EXHAUST VALVE ACTUATION UNIT FOR A MULTI- VALVE ENGINE

Technical Field

The present invention refers to an exhaust valve actuation unit

5 used in a reciprocating multi-valve engine to actuate multiple exhaust valves associated to one cylinder.

Technological Background

In multi-valve engines, each cylinder is equipped with more than two valves, particularly with more than one intake valve and with more than one

10 exhaust valve. By such a configuration, breathing or throughflow of the combustion chamber may be improved and the engine may be operated at higher revolutions per minute compared to an engine design in which each cylinder is associated to only one intake valve and only one exhaust valve.

For actuating the multiple exhaust valves associated to one

15 cylinder, the use of rocker arms is known which are actuated by a camshaft of the engine. Specifically, the known rocker arms are configured to convey rotational movement of a cam on the camshaft into linear movement of the exhaust valves. For doing so, one end of the rocker arm typically bears on the cam, optionally via a push rod, and the other end mechanically actuates the at least two exhaust

20 valves simultaneously. By such a configuration, the contact stress exerted by the rocker arm on the cam is typically determined by a cylinder pressure at the opening timing of the exhaust valves.

Due to recent developments, specific power of engines is increasing leading to higher cylinder pressure and thus to higher loads acting

25 upon the exhaust valve actuation unit, particularly the camshaft, which may cause increased wear and damage during operation of the engine.

Received at EPO via Web-Form on Apr 22, 2022 Summary of the Invention

Starting from the prior art, it is an objective to provide an improved exhaust valve actuation unit for a multi-valve engine which particularly enables to reduce the load acting upon the exhaust valve actuation train,

5 particularly the camshaft, during operation of the engine.

This objective is solved by the subject matter of the independent claim. Preferred embodiments are set forth in the present specification, the Figures as well as the dependent claims.

Accordingly, an exhaust valve actuation unit for a multi-valve 10 engine is provided. The exhaust valve actuation unit comprises a rocker arm pivotably actuatable by a camshaft and a valve bridge connected to the rocker arm, wherein the valve bridge has a first arm configured to actuate a first exhaust valve associated to a cylinder and a second arm configured to actuate a second exhaust valve associated to the cylinder, and wherein the actuation unit is 15 configured to open the first exhaust valve and the second exhaust valve such that, during an operating cycle of the cylinder, the first exhaust valve is opened prior to the second exhaust valve upon actuation of the rocker arm by the camshaft.

Brief Description of the Drawings

The present disclosure will be more readily appreciated by 20 reference to the following detailed description when being considered in connection with the accompanying drawings in which:

Fig. 1 schematically shows a part of a multi-valve engine which is equipped with an exhaust valve actuation unit, wherein the exhaust valve actuation unit is shown in a non-actuation state;

25 Fig. 2 schematically shows the exhaust valve actuation unit of Fig.

1 in a partially-actuated state;

Fig. 3 schematically shows an exhaust valve actuation unit according to a further embodiment; and

Received at EPO via Web-Form on Apr 22, 2022 Fig. 4 schematically shows an exhaust valve actuation unit according to a further embodiment.

Detailed Description of Preferred Embodiments

In the following, the invention will be explained in more detail 5 with reference to the accompanying figures. In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

Fig. 1 depicts an internal combustion engine 10, also referred to as the ‘engine‘ in the following, provided in the form of a reciprocating engine, such 10 as a diesel engine, which may be installed on a vehicle, a vessel or in a power plant as a main or auxiliary engine.

The engine 10 comprises at least one cylinder 12, preferably more than one cylinder 12, e.g. four, six, eight or more cylinders. Each cylinder is provided with a combustion chamber 14 delimited by a cylinder wall and a piston 15 (not shown) accommodated therein.

During operation of the engine 10, each one of the combustion chambers 14 is supplied with a fuel mixture which is to be ignited therein so as to produce high-temperature and high-pressure gases which apply forces to and thus axially move the associated pistons, thereby rotating a crankshaft. In this way,

20 chemical energy is transformed into mechanical energy. The fuel mixture to be supplied to and ignited in the combustion chamber 14 is formed by mixing a fuel medium, i.e. diesel fuel, with intake air, i.e. fresh or ambient air from outside the vehicle.

