What is throttle body? Why it is used? How it works?

1. What is throttle body? Why it is used? How it works? Types and future of throttle Body.
2. What is Drive By Wire / Electronic Throttle System? Why gold is used in TPS?
3. Why Aluminum ADC12 or PA66GF35 used ? Why Valve material is different from bore material?
4. Why Throttle Body Heating is done ? And why drain holes are provided in throttle?
5. Why plastic is becoming popular in place of ADC 12? 
6. How Bore of Throttle is decided? What parameters are taken into consideration?
7. What software or tools are needed to fully design throttle body (Not development)

Suppose vehicle is on and in idle condition and neutral RPM is 950. Now you switch on AC (air condition), now AC need power. so as you switch on AC, ECU will sense and inject more fuel. To burn this more fuel engine need more air ( 20.95 % Oxygen) - How to control this air amount? 

When we "burn" gasoline, we are combusting it or combining it with oxygen. That's why engines need a source of oxygen-containing air, and why engines emit carbon dioxide as a by-product of combustion. At different speed, load and environment, the amount of oxygen needed will not be same. So how will driver control the amount of air? In mechanical system an assembly of butter fly valve with idling speed control valve & TPS were used. This system is called mechanical throttle body. In this system driver press accelerator witch is connected to butter fly valve by metallic wire.

As driver press the accelerator by leg in car or by hand in bike, the throttle butter fly valve open to allow more or less air. As a result the engine power and torque changes. Which ultimately leads to desired speed, acceleration, and jerk. Idle speed control valve is part of mechanical throttle body but it is controlled by ECU signal based on fuel quantity calculation. This is complex calculation and involve feedback from various primary sensors, secondary sensors, empirical values and by default values considered by Mech-software engineers based on calibration, experience and expectation. TPS or throttle position sensor is mounted on valve shaft and give opening angle voltage to ECU to know the opening and calculate amount of fuel for next stroke. 

 If you remember there is a screw in some bikes, and you rotate it to balance idle rpm of bike. in traffic if it is too low vehicle will stop. In car it is done by ECU and ISV Valve.


What is Drive By Wire / Electronic Throttle System? 

Drive by wire is a technology where electric and software system is used to operate and control Throttle motor it can be stepper motor or DC motor depending upon manufacturing specification and requirement.  Throttle position tracking is taken as control object, and the structure of the electronic throttle is analysed, a mathematical model of the electronic throttle is established. TPS or throttle position sensor is mounted on valve shaft and give "opening angle voltage" to ECU to know the opening and calculate amount of fuel for next stroke. TPS is based on simple principal of whitestone bridge but this bridge has measuring wire or moving needle made of gold for accurate sensitivity and rust free contact.    

• The electronic throttle unit also controls the idle and cruise control operation
• These systems have a "limp home mode" that will allow the vehicle to be operated at low speed when a fault is detected

A method and system for controlling a limp-home function in an electronic throttle system adapted to prevent stalls which may occur due to failure of electronic throttle system by executing proper limp-home control to cater to a running state of the vehicle. Electronic throttle control systems can be designed so that the throttle closes if it is no longer receiving a signal from the pedal sensor.

Why Aluminum ADC12 or PA66GF35 used ? Why Valve material is different from bore material?


ADC12 body is used because it is easy to do casting. Now many companies shifted from Aluminium ADC12 to Plastic PA66GF35 because 1- Initial investment is high in plastic moulding machine but cost of each product is low so if vehicle is selling more than 200000 per year , it will be financially good decision to go for Plastic Glass Fiber. 2- There is no machining requirement and also ADC die needs replacement after each 40000 piece to 80,000 piece depending die designer recommendation. Thermal Expansion of valve and bore must be different to avoid sticking of valve inside bore.



Why Throttle Body Heating is done ? 
Also Throttle Body Heating is done in colder countries and hill areas to avoid icing inside throttle. This icing can fully block air flow. It can leads to accident. For this engine coolant circuit hose is attached near ISC valve or Electric Throttle Valve.

Why drain holes are provided in throttle?
Mechanical and Electronic Throttle Body both has small hole near TPS assembly area. Temperature of throttle body is very important parameter not only from CFD, Air Density and Change Density point of view but also to prevent rust on TPS bridge wires to give accurate value of valve opening to ECU. People Drive Vehicle to washing station and wash in hot condition - Throttle is water proof but water vapor can go inside TPS chamber - when this vapor condense it become water inside TPS. 

Why plastic is becoming popular in place of ADC 12? 

For cost reduction ( VA / VE), However even a company is designing throttle for highly popular vehicle, In early development stage they have to use Aluminium Body Only - As told in point 1 - for proto or mule engine sand casting throttle body or fully machined from Aluminium block can be low cost. Plastic moulding machine is very costly as a rust plastic body comes at later Production Trail Stage or Mass Production Trail Stage that is when 1D/2D/3D simulation and primary calibration is done.

How Bore of Throttle is decided? What parameters are taken into consideration?

• Stability in Idle RPM
• Fuel Efficiency at Idle RPM
• Air Fuel Ratio Variation with Butter Fly Valve Angle Resolution
• Limp Home Air Requirement
• DC / Stepper Motor Angle Resolution
• Maximum Torque Vs RPM Curve 
• Maximum Power Vs RPM Curve

What software or tools are needed to fully design throttle body (Not development)

• DFMEA – Do not start work without design failure mode effect analysis, if you start definitely your design will fail. Do DFMEA with each and every department of car such as fuel, brake, white body, manufacturing, production, supply chain, vendor development, and quality. Even if it a dummy or minor research take technical design failure from each one.
• Start with 1 D Simulation – Use Ricardo, GT or Lotus to get primary Bore 
• 2D Analysis – Make Drawing and check Geometric Tolerance (GDNT) with 2D drawing of intake manifold, Cylinder Port, Air Filter Pipe or Hose for making CAD for 3d Analysis
• 3D Analysis – CFD Analysis, Thermal Analysis, Fatigue Analysis, Stress Strain Analysis etc there are many software such as GT Suit, Fluent, NX, Solid works, StarCD, Matlab,
• Control Model - Matlab for component modelling from physical system to mathematical system
• Control Analysis – Matlab, ETAS
• Bench Calibration Analysis – Dyno bench for Engine - High Speed Test, Thermal Cycle Test, Up Down
• Vehicle Accident – Crash Test for Limp Home Check
• Vehicle Calibration – Emission Test, Fuel Efficiency Test
• Vehicle Fatigue and Endurance Test – 20,000 Km Run in different pattern such as Hugh Speed, Up Down, Dyno Endurance etc

Development testing word is used around die design, proto quality, instrumentation tools, manufacturing facility, Quality Tools etc – this we will discuss in separate article.