Variable valve timing
In internal combustion engines, variable valve timing is the process of altering the timing of a valve lift event, is used to improve performance, fuel economy or emissions. It is being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Strict emissions regulations are causing many automotive manufacturers to use VVT systems. Two-stroke engines use a power valve system to get similar results to VVT; the valves within an internal combustion engine are used to control the flow of the intake and exhaust gases into and out of the combustion chamber. The timing and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift, the valve timing is the same for all engine speeds and conditions, therefore compromises are necessary. An engine equipped with a variable valve timing actuation system is freed from this constraint, allowing performance to be improved over the engine operating range.
Piston engines use valves which are driven by camshafts. The cams exhaust cycle; the timing of the valve opening and closing, relative to the position of the crankshaft, is important. The camshaft is driven by the crankshaft through gears or chains. An engine requires large amounts of air. However, the intake valves may close before enough air has entered each combustion chamber, reducing performance. On the other hand, if the camshaft keeps the valves open for longer periods of time, as with a racing cam, problems start to occur at the lower engine speeds. Opening the intake valve while the exhaust valve is still open may cause unburnt fuel to exit the engine, leading to lower engine performance and increased emissions. Early variable valve timing systems used discrete adjustment. For example, one timing would be used below another used above 3500 rpm. More advanced "continuous variable valve timing" systems offer continuous adjustment of the valve timing. Therefore, the timing can be optimized to suit all conditions.
The simplest form of VVT is cam-phasing, whereby the phase angle of the camshaft is rotated forwards or backwards relative to the crankshaft. Thus the valves close earlier or later. Achieving variable duration on a VVT system requires a more complex system, such as multiple cam profiles or oscillating cams. Late intake valve closing The first variation of continuous variable valve timing involves holding the intake valve open longer than a traditional engine; this results in the piston pushing air out of the cylinder and back into the intake manifold during the compression stroke. The air, expelled fills the manifold with higher pressure, on subsequent intake strokes the air, taken in is at a higher pressure. Late intake valve closing has been shown to reduce pumping losses by 40% during partial load conditions, to decrease nitric oxide emissions by 24%. Peak engine torque showed only a 1% decline, hydrocarbon emissions were unchanged. Early intake valve closing Another way to decrease the pumping losses associated with low engine speed, high vacuum conditions is by closing the intake valve earlier than normal.
This involves closing the intake valve midway through the intake stroke. Air/fuel demands are so low at low-load conditions and the work required to fill the cylinder is high, so Early intake valve closing reduces pumping losses. Studies have shown early intake valve closing reduces pumping losses by 40%, increases fuel economy by 7%, it reduced nitric oxide emissions by 24% at partial load conditions. A possible downside to early intake valve closing is that it lowers the temperature of the combustion chamber, which can increase hydrocarbon emissions. Early intake valve opening Early intake valve opening is another variation that has significant potential to reduce emissions. In a traditional engine, a process called valve overlap is used to aid in controlling the cylinder temperature. By opening the intake valve early, some of the inert/combusted exhaust gas will back flow out of the cylinder, via the intake valve, where it cools momentarily in the intake manifold; this inert gas fills the cylinder in the subsequent intake stroke, which aids in controlling the temperature of the cylinder and nitric oxide emissions.
It improves volumetric efficiency, because there is less exhaust gas to be expelled on the exhaust stroke. Early/late exhaust valve closing Early and late exhaust valve closing can this time can be manipulated reduce emissions. Traditionally, the exhaust valve opens, exhaust gas is pushed out of the cylinder and into the exhaust manifold by the piston as it travels upward. By manipulating the timing of the exhaust valve, engineers can control how much exhaust gas is left in the cylinder. By holding the exhaust valve open longer, the cylinder is emptied more and ready to be filled with a bigger air/fuel charge on the intake stroke. By closing the valve early, more exhaust gas remains in the cylinder which increases fuel efficiency; this allows for more efficient operation under all conditions. The main factor preventing this technology from wide use in production automobiles is the ability to produce a cost effective means of controlling the valve timing under the conditions internal to an engine.
