DE102019004810A1 - Variable valve control for gasoline engines and diesel engines - Google Patents

Abstract

Variable valve control for gasoline and diesel engines, characterized in that at least one camshaft 1 is axially displaceable by a toothing 6 relative to a camshaft gear 4 5 and its cams 9 have ramp-like cam contours 8 in the axial direction perpendicular to the camshaft axis, which in engine operation by axial displacement 5 both varying valve lifts 12 of the valves 11, which can vary from 0 mm to the maximum cam height 8, and / or can also generate different valve opening periods through different circumferential angles of their cam profile 14, 15.

Description

The invention describes a variable valve control for gasoline engines and diesel engines.

One of the design objectives for gasoline engines with a throttle valve is to avoid losses at the throttle valve when supplying combustion air. Built into the intake tract, its opening angle determines the volume or the mass of combustion air that gets into the cylinder. What is unsatisfactory about this solution are the losses it incurs.

In engines with a throttle valve, the volume of the intake manifold between the valve and the throttle valve must be overcome when the intake valves are opened before the combustion air mass starts moving in the direction of the cylinders. The intake manifold volume thus forms a damper that delays the response of the engine. If the resistances of the throttle valve and damping volume are switched off and the inlet valve is moved to control the load, fuel consumption decreases, performance increases and the engine responds drastically better to the demands of the accelerator pedal.

Structural steps towards the ultimate goal of complete dethrottling are phase adjustment, exhaust gas recirculation, stratified charge operation with direct injection, supercharged engines with small displacement, coordination of intake manifold and exhaust system, variable compression, cylinder deactivation.

The maximum dethrottling is only achieved with the fully variable valve lift, as shown by the Valvetronic from BMW and the Multi-Air system from FIAT.

With the Valvetronic, the combustion air supply is controlled via the variable valve lift without a throttle valve. The fully variable valve lift is brought about by an intermediate lever that can be adjusted by an electric motor and is placed between the camshaft and the rocker arm that actuates the valve. As a result, the valve lift is variable. The throttle valve is only used for correction, not for load control. This happens exclusively via the variable lift of the inlet valves.

The disadvantage of the Valvetronic is its high construction cost. The intermediate lever with two additional friction rollers is required to transfer the movement of the camshaft to the inlet valve. This creates increased friction and reduces the system's speed of reaction.

Another disadvantage of the Valvetronic is the relative inertia of the valve adjustment. The adjustment time of 300 milliseconds from the minimum to the maximum lift of the intake valves is too slow to influence the valve lift or the valve opening time between successive intake strokes of two cylinders or even within the intake stroke of a cylinder.

In the multi-air system, the variable lift of the intake valves is effected by an electro-hydraulic transmission unit that transmits the lift of the cam of a camshaft to the intake valve stems. The Multi-Air cylinder head has an overhead camshaft that mechanically actuates the exhaust valves with the exhaust cams via bucket tappets. On this camshaft there is also one inlet cam per cylinder, which does not act directly on the inlet valves, but on an electro-hydraulic transmission unit, which consists of a roller rocker arm and a hydraulic system with a master piston, pressure chamber, solenoid valve and slave piston on the two inlet valves. The lift of the cam is transmitted to the intake valve stems by the oil hydraulics. If the solenoid valve arranged in the pressure chamber remains closed during a valve stroke, no oil can flow out and the valves follow the camshaft elevation curve predetermined by the cam shape. If, on the other hand, the solenoid valve is opened by the engine control unit, part of the oil can escape from the pressure chamber into a low-pressure circuit; the respective inlet valves open shorter and less than specified by the cam or not at all. As a result, both the valve lift and the times of valve opening and valve closing, i.e. the inlet control time, can be variably controlled by the electrical control of the solenoid valve - within the limits specified by the mechanical shape of the cam. However, when the electro-hydraulic system is activated, it can only ever reduce the valve lift and the valve opening time.

As usual, the valves are closed by springs. During the remaining strokes of the four-stroke engine, the low-pressure system of the oil hydraulics fills the pressure chamber and acts like a hydraulic valve clearance compensation.

