Camshaft drives are their device. The device and purpose of the camshaft

The main function of the camshaft (camshaft) is to ensure the opening / closing of the intake and exhaust valves, with the help of which the fuel assembly (air-fuel mixture) is supplied and the gases formed. The camshaft is the main part of the timing (gas distribution mechanism), which takes part in the complex process of gas exchange in a car engine.

The modern timing belt can be equipped with one or two camshafts. In a single-shaft mechanism, all intake and exhaust valves are serviced at once (1 intake and exhaust valve per cylinder). In a mechanism equipped with two shafts, one camshaft drives the intake valves, the other shaft drives the exhaust valves (2 intake and exhaust valves per cylinder).

The location of the gas distribution mechanism directly depends on the type of car engine. Distinguish between timing with an upper valve arrangement (in the cylinder block) and with a lower valve arrangement (in the cylinder head).

The most common option is the overhead location, which makes it possible to efficiently adjust and maintain the camshaft.

The principle of operation and the device of the camshaft

The gas distribution phases are set according to the alignment marks that are on the gears or pulley. Correct installation ensures that the engine cycle is in sequence.

The main part of the camshaft is the cams. In this case, the number of cams with which the camshaft is equipped depends on the number of valves. The main purpose of the cams is to adjust the phases of the gassing process. Depending on the type of timing design, the cams can interact with a rocker arm or a pusher.

"Nockenwelle ani". Under the Public domain license from Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Nockenwelle_ani.gif#mediaviewer/File:Nockenwelle_ani.gif

Cams are installed between bearing journals, two for each engine cylinder. During operation, the camshaft has to overcome the resistance of the valve springs, which serve as a return mechanism, bringing the valve to its original (closed) position.

Overcoming these efforts requires the useful power of the engine, so designers are constantly thinking about how to reduce power loss.

In order to reduce friction between the tappet and the cam, the tappet can be equipped with a special roller.

In addition, a special desmodromic mechanism has been developed, in which a springless system is implemented.

The camshaft bearings are equipped with covers, with the front cover being shared. It has thrust flanges that are connected to the shaft journals.

The camshaft is manufactured in one of two ways - forging from steel or casting from cast iron.

Timing systems

As mentioned above, the number of camshafts corresponds to the type of engine.

In in-line engines with one pair of valves (one intake and one exhaust valve each), the cylinder is equipped with only one shaft. Inline engines with two pairs of valves have two shafts.

Currently, modern engines can be equipped with various valve timing systems:

VVT-i. In this technology, the phases are adjusted by turning the camshaft in relation to the sprocket on the drive.
Valvetronic. The technology allows you to adjust the valve lift by shifting the axis of rotation of the rocker arm
VTEC. This technology involves the regulation of the phases of the distribution of gases through the use of cams on an adjustable valve

So, to summarize ... the camshaft, being the main link of the gas distribution mechanism, ensures timely and accurate opening of the engine valves. This is ensured by precisely fitting the shape of the cams, which push the tappets and force the valve to move.

Camshaft, in an abridged version camshaft - the main part or timing, an important element of an automobile engine. Its task is to synchronize the intake and exhaust strokes of the internal combustion engine.

Design features

The location of this mechanism depends entirely on the design of the internal combustion engine, since in some models the camshaft is located at the bottom, at the base of the cylinder block, and in others - at the top, right in. At the moment, the top location of the camshaft is considered optimal, since this greatly simplifies service and repair access to it. The camshaft is directly connected to. They are interconnected by a chain or belt drive by providing a connection between the pulley on the timing shaft and the sprocket on the crankshaft. This is necessary because the camshaft is driven by the crankshaft.

The camshaft is installed in bearings, which in turn are securely fixed in the cylinder block. Axial play of the part is not allowed due to the use of clamps in the design. The axis of any camshaft has a through channel inside through which the mechanism is lubricated. At the back, this hole is closed with a plug.

The important elements are the camshaft cams. In terms of quantity, they correspond to the number of valves in the cylinders. It is these parts that perform the main function of the timing belt - regulating the order of operation of the cylinders.

Each valve has a separate cam that opens it by pushing the pusher. By releasing the follower, the cam allows the spring to unfold, returning the valve to the closed state. The camshaft design assumes the presence of two cams for each cylinder - according to the number of valves.

Camshaft device.

It should be noted that the fuel pump and distributor are also driven from the camshaft.

