DE102015213627B3 - Hydraulic element with engine brake function for a four-stroke lift-piston internal combustion engine and four-stroke lift-piston combustion engine - Google Patents

Abstract

The invention relates to hydraulic element (1) with engine braking function for a four-stroke reciprocating internal combustion engine, which is arranged on at least one transmission element (5), such as a towing or rocker arm, a valve train of the four-stroke reciprocating internal combustion engine, wherein the transmission element (5) of a camshaft for actuating at least one exhaust valve a cylinder of the four-stroke reciprocating internal combustion engine is drivable by means of at least one outlet cam associated with the exhaust valve (3), and wherein the hydraulic element (1) has a lash adjuster (22) for compensating a valve clearance of the at least one exhaust valve. In this hydraulic element (1) according to the invention, a valve-controlled Leerhubelement (11) is present, which cooperates with the lash adjuster (22), wherein the Leerhubelement (11) is switchable between a no-lift for normal operation and a full stroke for engine braking operation, wherein in At least one brake cam lobe (8, 9) in the base circle (10) of the exhaust cam (3), separated from an exhaust cam lobe (3) 7), and in which a brake stroke of the exhaust valve is smaller than a maximum exhaust stroke of the exhaust valve.

Description

The invention relates to a hydraulic element with engine braking function for a four-stroke stroke piston internal combustion engine according to the preamble of patent claim 1 and a four-stroke stroke piston internal combustion engine according to the preamble of patent claim 7.

Hydraulic valve lash adjusters used in the valvetrain of reciprocating internal combustion engines operating at 4-stroke rates are widely known. The transmission elements or power transmission lever such as rocker arm, drag lever or plunger act on a camshaft, the gas exchange valves of the engine to open it. The gas exchange valves are closed by means of their valve springs. A defined movement of the valves according to a lift curve serves to ensure exact compliance with the gas exchange intervals in the cylinders or combustion chambers and thus ensures proper operation of the engine. The function of the automatic hydraulic lash adjusters in the power transmission between the camshaft and gas exchange valve is to ensure a valve play free and service-friendly operation.

Also known are wear-free endurance braking systems, which are mainly used in heavy-load traffic, in addition to a wear-prone service brake and a parking brake, and are also partially required by law. In addition to various hydrodynamic or electrodynamic retarders, which are based on a torque conversion to a drive shaft, so-called engine brakes, which act directly on the engine and ultimately convert drive energy into heat in order to achieve a permanent braking effect, are known in various embodiments. In addition to the braking effect, which is produced by a fuel cut in the withdrawal of the accelerator pedal, two different actively operable engine brake systems are common, especially in trucks. One of these systems is based on exhaust gas compression with deactivated or reduced combustion by means of an exhaust damper that is closed or partially closed to increase the braking torque of the engine.

Another engine braking system is based on a targeted decompression in the following on the compression or compression stroke work or expansion stroke, whereby the work stored in the compression stroke is at least partially lost to the drive. The desired compression loss (CR) in the expansion stroke can be achieved by selectively opening or partially opening the exhaust valve of the cylinder immediately before or during expansion, so that the work is not delivered to the crankshaft but escapes into the exhaust tract, causing throttle loss equivalent. This results in a higher braking torque of the engine. The increased pressure in the exhaust tract can also be used for an internal exhaust gas recirculation (BGR), wherein in the intake stroke of the cylinder following in the engine cycle with open inlet valve and deactivated fuel injection, the exhaust valve is opened again to inflate the gas filling of the follower cylinder the brake torque increase can be increased again. Furthermore, engine braking systems are known, the combinations of damper brakes and decompression brakes, possibly including the inclusion of the supercharger of a turbocharger use. When decompression brakes are used, a possible interaction between the control of the exhaust valves and the counter-pressure arising over the exhaust tract on the one hand and the actual function of the valve lash adjusters of the valve drive on the other hand must be taken into account. The cost of additional components, space and cost of known engine braking systems is often very high.

From the DE 10 2010 011 455 A1 is a working according to the 4-stroke method reciprocating internal combustion engine, in which an engine brake by temporarily opening one or more exhaust valves is switchable. For this purpose, the reciprocating internal combustion engine has a camshaft, in which at least one additional cam is formed in the base circle of an exhaust cam. Between a rocker arm and one or more exhaust valves, an automatically pressure-building Aufpumpelement is arranged, which has the components of a hydraulic valve clearance compensation element. These are a working piston, which is in operative connection with an outlet valve or a bridge with a plurality of outlet valves, a housing which is installed in the rocker arm, the working piston leads and forms with this a pressure chamber, a check valve, which is arranged on a valve piston and controls the pressure chamber and a built-in between the valve piston and the working piston return spring which loads the working piston in the direction of the exhaust valve. In addition to these components, a control piston is arranged, which adjoins the valve piston and the check valve and is loaded by a piston which is supported on the housing in the direction of the valve piston. The control piston is loaded on the one hand in the valve opening direction with the control piston spring and on the other hand counteracted by an opening of the valve produced by the spring with pressurized oil acted upon. This inflating element is controllable in its length via the oil pressure. At an elevated oil pressure that closes Valve counter to the spring force of the control piston spring, so that can extend by a pressure build-up in the pressure chamber of the working piston and the additional cam is effective and thereby an engine braking operation with decompression and / or internal exhaust gas recirculation is turned on. At a reduced oil pressure, however, the valve opens by the control piston spring, so that by a pressure reduction in the pressure chamber of the working piston can retract and the additional cam in normal operation, ie in pure engine operation is ineffective, with an uncontrolled play in the cam base circle is prevented by the return spring. To set the valve clearance, a spacer is interposed between the working piston of the inflating and the exhaust valve, which is selected in each case from a plurality of graded in height spacers and fitting installed or replaced.