A significant disadvantage of this fully variable valve train solution is that it is not possible to adjust the valve overlap of the exhaust valve and intake valve to the current operating point.

Another disadvantage of the Multi-Air is the high construction costs.

• • ein breiteres, nutzbares Drehzahlband,
• • die Entdrosselung des Motors
• • exzellentes Kaltstartverhalten
• • geringerer Verbrauch
• • verminderte Abgasemission
• • besseres Ansprechverhalten
• • Anhebung des Drehmomentes im unteren Drehzahlbereich durch eine erheblich bessere Verwirbelung der Verbrennungsluft bei Leerlauf und in der unteren Teillast, weil sie in dem engen Ventilspalt enorm beschleunigt wird

bei vergleichsweise geringerem Bauaufwand.The invention eliminates the disadvantages of the two valve control systems described. In this way she realizes the advantages of a without restriction fully variable intake valve lift compared to fixed control times, such as

• • a wider, usable speed range,
• • the de-throttling of the motor
• • excellent cold start behavior
• • lower consumption
• • reduced exhaust emissions
• • better responsiveness
• • Increase of the torque in the lower speed range through a significantly better turbulence of the combustion air at idle and in the lower part load, because it is accelerated enormously in the narrow valve gap

with comparatively less construction costs.

Another advantage of the invention is that the fully variable valve lift from 0 mm to the maximum lift also allows cylinder deactivation without additional mechanics by reducing a valve lift to 0 mm between the intake strokes of two cylinders and, depending on this, the valve lift of the other cylinder for a correspondingly higher filling with combustion air of the same increased. Furthermore, variable valve opening times can be generated by camshafts with different cam contours of the cams in the plane of rotation. This makes it possible according to the invention to avoid knocking combustion at full load, even with compression ratios that are only able to avoid knocking combustion at full load through a premature closing of the intake valve before the end of the intake stroke, and the intake phase for load requirements below full load to expand to the full intake stroke, preferably adapted to the current load requirement by knock sensors. Or, conversely, when the load requirement increases, the opening phase of the intake valves can be reduced from the full intake stroke to the Miller cycle with the intake valve closing prematurely along a characteristic curve or a map.

It is also possible to achieve different effective compression ratios for both gasoline engines and diesel engines. The result is an increase in the expansion work of the piston and a dethrottling in the partial load range, with the advantage of reduced consumption and early torque in full strength.

Furthermore, the invention enables the camshaft contour suitable for different gasoline fuels to be controlled by the axial displacement of the inlet camshaft according to the invention. When operating the gasoline engine with gasoline with a geometric compression ratio, the compression end temperature of which would exceed the self-ignition temperature of the gasoline fuel if the intake valves were to open over the entire intake stroke, the intake camshaft contours are shaped in such a way that the intake valves for the combustion air close long before the piston hits bottom dead center reached. The resulting expansion of the fuel-air mixture in the remaining downward phase of the piston cools the fuel-air mixture, which reduces the pressure and temperature at the end of the following compression stroke, so that when the engine is operated with gasoline, its auto-ignition temperature does not occur is exceeded (Miller cycle).

The auto-ignition temperatures of alternative petrol such as LPG, CNG or alcohol are considerably higher than the auto-ignition temperature of gasoline.

For this reason, a gasoline engine operated with these fuels does not require the temperature reduction due to the forced mixture expansion, as is the case with operation with gasoline, and can therefore use the complete filling of the combustion chamber with the fuel-air mixture over the entire intake stroke by following a suitable camshaft contour, with the associated advantages in terms of torque and power and lower pollutant emissions.

