Electronic Throttle Body operation and calibration

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HypoThermia
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Electronic Throttle Body operation and calibration

Post by HypoThermia »

This is a repost of an original thread by Fabrice (Rasputin) that has since expired. A classic for all members and non-members to enjoy =D> (or just stare at the pretty pictures :lol:).

(apologies, but my sig appears at the bottom of each post - this is all Rasputin's work).

:arrow: :arrow: :arrow: :arrow: :arrow:


Operation

Until recently, the throttle body that controls the air mass going into the cylinders (or rotors...) on a petrom engine, and therefore, the engine load (= torque), was directly linked to the accelerator pedal with a cable.
There was then a univocal relationship between the pedal position and the throttle opening, for all operating conditions. It was not necessarily linear as the progression could be affected by rounded levers to give more (= sproty feel) or less (= better driveability at lower speed) aggressiveness to the throttle body control.
Recently, theat system was replaced by electronics. The mechanical link disappeared in favour of an electrical wiring. The Electronic Throttle Body Control system contains :
- a pedal box with 2 position sensors ;
- an electronic control unit, nowadays integrated into the Engine Control Unit (as in our RX8) ;
- a motor-driven throttle body connected to 2 position sensors.

Its operation can be summarised so :
1) The Pedal Position Sensors (PPS) measure pedal position. There are 2 sensors to offer redundancy to :
- cancel any signal coming from a defective sensor ;
- ensure the car remains operative after a sensor failure.
2) The 2 PPS signals (PPS_A and PPS_B) are processed to obtain a single value : PPS.
3) The electronic control unit affect a requested throttle position value (TPS_DES) corresponding to the input PPS, according to the operating conditions (mapping).
4) Then, the control unit controls the motor driven throttle in closed loop in order to achieve the res-quested TPS-DES value. To do so, the system relies on the throttle position sensors (TPS) feeding TPS_A and TPS_B to the control unit that processes them into a single value, TPS. The control unit will make sure the TPS value stays as closely as possible to the TPS-DES value.

Fabrice

COM - MADE STICKY DONT WANT TO LOSE AGAIN G72
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Post by HypoThermia »

TPS/PPS relationship engine not running.

The data was collected with my Hymee sCANalyser Live OBD tool.

Reminder :
TPS : Throttle Position Sensor (also value in %)
PPS : Pedal Position Sensor (also value in %)

Tip-in = pressing the accelerator pedal
Tip-out = releasing the accelerator pedal

As you can see on the attache graph, the relationship is far from linear. Indeed, the throttle stays at his minimum crank value (8.2%) until you reach 50% of pedal travel. Comme vous pouvez le constater, la relation est loin d'être linéaire. Then, the system rapidly reaches 100% TPS before the driver reaches 70% pedal travel.

This mapping ensures the throttle remains at 8.2% (optimum for engine start) even if the driver accidently and sligthly apply some pressure on the pedal, in order to prevent overfuelling and, potentially, flooding of the engine.
In case of flooding, as the manual tell you, one must fully press the accelerator pedal in order to achieve 100% TPS. At this maximum throttle opening, the fuel map actually completely cuts out fuel in order to cure any flodding condition with induction air. To make sure one achieves 100% TPS even with a weak leg (before one's morning coffee) or a misplaced carpet, this wide open throlltle (WOT) condition is obtained with only 70% PPS. Failure to obtain 100% TPS would end up in adding massive quantities of fuel in the engine, aggravating the flooding condition.

Its seems there is some sort of hysteresis in the system. However, as I don't see the need for it, I guess it might be caused by some dashpot or timer strategy in the system.

Fabrice
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Post by HypoThermia »

TPS/PPS relationship engine running

The first graph contains all the data points recorded with my Hymee sCANalyser during normal driving, and contains city and motorway driving conditions.

There is a high concentration of data points in the low TPS/PPS area as that's where most of our commute driving takes place.

An important dispersion is visible in the area of low PPS. This looked suspicious to me and I decided to push the investigation a bit further by sorting the data points by gear (only 5 gears on mine I'm afraid).
The second graph seems to confirm a trend showing different throttle progression with regards to the gears. In 2nd, it looks like higher value of PPS are needed to obtain throttle movement. In 5th, the throttle almost opens immediately. Data points corresponding to the 1st gear are not clearly visible (only a few data points correspond in that gear, as traffic was flowing) but they are roughly in the same area as 2nd gear data points. Data poit in 3rd and 4th are roughly situated together somewhere between the 2nd and 5th data points.

