AU695596B2 - Variable duration and valve timing - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: VARIABLE DURATION AND VALVE TIMING.

The following statement is a full description of this invention, including the best method of performing it know to me.

*c 0* 0 0 000 00 0 00 -c~pll lil Invention Title: VARIABLE DURATION AND VALVE TIMING.

This invention relates to improvements in horse power, torque increase and a reduction of exhaust emission, through the use of controlled volumetric efficiency and physical compression.

BACKGROUND OF THE INVENTION: The present invention relates to the internal combustion engine, having a combustion cylinder with an inlet and exhaust valve of the poppet type. This invention is a method of varying the timing and duration of the valve opening and closing.

The method of varying the valve timing and duration, and an explanation of the terminology is detailed in its individual subsection.

DWELL:

The dwell occurs between the point the camshaft actuates the valve to open, and the point it allows the valve to close.

VOLUMETRIC EFFICIENCY: .20 Is the measurement in percentage of the air/fuel mixture, drawn in to the combustion chamber during the intake cycle.

VALVE OVERLAP PERIOD: Valve overlap period, also known as valve 25 overlap angle, is the sequence at which both inlet and exhaust valves are open during a rotational cycle of the engine.

PREIGINITION:

When the heat and compression reach a critical point in front of the burning air/fuel mixture, an explosion occasionally takes place that is undesired because of its damage to other internal components.

GAS REFLUX: Is a problem that occurs at low rotational speeds of the engine, the pressure in the combustion chamber is higher then that of the intake-track (inlet manifold) which interrupts the gas flow inertia "ramming effect".

II M 2 PHYSICAL COMPRESSION RATIO: Is the reference to the actual compres:ion of the air/fuel mixture, which starts from the point the inlet valve closes, this ratio is derived via the distance up the bore the piston has travelled, when the valve closes limiting the amount of compressable area of air/fuel, From the point of piston travel where the valve closes to when the piston reaches the top of its stroke (top dead centre of crankshaft rotation) this amount of piston travel or angle of crankshaft rotation is referred to in this application as physical compression.

SPARK IGNITION: Is in reference to the manner in which the fuel is ignited, an electrical discharge across two electrodes in the combustion chamber is the means of igniting the fuel, (most often petroleum).

COMPRESSION IGNITION: Engines, such as Diesel engines require heat from the compression of the air in the combustion chamber to ignite the fuel (thermal ignition).

PHOTO-SYNTHESIS SMOG: Oxides of Nitrogen, is one of the major problems S of pollution that society has to address, the high combustion temperatures of burning fossil fuel has brought on health problems in our major cities.

PRCBLEMS WITH EXISTING SYSTEMS: The majority of post 1976 motor vehicle engines required retarded value timing (intake) to lower the physical compression to stop preignition, there are two negative reactions, one is a decline in low speed torque, the second is the gas reflux, to overcome this problem Manufacturers have had to increase idle speed to obtain a smooth engine idle, this creates a problem with an increase in fuel use and exhaust emissions.

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Secondly, the octane level of the fuel having been lowered in petroleum has induced a problem with preignition.

Manufacturers have developed camshafts with retarded intake valve timing to reduce the physical compression to control preignition. The problem with this system is that it compromises the engines performance.

High-performance engines require a large dwell and valve overlap period to allow more time for the piston to draw in a significant amount of air and fuel at high crankshaft speeds, but at lower engine speeds gas reflux'retards the engine performance.

Low speed torque requires a reduced valve overlap and dwell period to lower the gas reflux, it also requires that the intake valve closure is early on the compression stroke to increase the physical compression.

Several automotive manufacturers have developed variable valve timing mechanisms, one problem with variable valve timing without variable duration, is that the dwell remains constant, the point at which the valve opens equally effects the point of the valve closing, this fixed angle effectively disadvantages the benefits gained from advancing or retarding of the valve timing. This effect becomes more pronounced for an engine with one camshaft that actuates both intake and exhaust valves.

OBJECTS AND SUMMARY OF THE INVENTION: The ±nformation about this invention is to provide a method that improves the volumetric efficiency.

Variable valve timing and duration, involves changing one or more camshaft actuations of the inlet and or exhaust valves to improve the Lorque, power output, fuel economy and exhaust emissions of the internal combustion engine.

4 The object is the optimisation of the valve timing, duration, dwell and overlap, to enhance gas-flow dynamics (inlet manifold ram effect and exhaust flow control) to achieve greater volumetric efficiency, and control of physical compression.

Varying the exhaust valve timing to control combustion temperature will assist in the lowering of oxides of nitrogen (photo-synthesis smog) by retaining some of the inert gas left over from the previous combustion cycle, to stifle the amount of oxygen, reducing the flame front speed and temperature to control preignition.

It is also an object of this invention to optimise and control the air/fuel induction into the combustion chamber of an internal combustion engine, at varying crankshaft rotational speeds.

Aii additional object of this invention is to lower idle speed, advancing the closure angle of the intake g valve to near bottom dead centre of the crankshaft rotation, and decreasing the valve overlap, lowers the gas reflux and increases compression (as the engine is not under load then preignition will not accrue under normal operating circumstances) so a lower idle speed is obtained, thus lowering the exhaust gas emission and fuel 25 usage.