An engine operating at 3000 revolutions per minute will rotate the camshaft 25 times per second
The BMW N46 is a aspirated four-cylinder petrol engine which replaced the BMW N42 and was produced from 2004 to 2015. The N46 serves as the basis for the smaller BMW N45 engine. In 2007, the N46's successor - the BMW N43 - was introduced. However, the direct-injected N43 was not sold in countries with high-sulfur fuel, so the N46 continued to be produced alongside the N43; the N46 continued production until 2015, when the last N46 models were replaced by the BMW N13 turbocharged four-cylinder engine. Compared with its N42 predecessor, the N46 features a revised crankshaft, intake manifold and valvetrain. In 2007, the N46 was updated, known as the N46N. Changes included the intake manifold, exhaust camshaft and the engine control unit was changed from Bosch Motronic version ME9.2 to version MV17.4.6. The redline is 6,500 rpm; the N46B18 has a 1,796 cc displacement and produces 85 kW and 175 N⋅m. Applications: 2004-2005 E46 316i/316ti The N46B20U1 produces 95 kW and 180 N⋅m. Applications: 2005-2007 E87 118i 2005-2007 E90/E91 318i The N46B20U2 produces 100 kW and 180 N⋅m.
It was used instead of the N43 engine in countries with high-sulfur fuel. Applications: 2007-2011 E81/E87 118i 2007-2013 E90 318i The N46B20A produces 105 kW and 200 N⋅m. Applications: 2004-2006 E46 318i, 318Ci and 318ti The N46B20O1 produces 110 kW and 200 N⋅m. On models with secondary air injection, peak torque occurs at 3750 rpm instead of 3600 rpm. Applications: 2004-2007 E83 X3 2.0i 2005-2008 E85 Z4 2.0i 2004-2007 E87 120i 2005-2007 E90/E91 320i The N46NB20 produces 115 kW and 200 N⋅m. It was used instead of the N43 engine in countries with high-sulfur fuel. Applications: 2007-2011 E81/E82/E87/E88 120i 2007-2013 E90/E91/E92/E93 320i 2007-2010 E60 520i 2009-2015 E84 X1 sDrive18i / xDrive18i 2007-2010 E83 X3 2.0i BMW List of BMW engines
The BMW N40 is a DOHC four-cylinder petrol engine which replaced the 1.6 litre versions of the BMW M43. It was produced from 2001-2004 and only sold in several countries, where taxes favoured cars with smaller displacement engines; the N40 was replaced by the BMW N45. The N40 is based on the BMW N42 engine and uses the same crankcase and bore size of 84 mm; the redline is 6,500 rpm. Unlike the N42, the N40 does not have Valvetronic; the other major difference is a 9 mm reduction in stroke to 72.0 mm, which results in the smaller displacement than the N40. Applications: 2001-2005 E46 316i/316ci/316ti BMW List of BMW engines
The BMW M5 is a high performance variant of the BMW 5 Series marketed under the BMW M sub-brand. It is considered an iconic vehicle in the sports sedan category; the majority of M5's have been produced in the sedan body style, however in some countries the M5 was available as a wagon from 1992–1995 and 2006–2010. The first M5 model was hand-built in 1985 on the E28 535i chassis with a modified engine from the M1 that made it the fastest production sedan at the time. M5 models have been produced for every generation of the 5 Series since 1985; the first BMW M5, based on the E28 5 Series, was manufactured from October 1984 to June 1988. It made its debut at the Amsterdam Motor Show in February 1985, it was based on the 535i chassis with various mechanical changes, most notably the M88/3 engine, derived from the engine used in the BMW E24. At its launch, the E28 M5 was the fastest production sedan in the world; the first generation of the M5 was hand-built in Preussenstrasse/Munich prior to the 1986 Motorsport factory summer vacation.
