ldquo; the most expensive thing is not necessarily the most profitable, the most profitable thing is not necessarily the best. rdquo; it is easy to find examples of this sentence in the automotive industry, everyone says that Japanese automakers shrewd, because they regarded the best things wisely. To be on the top of the engine technology, the most powerful of power output, in supercar circles which seems rare Japanese cars on the scene. But on the size of the annual production, it seems that the top few Japanese are familiar with our factory trademark. They put the best resources into developing better balance between power and fuel consumption models, to better adapt to consumer demand for products for the market. Japanese brands in the country has numerous engine considerable ownership, but to the number 4 most classic models than Honda i-VTEC series, series VVT-i Toyota, Nissan and Mitsubishi 4G series VQ series engine. Below we first make in-depth study of Honda’s i-VTEC engine series.
i-VTEC Honda technology is not only special skill, is the major manufacturers of similar ldquo; CVVTrdquo; originator of variable valve timing technologies. Since the new generation Fit 1.3L model abandoned i-DSI engine switch to i-VTEC formation, all Honda models in the domestic popularity of its official i-VTEC engine. 1.3L low-emission small, large displacement to 2.4L, whether hatchback car or MPV or SUV, as long as the hanging of Honda trademark, open the hood will be able to see the silver string of letters. Behind this simple in the end of the five letters in the end that contains what unique technology?
works
at the low speed, the engine required amount of the mixture is not high, to maintain a steady speed and reduce fuel consumption and pollutant emissions. However, it requires a larger amount of intake air reaches a high rotational speed to meet the demand for high power output, and the phase of the engine intake valve (opening and closing timing) and the lift (opening size) of the cylinder intake air amount is determined the most direct factor. After manufactured in conventional engines, valve timing and valve lift to a fixed, unable to meet the demand of the engine intake and exhaust at different speeds. Accordingly, it is desirable to have such an engine, which cam profile (profile of the cam curve) can accommodate any rotational speed, whether the fast or slowYou can get the best valve timing. Thus, the VVT control mechanism emerged. In 1989, Honda introduced a self-developed ldquo; variable valve timing and valve lift electronic control system rdquo ;, English full ldquo; Variable Valve Timing and Valve Life Electronic Control Systemrdquo ;, abbreviation is ldquo; VTECrdquo ;, is the world’s first simultaneous control valve opening and closing of the valve in two different situations such as the time and lift control system.
and, like many ordinary engine, VTEC engine has four valves per cylinder (2 intake row 2), camshaft and rocker arms, but different from ordinary engine cam number and control method of the rocker arm. In low speed with a small angle of the cam, the low speed at two different valve lift and valve timing, a valve lift at this time is small, almost does not participate in the intake process, the intake passage is substantially equivalent to a single feed valve engine. But at high speeds, the VTEC solenoid valve to control the hydraulic oil, so that the two intake rocker arm integrally connected by the longest on-time, the maximum lift of the cam to drive the intake valve, the intake valve at this time according to the two big profile of the cam simultaneously. Compared with low-speed operation, greatly increases the duration of the intake flow area and the opening, thereby improving the power performance at high engine speeds. The two output curves of completely different performance, Honda engineers so that they achieve the same engine.
i-VTEC = VTEC + VTC
However, VTEC valve timing system for changing stepwise is still , i.e. it changes the valve timing at a certain speed only jump rather than over a period of continuously variable speed range. In order to improve the performance of the system VTEC, Honda continued to innovate, launch i-VTEC system. Adds the called VTC device mdash (Variable timing controlldquo;; rdquo variable timing control); mdash; a set of intake camshaft timing variable control mechanism, i.e., i-VTEC = VTEC + VTC. At this time, the intake valve open timing overlap time is variable, controlled by the VTC, VTC mechanism is introduced in the engine rotational speed can have a wide range of suitable valve timing, which largely increase the performance of the engine.
But it is worth noting that the faithful car, although the engine of the same name i-VTEC bright signs, but R18A1 engine of Dongfeng Honda Civic i-VTEC but it has another meaning. I-VTEC actuating mechanism object of the above increase in horsepower output, but the effect Fengyun R18A1 i-VTEC engine is fuel-efficient means.
VTEC above time switch to a high angle of the cam, the engine is more than 4800 rpm, the water temperature is higher than 60 degrees, and the negative pressure in the intake manifold after the index line with the factory settings, will VTEC solenoid valve open, the hydraulic pressure is introduced into the rocker arm to push the free piston, the high-angle cam kicks in extended intake valve closing time, the intake air amount increase at the time of high engine speed.
VTEC engine on R18A1 actuation timing is set at a rotational speed within any possibility between 1000 ~ 3500rpm, Jie involved, and whether the rotational speed exceeds the outside this range are tall VTEC mechanism no longer actuated, so listen to VTEC is not above us very different from the actuation timing of it? And why the early switch to a high angle of the cam, fuel consumption achieved the purpose of saving it? The key is to control the intake resistance.
Usually petrol engine load at cruising speed is low, due to further increase speed without the driver only light throttle to maintain the same speed, the throttle angle is relatively narrow (i.e. high speed cruise throttle opening degree is small), reduce the amount of fresh air intake, the engine intake air resistance in this case, but because of the small throttle opening increases, and to increase the intake stroke of the piston down resistance, the relative thrust part of the piston explosion consumption, thereby reducing engine output power is reduced as straw, needed more drinks suction mouth in order to breathe the truth is the same. If the throttle opening degree at this time can become large, could slow down the intake resistance thereby improving the efficiency of the piston, so that the engine output power is used in all of the transmission system, but without already consumed during the operation portion, thereby improving high speed cruising the fuel-economy when.
i-VTEC system
R18A1 engine is for this case, the low speed high speed cruising of the vehicle when the camshaft so high angle involved, be reduced by increasing the valve opening degree intake resistance. i-VTEC system mentioned at the beginning of the outbreak can provide power at high engine speed, while the i-VTEC system is doing exactly the opposite of this R18A1 engine intervention to achieve the effect of fuel economy at low speed.
In addition to skillfully ldquo; just the opposite rdquo;, there are a variety of techniques for the fuel body R18A1 Civic engine, such as a piston oil cooling nozzle with variable-length intake manifolds, it will not be detailed here.
Conclusion:
Ultimately, Honda i-VTEC technology that would allow ldquo; static rdquo; the intake and exhaust valves can be adjusted according to the engine and vehicle operating conditions, such the benefits of change are predictable, like the transmission of only one gear to upgrade more than the same gear.
but i-VTEC also has some obvious shortcomings, such as the engine noise is too much noise in the valve fully open, although some people think that this apparent ldquo; VTECrdquo; sound very attractive, but also after all the traveling comfort of some impact. Especially long-term operation of the fuel consumption will be significantly increased in high angle camshaft state, for example, there are not any to introduce a high-performance version of the K20A engine, although the displacement of only 2.0 liters, but both sides of the intake and exhaust are i- VTEC multi-angle control camshaft may be transformed, resulting in fuel consumption at full force of close to 2.5 to 3.0 displacement engine. In addition, i-VTEC systems require complex control unit with the ECU, and the processing of high quality requirements for the operation member, the manufacturer is required more effort in terms of quality assurance.
Under this idea, many car manufacturers have developed similar variable valve timing technology, fuel consumption and power to deal with this contradiction.