Gas distribution of two-stroke engines. Types of purging the combustible mixture of an internal combustion engine, the basics of the design and operation of boat engines of watercraft, how a sports boat works, boat repair, boat repair, how to make a boat

02.07.2020

The quality of the internal combustion engine of a car depends on many factors, such as power, efficiency, cylinder capacity.

The gas distribution phases are of great importance in the engine, and the efficiency of the internal combustion engine, its throttle response, and the stability of idling depend on how the valves overlap.
In standard simple engines, timing change is not provided, and such motors are not very efficient. But recently, more and more often, on cars of leading companies such as Honda, Mercedes, Toyota, Audi, power units with the ability to change the displacement of camshafts as the number of revolutions in the internal combustion engine change more and more often.

Valve timing diagram of a two-stroke engine

A two-stroke engine differs from a four-stroke engine in that the duty cycle takes place in one revolution of the crankshaft, while on a 4-stroke internal combustion engine it occurs in two revolutions. The gas distribution phases in the internal combustion engine are determined by the duration of the opening of the valves - exhaust and intake, the valve overlap angle is indicated in degrees of position to / in.

In 4-stroke engines, the filling cycle of the working mixture occurs 10-20 degrees before the piston reaches top dead center, and ends after 45-65º, and in some internal combustion engines even later (up to one hundred degrees), after the piston has passed bottom point. The total duration of the intake in 4-stroke engines can last 240-300 degrees, which ensures good filling of the cylinders with the working mixture.

In 2-stroke engines, the duration of the intake of the air-fuel mixture lasts at a crankshaft turn of approximately 120-150º, and the purge also lasts less, so filling with the working mixture and exhaust gas cleaning in two-stroke internal combustion engines is always worse than in 4-stroke power units. The figure below shows the valve timing diagram of a two-stroke motorcycle engine of the K-175 engine.

Two-stroke engines are rarely used on cars, as they have lower efficiency, poorer efficiency and poor exhaust gas purification from harmful impurities. The last factor is especially relevant - in connection with the tightening of environmental standards, it is important that the engine exhaust contains a minimum amount of CO.

But still, 2-stroke internal combustion engines have their advantages, especially diesel models:

power units are more compact and lighter;
they are cheaper;
2-stroke motor accelerates faster.

Many cars in the 70s and 80s of the last century were mainly equipped with carburetor engines with a "trubler" ignition system, but many leading car manufacturers already then began to equip motors with an electronic engine control system, in which all the main processes were controlled by a single block (ECU). Now almost all modern cars have an ECM - the electronic system is used not only in gasoline, but also in diesel ICEs.

In modern electronics, there are various sensors that control the operation of the engine, sending signals to the unit about the state of the power unit. Based on all the data from the sensors, the ECU decides how much fuel needs to be supplied to the cylinders at certain loads (revs), which ignition timing to set.

The valve timing sensor has another name - the camshaft position sensor (DPRV), it determines the position of the timing relative to the crankshaft. It depends on its readings in what proportion fuel will be supplied to the cylinders, depending on the number of revolutions and the ignition timing. If the DPRV does not work, it means that the timing phases are not controlled, and the ECU does not “know” in what sequence it is necessary to supply fuel to the cylinders. As a result, fuel consumption increases, since gasoline (diesel oil) is simultaneously supplied to all cylinders, the engine runs randomly, and on some models of the car, the internal combustion engine does not start at all.

Valve timing regulator

In the early 90s of the 20th century, the first engines with automatic timing change began to be produced, but here it was no longer the sensor that controlled the position of the crankshaft, but the phases themselves shifted directly. The principle of operation of such a system is as follows:

the camshaft is connected to a hydraulic clutch;
also with this clutch has a connection and a timing gear;
at idle and low speeds, the camshaft with the camshaft is fixed in the standard position, as it was set according to the marks;
with an increase in speed under the influence of hydraulics, the clutch rotates the camshaft relative to the sprocket (camshaft), and the timing phases shift - the camshaft cams open the valves earlier.

One of the first such developments (VANOS) was applied on BMW's M50 engines, the first engines with variable valve timing appeared in 1992. It should be noted that at first VANOS was installed only on the intake camshaft (the M50 engines have a two-shaft timing system), and from 1996 the Double VANOS system began to be used, with which the position of the exhaust and intake r / shafts was already regulated.

What is the benefit of a timing belt regulator? At idle, overlapping of the valve timing is practically not required, and in this case it even harms the engine, since when the camshafts are shifted, the exhaust gases can enter the intake manifold, and part of the fuel will enter the exhaust system without completely burning out. But when the engine is running at maximum power, the phases should be as wide as possible, and the higher the speed, the more valve overlap is needed. The clutch of the timing change makes it possible to effectively fill the cylinders with the working mixture, which means to increase the efficiency of the motor and increase its power. At the same time, at idle, the r / shafts with the clutch are in their original state, and the combustion of the mixture is in full. It turns out that the phase regulator increases the dynamics and power of the internal combustion engine, while fuel is quite economically consumed.

The variable valve timing system (CVG) provides lower fuel consumption, reduces the level of CO in the exhaust gases, and allows more efficient use of the power of the internal combustion engine. Different global automakers have developed their own SIFG, not only changing the position of the camshafts, but also the level of valve lift in the cylinder head is used. For example, Nissan uses a CVTCS system, which is controlled by a variable valve timing (solenoid valve). At idle, this valve is open, and does not create pressure, so the camshafts are in their original state. The opening valve increases the pressure in the system, and the higher it is, the greater the angle the camshafts are shifted.