Specifically, for supplying intake gas, i.e. intake air or an air fuel 25 mixture, into the combustion chamber 14, the engine 10 comprises intake ports (not shown) which lead to the combustion chamber 14. For controlling the supply of intake gas into the combustion chamber 14, i.e. for controlling timing and quantity of intake gas flow, each port is provided with an intake valve (not shown) which is actuated by a valve actuation system 16.

Received at EPO via Web-Form on Apr 22, 2022 For expelling combustion gases from the combustion chamber 14, i.e. after combustion of the fuel mixture took place, the engine 10 comprises exhaust ports 18, 20 connected the combustion chamber 14. For controlling the discharge of combustion gases from the combustion chamber 14 into the exhaust 5 ports 18, 20, each port is provided with an exhaust valve 22, 24 which are actuated by the valve actuation system 16.

The engine 10 is a multi -valve engine which comprises more than one exhaust valve per cylinder 12. In other words, each cylinder 12 is provided with at least a first exhaust valve 22 and a second exhaust valve 24 via which 10 combustion gases from the same combustion chamber 14 are expelled. In other words, to each cylinder 14 at least two exhaust ports 18, 20 and at least two exhaust valves 22, 24 are associated. Further, the engine 10 may be provided with at least two intake valves per cylinder 12.

The basic structure and function of such a multi -valve engine 10 15 and its components are well known to a person skilled in the art and are thus not further specified. Rather, characteristics of the valve actuation system 16 of the engine 10 interlinked with the present invention are addressed in the following.

The valve actuation system is configured to control operation of the intake valves and the exhaust valves 22, 24, i.e. to open or close the valves,

20 thereby determining the timing and quantity of the gas flow into and from the combustion chamber 14. For doing so, the valve actuation system 16 comprises an exhaust valve actuation unit 26 configured to mechanically actuate the first and the second exhaust valve 22, 24 associated to the same cylinder 12. The valve actuation system 16 preferably comprises one exhaust valve actuation unit 25 26 per cylinder 12. In this way, exhaust valves associated to the same cylinder are actuated by the same exhaust valve actuation unit.

The intake valves and exhaust valve are provided in the form of poppet valves, the operation of which is exemplary described in the following

Received at EPO via Web-Form on Apr 22, 2022 with reference to the first exhaust valve 22 which accordingly applies to the other intake and exhaust valves used in the engine 10.

The first exhaust valve 22 is configured to open and close a first exhaust port 18 provided in a cylinder head 28 of the engine 10. For doing so, the 5 first exhaust valve 22 comprises a plug 29 which is translationally guided in a valve guide 30 arranged in the cylinder head 28. Thus, the plug 29 is movable in the valve guide 30 along its longitudinal axis. The plug 29 comprises a disc shaped valve head 32 and a valve stem 34. By such a configuration, the plug 29 is translationally movable between a closed position in which an opening of the first 10 exhaust port 18 is sealed, as shown in Fig. 1, and an opened position, in which the opening of the first exhaust port 18 is released or uncovered, as shown in Fig. 2. Specifically, in the closed position of the first exhaust valve 22, the valve head 32 seats on a valve seat 36 provided at the rim of the cylinder head 28, thereby covering the opening of the first exhaust port 18. In the opened position, 15 the plug and first exhaust valve 22 is moved in direction towards the combustion chamber 14 so as to uncover the opening of the first exhaust port 18, thereby fluid communicatively connecting the combustion chamber 14 to the first exhaust port 18. The first exhaust valve 22 further comprises a valve spring 38 which is provided between a support on the cylinder head 28 and a valve spring retainer 20 40 firmly fixed to an end section of the valve stem 34. The valve spring 38 is configured for preloading the plug 29 and thus the first exhaust valve 22 towards its closed position, thus keeping the valve head 32 tightly closed in the valve seat 36 unless actuated by exerting an actuation or pushing force on the end of the valve stem 34 which counteracts and exceeds the biasing force provided by the 25 valve spring 38.