From the pamphlets DE 10 2008 039 504 A1 . DE 10 2007 051 302 A1 and DE 10 2007 014 248 A1 generic reciprocating internal combustion engines are known with an engine brake having hydraulic valve clearance compensation elements with an actuable locking or stop device. By blocking or stop device, which is executed differently in the cited documents, prevents the hydraulic valve clearance compensation element in an engine braking operation, in which one or more exhaust valves are partially opened in a cam base, undesirably expands, so adjusts or inflates , This should in particular prevent unwanted open the exhaust valves after the end of the engine braking operation and increased mechanical stress on the valve train components by a possible negative valve clearance.

The DE 10 2008 031 765 A1 proposes for this purpose, instead of a mechanical locking of a hydraulic valve clearance compensation element, to generate a hydraulic holding force in the valve lash adjuster when the engine brake is activated, which counteracts the undesired adjusting force of the lash adjuster element.

Finally, out of the US 2013/0 319 370 A1 a mounted on a pivot axis rocker arm for an internal combustion engine, which is deflectable at one axial end by means of a camshaft, and which acts with its other axial side via a multi-part bridge element on two exhaust valves of the internal combustion engine. In addition to a base circle, the camshaft has a large cam lobe and two small cam lobes. The large cam lobe controls the actuation of the exhaust valves in normal operation and the two smaller cam lobes serve only a small and short-term operation of the exhaust valves during a switchable engine braking operation. A disadvantage of this rocker arm is that several components are arranged in the longer lever arm, including a valve lash adjuster, and that other components that enable the switching on and off of the engine braking operation, are arranged in said bridge element. As a result, the rocker arm adversely on a relatively high moving mass, and the mechanism for switching on and off of the engine braking operation is very complex and thus prone to failure and expensive to manufacture.

Against this background, the object of the invention is to provide a further developed hydraulic element with a switchable engine braking function for a reciprocating internal combustion engine based on a temporary opening of one or more exhaust valves, which is inexpensive, space-saving and easily adaptable to an existing valve drive. In addition, it should at the same time have the unrestricted function of a hydraulic valve lash adjuster within and outside of the engine brake operation while avoiding unwanted readjustment. A further object is to present a reciprocating internal combustion engine for motor vehicles, in particular for commercial vehicles, with an improved hydraulically switchable engine brake device.

The invention is based on the finding that a decompression brake and / or a brake gas recirculation brake for a reciprocating internal combustion engine operating according to the 4-stroke method can be controlled by means of a valve train, in which the exhaust cams which actuate the exhaust valves during the charge cycle of the cylinder, additional in the cam base circle Surveys. The control can take place by means of the exhaust valves respectively associated, switchable hydraulic elements, in the hydraulic control of the decompression brake and / or a brake gas recirculation brake is activated or deactivated. Such a hydraulic element can be constructed by a modification and expansion of a hydraulic valve lash adjuster, as it is usually installed in the valve train, with a hydraulically switchable, valveless similar second assembly to a hydraulic element, the functions of a lash adjuster and a hydraulically controllable switching element for activating the engine brake in united.

The invention is therefore based on a hydraulic element with engine braking function for a four-stroke stroke-piston internal combustion engine, to which at least one transmission element, such as a drag or rocker arm, a valve drive of the four-stroke reciprocating internal combustion engine is pivotally supported, wherein the transmission element of a camshaft for actuating at least one exhaust valve of a cylinder of the four-stroke reciprocating internal combustion engine by means of at least one exhaust valve associated exhaust cam is drivable, and wherein the hydraulic element has a lash adjuster for compensating a valve clearance of the at least one exhaust valve ,

To achieve the object, the invention also provides that in the hydraulic element, a valve-controlled Leerhubelement is arranged, which cooperates with the valve lash adjuster, that the Leerhubelement and the valve lash adjuster are axially movably guided in a pot-shaped cylinder housing and arranged one behind the other, and that wherein the Leerhubelement between a Leerhub for normal operation and a full stroke for an engine braking operation, wherein in the engine braking operation by the exhaust cam Bremshubkurve on the exhaust valve to an additional opening of the exhaust valve is transferable, wherein for generating the Bremshubkurve at least one brake cam lobe in the base circle of the exhaust cam, separated from an exhaust cam lobe, and wherein a brake stroke of the exhaust valve is smaller than a maximum exhaust stroke of the exhaust valve.

