Patent Application
20120210961
The invention relates to a device for variably adjusting the timing of gas exchange valves of an internal combustion engine, having a hydraulic phase adjustment unit, wherein the phase adjustment unit can be placed in drive connection with a crankshaft and with a camshaft and has at least one advance chamber and at least one retardation chamber, to and from which pressure medium can be supplied and discharged via pressure medium lines, wherein a phase position of the camshaft relative to the crankshaft can be adjusted by means of a supply of pressure medium to the adjustment chambers.
In modern internal combustion engines, devices for variably adjusting the timing of gas exchange valves are used to enable variable configuration of the phase position of a camshaft relative to a crankshaft within a defined angular range between a maximum advanced position and a maximum retarded position. For this purpose, a hydraulic phase adjustment unit of the device is integrated into a drive train via which torque is transmitted from the crankshaft to the camshaft. This drive train can be implemented for example as a belt, chain or gear drive. The phase adjustment speed and the pressure medium requirement are significant parameters of such devices. To enable the phase position to be adapted in an optimum manner to the various driving situations, high phase adjustment speeds are desirable. In the context of measures for reducing consumption, there is furthermore a demand for an ever smaller pressure medium requirement so as to enable the pressure medium pump of the internal combustion engine to be of smaller design or to enable the delivery rate to be reduced when using regulated pressure medium pumps.
A device of this type is known for example from EP 0 806 550 A1. The device comprises a vane-type phase adjustment unit with a drive input element, which is in drive connection with the crankshaft, and a drive output element, which is connected to the camshaft for conjoint rotation therewith. A plurality of pressure spaces are formed within the phase adjustment unit, wherein each of the pressure spaces is divided into two oppositely acting pressure chambers by means of a vane. The vanes are moved within the pressure spaces by means of a supply of pressure medium to or discharge of pressure medium from the pressure chambers, which brings about a change in the phase position between the drive output element and the drive input element. In this case, the pressure medium required for phase adjustment is provided by a pressure medium pump of the internal combustion engine and is directed selectively to the advance or retardation chambers by means of a control valve. The pressure medium flowing out of the phase adjustment unit is directed into a pressure medium reservoir, the oil sump of the internal combustion engine. Phase adjustment is thus accomplished by means of the system pressure provided by the pressure medium pump of the internal combustion engine.
A further device is known for example from U.S. Pat. No. 5,107,804 A. In this embodiment, the phase adjustment unit is likewise of the vane type, and a plurality of advance and retardation chambers is provided. In contrast to EP 0 806 550 A1, phase adjustment is not accomplished by supplying pressure medium to the pressure chambers by means of a pressure medium pump; instead, alternating moments acting on the camshaft are used. The alternating moments are caused by the rolling movements of the cams on the gas exchange valves, each of which is preloaded by a valve spring. In this case, the rotary motion of the camshaft is braked during the opening of the gas exchange valves and accelerated during closure. These alternating moments are transmitted to the phase adjustment unit, with the result that the vanes are periodically subjected to a force in the direction of the retardation stop and of the advance stop. As a result, pressure peaks are produced alternately in the advance chambers and the retardation chambers. If the phase position is supposed to be held constant, pressure medium is prevented from flowing out of the pressure chambers. In the case of a phase adjustment in the direction of earlier timing, pressure medium is prevented from flowing out of the advance chambers, even at times at which pressure peaks are being produced in the advance chambers. If the pressure in the retardation chambers rises owing to the alternating moments, this pressure is used to direct pressure medium out of the retardation chambers into the advance chambers, using the pressure of the pressure peak generated. Phase adjustment in the direction of later timing is accomplished in a similar way. In addition, the pressure chambers are connected to a pressure medium pump, although only to compensate for leaks from the phase adjustment unit. Phase adjustment is thus accomplished by diverting pressure medium out of the pressure chambers to be emptied into the pressure chambers to be filled, using the pressure of the pressure peak generated.
