GB2536799A - Valve train for an internal combustion engine - Google Patents

Abstract

A valve train 10 for an internal combustion engine, comprising at least one charge cycle valve 12 for a cylinder engine, comprising a valve stem 14, a cap 22 slidably coupled thereto, wherein the charge cycle valve 12 is actuatable via the valve stem 14 and the cap 22 by at least one actuating element (24, Fig. 1) at least one hydraulic chamber 38 bounded at least partially by the valve stem 14 and the cap 22 which has at least one through opening 40 for discharging hydraulic medium from the hydraulic chamber 38; at least one sleeve 42 slidably arranged on the cap 22, and being slidable in relation to the cap 22 between at least one covering position in which the through opening 40 is covered by the sleeve 42, and at least one release position in which the sleeve 42 uncovers the through opening 40; and an actuator 44 configured to slide the sleeve 42 in relation to the cap 22 thereby varying the actuation of the charge cycle valve 12. The invention is intended at providing a variable actuation valve with a relatively low complexity and installation space.

Description

Valve Train for an Internal Combustion Engine The invention relates to a valve train for an internal combustion engine, in particular for a vehicle.

For example, US 2010/0168987 Al shows an internal combustion engine comprising at least one intake valve for each cylinder, provided with elastic means tending to push the valve towards a closed position. The internal combustion engine further comprises at least one camshaft for controlling the intake valve by means of respective tappets. Moreover, an electronically controlled hydraulic system for variable actuation of the intake valves is provided.

The hydraulic system comprises a pressurized fluid chamber set between each of the tappets and a respective intake valve, the pressurized fluid chamber being designed to be connected to an exhaust channel by means of a passage controlled by a solenoid valve so that when said solenoid valve is opened the intake valve is uncoupled from the respective tappet and is kept closed by said elastic means.

Furthermore, US 2012/0240886 Al shows an internal combustion engine having an electrohydraulic valve control for a variable-stroke driving of a gas exchange valve upon which a spring force is applied in a closing direction. The internal combustion engine comprises a camshaft and a hydraulic system arranged to act as a drive between the camshaft and the gas exchange valve, wherein the hydraulic system is connected to a hydraulic medium supply of the internal combustion engine.

In internal combustion engines according to the prior art the actuation of respective charge cycle valves can be varied so as to vary, for example, valve lift and/or valve timing. In order to vary the actuation of the charge cycle valves hydraulic systems are used. However, said hydraulic systems used to vary the actuation of the charge cycle valves are complex and expensive and need a large installation space.

It is therefore an object of the present invention to provide a valve train by means of which the actuation of charge cycle valves can be varied in an easy and space-and cost-effective way.

This object is solved by a valve train having the features of patent claim 1. Advantageous embodiments with expedient developments of the invention are indicated in the other patent claims.

The invention relates to a valve train for an internal combustion engine, in particular for a vehicle. The valve train according to the present invention comprises at least one charge cycle valve for a cylinder of the internal combustion engine, the charge cycle valve comprising a valve stem. The charge cycle valve is also referred to as a gas exchange valve or valve. The valve train according to the present invention further comprises a cap which is slidably coupled to the stem, wherein the charge cycle valve is actuatable via the valve stem and the cap via at least one actuating element. For example, said actuating element can provide a force which can be transferred via the cap to the valve stem and thus the charge cycle valve thereby actuating the charge cycle valve.

For example, by actuating the charge cycle valve the charge cycle valve is translationally moved from a closed position to an open position. The charge cycle valve can be used as, for example, an intake valve or an exhaust valve. The valve train according to the present invention further comprises at least one hydraulic chamber bounded at least partially by the valve stem and the cap, wherein the cap has at least one through opening for discharging hydraulic medium from the hydraulic chamber. This means hydraulic medium contained in the hydraulic chamber can be drained from the hydraulic chamber through the through opening.

The valve train also comprises at least one sleeve which is slidably arranged on or around the cap, said sleeve being slidable in relation to the cap between at least one covering position and at least one release position. In the covering position the through opening of the cap is occluded and thus blocked by the sleeve. Hence, hydraulic medium contained in the chamber cannot flow through the through opening so that the hydraulic medium contained in the chamber does not flow out of the hydraulic chamber via the through opening. In the release position the sleeve uncovers the through opening so that hydraulic medium contained in the hydraulic chamber can be discharged from the hydraulic chamber since hydraulic medium contained in the hydraulic chamber can flow through the through opening and thus out of the hydraulic chamber.