Thereafter, the M5 production was moved to Daimlerstrasse in Garching where the remainder were built by hand. The official markets for the E28 M5 were Europe, Great Britain, the United States and South Africa; the European and South African cars utilised the M88/3 engine which has a power output of 210 kW. Cars sold in the United States and Canada used a detuned version of the M88/3 called the S38B35, equipped with a catalytic converter and has a power output of 191 kW. Due to an extended production run that exceeded BMW's original forecast of production volumes, a class action lawsuit was launched by owners in the United States; the results of this class action was that owners were given a voucher for US$4,000 in 1993. Production of North American specification M5 commenced in November 1986 and ended in November 1987. Aside from 96 cars which were assembled in kit form at BMW's Plant in Rosslyn, South Africa, all cars were assembled by hand at BMW Motorsport in Garching, Germany. With a total production of 2,241 units, the E28 M5 remains among the rarest regular production BMW Motorsport cars – after the M1, M5 Touring and the 850CSi.
The E34 generation of the M5 was produced from September 1988 to August 1995. Powered by the S38 engine, an evolution of the previous generation's straight-six, it was produced in a sedan body style, with a LHD Touring version following in 1992. Production of M5 models began with the painted shell of an E34 5 Series at the BMW Dingolfing plant; the shells were transported to BMW M GmbH in Garching, where the car was assembled by hand over a period of two weeks. Only the South African M5 was assembled at the Rosslyn, South Africa assembly plant from complete knock down kits supplied from Garching, Germany; the M5 Touring, BMW M Division's first wagon as well as the last hand built M car, saw 891 units produced. Total production of the E34 M5 was 12,254 units. Cosmetic changes to the exterior from the standard E34 included unique front and rear bumpers and side rocker panels, contributing to a drag coefficient of 0.32, interior updates included a unique gearshift surround and rear headrests. The second-generation M5 was introduced with the S38B36 engine, which generated 232 kW at 6,900 rpm and 360 N⋅m of torque at 4,750 rpm, touting a factory 0-97 km/h acceleration figure of 6.3 seconds.
Top speed was electronically limited to 250 kilometres per hour. In late 1991, the engine was upgraded to the 3.8-litre S38B38, with exception to North America and South Africa, which continued with the 3.6-litre engine due to emission laws. Power increased to 250 kW, leading to a factory 0-60 time of 5.9 seconds, the ignition changed to a distributor-less system with each cylinder having an individual coil. BMW used a dual-mass flywheel in place of the single in the 3.6 for a smoother idle and throttle input at the expense of response. The standard self-leveling suspension system, which maintained a constant ride height in the rear, was replaced with Electronic Damper Control, an electronically controlled and hydraulically regulated system that can switch between comfort "P" setting and a more track-oriented "S" setting. A 6-speed Getrag 420G manual transmission was introduced in 1994, which added an overdriven top gear; the M5 came with an unusual wheel design. From 1988–1992 the M5 featured the three-piece Style 20 "M-System" wheels, which consisted of directional bolted-on wheel covers and a fin assembly in front of the black, 5-spoke forged aluminum wheel.
The purpose of the M-System cover was to divert heat from the brake assembly to increase cooling. In 1992 BMW changed the design to the "M-System II" which improved brake cooling from the combination of the larger openings and fins placed in the driving direction. In May 1994, the M5 switched to 18-inch Style 37 "M Parallel" wheels that did away with the finned cover entirely. There were four special editions of the E34 M5; the Cecotto, Winkelhock and 20 Jahre editions which were offered as LHD Euro specification models while the RHD UK Limited edition was only sold in the United Kingdom. In 1991, BMW asked two race drivers to design their "ideal" version of the E34 M5; the Cecotto Edition M5, named after Johnny Cecotto, featured severy luxury items fitted, including Nappa leather for the steering wheel and heated seats. A total of 22 Cecotto E34 M5s were produced with options of having either Lagoon Green metallic and Mauritius Blue metallic paint and Light Parchment or Light Silvergrey for the interior.
