How to measure valve timing on a two-stroke engine. Gas distribution mechanism of two-stroke engines

The quality of operation of a car's internal combustion engine depends on many factors, such as power, efficiency, and cylinder volume.

The valve timing in an engine is of great importance, and the efficiency of the internal combustion engine, its throttle response, and stability at idle speed depend on how the valves overlap.
In standard simple engines, timing timing is not changed, and such engines are not highly 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 changes.

Valve timing diagram of a two-stroke engine

A two-stroke engine differs from a four-stroke engine in that its operating cycle takes place in one revolution of the crankshaft, while on a 4-stroke internal combustion engine it takes place in two revolutions. The valve timing in the internal combustion engine is determined by the duration of the opening of the valves - exhaust and intake; the valve overlap angle is indicated in degrees of c/v position.

In 4-stroke engines, the cycle of filling 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 intake duration 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 approximately 120-150º at the crankshaft turn, and purging also lasts less, so filling with the working mixture and cleaning exhaust gases 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, K-175 engine.

Two-stroke engines are used infrequently in cars, as they have lower efficiency, worse efficiency and poor purification of exhaust gases from harmful impurities. The last factor is especially relevant - due to tightening environmental standards, it is important that the engine exhaust contains a minimum amount of CO.

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

power units are more compact and lighter;
they are cheaper;
A two-stroke engine accelerates faster.

Many cars in the 70s and 80s of the last century were mainly equipped with carburetor engines with a “trawler” ignition system, but many leading car companies even then began to equip engines 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 internal combustion engines.

Modern electronics contain various sensors that monitor engine operation, sending signals to the unit about the state of the power unit. Based on all the data from the sensors, the ECU makes a decision - how much fuel needs to be supplied to the cylinders at certain loads (speeds), what ignition timing should be set.

The valve timing sensor has another name - the camshaft position sensor (CPS), it determines the position of the timing belt relative to the crankshaft. Its readings determine the proportion in which fuel will be supplied to the cylinders, depending on the number of revolutions and ignition timing. If the DPRV does not work, it means that the timing belt 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) is supplied to all cylinders simultaneously, the engine operates inconsistently, and on some car models 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 operating principle of such a system is as follows:

the camshaft is connected to a hydraulic coupling;
the camshaft is also connected to this clutch;
at idle and low speeds, the cam gear with the camshaft is fixed in the standard position, as it was installed according to the marks;
when the speed increases under the influence of hydraulics, the clutch turns 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 used on BMW 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 (M50 engines have a two-shaft timing system), and since 1996 the Double VANOS system began to be used, with the help of which the position of the exhaust and intake camshafts was already regulated.

What advantage does a timing adjuster provide? At idle, valve timing overlap is practically not required, and in this case it even harms the engine, since when the camshafts shift, exhaust gases can enter the intake manifold, and some of the fuel will enter the exhaust system without being completely burned. 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 timing clutch makes it possible to effectively fill the cylinders with the working mixture, which means increasing the efficiency of the engine and increasing its power. At the same time, at idle, the r/shafts with the clutch are in their original state, and combustion of the mixture occurs in full. It turns out that the phase regulator increases the dynamics and power of the internal combustion engine, while fuel consumption is quite economical.

The variable valve timing system (VPV) provides lower fuel consumption, reduces the level of CO in the exhaust gases, and allows for more efficient use of internal combustion engine power. Different global automakers have developed their own SIFG, which applies not only changes in the position of the camshafts, but also the level of valve lift in the cylinder head. For example, Nissan uses a CVTCS system that is controlled by a variable valve timing valve (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 move.

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

Tools for setting valve timing

In order for the engine to operate without interruption, it is important to set the timing timing correctly and install the camshafts in the desired position relative to the crankshaft. On all engines, the shafts are aligned according to marks, and a lot depends on the accuracy of the installation. If the shafts are not aligned correctly, various problems arise:

the engine is unstable at idle;
The internal combustion engine does not develop power;
There are shots in the muffler and popping noises in the intake manifold.

