An arrangement for the control of valve timing in a combustion engine

Abstract: An arrangement for controlling valve timing in a combustion engine, especially in a large diesel engine with several cylinders, in which the control of a valve (11) in a cylinder is carried out through a follower member (3,4), preferably a roll follower, receiving its guidance from a cam race (2a) of a camshaft (2) or the like. There are at least two follower members (3,4) per controlled valve (11), the follower members (3,4) being functionally independent from each other and being arranged in cooperation with the same cam race (2a) so that their control effect on the valve (11) is different. Only one follower member (3,4) is at a time arranged to control, e.g. in force transmission connection with, the valve (11) in the cylinder. In addition the arrangement includes means (7) for selecting the follower member (3,4) to be used in each case so that the control of the valve (11) corresponds as well as possible to the operating conditions of the engine.

Description: This invention relates to an arrangement for the control of valve timing in a combustion engine, especially a large diesel engine with several cylinders, in which the control of a valve in a cylinder is carried out through cam follower means, preferably a roll follower, receiving its guidance from a cam race of a camshaft or the like. In this specification, large diesel engines refer, for example, to such engines which are used as the main or auxiliary engines in ships or which are used in power plants for production of heat and/or electricity. The changing of the opening and closing times of exhaust valves in a diesel engine at varying running conditions has an advantageous effect on the operation of the engine. Thus by controlling the timing of the valves, lower fuel consumption rates can be achieved and the contents of harmful emissions in the exhaust gases of the engine can be lowered. Changing the timing may, if necessary, also be applied to suction valves. Naturally it must be possible to control the valve timing while the engine is running. In accordance with the prior art it is known, for example, to change valve timing by using two separate camshafts each provided with a separate cam follower member, by using on the same camshaft two different cam races each having a cam follower member of its own, or by using two different cam races with only one cam follower member which is selectively axially movable for cooperation with one or the other of the two cam races. Furthermore, according to the prior art, different mechanical lever arrangements, eccentric shafts, changing of the rotational position of the camshaft relative to the crankshaft, dividing and moving of cam segments etc. have been used. In FR-A-1378676 a control arrangement is disclosed in which different cam follower members are used in dependence on the direction of rotation of the engine. Most of these solutions have in common rather a complicated construction resulting in substantial extra costs. The extra members and constructions required for the change of valve timing also take up extra space. An aim of the present invention is to achieve a new solution with an uncomplicated, cost advantageous construction providing a simple and quick change in valve timing so as to comply with changed running conditions. According to the present invention there is provided an arrangement for the control of valve timing in a combustion engine, the arrangement being as claimed in the ensuing claim 1. The change of the valve timing is, thus, carried out simply by selecting either one of the follower members for use depending on the situation. An advantageous solution from the viewpoint of space requirements can be achieved when the follower members of the valve are arranged immediately in succession in the direction of the rotary movement of the camshaft so that their mutual angular difference relative to the rotation of the camshaft corresponds to the desired change in the timing of the valve. In practice the advantageous solution for the selection of each follower member is achieved by the transmission of force, preferably at least partly hydraulically, from the follower member to the valve. In such a case the arrangement suitably includes a hydraulic valve and a movable valve element which is in turn movable between a connecting position and a disconnecting position for the force transmission connection and disconnection, respectively, of the selected follower member to and from the valve in the cylinder. Advantageously the hydraulic valve comprises a three way valve which in its different positions connects hydraulic ducts of different follower members to the force transmitting means of the valve in the cylinder, whereby a change of position of the valve can be arranged by turning its valve element. In this case, the or each follower member which is not connected to the cylinder valve is with advantage connected to a hydraulic liquid container. For this purpose, the three way valve, typically hydraulically actuated, includes a chamber which is turnable to connect the hydraulic duct of any selected one of the follower members to the hydraulic liquid container. Two or several follower member pairs may be arranged in cooperation with the same cam race for the control of several valves. This solution is particularly suitable for use in gas diesel engines for power plant use, whereby, for example, the conventional camshaft of an engine may be replaced by a separate shaft including a cam race that controls several valves simultaneously. Embodiments of the invention will now be further described, by way of example only, with particular reference to the accompanying drawings, in which: Figure 1 is a schematic view illustrating the principle of an embodiment of an arrangement according to the invention; and Figure 2 is a schematic view illustrating a further developed embodiment based on the arrangement of Figure 1. In Figure 1, the reference numeral 1 indicates a camshaft, or the like rotatable shaft, of an engine with a cam 2 which together with a jacket portion of the camshaft at the corresponding location forms a continuous cam race 2a encircling the camshaft. The arrangement also includes roll followers 3 and 4 which "follow" the cam race 2a when the camshaft is rotating. The roll followers 3 and 4 are angularly spaced from each other at an angle a relative to the axis of rotation of the camshaft and, hence, are located slightly in different places along the cam race 2a. In the embodiment shown in Figure 1, the roll followers 3 and 4 are hydraulically operated, each being provided with a hydraulic piston and a hydraulic liquid space (details not shown) connected by means of a hydraulic duct 5 in the case of roll follower 3 and a hydraulic duct 6 in the case of roll follower 4 to a three way valve 7 included in the selection arrangement for the roll follower. A duct 10 connects the valve 7 to guiding and operating means 12 of a cylinder valve 11 associated with a cylinder (not shown). The three way valve 7 has ducts 7a and 7b for selectively connecting, on turning of the valve, either of the ducts 5 or 6 to the duct 10. Thus, one of the roll followers 3 and 4 can be switched to force transmission connection with the valve 11 with the other of the roll followers 3 and 4 connected, via a chamber 8 in the three way valve 7, to a hydraulic liquid container 9. The two different connection situations are illustrated in partial figures A and B of Figure 1. Control means and logic means (not shown in the drawings) are required in practice to control the turning movement of the three way valve 7. The control and logic means, on the basis of given boundary limits, make a selection of the correct roll follower 3 or 4 by turning the three way valve 7 into the position in which it connects the roll follower in question in force transmission connection with the valve 11. When desired, the arrangement can be operated so that, during the same cylinder stroke, both the roll followers 3 and 4 are used in turn for achieving either as long, or alternatively as short, open time period as possible for the valve 11. The principle of the embodiment shown in Figure 1 is thus based on hydraulic force transmission, whereby movement of the hydraulic piston of the roll follower 3 or 4 is transmitted via the hydraulic liquid directly to the guiding and operating means 12 of the valve 11. The arrangement may also be partly hydraulically operated so that the force transmission from the duct 10 is achieved through different lever arrangements of the valve 11. The force transmission from the roll followers 3 and 4 to the valve 11 may be achieved in many different ways instead of as described above. For example, the force transmission may also be achieved fully mechanically. In that case, a certain selection mechanism is required to ensure that only one of the roll followers 3 or 4 is at any time in force transmission connection with the valve 11. It is also possible that the roll followers 3 and 4 are not actually in force transmission connection with the valve 11. Instead, for example, control impulses generated by the roll followers may be transformed into electrical impulses for controlling the valve 11 according to separate operating devices. For example an electrically controlled solenoid valve may be used for this purpose. Figure 2 illustrates a modification of the embodiment shown in Figure 1, whereby two or several follower member pairs 3a-3f and 4a-4f are arranged in cooperation with the same cam race 2a for the control of several valves 11. This arrangement is especially suitable for engines for power plant use. The invention is not restricted to the embodiments shown.

