The full name of VTEC system isVariable valve timingIn 1989, Honda launched the self-developed "Variable Valve Timing and Valve Lift Electronic Control System",It is the first valve control system in the world that can simultaneously control the valve opening and closing time and lift.
Chinese name
VTEC system
Foreign name
Variable Valve Timing and Valve Lift Electronic Control System
Developers
Honda
Launch time
one thousand nine hundred and eighty-nine
Properties
electronic control system
Status
The first valve control system in the world that can simultaneously control the valve opening and closing time and lift
The full name of VTEC system isVariable valve timingAnd the lift electronic control system is Honda's proprietary technology. It can properly adjust the valve timing and valve lift with the change of engine speed, load, water temperature and other operating parameters, so that the engine can achieve the highest efficiency at both high and low speeds.In the VTEC system, there are three cam surfaces on the inlet camshaft, respectively jacking the three rocker arms on the rocker arm shaft. When the engine is at low speed or low load, there is no connection between the three rocker arms. The left and right rocker arms respectively jack the two inlet valves, so that they have different timing and lift, so as to form an air squeezing effect.At this time, the middle high-speed rocker arm does not jack the valve, but only makes invalid movement on the rocker arm shaft.When the speed is increasing, the sensors of the engine will send the monitored load, speed, speed, water temperature and other parameters to the computer, and the computer will analyze and process these information.When it is required to change to high-speed mode, the computer will send a signal to open VTECSolenoid valveMake the pressure oil enter the rocker arm shaft to jack the piston, so that the three rocker arms are connected as a whole, so that both valves operate in the high-speed mode.When the engine speed decreases to the valve timing and needs to be changed again, the computer sends a signal again to open the VTEC solenoid valve pressure head, so that the pressure oil will leak out and the valve will return to the low-speed operation mode again.
After an ordinary engine is manufactured, the valve timing and valve lift are fixed, which cannot meet the engine's intake and exhaust requirements at different speeds.Therefore, traditional engine designers are consideringCamshaft profileBoth high-speed and low-speed should be considered.However, this kind of comprehensive design scheme limits the performance of the engine to some extent, which is far from meeting the requirements of vehicle engines.Therefore, people hope to have an engine whose cam profile can adapt to any speed, and get the best valve timing no matter at high speed or low speed.therefore,Variable valve timingThe control mechanism came into being.The typical variable valve timing control mechanism is Honda's VTEC system.
form
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VTEC control system consists of control part, executive part and sensor.The control part includes engine control unit ECU and VTEC solenoid valve;The executive part includes cams, rocker arms, pistons, etc;The sensors include engine speed sensor, vehicle speed sensor andCoolant temperature sensor。When the engine is running, the control unit ECU judges whether to change the valve timing and valve lift according to the signals of each sensor.
Development history
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Honda launched the self-developed "Variable Valve Timing and Valve Lift Electronic Control System" in 1989. The English version of "Variable Valve Timing and Valve Lift Electronic Control System", abbreviated as "VTEC", is the first valve control system in the world that can simultaneously control the opening and closing time and lift of valves.HondaVTEC engineIt has always been known as "the synonym of variable valve engine". It not only has super horsepower output, but also has the characteristics of environmental friendly exhaust emissions and low fuel consumption at low speed. This completely different feature appears on the same engine because it has multiple cams at different angles on a camshaft.
Structure principle
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Like many ordinary engines,VTEC engineEach cylinder has four valves (two inlets and two rows), camshafts and rocker arms, etc., but the number and control method of cams and rocker arms are different from ordinary engines.Small angle cams are used at medium and low speeds. At medium and low speeds, the valve timing and lift of the two valves are different. At this time, one valve lift is very small and almost does not participate in the intake process. The intake channel is basically equivalent to a two valve engine. However, because the flow direction of the intake air is not through the center of the cylinder, a strong intake swirl can be generated. For low speeds,Especially under the cold car condition, it is beneficial to improve the mixture uniformity, increase the combustion rate, reduce the wall chilling effect and the influence of clearance, so that the combustion is more sufficient, thus improving the economy, and significantly reducing HC and CO emissions;At high speed, the VTEC solenoid valve controls the direction of the hydraulic oil, so that the two intake rocker arms are connected and the valves are driven by the intake cam with the longest opening time and the largest lift. At this time, the two intake valves are synchronized according to the contour of the large cam.Compared with low-speed operation, it greatly increases the intake flow area and opening duration, thus improving the power performance of the engine at high speed.Honda engineers made these two output curves of completely different performance realized on the same engine, and vividly called them "gentle driving in peacetime" and "fierce driving in wartime".
However, the change of valve timing by VTEC system is still phased, that is, the change of valve timing is only a jump at a certain speed, rather than a continuous change within a certain speed range.In order to improve the performance of the VTEC system, Honda continued to innovate and launched the i-VTEC system.