Principle of operation

The engine camshaft, located in the cylinder block, is driven by a gear or chain drive from the crankshaft.

Rotating, the camshaft rotates the cams located on it, which alternately act on the intake and exhaust valves of the cylinders, ensuring their opening-closing in a specific order, unique for each ICE model.

The working cycle of the engine (alternate movement of each of the cylinder valves) is carried out in 2 crankshaft revolutions. During this time, the camshaft only needs to make one revolution, so its gear has twice as many teeth.

One ICE can have more than one camshaft. The exact number is determined by the engine configuration. The most common budget in-line engines, which have a pair of valves for each cylinder, are equipped with only one camshaft. For systems with two pairs of valves, two camshafts must be used. For example, power units with a different cylinder arrangement have either a single camshaft installed in the camber, or a pair - for each block head separately.

The camshaft or simply the camshaft in the gas distribution mechanism provides the main function - the timely opening and closing of the valves, due to which the inflow of fresh air and the release of exhaust gases is produced. In general terms, the camshaft controls the gas exchange process in the engine.

To reduce inertial loads, increase the rigidity of the elements of the gas distribution mechanism, the camshaft should be located as close as possible to the valves. Therefore, the standard position of the camshaft on a modern engine in the cylinder head is the so-called. overhead camshaft.

The gas distribution mechanism uses one or two camshafts per cylinder bank. With a single-shaft arrangement, the intake and exhaust valves ( two valves per cylinder). In a two-shaft gas distribution mechanism, one shaft serves the intake valves, the other - the exhaust ( two intake and two exhaust valves per cylinder).

The design of the camshaft is based on cams... Typically one cam is used per valve. The cam has a complex shape that allows the valve to open and close at a set time and rise to a certain height. Depending on the design of the gas distribution mechanism, the cam interacts with either a pusher or a rocker arm.

When the camshaft is operating, the cams are forced to overcome the forces of the return springs of the valves and the frictional forces from the interaction with the pushers. All this consumes useful engine power. The springless system implemented in the desmodromic mechanism is devoid of these disadvantages. To reduce the friction between cam and follower, the flat surface of the follower can be replaced roller... In the long term, the use of a magnetic system to control the valves, ensuring complete rejection of the camshaft.

The camshaft is available in cast iron (cast) or steel (forged). The camshaft rotates in bearings, which are plain bearings. The number of supports is one more than the number of cylinders. The supports are mainly detachable, less often - one-piece (made as one piece with the block head). The supports, made in a cast-iron head, use thin-walled bushings, which are replaced when worn.

The camshaft is kept from longitudinal movement by thrust bearings located near the drive gear (sprocket). The camshaft is pressure lubricated. Individual oil supply to each bearing is preferred. The efficiency of the gas distribution mechanism is significantly increased with the use of various variable valve timing systems, which make it possible to achieve an increase in power, fuel efficiency, and a decrease in the toxicity of exhaust gases. There are several approaches to changing the valve timing:

turning the camshaft in different operating modes;
use of several cams with different profiles per valve;
changing the position of the rocker arm axis.

The camshaft is driven by the engine crankshaft. In a four-stroke internal combustion engine, the drive allows the crankshaft to rotate at twice the speed of the crankshaft.

On passenger car engines, the camshaft is driven by a chain or belt drive. These types of drive are used on equal terms both in gasoline engines and diesel engines. Previously, a gear drive was used for the drive, but due to its bulkiness and increased noise, it was no longer used.

Chain drive combines a metal chain that runs around the sprockets on the crankshaft and camshaft. In addition, a tensioner and a damper are used in the drive. The chain consists of links connected by hinges. One chain can serve two camshafts.

The camshaft chain drive is quite reliable, compact, and can be used at large center distances. At the same time, wear of the hinges during operation leads to stretching of the chain, the consequences of which can be the most sad for the timing. Even a tensioner with a damper does not help. Therefore, the chain drive requires regular condition monitoring.

IN belt drive The camshaft uses a timing belt that spans the corresponding timing pulleys on the shafts. The drive belt is equipped with a tension roller. The belt drive is compact, almost silent, reliable enough, which makes it popular with manufacturers. Modern timing belts have a significant resource - up to 100 thousand km or more.

The camshaft drive can be used for drive and other devices - oil pump, high pressure fuel pump, ignition distributor.