It should be noted that SIFGs are mainly used on engines with two camshafts, where 4 valves are installed in the cylinders - 2 intake and 2 exhaust.

Devices for setting the valve timing

In order for the engine to work without interruption, it is important to correctly set the timing phases, install the camshafts in the desired position relative to the crankshaft. On all engines, the shafts are set according to the marks, and a lot depends on the accuracy of the installation. If the shafts are set incorrectly, various problems arise:

the motor is unstable at idle;
ICE does not develop power;
there are shots in the muffler and pops in the intake manifold.

If the marks are mistaken by a few teeth, it is possible that the valves may bend and the engine will not start.

On some models of power units, special devices have been developed for setting the valve timing. In particular, for engines of the ZMZ-406/406/409 family, there is a special template with which the camshaft position angles are measured. The template can be used to check the existing angles, and if they are not set correctly, the shafts should be reinstalled. The fixture for 406 motors is a set consisting of three elements:

two goniometers (for the right and left shaft, they are different);
protractor.

When the crankshaft is set to TDC of the 1st cylinder, the camshaft cams should protrude above the upper plane of the cylinder head at an angle of 19-20º with an error of ± 2.4 °, moreover, the intake roller cam should be slightly higher than the exhaust camshaft cam.

There are also special tools for installing camshafts on BMW M56 / M54 / M52 engines. The installation kit for the gas distribution phases of the internal combustion engine BVM includes:

Malfunctions of the variable valve timing system

The valve timing can be changed in various ways, and recently the rotation of the p / shafts has been most common, although the method of changing the valve lift, the use of camshafts with modified cams, is often used. Periodically, various malfunctions occur in the gas distribution mechanism, due to which the motor starts to work intermittently, “dulls”, in some cases it does not start at all. The causes of problems can be different:

defective solenoid valve;
the phase change clutch is clogged with dirt;
the timing chain has stretched;
chain tensioner defective.

Often in the event of malfunctions in this system:

idle speed decreases, in some cases the internal combustion engine stalls;
fuel consumption increases significantly;
the engine does not develop speed, the car sometimes does not even accelerate to 100 km / h;
the engine does not start well, it has to be driven with a starter several times;
a chirp is heard coming from the SIFG coupling.

By all indications, the main cause of problems with the engine is the failure of the SIFG valve, usually with computer diagnostics revealing an error in this device. It should be noted that the Check Engine diagnostic lamp does not always light up, so it is difficult to understand that failures occur in electronics.

Often, timing problems arise due to hydraulic clogging - bad oil with abrasive particles clogs the channels in the clutch, and the mechanism jams in one of the positions. If the clutch “wedges” in the initial position, the internal combustion engine quietly works at idle, but does not develop speed at all. In the case when the mechanism remains in the position of maximum valve overlap, the engine may not start well.

Unfortunately, SIFG is not installed on Russian-made engines, but many motorists are tuning internal combustion engines, trying to improve the performance of the power unit. The classic version of the engine modernization is the installation of a “sports” camshaft, in which the cams are shifted, their profile is changed.

This r / shaft has its advantages:

the motor becomes torquey, clearly responds to pressing the gas pedal;
the dynamic characteristics of the car are improved, the car literally vomits from under itself.

But in such tuning there are also disadvantages:

idle speed becomes unstable, you have to set them within 1100-1200 rpm;
fuel consumption increases;
it is quite difficult to adjust the valves, the internal combustion engine requires careful tuning.

Quite often, VAZ engines of models 21213, 21214, 2106 are subjected to tuning. The problem of VAZ engines with a chain drive is the appearance of “diesel” noise, and often it occurs due to a failed tensioner. Modernization of the VAZ internal combustion engine consists in installing an automatic tensioner instead of the standard factory one.

Often, a single-row chain is installed on the VAZ-2101-07 and 21213-21214 engine models: the motor runs quieter with it, and the chain wears out less - its average life is 150 thousand km.

So, what is it and why is it needed. I will not describe the basics of the operation of 2T engines, since everyone knows them, but not everyone understands what the gas distribution phases are and why they are exactly like that and not others.
The valve timing is the period of time during which the windows in the cylinder open and close when the piston moves up and down. They are considered in degrees of rotation of the knees of the engine shaft. For example, an exhaust phase of 180 degrees means that the exhaust port will start to open, be open, and then close at half a turn (180 out of 360) of the engine crankshaft. It must also be said that the windows open when the piston moves down. And open to maximum at bottom dead center (BDC). Then, when the piston moves up, they close. Due to this design feature of 2T engines, the valve timing is symmetrical with respect to dead points.

To complete the picture of the gas distribution process, it must also be said about the area of windows. The phase, as I already wrote, is the time during which windows open and close, but the window area plays an equally important role. After all, with the same window opening time, the mixture (purge) will pass more through the window, which is larger in area and vice versa. The same is true for exhaust, exhaust gases will leave the cylinder more if the window area is larger.
The general term that characterizes the entire process of the flow of gases through windows is called time-section.
And the larger it is, the higher the engine power and vice versa. That is why we see such huge cross-sectional purge, intake and exhaust channels, as well as high valve timing on modern highly forced 2T engines.