The arrangement of the Leerhubelements and the valve clearance compensation element in a single pot-shaped cylinder housing a very compact and only comparatively few components exhibiting hydraulic element is provided by means of a towing or rocker arm is pivotally mounted, which allows a valve clearance compensation, and switching on and off of an engine braking function allowed.

An engine braking function of a hydraulic element is understood to mean a shiftable function of a hydraulic element which in an internal combustion engine leads in one or more of the four engine cycles to the additional temporary opening of one or more of the exhaust valves of one or more cylinders operated by a camshaft and by the request of an operator , in particular a driver in a passenger compartment, can be activated and deactivated.

Normal operation is understood to mean engine operation in which this engine braking function is deactivated. In particular, this is understood to mean a normal driving operation of a motor vehicle when the internal combustion engine is fired.

Accordingly, the invention proposes a modified hydraulic valve clearance compensation element with a controllable braking function by means of a Leerhubelements, which is activated or deactivated by switching between a no-lift in a normal operation or driving and a full stroke in an engine braking operation. This is achieved by a hydraulic element, in which both the valve clearance compensation and the transmission of a Bremshubkurve valve-controlled. The arrangement is particularly compact compared to known engine brake systems and requires relatively few components. In particular, no spacers or the like are needed to set a valve clearance; Likewise, no elaborate locking devices for a switchable locking of the valve clearance compensation element are required. As a further advantage, it has surprisingly been found that by means of the Leerhubelements very short switching times for the change between driving and engine braking operation can be achieved.

The engine braking function is achieved in that in the base circle of the exhaust cam of the camshaft, in addition to the usual ejection stroke for the exhaust stroke for expelling the exhaust gas from the cylinder at least one further cam lobe for a brake stroke of the exhaust valve is formed. This additional stroke allows the movement of the exhaust valve required for the brake function. However, the maximum elevation of the brake stroke is significantly less than the cam lift for the maximum exhaust stroke of the exhaust valve. The exhaust valve is thus not fully opened by the brake stroke. The positioning of the cam lobes on the exhaust cam is coordinated with the four strokes of the engine intake, compression, expansion, ejection. Accordingly, during braking operation, with the fuel injection deactivated, the exhaust valves are each partially opened in at least one further cycle in addition to the exhaust stroke in order to achieve an internal braking effect in the engine.

To activate the braking function, the idle-stroke element is switched so that the idle-stroke function is inactive, ie no idle stroke but a full-stroke is performed. The full stroke causes the transmission element, such as a drag lever, when passing the exhaust cam transmits both the exhaust cam lobe and the brake cam lobe on the exhaust valve. The circuit of this braking operation via a hydraulic actuation of the Leerhubelements by means of an application of a separate switching oil connection with pressure oil via a control line which supplies the switching oil. The control line is in communication or in operative connection with an actuating unit which can be operated, for example, in a passenger compartment of a commercial vehicle and which transmits the driver's request in a corresponding switching operation.

When driving, so when the engine is fired, the additional brake stroke is not needed and must be necessarily disabled, otherwise malfunctions and damage to the engine could occur. This is done according to the invention in that the Leerhubelement is turned on, so that the idle stroke is active. The idle stroke is limited and causes the transmission element to transfer the exhaust cam lobe when passing the exhaust cam, but not the much smaller brake cam lobe to the exhaust valve. The circuit of the driving operation via a hydraulic actuation of the Leerhubelements by means of a removal of the hydraulic pressure at the switching oil connection. Regardless of the operation of the Leerhubelements the valve clearance compensation function in both modes of operation remains in full, so with a continuous clearance compensation, but avoiding unwanted readjustment or inflation obtained.

According to a preferred embodiment of the invention may be provided according to the features of claim 2 that the Leerhubelement has a Leerhubkolben and a control piston, the Leerhubkolben is operatively connected as working piston with the exhaust valve and having an axial bore, wherein the axial bore is dominated by a Leerhubrückschlagventil wherein the Leerhubrückschlagventil is hydraulically actuated via a switching oil connection and biased in the closing direction of a spring, the Schaltkolbenradial is axially movable within the Leerhubkolbens and forms a switching oil space with the Leerhubkolben, the Leerhubrückschlagventil hydraulically separates the switching oil chamber and the switching oil connection in the closed position and hydraulically interconnected in the open position, wherein the valve lash adjuster comprises a differential piston and a balance piston, wherein the differential piston to axially adjoins the Leerhubkolben, wherein the balance piston is guided axially movable axially within the differential piston and having an oil reservoir, which is connected to a pressure oil connection and controlled by a Ausgleichsrückschlagventil, wherein the compensating check valve in the closing direction of a spring, wherein the balance piston with the differential piston and the cylinder housing forms a high-pressure chamber, wherein the compensating check valve hydraulically separates the oil reservoir and the high-pressure chamber from each other in the closed position and hydraulically connected in the open position, wherein in the high pressure space between the differential piston and the cylinder housing, a return spring is installed, which loads the differential piston in the direction of the exhaust valve, and wherein in the oil reservoir between the balance piston and the axially adjoining this switching piston a Leerhubfeder is installed, located at the Ausgle ichskolben and the control piston is supported, wherein a travel of the control piston is limited in the direction of the valve clearance compensation element by an axial stop on the differential piston, and in which a travel of the balance piston in the direction of Leerhubelements is limited by an axial stop on the control piston.

