Valve drive for an internal combustion engine

Abstract

The invention relates to a valve drive for internal combustion engines, comprising at least one cam assembly which can be axially displaced on a camshaft. The assembly consists of at least two cams having different profiles and actuating optionally at least one gas exchange valve for adjusting different valve lifts and/or valve timing. The aim of the invention is to create a space-saving and simple valve drive for an internal combustion engine of the aforementioned type, which allows valve lift and/or valve timing to be adjusted without an additional actuation stage. For this purpose, one cam is connected to the camshaft so as to rotate with the camshaft and the other cam is mounted so as to be rotated on the camshaft. The cam that is rotationally mounted on the camshaft can be positively connected to and released from the cam that is connected so as to rotate with the camshaft via a controlled pilot and main locking plunger. The rotationally fixed cam has a larger profile height than the rotationally mounted cam. The larger profile height is designed for a relatively large lift of the gas exchange valve, while the lower cam profile height is designed for smaller lift heights. By displacing the cam assembly when the cams are coupled, the cam with the larger or the smaller profile height can be engaged with the gas exchange valve. A zero lift of the gas exchange valve can be adjusted, when the cam with the smaller profile height engages, by decoupling the rotational cam from the cam that is arranged on the camshaft so as to rotate therewith.

Description

The invention relates to a valve drive for internal combustion engines with the features indicated in the preamble of claim 1.

A variable valve drive for internal combustion engines is already known from DE 10054623 A1, wherein a cam assembly with at least two different cams is disposed on a camshaft so as to rotate with it. The cam assembly is disposed on the camshaft so as to be axially displaceable by a positioning element in interaction with a slideway. By displacement of the cam assembly, a different cam contour of the cam assembly can be respectively engaged for actuation of the gas-exchange valve. The valve lift and/or the valve control times can be differently adjusted by means of the cam contours that can be differently engaged.

From DE 4228796 A1, a variable valve drive for internal combustion engines is also already known, wherein the gas-exchange valve is operated with different cam contours for adjustment of the valve lift and/or of the valve control times. For this purpose, one cam is mounted rotatably on the camshaft, and the other cam rigidly on the camshaft. In the full-load range of the internal combustion engine, an electronic controller injects pressurized oil into a hydraulic chamber of the fixed cam by way of an isolating valve, and thus displaces corresponding plungers, whereby the fixed cam is coupled positively with the cam mounted rotatably on the camshaft. The cam coupled by means of shape fit actuates the respective gas-exchange valves with relatively large lift, by way of a tappet. In the part-load range with the oil pressure disconnected, the two cams coupled with one another become separated. The fixed cam with small lift actuates the tappet, while the cam mounted rotatably on the camshaft is uncoupled and the camshaft rotates freely in this cam.

It is disadvantageous in these solutions that only a limited number of switching stages is available for operation of the gas-exchange valves. In the solution according to DE 10054623 A1, a further switching stage can be achieved by providing an additional cam. A further cam means an additional space requirement with regard to overall installation length. However, such space does not exist or is very limited in compactly built engines with small cylinder spacing. Moreover, additional masses would have to be moved by the further cam.

The object of the invention is to create a valve drive for an internal combustion engine of the type in question, with which valve lift and/or the valve control times can be adjusted in an additional switching stage, and which is distinguished by a space-saving and simple construction.

This object is achieved, according to the invention, by the characterizing features of claim 1.

According to the invention, in a valve drive for an internal combustion engine, with at least one cam assembly that is axially displaceable on a camshaft and consists of at least two cams provided with different profiles, which selectively actuate at least one gas-exchange valve for adjusting different valve lifts and/or valve control times, one cam is connected to the camshaft so as to rotate with it, and the other cam is mounted rotatably on the camshaft. The cam mounted rotatably on the camshaft can be positively connected to and separated from the cam disposed on the camshaft so as to rotate with it, by way of a controllable pilot and main locking plunger. The non-rotatable cam possesses a larger profile height than the rotatably mounted cam. The larger profile height is designed for a relatively large lift of the gas-exchange valve, whereas the smaller cam profile height is designed for small lift heights. By displacement of the cam assembly, either the cam with the large or the small profile height can be engaged with the gas-exchange valve while the cams are coupled. During engagement of the cam with the smaller profile height, zero lift of the gas-exchange valve can be adjusted by uncoupling the rotatable cam from the cam disposed on the camshaft so as to rotate with it. The rotatably mounted cam will no longer be driven by the non-rotatable cam and is therefore inactive with regard to the gas-exchange valve.

The advantage of the solution according to the invention consists in the fact that, in a switchable cam assembly, the minimal cam in service can be decoupled from the drive and thereby the cam is not in active communication with the gas-exchange valve. By this solution, one more switching stage for actuation of the valves can be achieved with the same space requirement. Thus the valves can be operated with a maximal and minimal as well as idle lift and/or valve opening times.