The variable valve control was ignored for a long time in the diesel engine, because they run with maximum excess air and therefore do not require any throttling. Variable valve timing in diesel cars did not come into series production for the first time until 2010. In these engines, the raw exhaust gas quality is the most important driver for such solutions, which were previously expensive in production. The advantage of the variable valve control is the possibility to bring the engine and the catalytic converters to operating temperature more quickly, to let them cool down less quickly and to promote the regeneration of the particulate filter by increasing the exhaust gas temperature. An early opening of the exhaust valve means an additional heating measure for the exhaust gas aftertreatment to reduce the NOx emissions in the cold engine. Variable valve timing also enables a warming function in idle phases in order to reduce undesired cooling of the exhaust gas cleaning system. In addition, there is the option in quasi-stationary part-load operation to use the longer expansion stroke of the Miller cycle compared to the compression stroke, and thus to reduce fuel consumption through improved efficiency.

• 1a zeigt eine erfindungsgemäß axial verschiebbare 5 Nockenwelle 1, mit einem Nocken 9 mit erfindungsgemäßer rampenförmigen Nockenkontur in axialer Richtung 8, der über den erfindungsgemäßen Kugelschlepphebel 10,13 ein Ventil 11 betätigt und einen Aktuator zur axialen Verschiebung 5 dieser Nockenwelle 1, hier ein Linearmotor 7.
• 1b unterscheidet sich von 1a durch die Gabelung 16 des Kugelschlepphebels 10,13 in Richtung der paarigen Ventilschäfte 11 bei Vierventilmotoren.
• 1c zeigt eine Variante mit Stütze 17 zur Aufnahme der auf den Kugelschlepphebel 10,13 einwirkenden axialen Kraft.
• 2 zeigt ebenfalls eine erfindungsgemäß axial verschiebbare Nockenwelle 5 mit unterschiedlichen rotatorischen Konturen 14,15 eines Nockens 9 die durch einen Aktuator zur axialen Verschiebung 7 über eine axiale Rampe 8 angesteuert werden können.
• 3 zeigt eine erfindungsgemäß axial verschiebbare Nockenwelle 5 mit einem Nocken 9 mit erfindungsgemäßer Kombination unterschiedlicher rotatorischen Nockenkonturen 14,15, die durch ihre axiale Rampen 8 differentiell unterschiedliche Ventilhübe 12 bewirken.

In the following, exemplary embodiments of the invention are illustrated and explained in an exemplary and simplified manner.

• 1a shows an axially displaceable camshaft according to the invention 1 , with a cam 9 with the inventive ramp-shaped cam contour in the axial direction 8th , the about the inventive ball rocker arm 10 , 13 a valve 11 operated and an actuator for axial displacement 5 this camshaft 1 , here a linear motor 7th .
• 1b differs from 1a through the fork 16 of the rocker arm 10 , 13 towards the paired valve stems 11 with four-valve engines.
• 1c shows a variant with a support 17th for receiving the on the rocker arm 10 , 13 acting axial force.
• 2 also shows an axially displaceable camshaft according to the invention 5 with different rotatory contours 14th , 15th of a cam 9 by an actuator for axial displacement 7th via an axial ramp 8th can be controlled.
• 3 shows an axially displaceable camshaft according to the invention 5 with a cam 9 with the inventive combination of different rotary cam contours 14th , 15th by their axial ramps 8th differentially different valve lifts 12 effect.

In 1a is a camshaft 1 with a cam 9 , having the inventive, axially ramp-shaped cam contour 8th , in a camshaft housing 2 pictured. By axial displacement 5 the camshaft 1 by an actuator, here a linear motor 7th , is on the inclined plane of the ramp 8th the vertical stroke 12 of the ball lever 10 changes, which in turn sets the optimum stroke, preferably calculated by the engine control unit 12 of the valve 11 between 0 and maximum. The ball lever 10 instead of a role on which the cam has 9 expires a ball 13 that are on the cam contour 8th can run both rotationally and axially (ball lever).

The camshaft 1 is with a toothing 6th with the camshaft gear 4th axially displaceable 5 connected. About the gearing 6th is the rotational force of the (not shown) crankshaft of the engine for actuating the valves on the camshaft 1 transfer. The camshaft gear 4th in turn, preferably with a deep groove ball bearing 3 , against the camshaft housing 2 stored. Warehousing 3 fixes the camshaft gear 4th opposite the camshaft housing 2 and absorbs the axial force that occurs when moving 5 the camshaft 1 arises. The actuator for axial displacement 5 is a linear motor in this figure 7th , the one here at the other end of the intake camshaft 1 is positioned.