So, we see that the gas distribution functions are performed by the cylinder windows and the piston that opens and closes them. However, because of this, time is lost during which the piston would do useful work. In fact, the engine power is formed only before the opening of the exhaust port, and with further downward movement of the piston, no or very little torque is generated. In general, the engine capacity of 2T, unlike 4T, is not fully utilized. Therefore, the primary task of designers is to increase the time - the cross section at minimum phases. This gives better torque and economy curves than the same time section but higher phases.
But since the diameter of the cylinder is limited, and the width of the windows is also limited, in order to achieve a high level of forcing the engine, it is necessary to increase the valve timing.
Many people, wanting to achieve more power, begin to increase the windows in the cylinder, either at random, or on someone's advice, or having subtracted advice somewhere, but they do not really understand what they will get in the end, and whether they are doing it right. Or maybe they need something else?
Let's say we have some kind of engine and we want to get more out of it. What do we do with the phases? The first thing that comes to mind for many is sawing the exhaust windows up, or raising the cylinder with a gasket, and sawing the intake down or cutting the piston from the intake side. Yes, in this way we will achieve an increase in phases and, as a result of time, a cross section, but at what cost. We have reduced the time during which the piston will do useful work. Why does the power generally increase with an increase in phases, and not decrease? Time is increasing - you say the cross section, yes it is. But do not forget that this is a 2T engine and in it the whole principle of operation is based on resonant pressure and discharge waves. And for the most part, the exhaust system plays a key role here. It is she who creates a vacuum in the cylinder at the start of exhaust, drawing out the exhaust gases, and also draws the mixture from the purge channels afterward, increasing the purge time-section. It also refuels the mixture that has flown out of the cylinder back into the cylinder. As a result, we have an increase in power with increasing phases. But we must also not forget that the exhaust system is set to a certain speed, beyond which the mixture that has flown out of the cylinder does not return, and the useful piston stroke is reduced due to high phases. So there is a power failure and excessive fuel consumption at non-resonant engine frequencies.
So is it possible to get the same power and reduce dip and fuel consumption? Yes, if you achieve the same time - cross sections without increasing the valve timing!
But what does this mean in practice? The increase in the width of the windows and the cross section of the channels is limited by the thickness of the walls of the channels and the limiting values of the width of the windows due to the operation of the rings. But as long as there is a reserve, it must be used, and only then the phases should be increased.
So, if you yourself don’t really know what you want and, as many say, I want power, but also so that the bottoms do not disappear, then increase the bandwidth of channels and windows without increasing the phases. If this is not enough for you, increase the phases gradually. For example, it will be optimal for 10 degrees of exhaust, for 5 degrees of purge.
I would like to step back a bit and say separately about the intake phase. Here we were very lucky when people came up with a check plate valve, in the common people a reed valve (LK). Its plus is that it automatically changes the intake phase and intake area. Thus, it changes the intake time-section according to the needs of the engine at that particular moment. The main thing is to initially choose and install it correctly. The valve area should be 1.3 times larger than the carburetor cross-sectional area so as not to create unnecessary resistance to the flow of the mixture.

The intake windows themselves should be even larger, and the intake phase should be as large as possible so that the LC starts working as early as possible. Ideally, from the very beginning of the piston movement upwards.
An example of how to achieve the maximum intake phase can be the following photos of intake modifications (not Java, but the essence of this does not change):

This is one of the best options for finalizing the intake. In fact, the inlet here is a combined version of the inlet to the cylinder and the inlet to the crankcase (the inlet channel is constantly connected to the crank chamber, CSC). It also increases the life of the NGSH due to better blowing with a fresh mixture.

To form this channel connecting the inlet channel with the crankcase, the maximum possible amount of metal is selected, which is located on the inlet side near the sleeve.

In the sleeve itself, additional windows are made below the main ones.

In the cylinder jacket, metal is also selected near the sleeve.
A properly installed LC allows you to once and for all solve the problem with the selection of the intake phase.
Who nevertheless decided to achieve more power and knows what he is aiming for, is ready to sacrifice the lower classes for the sake of an explosive pickup at the top, he can safely increase the gas distribution phases. The best solution would be to use someone else's experience in this matter.
For example, in foreign literature such recommendations are given:

I would exclude the Road race option, since the phases are very extreme, designed for road-ring races and are not practical when driving on ordinary roads. Yes, and most likely designed for a power valve, which reduces the exhaust phase at low and medium speeds to an acceptable level. In any case, it is not worth making the release phase more than 190 degrees. The best option, as for me, is 175-185 degrees.

Regarding the purge ... here everything is more or less indicated optimally. However, how to understand how much your engine will turn? You can look for the improvements of people and find out from them, or you can just take the average numbers. It's around 120-130 degrees. Optimal 125 degrees. Higher numbers refer to smaller engine cubic capacities.
And yet, with an increase in the purge phases, it is also necessary to increase its pressure, i.e. crankcase compression. To do this, you need to minimize the volume of the crank chamber by removing unnecessary voids. For example, to begin with, by plugging the balancing holes in the crankshaft. Plugs should be made of the lightest possible material so that they do not affect the balance of the HF. Usually they are cut from wine corks (cork wood) and driven into balancing holes, after which they are coated with epoxy on both sides.

Regarding the intake, I wrote above that it is better to put the LC and not rack your brains with the selection of the phase.