If the marks are wrong 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 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 incorrect, the shafts should be reinstalled. The device for 406 motors is a set consisting of three elements:

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

When the crankshaft is set at 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°, and the intake cam should be slightly higher than the exhaust camshaft cam.

There are also special devices for installing camshafts on BMW engines of the M56/ M54/ M52 models. The kit for installing the valve timing of the internal combustion engine of the BVM includes:

Malfunctions of the variable valve timing system

The valve timing can be changed in various ways, and recently the most common is turning the r/shafts, although the method of changing the amount of valve lift and using camshafts with cams of a modified profile are often used. From time to time, various malfunctions arise in the gas distribution mechanism, due to which the engine begins to work intermittently, becomes “stupid”, and in some cases does not start at all. The causes of problems may be different:

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

Often when malfunctions occur 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, you have to turn it with the starter several times;
a chirping sound 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, computer diagnostics reveal 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 are occurring specifically in the electronics.

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

Unfortunately, SIFG is not installed on Russian-made engines, but many motorists are engaged in tuning the internal combustion engine, trying to improve the characteristics of the power unit. The classic option for upgrading an engine is to install a “sports” camshaft, whose cams are shifted and their profile is changed.

This r/shaft has its advantages:

the engine becomes responsive and clearly responds to pressing the gas pedal;
The dynamic characteristics of the car improve, the car literally tears out from under itself.

But this tuning also has its disadvantages:

idle speed becomes unstable, you have to set it 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 subject to tuning. The problem with 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 of installing an automatic tensioner instead of the standard factory one.

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

Device in operation

Two-stroke engines with crank-chamber scavenging do not have a special gas distribution mechanism. Gas distribution is carried out using a cylinder, piston and crankcase, while the crank chamber serves as the body of the scavenge pump.

The cylinder has windows that are opened and closed by a moving piston. Through the windows, the combustible mixture from the crankcase enters the cylinder and exhaust gases exit the cylinder.

In two-stroke engines, loop and direct-flow purge schemes are used. Loop circuits are characterized by rotation of the combustible mixture as it moves inside the cylinder in such a way that it forms a vapor. There are return and transverse loop schemes.

With a direct-flow design, the combustible mixture usually enters from one end of the cylinder, and the combustion products exit from the other end.

Engines with different types of gas distribution systems are described below.

In Fig. 54, a shows a cylinder with a purge window located opposite the outlet window. When purging, when the piston is near the no. m.t., the combustible mixture, pre-compressed in the crankcase, enters the cylinder through the purge window and is directed upward by the deflector on the piston to the combustion chamber. Then the combustible mixture falls down, displacing the exhaust gases through the exhaust window, which closes at the end of the purge. When exhaust gases are forced out of the cylinder through the exhaust window, a slight leak of the combustible mixture occurs.

The described transverse blowing is almost never used. More advanced is the return-loop blowing, carried out with a conventional piston with a flat or slightly convex head. Such pistons make it possible to use a combustion chamber close in shape to a hemispherical chamber.

With return-loop purge, there are two purge windows in the engine cylinder (Fig. 54, b), directing two jets of the combustible mixture at an angle to one another onto the cylinder wall located opposite the exhaust window. Jets of the combustible mixture rise up to the combustion chamber and, making a loop, fall down to the exhaust window. In this way, the exhaust gases are displaced and the cylinder is filled with fresh mixture.

The most common type is return two-channel purge. It is used in engines of both domestic and foreign motorcycles (M-104, Kovrovets-175A, Kovrovets-175B and Kovrovets-175V, IZH Jupiter, Java, Panonia, etc. ).

Three-channel purge (Fig. 54, e) is used, for example, in Tsundap engines, four-channel purge (Fig. 54, d) - in IZH-56 motorcycle engines, cross-shaped two-channel purge (Fig. 54, e) - in Ardi engines, four-channel (Fig. 54, e) -_.for Villiers engines.