Sometimes in a large flow of information (especially new) it is very difficult to find some important little things, to single out the "seeds of truth." In this short article I will talk about the gear ratios of the gears and the drive in general. This topic is very close to the topics covered in ...

The drive is the engine and everything that is and works between the motor shaft and the shaft of the working body (couplings, gearboxes, various gears). What is “engine shaft” is clear, I think, to almost everyone. What is the "shaft of the working body" is probably not clear to many. The shaft of the working body is the shaft on which the element of the machine is fixed, which is set in rotary motion by the entire drive with the required specified torque and speed. This can be: wheel of a carriage (car), drum of a belt conveyor, sprocket of a chain conveyor, winch drum, pump shaft, compressor shaft, and so on.

U Is the ratio of the engine speed nдв to the frequency of rotation of the working body of the machine nro.

U \u003d nдв / nro

Total drive ratio U often, in practice, a sufficiently large number is obtained from the calculations (more than ten, or even more than fifty), and it is not always possible to perform it in one gear due to various restrictions, including power, strength and overall dimensions. Therefore, the drive is made consisting of several gears connected in series with their optimal gear ratios Ui... In this case, the total gear ratio U is found as the product of all gear ratios Uiincluded in the drive.

U \u003d U1 * U2 * U3 *… Ui *… Un

Gear ratio Ui Is the ratio of the speed of the transmission input shaft nin to the speed of the output shaft of this gear nout.

Ui \u003d nin i / nouti

When choosing, it is desirable to give preference to values \u200b\u200bclose to the beginning of the range, that is, to the minimum values.

The proposed table is just a recommendation and not a dogma! For example, if you assign a chain drive U\u003d 1.5, then this will not be an error! Of course, everything must be justified. And, perhaps, to reduce the cost of the entire drive, it is better to U\u003d 1.5 "hide" inside the gear ratios of other gears, increasing them accordingly.

Various scientists have paid a lot of attention to optimization issues in the design of gear reducers. Dunaev P.F., Snesarev G.A., Kudryavtsev V.N., Niberg N.Ya., Niemann G., Wolf V. and other well-known authors tried to simultaneously achieve equal strength of gears, compactness of the gearbox as a whole, good lubrication conditions , reduction of losses due to oil splashing, uniform and high durability of all bearings, good stiffness of shafts. Each of the authors, having proposed their own algorithm for dividing the gear ratio into gear stages, has not completely and unambiguously solved this controversial problem. Very interesting and detailed about this is written in the article at: http://www.prikladmeh.ru/lect19.htm.

I will add a little more ambiguity to the solution of this question ... Let's look at another table in Excel.

We set in the combined cell C4-7 the value of the total gear ratio of the gearbox U and read the calculation results in cells D4 ... D7 - Ub and in cells E4 ... E7 - Ut performed for four variants of different conditions.

The values \u200b\u200bgiven in the table are calculated using the formulas:

1. In cell D4: \u003d H4 * $ C $ 4 ^ 2 + I4 * $ C $ 4 + J4 =4,02 Ub \u003d a * U ^ 2 + b * U + c

in cell E 4: \u003d $ C $ 4 / D4 =3.91 Ut = U / Ub

in cell H 4: a =-0,0016111374

in cell I 4: b =0,24831562

in cell J 4: c =0,51606736

2. In cell D5: \u003d H5 * $ C $ 4 ^ 2 + I5 * $ C $ 4 + J5 =5.31 Ub \u003d a * U ^ 2 + b * U + c

in cell E 5: \u003d $ C $ 4 / D5 =2.96 Ut = U / Ub

in cell H 5: a =-0,0018801488

in cell I 5: b =0,26847174

in cell J 5: c =1,5527345

3. In cell D6: \u003d H6 * $ C $ 4 ^ 2 + I6 * $ C $ 4 + J6 =5.89 Ub \u003d a * U ^ 2 + b * U + c

in cell E 6: \u003d $ C $ 4 / D6 =2.67 Ut = U / Ub

in cell H 6: a =-0,0018801488

in cell I 6: b =0,26847174

in cell J6: c =1,5527345

4. In cell D 7: \u003d C4 / E7 =4.50 Ub = U / Ut

in cell E 7: \u003d 0.88 * C4 ^ 0.5 =3.49 Ut =0,88* U ^0,5

In conclusion, I dare to recommend: do not design a single-stage spur gear reducer with a gear ratio U\u003e 6 ... 7, two-stage - with U\u003e 35 ... 40, three-stage - with U>140…150.