Accordingly, the arrangement essentially comprises a pot-shaped housing, four mutually or axially relative to each other axially movable pistons, two central helical compression springs and two spring-biased in the closing direction check valves, these components interact at least partially with each other.

To switch on the brake function of the switching pressure is activated, whereupon the Leerhubrückschlagventil opens by overcoming its spring preload and the switching piston of the Leerhubelements moves in the direction of the balance piston of the valve lash adjuster until it rests on the stop of the differential piston of the valve lash adjuster. At the same time, the compensating piston is pretensioned via the central idle stroke spring and thus fixed in its position. Under load, the pressure in the switching oil chamber increases and closes the idle-stroke check valve, since the oil pressure and the spring force together exceed the pressure at the switching oil connection. The high pressure space of the lash adjuster is also under pressure. The balance check valve is closed. The differential piston does not sink. The idle stroke now acts as a rigid plunger with the result that the contour of the brake cam elevation of the exhaust cam of the camshaft via the transmission element is transmitted directly as a movement to the associated exhaust valve. The default total cam profile of the exhaust cam, including the brake stroke, is fully reproduced.

To switch off the brake function or to switch on the driving function of the switching pressure is deactivated, after which the Leerhubfeder presses the balance piston and the control piston apart. This creates an additional free volume in the oil reservoir of the valve clearance compensation element. When the hydraulic element is now under load due to a cam lift, the high-pressure space of the valve lash adjuster comes under hydraulic tension. The compensating piston is thereby forced displaced until it reaches its stop on the control piston. By the displacement of the balance piston is a additional volume released in the high-pressure chamber of the lash adjuster element. The hydraulic tension in the high pressure chamber is thus compensated by the evasive movement of the balance piston. The hydraulic element thus completes a limited idle stroke and gives way to the load. This limited idle stroke is designed for the brake cam lobe and is used to hide the brake cam lobe and not to transfer to the exhaust valve. The exhaust cam lobe beyond the idle stroke, on the other hand, is transferred to the exhaust valve due to the limitation of the idle stroke.

When clearance compensation after a further rotation of the cam in its base circle outside the cam lobes, the return spring pushes apart the differential piston and the cylinder housing so that the hydraulic element extends axially until the valve clearance is balanced, via the compensating check valve differential pressure hydraulic fluid between the (oil reservoir and the high pressure chamber the lash adjuster flows.

In addition, it can be provided that on the valve play compensation element facing bottom of the control piston an annular surface-shaped increase is formed, in which the switch piston end of the Leerhubfeder is added and which is also effective as a stop for the balance piston. As a result, a secure fixation of the Leerhubfeder is achieved and shown a simple travel limit for the balance piston. The annular increase as a stop and spring mount also allows a large hydraulic effective area of the control piston.

Furthermore, it can be provided that the Leerhubseitige axial end of the differential piston and the compensation-side axial end of Leerhubkolbens abut each other flat, wherein the axial end of the differential piston at the same time as a stop ( 36 ) is effective for the switching piston. As a result, a homogeneous force transmission is ensured between the differential piston and the idle stroke piston, so that the two pistons can always be moved smoothly in the cylinder housing.

According to a further embodiment of the invention can be provided that in the base circle of the exhaust cam two Bremsnockenerhebungen are formed, wherein a first brake cam lobe for generating a Dekompressionshubs in the expansion stroke and a second brake cam lobe for generating a Abgasrückführungshubs are formed in the intake stroke of the four-stroke reciprocating internal combustion engine.

Accordingly, in engine braking operation, two additional strokes of the exhaust valve may occur. The CR (Compression Release) stroke serves to destroy the expansion work of the engine and thus to escape the drive. The BGR (brake gas recirculation) stroke is used to use the increased pressure during the braking operation in the exhaust tract of the engine to an inflated filling of the next following in the engine cycle next cylinder when sucking to increase the braking performance of the engine. By switching the idle stroke element, the hydraulic element according to the invention can transmit a lift curve with two elevations in the base circle of the exhaust cam coordinated for the engine cycles for both engine brake operating modes.

It can also be provided that between the outer circumferential surface of the differential piston and the inner wall of the cylinder housing and between the outer lateral surface of the Leerhubkolbens and the inner wall of the cylinder housing, a leakage gap is formed, which causes a sinking of the Leerhubkolbens and the differential piston in the cylinder housing under load such that a maximum exhaust stroke of the exhaust valve during engine braking operation is less than a maximum exhaust stroke of the exhaust valve in normal operation.