In brief, i-VTEC system is a device called VTC (Variable timing control) added on the basis of VTEC system - a set of variable timing control mechanisms for inlet camshaft, namely i-VTEC=VTEC+VTC.At this point,Exhaust valveThe overlap time between timing and starting of is variable, which is controlled by VTC. The introduction of VTC mechanism enables the engine to have appropriate valve timing in a wide range of rotating speeds, which greatly improves the engine performance.
The typical VTC system is composed of VTC actuator, VTC oil pressure control valve, various sensors and ECU.The VTC actuator and VTC oil pressure control valve can act according to the ECU signal to continuously change the phase of the inlet camshaft.VTC makes the valve overlap time more accurate, ensures the optimal overlap time of inlet and exhaust valves, and can increase the engine power by 20%.
VTC system function
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The introduction of VTC mechanism enables the valve timing to "intelligently" adapt to the change of engine load.The role of VTC in coordinating with VTEC system during engine operation is mainly applied in three aspects.
Optimum idle speed/lean combustion area
In this area, the VTC system stops working. At this time, the valve overlap angle is the smallest. Due to the action of VTEC, a strong eddy current is generated, so thatEngine idlingStable operation.
Optimum fuel consumption, exhaust control area
In this area, VTEC plays a role in generating strong vortices, which makes the mixture of combustible mixture more uniform. At the same time, VTC plays a role in increasing the valve overlap angle and re sucking some exhaust gases into the cylinder, playing the role of EGR, so as to achieve the best fuel consumption and exhaust control.
Optimum torque control area
In this area, through the control of VTCValve overlap At the same time, with the help of VTEC system, the output torque of the engine is maximized.
In addition, i-VTEC engine adoptsIntake manifoldIn front, the exhaust manifold is arranged in the rear.The length of the exhaust manifold is shortened, that isThree way catalytic converterThe distance between them enables the three-way catalytic converter to enter the appropriate operating temperature faster, which can effectively control exhaust emissions.Since the i-VTEC system enters the state after the engine is started, VTC is working at both low speed and high speed, which eliminates the defects of the original VTEC system.
In conclusion, due to the introduction of VTC mechanism in i-VTEC system, the valve timing of the engine can be flexibly matched with the load of the engine. Under any working condition of the engine, the best valve timing can be found. With the best valve overlap angle, low fuel consumption and emissions can be achieved at medium and low speeds, and high power and torque can be achieved at high speeds,This is just like controlling according to the requirements of human brain, so it is vividly called "intelligent" VTEC
overhaul
1. Manual inspection method
① Set the piston of cylinder 1 at the top dead center (TDC) position;
② Remove the cylinder head cover;
③ Push the middle intake rocker arm on the cylinder 1 stopcock by hand;
④ Gun check the middle intake rocker arm, which should be able to move independently;
⑤ Check whether the middle intake rocker arm can move freely when the piston of each cylinder is at the top dead center position.
If it cannot move, remove the middle intake rocker arm, main intake rocker arm and auxiliary intake rocker arm as a whole, and check the pistons in the middle and main rocker arm. The pistons should move smoothly.If the rocker arm needs to be replaced, the middle, main and auxiliary rocker arms should be replaced as a whole.
2. Special tool inspection method
be careful:
● Before using the special inspection tool, make sure that it is connected to theAir compressorThe barometer reading on the exceeds 400kPa.
● Check the valve clearance before checking the rocker arm.
● Check the main intake rocker arm of each cylinder one by one when the piston is at the top dead center position.
Step:
① Remove cylinder head cover.
② Plug the vent hole with a special tool.
③ Unscrew the sealing bolt from the inspection hole, and then connect the valve inspection tool.
Note: Before retightening the sealing bolt, wipe off the oil stain on the bolt thread and camshaft bracket thread.
④ Loosen the regulator valve on the valve inspection tool, and apply 400kPa air pressure to the synchronous pistons A and B of the rocker arm.
⑤ Push the timing plate upward for 2-3mm, and then the synchronizing piston will pop up to mesh the intermediate, main and auxiliary intake rocker arms.Check whether synchronous pistons A and B are engaged (should be engaged).
be careful:
● Synchronizing piston can be seen from the clearance between intermediate rocker arm, main rocker arm and auxiliary rocker arm.
● When the timing plate is inserted into the groove on the timing piston, the piston will be locked in the pop-up position.
● When pushing the timing plate upward, do not use too much force.
⑥ Make sure that the main intake rocker arm and the auxiliary intake rocker arm are connected together through the piston. When the intermediate rocker arm is pushed by hand, the intermediate rocker arm should not move independently.If the middle rocker arm can move independently, replace the middle rocker arm, main rocker arm and auxiliary rocker arm as a whole.
⑦ Stop applying air pressure to the synchronizing pistons A and B, and push the timing plate upward. At this time, the synchronizing piston should return to its original position, and the synchronizing pistons A and B should be disengaged. Otherwise, the intake rocker arm should be replaced as a whole.
⑧ Remove the special tool.
⑨ Check whether each traveling part assembly can move smoothly. If not, replace the traveling part assembly.
⑩ After inspection, MIL (fault warning light) should not be on.[1]