So, let's say you have decided how you will refine your engine, what valve timing it will have. Now, what is the easiest way to calculate how much it is in mm.? Very simple. There are mathematical formulas for determining the stroke of the piston that can be adapted to our purposes, which I did. Once I entered the formulas into the Excel program and received a program for calculating the gas distribution phases of purge and exhaust ( download link at the end of the article).
You only need to know the length of the connecting rod (Java 140mm, IZH Jupiter, Sunrise, Minsk 125mm, IZH ps 150mm. If you wish, you can find the length of almost any connecting rod on the Internet) and the piston stroke.
The program is made in such a way that it determines the distance from the upper edge of the window to the edge of the sleeve. Why so, and not just say the height of the window? Because this is the most accurate definition of phases. Top dead center piston crown MUST be on the same level with the edge of the sleeve due to squish (features of the shape of the combustion chamber for knock-free operation), and if it is suddenly not on the same level, then you will have to adjust the cylinder in height (for example, by selecting the thickness of the gasket under the cylinder). But at the bottom dead center, the bottom of the piston, as a rule, is not on the same level with the edges of the windows, but a little higher, i.e. The piston does not fully open the windows! Such design features, nothing can be done. But this means that the windows do not work to their full height, and therefore the phases cannot be determined from them!

Motors run on gasoline, gas, alcohol or diesel fuel - on a 2- or 4-stroke cycle. And in any case, their character is highly dependent on what is called the valve timing. So what do they eat with? Why do you need to adjust the phases? Let's get a look.

Gas exchange

Much of our life depends on how we breathe. Yes, and life itself; in the world of a.v.s. about the same. Let's take a 1.5-liter VAZ 16-valve; want it to pull at V at 600 min -1 ? For fun. The question of choosing the valve timing: let's select the profile of the intake camshaft cams so that the intake starts at about 24 ° (according to the angle of rotation of the crankshaft) after the top dead center. We will make the cams so “blunt” that the valves rise only by 3 mm, and the inlet ends somewhere at 6 ° after N.M.T.

The start of the release is adjustable by 12 ° BC, and the exhaust valves are closed even just at the BT; we leave their rise “according to the state”. Degrees and millimeters of valve lift are those very phases: earlier, later.

4-stroke engine timing circle diagram

Check experimentally: with the correct setting of the ignition and fuel injection, the modified "four" will show the largest of 75-80 Nm - somewhere at 6 hundred revolutions! Maximum power - 10-12 hp at 1500 min -1 ; don't judge. However, the motor will actually pull from the very "bottom" - like a (small) steam engine. The only pity is that it does not develop either speed or power.

Complete intake (exhaust) diagram: millimeters of valve lift by crank angle

I don’t like it ... Let’s go from the other end: the cam profile is such that the intake starts at 90 ° BTDC and ends at 108 ° AFB; rise - up to 14 mm. There is a difference? And release too: beginning at 102° BC, ending at 96° after BT. As the experts say, the overlap of the exhaust and intake is 186 ° in terms of the angle of rotation of the crankshaft! And what? See: with the correct setting of the ignition and injection [Also with oversized valve heads, bored and polished intake and exhaust ports…] your 1.5-liter VAZ will give out something like 185 Nm of torque - under ... 11 thousand revolutions! And at 13500 min -1 it will develop about 330 hp. - without any boost. Of course, if the timing and the crank mechanism survive (hardly). About 40 years ago, a good 3-liter Formula 1 engine showed such power ... True, below 6000 min -1 the forced VAZ will be completely dead [The idle speed will have to be set somewhere at 3500 min -1 ...]; its operating range is 9-14 thousand revolutions.

At the “tops”, on the contrary: wide valve timing will allow 100% to mobilize the resonance of gas flows at the inlet and outlet, as they say, acoustic boost. With the correct selection of the lengths and sections of (individual) inlet and outlet pipes, the filling ratio of the cylinders will reach the level of 1.25-1.35 in the zone of 11 thousand revolutions; get the desired 185 Nm.

This is what the valve timing is: they set the gas exchange of the A.V.S. - inlet-outlet. And gas exchange determines everything else: the flow of torque, engine speed, its maximum power, elasticity ... A couple of examples show how much the character of the same motor changes depending on the phases. The thought immediately arises: the gas distribution phases need to be adjusted - right on the go. And then under the hood of your car there will be not one single engine - for all occasions, but many different ones!

As the best friend of motorists taught, "cadres decide everything." To paraphrase the famous expression, we assume that everything is decided by the phases (gas distribution). The Generalissimo knew how to regulate personnel issues, and engine builders have always sought to control the phases.

phase rotation

Easy to say but hard to do; in a 4-stroke engine, the valve timing is set by the profile of the cams (made of high-strength hardened steel). Changing it along the way is not an easy task. However, something can be done even with the same profile, for example, to shift the camshaft along the angle of rotation of the crankshaft. Back and forth; that is, the duration of the inlet remains unchanged (in the 2nd example - 378 °), but it both starts and ends earlier. Suppose the intake valves now open 120° BTDC. and close at 78° a.s.l. So to speak, on "earlier-earlier". Or vice versa - on the "later-later": the intake starts at 78 ° before the top deadweight. and ends at 120° after n.m.t.

