Patent Application
20190072009
The present disclosure relates to a sliding cam system for an internal combustion engine.
Valve-controlled internal combustion engines have one or more controllable inlet and outlet valves per cylinder. Variable valve control mechanisms make flexible actuation of the valves possible in order to change the opening time, closing time and/or the valve lift. As a result, the engine operation can be adapted, for example, to a specific load situation.
A variable valve train can be configured, for example, as a sliding cam system. A sliding cam system can have a plurality of cam carriers with a plurality of cams. The cam carriers are arranged fixedly on the camshaft so as to rotate with it and in an axially displaceable manner. The cam carriers can be displaced axially via actuators. A transmission apparatus, for example a rocker arm, sets one cam of the plurality of cams of the cam carrier in an operative connection with at least one gas exchange valve in a manner which is dependent on an axial position of the cam carrier. The cam carrier can be displaced axially in order to change a valve control curve of the at least one gas exchange valve, with the result that another cam of the cam carrier passes into engagement with the transmission apparatus. One example for a sliding cam system is disclosed in WO 2004/083611 A1.
EP 0 798 451 A1 has likewise disclosed a valve train with a sliding cam system. An actuating element is provided for displacing a cam with three cam tracks which lie axially next to one another. The actuation of the actuating element can take place pneumatically.
One disadvantage of known sliding cam systems frequently lies in the complex control system of the actuator apparatuses for displacing the cam carriers or cams with a plurality of cam tracks.
DE 10 2010 025 099 A1 discloses an adjustable camshaft, having at least one shaft, and having at least one cam pack which has at least two different cams and/or cam contours. The cam pack can be displaced axially on the shaft. An adjusting element is provided in the shaft, which adjusting element can be displaced at least axially relative to a longitudinal axis of the shaft. The adjusting element is coupled mechanically to the cam pack via a contact element. For example, at least two of the cam packs can be coupled mechanically to the adjusting element.
The present disclosure is based on the object of providing an alternative or improved sliding cam system which overcomes disadvantages in the prior art and, in particular, has a simplified control system.
The sliding cam system is suitable for an internal combustion engine. The sliding cam system has a camshaft and a plurality of cam carriers with in each case at least two cams. The plurality of cam carriers are arranged fixedly on the camshaft so as to rotate with it and in an axially displaceable manner. The sliding cam system has a plurality of fluid-actuated actuator apparatuses which are configured in each case for axially displacing one cam carrier of the plurality of cam carriers. The sliding cam system has a fluid feed apparatus which is provided for feeding a fluid in a fluid connection upstream of the plurality of actuator apparatuses for actuating the plurality of actuator apparatuses. At least two actuator apparatuses of the plurality of actuator apparatuses are coupled fluidically for simultaneous actuation.
The fluid coupling between at least two actuator apparatuses makes the simultaneous actuation of the two actuator apparatuses possible by way of a fluid being fed. In this way, the control complexity can be simplified considerably, since not every actuator apparatus has to be actuated individually at a defined time. Instead, for example, only a single valve is opened in a fluid connection upstream of the actuator apparatuses, as a result of which the actuator apparatuses are actuated.
In particular, the at least two cams of the cam carriers can be of different configuration.
A plurality of transmission apparatuses, for example rocker arms or toggle levers, are preferably additionally provided, which set a first cam or a second cam of the respective cam carrier in an operative connection with at least one gas exchange valve in a manner which is dependent on an axial position of a respective cam carrier. The gas exchange valves can be, for example, inlet valves or outlet valves. The transmission apparatuses can have, in particular, a cam follower, for example a rotatable roller, for following a cam contour of a cam.
The actuator apparatuses may be of identical configuration.
For example, the actuator apparatuses can engage by way of displaceable elements into engagement tracks of the cam carriers for axially displacing the cam carriers.
For example, the actuator apparatuses can have displaceable elements which can be displaced in a radial direction with regard to a longitudinal axis of the camshaft or in an axial direction with regard to the longitudinal axis of the camshaft for axially displacing the respective cam carrier.