Another device is known from US 2009/0133652 A1. In this embodiment, phase adjustment in the case of small alternating moments is accomplished, in a manner similar to the device in EP 0 806 550 A1, by supplying pressure to the advance chambers or the retardation chambers by means of a pressure medium pump while simultaneously allowing pressure medium to flow out of the other pressure chambers to the oil sump of the internal combustion engine. In the case of high alternating moments, these are used, as in the device in U.S. Pat. No. 5,107,804 A, to direct the pressure medium under high pressure out of the advance chambers (retardation chambers) into the retardation chambers (advance chambers). During this process, the pressure medium expelled from the pressure chambers is fed back to a control valve, which controls the supply of pressure medium to or discharge of pressure medium from the pressure chambers. This pressure medium passes via check valves within the control valve to the inlet port, which is connected to the pressure medium pump, wherein some of the pressure medium is expelled into the pressure medium reservoir of the internal combustion engine.
EP 2 075 421 A1 discloses a valve for a camshaft adjuster. The valve comprises a valve piston which is arranged in a rotatable manner in a valve housing. Inlets and outlets for pressurized oil are arranged such that, by adjusting the valve piston, pressurized oil can be conducted to the adjustment chambers and to a locking mechanism. Here, the locking mechanism can be activated not only in an end position of the camshaft adjuster, that is to say at a stop in the retarded or advanced position, but also in an intermediate position. This permits mid-position locking, which may be expedient depending on the engine application.
DE 198 50 947 presents a device for controlling the timing of an internal combustion engine, having at least one drive means, at least one camshaft with cams, at least one hydraulically actuable adjustment unit for adjusting the angle of relative rotation between the drive means and the camshaft, at least one hydraulic fluid supply device for charging the adjustment unit, and at least one positive control unit by means of which the hydraulic charging of the adjustment unit can be influenced at least at times and/or at least in part as a function of the absolute angle of rotation of the camshaft and/or of the cams. Here, a flow connection to the adjustment chambers is shut off in a targeted manner when pressure fluctuations caused by torques arise which would be imparted back to the adjustment chambers by the camshaft when cams are running on or running off.
U.S. Pat. No. 6,186,104 B1 discloses a vane-type valve timing control device for an internal combustion engine, in which, between the pressure cells and the control valve which actuates them, there is connected a pressure distributor device which serves to suppress disturbance camshaft torques. For this purpose, for example during a retardation, the oil supply to the pressure cells is shut off when an advance torque arises. Conversely, during an advance, the oil supply to the pressure cells is shut off when a retardation torque arises. Similarly to DE 198 50 947, therefore, a return swing of the adjustment unit is suppressed due to the adjustment of opposing camshaft torques.
The invention is based on the objective of providing a device for variably adjusting the timing of gas exchange valves of an internal combustion engine with a high phase adjustment speed.
The objective is met according to the invention by specifying a camshaft adjuster for a camshaft which serves to actuate cylinder valves of an internal combustion engine, wherein retardation torques in the direction of retarded cylinder valve opening times are imparted back to the camshaft adjuster by the camshaft when cams are running on, and oppositely directed advance torques in the direction of advanced cylinder valve opening times are imparted back to the camshaft adjuster by the camshaft when cams are running off,
having a pressure chamber and having an adjusting means arranged in the pressure chamber,
wherein the adjusting means divides the pressure chamber into a first chamber part and a second chamber part,
wherein pressure medium can be supplied to the first and the second chamber part and pressure medium can be discharged from the first chamber part and second chamber part,
such that the adjusting means can be moved by a pressure difference between the first chamber part and second chamber part, resulting in a rotation of the camshaft, wherein, when a relatively high pressure prevails in the first chamber part, the camshaft is rotated in the direction of advanced cylinder valve opening times, and when a relatively high pressure prevails in the second chamber part, the camshaft is rotated in the direction of retarded cylinder valve opening times,
and wherein the supply and discharge of pressure medium can be controlled by means of a control device,
wherein a torque mode or a pump mode can be selectively set by means of the control device,
wherein in the torque mode, predominantly camshaft torques are utilized to build up pressure in the first chamber part or in the second chamber part,
whereas in the pump mode, the pressure build-up in the first chamber part or in the second chamber part is realized predominantly by means of pressure medium provided by a pressure medium pump.