The postponement 5 but can also be done hydraulically or pneumatically or electromechanically and the actuator 7th elsewhere on the camshaft 1 be positioned.

1b differs from 1a in that in four-valve engines, for reasons of space, the paired valves have one in the direction of the valve stems 11 forked ball lever 16 , 13 only from one cam 9 be operated.

1c shows a variant of the, through the ramp-shaped contour 8th the cam 9 , generated axial forces when moving the camshaft 1 on the ball lever 10 , 13 act through a perpendicular to the housing 2 connected tread 17th against which the bullets 13 support axially, be caught.

2 differs from the 1a, b in that instead of in the axial direction 5 linearly increasing cam contour of identical rotary profile 8th Cam contours of various rotary profiles 14th , 15th by axial displacement 5 the camshaft 1 are controllable. This enables different strokes instead of differentially 12 of the valves 11 to generate different valve opening times. On the one hand, this allows high-compression gasoline engines to be operated at the respective auto-ignition limit of fuels of different octane numbers and, on the other hand, the longer expansion stroke of the Miller cycle compared to the compression stroke in diesel engines and thus, due to the improved efficiency, lower fuel consumption.

In 3 the embodiments of the invention 1 and 2 brought together in one construction. The cam contours with different rotatory profiles 14th , 15th can each use an axial ramp 8th with differentially different valve lifts 12 be controlled. This enables a gasoline engine with fuels of different octane numbers with the optimal stroke for the current operating state of the engine 12 its valves 11 to operate at their respective self-ignition limit. Alternatively, only one axial ramp can be used instead of two 8th be present both the inventive, axially ramp-shaped cam contour 8th possesses as well as with different rotational profiles according to the invention 14th , 15th is provided.

Claims (8)

Variable valve control for gasoline and diesel engines, characterized in that at least one camshaft 1 is axially displaceable by a toothing 6 with respect to a camshaft gear 4 5 and its cams 9 in the axial direction Have ramp-like cam contours 8 perpendicular to the camshaft axis, which during engine operation by axial displacement 5 generate both varying valve lifts 12 of the valves 11, which can vary from 0 mm to the maximum cam height 8, or / and also produce different valve opening periods due to different circumferential angles of their cam profile 14,15 can. Variable valve control for gasoline and diesel engines according to Claim 1 characterized in that the conversion of the cam contour 8 during the rotary movement of the camshaft 1 into a stroke of the valves 11 takes place via ball levers 10, 13, which are arranged as rocker arms or rocker arms or in bucket tappets as intermediate levers, the balls 13 of which are axially against running surfaces perpendicular thereto Support 17 on housing 2. Variable valve control for gasoline and diesel engines according to Claim 2 characterized in that, in four-valve engines, the ball levers 10, 13 can fork in the direction of the valves 11 and, as a result, each valve pair 11 is actuated by only one cam 9 instead of a cam for each valve. Variable valve control for gasoline and diesel engines according to the preceding claims, characterized in that the axial displacement 5 of the camshaft 1 takes place electromagnetically or hydraulically or pneumatically or electromechanically. Variable valve control for gasoline and diesel engines according to Claim 4 characterized in that the axial displacement 5 of the camshaft 1 is at least less than the duration of two successive intake strokes. Variable valve control for gasoline and diesel engines according to Claim 5 characterized in that cylinder deactivation is achieved by successively displacing the intake camshaft between a valve lift of 0 mm and the subsequent increased valve lift. Variable valve control for gasoline and diesel engines according to the Claims 1 - 5 characterized in that in gasoline engines the cam contour 8,14,15 of an intake camshaft is activated, which generates the intake valve control time for each gasoline fuel, with which it can be operated even at full load without fuel knocking. Variable valve control for gasoline and diesel engines according to the Claims 1 - 4th characterized in that, in diesel engines, camshafts have cam contours 14, 15 which generate a longer expansion stroke compared to the compression stroke.

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