In one embodiment, the fluidically coupled, at least two actuator apparatuses are coupled fluidically by means of a group control valve of the fluid feed apparatus. In particular, a fluid can be fed at the same time to the fluidically coupled, at least two actuator apparatuses by way of opening of the group control valve. For example, the group control valve can be provided in a fluid connection downstream of a compressor or a pump and upstream of the at least two actuator apparatuses.
It is also possible that actuator-specific valves are additionally provided in a fluid connection between the group control valve and the actuators of the actuator apparatuses. Thus, actuator-specific control of the sliding cam system can in turn be made possible if this is desired.
In one embodiment, a plurality of actuator apparatus groups are provided which have in each case at least two fluidically coupled actuator apparatuses of the plurality of actuator apparatuses. The grouping of the actuator apparatuses in actuator apparatus groups makes a grouped actuation of the actuator apparatuses possible, as a result of which every actuator apparatus of an actuator apparatus group does not have to be actuated individually.
In another embodiment, the actuator apparatus groups of the plurality of actuator apparatus groups are provided in each case downstream of a respective group control valve of the fluid feed apparatus, with the result that the fluid can be fed by the fluid feed apparatus at the same time to the fluidically coupled, at least two actuator apparatuses of the respective actuator apparatus group by way of opening of the respective group control valve.
For example, a first actuator of a first actuator apparatus and a first actuator of a second actuator apparatus and optionally a first actuator of a third actuator apparatus can be provided in a first actuator apparatus group. In addition, a second actuator of the first actuator apparatus and a second actuator of the second actuator apparatus and optionally a second actuator of the third actuator apparatus can be provided in a second actuator apparatus group. Furthermore, a first actuator of a fourth actuator apparatus, a first actuator of a fifth actuator apparatus and optionally a first actuator of a sixth actuator apparatus can be provided in a third actuator apparatus group. In addition, a second actuator of the fourth actuator apparatus, a second actuator of the fifth actuator apparatus and optionally a second actuator of the sixth actuator apparatus can be provided in a fourth actuator apparatus group.
A first group control valve can be provided in a fluid connection upstream of the first actuator apparatus group, a second group control valve can preferably be provided in a fluid connection upstream of the second actuator apparatus, a third group control valve can be provided in a fluid connection upstream of the third actuator apparatus group, and/or a fourth group control valve can be provided in a fluid connection upstream of the fourth actuator apparatus group.
In a further embodiment, the group control valves are arranged in parallel to one another.
In a further embodiment, a first actuator of a first actuator apparatus is coupled fluidically to a first actuator of a second actuator apparatus. As an alternative or in addition, a second actuator of the first actuator apparatus is coupled fluidically to a second actuator of the second actuator apparatus. The couplings make it possible for the first actuators to be actuated simultaneously and for the second actuators to be actuated simultaneously.
In a further embodiment, the plurality of actuator apparatuses have in each case a first actuator for displacing a respective cam carrier in a first direction and a second actuator for displacing the respective cam carrier in a second direction which is opposed with respect to the first direction. The first direction and the second direction can run, in particular, parallel to a longitudinal axis of the camshaft.
The respective first actuators can be coupled fluidically at least partially to one another and/or the respective second actuators can be coupled fluidically at least partially to one another.
The plurality of actuator apparatuses may be actuated hydraulically or pneumatically. The actuator apparatuses can be connected, for example, to a hydraulic system or pneumatic system which is already present in a motor vehicle.
In a further embodiment, the sliding cam system additionally has a position sensor which detects a rotational position of the camshaft, an internal combustion engine sensor which detects an operating parameter of the internal combustion engine, and/or a user interface for a user input. The sliding cam system additionally has a control unit which is configured, based on the detected rotational position, the detected operating parameter and/or the user input, to control the fluid feed apparatus for feeding the fluid to the plurality of actuator apparatuses. The inclusion of the rotational position of the camshaft can ensure that the actuator apparatuses are actuated in such a way that, for example, displaceable elements of the actuator apparatuses are engaged completely before the respective cam carrier is displaced. A displacement of the cam carrier can be triggered, for example, via the detected operating parameter, for example a load of the internal combustion engine, or the user input.
The term “control unit” relates to control electronics which, depending on the configuration, can undertake control tasks and/or regulation tasks.