Moreover, the valve train according to the present invention comprises an actuator configured to slide the sleeve in relation to the cap thereby varying the actuation of the charge cycle valve.

At least the cap, the valve stem, and the sleeve are components of a hydraulic system by means of which the actuation of the charge cycle valve, can be varied, i.e. adjusted in a need-based manner in such a way that the sleeve is slid in relation to the cap by means of the actuator thereby covering and uncovering the through opening. Thus, said components form a hydraulic lost-motion mechanism which can be integrated into an internal combustion engine in a particularly easy and cost-effective way since the installation space as well as the number of parts of said hydraulic system can be kept particularly low. Moreover, the hydraulic lost-motion mechanism provides automatic valve lash compensation.

For example, the valve train comprises an electronic control unit (ECU) configured to control the actuator. Thus, the sleeve, under ECU control, can either open or occlude the through opening acting as a spill port which manages a hydraulic lost-motion link between the valve stem and the cap. When the through opening is occluded by the sleeve the valve stem and thus the charge cycle valve is hydraulically connected to the cap and thus the actuating element by means of the hydraulic medium contained in the hydraulic chamber. Thus, the charge cycle valve can be actuated via the valve stem and the cap by the actuating element. In the covering position the hydraulic medium contained in the hydraulic chamber cannot flow out of the hydraulic chamber so that the cap cannot be slid in relation to the stem. Thus, a force provided by the actuating element is transferred via the cap and the hydraulic medium contained in the chamber to the valve stem and thus the charge cycle valve so that the charge cycle valve can be actuated.

However, in the uncovering position said hydraulic connection or link is canceled since the hydraulic medium can be discharged from the hydraulic chamber through the uncovered through opening. Thus, the cap can be slid in relation to the valve stem so that a force provided by the actuating element cannot be transferred via the cap to the valve stem which is also referred to as stem. This means the sleeve acts as a spill sleeve configured to cover and uncover the through opening of the cap in a need-based manner. For example, the actuator is configured as a solenoid actuator which can accurately position the sleeve in relation to the cap.

By means of said hydraulic system a standard gas exchange valve motion statement can be modified to enable advanced strategies such as Miller Cycle. Said hydraulic system is a controllable mechanism that offers the prospect of flexibility in valve event lift and/or timing. In other words, by varying the actuation of the charge cycle valve, valve lift and/or valve timing can be varied.

For example, said lost-motion mechanism is used for valve event control, wherein said lost-motion mechanism can be seen as a cost-effective intermediate step between conventional mechanical cam control and the ultimate objective of a completely camless system. The lost-motion mechanism can be straight forward to adapt to existing architectures while offering a desired valve event flexibility. The lost-motion mechanism according to the present invention is particularly simple, elegant and a low cost solution in comparison to hydraulic systems according to the prior art. For example, the lost-motion mechanism according to the present invention can be packaged between a valve rocker arm and a spring retainer particularly easily and in a cost-effective way.

Further advantages, features, and details of the invention derive from the following description of a preferred embodiment as well as from the drawings. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respectively indicated combination but also in other combination or taken alone without leaving the scope of the invention.

The drawings show in: Fig. 1 a schematic sectional side view of a valve train according to the present invention; Fig. 2 part of a schematic sectional view of the valve train; Fig. 3 a diagram illustrating the functionality of the valve train; Fig. 4 5 Fig. 5 a further diagram illustrating the functionality of the valve train; Fig. 6 a further diagram illustrating the functionality of the valve train; and part of a schematic sectional side view of a valve train according to the present invention.

In the figures the same elements or elements having the same functions are indicated by the same reference signs.

Fig. 1 shows a valve train 10 for an internal combustion engine which may for example be configured to drive a vehicle such as a motor vehicle. As will be described in the following in greater detail the valve train 10 is designed as a lost-motion valve train concept being a relatively simple mechanism that provides variable valve actuation (VVA) functionality which can be integrated into an internal combustion engine in a particularly easy and cost-effective way.