With all the described methods of purging, a single-piston engine has a symmetrical valve timing diagram (Fig. 55). This means that* if the intake phase begins before the piston reaches c. m.t. (for example, beyond 67.5°), then its end occurs after 67.5° of the crankshaft rotation angle after c. m.t. Also begin and end relative to n. m.t. exhaust and purge phases. The exhaust phase is longer than the purge phase. The cylinder is filled with a combustible mixture all the time with the exhaust window open. This feature of the symmetrical valve timing limits the possibility of increasing the engine's liter power. In addition, the compressed working mixture contains relatively many residual gases. To reduce the amount of residual gases and improve the filling of the cylinder with the combustible mixture, purging is improved. To do this, the engine design is sometimes changed, although it is more advisable to increase the power of a conventional two-stroke engine without complicating its design. The Dunelt engine (Fig. 56, a) uses a stepped piston to increase the amount of incoming combustible mixture. The volume described by the lower part of the increased diameter piston is approximately 50% greater than the volume of the upper part of the cylinder.

The Bekamo engine (Fig. 56, b) has an additional large-diameter cylinder with a piston with a short stroke. The piston is driven by a connecting rod from an additional crank on the crankshaft. Such engines, in contrast to engines with superchargers, are called engines with “support” (engines of this type were installed, in particular, on some domestic sports motorcycles). These engines have symmetrical valve timing using a single piston. However, the outlet window closes later than the purge window. The piston delivers an additional amount of mixture when the exhaust port is open, as a result of which the cylinder is not filled with a compressed combustible mixture, as is observed in a supercharged engine, in which part of the intake occurs with the exhaust port or valve closed.

To increase the filling of the engine with the combustible mixture, spool devices are also used, with the help of which the intake phase is increased. Possible options for the spool device are the installation of a spool on the cylinder instead of the carburetor pipe (Fig. 57, a) or on the crankcase (Fig. 57, b), as well as the spool proposed by the author in the hollow main journal of the crankshaft. In the latter case, you can change the valve timing while the engine is running (Fig. 57, c) and use its vortex movement in the crankcase to form and stop jets of the combustible mixture. This design, but without a device for changing valve timing, was used, in particular, on the D-4 bicycle engine.

Record results are shown by MZ motorcycle engines manufactured in the GDR, in which the combustible mixture is supplied to the central part of the crankcase through a device located in it with a rotating spring spool (Fig. 57, d) made of sheet steel.

Engines with direct-flow scavenging, which have two pistons in two cylinders with a common combustion chamber (so-called two-piston engines), are distinguished by their high power.

The Junkers engine with direct-flow blowing has the following device (Fig. 58, a). The cylinder contains two pistons moving towards each other. The middle part of the cylinder between the piston heads when they are in position. m.t. serves as a combustion chamber. It contains a spark plug. The combustible mixture enters through the windows on the right side of the cylinder and displaces the exhaust gases into the exhaust windows located on the left side of the cylinder. In this case, the combustible mixture almost does not mix with the exhaust gases.

The cylinder can be fed in the usual way using a crank-chamber purge or a separate compressor supplying the mixture with a spool device. Each piston is connected by a connecting rod to a separate crankshaft. The crankshafts are connected to each other by gears so that when approaching N. m.t. the left piston opens the exhaust ports approximately 19° earlier than the right piston opens the purge ports. The release of exhaust gases begins earlier than in a single-piston engine, and accordingly the pressure in the cylinder at the start of purging is lower. When the piston moves from N. m. t. sq. m.t., unlike single-piston engines, the exhaust windows close before the purge windows and the cylinder is filled with the exhaust windows closed approximately during the time corresponding to the crankshaft turning by 29*. The asymmetrical diagram of the purge and exhaust phases during direct-flow purge makes it possible to effectively use a supercharger to obtain high power.