In the prior art, two strategies have hitherto been followed for hydraulic camshaft adjustment: firstly, a provision of pressure medium by means of a pressure medium pump, generally an oil pump of an engine oil lubricating circuit, or a utilization of camshaft torques for generating the required adjustment pressure. The first strategy is also referred to as “oil pressure actuated” (OPA) and the second is referred to as “cam torque actuated” (CTA). The invention is now based on the realization that respective advantages of OPA and CTA methods can be expediently combined with one another as a function of an operating state of the internal combustion engine. In operating states in which a high pump pressure of the pressure medium pump is provided, the pump mode, that is to say an OPA method, is expediently selected, whereas in the event of low pump pressures but high camshaft torques, the torque mode, that is to say the CTA method, is used. Here, it is self-evidently possible for an adjustment in the CTA method to be assisted by the pressure medium pump in addition to the utilization of the camshaft torques, and vice versa.
Here, the invention is not restricted to a particular design of camshaft adjuster, that is to say, for example, use may be made of a vane-type adjuster in which multiple pairs of chamber parts are formed, wherein the adjustment means is a vane which divides the chamber parts and which is for example formed in one piece from a rotor or plugged into said rotor.
The control device preferably has a control valve which is positioned centrally in the camshaft and which has a valve piston which can be guided in a valve housing, wherein the valve housing has an inner sleeve and an outer sleeve which is radially outside the inner sleeve and surrounds the latter, wherein the inner sleeve is fixed against rotational movement by a rotation prevention means, while the outer sleeve is rotatable.
In the case of a single-piece design of the valve housing and therefore a relative rotation of the valve piston, which is fixed against rotation, and of the rotatable valve housing, it is possible under some circumstances for jamming, or an impairment of the adjustment speed or accuracy, to occur during the axial adjustment of the valve piston. This possible disadvantage is now counteracted in that the valve housing is of two-piece design, with an inner sleeve which is fixed against rotation and with a rotatable outer sleeve. This concept furthermore has other advantages such as an expedient configuration of the shift sequence and an improved locking function, which will be explained in more detail further below.
It is preferable for an orifice cover to be formed on the outer side of the inner sleeve, wherein in the orifice cover there are formed first orifices, which communicate with the first chamber part A, and second orifices, which communicate with the second chamber part B, and wherein the first orifices and second orifices are opened up or closed off by the orifice cover in accordance with the rotational angle position of the inner sleeve with respect to the outer sleeve.
In this embodiment, therefore, the supply and discharge of pressure medium to and from the chamber parts is realized by means of the control valve, the inner and outer sleeve and orifices or oil ducts in the camshaft. Here, the supply and discharge of pressure medium takes place as a function of a rotational angle of the camshaft. This rotational angle corresponds in turn to the camshaft torques, such that a supply and discharge of pressure medium can be correspondingly synchronized with the respective camshaft torques as a function of the desired adjustment direction. Here, the orifice cover opens up the first or second orifices, which respectively correspond to the chamber part to be actuated, depending on the occurrence of camshaft torques and the desired adjustment direction. Here, the first and second orifices need not lie in a region formed in one piece with the rest of the camshaft; in this regard the camshaft should also be regarded as including a component, an adapter or the like, which is mounted on the camshaft and rotates therewith.
It is furthermore preferable for the first orifices and the second orifices to be arranged relative to one another on the circumference at an angular interval, in each case spaced apart uniformly, and arranged in the correct phase with respect to the orifice cover, such that a relative rotation of the valve piston with respect to the valve housing by the angular interval leads to a geometrically identical arrangement. It is furthermore preferable for the orifice cover to be designed so as to be adapted with regard to an asymmetrical displacement of camshaft torques in relation to the zero line. Such an asymmetrical displacement occurs in particular as a result of a friction torque which acts on the camshaft in the retardation direction in an angle-independent manner. In this way, the approximately sinusoidal curve of the camshaft profile is thus displaced, as a whole, by a magnitude corresponding to the friction torque. It may thus be advantageous for the respective local widths of the orifice cover to be adapted to the now shortened or lengthened effective times of an advance or retardation torque. For example, an orifice cover illustrated in a “developed” view would no longer correspond to a symmetrical rectangular waveform curve with maximum and minimum phases of equal length, but rather would have in each case different lengths for the maximum and minimum phases.
