Boostcontroll PWM frequency issue

[jasso]

Im running a Garret VNT turbo in Toyota 4A-FE engine. Currently using a standard wastegate actuator for VNT controll, now im trying to get more accurate controll for the turbinevanes. 

Got my hands on some Garret/Hella VNT actuators. Kind of a servo unit that has the driver circuit builtin. All it needs is +12v, GND and pwm signal for controlling the movement.  Problem i have at the moment is that the actuator needs 140 Hz pwm signal. Seems like current firmware versions i have looked into have only 125 Hz at max.

What would be the easiest way to 140 Hz controll, some FW modifications or do i need a separate pwm frequency converter circuit.

[Sprocket]

Bear with me here as my understanding of the PWM requirements of devices is not very good. I think you have read the same forum topic on google as I have?

So this is really just me thinking out loud trying to understand this better. The frequency is  how often the pulse occurs, and the duty cycle determins how long each pulse is, the end result is an average voltage. Would using 125hz instead of 140hz be that much of a problem for the servo actuator? is it not the same thing?

for example using 12v for ease of explanation, 125hz at 50% DC is 6v, and 140hz at 50% DC is still 6v, there will just be 15 less cycles for every one second

I will assume the actuator is looking for an analog curve that the PWM voltage mimics. will the actuator really know the difference of losing 15 cycles? it just means that the 125 pulses are a little bit longer (4us at 50% DC)

I'd be tempted to try it first before getting complicated with converters.

If you want to request a higher Frequency, you'll be better posting on the Wiki expalining the requirements.

Don't mind me, I'm just trying to understand it better, but I'd certainly be experimenting with it. I'm more of a practical person, rather than an academic, and find it easier to understand stuff by testing and playing around with stuff :)

[gunni]

Some electrical devices like a vnt motor is feed PWM of specific frequency, i.e. it´s specifically monitoring the ON and OFF times in a certain time space.

for 140Hz this is 7.142857142857143 milliseconds for a total signal start to end.

However for actuators who are just dump solenoids like injectors, wastegate solenoids and idle control valves they are not actively monitoring the frequency, they simply try to turn on when they get current and then shut off.

I wouldn´t say 50%DC at 12v would act the same as 6v and 100Dc. That is at least not my experience with LED´s for instance.

[Mads Lund]

Hi, have you got any further on this topic ?

I'm planning to use a Hella VNT accutuator to control an exup / exhaust flap (for noise reduction purpose) on my rally car. But would like to know if anybody have had any luck driving it from the VEMS. From what I can see, will it be possible to use the secondary boost PWM, and controlling from rpm and map will be perfect.

But need to know if the current 125HZ or 187HZ will work ?

Br Mads