On this, a short excursion into the topics "How to optimally" split "the gear ratio of the drive in stages?" and "How to choose a gear ratio?" completed.

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What is a camshaft (camshaft)? Camshaft

What is a camshaft in a car

The camshaft is a functional element of the vehicle's fuel system, responsible for the correct sequential opening and closing of the engine valves. Fuel consumption, developed power, stability of its operation, and other driving characteristics depend on the correctness of its functioning. Let's look at what a camshaft is in a car, what is its principle of operation, and how improper operation affects the car.

What is a camshaft

What the camshaft looks like.

The camshaft is a rod on which several so-called cams are located. These are irregularly shaped parts rotating on the shaft axis. They correspond to the number of intake valves in the cylinders and are located exactly opposite them. The set of cams is selected so that rotation guarantees stable and even combustion of fuel in the cylinders. And the work of the entire camshaft is clearly synchronized with other engine mechanisms.

On both sides of the cams, support journals are put on the shaft, holding it in the bearings. One of the most important shaft assemblies are oil channels. The physical wear of parts, the power characteristics of the motor and the stability of its operation depend on their condition. To supply oil, a through hole was made in the camshaft axles with leads to the support bearings and cams.

How the camshaft works

Camshafts in the cylinder head.

The camshaft is a key functional component of the timing mechanism that determines the order in which the valves are opened to start the air / fuel mixture inside the cylinders. The synchronous operation of this mechanism ensures continuous alternate combustion of fuel portions in the engine chambers. In some car models, the gas distribution mechanism has multiple camshafts.

The design, location, composition and characteristics of the camshaft cams are completely dependent on the engine model. In some cars, the camshaft is located in the cylinder head, while in others it is located in the base. The top location is currently considered optimal as it facilitates repair and maintenance. The camshaft is connected to the engine crankshaft by a belt or chain drive, because it is it that is driven.

How the camshaft works

How the camshaft works.

When viewed laterally, the cam is shaped like a drop. When rotating, the extended part of the cam clicks on the valve tappet and causes the valve to open. This provokes the supply of an air / fuel mixture for combustion. With further rotation, the cam "releases" the pusher, and that, under the action of the spring mechanism, returns the valve to the closed position.

The camshaft gear has twice as many teeth as the crankshaft. This is due to the fact that in one working cycle of the engine, the crankshaft makes 2 revolutions, and the camshaft - 1.

The engine can be configured with two camshafts. The layout of the gas distribution mechanism with one shaft is used in budget cars, where the cylinders have 1 pair of valves. Two camshafts are needed in models with two pairs of valves on the cylinders.

What is the camshaft sensor responsible for?

The camshaft position sensor detects the angular position of the timing relative to the crankshaft and generates the corresponding signals in the electronic engine control system. As a result, the ignition and fuel injection are adjusted. On gasoline vehicles, a malfunction of this device blocks the operation of the ECU and prevents the engine from starting. On diesel models, starting is possible, but still difficult.

Like the crankshaft sensor, the camshaft sensor works on the basis of the Hall principle - the magnetic field in the device changes when the magnetic gap closes with a special tooth, which is located on the shaft or master disk. When the prong passes near the sensor, a signal is generated that is sent to the electronic control unit. The frequency of the pulses is directly related to the rate of rotation of the camshaft, based on which the ECU makes adjustments to the operation of the engine. Continuous acquisition of data on the piston position of the first cylinder ensures consistent and timely injection.

Breakdowns and their causes

A faulty camshaft most often gives out its condition with a characteristic knock, which occurs due to wear of bearings or cams, shaft deformation, mechanical failure of one of the elements. Such breakdowns occur, both due to factory defects and as a result of natural wear and tear.

Camshaft knocking also occurs when using poor engine oil or due to unregulated fuel supply. Because of this, the cylinder valves and cams do not work synchronously - the engine loses power, consumes too much fuel and is unstable.

Video on the topic

Avtonov.com

All about the camshaft (camshaft) »AvtoNovator

Good day, dear motorists! Let us together try to put on shelves, in the literal sense of the word, the device of one of the important components of the engine's gas distribution mechanism (timing) - the camshaft.

Camshaft device

The camshaft performs far from the last function in the operation of the car engine - it synchronizes the intake and exhaust of engine strokes.

