TMF Idle Speed Control

Introduction

Throttle Mass Flow (TMF) as the name indicates, is the rate at which air mass is flowing through a throttle body in units of grams/second (g/s).

The flow through a throttle body is governed by three physical elements:

1. Conversation of mass
2. Newtons second law of motion for fluids
3. Conservation of energy

By combining all these elements the ECU can model the flow of fluid through the throttle body accounting for throttle plate thickness and throttle shaft size. One key piece of data is knowing the pressure ratio across the throttle body as shown in the below diagram, the other key piece of data is the current throttle area. If the pressure ratio and throttle area is known, the ECU can very accurately calculate the mass flow rate through a throttle body.

Although the ECU completes these complex calculations internally, the process of calculating Throttle Mass Flow is kept as simple as possible for the user with the following inputs and setup required:

Inputs required

1. Pressure Before the throttle Plate
2. Pressure After the throttle Plate

Setting required

1. Throttle Body Size
2. Throttle Area to Servo Position Correlation Table (Throttle Body Area Table)

The TMF calculation can summarised in the below equation :

Throttle Mass Flow Idle Speed Control

The Throttle Mass Flow (TMF) idle speed control function delivers extremely accurate and rapid idle calculation based on actual engine’s airflow requirements. Any engine load change will be detected by a pressure ratio change across the throttle body allowing the ECU to make instantaneous corrections. In all DBW applications we strongly recommend that the TMF Idle speed control is employed. TMF Idle speed control is an independent idle speed control function that utilises the Emtron’s comprehensive air mass flow modelling without effect on the fuel model used.

The Throttle Mass Flow (g/s) becomes the target flow for the Idle Speed Control system i.e how much air mass flow is required for a given target rpm. So the TMF becomes the feed-forward/Initial value. The ECU will then apply a PID correction to this flow target until the Target RPM is reach. By rearranged the TMF equation, the ECU will convert the final Throttle Mass Flow(g/s) into Throttle Area and move the plate to that position. A feed-forward/Initial value table example is shown below.

Typical TMF Idle Feed forward table in units of g/s

NOTE:

Any fuel model mode can be selected and does not need to include TMF for the TMF idle speed control function to work correctly.

TMF fuel model is covered in the Fuel section and not discussed here.

Warning - DBW setup must be completed before setting up TMF idle

Throttle Body Area Table

Overview

The Throttle Body Area table is a 40-cell correlation table; it gives the direct relationship between Throttle Area and Throttle Position (Servo Position). The ECU uses this table to convert any Throttle Area request into Servo Position which is then used as the DBW Target. Throttle Body templates are available to load into the ECU from the File -> Import Module File menu.

Example:

Throttle Area Demand from the pedal = 4.37%

Using the table in the below image, the ECU would find the 4.37% area and correlate this to 9.0% Servo Position. The DBW Servo Position Target therefore becomes 9.0%

i.e the ECU is asking for 4.37% area and moves the throttle plate to 9.0% servo position to achieve this.

Nissan GT-R R35 Throttle Body Area table

Throttle body templates are also available to load into the ECU from the File -> Import Module File menu

There are multiple ways to calibrate the appropriate throttle area.

Method 1 – MAF verification

If the application is using a calibrated MAF sensor. Then the throttle area % can be adjusted and matched to TMF air mass VS MAF air mass at different throttle/DBW servo positions.

Method 2 – Matching Lambda

If no MAF sensor is available, setting fuel trims to 0 (or near 0), you can adjust the throttle area to match the target mixture very quickly.

** The only way to truly validate error in the TMF calculation is to use Method 1

** Some extreme applications where live Lambda is unstable may be more difficult to map with Method 2

See Torque Management Tuning Guide, Throttle Mass Flow, and Torque Reduction(throttle) sections for more specific information, and guides on how to tune.

Tuning Tip:

Per the Matching Lambda validation method, the Throttle Area Table is used to quickly tune the engine operating in TMF by simply manipulating the table at the various throttle areas to match the Lambda Target Table values for that given load. When the correct air fuel ratio is achieved, the Throttle Area Table is essentially validated for the purpose of running the engine. To do this the wideband lambda control should be turned off and the blend bias toward TMF be set to 100%.

Throttle Body Model

Overview

The throttle body model is a key component to unlocking the advanced tuning features of the Emtron ECU. That is Throttle Mass Flow & Torque Modeling & Management. The accuracy of your setup in the throttle body mode is critical for good results.

Once the throttle mass flow feature is characterized and enabled, the throttle body model setup can be accessed and setup

The Throttle Body setup consists of 2 main parts:

• Throttle body diameter and scaler.
• Throttle body area table.

See the DBW Torque Management  help topic for more information on the process of converting Pedal Position to Throttle Area to DBW Servo target.  

Throttle Body Setup

Overview

The Throttle Body setup consists of 2 main parts:

• Throttle body diameter and scaler.
• Throttle body area table.

Settings are adjusted from the Engine Functions -> Throttle Body Model menu. Throttle body templates are also available to load into the ECU from the File -> Import Module File menu

See the DBW Torque Management help topic for more information on the process of converting Pedal Position to Throttle Area to DBW Servo target.

Throttle Body Setup

The Throttle Body diameter and scaler can be adjusted from this menu.

Throttle Body Area Table

The Throttle Body Area table is a 40 cell correlation table; it gives the direct relationship between Throttle Area and Throttle Position (Servo Position). The ECU uses this table to convert any Throttle Area request into Servo Position which is then used as the DBW Target. Throttle Body templates are available to load into the ECU from the File -> Import Module File menu.

Example:

Throttle Area Demand from the pedal = 4.37%

Using the table in the below image, the ECU would find the 4.37% area and correlate this to 9.0% Servo Position. The DBW Servo Position Target therefore becomes 9.0%

i.e the ECU is asking for 4.37% area and moves the throttle plate to 9.0% servo position to achieve this.

Nissan GT-R R35 Throttle Body Area table