The valve train 10 comprises at least one charge cycle valve 12 which is also referred to as a gas exchange valve. For example, the charge cycle valve 12 can be an intake valve or an exhaust valve. The charge cycle valve 12 comprises a valve stem 14 and a valve disc 16 connected to the valve stem 14. For example, the valve stem 14 and the valve disc 16 are designed in one piece. The charge cycle valve 12 can be actuated and thus translationally moved from a closed position to at least one open position. Since the valve train 10 provides a variable valve actuation functionality the actuation of the charge cycle valve 12 can be varied or adjusted so that valve timing and/or valve lift can be varied. When the charge cycle valve 12 is moved the charge cycle valve 12 performs a lift which is also referred to as a valve lift. For example, by varying the actuation of the charge cycle valve 12 the lift performed by the charge cycle valve 12 can be varied which is generally understood as varying or adjusting the valve lift. Moreover, the charge cycle valve 12 is opened and closed at respective points in time. For example, by varying the actuation of the charge cycle valve 12 the points in time at which the charge cycle valve 12 opens and/or closes can be varied which is generally understood as varying the valve timing. This means the valve train 10 is configured to vary the valve lift and/or the valve timing. Since, for example, the valve lift can be varied the charge cycle valve 12 can be moved from the closed position to multiple open positions.

The valve train 10 comprises a spring 18 which is supported on the valve stem 14 via a spring retainer 20. For example, the spring 18 is at least indirectly supported on the spring retainer 20. Moreover, the spring 18 is at least indirectly supported on a cylinder head of the internal combustion engine. Preferably, the spring 18 is loaded in the closed position of the charge cycle valve 12 so as to provide a spring force in the closed position. The spring force provided by the spring 18 acts on the charge cycle valve 12 via the spring retainer 20 thereby holding the charge cycle valve 12 in the closed position. By moving the charge cycle valve 12 from the closed position to one of the open positions the spring 18 is loaded stronger so that the spring 18 provides a spring force in the respective open position. Said spring force provided by the spring 18 in the open position acts from the spring 18 via the spring retainer 20 on the charge cycle valve 12. Thus, the charge cycle valve 12 can be moved from the respective open position to the respective closed position by means of said spring force exerted by the spring 18 via the spring retainer 20 on the charge cycle valve 12.

The valve train 10 comprises a cap 22 which is slidably coupled to the valve stem 14. For example, at least a portion of the cap 22 is slidably arranged on the valve stem 14. The valve train 10 further comprises at least one actuating element 24, wherein the charge cycle valve 12 is actuatable, i.e. translationally movable via the valve stem 14 and the cap 22 by the actuating element 24. As can be seen from Fig. 1 the actuating element 24 is configured as a so-called elephant's foot having a receptacle 26 which has the shape of a sphere or a spherical segment. The valve train 10 further comprises an actuating element 28 which is designed as an adjusting screw. The actuating element 28 has a spherical head 30 engaging the corresponding receptacle 26. Thus, the actuating elements 24 and 28 are linked together in the manner of a ball joint so that the elephant's foot can swivel in relation to the actuating element 28 whilst the elephant's foot is connected to the actuating element 28 (adjusting screw). The valve train 10 further comprises a rocker arm 32 which is also referred to as a valve rocker arm. The rocker arm 32 is coupled to a stationary rocker shaft 34 so that, for example, the rocker arm 32 rotates about a rotation axis 36 on a bushing (not shown).

For example, the valve train 10 comprises at least one camshaft which cannot be seen in Fig. 1. The camshaft has at least one cam for actuating the rocker arm 32. For example, a rocker arm roller is rotatably connected to the rocker arm 32 so that the rocker arm 32 can be actuated by the cam via the rocker arm roller. By actuating the rocker arm 32 the rocker arm 32 is rotated about the rotation axis 36. Thus, the rocker arm 32 provides a force which can be transferred via the actuating elements 24 and 28 and via the cap 22 to the valve stem 14 and thus the charge cycle valve 12 thereby actuating, i.e. translationally moving the charge cycle valve 12 from the closed position to the open position.