Depending on the type of engine, the timing belt can be with a lower valve arrangement (in the cylinder block) or with an upper valve arrangement (in the cylinder head).

In modern engine building, preference is given to the upper timing belt. This allows you to simplify the process of maintenance, adjustment and repair of the camshaft, due to ease of access to the timing parts.

Structurally, the camshaft is connected to the engine crankshaft. This connection is made by means of a belt or chain. The camshaft belt or chain is fitted to the camshaft pulley and crankshaft sprocket. The camshaft is driven by the crankshaft.

The most effective is the camshaft pulley - a split gear, which is used to tune the camshaft in order to increase the power characteristics of the engine.

On the cylinder head there are bearings in which the camshaft journal journals rotate. In the case of repairs, the camshaft repair liners are used to secure the bearing journals.

Camshaft end play is prevented by camshaft clips. A through hole is made along the camshaft axis. Through it, the rubbing surfaces of the parts are lubricated. On the rear side, this hole is covered by the camshaft plug.

The camshaft cams are the most important component. Their number corresponds to the number of intake and exhaust valves of the engine. It is the cams that perform the main purpose of the camshaft - adjusting the valve timing of the engine and the order of operation of the cylinders.

Each valve has its own, individual cam, which opens it, "running" on the pusher. When the cam leaves the tappet, a powerful return spring closes the valve.

The camshaft cams are located between the bearing journals. Two cams: inlet and outlet for each cylinder. In addition, a gear is attached to the shaft to drive the breaker-distributor and the oil pump. Plus an eccentric to drive the fuel pump.

The gas distribution phase of the camshaft is selected empirically, and depends on the design of the intake and exhaust valves and the engine speed. Manufacturers for each engine model indicate the camshaft phases in the form of diagrams or tables.

A camshaft cover is installed on the camshaft supports. The front camshaft cover is common. It has thrust flanges that enter the grooves in the camshaft journals.

The main parts of the timing

Valves: inlet and outlet. The valve consists of a stem and a poppet. The valve seats are plug-in for easy replacement. The intake valve head is larger in diameter than the exhaust valve head.
The rocker arm serves to transfer force to the valve from the rod. There is a screw in the short arm of the rocker for adjusting the thermal gap.
The rod is designed to transfer force from the pusher to the rocker arm. One end of the bar rests against the pusher, and the other against the rocker arm adjusting bolt.

How the camshaft works

The camshaft is located in the camber of the cylinder block. The camshaft is driven by a gear or chain drive from the crankshaft.

The rotation of the camshaft causes the cams to act on the operation of the intake and exhaust valves. This happens in strict accordance with the valve timing and the order of the engine cylinders.

To correctly set the valve timing, there are timing marks located on the timing gears or on the drive pulley. For the same purpose, the crankshaft cranks and camshaft cams must be in a strictly defined position relative to each other.

Thanks to the installation made according to the marks, the sequence of the alternation of strokes is observed - the order of operation of the engine cylinders. The order of operation of the cylinders depends on their location and design features of the crankshaft and camshaft.

Engine duty cycle

The period when the intake and exhaust valves in each cylinder must open once is the engine's duty cycle. It takes 2 crankshaft revolutions. At this time, the camshaft should make one revolution. It is for this that the camshaft gear has twice as many teeth.

Number of camshafts in the engine

This value usually depends on the engine configuration. Engines with in-line configuration and one pair of valves per cylinder have one camshaft. If there are 4 valves per cylinder, then two camshafts.

Boxer and V-shaped engines have one camshaft in the camber, or two, one camshaft in each block head. There are also exceptions related to the design features of the engine model. (for example, an in-line arrangement of four cylinders - one camshaft with 4 valves per cylinder, like the Mitsubishi Lancer 4G18).

The modern market offers the consumer different engines with different variable valve timing systems. The most characteristic ones are:

VTEC is a technological development of the Honda company. The phases are adjusted by using 2 cams for the variable valve.

VVT-i - from Toyota. The phases are adjusted by turning the camshaft relative to its drive sprocket.

Valvetronic is a technological development of the BMW company. Adjustment of the valve lift is performed by changing the position of the axis of rotation of the rocker arms.

