The throttle is an important element of a gasoline engine. And the gas pedal just regulates the position of the throttle valve, which “measures” the amount of air entering the engine. We understand where the throttle is located, how the throttle assembly is arranged, and what are the symptoms of its malfunction.
What is the throttle plate for
So, what is a throttle in a car? This is a flap that regulates the amount of fuel-air mixture when the engine is running, changing the passage section of the air channel.
Structurally, the throttle assembly is quite simple. It is a housing part with a round channel, which overlaps a metal “petal”. It is controlled by the gas pedal – when maximum power is needed (the driver presses the gas pedal to the floor), the flap turns around its axis and fully opens. When the engine is running smoothly or idling, it is only slightly open. When the choke is open, the pressure in the intake manifold is equal to atmospheric pressure or that generated by the turbocharger. If the choke is closed, the pressure drops and a vacuum is created – the engine works like a pump. By the way, this effectively brakes the car.
In addition to the main function – air dosing for correct engine operation under load, the throttle unit allows the engine to run at idle (with the accelerator pedal fully released). This is done by means of an idle speed sensor (regulator) on the throttle.
In addition, the throttle is responsible for the performance of the brake booster. It works on the vacuum principle and is connected to the intake manifold. Therefore, when the engine stops, the brake pedal becomes “stone” – the driver is forced to slow down the car only by the force of his own foot. The same property of the throttle is used to blow out the adsorber, which captures gasoline vapors. Finally, the throttle can be used to shut down the engine in an emergency by completely cutting off the air supply.
So, what is the responsibility of the throttle in a gasoline engine? For its stable operation, regulation of revs and, accordingly, the output power, for an adequate level of fuel consumption, the effectiveness of brakes and partly for the fulfillment of environmental requirements. In diesels, where the combustion air is freely available, the throttle is also installed. However, its role is limited to two functions: stopping the engine (regular or emergency) and limiting the air flow for more efficient operation of the EGR system. A similar situation – with gasoline engines equipped with a system of changing the valve height, which itself regulates the amount of air entering the engine.
Design and types of throttle plates
Let’s analyze the design of the throttle in gasoline engines. Throttle valves can be of three types: with mechanical, electronic, as well as electromechanical control. Let’s consider how the first two types work, since the third is a combination of them.
Mechanical throttle actuator
Mechanically actuated throttle plates are equipped with most older cars. This is a cheaper, but not always simple design, involving a direct mechanical connection between the gas pedal and the throttle plate – with the help of levers and rods, or a metal cable.
How does a mechanical-type throttle valve work? It is forced to turn and, accordingly, to open by pressing the accelerator pedal – through the same rods or cable. When the driver releases the pedal, a special spring returns the choke to the closed position.
When the choke is closed, the idle speed regulator (COC) maintains the minimum steady crankshaft speed. It is essentially a stepper electric motor with a valve that doses the air entering the intake system to bypass the closed throttle. In very old cars with a carburetor, a bypass channel is simply made, which can also be bypassed by a solenoid or vacuum valve.
Electronic throttle actuator
A more modern (and expensive solution) is an electronic throttle actuator. The principal difference in this design is the absence of a direct mechanical connection between the gas pedal and the choke. Instead of a system of rods and cables, electronics is used.
The electronic system has many components: electric throttle actuator, throttle pedal and throttle position sensors, electronic engine control unit (ECU).
The process of throttle control in electronic throttle actuator is as follows. The signal from the gas pedal position sensor goes to the ECU, where the required amount of fuel and air is calculated. The throttle is then signaled and the electric actuator opens or closes the choke.
The electronic actuator is primarily designed to ensure the desired environmental performance of the engine – that’s why it is widely used on modern engines. Even when the driver sharply presses the gas pedal, the choke opens not completely, but exactly to the extent that the engine receives the optimal portion of air and, consequently, fuel for its revolutions.
What else is an electrically operated throttle valve for? It allows you to change the engine torque without having to press the pedal. Cruise control, for example, is based on this ability. Engine idle speed, like many other things, is regulated automatically. After all, the electronic throttle control system, in addition to the gas pedal position sensor, is guided by signals from many sources: from the gearbox, climate control system, brake pedal position sensor and so on.
In all variants of the design, the throttle components are incorporated into a separate housing on which the choke position sensor and idle speed control are mounted. Also the housing is included in the engine cooling system. The fact is that when the air pressure drops, occurring on the flap, moisture condenses from it – and in cold weather, without heating the throttle with antifreeze, it will freeze, blocking the operation of the assembly.
Throttle valve malfunctions, prevention and repair
About the malfunction of the throttle plate will prompt obvious symptoms. If there are problems with it, the engine runs erratically at idle, accelerates the car with interruptions (failures) and loses power. Think about the malfunction of the throttle should be difficult to start the engine, its inadequate response to the gas pedal, as well as if it stalls when releasing the accelerator pedal.
Most often, problems with the throttle are caused by the formation of soot and carbon deposits on its surfaces. The cause of this phenomenon is crankcase gases with engine oil vapor, which penetrate the throttle through the intake manifold. And in old cars with carburetor, where the ready fuel mixture passes through the throttle – and impurities in gasoline, leaving a characteristic “lacquer” deposit.
Over time, deposits accumulate, and the cross-section of the throttle channels decreases. In parallel, the deposits change the geometry of the flap and the channel it covers, causing it to close loosely. The node begins to work incorrectly, fuel consumption increases.
In order that the flap does not remind about itself problems, about every 50 thousand kilometers it should be cleaned with a special tool for throttle flaps. For this purpose, the throttle will have to be removed, which in most cases is not so difficult.
There are breakdowns, which such prevention will not always prevent. Can fail the idle speed regulator, the sensor of the position of the flap, the gear in the gearbox. Finally, in the throttle with a mechanical drive can eventually fray and break the cable. Sometimes flowing pipes and sockets, through which the antifreeze goes.
The cost of cleaning the choke at the service station is low, in the neighborhood of 1500 rubles, if the design of the car does not imply for the removal of the throttle dismantling of the intake manifold (it is rare). And for the engine to start working correctly after repair or even replacement of the electronic throttle, the choke must be adapted.
Before the repair, so that there are no surprises later, it is recommended to clarify whether the adaptation is included in the total cost. It happens that the bill for it at the end of repair in unscrupulous service stations is billed separately.
Without adaptation, the car may not start well. It may also happen that the ECU itself will simply change the settings in such a way that the engine will work incorrectly and inefficiently.
Total
- The throttle is a device in internal combustion engines that regulates the amount of air to feed it.
- The throttle is responsible for the smooth operation of the engine, the level of fuel consumption, the effectiveness of brakes and partly fulfillment of environmental requirements depends on it.
- There are two main types of throttle valves: with mechanical and electric drive. The latter is distinguished by the absence of a direct mechanical connection between the gas pedal and the choke.
- To avoid failures and malfunctions in the throttle valve, every 50,000 km of mileage should be carried out preventive cleaning of the node with the help of special auto chemistry.