By providing a controllably displaceable pilot locking plunger in a blind-hole bore, which is disposed in the base circle of the cam connected to the camshaft so as to rotate with it, the cam connected to the camshaft so as to rotate with it can be engaged with and disengaged from the cam mounted rotatably on the camshaft by displacement of the pilot locking plunger. In the process, the pilot locking plunger is inserted into a groove-like guide, which is disposed in the base circle of the cam mounted rotatably on the camshaft, thus interlocking the two cams with one another. Thereafter, interlocking takes place by a main locking plunger, which is mounted so as to be controllably displaced in a blind-hole bore in the cam region of the non-rotatable cam.

The advantage of providing a pilot locking and a main locking plunger consists in the fact that, by virtue of the groove-like guide disposed over approximately 180°, reliable insertion of the pilot locking plunger during the interlocking operation is achieved. Because the rotatably mounted cam is driven by the pilot locking plunger, the main locking plunger can then snap securely into the bore of the rotatable cam.

Further advantageous configurations are described in the dependent claims, and will be explained together with their effects in the description.

The invention will be described in more detail hereinafter on the basis of exemplary embodiments, with reference to drawings. In the associated drawings:

FIG. 1: shows a schematic diagram of the valve drive drive according to the invention, in section, with interlocked cams,

FIG. 2: shows a section z-z according to FIG. 1,

FIG. 3: shows a section y-y according to FIG. 2,

FIG. 4: shows a schematic diagram of the valve drive according to the invention, in section, with de-interlocked cams,

FIG. 5: shows a section z-z according to FIG. 4, and

FIG. 6: shows a section y-y according to FIG. 5.

FIG. 1 illustrates a longitudinal section of the valve drive according to the invention. On a camshaft 1, a cam assembly is disposed so as to be axially displaceable, which consists of cams 2 and 3 as well as 2′ and 3′. The displacement of the cam assembly, which is not subject matter of the solution according to the invention, can take place, for example, in a manner corresponding to that of the device described in DE 100 54 623 A1.

The cams 2 and 2′ as well as 3 and 3′, respectively, have an identical cam contour, cams 2 and 2′ having a larger profile height compared with cams 3 and 3′, for maximum valve lift during full-load operation. Cams 3 and 3′ are designed for a smaller lift during part-load operation of the internal combustion engine. By means of appropriate displacement of the cam assembly, the two gas inlet valves of a cylinder of the internal combustion engine are actuated either by cams 2 and 2′ or by cams 3 and 3′, by way of roller-type cam followers, which are not shown.

According to the invention, cams 2 and 2′ are connected to camshaft 1 so as to rotate with it, whereas cams 3 and 3′ are mounted rotatably on camshaft 1. Cam 3 or 3′ can be coupled with and uncoupled from cam 2 or 2′, respectively, by way of a pilot locking plunger 16; 16′ and a main locking plunger 6, 6′.

The pilot locking plunger 16; 16′ is mounted so as to be displaceable in a blind-hole bore 17; 17′, which is disposed in the region of the base circle 14; 14′ of the cam 2; 2′, preferably in the peripheral region of it. A groove-like guide 8; 8′, with which and from which the controllably displaceable pilot locking plunger 16; 16′ can be engaged and disengaged, respectively, is disposed in the region of the base circle 15; 15′ of the cam 3; 3′ mounted rotatably on the camshaft 1. The groove-like guide 8; 8′ extends over approximately 180° in the region of the base circle 15; 15′ of the cam 3; 3′.

The displacement of the pilot locking plunger 16; 16′ in the direction of the groove-like guide 8; 8′ takes place in a manner so as to be regulated, by means of oil pressure of the pressurized circulating lubricating-oil system of the internal combustion engine, from the control-oil duct 11c in a position according to FIG. 3. For this purpose, a supply duct, which is in communication with a bore 12 running in the longitudinal direction of the camshaft 1, opens into the blind-hole bore 17; 17′. The blind-hole bore 17; 17′ is therefore in communication with a control-oil duct 11c disposed in the bearing 5 of the camshaft 1, by way of a radial duct branched off from the bore 12. The pressurized-oil supply to the control-oil ducts 11a; b and c takes place by way of isolating valves that can be regulated, which are not shown. Oil pressure is continuously admitted to the lubricating-oil duct 11a, the control-oil duct 11b is supplied with connectable and disconnectable oil pressure for de-interlocking the cams 3 and 3′, and the control-oil duct 11c is also supplied with connectable and disconnectable oil pressure for interlocking the cams 3 and 3′. A spring 18; 18′, which acts against the oil pressure acting to displace the pilot locking plunger 16; 16′ in the direction of the groove-like guide 8; 8′, is disposed at the bottom of the pilot locking plunger 16; 16′.