The valve train 10 further comprises at least one hydraulic chamber 38 configured to receive a hydraulic medium such as a lubricant. For example, said lubricant is oil used to lubricate the internal combustion engine. The hydraulic chamber 38 is bounded at least partially by the valve stem 14 and the cap 22 respectively. Moreover, the cap 22 has at least one through opening 40 for discharging hydraulic medium from the hydraulic chamber 38. For example, the cap 22 has a plurality of through openings 40 opening into the hydraulic chamber 38 on one side and the surroundings of the cap 22 on the other side.

The valve train 10 also comprises at least one sleeve 42 which is slidably arranged on or around the cap 22 so that the sleeve 42 can be slid, i.e. translabonally moved in relation to the cap 22. The sleeve 42 is slidable in relation to the cap 22 between at least one covering position shown in Fig. 1, and at least one release position shown in Fig. 2. In the covering position the through opening 40 of the cap 22 is occluded, i.e. closed or covered by the sleeve 42 so that, in the covering position, hydraulic medium contained in the hydraulic chamber 38 cannot flow through the through opening 40. In the release position the sleeve 42 uncovers the through opening 40 so that hydraulic medium contained in the chamber 38 can flow through the through opening 40 and, thus, out of the hydraulic chamber 38.

The valve train 10 further comprises an actuator 44 configured to slide the sleeve 42 in relation to the cap 22 thereby varying the actuation of the charge cycle valve 12. The actuator 44 has a control arm 46 which engages a corresponding receptacle 48 of the sleeve 42. The control arm 46 can be rotated about the rotation axis 50. For example, the actuator 44 has a motor such as an electric motor configured to drive the control arm 46. By driving the control arm 46 the control arm 46 is rotated about the rotation axis 50. As illustrated by a directional arrow 52 the control arm 46 can be rotated about the rotation axis 50 in a first direction of rotation and in a second direction of rotation, wherein the second direction of rotation is opposite of the first direction of rotation. By rotating the control arm 46 about the rotation axis 50 the sleeve 42 is slid in relation to the cap 22. With respect to the image plane of Fig. 1, by rotating the control arm 46 counterclockwise

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the sleeve 42 is translationally moved upwards in relation to the cap 22. Accordingly, by rotating the control arm 46 clockwise the sleeve 42 is slid downwards in relation to the cap 22. The through opening 40 is also referred to as a spill port since hydraulic medium contained in the hydraulic chamber 38 can be discharged from the hydraulic chamber 38 by the spill port.

The valve train 10 further comprises a check valve 54 which is also referred to as a non-return valve (NRV). The check valve 54 has at least one closing element in the form of a ball 56. The check valve 54 further comprises a cage 58. Moreover, the check valve 54 comprises a spring 59 which can be seen in Fig. 6. The spring 59 is supported on the ball 56 on one side and on the cage 58 on the other side so that both the ball 56 and the spring 59 the check valve 54 are retained by the cage 58 which is, for example, made of steel. Thus, the ball 56, the spring 59 and the cage 58 form a sub-assembly.

Moreover, the valve train 10 comprises a bias spring 60 which is at least indirectly supported on the valve stem 14 on one side and the cage 58 on the other side. Although not shown as such, in a preferred embodiment, the bias spring 60 can also be captured by the cage 58 so that it too would be part of the said sub-assembly. This would be for ease of handling and assembly on the production line. The purpose of bias spring 60 is to maintain contact of the cap 22 to the elephant's foot even when there is no oil pressure to do so.

The cap 22 has at least one feed opening 62 for feeding hydraulic medium into the hydraulic chamber 38. This means hydraulic medium such as oil can flow through the feed opening 62 and into the hydraulic chamber 38 since the feed opening 62 opens into the hydraulic chamber 38. The feed opening 62 is also referred to as an orifice. The ball 56 acting as a valve seals against a seat coincident with the feed opening 62 in the cap 22 and is biased onto that seat by a the spring 59 being, for example, a light spring. This means the ball 56 is configured to close the feed opening 62 in order to prevent hydraulic medium flowing from the hydraulic chamber 38 back through the feed opening 62. However, the check valve 54, i.e. the ball 56 and the spring 59 allow oil flowing through the feed opening 62 into the hydraulic chamber 38. The check valve 54 is at least partially arranged in the hydraulic chamber 38, wherein the ball 56 and the cage 58 are arranged in the hydraulic chamber 38. Moreover, the bias spring 60 is partly arranged in the hydraulic chamber 38 and in the valve stem 14 respectively.