The valve piston can preferably be displaced axially by means of an electromagnet, wherein the electromagnet presses the valve piston against a restoring spring which can effect a restoring movement of the valve piston, wherein the restoring spring is supported in a mounting sleeve and wherein at the same time a mounting spring is provided which, oppositely with respect to the restoring spring, is supported at one side in the bearing sleeve and at the other side on the camshaft. It is furthermore preferable for the mounting spring to support a mounting piston which is supported in an approximately punctiform manner on a mounting pin which is connected to the camshaft. In this embodiment, it is possible in particular for a production tolerance chain to be kept small by means of the compensating mounting spring. Furthermore, low-friction mounting of the stationary valve piston relative to the rotating camshaft is attained by means of the approximately punctiform support of the bearing piston on the mounting pin.
The pump mode or the torque mode can preferably be set by means of an axial displacement of a valve piston arranged in a valve housing of the control valve. It is furthermore preferable for the valve housing to have a pump orifice by means of which the supply of pressure medium either to the first chamber part or to the second chamber part can be set such that in each case either the first chamber part or the second chamber part is pressurized, wherein the flow of pressure medium out of the first chamber part or the second chamber part can be set by means of chamber part orifices in the valve housing.
The concept is thus followed of realizing an adjustment by controlling the outflow of pressure medium. Pressure medium is supplied to the chamber parts via the pump orifice in the valve housing, wherein depending on the position of the first orifices or of the second orifices, the pump orifice corresponds to the first chamber part or second chamber part. By opening up the chamber part which is reduced in size in the desired adjustment direction, an outflow of pressure medium from said chamber part is permitted, such that the pressure medium is expelled by the pressure in the other chamber part, and the adjustment is realized.
It is preferable if, for the relative axial position of the valve piston, five switching positions can be set, wherein
in a first position, the pump mode is set for an adjustment of the camshaft in the direction of retarded cylinder valve opening times,
in the second, axially subsequent switching position, the torque mode is set for an adjustment of the camshaft in the direction of retarded cylinder valve opening times,
in the third, axially subsequent switching position, a camshaft adjustment is blocked,
in the fourth, axially subsequent switching position, the torque mode is set for an adjustment of the camshaft in the direction of advanced cylinder valve opening times, and
in the fifth, axially subsequent switching position, the pump mode is set for an adjustment of the camshaft in the direction of advanced cylinder valve opening times.
These five switching positions thus generally yield adequate adjustment possibilities, in a manner adapted to the respective engine operating state. For example: whereas, when there is adequate pressure from the pressure medium pump, a retardation of the camshaft takes place in switching position one and an advance takes place in switching position five, it is possible in the case of low pressure, utilizing the camshaft torques, for a retardation to take place in switching position two and an advance to take place in switching position four. The middle position, switching position three, can be utilized for a blocking of the adjustment. The double sleeve design furthermore offers the design possibility of the switching positions being axially adjacent to one another as described above, that is to say of an advance switching position not being axially adjacent to a retardation switching position, resulting in reduced switching speeds and reduced regulating outlay.
A locking mechanism is preferably provided by means of which the camshaft adjuster is mechanically blocked in a locking position so as to be prevented from being adjusted, wherein the locking mechanism can be hydraulically unlocked by the pressure medium, and wherein a supply of pressure medium to the locking mechanism is connected such that the locking device unlocks only when the valve piston is in an axial switching position which corresponds to an adjustment in the direction of advanced cylinder valve opening times.
Locking of a camshaft adjuster is necessary in particular during a shutdown of the engine, such that during a restart, when there is still only an insufficient oil pressure in the adjuster, rattling impacting of the freely movable adjuster elements does not occur. During the shutdown of the engine, therefore, it is generally the case that an adjustment in the retardation direction and locking by means of a locking pin takes place. In a conventional embodiment, the locking pin corresponds to one of the chamber parts, such that after an adequate pressure has built up after an engine start, pressure medium from the chamber parts pushes the hydraulically unlockable locking pin back counter to a spring, and the adjuster is thereby unlocked. In the above-described concept, it is now provided that a separate supply of pressure medium to the locking device is connected such that, during a state corresponding to an adjustment in the retardation direction, no pressure medium passes via the control valve to the locking pin. It is ensured in this way that, after an engine start, the locking mechanism is not unlocked already by a pressure pulse, for example by air forced in by the incoming pressure medium. Since the base position is set retarded, the adjuster must first be unlocked when the rotational position of the camshaft is to be changed, that is to say in the event of an adjustment in the advance direction. For this purpose, the valve piston is moved axially from the basic position.