The valve actuation system 16 is configured to actuate the different valves in dependence on the operating cycle of the associated cylinders 12. For doing so, the valve actuation system comprises a camshaft 40 which is mechanically coupled and thus actuated by a crankshaft (not shown).

Received at EPO via Web-Form on Apr 22, 2022 In the context of the present disclosure, the term 'operating cycle of the cylinder' refers to successive events performed in the cylinder and associated to one combustion cycle. Typically, the operating cycle of a cylinder begins with intake of gas into the combustion chamber 14, particularly referred to 5 as intake stroke, and ends after expelling combustion gases from the combustion chamber 14, particularly referred to as exhaust stroke.

The camshaft 40 is provided with a plurality of cams or cam lobes, each of which is associated to one cylinder 12 of the engine 10. Specifically, per cylinder 12, the camshaft 40 is provided with two cams, namely one intake cam 10 configured to actuate the intake valves of the cylinder 12 and one exhaust cam 42 configured to actuate the exhaust valves 22, 24 of the associated cylinder 12. The exhaust cam 42 forms part of the exhaust valve actuation unit 26 which is specified in the following.

In general, the exhaust valve actuation unit 26 is configured for 15 mechanically coupling the first and the second exhaust valve 22, 24 of one cylinder 12 to the camshaft 40, in particular the exhaust cam 42, so as to actuate the first and the second exhaust valve 22, 24 in dependence on the rotational angle of the camshaft 40, particularly as a function of the position or rotational angel of the exhaust cam 42. In this way, the exhaust valve actuation unit 26 is 20 configured to translate the rotational movement of the exhaust cam 42 into and a reciprocating translational movement of the first and the second exhaust valve 22, 24, particularly into an oscillating translational movement of the plug 29 between the opened position and close position.

For mechanically coupling the exhaust cam 42 to the first and 25 second exhaust valve 22, 24, the exhaust valve actuation unit 26 comprises a rocker arm arrangement 44 which is configured to convey radial movement of the exhaust cam 42, i.e. radial variation of the cam profile circumferentially provided around the cam shaft 40, into oscillating linear movement of the first and the second exhaust valves 22, 24. For doing so, the rocker arm arrangement 44

Received at EPO via Web-Form on Apr 22, 2022 comprises a rocker arm 46 which is pivotably mounted on a pivot pin or shaft 48 and pivotably actuatable by the camshaft 40. The rocker arm 46 comprises a first end 50 which is mechanically coupled to the exhaust cam 42 via a push rod 52. Specifically, the push rod 52, also referred to as lifter, at one end is coupled to the 5 rocker arm 46 and on the opposed end is provided with a cam roller 54 which bears on the exhaust cam 42 such that rotational movement of the cam shaft 40 causes the rocker arm 46 to oscillatingly pivot around the pivot pin or shaft 48. In an alternative configuration, the push rod 52 may be omitted. Accordingly, the first end 50 of the rocker arm 46 may be provided with the cam roller 54 bearing 10 on the exhaust cam 42. In this way, the rocker arm 46 oscillatingly pivots between a first end position, shown in Fig. 1, in which the push rod 52 is fully retracted and the first and the second exhaust valve 22, 24 are in the closed position, and a second end position in which the push rod 52 is fully or almost fully extracted or advanced by bearing onto the tip of the cam 42 and the first and 15 the second exhaust valve 22, 24 are in the opened position.

A second end 56 of the rocker arm 46 is mechanically coupled to the first and second exhaust valve 22, 24, particularly to the end of their corresponding valve stem 34. For doing so, the rocker arm arrangement 44 comprises a valve bridge 58 fastened to the second end 56 of the rocker arm 46 20 via a bar 57. In the shown configuration, the valve bridge 58 is translationally guided along a direction parallel to the longitudinal axis of the plug 29 by means of a valve bridge guide 59 provided in the cylinder head 26. In this way, the valve bridge 58 is translationally moved along the longitudinal axis upon pivot movement of the rocker arm 46 around the pivot pin or shaft 48.