When the support element, that is to say the idling piston in the cylinder housing, sinks due to a cam lift, the axial distance between the differential piston and the cylinder housing is shortened, with a small amount of hydraulic fluid escaping from the high pressure chamber of the valve play compensation element via a leakage gap in the direction of the oil reservoir. This leakage gap can be specifically dimensioned so that in braking mode, ie without the pressure of the compensating piston during the idle stroke, the maximum valve lift of the exhaust valve, so the tip of the exhaust cam is quasi hidden and is not transmitted to the exhaust valve. The lift curve is slightly flattened in this area. Thereby, the thermal load of the particularly stressed valve components such as valve seat inserts and valve disc, which may be increased in the engine braking operation by the multiple opening and closing of the exhaust valve within the four engine cycles can be reduced.

The invention also relates to a four-stroke reciprocating internal combustion engine in which the exhaust valves of the cylinders are operable via transmission elements such as towing or rocker arms driven by one or more camshafts in normal operation and engine braking operation, and in which the transmission elements are each on a hydraulic element are pivotally mounted.

In this internal combustion engine is provided according to the invention that in the respective hydraulic element, a valve-controlled Leerhubelement and a valve lash adjuster are arranged in combination, and that the Leerhubelement and the valve lash adjuster are axially movably guided in a pot-shaped cylinder housing and arranged one behind the other, wherein the Leerhubelement between an idle stroke for a normal operation and a full lift for an engine braking operation is switchable, wherein in the engine braking operation by an exhaust cam a Bremshubkurve is transferable to an exhaust valve to an additional opening of the exhaust valve, wherein for generating the Bremshubkurve at least one brake cam lobe in the base circle of the exhaust cam, separated from a discharge cam lobe, is arranged, wherein the braking stroke of the exhaust valve is smaller than a maximum exhaust stroke of the exhaust valve.

The invention will be explained in more detail below with reference to an exemplary embodiment shown in the attached drawing. In the drawing shows

1 an overview of a hydraulic element according to the invention together with a cam follower and an exhaust cam of a camshaft,

2 the hydraulic element according to 1 in an enlarged section in a longitudinal section,

3 the hydraulic element according to 2 in normal operation in a first operating position (a) and in a second operating position (b), and

4 the hydraulic element according to 2 in engine braking mode in the first operating position (a) and in three other operating positions (c), (d), (e).

1 shows therefore designed as a finger lever transmission element 5 a valve train of a working according to the 4-stroke method reciprocating internal combustion engine in the embodiment of a roller finger follower. The transmission element 5 has in a conventional manner a roller bearing roller cam roller 2 for the installation of an exhaust cam 3 a camshaft, not shown. At one end of the transmission element 5 is an inward facing dome 4 for movably receiving a ball head 21 a hydraulic element 1 formed according to the invention, wherein the transmission element 5 recognizable on the ball head 21 of the hydraulic element 1 supported. At its other axial end which has the transmission element 5 a contact surface 6 for a plunger of an exhaust valve, not shown, of a cylinder of the reciprocating internal combustion engine. The plunger of the exhaust valve is due to the drainage movement of the exhaust cam 3 on the cam roller 2 actuates and executes a movement according to a lift curve corresponding to the cam profile of the exhaust cam 3 ,

The exhaust cam 3 points next to a discharge cam lobe 7 two more cam lobes 8th . 9 extending from a cam base circle 10 raise radially outward. The exhaust cam lobe 7 serves for the complete opening of the exhaust valve in the exhaust stroke. The two other cam lobes 8th . 9 In addition, the exhaust valve can partially open. They are for transmitting a Bremshubkurve for the movement of the valve stem as a CR brake cam lobe 8th for a decompression outlet in the expansion stroke and as a GR brake cam lobe 9 formed for an internal exhaust gas recirculation for pre-charging in the intake stroke. As a result of the additional opening of the exhaust valve outside the exhaust stroke, an internal braking torque is generated and amplified in the engine.

The valve train has a plurality of such units of cams 3 , Cam followers 1 and hydraulic elements 1 as in 1 shown on. In the following, such a hydraulic element 1 described in more detail. About the hydraulic element 1 the Bremshubkurve can be switched for a movement of the valve lifter to activate the engine braking operation. Otherwise, the two flat additional cam lobes 8th and 9 over a Leerhub hydraulic element 1 not effective for the movement of the valve stem.

2 shows the structure of the hydraulic element 1 in detail. Accordingly, the hydraulic element 1 a Leerhubelement 11 and a lash adjuster 22 on, in a pot-shaped cylinder housing 23 guided axially movable and arranged axially one behind the other. The idle stroke element 11 includes a Leerhubkolben 12 and a control piston 13 , The idle piston 12 has at its towing lever side upper end a ball head 21 ( 1 ), with whom he is in the dome 4 of the rocker arm 5 is received approximately form-fitting and mutually movable, and he is working piston of the hydraulic element 1 effective.