The main locking plunger 6; 6′ is displaceably mounted in a blind-hole bore 20; 20 disposed in the region of the cam 2 or 2′, respectively. The controlled displacement of the main locking plunger 6; 6 in the direction of the cam 3; 3′ takes place by means of a spring 7; 7′ disposed between the bottom of the main locking plunger 6; 6′ and the bottom of the blind-hole bore 20; 20′, and also by means of the oil pressure of the pressurized circulating lubricating-oil system of the internal combustion engine, which can be regulated, from the control-oil duct 11c. For this purpose, the blind-hole bore 20; 20′ in the region of the cam 2; 2′ is in communication, by way of a radial duct, a groove 9; 9′, an axial duct 12 disposed in the camshaft 1, and a further radial duct disposed in the camshaft 1, with a control-oil duct 11c disposed in the bearing 5.

A blind-hole bore 13; 13′, in which a sealing plunger 19 is displaceably disposed, is disposed in the region of the cam 3; 3′, pointing in the direction of the cam 2; 2′. The blind-hole bore 13; 13′ is in communication with a control-oil duct 11b of the controllable pressurized-oil supply, by way of a radial bore 10; 10′ disposed in the camshaft 1, the axial duct 4 disposed in the camshaft 1, and a further radial duct disposed in the camshaft 1, in a position according to FIG. 4.

The principle of action of the valve drive for internal combustion engines, according to the invention, is the following:

During full-load operation, the cam assembly on the camshaft 1 was displaced by the positioning device, which is not shown, in such a way that the two cams 2; 2′ provided with the larger cam profile are engaged with the inlet valves by way of corresponding cam followers. In the process, the cam 3; 3′ mounted rotatably on the camshaft 1 is connected, with shape fit, with the cam 2; 2′ disposed on the camshaft 1 so as to rotate with it. For this purpose, a corresponding oil pressure bears on the bottom of the pilot locking plunger 16; 16′, which pressure has displaced the pilot locking plunger 16; 16′ into the groove-like guide 8; 8′ of the cam 3; 3′. In an interlocked position of the cam 3; 3′ with the cam 2; 2′, the pilot locking plunger 16; 16′ bears on the outer boundary of the guide 8; 8′, as viewed in the direction of rotation of the camshaft 1. By virtue of the oil pressure acting on the main locking plunger 6; 6′, the main locking plunger 6; 6′ was partly displaced into the blind-hole bore 13; 13′ of the cam 3; 3′, and so shape-fit contact between the cam 3; 3′ and the cam 2; 2′ exists by way of the locking plunger 6; 6′.

During part-load operation of the internal combustion engine, the cam assembly on the camshaft 1 is displaced by way of the positioning device, in such a way that the two cams 3; 3′ provided with the smaller cam profile are engaged with the inlet valves by way of corresponding cam followers. Because of the interlocking of the cam 3; 3′ with the cam 2; 2′, the cam 3; 3′ is driven by the camshaft 1. Interlocking is maintained, according to FIG. 3, by way of the control-oil duct 11c.

In order to achieve zero lift or cylinder disconnection, separation of the connection between the cam 3; 3′ and the cam 2; 2′ takes place. In the process, the oil pressure present on the control-oil duct 11c is disconnected by a control device that can be regulated. The pilot locking plunger 16; 16′ is retracted, by means of the spring 18; 18′, into the blind-hole bore 17; 17′. At the same time, pressurized oil is admitted to the control-oil duct 11b, and thereby to the blind-hole bores 13; 13′. The oil pressure displaces the sealing plunger 19; 19′, and thus the main locking plunger 6; 6′, until the latter is located completely in the blind-hole bore 20; 20′ of the cam 2; 2′. The cam 3; 3′ is therefore de-interlocked, and the cam 3; 3′ is no longer driven by the camshaft 1. FIGS. 4, 5 and 6 show the valve drive according to the invention in the de-interlocked condition, in the respective three sectional diagrams.

By means of appropriate construction of the oil-control ducts or provision of valves within the control-oil circuit, it is possible to de-interlock the cams 3 or 3′ separately and independently from one another. The layout of the cam interlock can also be constructed in such a way that the described switching is executed only on one cam 3 or 3′.