The rocker arm 32 has a through opening 64 through which the actuating element 28 penetrates. The actuating element 28 has a male thread 66. The valve train 10 further comprises a fastening member configured as a nut 69 having a female thread corresponding to the male thread 66. The actuating element 28 and the nut 69 are screwed together by means of the male thread 66 and the female thread so that the actuating element 28 is coupled to the rocker arm 32. By rotating the nut 69 in relation to the actuating element 28 the actuating element 28 can be translationally moved in relation to the rocker arm 32 in the through opening 64 so that the actuating element 28 can be moved to different positions in relation to the rocker arm 32. Thereby, the position of the actuating element 28 in relation to the rocker arm 32 can be adjusted so as to compensate tolerances.

When incorporating the valve train 10 into an existing internal combustion engine only minor alterations to an existing overhead architecture are required. As can be seen from Fig. 1 the valve train 10 utilizes a lost-motion hydraulic link between the rocker arm 32 and the charge cycle valve 12. Said lost-motion hydraulic link is realized by means of the valve stem 14, the cap 22, and the hydraulic chamber 38 in which hydraulic medium can be contained. When the through opening 40 is covered and, thus, closed by the sleeve 42 hydraulic medium contained in the hydraulic chamber 38 cannot flow out of the hydraulic chamber 38 so that a hydraulic link or connection between the cap 22 and the valve stem 14 is established. Thereby, a force provided by the rocker arm 32 and acting on the cap 22 via the actuating elements 24 and 28 can be transferred from the cap 22 via the hydraulic medium contained in the hydraulic chamber 38 to the valve stem 14 and, thus, the charge cycle valve 12 thereby actuating the charge cycle valve 12. The force provided by the rocker arm 32 can be transferred to the charge cycle valve 12 since the through opening 40 is occluded by the sleeve 42 and the cap 22 cannot be slid in relation to the valve stem 14.

However, by opening or uncovering the through opening 40 said hydraulic link is canceled since hydraulic medium contained in the hydraulic chamber 38 can flow out of the hydraulic chamber 38. Hence, that the cap 22 is slid in relation to the valve stem 14 when a force provided by the rocker arm 32 acts on the cap 22 via the actuating elements 24 and 28. Thus, the charge cycle valve 12 is not actuated. In other words, by opening the through opening 40 said lost-motion hydraulic link which is also referred to as a hydraulic link is canceledthus collapses.

For example, the cap 22, the hydraulic chamber 38, the sleeve 42 and valve stem 14 are components of a hydraulic system by means of which the actuation of the charge cycle valve 12 can be varied. For example, said cylinder of the internal combustion engine can be equipped with a plurality of charge cycle valves so that a plurality of said hydraulic system can be provided. Moreover, the internal combustion engine can comprise a plurality of cylinders which are each equipped with at least one hydraulic system. For example, one control actuator such as the actuator 44 may have authority of a single sleeve 42 or potentially multiple sleeves 42. The sleeve 42 acts as a valve since the flow of hydraulic medium from the hydraulic chamber 38 through the through opening 40 is controlled by the sleeve 42. By means of the valve train 10 different valve event strategies can be realized. Said valve event strategies that may be enabled may include, in comparison with a normal strategy, delayed valve opening with reduced lift and early closing, normal valve opening and lift by early valve closing as for a Miller Cycle, and other event strategies that can provide for valve deactivation.

An outcome of ongoing technology analysis is that flexible control over gas exchange valve events will be a highly ranked attribute in meeting future engine performance objectives. The current paradigm of a rigid mechanical link between cam profile and valve motion has served the industry well for over a century, and the perceived complexity and cost of VVA mechanisms that offer greater authority over valve events have inhibited the introduction of such flexible systems. Both the technical and the patent literature discuss many VVA systems and indicate a generally positive impact on engine performance, but only a few such systems have reached production status in commercial diesel engines.

