Glow-plug relay and control

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Glow-plug relay and control

Post by white exec » 06 Oct 2018, 21:08

Have been trying to collect some info on GP pre-heat and post-heat control, for our diesel engines.

On all engines, the GPs are switched by the heavy-duty GP relay (capable of handing up to 70A or so):
- some of these relays provide a fixed period of pre-heat (eg 7 secs) only
- others provide a post-heat too, which continues to power up the GPs after starting, to provide a better and cleaner start with a cold engine

Post-heat
The length of the post-heat is usually variable, according to "temperature". A hot engine will typically produce little or no post-heating.

Now the bit I'm interested in...

The "temperature" appears to be sensed, according to model, by different means:
- some GP relays have 'internal' temp sensing, whereby I guess the GP relay itself responds to under-bonnet temperature
- other cars use Coolant temperature measurement, with the engine's ECU using its (injection) coolant temp sensor's reading to instruct the GP relay how long to operate (eg Xantia, XM, and Toyota for that matter)
- But are there other systems?
There has been mention of a thermal device/switch incorporated on to the injector pump. What is this, and how does it work? Which engines/models was it fitted to?

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Re: Glow-plug relay and control

Post by EDC5 » 06 Oct 2018, 21:15

This is very interesting.

When I was reading something the other day I saw somebody mention the wax-stat on the mechanical Lucas pumps also had an auxiliary contact that might have been used for this purpose. I'm not sure if it's true but might be a good lead :)

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Re: Glow-plug relay and control

Post by GiveMeABreak » 06 Oct 2018, 22:02

I will do some tunnelling

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Re: Glow-plug relay and control

Post by myglaren » 06 Oct 2018, 22:05

GiveMeABreak wrote:
06 Oct 2018, 22:02
I will do some tunnelling


You are a Morian* and I claim my £5!



*Note - not "Moron"

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Re: Glow-plug relay and control

Post by GiveMeABreak » 06 Oct 2018, 22:20

Although I do feel as though I am in Mount Doom at times Steve! 🌋

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Re: Glow-plug relay and control

Post by Hell Razor5543 » 06 Oct 2018, 22:29

Just watch out for the Balrog!

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Re: Glow-plug relay and control

Post by GiveMeABreak » 06 Oct 2018, 23:16

white exec wrote:
06 Oct 2018, 21:08
The "temperature" appears to be sensed, according to model, by different means:
- some GP relays have 'internal' temp sensing, whereby I guess the GP relay itself responds to under-bonnet temperature
- other cars use Coolant temperature measurement, with the engine's ECU using its (injection) coolant temp sensor's reading to instruct the GP relay how long to operate (eg Xantia, XM, and Toyota for that matter)
- But are there other systems?
There has been mention of a thermal device/switch incorporated on to the injector pump. What is this, and how does it work? Which engines/models was it fitted to?
As far as the X7 DW10BTED4 engine goes Chris,

For Pre-Heating:
The pre-heating and postheating times are determined by the engine ECU as a function of the engine coolant temperature, the air temperature, the atmospheric pressure as well as the engine operating phase that is in use (for example engine speed and load too high).
The pre-heating time varies as a function of the following values :
  • Engine coolant temperature
  • Temperature of the air inducted
For Post Heating:
The postheating starts as soon as the pre-heating phase is finished.
The pre-heating plugs are supplied without limit of power.
The length of activation of the plugs depends on the engine coolant temperature value, the atmospheric pressure (air density) as well as on the quantity of fuel injected (air temperature / fuel, air density).

The postheating stops in the following cases:
  • The postheating time is exceeded
  • The ideal value for the coolant temperature has been attained
  • The value for the inlet air temperature is wrong
  • The value for engine speed and load is too high
Postheating is used for limiting the emissions of hydrocarbons and carbon monoxide.
Postheating is used for loading the engine in order to bring the catalytic converter and/or the particle filter up to an optimal operating temperature as rapidly as possible.
Actions of postheating:
  • Prolonging the operation of the pre-heater plugs after the starting phase
  • Reducing the emissions of pollutants in the first few minutes after starting
  • Reducing blue fumes especially at altitude
Post Heating in Regeneration (FAP - Equipped Vehicles):
During a regeneration phase, the BSI may ask the engine ECU to operate the pre-heater plugs so as to "load" the engine (To increase the electrical consumption in order to augment the engine temperature for the requirements of the particle filter).
The plugs are activated for a maximum duration of one second and their activation depends on engine speed and also fuel flow (Risk of overheating and knock).

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Re: Glow-plug relay and control

Post by white exec » 07 Oct 2018, 09:02

Thanks, Marc, that's a really detailed description of the late (X7) system.
Wonder how often the 1 sec operation of the GPs (for partic filter clearance) occurs? What a way to load up the engine! Who said electronics didn't rule ok, these days?!

That all makes sense, and is obviously not very far off how diesel Xantia, XM etc (with injection ECU) worked. Just waiting for someone to dream up PWM operation of the GPs, rather than a 70A relay. Ssshh... :-$

As said, would be good to know more about the pump-mounted temp sensing widget. Couldn't definitively find it on a circuit diagram. Presumably applies to non-ECU injected XUD engines.

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Re: Glow-plug relay and control

Post by GiveMeABreak » 07 Oct 2018, 09:41

That was just for the Delphi DW10BTED4, the DW10CTED4 is similar but different as it was changed for Euro 5 compliance and many more changes were made to decrease the time taken to reach operating temp again.

This included different glow plugs, engine ECU, air doser unit and various other components.

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Re: Glow-plug relay and control

Post by moizeau » 07 Oct 2018, 10:25

Hope this sheds some light Chris. The wax stat cable goes to the fast idle lever on the pump. The fast idle lever is connected to a contact switch which is in turn connected to an 'electromagnetic timing device'. The 12v feed actually travels in the opposite direction, i.e. from the fuel solenoid in to the timing device then on to the contact, which presumably earths it completing the circuit. This is for a Lucas pump on the older XUD (my BX). What the timing device does? Sorry can't help further. If you want a scan of my BOLs page let me know. I believe that on the bosch pump there is something that looks like a secondary stop solenoid on the side of the pump. Looking again at mine the timing device does look like a stop solenoid without the feed wire on the end.