Good luck in studying the engine of your car.

carnovato.ru

Camshaft - Auto Mechanic's Dictionary

The camshaft, in its abbreviated form, the camshaft is the main part of the main timing mechanism or timing, an important element of an automobile engine. Its task is to synchronize the intake and exhaust strokes of the internal combustion engine.

Design features

The location of this mechanism depends entirely on the design of the internal combustion engine, since in some models the camshaft is located at the bottom, at the base of the cylinder block, and in others, at the top, right in the cylinder head. At the moment, the top location of the camshaft is considered optimal, since this greatly simplifies service and repair access to it. The camshaft is directly connected to the crankshaft. They are interconnected by a chain or belt drive by providing a connection between the pulley on the timing shaft and the sprocket on the crankshaft. This is necessary because the camshaft is driven by the crankshaft.

Camshaft device.

It should be noted that the fuel pump and the oil pump distributor are also driven from the camshaft.

Principle of operation

The engine camshaft, located in the cylinder block, is driven by a gear or chain drive from the crankshaft.

Camshaft breakage

There are quite a few reasons why the knock of the camshaft is intertwined with the operation of the engine, which indicates the appearance of problems with it. Here are just the most typical ones:

The camshaft requires proper maintenance: replacement of oil seals, bearings and periodic troubleshooting.

wear of the cams, which leads to the appearance of knocking immediately only at startup, and then all the time the engine is running;
bearing wear;
mechanical failure of one of the shaft elements;
problems with the regulation of the fuel supply, due to which there is an asynchronous interaction between the camshaft and cylinder valves;
shaft deformation leading to axial runout;
low-quality engine oil, full of impurities;
lack of engine oil.

According to experts, if a slight knock of the camshaft occurs, the car can drive for more than one month, but this leads to increased wear of the cylinders and other parts. Therefore, if you find a problem, you should start fixing it. The camshaft is a collapsible mechanism, therefore, repairs are most often carried out by replacing it all or only some of its elements, for example, bearings.

Related terms

etlib.ru

Timing camshaft

The camshaft (camshaft) is a key element of the gas distribution mechanism, which is responsible for the timely opening and closing of the intake or exhaust valve to supply the fuel-air mixture or release the exhaust gases.

The camshaft is used to synchronize the intake and exhaust during the engine strokes. The part ensures the operation of the entire gas distribution mechanism, taking into account the order of operation of the cylinders and valve timing in relation to a particular engine.

The camshaft is a shaft with cams located on it. The camshaft rotates in journal bearings, which are designed as bearings. The camshaft bearings are ducted to supply engine oil under pressure from the lubrication system. The number of cams on the camshaft corresponds to the number of intake and exhaust valves in the engine. One valve receives its own cam, which opens it by pressing the pusher. The moment the camshaft cam comes off the tappet, then the valve closes under the powerful influence of the return spring.

The valve timing depends on the shape of the camshaft cams. These phases are understood as the moments of opening and closing of the valves, as well as the duration of the stay of the valve in the open or closed state. Modern power units also have a variable valve timing system to improve the overall efficiency of the timing and improve the characteristics of the internal combustion engine.

In modern car engines, the camshaft is located at the top of the cylinder head. The camshaft is connected to the sprocket or pulley of the engine crankshaft by means of a belt or chain drive. The camshaft is driven by the crankshaft.

On four-stroke engines, the entire timing belt rotates two times slower than the crankshaft, since the full working cycle of such internal combustion engines is carried out in two crankshaft revolutions. The inlet and outlet valves should only open once per these two turns. It turns out that the camshaft, which controls the opening of the valves, must make only one revolution per operating cycle.

More than one camshaft may be present in the timing design. This is often due to the number of valves per cylinder. Today, the most widely used scheme is four valves per cylinder and a two-shaft timing belt (one camshaft drives the intake valves, and the other interacts with the exhaust valves). For V-shaped internal combustion engines, four camshafts are installed, since each cylinder bank has a separate cylinder head with two shafts. The timing system with one shaft is called SOHC (Single OverHead Camshaft), the two-shaft was named DOHC (Double OverHead Camshaft).

The device and principle of operation of the camshaft

In a modern engine, the camshaft (usually two) is located at the top of the cylinder head.

The camshaft is connected to the crankshaft of the vehicle's engine. The connection is carried out by means of a timing chain (or belt). For reliable transmission of force, a driven gear is attached to the end part of the camshaft, resembling an "sprocket" on the rear wheel of a bicycle.

