Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2001-01-04
2002-05-14
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090310, C464S002000, C464S161000
Reexamination Certificate
active
06386165
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an adjusting device for adjusting the phase position of a shaft, especially a camshaft.
The valves of internal combustion engines, in particular reciprocating internal combustion engines, are actuated by means of camshafts. The camshafts are caused to rotate by a drive shaft or by the crankshaft, via a transmission device. To be able to adapt the opening and closing times of valves to the respective current power output and/or speed of the engine, transmission devices having adjusters for adjusting the phase position of the rotary orientation of the camshafts are used. Such adjusters enable the control times of the intake and/or outlet valves to be influenced according to requirements, so that in particular the so-called overlap of the valve lift curves can be altered. At present, the use of these adjusters for the angle of rotation in the case of the camshafts of the intake valves is preferred. Increasingly, however, the camshafts of the outlet valves are also being rotationally adjusted.
The adjuster is preferably located between the camshaft wheel driven by a chain or a toothed belt and the camshaft. Depending on the respective transmission device, however, another arrangement of the adjuster, for example between the drive shaft and the drive shaft wheel, would also be possible. The relative rotational position between the camshaft wheel and the camshaft can be varied in a predetermined angular range. Preferably, a camshaft rotational range of only 0° to 30° is sufficient. In the case of four-cycle engines, in which the camshaft rotates at half the speed of the crankshaft, this range corresponds to a crankshaft rotational range of 0° to 60°. If both camshafts are simultaneously adjustable, the term doubly variable camshaft control is used. It produces a fuller engine torque curve and optimizes the preparation of the mixture so that the pollutants in the exhaust gas are reduced.
The object of the adjuster is to adjust the beginning and the end of the valve stroke from “late” to “early” and vice versa by means of the camshaft. This must be achievable over a large speed range of the engine. Preferably, the adjustment should be effected continuously and automatically. The advantages of correct adjustment are: more torque in the lower and middle speed range, less uncombusted residual gases during idling, improved idling, lower pollutant output, internal exhaust gas recycling even at low speed, faster heating up of the catalyst and less raw emission after a cold start, specific functions for adapting the mixture during warm running, reduced fuel consumption and less engine noise.
The invention relates in particular to adjusters which are hydraulically actuated. If required, the adjuster is fed by an additional hydraulic pump. Preferably, however, feeding by the lubricating oil pump of the engine should be sufficient, this being particularly economical and favourable in terms of consumption.
As a result of the valve actuation, the camshaft experiences large torque variations, which the transmission device must withstand. A preferred adjuster should be capable of setting and maintaining any desirable angular adjustment in a sufficiently short time, independently of the respective torque acting on the camshaft. For this purpose, its working capacity or its adjusting capacity must be correspondingly large. In the case of feeding by the lubricating oil pump, problems occur at high oil temperature and also at low speed of the engine and hence of the pump, owing to the low oil pressure available. A high adjusting speed is desired. The required feed pressure and/or feed flow rate should be as low as possible. At the same time, the dimensions should be so small that no further design modifications on the engine are required. Preferably, the adjuster should be located radially inside the camshaft wheel and should be axially short.
A known adjuster uses an axially acting hydraulic piston for axial adjustment of a sleeve. The sleeve comprises an inner and an outer spiral gear, the two gears being formed with opposite pitches. The outer gear of the sleeve engages an inner gear firmly connected to the camshaft wheel, and the inner gear of the sleeve engages a gear connected to the camshaft. As a result of an axial adjustment of the sleeve, an angular adjustment is achieved between the camshaft wheel and the camshaft. Owing to the limited axial length, the adjustment range is limited. If the spiral angle is increased, the working piston must be enlarged in the case of an identical transmittable adjusting moment, which in turn leads to a larger piston diameter. Furthermore, the inevitable tooth play thus becomes more effective, which, owing to the periodically changing torques of the camshaft, leads to undesired noises and to increased wear. The oil actuating the hydraulic piston can flow in the wrong direction during torque peaks, particularly if, at low engine speed, the actuating oil pressure is lower than the compression pressure generated by the camshaft torque. In this way, the speed of adjustment and the accuracy of positioning are reduced. If this is to be avoided, the oil pump must be dimensioned substantially larger. Particularly at high engine speeds, this leads to higher energy losses. A further disadvantage of opposite spiral gears is their complicated production.
A further known adjuster is in the form of a so-called wing adjuster. An outer housing part is firmly connected to the camshaft wheel and comprises regions which project radially inward and divide an annular space into compartments. Wings project radially outward, each in a compartment, from a shaft part fastened to the camshaft. These wings rest tightly against the compartment border, laterally and radially on the outside, so that a rotary piston system is formed. By feeding oil to one side of all wings and discharging oil on the other side of all wings, it is possible to achieve a rotation of the outer housing part relative to the shaft part. By integration of the product of radius and operating pressure over the wing areas, a transmission and adjustment torque is determined. The more wings arranged on the circumference, the higher is the torque generated at a given oil pressure. At the same time, however, the maximum adjustment angle decreases in the case of a larger number of wings, because in fact the construction space in the circumferential direction is limited.
On starting the engine and possibly also at a high oil temperature, the oil pressure of the lubricating oil pump is too low to produce in the adjuster a torque which is greater than the maximum camshaft torques. The peaks of the camshaft torques adjust the rotational position of the adjuster until the wings rest against a compartment border. Because the camshaft torques oscillate between positive and negative maxima, the adjuster is deflected, at excessively low oil pressure, away from a desired rotational position alternately in the two directions of rotation until the wings make contact. This leads to considerable wear and to unpleasant noises. This undesired effect is reduced by using, for example, a brake element which damps the oscillating movements at low oil pressure.
For adjusting and maintaining the rotational position, an oil supply valve, a rotational position detector and a control are formed in such a way that deviations from a setpoint position are corrected by a corresponding valve actuation. The required oil pressure and correspondingly also the oil consumption of this rotary piston adjuster resulting from leakage are high because the full pressure is required also for maintaining a set rotational position or for transmitting the camshaft torques. Depending on the maximum camshaft torques occurring in both directions of rotation, high peak values occur in the working areas of the rotary piston system. If the oil supply valve is closed, these high compression pressures are troublesome only because correspondingly high leakage losses occur. When the adjusting valve is opened in the adjusting
Eisenmann Siegfried
Harle Hermann
Dahbour Fadi H.
Rothwell Figg Ernst & Manbeck
Trochocentric International AG
Walberg Teresa
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