The domestic engine of the GK-1 racing motorcycle is designed in a similar way.

Engines of this design are complex and expensive to manufacture, but not correspond to the layout accepted in the motorcycle industry and therefore have not received mass distribution.

There are engines with direct-flow scavenging, which are more convenient for placement on a motorcycle. In engines with direct-flow scavenging according to the Zoller scheme, two pistons move in a U-shaped cylinder. The combustion chamber is located in the middle. The combustible mixture enters through the window on the right side of the cylinder, and the exhaust gases exit through the window on the left side. The movement of the pistons, providing asymmetrical purge and exhaust phases, is carried out using various crank mechanisms. For DKV engines (Fig. 58, b), one piston is installed on the main connecting rod, and the other on the trailing rod. The Pooh engine (Fig. 58, c) uses a forked connecting rod. For Triumph engines with a Zoller design, the crankshaft consists of two cranks offset from one another and two connecting rods (Fig. 58, d).

With direct-flow blowing, the cylinders can be positioned at an acute angle, with the combustion chamber at the apex of the angle (Fig. 58, e). In this case, the combustion chamber is less stretched than with a U-shaped cylinder. Otherwise, such an engine is similar to the engine of the Juncker system.

Domestic engines with superchargers of racing motorcycles S-1B, S-2B and S-ZB, characterized by high liter power, have direct-flow blowing and angled parts of the cylinder.

Service

Gas distribution in a two-stroke engine is most often disrupted when excess air penetrates into it and when the exhaust tract resistance increases. It is necessary to monitor the tightness of the crankcase, tighten connections in a timely manner, change damaged gaskets and seals, and also clean the cylinder exhaust windows, pipe and muffler from carbon deposits.

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

Gas exchange

Much in our life depends on how we breathe. And life itself; in the world of internal combustion engines about the same. Let's take a 1.5-liter VAZ 16-valve; do you want it to pull to V at 600 rpm? For fun. The question of choosing valve timing: let’s select the profile of the intake camshaft cams so that the intake starts at approximately 24° (according to the angle of rotation of the crankshaft) after TDC. We will make the cams so “dumb” that the valves rise only 3 mm, and the intake ends somewhere at 6° after ground level.

We adjust the start of exhaust to 12° BC, and let the exhaust valves close just at BT; we leave their rise “according to the state.” Degrees and millimeters of valve lift are those very phases: earlier, later.

Circular diagram of valve timing of a 4-stroke engine

Check it experimentally: with the correct ignition and fuel injection settings, the modified “four” will show the highest 75-80 Nm - at about 6 hundred rpm! Maximum power - 10-12 hp. at 1500 min -1 ; don't blame me. However, the motor will indeed pull from the very “bottoms” - like a (small) steam engine. It’s just a pity that it doesn’t develop any speed or power.

Full intake (exhaust) diagram: millimeters of valve lift by crankshaft angle

I don’t like it... Let’s come from the other end: the profile of the cams is such that the intake starts at 90° before ground dead center and ends at 108° after ground dead center; rise - up to 14 mm. There is a difference? And the release too: start at 102° BC, end at 96° after MT. As the experts say, the exhaust and intake overlap is 186° according to the crankshaft rotation angle! And what? See: with the correct ignition and injection settings [Also with oversized valve heads, bored and polished intake and exhaust ports...] your 1.5-liter VAZ will produce something like 185 Nm of torque - at... 11 thousand revolutions! And at 13500 min -1 it will develop about 330 hp. - without any boost. Of course, if the timing belt and crank mechanism can withstand it (unlikely). About 40 years ago, such power was shown by a good 3-liter Formula 1 engine... True, below 6000 min -1 the forced VAZ will be completely dead [Idle speed will have to be set at about 3500 min -1 ...]; its operating range is 9-14 thousand revolutions.