It is preferable if, during installation of the control valve in the camshaft, the inner sleeve and the outer sleeve are displaced relative to one another such that a rotationally conjoint connection between the inner sleeve and outer sleeve 105 is released. It is furthermore preferable for the rotation prevention means to engage into a cutout of the electromagnet, wherein the inner sleeve can be displaced axially relative to the outer sleeve as a result of the assembly of the electromagnet.
The above-described adjustment concept demands a defined angular position of the inner sleeve and outer sleeve relative to the camshaft, because the interaction must be synchronized with the camshaft torques occurring at fixed angular positions. This defined rotational position is now attained by means of a simplification of installation such that the inner and outer sleeve are fixed in the correct position relative to one another, and then the entire control valve is attached to the camshaft, which has likewise previously been rotated into a defined angular position. During the attachment, a positive locking action between the inner sleeve and outer sleeve is released by means of an axial displacement, such that the relative rotation between the inner sleeve and outer sleeve is made possible. This is advantageously achieved by virtue of the magnet which is used for adjusting the valve piston being flange-mounted centrally in front of the camshaft, and in so doing displacing the inner sleeve. It is furthermore possible here for a rotation prevention means, for example a pin or a lug on the inner sleeve, to engage into a corresponding cutout in the magnet, wherein said engagement advantageously takes place first, and then the magnet is fastened and in so doing, via the rotation prevention means, displaces the inner sleeve.
Further features of the invention will emerge from the following description and from the drawings, which illustrate exemplary embodiments of the invention in simplified form. In the drawings:
The valve piston 27 should now be arranged in the valve housing 29 in the correct rotational position such that the orifice cover 51 opens up and blocks the first orifices 41 and second orifices 43, respectively, for the correct phase position in each case. A supply of pressure medium to chamber parts of a pressure chamber, and therefore also the adjustment of the phase position of the camshaft, is controlled in this way. This will be explained in detail further below.
In
Also schematically illustrated are the first orifices 41 and the second orifices 43, as they are arranged relative to the orifice cover 51 corresponding to the axial position and rotational position of the valve housing 29 relative to the valve piston 27. The first orifices 41 correspond to a second chamber part B, and the second orifices 43 correspond to a first chamber part A. The chamber parts A, B are divided by a vane 67 which forms an adjustment means 67 and which divides a pressure chamber 69 into the chamber parts A, B. The vane 67 is connected to a rotor 65 of a camshaft adjuster 11. The pressure chamber 69 is formed in a stator 63 of the camshaft adjuster 11. A first oil duct 71 leads to the first chamber part A, a second oil duct 73 leads to the second chamber part B. Only a detail of the camshaft adjuster 11 is shown here. The camshaft adjuster 11 is designed as a vane-type adjuster and has a plurality of pressure chambers, chamber parts, vanes and supply ducts, which are not illustrated here for the sake of clarity.
In the example of
As a result of the great extent to which the first orifices 41 are opened up, intense dethrottling is attained, as a result of which the risk of air induction is greatly reduced. Discharge control is realized through the lesser opening-up of the second orifices 43 to the tank.
The switching positions illustrated above can thus be summarized as follows: two OPA adjustment methods are provided, one in the case of low pump pressure and one in the case of high pump pressure. The axial switching positions can be abbreviated as follows:
Switching position I: high pump pressure, retardation adjustment,
Switching position II: low pump pressure, retardation adjustment,
Switching position III: blocked adjustment,
Switching position IV: low pump pressure, advance adjustment,
Switching position V: high pump pressure, advance adjustment,
The advantage of said adjustability lies in particular in the fact that, by means thereof, in the case of high pump pressure and a torque which counteracts the desired adjustment direction, the inflow openings 41 and 43 to the respective chamber parts A, B are not fully closed, as a result of which the pump power, which is higher than the relatively low camshaft torque, can nevertheless still be utilized for adjustment despite the oppositely acting camshaft torque. The times at which oppositely acting camshaft torques arise can thus be utilized for the adjustment, resulting in a fast adjustment. If, however, the pump power is lower than the camshaft torques, the oppositely acting torques are suppressed by means of the completely closed orifices 41 and 43, such that no reverse adjustment takes place.