The other M5 special edition dedicated to a race driver was the Winkelhock Ed
The firing order is the sequence of power delivery of each cylinder in a multi-cylinder reciprocating engine. This is achieved by sparking of the spark plugs in a gasoline engine in the correct order, or by the sequence of fuel injection in a Diesel engine; when designing an engine, choosing an appropriate firing order is critical to minimizing vibration, to improve engine balance and achieving smooth running, for long engine fatigue life and user comfort, influences crankshaft design. In a gasoline engine, the correct firing order is obtained by the correct placement of the spark plug wires on the distributor. In a modern engine with a direct ignition and the Engine Control Unit or Engine Management system takes care of the correct firing sequence. On cars with distributors, the firing order is cast on the engine somewhere, most on the cylinder head, the intake manifold or the valve cover. Although the vast majority of automobile engines rotate clockwise as viewed from the front, some engines are designed by the manufacturer to rotate counter-clockwise to accommodate certain mechanical configurations.
In these applications, the firing order is shown in a reverse order. For the most common inline configurations, this gives firing orders of 1-3-2, 1-2-4-3, 1-4-2-6-3-5. In addition to the reconfiguration of the plug wires or injector tubes, the valve timing must be accordingly modified; when referring to cars, the left-hand side of the car is the side that corresponds with the driver's left, as seen from the driver's seat. It can be thought of as the side that would be on the left if one was standing directly behind the car looking at it; when referring to engines, the front of the engine is the part where the pulleys for the accessories are, the rear of the engine is where the flywheel is, through which the engine connects to the transmission. The front of the engine may point towards the front, side or rear of the car. In most rear-wheel drive cars, the engine is longitudinally mounted and the front of the engine points to the front of the car. In front-wheel drive cars with a transverse engine, the front of the engine points towards the right-hand side of the car.
One notable exception is Honda, where many models have the front of the engine at the left-hand side of the car. In front-wheel-drive cars with longitudinally mounted engines, most the front of the engine will point towards the front of the car, but some manufacturers have at times placed the engine'backwards', with #1 towards the firewall. One notable car with this layout is the Citroën Traction Avant; this layout is uncommon today. In a straight engine the spark plugs are numbered, starting with #1 from the front of the engine to the rear. In a radial engine the cylinders are numbered around the circle, with the #1 cylinder at the top. There are always an odd number of cylinders in each bank, as this allows for a constant alternate cylinder firing order: for example, with a single bank of 7 cylinders, the order would be 1-3-5-7-2-4-6. Moreover, unless there is an odd number of cylinders, the ring cam around the nose of the engine would be unable to provide the inlet valve open - exhaust valve open sequence required by the four-stroke cycle.
In a V engine, cylinder numbering varies among manufacturers. Speaking, the most forward cylinder is numbered 1, but some manufacturers will continue numbering along that bank first while others will number the cylinders from front to back along the crankshaft, so one bank would be 1-3-5-7 and the other bank would be 2-4-6-8.. To further complicate matters, manufacturers may not have used the same system for all of their engines, it is important to check the numbering system used before comparing firing orders, because the order will vary with crankshaft design. As an example, the Chevrolet Small-Block engine has cylinders 1-3-5-7 on the left hand side of the car, 2-4-6-8 on the other side, uses a firing order of 1-8-4-3-6-5-7-2. Note that the order alternates irregularly between the left and right banks. In most Audi and Ford V8 engines cylinders 1-2-3-4 are on the right hand side of the car, with 5-6-7-8 are on the left; the firing pattern is the same for Chevrolet & Chrysler V8 engines with a firing order of 1-8-4-3-6-5-7-2, for Ford's V8 engines with a firing order of 1-5-4-2-6-3-7-8.