At the “tops” it’s the other way around: wide valve timing will allow 100% mobilization of the resonance of gas flows at the inlet and outlet - as they say, acoustic supercharging. With the correct selection of the lengths and cross-sections of (individual) inlet and outlet pipes, the cylinder filling ratio will reach a level of 1.25-1.35 in the 11 thousand rpm zone; get the required 185 Nm.

This is what valve timing is: they determine the gas exchange of the internal combustion engine. — 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. A thought immediately arises: the valve timing needs to be adjusted - right on the go. And then under the hood of your car there will be not just one engine - for all occasions, but many different ones!

As the best friend of motorists taught, “personnel decide everything.” To paraphrase the famous expression, let’s assume that everything is decided by the phases (gas distribution). The Generalissimo knew how to regulate personnel issues, and engine builders always sought to manage the phases.

Phase rotation

It's easy to say, but hard to do; on a 4-stroke engine, the valve timing is determined 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 an unchanged profile - for example, moving the camshaft according to the angle of rotation of the crankshaft. Back and forth; that is, the duration of the intake remains unchanged (in the 2nd example - 378°), but it begins and ends earlier. Let's say the intake valves now open 120° BT. and close at 78° after b.m.t. So to speak, “earlier-earlier.” Or vice versa - “later-later”: the intake starts at 78° b.c.t. and ends at 120° after b.m.t.

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

This solution (for the intake) was first used by ALFA Romeo on a 2-liter 8-valve “four” Twin spark [It is clear that phasing is applicable 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 phasing.]- back in 1985. It is called phasing and is used (at the inlet and/or outlet) quite widely. And what does it give? Not much, but still better than nothing. Thus, during a cold start of an engine with a catalytic converter, the exhaust camshaft is advanced. The exhaust starts early, and high-temperature exhaust gases go to the converter; it warms up to working condition faster. Fewer harmful substances are released 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 engine. This means that the throttle valve is tightly closed; increased pumping losses, excessive fuel consumption. And if you strongly move the intake camshaft “later-later”, then part (say, 1/3) of the fuel-air mixture is thrown back into the intake manifold during compression [Don't worry, she's not going anywhere. The so-called "5-stroke" cycle.]. and engine power is reduced (to the level required by driving conditions) without excessive throttling at the inlet. That is, although the throttle valve is closed, it is 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 out, the nose is stuck.” When you reduce the valve opening advance, the closing lag increases by exactly the same amount.

It doesn't get any easier hour by hour. Now, if you somehow change the duration of the intake-exhaust... Let's say, in the 2nd example, reduce it, when necessary, from 378 to 225°. The engine will also be able to operate normally “at the bottom” - without loss of power “at the top”.

Dreams are coming true: 4 years have passed since the appearance of Twin spark with phase rotation, and Honda Motor showed a 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 (inlet and outlet); the process has begun. However, sometimes you hear: just think, VTEC - only 2 modes. And on the motor of my Corolla, the phases are steplessly regulated - a continuum of modes. Well, yes, if you don’t 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”. Locking 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 of the hour - to “earlier-earlier” in the spring and to “later-later” in the fall. God be their judge, we are talking about something else. It is technically easy to move the hands not only by an hour every six months, but even by a minute every day. So to speak, stepless. Phase rotation is like changing a clock - and the effect is about the same.

Have you tried changing the length of daylight hours? It may not be stepless, but only two modes - say, 9 hours and 12? So, Honda engineers have found a solution to a problem of this class; feel the difference. Let’s say that in the “lower” mode the intake duration is 186° (according to the angle of rotation of the crankshaft), and in the “upper” mode it is 252°. A radical change in gas exchange conditions: under the hood there are, as it were, two unequal engines. One is elastic and high-torque at the “bottoms”, the other is “sharp”, torsional and powerful at the “tops”; 25 years ago we would not have dreamed of this. And by the way, it doesn’t cost anything to add phase rotation to VTEC, which is what Honda did in the i-VTEC design. Whereas the opposite - giving VTEC phase rotation - will not work; the proprietary mechanism is not so simple and is subject to patents.

