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02:34 |
We've discussed a common example of switching a boost control solenoid at a frequency of 20 hertz.
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02:39 |
But there are other actuators you may want to switch faster than this.
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02:43 |
The actuator documentation will provide you with its optimum switching speed which you will need to ensure your ECU is capable of.
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02:50 |
Most actuators we want to pulse width modulate are low current devices, and can be wired to the ECU output channel directly.
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