VEMS Community Forum

Has anyone messed about with using VEMS output to control a variable geometry turbo such as the Holset 351VGT? These vary the turbine housing volume from 3mm² to 25mm².

I am looking at using this set up to achieve fast spool using TPS and RPM to activate it on an BMW s38b36 engine. My idea is that for:

TPS<50% all RPM range to set the housing to 25mm² which I have calculated to to spool 1 bar from ~4500rpm.

TPS >50, RPM 1000 to 2500 to set the housing to say 10mm² for spool at 1800 RPM,

TPS > 50%, RPM 2501 to 4500 housing 18mm²

TPS > 50%, RPM 4501 to Redline (Set to 7000) housing at 25mm²

The concept is to control spool. The built in boost control will monitor boost. 

People have been messing about with controlling this turbo. See here http://www.homemadeturbo.com/f7/holset-vgt-he351ve-controller-117261/
It is a long read but with good info.

PWM - yes
CAN - no.

I thought about this 2 years ago and at that time was going to use a mechanical linkage to the turbo to control the movement.
But with a pressure actuated one a boost solenoid would work the same.

You can use the alternative pwm table to do this based on manifold pressure against rpm.

Which should provide you with the control ability . If needed then you should be able to get a TPS/RPM pwm table from the developers.

Its CAN :(

So I think I have 3 options:
1) A PWM solenoid and lever and not the stock actuator.
2) A on/off solenoid activated on TPS and RPM
3) The mechanical route (Boost activated).

Thanks guys.

Some drives for VNT was just PWM. May be it is possible to find some..

Quote from: BimmerDread on December 05, 2010, 07:38:45 PM
Its CAN :(

So I think I have 3 options:
1) A PWM solenoid and lever and not the stock actuator.
2) A on/off solenoid activated on TPS and RPM
3) The mechanical route (Boost activated).

Thanks guys.

What is the actuation process ? is it pressure based or mechanical linkage within the adjustment unit?

The turbo uses a mechanical linkage operated by a motor.

then just replace the motor?

my idea was to use a servo motor to handle the mechanical movement.

Servomotor from what?
There is harsh environment!

Maybe the steppermotor driver can be used

Quote from: GintsK on December 06, 2010, 11:17:02 AM
Servomotor from what?
There is harsh environment!

the servo doesn´t have to be directly close to the turbo, it can be mounted elsewhere and rotate a arm.

Ok. What servo?
===
Stepper isn't best idea. It require firmware modificatons. Servo usually use pulse width. So PWM with right frequency could be used. VEMS can control VNT + control W-gate using two independent PWMs.
SI engine require w-gate too.

I can´t remember which, but it has to have a bit of torque available

So... after some thought I decided to modify my parameters. This is what I came up with:
At 12mm² spool comes on at 2000 rpm and back pressure effect begins at 4100 rpm.
At 23mm² spool comes on at 4000 rpm and back pressure effect begins at 8000 rpm.

I want to have a two state (on/off) solenoid that when off keeps the volume at 23mm² and at
12mm² when on.

A function table would look like this:

TPS            RPM           State      Volume
<50%         Varies         Off          23mm²   
>50%         0 - 4k         On          12mm²
>50%         4k - 8k        Off          23mm²

The waste gate would manage any boost ripples on transition.

I needed a mechanical system that would have pressure at all rpms so I am opting for an oil pressure based system (like vanos ;))

I want to feed the oil to the waste gate port that would operate the system.

What do you think?

Most wastegates would leak.

I suspect it would. I am going to test an old one to see how much leakage occurs. I wonder what pressure would damage the diaphragm. I believe that they are good to ~4bars and it should not see more than 5bars under any driving conditions.

Early VGTs on diesels all used vacuum and an N75 type valve to control the position.   Surely that would be easier than oil?

I thought the purpose of the variable geometry compressor was to keep the compressor in its operating limits at varying mass flow conditions. For example, at low load rpm mass flow is low, but at high load high rpm, mass flow is high. To satisfy the high mass flow you need a big compressor which falls off the map at the low mass flow. Inversely  a compressor that satisfies the low mass flow falls of the map at the high mass flow. Variable geometry compressors allow a much bigger compressor to work at the low mass flow and keep it on the map.

Thats the way at least it works on our VERY large turbo compressors with the variable diffuser opening up as the mass flow increases. It is CRITICAL that the diffuser is in the correct position during operation. Failure to have the diffuser in the correct position results in catastrophic failure of the bearings, which results in damage to the compressor wheel, rendering the £10,000 impellor, scrap! Not so much of a bother with a small turbo charger costing maybe £450 all in. Incorrect diffuser position creates a little know phenomenon called 'Rotating Stall', is a pre curser to surge, and is as damaging if not more so.

(http://www.turbominis.com/uploads/i/wh682-oe1/sprocket-1712.JPG)

I am not saying that the variable geometry turbos work the same way. Awareness of the phisics of why it is variable geometry in the first instance, have the data on the diffuser position at varying mass flows before deciding on how to control it. It could be as simple as an on off actuator as suggested, but I remain sceptical. Having said that, the small turbo chargers appear to be much more tollerable of unsatisfactory conditions than our turbo compressors are.

One of the lads over on Turbo Minis used a VNT turbo and used another actuator to control it. Not really sure if it worked that well.

a VGT from Holset is designed to accelerate the exhaust air onto the turbine blades the best possible to create torque on the compressor axle. This is done by varying the area the discharge has on to the blades.

Quote from: paul_f on December 08, 2010, 09:30:17 PM
Early VGTs on diesels all used vacuum and an N75 type valve to control the position.   Surely that would be easier than oil?

I thought about that as well where boost pressure would be used to switch the system on. However if you look at my function map,there is a case were boost pressure is needed to activate the valve when boost is not available.

Sprocket, you mention varying the compressor or cold side of the turbo. The VGT turbos vary the size of the turbine housing or hot side. There is till a concern for surge if the there isnt enough flow at 2000rpm to support the suggested 1bar boost level. I will triple check the compressor map :).

This vgt turbos are good for petrol engines? Are they accept the higher egt temp?

They are being used with good success. It seems the additional heat doesn't bother them too much. It is always better to use a tubular manifold to get rid of some of the heat pre-turbo. The issue with the older VGT's is the shaft wearing out earlier than the non VGT's.

I did the calculations and 1 bar of boost @2000rpm will create surge. So I will limit it to 0.5 bar @2k and 1.5 bar for the rest of the range. ;D