We move the unchanged intake diagram to “later-later”: phase rotation

This solution (for intake) was first used by ALFA Romeo on a 2-liter 8-valve "four" Twin spark [Clearly, phasing applies when the intake and exhaust valves are driven by 2 separate camshafts; in the mid-80s the Twin spark was one of the rare DOHC designs. And since then, 2 shafts in the cylinder head have become widespread - precisely for the sake of phase rotation.]— back in 1985. It is called phase rotation and is used (at the inlet and / or outlet) quite widely. And what does it give? Not much, but still better than nothing. So, during a cold start of an engine with a catalytic converter, the exhaust camshaft is turned ahead of the curve. The release starts early, and the exhaust gases of elevated temperature go to the converter; it warms up faster. Less harmful substances are emitted into the atmosphere.

Or you are driving evenly at a speed of 90 km / h, only 10% of its maximum power is required from the motor. This means that the throttle valve is strongly covered; increased pumping losses, excessive fuel consumption. And if you strongly shift the intake camshaft to “later-later”, then part (say, 1/3) of the air-fuel mixture is ejected during compression back into the intake manifold [Don't worry, she's not going anywhere. The so-called "5-stroke" cycle.]. and engine power are reduced (to the level required by the driving conditions) without excessive intake throttling. That is, although the throttle valve is closed, but not so much, pumping losses are much less. Saving gasoline - and something else; isn't it worth it?

VTEC

The possibilities of phase rotation are limited by the fact that, as they say, "the tail is pulled out - the nose is stuck." When you reduce the valve opening advance, the closing delay increases by exactly the same amount.

It doesn't get any easier from time to time. Now, if you somehow change the intake-exhaust duration ... Let's say, in the 2nd example, reduce it - when necessary - from 378 to 225 °. The engine will be able to work normally also "on the bottoms" - without loss of power "on the tops".

Dreams come true: 4 years have passed since the introduction of the twin spark with phase rotation, and Honda Motor showed the 1.6-liter 16-valve B16A with revolutionary VTEC. The engine was equipped - for the first time in history - with a 2-mode valve mechanism (at the inlet and outlet); the process started. However, sometimes you have to hear: just think, VTEC - only 2 modes. And in the motor of my Corolla, the phases are regulated steplessly - a continuum of modes. Well, yes, - if you do not see two big differences ...

Classic Honda VTEC mechanism: 3 cams per pair of valves. The central cam is “wide”, 2 side cams (for symmetry) are “narrow”. Blocking the rocker arms with a piston gives wide intake (exhaust) phases

In our sunny country, for some reason, it is customary to torture people twice a year by moving the hands for an hour - to “earlier-earlier” in spring and to “later-later” in autumn. God be their judge, it's about something else. It is technically easy to switch arrows not only for an hour every six months, but even for a minute every day. So to speak, stepless. Phase rotation is like moving a clock - and the effect is about the same.

Have you tried changing the daylight hours? Let not stepless, only two modes, say, 9 hours and 12? So, Honda engineers found a solution to this class of problem; feel the difference. Suppose, in the "lower" mode, the duration of the intake is 186 ° (according to the angle of rotation of the crankshaft), and in the "upper" mode - 252 °. A radical change in the conditions of gas exchange: under the hood, as it were, two unequal motors. One is elastic and high-torque on the “bottoms”, the other is “sharp”, torsional and powerful on the “tops”; 25 years ago, this was unthinkable. And by the way, it doesn’t cost anything to add phase rotation to VTEC, which Honda did in the i-VTEC design. Whereas on the contrary - to give VTEC to phase rotation - will not work; the proprietary mechanism is not so simple and is subject to patents.

Two unequal intake diagrams for the same motor

Please note: VTEC allows you to vary the intake (and exhaust) pattern! Not just move it to “earlier-earlier” or “later-later”, but change the profile. Qualitative advancement against banal phase rotation - although there are only 2 modes (in later versions - as many as 3). Honda has a lot of imitators and followers: Mitsubishi MIVEC, Porsche VarioCam Plus, Toyota VVTL-i. In all cases, cams of unequal profiles are used with blocking of the valve drive; imagine it works.

Valvetronic

Well, in 2002, Bavarian designers unveiled the famous Valvetronic timing. And if VTEC is "montana", then Valvetronic is "full ...". The mechanism has been in mass operation for 5 years, but auto reviewers still have not comprehended its meaning and principle of operation. Yes, journalists, if the BMW press service ... Look and see: in branded press releases, Valvetronic is interpreted as a mechanism for changing valve lift! What if you think about it? There is nothing easier than adjusting the lift - no more difficult than phase rotation. However, Valvetronic is a sophisticated device; there is probably more than that.

Infinitely variable intake pattern (base width changes): Bavarian Valvetronic. Please note: the diagram of the mechanism is shown incorrectly - it will not be able to work. Corporate press service… max = 9.5 mm; min = 0.2 mm

Let's talk about the unusual mechanism separately. In the meantime, we admit that the Bavarian Valvetronic motors were the first Otto engines, the power of which is regulated without inlet throttling! Like diesels. They do without the most pernicious part in the construction of a spark-ignition engine; comparable to the invention of the carburetor. Or magneto. In 2002, the world changed without anyone noticing...

electromagnets

I take my hat off to BMW engineers, and yet Valvetronic is just an episode in the development of the Otto engine. An intermediate solution is in anticipation of a radical one. And it is already on the threshold: a camless timing with an electromagnetic valve drive. No camshafts with their drive, pushers, rocker arms, hydraulic gap compensators, etc. Just the valve stem enters a powerful electromagnet [With a force on the valve axis up to 80-100 kg! Otherwise, the valves do not keep up with their phases. And it is not easy to provide such efforts in a compact mechanism, which is the main difficulty in creating an e-magnetic timing.], the voltage to which is supplied under the control of the CPU. That's all: on each revolution of the crankshaft, the CPU controls the moments of the beginning of the opening and closing of the valves - and the height of their rise. There are no cams with their unchanged profile, there are no once and for all set valve timing.