If the idle valves are connected once again, coupling of the cam 3; 3′ with the cam 2; 2′ takes place once again, as a function of the engine-specific parameters. Pressurized oil is supplied to the blind-hole bore 17; 17′ and the blind-hole bore 20; 20′ by way of a control-oil duct 11c. The pilot locking plunger 13; 13′ is displaced, by means of the oil pressure, in the direction of the cam 3; 3′, and can be inserted into the groove-like guide 8; 8′. Secure insertion of the pilot locking plunger 16; 16 during the interlocking operation is achieved by means of the fact that the guide 8; 8′ extends over approximately 180° in the region of the base circle 15; 15′. After the pilot locking plunger 16; 16′ has been inserted into the guide 8; 8′, the cam 3; 3′ is driven by means of the pilot locking plunger 16; 16′. Because of the force of spring 7; 7′ and the oil pressure bearing on the main locking plunger 6; 6, the main locking plunger 6; 6′ is displaced into the blind-hole bore 13; 13′ during axial alignment of the blind-hole bore 20; 20′ and the blind-hole bore 13; 13′. In this way, the interlocking process is completed. FIGS. 1, 2 and 3 show the valve drive according to the invention in the interlocked condition, in the respective three sectional diagrams.

Safety locking of the cams 3 and 3′ not engaged with a roller-type cam follower takes place by way of a continuous pressurized-oil supply to the locking plungers 6; 6′ and 16; 16′ by way of the lubricating-oil duct 11a.

List of Reference Symbols Used

• 1 Camshaft
• 2 Cam
• 3 Cam
• 4 Duct
• 5 Bearing
• 6 Main locking plunger
• 7 Spring
• 8 Guide
• 9 Groove
• 10 Radial bore
• 11 a Lubricating-oil duct, to which oil pressure is continuously admitted
• 11 b Control-oil duct, oil pressure connectable and disconnectable, for de-interlocking the cams 3 and 3′
• 11 c Control-oil duct, oil pressure connectable and disconnectable, for interlocking the cams 3 and 3′
• 12 Bore
• 13 Blind-hole bore
• 14 Base circle of the cam 2
• 15 Base circle of the cam 3
• 16 Pilot locking plunger
• 17 Blind-hole bore
• 18 Spring
• 19 Sealing plunger
• 20 Blind-hole bore

Claims

1. Valve drive for an internal combustion engine, with at least one cam assembly that is axially displaceable on a camshaft and consists of at least two cams, which are provided with different profiles and which selectively actuate at least one gas-exchange valve for adjustment of different valve lifts and/or valve control times, whereinone cam (2; 2′) is connected to the camshaft (1) so as to rotate with it, and the other cam (3; 3′) is mounted rotatably on the camshaft (1) and, can be connected, with shape fit, with the cam (2; 2′) disposed on the camshaft (1) so as to rotate with it, by way of a controllable main locking plunger (6; 6), and separated from it.

2. Valve drive according to claim 1, whereinthe profile height of the cam (2; 2′) is larger, as compared with the profile height of the cam (3; 3′) mounted rotatably on the camshaft (1).

3. Valve drive according to claim 1, whereina groove-like guide (8; 8′) is disposed in the region of the base circle (15; 15′) of the cam (3; 3′) disposed rotatably on the camshaft (1), with which guide a pilot locking plunger (16; 16′) can be engaged and disengaged, which is mounted and is controllably displaceable in a blind-hole bore (17; 17′) of the base circle (14; 14′) of the cam (2; 2′) connected with the camshaft so as to rotate with it.

4. Valve drive according to claim 1, whereinthe blind-hole bore (17; 17′) is in communication, by way of supply ducts, with a controllable pressurized-oil supply for displacement of the pilot locking plunger (16; 16′) in the direction of the groove-like guide (8; 8′).

5. Valve drive according to claim 1, whereina spring (18; 18′) is disposed on the bottom of the pilot locking plunger (16; 16′), which spring acts against the oil pressure acting to displace the pilot locking plunger (16; 16′) in the direction of the groove-like guide (8; 8′), and displaces the pilot locking plunger (16; 16′) in the direction of the bottom of the blind-hole bore (17; 17′) upon disconnection of the oil pressure for displacing the pilot locking plunger (16; 16′) in the direction of the groove-like guide (8; 8′), and the connection of the cam (3; 3′) with the cam (2; 2′) is de-interlocked by means of the pilot locking plunger (16; 16′).

6. Valve drive according to claim 1, whereinthe groove-like guide (8; 8′) extends over approximately 180° in the region of the base circle (15; 15′) of the cam (3; 3′).

7. Valve drive according to claim 1, whereina blind-hole bore (20; 20′) is disposed, in the region of the cam (2; 2′), in which bore a displaceable main locking plunger (6; 6′) is controllably mounted, which can be engaged with and disengaged from a blind-hole bore (13; 13′) disposed in the region of the cam (3; 3′).

8. Valve drive according to claim 1, whereinthe blind-hole bore (20; 20′) in the cam (2; 2′) and the blind-hole bore (13; 13′) in the cam (3; 3′) are in communication with a controllable pressurized-oil supply for displacement of the main locking plunger (6; 6′).

9. A valve drive according to claim 1, whereina spring (7) is disposed between the bottom of the main locking plunger (6; 6′) and the bottom of the blind-hole bore (20; 20′) in the cam (2; 2′).