The idle piston 12 also has a central axial bore 14 on, which has a sloping radial bore 15 with a switching oil connection 16 on the cylinder housing 23 hydraulically connected. At its lower end is the Leerhubkolben 12 cup-shaped and limited with the radially and axially received in it control piston 13 a switching oil space 17 , In the switching oil dream 17 is a Leerhubrückschlagventil 18 arranged, whose designed as a ball valve body 19 from a valve cap 20 at the Leerhubkolben 12 is held and in the direction of a valve seat on the axial bore 14 by means of a spring 18a is biased so that the Leerhubrückschlagventil 18 the axial bore 14 normally closes. The control piston 13 is in the idle stroke piston 12 axially movable, so that the volume of the switching oil space 17 is variable.

The valve clearance compensation element 22 has a differential piston 24 and a balance piston 25 on, which are formed as a hollow cylinder, wherein the balance piston 25 radially in the differential piston 24 is arranged axially movable. In the balance piston 25 is an oil storage room 26 trained, with a pressure oil connection 32 is connected, and an axial bore 27 that is from a compensating check valve 28 is mastered. The balancing check valve 28 is essentially identical to the Leerhubrückschlagventil 18 , Its trained as a ball valve body 29 is from a valve cap 30 on balance piston 25 held and is in the direction of a valve seat on the axial bore 27 of the oil storage room 26 from a spring 28a biased, causing the pantry 26 usually from a high pressure room 31 hydraulically isolated. This high pressure room 31 is from the balance piston 25 , the differential piston 24 and the cylinder housing 23 educated. In the open position of the compensating check valve 28 , after a hydraulic overcoming the spring preload, are the pantry 26 and the high pressure room 31 hydraulically connected to each other.

In the high pressure room 31 between the differential piston 24 and the cylinder housing 23 is formed as a helical compression spring return spring 33 installed, which is the differential piston 24 and by this at the same time the Leerhubkolben 12 loaded in the direction of the exhaust valve to compensate for an existing valve clearance.

The differential piston 24 and the Leerhubkolben 12 lie with their mutually facing axial ends flat against each other, due to a smaller wall thickness of the Leerhubkolbens 12 a free end surface 36 remains. This free end surface 36 is as a limit of the travel s ( 4 ) of the switching piston 13 in the direction of the valve clearance compensation element 22 effective.

In the oil storage room 26 is between the balance piston 25 and the control piston 13 designed as a helical compression spring Leerhubfeder 34 installed, which are axially on balance piston 25 and the control piston 13 supported. The Leerhubfeder 34 is with her schaltkolbenseitigen end in an annular surface elevation 35 of the control piston 13 added. This increase 35 is simultaneously as a stop for limiting a travel of the balance piston 25 in the direction of the Leerhubelement 11 effective.

3 shows two operating states (a) and (b) of the hydraulic element 1 in normal operation, ie without engine braking function. In the left illustration (a) is the hydraulic element 1 not under load, so without Nockenbeaufschlagung. The Leerhubfeder 34 presses the balance piston 25 and the control piston 13 axially apart. The Leerhubrückschlagventil 18 is closed. The idle stroke of the Leerhubelements 11 is aviable. The valve clearance compensation element 22 ensures play-free operation in the mechanical transmission chain to the outlet valve.

In right representation (b) of 3 is the hydraulic element 1 under load by cam loading a CR brake cam lobe 8th or a BGR brake cam lift 9 ( 1 ). The hydraulic element 1 thereby sinks into the cylinder housing 23 and makes an idle stroke. The cam application by the brake cam lobe 8th . 9 is hidden, so the outlet valve is therefore not operated. This is possible because the balance piston 25 performs a counter-movement to the volume of the pressurized high-pressure chamber 31 to enlarge. As soon as the balance piston 25 and the control piston 13 in their opposite movement at the stop 35 Touch each other, another Leerhubbewegung is locked. Another pressure increase due to the increase of the cam profile of the exhaust cam 3 in the area of the exhaust cam lobe 7 is thus not compensated. The Leerhubbegrenzung is therefore designed so that the brake cam lobe 8th . 9 is completely ineffective for a movement of the valve plunger, and that is the part beyond the ejection cam lobe 7 causes a movement of the plunger of the exhaust valve. With a reduction of the load in the area of the cam base circle 10 pushes the Leerhubfeder 34 the balance piston 25 and the control piston 13 again axially apart and the return spring 33 moves the hydraulic element 1 again axially apart.