What is required therefore is a concept mechanization that is simple, robust, low cost, easy to assemble, has a low space-claim, makes a low parasitic demand, and requires minimal alteration to existing engine architecture. These criteria are met by the valve train 10.

As can be seen from Fig. 1, the cap 22, the valve stem 14, the hydraulic chamber 38 and the sleeve 42 form a lost-motion mechanism interposed between the elephant's foot (actuating element 24) and the charge cycle valve 12. With respect to already existing internal combustion engines, essentially, the rocker arm 32 and its adjuster formed by the actuating element 28 and the nut 69 can remain unchanged. However, the valve stem 14 is now shorter and includes a receptacle 68 in form of a counterbore in which the spring 60 is arranged at least partially. Placed over the valve stem 14 is the cap 22 that is, for example, round internally and externally to give a class fit to its mating components such as the valve stem 14 and the sleeve 42. The cap 22 has a head 70 having the feed opening 62 being an axial hole that aligns with or is fluidically connected to ducts 72 and 74 in the elephant's foot (actuating element 24) and the actuating element 28. The ducts 72 and 74 are oil passage ways for supplying the feed opening 62 and, thus, the hydraulic chamber 38 with the hydraulic medium (oil).

The rocker shaft 34 and the rocker arm 32 have further ducts 76 and 78 respectively which are fluidically connected with each other. Thus, hydraulic medium such as oil flowing through the duct 76 can flow from the duct 76 into the duct 78 and through the duct 78. The duct 78 is fluidically connected to the duct 74 so that the oil flowing through the duct 78 can flow from the duct 78 into the duct 74. Moreover, the hydraulic medium flowing through the duct 74 can flow into and through the duct 72 and through the feed opening 62 into the hydraulic chamber 38.

Internal to the cap 22 a small spring biased non-return check valve in the form of the check valve 54 is pressed into place so that the check valve 54 cooperates with a seat associated with the axial hole (feed opening 62). The check valve 54, in particular its ball 56, and the cage 58 are standard commodity components of almost all hydraulic lash adjusters. The long bias spring 60 is provided, which for ease of assembly reasons would ideally be attached to the cage 58. Forming a sliding fit to the external diameter of the cap 22 is a control sleeve in the form of the sleeve 42 which may be retained on the cap 22 by circlips or other retaining means 80 located in respective grooves adjacent either end of the cap 22. Thus a sub-assembly is formed by the cap 22 with the sleeve 42, the check valve 54 and its bias spring 60. Within the range of travel between the cap 22 and the sleeve 42, there is the through opening 40 acting as a vent hole which, when uncovered, allows venting of the hydraulic medium (oil) trapped in the hydraulic chamber 38 being an internal cavity. When the through opening 40 is occluded by the sleeve 42, a hydraulic lock or link is created between the cap 22 and the valve stem 14, thus providing a solid link in the form of said hydraulic link.

When assembled on an engine, the cap 22 fits over the valve stem 14 with the bias spring 60 sitting in the counterbore (receptacle 68). The purpose of the bias spring 60 is to maintain engagement of the cap 22 with the elephant's foot (actuating element 24) at all times. This means the bias spring 60 provides a spring force by means of which the cap 22 is held in contact with the actuating element 24. Thus, the bias spring 60 is used to maintain engagement of the cap 22 to the elephant's foot at all time so that there is a minimal loss of hydraulic oil at an interface via which the cap 22 and the elephant's foot cooperate. The sleeve 42 is engaged by the control arm 46 which is configured as, for example, a fork, the control arm 46 being positioned by the actuator 44 under ECU control. The actuator 44 may be selected from one of many different types including rotary solenoid, rotary stepper motor, voice-coil solenoid, linear stepper motor, and more. In a preferred embodiment, the actuator control shaft 82 to which is affixed the control arm 46 -will lie parallel to the rocker shaft 34 and can be located by intra-cylinder bulkheads of a cam carrier. For example, control arms for two similar charge cycle valves of any one cylinder may be independently controlled, but most likely would be linked so that one actuator can control both valves, i.e. a plurality of sleeves 42.