25 The valve bridge 58 comprises a first arm 60 configured to mechanically actuate the first exhaust valve 22 and a second arm 62 configured to mechanically actuate the second exhaust valve 24. Specifically, the first arm 60 is configured to push the valve stem 34 of the first exhaust valve 22 to move the first exhaust valve 22 into its opened position upon pivot motion of the rocker

Received at EPO via Web-Form on Apr 22, 2022 arm 46. The second arm 62 of the valve bridge 58 is configured to push the valve stem 34 of the second exhaust valve 24 to move the second exhaust valve 24 into its opened position upon pivot motion of the rocker arm 46.

The exhaust valve actuation unit 26 is designed and configured 5 such that, during an operating cycle of the cylinder 12, the first exhaust valve 22 is opened prior to the second exhaust valve 24 upon actuation of the rocker arm 46 by the camshaft 40. In other words, the exhaust valve actuation unit 26 is designed and configured such that, in a starting phase of an actuation period of the first and the second exhaust valve 22, 24 during the operating cycle, the first 10 exhaust valve 22 is moved from its closed position towards its opened position while the second exhaust valve 24 is maintained in a closed position, as can be gathered from Fig. 2 which depicts the exhaust valve actuation unit 26 in a state in which the first exhaust valve 22 is opened and the second exhaust valve 24 is closed. This state is therefore also referred to as a partially-actuated state.

15 Specifically, the starting phase of said actuation period is induced by a cam lobe of the exhaust cam 42, particularly when the cam lobe starts to push the cam roller 54 and thus pivots the rocker arm 46 from its first end position towards its second end position. In this way, the exhaust valve actuation unit 26 subsequently opens the first exhaust valve 22 and the second exhaust 20 valve 24 upon actuation of the rocker arm 46 by the camshaft 40 during a cylinder operating cycle.

By such a configuration, the exhaust valve actuation unit 26 is configured to actuate, i.e. open and close the first and the second exhaust valve 22, 24 in dependence on a camshaft angle or crankshaft angle. Specifically, the 25 rocker arm arrangement 44 is configured to open the first exhaust valve at a predefined first camshaft or crankshaft angle and to open the second exhaust valve at a predefined second camshaft or crankshaft angle which differs from the first camshaft or crankshaft angle. Specifically, the first and the second camshaft angle may differ by 20 to 40 degree, particularly by 10 to 20 degree.

Received at EPO via Web-Form on Apr 22, 2022 Alternatively or additionally, the first and the second crankshaft angle may differ by 10 to 20 degree, particularly by 5 to 10 degree. In other words, the exhaust valve actuation unit 26 may be configured such that, upon actuation of the rocker 46 by the camshaft 40, the first exhaust valve 22 is opened, i.e. moved from its 5 closed position towards its opened position, 10 to 20 crankshaft degrees, particularly 5 to 10 crankshaft degrees, earlier than the second exhaust valve 24 during the operating cycle.

Further, during the operating cycle of the cylinder 12, the second exhaust valve 24 is closed prior to the first exhaust valve 22 upon actuation of the 10 rocker arm 46 by the camshaft 40.

For subsequently opening the first and the second exhaust valve 22, 24 during the operating cycle, in the configuration depicted in Fig. 1, the rocker arm arrangement 44 is configured such that, in a state in which the first and the second exhaust valve 22, 24 are arranged in the closed position, i.e. in 15 which the rocker arm 46 is in the first end position, a first gap 64 between the first arm 60 of the valve bridge 58 and an end of the valve stem 34 of the first exhaust valve 22 is smaller than a second gap 66 between the second arm 62 of the valve bridge 58 and an end of the valve stem 34 of the second exhaust valve 24. This state, i.e. in which the first and second exhaust valve 22, 24 are in the 20 closed position, is also referred to as the non-actuation state.