The 4 shows three further operating states (c), (d), (e) of the hydraulic element 1 to illustrate the switchable engine braking function. For comparison, the first illustration on the left in the direction of view shows the already explained operating state (a) during normal operation when the idle stroke function is active. In the next operating state (c), the brake function is switched on. The switching oil connection 16 is subjected to a switching oil pressure P_Schalt, wherein the switching oil pressure P_Schalt much greater than the pressure P_HLA (Hydraulic Lash Adjuster) at the pressure port 32 of the oil storage room 26 of the valve clearance compensation element 22 is. This opens the Leerhubrückschlagventil 18 and the control piston 13 moves by the hydraulic actuation a travel s in the direction of the differential piston 24 until he is on the differential piston 24 at the stop 36 seated. The balance piston 25 is doing by the Leerhubfeder 34 biased and is thus fixed in its axial position. The engine braking function is now available.

Will the hydraulic element 1 now by a brake cam lift 8th . 9 loaded, as shown in the subsequent operating state (d), the pressure in the switching oil chamber increases 17 and the Leerhubrückschlagventil 18 closes. The pressure in the high pressure room 31 of the valve clearance compensation element 22 Also increases, with the balancing check valve 28 closed is. This will cause the differential piston to sink 24 prevents, with the result that the hydraulic element 1 now works as a rigid plunger, with a full stroke of Leerhubelements 11 acts, the cam profile including the brake cam lobe 8th . 9 on the plunger transfers the exhaust valve as an actuating movement. As a result, this exhaust valve opens in accordance with the lift curve in the relevant engine cycles in addition and the engine braking device is thus active. Under load, a small amount of oil from the high-pressure chamber 31 over a leakage gap 37 escape (operating state (s)). This leads to a slight drop in the hydraulic element 1 , To deactivate the engine braking function, the switching pressure P_Schalt is switched off again, whereupon the hydraulic element 1 returns to idle mode.

LIST OF REFERENCE NUMBERS

1

hydraulic element

2

Cam nose role

3

exhaust

4

dome

5

Transmission element, drag lever

6

contact surface

7

Output cam lobe

8th

Brake cam lobe

9

Cam base circle

10

Brake cam lobe

11

Leerhubelement

12

idle stroke piston

13

switching piston

14

axial bore

15

radial bore

16

Switching oil port

17

Switching oil space

18

Leerhubrückschlagventil

18a

Spring of Leerhubrückschlagventils

19

valve body

20

valve cap

21

ball head

22

Lash adjuster

23

cylinder housing

24

differential piston

25

balance piston

26

Oil reservoir

27

axial bore

28

Compensating check valve

28a

Spring of the compensation check valve

29

valve body

30

valve cap

31

High-pressure chamber

32

Pressure oil connection

33

Return spring

34

Leerhubfeder

35

Balancing piston stop, control piston increase

36

Switching piston stop, differential piston end face

37

leakage gap

P_HLA

Valve clearance compensation pressure

P_Schalt

Oil pressure switch

s

Schaltkolbenstellweg

Claims (7)