The camshaft cams are responsible for adjusting the valve timing and the order of operation of the cylinders - there are exactly the same number of intake and exhaust valves used in the timing mechanism. The work is organized as follows: the cam of the camshaft "runs" on the valve tappet, presses on it and opens the valve. After the cam comes off the tappet, the valve is closed by a tight return spring.

The more valves in the gas distribution mechanism, the more camshafts are installed in it. The Bugatti Veyron has four camshafts and 64 valves

So, the camshaft rotates, which ensures that the cams act on the operation of the intake and exhaust valves. The location of the cams relative to each other has been carefully calculated in strict accordance with the valve timing and the order of cylinder firing. In other words, as long as the intake valve (or two valves) of one cylinder is open, all the other intake valves are at rest.

The number of camshafts in an engine is determined by the configuration of the engine itself: if the engine has an in-line design and one pair of valves per cylinder, then one camshaft is sufficient. If there are 4 valves per cylinder, it is advisable to use 2 camshafts - one of them serves only the intake valves, the other only the exhaust valves. Among other things, the system with paired shafts has another plus - speed.

As for V-shaped and boxer engines, they can have either one camshaft in the place of the so-called "camber" of the cylinders (the base of the imaginary letter V), or two - one on each cylinder head. It is possible to try to implement a complex scheme of opening and closing 16 valves using one camshaft, but it is not rational - the part will turn out to be too complicated. Such schemes are rare, but Honda nevertheless decided to take one of them into service: an in-line four-cylinder engine with one camshaft is installed, for example, on the popular Honda Fit / Jazz model. The undoubted advantage of such a system is the ability to make the engine compact and lightweight.

Camshaft characteristics

It is usually customary to distinguish three important characteristics of the camshaft: the amount of valve lift, the duration of the valve opening and the camshaft phase.

Engineers sacrifice idle speed to maximize valve opening when designing sports motors. In racing cars, it rarely goes below 2000 rpm.

Valve lift is measured in millimeters. This value is used to measure the maximum distance that the valve moves away from the so-called "seat" in which it is at the moment of closing. Valve open time is the length of time the valves remain open. This value is measured in degrees of crankshaft rotation. Moreover, each of the listed criteria can affect the operation of the engine: with an increase in valve lift, the duration of its opening or optimization of the valve timing, the engine power increases. It should be noted that it is the opening duration that is the main parameter with which the designers of forced motors work.

For example, camshafts used in sports cars provide longer valve opening times than standard camshafts. This means that the valves remain open as long as possible, allowing you to burn the maximum dose of fuel for such a volume of the combustion chamber in one stroke. Unfortunately, in technology, in order to achieve one thing, you have to sacrifice something else: the installation of sports camshafts does not allow keeping the idle speed below 2000 rpm. Naturally, this kind of operation consumes a huge amount of fuel.

If we talk about the phases of the camshaft (the moments when the valves open and close in relation to the position of the camshaft), then all information about them is usually contained in the data table that is attached to the camshaft. The table shows the angular positions of the camshaft, as well as information about when the intake and exhaust valves open and close.

Modern engines are often equipped with variable valve timing systems. For example, some Toyota cars have a VVT-i system. valve timing is adjusted by turning the camshaft relative to its drive sprocket. Another example is the development of the Japanese manufacturer Honda, which received the designation VTEC - it allows you to change phases using two cams for a variable valve.

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What is a camshaft (camshaft)?

The camshaft in the engine is a finger-shaped axial mechanism driven by the crankshaft and has several elliptical protrusions (cams) on its surface - one for each intake and exhaust valve located in the engine. As the camshaft rotates (driven by the crankshaft), these elliptical lugs control the opening and closing of the valves by pushing them in a specific sequence.

The first symptoms of a camshaft failure:

Abnormal valve noise
Engine misfires.

Maintenance of the camshaft consists in regularly checking and, if necessary, replacing its oil seals. So, replacement is usually carried out when the timing belt is replaced.

What is a camshaft (camshaft)? Video

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Engine camshaft

For all its external complexity and seeming inaccessibility for understanding, the internal combustion engine is a surprisingly rational and purposefully designed device. The purpose of any of its parts is to ensure proper operation and maximum output from the engine. At the same time, literally all of its elements are interconnected, but nevertheless, the operation of the timing (gas distribution mechanism), as well as its basis - the camshaft, should be considered separately.