Solenoid valve train (Valeo): endless possibilities 1 - washers; 2 – electromagnet; 3 - plate; 4 - valve; 5 - springs; 6 - compression; 7 - stretching

The intake and exhaust diagrams are freely adjustable and within wide limits (limited only by the physics of the processes). Separately for each of the cylinders and from cycle to cycle - as the moment of injection and the amount of fuel supplied. Or ignition. In essence, the Otto engine will become itself - for the first time in history. And will not leave any chance to diesel. How computers found themselves with the advent of micro "chips" and pocket calculators instantly replaced electromechanical adding machines. Whereas in the late 1940s, computers were built on vacuum tubes and electromagnetic relays; consider that spark ignition engines are still at that very stage. Well, maybe Valvetronic ...

The quality of the internal combustion engine of a car depends on many factors, such as power, efficiency, cylinder capacity.

Valve timing diagram of a two-stroke engine

But still, 2-stroke internal combustion engines have their advantages, especially diesel models:

power units are more compact and lighter;
they are cheaper;
2-stroke motor accelerates faster.

Valve timing regulator

the camshaft is connected to a hydraulic clutch;
also with this clutch has a connection and a timing gear;
at idle and low speeds, the camshaft with the camshaft is fixed in the standard position, as it was set according to the marks;
with an increase in speed under the influence of hydraulics, the clutch rotates the camshaft relative to the sprocket (camshaft), and the timing phases shift - the camshaft cams open the valves earlier.

It should be noted that SIFGs are mainly used on engines with two camshafts, where 4 valves are installed in the cylinders - 2 intake and 2 exhaust.

Devices for setting the valve timing

the motor is unstable at idle;
ICE does not develop power;
there are shots in the muffler and pops in the intake manifold.

If the marks are mistaken by a few teeth, it is possible that the valves may bend and the engine will not start.

two goniometers (for the right and left shaft, they are different);
protractor.

There are also special tools for installing camshafts on BMW M56 / M54 / M52 engines. The installation kit for the gas distribution phases of the internal combustion engine BVM includes:

Malfunctions of the variable valve timing system

defective solenoid valve;
the phase change clutch is clogged with dirt;
the timing chain has stretched;
chain tensioner defective.

Often in the event of malfunctions in this system:

idle speed decreases, in some cases the internal combustion engine stalls;
fuel consumption increases significantly;
the engine does not develop speed, the car sometimes does not even accelerate to 100 km / h;
the engine does not start well, it has to be driven with a starter several times;
a chirp is heard coming from the SIFG coupling.

This r / shaft has its advantages:

the motor becomes torquey, clearly responds to pressing the gas pedal;
the dynamic characteristics of the car are improved, the car literally vomits from under itself.

But in such tuning there are also disadvantages:

idle speed becomes unstable, you have to set them within 1100-1200 rpm;
fuel consumption increases;
it is quite difficult to adjust the valves, the internal combustion engine requires careful tuning.

Often, a single-row chain is installed on the VAZ-2101-07 and 21213-21214 engine models: the motor runs quieter with it, and the chain wears out less - its average life is 150 thousand km.

Those who are connected with racing automotive or motorcycle technology, or are simply interested in the design of sports cars, are well aware of the name of engineer Wilhelm Wilhelmovich Beckman, author of the books "Racing Cars" and "Racing Motorcycles". More than once he spoke on the pages of "Behind the wheel".

Recently, the third edition of the book "Racing Motorcycles" (the second was released in 1969) was published, revised and supplemented with information about new design solutions and an analysis of the trend of the further development of two-wheeled machines. The reader will find in the book an essay on the history of the origin of motorcycling and its influence on the development of the motorcycle industry, receive information about the classification of cars and competitions, get acquainted with the design features of engines, transmissions, chassis and ignition systems of racing motorcycles, learn about ways to improve them.

Much of what is used for the first time on sports cars, then implemented on serial road bikes. Therefore, acquaintance with them allows you to look into the future and imagine the motorcycle of tomorrow.

The vast majority of motorcycle engines currently being built in the world operate on a two-stroke cycle, so motorists are showing the greatest interest in them. We bring to the attention of readers an excerpt from the book by V. V. Beckman, devoted to one of the most important issues in the development of two-stroke engines. We have made only minor cuts, renumbered the figures, and brought some titles in line with those used in the journal.

Currently, two-stroke racing engines outperform their four-stroke rivals in the 50 to 250cc classes: in the larger displacement classes, four-stroke engines are still competitive. since the high boost of two-stroke engines of these classes is more difficult, and the well-known disadvantage of the two-stroke process becomes more noticeable - increased fuel consumption, requiring an increase in the volume of fuel tanks and more frequent stops for refueling.

The prototype of most modern two-stroke racing engines is a design developed by MC (GDR). The work on the improvement of two-stroke engines performed by this company provided the racing motorcycles of the 125 and 250 cm3 classes of MC with high dynamic qualities, and their design was copied to one degree or another by many companies in other countries of the world.

MC racing engines (Fig. 1) have a simple design and are similar both in design and appearance to conventional two-stroke engines.