The statements made up to this point relate to an adjustment method in which adjustment is carried out predominantly by means of the pressure provided by the pump P and in which pressure generated by camshaft torques has an assisting action in suitable switching positions. It is now sought below to describe, in addition to a pump mode of said type, a torque mode in which predominantly the pressure peaks generated by camshaft torques are utilized for adjustment, while the pressure provided by the pump P possibly assists the adjustment.
A particularly expedient sequence of switching positions can now be established by selecting axially successive switching positions as follows:
Switching position I: pump mode (OPA), retardation adjustment,
Switching position II: torque mode (CTA), advance adjustment,
Switching position III: blocked adjustment,
Switching position IV: torque mode (CTA), retardation adjustment,
Switching position V: pump mode (OPA), advance adjustment,
It is therefore possible, depending on the presence either of a dominating pressure of the pump P or of dominating camshaft torques for the camshaft adjustment, to set either a pump mode or a torque mode.
The illustrations and examples up to this point related to a variant suitable in particular as a so-called central valve embodiment, that is to say a control valve for controlling the supply and discharge of pressure medium to and from the chamber parts is arranged centrally in a camshaft. Below, a variant will be illustrated in which the control valve is arranged outside the camshaft and interacts with a rotary transmitter which, together with the control valve and the camshaft, controls a control device 20 for controlling the supply and discharge of pressure medium to and from the chamber parts. Here, the rotary transmitter performs the function of adaptation to the respective camshaft torques, whereas the control valve sets the setting for advancement, retardation or holding. This may be realized for example by means of the following embodiments:
At an axial end which, in the installed state, faces toward a magnet 21, a rotation prevention element 25 in the form of an axial projection is formed on the inner sleeve 103. Engagement of the rotation prevention element 25 into a rotation prevention means receptacle 153 (see
A magnet 21 serves for axial adjustment of a valve piston 27 in the axial direction, to the right in the Figure. A restoring movement is effected by means of a restoring spring 31. The restoring spring 31 is supported in a mounting sleeve 135 which, on the opposite side, is itself supported by a mounting spring 131. A mounting piston 133 is held in the mounting spring 131. This mounting piston bears with a flat head against a mounting pin 137 which is in turn screwed into the camshaft 35. During operation, the valve piston 27, its restoring spring 31, the mounting sleeve 135, the mounting spring 131 and the mounting piston 133 are fixed in terms of rotation, while the mounting pin 137 rotates with the camshaft 35. The mounting pin 137 has a rounded head against which the mounting piston 133 bears. This results in approximately punctiform contact with low friction. The mounting pin 137 also serves to fix a check valve 139 which is formed as a sheet-metal flap and by means of which a supply orifice 141 through which pressure medium can be supplied can be closed off.
The valve piston 27 has control edges KAT, KPA, KBT, KPB which are formed by two radial projections and by means of which the outflow and inflow from and to the chamber parts A, B can be regulated. Two further radial projections form the control edges V1, V2, P1, P2. In relation to valve designs in the prior art by means of which conventional hydraulic control of a camshaft adjustment is realized, the present design has in particular the special feature of the additional control edges P1, P2 and V1, V2, the latter serving for the supply to the locking device 121. In interaction with the first and second orifices 41, 43 in the camshaft 35 and the orifice cover 51, it is now possible to set different switching positions as a function of the engine operating state, in particular of the engine oil pressure and of the magnitude of the camshaft torques. This will be explained in more detail on the basis of the following Figures.
Corresponding to the illustration in
The switching position of
Corresponding to
It can also be seen from
The five axial switching positions and the camshaft-torque-dependent rotational position can be summarized in a hydraulic circuit diagram shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 102009056020.3 | Nov 2009 | DE | national |
This application is a continuation of PCT/EP2010/067168, filed Nov. 10, 2010, which claims the benefit of German Patent Application No. 10 2009 056 020.3, which are incorporated herein by reference as if fully set forth.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2010/067168 | Nov 2010 | US |
| Child | 13462924 | US |