An exception is the Ford Flathead V8 where the number 1 cylinder is on the right front of the engine but this cylinder is not the front cylinder of the engine. In this case number 5 is the front cylinder. A similar situation exists with the Pontiac V8's 455 etc. where the cylinders are numbered like a Chevrolet V8 but the right side bank is in front, this puts cylinder number 2 in front of number 1. Firing order affects the balance, vibration, smoothness and sound of the engine. Evenly spaced firing order means that the angle between each firing is equal. In four-stroke engines this requires a firing interval of 720° divided by the number of cylinders. On the other hand, engines with unevenly spaced firing order not all angles between firings are equal, for example a six-cylinder engine with unevenly spaced firing order can have a combination of 90° and 150° firing intervals compared to a six-cylinder engine with firing order which must have 720° / 6 = 120° firing interval. Engines that are even-firing
A valvetrain or valve train is a mechanical system that controls operation of the valves in an internal combustion engine, whereby a sequence of components transmits motion throughout the assembly. A conventional reciprocating internal combustion engine uses valves to control the flow of the air/fuel admix into and out of the combustion chamber. A typical ohv valvetrain consists of valves, rocker arms, pushrods and camshaft. Valvetrain opening/closing and duration, as well as the geometry of the valvetrain, controls the amount of air and fuel entering the combustion chamber at any given point in time. Timing for open/close/duration is controlled by the camshaft, synchronized to the crankshaft by a chain, belt, or gear. Valvetrains are built in several configurations, each of which varies in layout but still performs the task of opening and closing the valves at the time necessary for proper operation of the engine; these layouts are differentiated by the location of the camshaft within the engine: Cam-in-block The camshaft is located within the engine block, operates directly on the valves, or indirectly via pushrods and rocker arms.
Because they require pushrods they are called pushrod engines. Overhead camshaft The camshaft is located above the valves within the cylinder head, operates either indirectly or directly on the valves. Camless This layout uses no camshafts at all. Technologies such as solenoids are used to individually actuate the valves; the valvetrain is the mechanical system responsible for operation of the valves. Valves are of the poppet type, although many others have been developed such as sleeve and rotary valves. Poppet valves require small coil springs, appropriately named valve springs, to keep them closed when not actuated by the camshaft, they are attached to the valve stem ends, seating within spring retainers. Other mechanisms can be used in place of valve springs to keep the valves closed: Formula 1 engines employ pneumatic valve springs in which pneumatic pressure closes the valves, while motorcycle manufacturer Ducati uses desmodromic valve drive which mechanically close the valves. Depending on the design used, the valves are actuated directly by a rocker arm, finger, or bucket tappet.
Overhead camshaft engines use fingers or bucket tappets, upon which the cam lobes contact, while pushrod engines use rocker arms. Rocker arms are actuated by a pushrod, pivot on a shaft or individual ball studs in order to actuate the valves. Pushrods are slender metal rods seated within the engine block. At the bottom ends the pushrods are fitted with lifters, either solid or hydraulic, upon which the camshaft, located within the cylinder block, makes contact; the camshaft pushes on the lifter, which pushes on the pushrod, which pushes on the rocker arm, which rotates and pushes down on the valve. Camshafts must actuate the valves at the appropriate time in the combustion cycle. In order to accomplish this the camshaft is linked to and kept in synchronisation with the crankshaft through the use of a metal chain, rubber belt, or geartrain; because these mechanisms are essential to the proper timing of valve actuation they are named timing chains, timing belts, timing gears, respectively. Typical normal-service engine valve-train components may be too lightweight for operating at high revolutions per minute, leading to valve float.
This occurs when the action of the valve no longer opens or closes, such as when the valve spring force is insufficient to close the valve causing a loss of control of the valvetrain, as well as a drop in power output. Valve float will damage the valvetrain over time, could cause the valve to be damaged as it is still open while the piston comes to the top of its stroke. Upgrading to high pressure valve springs could allow higher valvetrain speeds, but this would overload the valvetrain components and cause excessive and costly wear. High-output and engines used in competition feature camshafts and valvetrain components that are designed to withstand higher RPM ranges; these changes include additional modifications such as larger-sized valves combined with freer breathing intake and exhaust ports to improve air flow. Automakers offer factory-approved performance parts to increase engine output, numerous aftermarket parts vendors specialize in valvetrain modifications for various engine applications.