A - general view; b - location of gas distribution channels

For 13 years, the power of the MC 125 cm3 racing engine has grown from 8 to 30 hp. With.; already in 1962, a liter capacity of 200 liters was achieved. s./l. One of the essential elements of the engine is a disk rotary valve proposed by D. Zimmerman. It allows you to get asymmetric intake phases and an advantageous shape of the intake tract: due to this, the filling ratio of the crankcase increases. The disc spool is made from thin (about 0.5 mm) sheet spring steel. The optimal thickness of the disc was found empirically. The disc spool works like a diaphragm valve, pressing against the inlet port when the combustible mixture is compressed in the crankcase. With an increased or reduced thickness of the spool, accelerated disc wear is observed. A disc that is too thin bends towards the intake port, which entails an increase in the friction force between the disc and the crankcase cover; increased disc thickness also leads to increased friction losses. As a result of fine-tuning the design, the service life of the disc spool was increased from 3 to 2000 hours.

The disc spool does not add much complexity to the engine design. The spool is mounted on the shaft by means of a sliding key or spline connection so that the disc can take a free position and not be pinched in the narrow space between the crankcase wall and the cover.

Compared to the classic intake port control system by the lower edge of the piston, the spool enables the intake port to be opened earlier and kept open for a long time, which contributes to increased power at both high and medium speeds. With a conventional gas distribution device, an early opening of the intake window is inevitably associated with a large delay in its closing: this is useful for obtaining maximum power, but is associated with a reverse emission of a combustible mixture in medium modes and a corresponding deterioration in the torque characteristics and starting qualities of the engine.

On two-cylinder engines with parallel cylinders, disc valves are installed at the ends of the crankshaft, which, with carburetors protruding to the right and left, gives large dimensions across the width of the engine, increases the frontal area of \u200b\u200bthe motorcycle and worsens its external shape. To eliminate this drawback, a design was sometimes used in the form of two single-cylinder engines coupled at an angle with a common crankcase and air cooling (Derby, Java).

Unlike the Java engine, the cylinders of twin engines can occupy a vertical position: this requires water cooling, since the rear cylinder is obscured by the front one. According to this scheme, one of the racing engines MTs 125 cm3 was made.

The three-cylinder Suzuki engine (50 cm3, liter power of about 400 hp / l) with disc spools essentially consisted of three single-cylinder engines combined in one block with independent crankshafts: two cylinders were horizontal. one vertical.

Engines with gold intakes were also designed in four-cylinder versions. A typical example would be Yamaha engines, made as two twin-geared parallel-cylinder engines; one pair of cylinders is located horizontally, the second - at an angle upwards. The 250 cm3 engine developed up to 75 hp. s., and the power of the 125 cm3 option reached 44 liters. With. at 17,800 rpm.

A four-cylinder Java engine (350 cm3, 48x47) with intake spools, which is two twin two-cylinder water-cooled engines, was designed according to a similar scheme. It develops a power of 72 hp. With. at 1300 rpm. The power of the four-cylinder Morbidelli engine of the 350 cm3 class of the same type is even greater - 85 hp. With.

Because the valve stems are mounted at the ends of the crankshaft, power take-off in multi-cylinder designs with this intake system is usually through a gear on the middle journal between the crankcase compartments. With disc spools of the type in question, an increase in the number of engine cylinders over four is impractical, since further pairing of two-cylinder engines would lead to a very cumbersome design; even in a four-cylinder version, the engine turns out to be at the limit of permissible dimensions.

Recently, on some Yamaha racing engines, automatic diaphragm valves have been used in the intake channel between the carburetor and the cylinder (Fig. 2, a). The valve is a thin elastic plate that bends under the action of vacuum in the crankcase and frees the passage for the combustible mixture. In order to avoid breakage of valves, limiters of their stroke are provided. At medium duty cycles, the valves close quickly enough to prevent back-burning, which improves the engine's torque characteristics. Based on practical observations, such valves can function normally at speeds up to 10,000 rpm. At higher speeds, their performance is problematic.

: a - device diagram; b - the beginning of filling the crankcase; c - suction of the mixture through the valves into the cylinder; 1 - limiter; 2 - membrane; 3 - a window in the piston

In engines with diaphragm valves, to improve filling, it is advisable to maintain communication between the inlet channel and the under-piston space or purge channel when the piston is close to N.M.T. To do this, appropriate windows 3 are provided in the piston wall from the inlet side (Fig. 2, b). Diaphragm valves provide additional suction of the combustible mixture when a vacuum is formed in the cylinders and crankcase during the purge (Fig. 2, c).

High power is also developed by two-stroke engines, in which the process of inlet of a combustible mixture into the crankcase is controlled by a piston, as in the vast majority of conventional mass-produced engines. This mainly applies to engines with a displacement of 250 cm3 or more. Examples are motorcycles "Yamaha" and "Harley-Davidson" (250 cm3 - 60 hp;

350 cm3 - 70 l. s.), as well as a Suzuki motorcycle with a two-cylinder engine of the 500 cm3 class with a capacity of 75 hp. s., who won first place in the race T.T. (Tourist Trophy) 1973. The forcing of these engines is carried out in the same way as in the case of using disk valves, by careful design study of the gas distribution organs and on the basis of studying the mutual influence of the intake and exhaust tracts.