Another object of this present invention is to provide an apparatus and method for varying intake timing to allow the engine management system to control preignition by closing the intake valve at a later point of crankshaft rotation, causing a drop in physical compression when required.

To achieve the objects of this invention, in accordance to what has been explained previously, here is a description of the invention.

THE APPARATUS COMPRISING: The actuation of the valve intake or exhaust ccomplished via the means of a rocker assembly, which is illustrated in the accompanying drawings.

The rocker assembly comprises of a pivot point (2) two lash pads or roller bearings (3 and 4) and a thrusting point which maybe mechanically adjusted or hydraulicly adjusted, (hydraulic lifter).

On Fig A shows a cross section of the rocker with a common type poppet valve and the two camshafts whicn actuate the rocker.

The drawing Fig B illustrates the drive mecharism, the crankshaft which is the rotational drive of the engine, timing belt transfers the rotational drive from the crankshaft hub to the planetary hubs (10 and 11) of the two sun gear assemblies, sun gear assembly (21) drives the intake camshafts (13 and 14) and sun gear assembly (15) drives the exhaust camshafts (16 and 17), Fig C shows the sun gear assembly in a broken down view, the illustration .20 has the planetary assembly (10) with its tooth belt hub, the hub is rotated by the drive belt, from the crankshaft the annulus (18) is held in a stationary position by the servomechanism the planetary assembly (10) is rotationally timed to the '"25 crankshaft via the timing belt as the crankshaft rotates, it drives the planetary assembly which rotates in the annulus the planetary gears (20) which are in mesh with the annulus inner gear teeth. As the planetary assembly rotates, the planetary gears walk on the annulus inner gear teeth, as the planetary gears rotate they drive the sun gear and belt hub (21) to transfer drive to the tooth belt which drives the camshafts.

The method in which the sun gear assembly changes the timing is via the servomechanism (19) rotating the annulus (18) clockwise or anticlockwise several degrees to achieve advancement cr retardation of the sun gear and belt drive hub (21).

Another method of describing this mode of operation of the sun gear set assembly is to break it up into simplified form, the annulus is the surface inwhich the planetary gears walk upon, the planetary gears are mounted on pins, which are fitted to planetary hub assembly, the hub assembly is rotated via the crankshaft drive, which forces the planetary gears to rotate on the pins as the planetary hub s rotated by the crankshaft, the rotation of the planetary gears which are meshed with the sun gear transfers the rotational drive through the sun gear to the timing belt.

The annulus is the governing component of the drive set, which is held in position by the servomechanism.

The servomechanism rotationally controls the position of the annulus, to advance or retard the camshaft timing as required.

i :20 The servomechanisms are controlled via the use of a E.C.U. (Electronic Control Unit), the information from the several sensor which include a M.A.P. (Manifold Air Pressure), engine temperature, crankshaft angle sensor, camshaft angle sensors, 25 ignition diagnostic signal and anti knock sensor, which are used to formulate and control the camshaft timing to obtain the optimum engine performance under the variable load condition.

The sun gear hub (21) rotationally drives the timing belt which drives the primary or leading camshaft (13) which actuates the valve For ease of understanding the description and explanation is based on the inlet valve drive mechanism only, for simplicity, the exhaust valve is also actuated via the same method as described in this embodiment.

I L I The phasing of the camshafts (13 and 14) are in a timing sequence with the crankshaft a timing ratio of two to one is maintained as the sta.idard.

Varying the timing of the intake camshafts (13 and 14) independent of the exhaust camshafts (16 and 17) provides the means of varying the valve overlap, this is achieved via the independent use of the sun gear assemblies (12 and Varying the duration of the valve is achieved by altering the position of the idle gear the camshaft (13) is the primary camshaft which transfers drive through the helical gear mounted on the shaft, to the idler gear assembly which transfers the rotational drive to the secondary camshaft (14).

The method in which the duration is altered is the angle of the helical teeth, each gear has an opposite partner, the helical teeth on the drive gear (camshaft 13) spiral in a anticlockwise directtion, the driven gear helical teeth are in a clock- .20 wise direction, the idler gear assembly (23) is made up of two fixed gears on a moveable shaft, the second on the idler assembly is a helical tooth gear, the teeth are in an anticlockwise direc-

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tion, with the teeth on the secondary camshaft (14) 25 in a clockwise direction, A servomechanism moves the idler gear assembly (23) along the length of the drive gear, the opposing angles cause the gears to rotate several degrees in comparison with each other, this system allows the camshafts (13 and 14), to vary independently the duration of the valve timing.

Fig D illustrates the servomechanism and the idler gear assembly.

The two camshafts (13 and 14) actuate the rocker assembly, the primary camshaft lobe, opens the valve via actuating the rocker (24) then as the camshaft P P I

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8 lobe comes off the lash pad, the secondary camshaft(14) lobe is still in contact with the lash pad, thus increasing the duration.

For short duration of the valve opening the phasing of the two camshaft lobes (25 and 26) are timed together so that they come in contact with the lash pads (3 and 4) simultaneously and exit to allow the valve to close in the minimum of dwell.

This description, servs to explain the principles of this invention, Fig E shows both inlet and exhaust valve train assembly.

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