Hydraulic element ( 1 ) with engine braking function for a four-stroke, reciprocating internal combustion engine, to which at least one transmission element ( 5 ), such as a towing or rocker arm, a valve train of the four-stroke Hubkolbenbrennkraftmaschine pivotally supported, wherein the transmission element ( 5 ) of a camshaft for actuating at least one exhaust valve of a cylinder of the four-stroke stroke-piston internal combustion engine by means of at least one outlet cam associated with the exhaust valve (US Pat. 3 ) is drivable, and wherein the hydraulic element ( 1 ) a valve clearance compensation element ( 22 ) for compensating a valve clearance of the at least one exhaust valve, characterized in that in the hydraulic element ( 1 ) a valve-controlled Leerhubelement ( 11 ) is arranged, which with the lash adjuster ( 22 ) cooperates, that the Leerhubelement ( 11 ) and the valve clearance compensation element ( 22 ) in a pot-shaped cylinder housing ( 23 ) are guided axially movable and arranged one behind the other, and that the Leerhubelement ( 11 ) is switchable between an idle stroke for a normal operation and a full stroke for an engine braking operation, wherein in the engine brake operation by the exhaust cam ( 3 ) a Bremshubkurve to the exhaust valve to an additional opening of the exhaust valve is transferable, wherein for generating the Bremshubkurve at least one brake cam lobe ( 8th . 9 ) in the base circle ( 10 ) of the exhaust cam ( 3 ), separated from an exhaust cam lobe ( 7 ), and wherein a brake stroke of the exhaust valve is smaller than a maximum exhaust stroke of the exhaust valve. Hydraulic element according to claim 1, characterized in that the Leerhubelement ( 11 ) a Leerhubkolben ( 12 ) and a control piston ( 13 ), wherein the Leerhubkolben ( 12 ) is in operative connection as a working piston with the outlet valve and an axial bore ( 14 ), wherein the axial bore ( 14 ) of a Leerhubrückschlagventil ( 18 ), wherein the Leerhubrückschlagventil ( 18 ) via a switching oil connection ( 16 ) hydraulically actuated and in the closing direction of a spring ( 18a ) is biased, wherein the control piston ( 13 ) radially within the Leerhubkolbens ( 12 ) is guided axially movable and with the Leerhubkolben ( 12 ) a switching oil space ( 17 ), wherein the Leerhubrückschlagventil ( 18 ) the switching oil space ( 17 ) and the switching oil connection ( 16 ) hydraulically separated in the closed position and hydraulically connected together in the open position, wherein the valve clearance compensation element ( 22 ) a differential piston ( 24 ) and a balance piston ( 25 ), wherein the differential piston ( 24 ) to the Leerhubkolben ( 12 ) axially adjoins, wherein the balance piston ( 25 ) radially inside the differential piston ( 24 ) is guided axially movable and an oil reservoir ( 26 ) which is connected to a pressure oil connection ( 32 ) and a compensating check valve ( 28 ), wherein the compensating check valve ( 28 ) in the closing direction of a spring ( 28a ), wherein the balance piston ( 25 ) with the differential piston ( 24 ) and the cylinder housing ( 23 ) a high pressure room ( 31 ), wherein the compensating check valve ( 28 ) the oil reservoir ( 26 ) and the high-pressure space ( 31 ) hydraulically separated from each other in the closed position and hydraulically connected in the open position, wherein in the high-pressure chamber ( 31 ) between the differential piston ( 24 ) and the cylinder housing ( 23 ) a return spring ( 33 ) is installed, which the differential piston ( 24 ) is loaded in the direction of the outlet valve, and wherein in the oil reservoir ( 26 ) between the balance piston ( 25 ) and at this axially adjoining control piston ( 13 ) a Leerhubfeder ( 34 ), which is located on the balance piston ( 25 ) and the control piston ( 13 ) is supported, wherein a travel (s) of the control piston ( 13 ) in the direction of the valve clearance compensation element ( 22 ) by an axial stop ( 36 ) on the differential piston ( 24 ) is limited, and in which a travel of the balance piston ( 25 ) in the direction of the Leerhubelements ( 11 ) by an axial stop ( 35 ) on the control piston ( 13 ) is limited. Hydraulic element according to claim 1 or 2, characterized in that on the the valve clearance compensation element ( 22 ) facing the underside of the control piston ( 13 ) an annular surface-shaped elevation is formed, in which the switching piston-side end of the Leerhubfeder ( 34 ) and at the same time as a stop ( 35 ) for the balance piston ( 25 ) is effective. Hydraulic element according to one of claims 2 to 3, characterized in that the leerhubseitige axial end of the differential piston ( 24 ) and the compensation-side axial end of Leerhubkolbens ( 12 ) lie flat against each other, wherein the axial end of the differential piston ( 24 ) as a stop ( 36 ) for the control piston ( 13 ) is effective. Hydraulic element according to one of claims 1 to 4, characterized in that in the base circle ( 10 ) of the exhaust cam ( 3 ), separated from the exhaust cam lobe ( 7 ), two brake cam lobes ( 8th . 9 ), wherein a first brake cam lobe ( 8th ) for generating a decompression stroke in the expansion stroke and a second brake cam lobe ( 9 ) is configured to generate an exhaust gas recirculation stroke in the intake stroke of the four-stroke stroke reciprocating internal combustion engine. Hydraulic element according to one of claims 2 to 5, characterized in that between the outer circumferential surface of the differential piston ( 24 ) and the inner wall of the cylinder housing ( 23 ) and between the outer circumferential surface of the Leerhubkolbens ( 12 ) and the inner wall of the cylinder housing ( 23 ) a leakage gap ( 37 ) is formed, the sinking of Leerhubkolbens ( 12 ) and the differential piston ( 24 ) in the cylinder housing ( 23 ) under load such that a maximum exhaust stroke of the exhaust valve during engine braking operation is less than a maximum exhaust stroke of the exhaust valve in normal operation. Four-stroke reciprocating internal combustion engine, in which the exhaust valves of the cylinders by means of transmission elements ( 5 ), such as towing or rocker arms, which are drivable by one or more camshafts, are operable in a normal operation and in an engine braking mode, and in which the transmission elements ( 5 ) on each hydraulic element ( 1 ) are pivotally mounted, characterized in that in the respective hydraulic element ( 1 ) a valve-controlled Leerhubelement ( 11 ) and a valve clearance compensation element ( 22 ) are arranged in combination, and that the Leerhubelement ( 11 ) and the valve clearance compensation element ( 22 ) in a pot-shaped cylinder housing ( 23 ) are guided axially movable and arranged one behind the other, wherein the Leerhubelement ( 11 ) is switchable between an idle stroke for a normal operation and a full stroke for an engine brake operation, wherein in the engine brake operation by an exhaust cam ( 3 ) a Bremshubkurve is transferable to an exhaust valve to an additional opening of the exhaust valve, wherein for generating the Bremshubkurve at least one brake cam lobe ( 8th . 9 ) in the base circle of the exhaust cam, separated from a discharge cam lobe ( 7 ), is arranged, and wherein the brake stroke of the exhaust valve is smaller than a maximum exhaust stroke of the exhaust valve.

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