In operation, hydraulic medium enters the feed opening 62 acting as a control cavity through the check valve 54 and, assuming that the through opening 40 is occluded by the sleeve 42, the hydraulic chamber 38 will be pressurized to a value similar to prevailing system pressure. This will create a separating force between the valve stem 14 and the cap 22 and thus maintain a positive contact throughout the valve train 10 from valve 12 to rocker arm roller and the cam. It will also automatically compensate for valve lash variation due to valve recession or temperature-induced valve expansion. For a normal operation it is desired that the valve (charge cycle valve 12) should follow the cam profile, and in this mode, the sleeve 42 is positioned so that the at least one through opening 40 (vent hole) is covered throughout the full lift or travel of the charge cycle valve 12 (valve). This implies that the height of the control sleeve 42 is somewhat greater than the sum of the valve lift plus the diameter of the through opening 40. Thus the only oil flow demand will be for replenishment due to leakage past clearances.

If a strategy requiring early valve closing is required, as for example in a Miller Cycle regime, and starting from a default position in which the through opening 40 is covered by the sleeve 42, it is necessary for the actuator 44 and the sleeve 42 to follow the cap 22 down during the valve lift event but stop at a height that corresponds to the desired valve closing point on the closing flank of the cam while the valve 12 and the cap 22 continue their preordained motion. As soon as the at least one through opening 40 is uncovered, the hydraulic link collapses and the valve (charge cycle valve 12) will close, which can be seen in Fig. 2. Fig. 2 shows a diagram 84 having a valve lift curve 86 showing the valve lift in relation to the rotation of the cam. Moreover, Fig. 2 shows a rotational position P of the cam, wherein at said rotational position P the sleeve 42 uncovers the through opening so that the hydraulic link is canceled or collapses. Moreover, the valve lift curve 86 illustrates the opening flank 88 of the cam and the closing flank 90 of the cam.

While it is typically required in a Miller Cycle regime to have the intake valve close early, i.e. before the beginning of the compression cycle, it is advantageous to arrest the valve closing velocity before full closure to protect components from impact damage and facilitate optimized closure time. However, if the flow area of the through opening 40 acting as a spill port in the cap 22 is sized to the appropriate closing velocity when the engine is operating at rated speed, then the through opening 40 will be progressively too large as engine speed reduces, leading to a faster than desired valve closure. Options to control valve seating velocity include appropriate sizing of the at least one through opening 40, and/or further movement of the actuator 44 and the sleeve 42 to arrest valve motion prior to final seating. The term final seating means that the charge cycle valve 12 fully reaches its closed position.

Early valve closing functionality is also useful for control of effective compression ratio during cold start. By closing the inlet valve during cold start at bottom dead center (BDC) instead of at around 30 degrees after BDC which is used for normal operation, a beneficial increase of typically one ratio over the geometric compression ratio becomes possible. Conversely, by moving the control sleeve 42 down immediately prior to cam lift, a late opening centered-lift valve event is obtained. This can be used to control air flow through the engine at part loads, which may be applicable for stoichiometric engines or where exhaust thermal management is required.

By moving the sleeve 42 down beyond the stroke range of the through opening 40 in the cap 22 just prior to the intended valve event, then it becomes possible to deactivate valve motion all together. Thus, cylinder deactivation is realized. Cylinder deactivation becomes possible when all valves for any one cylinder are deactivated and this can be a useful strategy at cruise or other partload conditions as a means to improve fuel efficiency. However, there is an oil flow parasitic loss involved, since each valve event will displace a small volume of hydraulic fluid.

Fig. 3 shows a diagram 92 showing multiple valve lift curves 94 illustrating early valve closing. Fig. 4 shows a diagram 96 illustrating a plurality of valve lift curves 98 illustrating centered lift with delayed valve opening. Moreover, Fig. 5 shows a diagram 100 illustrating a plurality of valve lift curves 102 illustrating centered lift with early valve closing.