In a further embodiment, the control unit is configured, based on the detected rotational position, the detected operating parameter and/or the user input, to selectively actuate the group control valves.
In one embodiment, actuators of the plurality of actuator apparatuses have in each case a control fluid space and a retractable and extendable element, in particular a pin, in operative connection with the control fluid space. The retractable and extendable element extends by way of feeding of the fluid to the control fluid space in order to displace the respective cam carrier. In this way, a fluid-actuated actuator can be provided in a structurally simple way.
In a further embodiment, the fluid is a compressible gas, in particular air, and the control fluid space which is filled with the compressible gas acts as a pneumatic spring during the retraction of the retractable and extendable element. In this way, impacts and therefore premature wear of the actuator can be prevented. The pneumatic spring is effected by way of compression of the compressible gas and expelling of the compressed gas.
In a further embodiment, the retractable and extendable element engages into an engagement track of the cam carrier in order to displace the cam carrier. The control fluid is fed to the control fluid space (in particular, by way of corresponding opening of the corresponding group control valve) in such a way that the retractable and extendable element makes contact with an outer circumferential face of the cam carrier before the retractable and extendable element engages into the engagement track. In other words, the fluid-actuated actuator apparatuses make it possible for the cam-free sections which have the engagement tracks to be moved over by the displaceable elements before the displaceable elements finally engage into the engagement tracks. In this way, control complexity for the actuator apparatus is reduced considerably, since the time window for actuating the actuator apparatuses is increased.
The retractable and extendable element may be prestressed by way of an elastic element into a retracted state. As a result, the retractable and extendable element can be returned into a basic position.
In a further embodiment, the control fluid space is configured as an annular space in the retracted state of the retractable and extendable element. This makes it possible that a contact area between a bottom face of the control fluid space and the retractable and extendable element is small. In particular, the control fluid can bear directly against the retractable and extendable element and/or only a low adhesion force can exist between the bottom face and the retractable and extendable element.
For example, the retractable and extendable element may have a journal which extends in a direction of a bottom face of the control fluid space. Alternatively or additionally, a bottom face of the control fluid space may have a journal which extends in a direction of the retractable and extendable element.
In a further embodiment, the control fluid space is sealed towards a surrounding area of the actuator apparatus by way of a fluid seal, in particular an O-ring. In this way, the penetration of oil mist into the control fluid space can be prevented.
The present disclosure also relates to a motor vehicle, in particular a commercial vehicle (for example, an omnibus or a lorry), having a sliding cam system as disclosed herein. The fluid feed apparatus preferably has a compressed air tank of the motor vehicle and/or the fluid feed apparatus is integrated into a pneumatic system of the motor vehicle.
The above-described preferred embodiments and features of the present disclosure can be combined with one another as desired.
Further details and advantages of the present disclosure will be described in the following text with reference to the appended drawings, in which:
The embodiments which are shown in the figures correspond to one another at least in part, with the result that similar or identical parts are provided with the same reference numerals and reference is also made to the description of the other embodiments and figures in order to explain them, in order to avoid repetitions.
The variable valve train 10 has a camshaft 12 and a cam carrier 14. In addition, the variable valve train 10 has a transmission apparatus 16 and a first and second gas exchange valve 20 and 22. In addition, the variable valve train 10 has a first actuator 24 and a second actuator 26. The first actuator 24 and the second actuator 26 form an actuator apparatus 27. In other embodiments, the actuator apparatus can have, for example, only one actuator or a plurality of actuators which are provided in a common housing.
The cam carrier 14, the camshaft 12 and the actuator apparatus 27 form a part of a sliding cam system 11. The sliding cam system 11 has a plurality of cam carriers 14 and actuator apparatuses for a plurality of cylinders of the internal combustion engine. In the following text, the construction of the sliding cam system is described by way of example for a cam carrier 14 and an actuator apparatus 27 for a cylinder of the internal combustion engine, as shown in
The camshaft 12 can be configured as an inlet camshaft, an outlet camshaft or a mixed camshaft which actuates both inlet valves and outlet valves. The camshaft 12 can be part of a double camshaft system (not shown in detail) which additionally has a further camshaft (not shown). The camshaft 12 is arranged as an overhead camshaft. In other embodiments, the camshaft 12 can also be arranged as an OHV camshaft.