More specifically, in the shown configuration, the rocker arm arrangement 44 is configured such that in the state in which the rocker arm 46 is in the first end position, the first arm 60 of the valve bridge 58 abuts on the valve stem 34 of the first exhaust valve 22 while the second arm 62 of the valve bridge 25 58 is positioned spaced apart from the valve stem 34 of the second exhaust valve

24, as can be gathered from Fig. 1. For doing so, the first arm 60 of the valve bridge 58 is designed such it extends beyond the second arm 62 of the valve bridge 62 in a direction pointing from the valve bridge 58 towards the cylinder 12 and being parallel to a longitudinal axis of the valve stem 34 of the first and the

Received at EPO via Web-Form on Apr 22, 2022 second exhaust valve 22, 24. According to a further development, the first and/or the second gap may be variably adjusted, for example, by providing an adjustable bar at the first and/or the second arm 60, 62 of the valve bridge 58. Alternatively or additionally, the valve stem 34 of the first exhaust valve 22 may be longer than 5 a valve stem 34 of the second exhaust valve 24. In other words, the plug 29 of the first exhaust valve 22 may have a length along its longitudinal axis which may by greater than a length of the plug 29 of the second exhaust valve 24.

In the shown configuration, the valve bridge 58 is torque- transmittingly connected to the bar 57. In other words, the valve bridge 58 is 10 fastened to the bar 57 such that it cannot be rotated relative thereto. Thus, no degree of freedom is provided between the valve bridge 58 and the bar 57 connecting the valve bridge 58 to the rocker arm 46.

Fig. 3 depicts another configuration of the exhaust valve actuation unit 26. Compared to the arrangement depicted in Fig. 1 and 2, the valve bridge 15 58 is pivotably mounted to the bar 57 connecting the valve bridge 58 to the rocker arm 46 such that the valve bridge 58 can be pivoted relative to the rocker arm 46 around a pivot axis 68 which extends perpendicular to a movement direction of the first and second exhaust valve 22, 24, i.e. of a movement direction of the plug 29 thereof. Further, the first exhaust valve is biased towards 20 its closed position by a first valve spring 70 and the second exhaust valve 24 is biased towards its closed position by a second valve spring 72. The first and the second valve spring 70, 72 are designed and configures such that, in the non actuation state of the valve actuation system 18 in which both the first and the second exhaust valve 22, 24 are positioned in their closed position, a first biasing 25 force exerted by the first valve spring 70 onto the first exhaust valve 22, i.e. onto the plug 29 of the first exhaust valve 22, has an absolute value that is smaller than a second biasing force exerted by the second valve spring 72 onto the second exhaust valve 24, i.e. onto the plug of the second exhaust valve 24. For doing so,

Received at EPO via Web-Form on Apr 22, 2022 the first valve spring 70 may be provided with a smaller spring stiffness than the second valve spring 72.

By such a configuration, the valve actuation system 18 depicted in Fig. 3 enables that during an operating cycle of the cylinder, the first exhaust 5 valve is opened prior to the second exhaust 12 upon actuation of the rocker arm 46 by the camshaft 40, i.e. the exhaust cam 42.

Fig. 4 depicts another configuration of the exhaust valve actuation unit 26. Compared to the arrangement depicted in Fig. 1 and 3, the second exhaust valve 24 is coupled to the second arm 62 of the valve bridge 58 via a 10 damper unit 74. The damper unit 74 is be configured such that, when the rocker arm 46 is moved from the second end position towards the first end position, the closing movement of the second exhaust valve 24 is delayed by the damper unit 74'. Specifically, the closing movement of the second exhaust valve 24 is delayed such that the first exhaust valve 22 and the second exhaust valve 24 are moved 15 into their closed position at substantially the same time, i.e. simultaneously, during the operating cycle of the associated cylinder 12.

It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities.

Hence, the embodiments shown here should not be understood to form a 20 limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention. This particularly applies in view of the technical features described in the following.