It seems several ETB progression maps (it could just be a different gain, not full map) are available as a function of gear, or engine speed, as there is a relantionship between them. Please note that a gear selector sensor is not needed for the ECU/PCM to know in which gear the car is running. It just needs to divide engine speed by vehicle speed. That's what I did to determine the gears in my data set. Indeed, I already suspected previously, just by driving the car, that such a difference in progression was built into the system.

Going back to the graphs, the progression at low PPS is smooth in 2nd gear in order to give the driver a better feeling and control on the engine torque for a more confortable drive, or better control on slippery surfaces (snow).
As soon as the pedal position reaches 85%, you have WOT! No need to try to smash the pedal through the firewall to go faster Very Happy . Moreover, at low engine speeds, very high loads are reached with small throttle opening as relatively low air delivery is sufficient at these speeds. But we'll discuss that somewhere else.

As you probably noticed, there is a relatively high disparity of some data points. I believe it is due to the relatively slow response of the motor-driven throttle to very swift pedal tip-ins or tip-outs. There is one data point situated at PPS = 0% and TPS = 28% which can definitely corresponds to a very quick tip-out : the pedal already is at 0% while the motor is still working at closing the throttle.

Anothe point : TPS never goes under 2%, even in the most violent overrun. More info on this later.

Fabrice
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Post by HypoThermia »

Done posting! And a might fine read too, Fabrice! =D> =D> =D> =D>

If any more was posted (as the third post seems to suggest) then I'm afraid that I don't have it.

Ian.
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Post by Rasputin »

Thanks Hypothermia!

I'll sue you now for breaching copyright... :lol:

Re the Pedal Position Sensors (and probably TPS too), I now know they are of the Hall effect type whereas they usually are/were of the potentiometer type. The advantage of Hall effect is the absence of contact and, therefore, of wear that can cause failures or restrict longevity.

Electronic Throttle Body also is an important actuator in Traction Control and Stability Control (ESP/DSC). These 2 vehicle safety systems take control of the ETB in order to limit engine load.

One other possible functionality with an ETB, is the ability for the PCM to compensate for altitude (and less dense air) by changing the relationship between the Pedal Position and Throttle Position and increasing engine load and maintaining the same performance feel.
Obviously, it only works in part load operation as your WOT BMEP/torque will remain limited by the ambient conditions.

Fabrice
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Post by Harrizone »

Ooooppppsss! :oops:

Apology Fabrice I do seem to remember this post now.

Senility fast approaching methinks. :D

Ray
Now a distant memory unfortunately.
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Post by HypoThermia »

Rasputin wrote:I'll sue you now for breaching copyright... :lol:
Wonder how that works when you don't have the original to hand... :-s :P

(Edit: too bad we're not in France at the moment :shock: :lol:)

Had a thought about the hysteresis of the pedal travel (second post). It's probably there to emulate the behaviour/feeling that a physical pedal has. They also have some neutral travel (a "loose" feeling, or hysteresis) when you change pressure from "push down" to "back off".

A pedal that gave very precise positioning would feel very different to a physically connected system.

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Post by Rasputin »

HypoThermia wrote:
Rasputin wrote:I'll sue you now for breaching copyright... :lol:
Wonder how that works when you don't have the original to hand... :-s :P
You might have a point there. :?
HypoThermia wrote:
Had a thought about the hysteresis of the pedal travel (second post). It's probably there to emulate the behaviour/feeling that a physical pedal has. They also have some neutral travel (a "loose" feeling, or hysteresis) when you change pressure from "push down" to "back off".

A pedal that gave very precise positioning would feel very different to a physically connected system.

Ian.
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Re: Electronic Throttle Body operation and calibration

Post by RX8R3Rod »

And once you have this stuff, it gives access to potentially even neater things. I notice Tanabe's latest coil over system offers not only electronic damping adjustment, but by linking up with the speedo communications it will automatically vary damping according to speed, and the extent to which it does that can be adjusted from the drivers chair . Hmmmm.
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Re: Electronic Throttle Body operation and calibration

Post by chiron »

A lot of this is accessible in Mazdaedit. When I remapped mine I spent a while "linearising" the pedal map as I didn't like the non-linear pedal map below 30%.
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