2JZ-GTE VVT-i FULLY OPERATIONAL

[Big rob]

Just wondering but how does one actually tune VVT-i and how it mapped? Do you just go along at load points and tune for max torque then once all done interpolate? What do you need to look in an ECU to run this i.e. the input and outputs required?

[Mos]

The VVTi 1UZ has a crank rotor with something like 32-2 teeth, a sync pulse for no 1 TDC, and an additional sensor on each variable cam.
The cam sensor uses a rotor with 3 unequally spaced lobes - the SM4 should cope with that, otherwise some lobes need to be removed. This also implies 4 engine position sensor inputs into the ECU.

The 1G-FE appears to have the crank rotor and a single cam sensor.
The 1GZ-FE appears to have the crank rotor (with two pickups - one for each ECU), and a single tooth cam sensor on each bank.
The ECU on these two would need two and three engine position signal inputs respectively.

With the SM4 apparently you set up what degrees of advance you want under whatever conditions and the ECU does the rest. I think you can set up the map to run off various inputs, eg rpm, load, map, etc... I imagine the advance would be tuned for max torque.

The ECU has to be specifically designed and optioned to run VVTi. The software algorithms involved in running VVTi (sensor pickup, solenoid control servo loops, etc) have to be there otherwise you simply can't run it (properly). The solenoid waveform will be some sort of PWM but the control of this PWM is what makes the VVTi function unique.

Mos.

[teamdrinkalot]

Thanks, but how does a 3 positional solenoid work if it has only two wires? Are the two wires 2 coil windings and they use the solenoid body as the earth/negative?

I have tested that and it is only one coil for one operation.

[Mos]

Could you elaborate on how you tested it?
Mos.

[CrUZida]

I was under the impression that it is a PWM controlled solenoid, and thus only open as much as the PWM signal tells it too.

Different openings = different oil pressure reaching actuator = different degree of rotation.

[teamdrinkalot]

[QUOTE=Mos]Could you elaborate on how you tested it?
Mos.[/QUOT

I connected one wire at a time to the positive terminal of the battery, and had no response until I connected one wire to positive and one wire to negative.

[teamdrinkalot]

I was under the impression that it is a PWM controlled solenoid, and thus only open as much as the PWM signal tells it too.

Different openings = different oil pressure reaching actuator = different degree of rotation.

So what is a PWM controlled solenoid? I thought a coil is a coil and is either energized or not, no in between. I am led to believe that the ECU sends pulses to the coil depending on engine requirements.

[ed]

PWM solenoid: its a like a fuel injector

can be pulsed: little -> lot

[Mos]

Injectors are solenoids which open and shut very quickly. The width of the pulse is modulated to allow a specific opening time for the appropriate amount of fuel. The maximum frequency at which an injector opens and closes depends on the rpm of the engine and whether the injector opens once or twice per engine revolution - typically this frequency is very low - in the order of 50 to 200 Hz (cycles per second).

A device that is controlled by what is referred to as PWM (pulse width modulation) uses pulses, similar to an injector, but at a much higher frequency, eg 20kHz (thousands per second). The effect of this high frequency is that the solenoid cannot see each individual pulse, but sees the average effect of the pulses. Pulses with a low duty cycle (On for short time, and OFF for a long time) will develop a low average effect on the device; vice versa, high duty cycle will develop a high average effect.

Depending on the design of the solenoid, this duty cycle will determine how much the solenoid moves - low duty cycle = small opening, high duty cycle = large opening.

In addition, depending on how the solenoid is designed, applying power in one direction can have a different effect to applying power in the other direction.
So it's possible to have a solenoid that will open either one valve, or another valve, depending on the direction of current flow, and then using PWM it can open them to specific amounts.

It is also possible that the solenoid might always have 50% duty cycle pulses applied which means "do nothing". Decreasing the duty cycle (and pulse width) could have the effect of opening one valve, and increasing the duty cycle (pulse width) might open another valve.

Edit: Manual extract on the VVTi solenoid.


As can be clearly seen from the extract, the solenoid has a number of valves that open and close depending on the location of the valve piston. I don't know what the various channels are but I would imagine there would be at least a high pressure oil supply, a low pressure drain and the actuator - there may be some sort of mechanism to promote flow through the actuator rather than just pressure supply which would involve more individual valve ports. If anyone can elaborate on exactly what happens when, it would help greatly in understanding the operation.

It can also be seen the piston is pushed by the solenoid against a spring - varying the duty cycle varies the force with which the piston is pushed against the spring - low duty cycle = piston moves a little to the left, high duty cycle = piston moves further to the left (applying power directly is equivalent to 100% duty cycle).

Mos.