Two unequal intake diagrams for the same engine

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

Valvetronic

Well, in 2002, Bavarian designers unveiled the famous Valvetronic timing belt. And if VTEC is “montana”, then Valvetronic is “full...”. The mechanism has been in mass use for 5 years, but auto reviewers still have not understood its meaning and operating principle. What about journalists, if the BMW press service... Look and see: in company 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 phasing. However, Valvetronic is a sophisticated device; there's probably something beyond that.

Stepless variation of the intake diagram (base width changes): Bavarian Valvetronic. Please note: the diagram of the mechanism is shown incorrectly - it will not work. Corporate press service... max = 9.5 mm; min = 0.2 mm

Let's talk about the unusual mechanism separately. In the meantime, let’s admit that the Bavarian Valvetronic engines were the first Otto engines whose power is regulated without throttling at the inlet! Like diesels. They do without the most harmful part in the design of a spark-ignition engine; comparable to the invention of the carburetor. Or magneto. In 2002, the world changed, although no one noticed...

Electromagnets

Hats off to the BMW engineers, and yet Valvetronic is just an episode in the development of the Otto engine. An intermediate solution awaiting a radical one. And it’s already on the doorstep: a camless timing belt with an electromagnetic valve drive. No camshafts with their drive, pushers, rocker arms, hydraulic clearance compensators, etc. The valve stem simply enters a powerful electromagnet [With a force along the valve axis of up to 80-100 kg! Otherwise, the valves cannot keep up with their phases. And it is not easy to provide such forces in a compact mechanism, which is the main difficulty in creating an e-magnetic timing belt.], the voltage to which is supplied under the control of the CPU. That's all: at each revolution of the crankshaft, the CPU controls the timing of the opening and closing of the valves - and the height of their lift. There are no cams with their unchanged profile, there are no once and for all specified valve timing.

Electromagnetic valve mechanism (Valeo): limitless possibilities 1 – washers; 2 – electromagnet; 3 – plate; 4 – valve; 5 – springs; 6 – compression; 7 – stretching

The intake and exhaust diagrams are adjustable freely and within wide limits (limited only by the physics of the processes). Separately for each of the cylinders and from cycle to cycle - both the injection moment and the amount of fuel supplied. Or ignition. Essentially, the Otto engine will become itself - for the first time in history. And it will leave no chance for diesel. How computers found themselves with the advent of micro-chips, and pocket calculators instantly replaced electromechanical calculating machines. Whereas in the late 40s, computers were built on vacuum tubes and electromagnetic relays; consider spark ignition engines still at that very stage. Well, maybe Valvetronic...

So, what is it and what is it for? I won’t describe the basics of how 2T engines work, since everyone knows them, but not everyone understands what valve timing is and why they are the way they are and not others.
Valve timing is the period of time during which the windows in the cylinder open and close as the piston moves up and down. They are calculated in degrees of rotation of the engine shaft. For example, an exhaust phase of 180 degrees means that the exhaust port will start to open, will be open, and then close at half a revolution (180 out of 360) of the engine cranks. It should also be said that the windows open when the piston moves down. And they open to maximum at bottom dead center (BDC). Then, when the piston moves upward, they close. Due to this design feature of 2T engines, the valve timing is symmetrical relative to dead centers.