Two-stroke engines, regardless of the intake control system, have a rectified intake tract, which is directed into the under-piston space, where the combustible mixture enters; with respect to the axis of the cylinder, the intake tract can be perpendicular or inclined from bottom to top or top to bottom. This shape of the intake tract is favorable for using the effect of resonant boost. The flow of the combustible mixture in the intake tract continuously pulsates, and waves of rarefaction and high pressure occur in it. Adjusting the intake tract by selecting its dimensions (length and flow sections) makes it possible to ensure that, in a certain range of revolutions, the intake window is closed at the moment an overpressure wave enters the crankcase, which increases the filling factor and increases engine power.

With crankcase fill ratios greater than one, a two-stroke engine would have to deliver twice as much power as a four-stroke engine. In reality, this does not happen due to significant losses of the fresh mixture into the exhaust and mixing of the charge that entered the cylinder with residual gases from the previous working cycle. The imperfection of the working cycle of a two-stroke engine is due to the simultaneous flow of the processes of filling the cylinder and cleaning it from combustion products, while in a four-stroke engine these processes are separated in time.

Gas exchange processes in a two-stroke engine are very complex and still difficult to calculate. Therefore, the forcing of engines is carried out mainly by experimental selection of the ratios and dimensions of the structural elements of the gas distribution organs from the inlet pipe of the carburetor to the end pipe of the exhaust pipe. Over time, a lot of experience has been accumulated in forcing two-stroke engines, described in various studies.

In the first designs of MC racing engines, a back-loop purge of the Schnyurle type with two purge channels was used. A significant improvement in power performance was obtained by adding a third purge channel (see Fig. 1), located in front opposite the exhaust windows. A special window is provided on the piston for bypassing through this channel. An additional scavenging channel eliminated the formation of a hot gas cushion under the piston bottom. Thanks to this channel, it was possible to increase the filling of the cylinder, improve cooling and lubrication with a fresh mixture of the needle bearing of the upper head of the connecting rod, and also facilitate the temperature regime of the piston bottom. As a result, engine power increased by 10 percent, and piston burnout and bearing failure of the upper head of the connecting rod were eliminated.

The quality of the purge depends on the degree of compression of the combustible mixture in the crankcase; on racing engines, this parameter is maintained within 1.45 - 1.65, which requires a very compact design of the crank mechanism.

Obtaining high liter capacities is possible due to the wide distribution phases and the large width of the gas distribution windows.

The width of the windows of racing engines, measured by the central angle in the cross section of the cylinder, reaches 80 - 90 degrees, which creates difficult working conditions for the piston rings. But with such a width of windows in modern engines, jumpers prone to overheating are dispensed with. Increasing the height of the scavenge ports shifts the maximum torque to a lower RPM area, while increasing the height of the exhaust ports has the opposite effect.

Rice. 3. Purge systems: a - with a third purge window, b - with two additional purge channels; c - with branching purge channels.

The purge system with a third additional purge channel (see Fig. 1) is convenient for engines with a spool, in which the inlet port is located on the side, and the cylinder area opposite the outlet port is free to accommodate a purge port; the latter may have a jumper, as shown in fig. 3, a. An additional purge window promotes the formation of a combustible mixture flow around the cylinder cavity (loop purge). The entry angles of the purge channels are of great importance for the efficiency of the gas exchange process; the shape and direction of the flow of the mixture in the cylinder depend on them. Horizontal angle a, ranges from 50 to 60 degrees, with a larger value corresponding to a higher engine boost. The vertical angle a2 is 45 - 50 degrees. the ratio of the sections of the additional and main purge windows is about 0.4.

On engines without a spool, the carburetors and intake ports are usually located on the rear side of the cylinders. In this case, a different purge system is usually used - with two additional side purge channels (Fig. 3b). The horizontal entry angle a, (see Fig. 3, a) of the additional channels is about 90 degrees. The vertical angle of entry of the purge nanals varies for various models within a fairly wide range: on the Yamaha TD2 model of the 250 cm3 class, it is 15 degrees for the main purge channels, and 0 degrees for additional ones; on the model "Yamaha" TD2 class 350 cm3, respectively, 0 and 45 degrees.

Sometimes a variant of this purge system with branching purge channels is used (Fig. 3c). Additional purge windows are located opposite the outlet window, and, therefore, such a device approaches the first of the considered systems having three windows. The vertical angle of entry of additional purge channels is 45 - 50 degrees. The ratio of the cross sections of the additional and main purge windows is also about 0.4.

Rice. 4. Schemes of the movement of gases in the cylinder: a - with branching channels; b - with parallel.

On fig. 4 shows diagrams of the movement of gases in the cylinder during the purge process. With an acute entry angle of the additional purge channels, the fresh mixture flow coming from them removes the exhaust gas tangle in the middle of the cylinder, which is not captured by the mixture flow from the main purge channels. There are other options for purge systems according to the number of purge windows.

It should be noted that on many engines the duration of opening of additional purge windows is 2-3 degrees less than that of the main ones.

On some Yamaha engines, additional scavenging channels were made in the form of grooves on the inner surface of the cylinder; Here, the inner wall of the channel is the wall of the piston at its positions close to the N.M.T.

The profile of the purge channels also affects the purge process. The smooth shape without sharp bends gives less pressure drops and improves engine performance, especially in intermediate conditions.

The information in this section shows that two-stroke engines stand out for their simplicity.

The increase in power density of engines of this type over the past decade has not been accompanied by any significant changes in the basic design; it was the result of a careful experimental selection of ratios and dimensions of previously known structural elements.