The disclosed invention is applicable where the charge cycle valve 12 has a long exposed length of the valve stem 14 between the spring retainer 20 and the elephant's foot (actuating element 24), wherein said lost-motion mechanism -may be packaged in that space. The check valve 54 is a commodity lash adjuster non-return valve assembly. The class fits between the cap 22 and the valve stem 14 and between the cap 22 and the sleeve 42 can be realized in a particularly cost-effective way since said class fits are standard for the lash adjuster industry. For a long life and low friction, it is proposed that the cap 22 will receive a diamond like carbon (DLC) coating or similar. A cost reduction/value analysis may find that the adjuster screw assembly comprising the nut 69, the actuating element 28 and the elephant's foot (actuating element 24) might be able to be replaced with a non-adjustable press-fit peg with elephant's foot attached since the mechanism will be fully lash compensating. Rotational adjustment of control arms 46 relative to shaft 82 can be provided to equalize sleeve height relative to the through opening 40 across the plurality of charge cycle valves in any one engine so that uniformity of behavior is attained.

In the context of this disclosure, said lost-motion mechanism is one in which the driving member, being in this case the cam-driven rocker arm 32 always makes its assigned motion as determined by the cam profile which would normally be transferred directly to the charge cycle valve 12. In this disclosure, the lost-motion mechanism is interposed between the rocker arm 32 and the charge cycle valve 12 that under operator control is either able to transfer that unadulterated motion through the solid hydraulic link to the charge cycle valve 12, or is able to modify that motion statement by subtracting (but not adding to) that standard motion. This is achieved by allowing a controlled volume of hydraulic medium to escape from the hydraulic chamber 38 which is acting as a hydrauliclink.

List of reference signs valve train 12 charge cycle valve 14 valve stem 16 valve disc 18 spring spring retainer 22 cap 24 actuating element 26 receptacle 28 actuating element head 32 rocker arm 34 rocker shaft 36 rotation axis 38 hydraulic chamber through opening 42 sleeve 44 actuator 46 control arm 48 receptacle rotation axis 52 directional arrow 54 check valve 56 ball 58 cage 59 spring bias spring 62 feed opening 64 through opening 66 male thread 68 receptacle 69 nut head 72 duct 74 duct 76 duct 78 duct retaining means 82 control shaft 84 diagram 86 valve lift curves 88 opening flank closing flank 92 diagram 94 valve lift curves 96 diagram 98 valve lift curves diagram 102 valve lift curves P rotational position

Claims (7)

1. Claims 1. A valve train (10) for an internal combustion engine, the valve train (10) comprising: -at least one charge cycle valve (12) for a cylinder of the internal combustion engine, the charge cycle valve (12) comprising a valve stem (14); -a cap (22) slidably coupled to the valve stem (14), wherein the charge cycle valve (12) is actuatable via the valve stem (14) and the cap (22) by at least one actuating element (24); at least one hydraulic chamber (38) bounded at least partially by the valve stem (14) and the cap (22) which has at least one through opening (40) for discharging hydraulic medium from the hydraulic chamber (38); - at least one sleeve (42) slidably arranged on or around the cap (22), the sleeve (42) being slidable in relation to the cap (22) between at least one covering position in which the through opening (40) is occluded by the sleeve (42), and at least one release position in which the sleeve (42) uncovers the through opening (40); and - an actuator (44) configured to slide the sleeve (42) in relation to the cap (22) thereby varying the actuation of the charge cycle valve (12).
2. 2. The valve train (10) according to claim 1, wherein the cap (22) has at least one feed opening (62) for feeding hydraulic medium into the hydraulic chamber (38).
3. 3. The valve train (10) according to claim 2, wherein the valve train (10) comprises a check valve (54) having at least one closing element (56) configured to close the feed opening (62).
4. 4. The valve train (10) according to claim 3, wherein the check valve (54) comprises at least one spring (59) supported at least indirectly on the closing element (56) and at least indirectly on the valve stem (14).
5. 5. The valve train (10) according to claim 2 or 3, wherein the closing element (56) is arranged in the hydraulic chamber (38).
6. 6. The valve train (10) according to any one of the preceding claims, wherein the valve train (10) comprises a rocker arm (32) and the actuating element (24) connected to the rocker arm (32) at least indirectly so that the charge cycle valve (12) is actuatable via the valve stem (14), the cap (22), and the actuating element (24) by the rocker arm(32), wherein the rocker arm (32) and the actuating element (24) have respective ducts (72, 78) configured to supply the hydraulic chamber (38) with hydraulic medium.
7. 7. An internal combustion engine for a vehicle, the internal combustion engine having at least one valve train (10) according to any one of the preceding claims.