To complete the picture of the gas distribution process, it is also necessary to say about the area of the windows. The phase, as I already wrote, is the time during which windows open and close, but the area of the window also plays an equally important role. After all, at the same time of opening the window, more mixture (blowing) will pass through the window that is larger in area and vice versa. The same is true for exhaust; more exhaust gases will leave the cylinder if the window area is larger.
The general term characterizing the entire process of gas flow through windows is called time-section.
And the larger it is, the higher the engine power and vice versa. This is why we see such huge cross-sectional purge, intake and exhaust channels, as well as high valve timing on modern highly accelerated 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, the time during which the piston would do useful work is lost. In fact, engine power is generated only before the exhaust window opens and with further downward movement of the piston, no or very little torque is created. In general, the engine capacity of 2T, unlike 4T, is not fully used. Therefore, the primary task of designers is to increase the time - cross-section with minimal phases. This gives better indicators of torque and efficiency curves than at the same time - cross-section, but at higher phases.
But since the cylinder diameter is limited, and the width of the windows is also limited, in order to achieve a high level of engine boost it is necessary to increase the valve timing.
Many people, wanting to achieve more power, begin to enlarge the windows in the cylinder either at random, or on someone’s advice or after reading advice somewhere, but they don’t really understand what they will get in the end, and whether they are doing the right thing. Or maybe they need something completely different?
Let's say we have some kind of engine and we want to get more efficiency from it. What should we do with the phases? The first thing that comes to mind for many is to cut the exhaust ports upward, or raise the cylinder using a gasket, and also cut the intake down or trim 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 power generally increase with increasing phases, and not decrease? The time increases - the cross section, you say, yes it is. But do not forget that this is a 2T engine and its entire operating principle is based on resonant pressure and vacuum waves. And for the most part, the exhaust system plays a key role here. It is this that creates a vacuum in the cylinder at the start of exhaust, drawing out exhaust gases, and also subsequently drawing out the mixture from the purge channels, increasing the purge time and cross-section. It also refills the escaping mixture 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 tuned to certain speeds, beyond which the mixture ejected from the cylinder does not return, and the useful stroke of the piston is reduced due to high phases. This results in a loss of power and excessive fuel consumption at non-resonant engine frequencies.
So is it possible to get the same power and reduce sag and fuel consumption? Yes, if you achieve the same cross-section time 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 maximum width of the windows due to the operation of the rings. But while there is a reserve, it must be used, and only then the phases must 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 lows don’t disappear, then increase the capacity of channels and windows without increasing the phases. If this is not enough for you, increase the phases gradually. For example, it would be optimal to release at 10 degrees and purge at 5 degrees.
I would like to step back a little and talk separately about the intake phase. Here we were very lucky when people came up with a check plate valve, popularly known as a reed valve (LP). Its advantage 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 select and install it correctly from the very beginning. The valve area should be 1.3 times larger than the cross-sectional area of the carburetor, 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 upward movement of the piston.
An example of how you can achieve maximum intake phase is the following photos of intake modifications (not Java, but the essence does not change):

This is one of the best options for modifying the intake. In fact, the intake here is a combined version of the intake into the cylinder and the intake into the crankcase (the intake duct is permanently connected to the crank chamber, KShK). This also increases the resource of the NGSH due to better airflow with fresh mixture.

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

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

The metal near the liner is also selected in the cylinder jacket.
A correctly installed LC allows you to solve the problem of selecting the intake phase once and for all.
Anyone who has finally decided to achieve more power and knows what he is aiming for, is ready to sacrifice the bottom for the sake of explosive pickup at the top, can safely increase the valve timing. The best solution would be to use someone else's experience in this matter.
For example, in foreign literature the following recommendations are given:

I would exclude the Road race option, since the phases are very extreme, designed for road racing and are not practical when driving on regular roads. And most likely they are designed for a power valve that 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 optimal option, as for me, is 175-185 degrees.

Regarding purging... here everything is more or less indicated optimally. However, how do you know how much your engine will spin? You can look for people’s improvements and find out from them, or you can just take average numbers. This is around 120-130 degrees. Optimally 125 degrees. Higher numbers refer to smaller engine displacements.
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 reduce the volume of the crank chamber as much as possible by removing excess voids. For example, to begin with, plugging the balancing holes in the crankshaft. The plugs should be made from the lightest possible material so that they do not affect the balancing of the HF. Usually they are cut from wine corks (cork wood) and driven into the balancing holes, after which they are coated with epoxy on both sides.