An exhaust valve actuation unit for a multi-valve engine may be 25 provided, comprising a rocker arm pivotably actuatable by a camshaft and a valve bridge connected to the rocker arm, wherein the valve bridge has a first arm configured to actuate a first exhaust valve associated to a cylinder and a second arm configured to actuate a second exhaust valve associated to the cylinder, and wherein the actuation unit is configured to open the first exhaust valve and the

Received at EPO via Web-Form on Apr 22, 2022 second exhaust valve such that, during an operating cycle of the cylinder, the first exhaust valve is opened prior to the second exhaust valve upon actuation of the rocker arm by the camshaft.

In the context of the present invention, it has been found that the 5 exhaust cam of known valve actuation systems may be prone to wear and damage due to the high contact stress the cam is exerted when simultaneously opening two exhaust valves. The maximum contact stress acting onto the exhaust cam is determined by the cylinder pressure at the moment of opening the two exhaust valves. Thus, for avoiding excessive loads on the exhaust cam, the present 10 invention suggests the exhaust valve actuation unit in which the first and the second exhaust valves are successively opened, i.e. one after the other, during the operating cycle. In this way, the maximum load acting upon the exhaust cam during the operating cycle can be substantially lowered since opening one exhaust valve instead of opening two exhaust valves simultaneously requires a 15 smaller force application.

The exhaust valve actuation unit may be configured such that, in a starting phase of an actuation period of the first and the second exhaust valve during the operating cycle, the first exhaust valve is moved from a closed position towards an opened position while the second exhaust valve is maintained 20 in a closed position. Further, the exhaust valve actuation unit may be configured to subsequently open the first exhaust valve and the second exhaust valve upon actuation of the rocker arm by the camshaft during a cylinder operating cycle.

In a further development, the exhaust valve actuation unit may be configured such that, upon actuation of the rocker arm by the camshaft, the first 25 exhaust valve is opened 10 to 20 crankshaft degrees earlier than the second exhaust valve during the operating cycle.

Alternatively or additionally, the exhaust valve actuation unit may be configured such that, in a non-actuation state in which the first and the second exhaust valve are in the closed position, a first gap between the first arm and a

Received at EPO via Web-Form on Apr 22, 2022 first valve stem of the first exhaust valve is smaller than a second gap between the second arm and a second valve stem of the second exhaust valve.

For doing so, the first arm of the valve bridge may extend beyond the second arm of the valve bridge in a direction pointing from the valve bridge 5 towards the cylinder and being parallel to a longitudinal axis of a valve stem of the first or the second exhaust valve. Alternatively or additionally, a valve stem of the first exhaust valve may be longer than a valve stem of the second exhaust valve.

In a further development, the valve bridge may pivotably mounted 10 to a bar connecting the valve bridge to the rocker arm. Further the first exhaust valve may be biased towards its closed position by a first valve spring and the second exhaust valve may be biased towards its closed position by a second valve spring, wherein in the non-actuation state in which the first and the second exhaust valve are in the closed position, a first biasing force exerted by the first 15 valve spring onto the first exhaust valve may have an absolute value that is smaller than a second biasing force exerted by the second valve spring onto the second exhaust valve. Specifically, the first valve spring may have a smaller spring stiffness than the second valve.

In a further development, the exhaust valve actuation unit may be 20 configured such that, during the operating cycle of the cylinder, the second exhaust valve is closed prior to the first exhaust valve upon actuation of the rocker arm by the camshaft.

Alternatively, the exhaust valve actuation unit may be configured such that, during the operating cycle of the cylinder, the first exhaust valve and 25 the second exhaust valve are moved into their closed position at substantially the same time upon actuation of the rocker arm by the camshaft.

For doing so, the exhaust valve actuation unit may further comprise a damper unit. Specifically, the second exhaust valve may be connected to the second arm of the valve bridge via the damper unit.

Received at EPO via Web-Form on Apr 22, 2022 Industrial Applicability

With reference to the Figures, an exhaust valve actuation unit for a multi-valve engine is suggested. The exhaust valve actuation unit as mentioned above is applicable in any reciprocating multi-valve engine. The suggested 5 exhaust valve actuation unit may replace conventional exhaust valve actuation unit and may serve as a replacement or retrofit part.

Received at EPO via Web-Form on Apr 22, 2022