The cam carrier 14 is arranged fixedly on the camshaft 12 so as to rotate with it. The cam carrier 14 is additionally arranged such that it can be displaced axially along a longitudinal axis of the camshaft 12. The cam carrier 14 can be capable of being displaced axially between a first stop 28 and a second stop 30.
The cam carrier 14 has two cams 32 and 34 which are offset from one another in a longitudinal direction of the cam carrier 14 and the camshaft 12. The first cam 32 and the second cam 34 are arranged in a central section of the cam carrier 14. The first cam 32 and the second cam 34 adjoin one another. The first cam 32 and the second cam 34 are of different configuration, with the result that they can bring about different valve lift curves of the gas exchange valves 20, 22. The first cam 32 can be, for example, an engine brake cam for an outlet valve, and the second cam 34 can be a normal cam. In other embodiments, the cam carriers can have a different number of cams, different arrangements of the cams and/or different cam contours of the cams.
In addition, the cam carrier 14 has a first cam-free section 38 and a second cam-free section 40. The first cam-free section 38 and the second cam-free section 40 are arranged at opposite ends of the cam carrier 14. A first engagement track (switch guide plate) 42 extends spirally about a longitudinal axis of the cam carrier 14 in the first cam-free section 38. A second engagement track (switch guide plate) 44 extends spirally about the longitudinal axis of the cam carrier 14 in the second cam-free section 40.
In order to displace the cam carrier 14 between the stops 28 and 30, the actuators 24 and 26 can engage with extendable elements (not shown in detail in
The displacement is triggered by virtue of the fact that the extended element of the respective actuator 24, 26 is stationary with regard to an axial direction of the camshaft 12. As a consequence, the displaceable cam carrier 14 is displaced in a longitudinal direction of the camshaft 12 on account of the spiral shape of the engagement tracks 42, 44 when the extended element engages into the respective engagement track 42, 44. At the end of the displacement operation, the displaceable element of the respective actuator 24, 26 is guided by the respective engagement track 42, 44 in an opposite direction to the extending direction and is therefore retracted. The displaceable element of the respective actuator 24, 26 passes out of engagement with the respective engagement track 42, 44.
The transmission apparatus 16 establishes an operative connection between the cam carrier 14 and the gas exchange valves 20, 22. The gas exchange valves 20, 22 are actuated (opened) when the first cam 32 or the second cam 34 presses the transmission apparatus 16 downwards.
If the cam carrier 14 is situated in the first axial position, the transmission apparatus 16 is in an operative connection between the first cam 32 and the gas exchange valves 20, 22. In other words, the transmission apparatus 16 is not in an operative connection between the second cam 34 and the gas exchange valves 20, 22 in the first axial position of the cam carrier 14. The gas exchange valves 20, 22 are actuated in accordance with a contour of the first cam 32. In the second axial position of the cam carrier 14, the transmission apparatus 16 is in an operative connection between the second cam 34 and the gas exchange valves 20, 22 which are actuated in accordance with a contour of the second cam 34.
In the embodiment which is shown, the transmission apparatus 16 is configured as a rocker arm. In other embodiments, the transmission apparatus 16 can be configured as a toggle lever or as a tappet. In some embodiments, the transmission apparatus 16 can have a cam follower, for example in the form of a rotatable roller.
A locking apparatus 46 is shown with reference to
The actuator 24 is fluid-actuated. In particular, the actuator 24 is a pneumatic or hydraulic actuator. The actuator 24 is preferably actuated pneumatically, since this can be advantageous with regard to a temperature insensitivity and a speed which can be achieved.
The actuator 24 has a displaceable pin (piston) 56, an elastic element 58, a control fluid space 60 and a control fluid feed duct 62.
A control fluid, for example air or hydraulic liquid, can be fed to the control fluid space 60 via the control fluid feed duct 62. The feed of control fluid to the control fluid space 60 brings about ejection of the pin 56 from the control fluid space 60. The extended pin 56 can engage into the engagement track 42, in order to displace the cam carrier 14 axially.