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

So, let's say you have decided how you will modify 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 is what 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 ( link to download the program at the end of the article).
You just need to know the length of the connecting rod (Java 140mm, IZH Jupiter, Voskhod, 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 designed in such a way that it determines the distance from the top edge of the window to the edge of the sleeve. Why is this so, and not just say the height of the window? Because this is the most accurate phase determination. At top dead center the piston crown MUST be at the same level with the edge of the liner due to squish (a feature of the shape of the combustion chamber for detonation-free operation), and if it is suddenly not at 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 bottom dead center, the piston bottom is usually not at the same level with the edges of the windows, but slightly 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 operate to their full height, and therefore the phases cannot be determined by them!

The exhaust valve begins to open at the end of the expansion process ahead of the b.m.t. by angle φ o.v. = 30h-75° (Fig. 20) and closes after T.M.T. with a delay by the angle φ s.v., when the piston moves during the filling stroke in the direction to ground level. The beginning of the opening and closing of the intake valve is also shifted relative to the dead points: the opening begins before TDC. advanced by angle φ 0 . vp, and closing occurs after n.m.t. with a delay by the angle φ W.W. at the beginning of the compression stroke. Most of the release and filling processes occur separately, but around the b.m.t. the intake and exhaust valves are open for some time at the same time. The duration of valve overlap, equal to the sum of the angles φ s.v + φ o.vp, is short for piston engines (Fig. 20, a), but for combined engines it can be significant (Fig. 20, b). The total duration of gas exchange is φ o.v + 360 o + φ w.vp = 400-520 o; for high-speed engines it is greater.

Gas exchange periods in two-stroke engines

In a two-stroke engine, gas exchange processes occur when the piston moves near ground level. and occupy part of the piston stroke during the expansion and compression strokes.

In engines with a loop gas exchange scheme, both the intake and exhaust windows are opened by the piston, so the gas distribution phases and cross-sectional area diagrams of the windows are symmetrical relative to the b.m.t. (Fig. 24, a). In all engines with direct-flow gas exchange schemes (Fig. 24, b), the opening phases of the exhaust ports (or valves) are asymmetrical relative to the b.m.t., thereby achieving better filling of the cylinder. Typically, inlet ports and outlet ports (or valves) close at the same time or with slight angle differences. It is also possible to implement asymmetrical phases in an engine with a loop gas exchange scheme,

if you install (at the inlet or outlet) additional devices - spools or valves. Due to the lack of reliability of such devices, they are not currently used.

The total duration of gas exchange processes in two-stroke engines corresponds to 120-150° crankshaft rotation angle, which is 3-3.5 times less than in four-stroke engines. Opening angle of exhaust windows (or valves) φ r.o. = 50-90° BC, and the angle of advance of their opening φ pr = 10-15 0. In high-speed engines with exhaust through valves, these angles are larger, and in engines with exhaust through windows, they are smaller.

In two-stroke engines, the exhaust and filling processes occur mostly together - with the intake (scavenge) and exhaust ports (or exhaust valves) open simultaneously. Therefore, air (or a combustible mixture) enters the cylinder, as a rule, provided that the pressure in front of the inlet windows is greater than the pressure behind the outlet windows (valves).

Literature:

Nalivaiko V.S., Stupachenko A.N. Sypko S.A. Methodological instructions for conducting laboratory work on the course “Marine internal combustion engines”, Nikolaev, NKI, 1987, 41 p.

Marine internal combustion engines. Textbook/ Yu.Ya. Fomin, A.I. Gorban, V.V. Dobrovolsky, A.I. Lukin et al.-L.: Shipbuilding, 1989 – 344 p.: ill.

Internal combustion engines. Theory of piston and combined engines: Ed. A.S. Orlina, M.G. Kruglova – M.: Mechanical Engineering, 1983 – 372 pages.

Vanscheidt V.A. Marine internal combustion engines. L. Shipbuilding, 1977.-392 p.

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