Cam-in-block Overhead camshaft Camless Animation
The BMW M42 is a DOHC four-cylinder petrol engine, produced from 1989-1996. It is BMW's first mass-production DOHC engine and was produced alongside the BMW M40 SOHC four-cylinder engine as the higher performance engine; the M42 was replaced by the BMW M44, introduced in 1996. Compared with the M40, the M42 features a DOHC valvetrain, a timing chain, hydraulic valve lifters and an increased 10.0:1 compression ratio. Versions of the M42 feature a dual length intake manifold; the M42 was used as the basis for the S42 racing engine, which powered the BMW 320i in the German Super Tourenwagen Cup. Following BMW's typical construction techniques at the time, the motor incorporates a cast-iron block and aluminium head. Weight-saving measures include aluminium chain cases, oil sump, motor mount arms, accessory mounts and a cartridge-style oil filter housing. Other features included a forged steel crankshaft and tubular stainless steel exhaust manifold instead of the more typical cast-iron items. BMW fitted hydraulic motor mounts to decrease the inline four's inherent noise and harshness compared to the smoother straight-six engines in production at that time.
When installed in the BMW E30, a two-piece oil pan with a removable front sump was fitted to the M42. In this two-piece arrangement, the upper oil pan casting incorporates the oil pump's supply passage, is sealed to the crankcase oil filter housing with a paper gasket; this can cause problems, because thermal cycles and engine vibration tend to loosen the upper pan mounting bolts inside the motor. All versions featured a low-maintenance timing chain with a self-adjusting hydraulic chain tensioner and hydraulic valve tappets; the M42 uses the Bosch Motronic M1.7 engine management system, eliminating a distributor in favor of electronic ignition timing. The ignition system uses a coil-on-plug system. In markets that required emissions controls, the DME incorporates an oxygen sensor and three-way catalytic converter; the M42B18 has a displacement of 1,796 cc, achieved through a bore of 84 mm and a stroke of 81 mm. Versions equipped with a catalytic converter produce 100 kW and 172 N⋅m. and meet the Euro 2 emissions standard.
Applications: 1989-1991 E30 318i 1989–1991 E30 318iS 1992–1996 E36 318i/318ti 1992–1996 E36 318iS The racing version of the M42 engine is called the S42 and was used in BMW's 320 4-door touring car, participating in the German Super Tourenwagen Cup. Compared with the M42, the S42 has individual throttle bodies, the displacement increased to 1,999 cc, two fuel injectors per cylinder, an increased compression ratio and an aluminium cylinder head; the valve cover and airbox were made from carbon fiber and the lubrication system used a dry sump. In 1995, the initial version of the S42 engine produced 224 kW, increasing t o| 235 kW for the final version in 1997; the earliest versions of the M42 developed problems with the camshaft chain drive. The hydraulic tensioner, chain guides, idler wheel and rear lower chain case were updated to resolve wear problems experienced in the early versions of the M42. In September 1993, BMW redesigned the M42's timing chain guide rails, replacing the troublesome lower idler gear with a curved nylon guide rail.
The idler gear's retaining bolt could break away from the timing case taking a chunk of alloy timing case with it. Early models of the M42 experienced failures of a profile gasket sealing the lower cam chain case to the underside of the cylinder head; this gasket seals the primary coolant passage within the timing chain case. A significant failure would thus discharge pressurized steam and hot coolant into the timing chain case. In many cases this coolant contaminates the motor oil in the sump, causing main bearing failure. BMW instituted a program to repair motors under warranty. In extreme cases, the aluminum mating surfaces in the head and chain case would corrode. BMW List of BMW engines