On the cycles and operation of the internal combustion engine

The ICE is a four-stroke power unit, which means that all processes associated with its operation are carried out in four strokes. Their sequence is strictly defined, and if it is violated, the operation of such a motor is impossible. Sequence, i.e. opening the valves at the right time to exhaust the exhaust gases and start the combustible mixture determines the camshaft, which can be seen in the picture below.
Cams must be considered its main working element. It is they who, through the drive system, which includes pushers, rocker arms, springs and other parts determined by the timing design, open the valves at the right time. Each valve has its own cam, when it presses on the valve through the pusher with the available protrusion, it rises, and a fresh mixture can enter the cylinder, or the products of its combustion are removed. When the protrusion leaves the pusher, the valve closes under the action of the spring.

The bearing journal of the camshaft is designed to be installed in specified places, on which it rotates during operation. The rubbing parts are hardened using high frequency currents and lubricated in the process.

About the design of the camshaft

The device and drawing of the timing, including the camshaft, are shown below.
Structurally, the camshaft can be located either in the cylinder block or in the head of the power unit. Depending on its location, the drive also changes, due to which the force is transferred from the cams to the valve. The camshaft drive is connected to the crankshaft. The drive can be made using a chain drive (see drawing above), or using a flexible belt. In addition, there may be other ways of transmitting the control force to the valves, but this is already determined by the drawing and documentation of the motor.

Which camshaft drive is best used is determined by the engine design. In cases where the camshaft is located in the cylinder block, (the so-called bottom position), then a gear drive can even be activated. The latter, however, has not been used recently because of its bulkiness and increased noise during operation. Both the chain drive and the belt drive are distinguished by sufficient reliability, but each of them has its own operating characteristics that must be taken into account when servicing the engine.
Its device may provide that the camshaft in the motor may not be one. As a rule, in modern multi-valve engines, it is placed as close as possible to the valves to reduce the load on it. The design and drawing, for example, of a V-shaped engine, provides at least two shafts, whereas in a conventional in-line, as a rule, one camshaft. Although for multivalve engines, their purpose will be decisive - there may be separate exhaust and intake camshafts, i.e. they control the operation of the exhaust or intake valves.

About working together with the crankshaft

Do not forget that for the camshaft, the main purpose is to ensure correct timing when the engine is running. For this, the operation of the camshaft and crankshaft must be coordinated, i.e. the opening and closing of the valves must occur at the right times - in the TDC or BDC position of the piston, or in accordance with the advance that is established by the drawing or design documentation.

To perform such a connection, special marks are made on the timing gears, the coincidence of which means ensuring the desired position of the camshaft and crankshaft. To achieve this, a special technique is used to adjust their position.

Camshaft position sensor

With the transition to injection engines, a special camshaft position sensor was used for these purposes. So, on VAZ cars, a Hall sensor is used for this. Its work is based on changing the magnetic field, for the creation of which the sensor device provides a magnet. When the magnetic field changes, which occurs when the camshaft is in the desired position, the sensor detects that the piston in the first cylinder is in the TDC position and transmits this data to the controller. In accordance with them, it provides fuel injection and combustion, as the drawing or documentation provides for the operation of individual engine cylinders.

Camshaft maintenance

First of all, when carrying out routine maintenance affecting the camshaft, it is necessary to pay attention to the condition of the belts or its drive chain. The point is not so much that the entire gas distribution mechanism, which the camshaft provides, is disrupted, but that mechanical damage to both the valves and the piston is possible.

Sometimes the cause of engine failure or malfunction is the position sensor. A manifestation of this can be poor vehicle dynamics and significant fuel consumption, as well as the engine health indicator light on the instrument panel. Fault detection and determination of its source - whether it is a sensor or not - is performed using a multimeter. Often the probable cause is not the sensor itself, but the wiring. If the fault detection shows that the sensor is faulty, then it must be replaced.

The reasons for sensor failure can be:

failure of the toothed disk of the impulse sensor;
its displacement due to a violation of the fastening;
short circuit in the internal circuit of the sensor;
exposure to increased temperature from engine overheating.

Correctly performed fault detection will avoid the failure of a new sensor installed instead of the old one.

The camshaft is the main component for ensuring correct timing when the engine is running, and is often the main component for efficient operation. Its timely maintenance and technical condition monitoring will allow to operate the car correctly and without additional costs.