The pin 56 and the control fluid space 60 can be configured in such a way that the control fluid space 60 is configured as an annular space in the retracted state of the pin. For example, the pin 56 can be provided with a journal, as shown in
The fluid actuation of the actuator 24 makes it possible that the pin 56 moves over the cam-free section 38 (see
At the end of the displacement operation of the cam carrier 14, a ramp of the engagement track 42 presses the pin 56 in the direction of the control fluid space 60. If a compressible fluid is used as control fluid, the fluid is compressed and expelled during the retraction of the pin 56. The fluid which is situated in the control fluid space 60 therefore acts as a pneumatic spring during the retraction operation of the pin 56. The elastic element 58 brings about a complete return of the pin 56 into the basic position (into the retracted state).
In order to prevent penetration of, for example, oil mist into the control fluid space 60, a fluid seal 64, for example a sealing ring, can be provided. In addition, the control fluid space 60 can have, for example, a ventilating duct (not shown).
With reference to
The sliding cam system 11 has a first actuator apparatus 27, a second actuator apparatus 127, a third actuator apparatus 227, a fourth actuator apparatus 327, a fifth actuator apparatus 427 and a sixth actuator apparatus 527. The second to sixth actuator apparatuses 127, 227, 327, 427, 527 can be configured like the actuator apparatus 27. In particular, the second to sixth actuator apparatuses 127, 227, 327, 427, 527 can have in each case two actuators 124, 126; 224, 226; 324, 326; 424, 426 and 524, 526 for displacing a respective cam carrier (not shown). The actuators 26, 124, 126, 224, 226, 324, 326, 424, 426, 524 and 526 can be configured like the actuator 24 which is described with reference to
A fluid feed apparatus 66 is provided in a fluid connection upstream of the fluid-actuated actuator apparatuses 27, 127, 227, 327, 427, 527. The fluid feed apparatus 66 is configured by way of example as a pneumatic fluid feed apparatus. The fluid feed apparatus 66 has a compressor 68, a pressure tank 70 and four group control valves 72, 74, 76 and 78.
The compressor 68 conveys a fluid for storage into the pressure tank 70. For example, the compressor 68 can convey air into the pressure tank 70. The pressure tank 70 can be, in particular, a compressed air tank of a commercial vehicle, which compressed air tank also provides compressed air, for example, for other pneumatically actuated apparatuses of the commercial vehicle. The pressure level can lie, for example, between 8 bar and 12 bar.
The compressor 68 and the four group control valves 72, 74, 76 and 78 are controlled by a control unit 80. The control unit 80 is connected to a position sensor 82, an internal combustion engine sensor 84 and a user interface 86. The position sensor 82 detects a position of the camshaft 12 (see
The group control valves 72, 74, 76 and 78 are provided downstream of the compressor 68 and the pressure tank 70. The first group control valve 72 is provided in a fluid connection upstream of the actuators 24, 124, 224. The second group control valve 74 is provided in a fluid connection upstream of the actuators 26, 126, 226. The third group control valve 76 is provided in a fluid connection upstream of the actuators 324, 424, 524. The fourth group control valve 78 is provided in a fluid connection upstream of the actuators 326, 426, 526. In this way, the group control valves 72, 74, 76 and 78 couple the actuator apparatuses 27, 127, 227, 327, 427 and 527 partially. Thus, for example, merely the first group control valve 72 has to be opened by the control unit 80 in order to actuate the actuators 24, 124, 224.
In the present embodiment, the actuators 24, 26, 124, 126, 224, 226, 324, 326, 424 and 426 are divided via the group control valves 72, 74, 76 and 78 into four groups for common actuation. The actuators are coupled fluidically within one group. In other embodiments, more or fewer groups can be provided with in each case more or fewer actuators, in order to reduce a control complexity for the sliding cam system.
The present disclosure is not restricted to the above-described preferred exemplary embodiments. Rather, a multiplicity of variants and modifications are possible which likewise utilize the concept of the present disclosure and therefore fall within the scope of protection. In particular, the present disclosure includes a configuration of the fluid feed apparatus and the fluid coupling of at least two actuator apparatuses.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017120145.9 | Sep 2017 | DE | national |