Claims: An arrangement for controlling valve timing in a combustion engine, especially in a large diesel engine with several cylinders, in which the control of a valve (11) in a cylinder is carried out through at least two cam follower members (3,4) which receive guidance from the same cam race (2a) of a camshaft (2) or the like, which are functionally independent of each other and which are arranged so that no more than one follower member (3,4) is at any time effective to control operation of the valve (11) in the cylinder, characterised in that the control effect of each cam follower member on the valve (11) is different, and in that the arrangement includes means (7) for selecting, while the engine is running, the follower member (3,4) to be used in each case so that the control of the valve (11) corresponds as well as possible to the operating conditions of the engine in each case such that lower fuel consumption rates can be achieved and the contents of harmful emissions in the exhaust gases of the engine can be lowered. An arrangement according to claim 1, characterised in that each cam follower member (3,4) comprises a roll follower. An arrangement according to claim 1 or 2 characterised in that each follower member (3,4) controls operation of the valve (11) by force transmission connection therewith. An arrangement according to claim 1 2 or 3, characterised in that the follower members (3,4) of the valve are arranged immediately in succession in the direction of the rotation of the camshaft (2) so that their mutual angular difference (a) relative to the axis of rotation of the camshaft (2) corresponds to the desired change in the timing of the valve (11). An arrangement according to claim 3, or claim 4 when dependent on claim 2, characterised in that the transmission of force from the follower member (3,4) to the valve (11) is at least partly hydraulic and in that the arrangement includes a hydraulic valve (7) having a movable valve element movable between a connecting position and a disconnecting position for selectively connecting or disconnecting the force transmission of a selected follower member (3,4) to or from the valve (11) in the cylinder. An arrangement according to claim 5, characterised in that the hydraulic valve is a three way valve (7) which in its different positions connects different hydraulic ducts (5,6) associated with the different follower members (3,4) to the force transmission of the valve (11) in the cylinder, whereby a change in position is accomplished by turning the valve element of the three way valve (7). An arrangement according to claim 6, characterised in that the arrangement includes a hydraulic liquid container (9) and in that the hydraulic valve (7) comprises a chamber (8) which is successively arranged to connect the said hydraulic liquid container (9) to the hydraulic duct (5,6) of that follower member (3,4) which is not connected to transmit force to the cylinder valve (11). An arrangement according to any of the preceding claims, characterised in that at least two follower member pairs (3a-3f,4a-4f) are arranged in cooperation with the same cam race (2a) for control of at least two valves (11).

Inventors: PARO DANIEL, PARO, DANIEL
Applicants: WAERTSILAE NSD OY AB
Application year: 1995
Main classification: F01L9
IPC codes: F02B3, F01L9