Patent Application
20070169730
The invention relates to a camshaft adjuster for relative angle adjustment of a camshaft with respect to a driving crankshaft, having a hydraulically operable adjustment apparatus with chambers into which and from which a hydraulic fluid can be supplied and carried away alternately for angle adjustment of the chamber-specific pressure-medium channels, and having a control valve via which the hydraulic fluid, which is supplied via a pump, can be supplied to the pressure-medium channels and can be carried away from the pressure-medium channels into a tank, with operating connections A and B, which lead to the pressure-medium channels, a pressure connection P which can be coupled to the pump, and an outlet connection T which can be coupled to the tank being provided on the valve body of the control valve, which operating connections A and B can be selectively coupled to the pressure connection P or to the outlet connection T, depending on the angle adjustment required, via a valve piston which can be moved in a controlled manner via a decoupled pulling or pushing magnet which is arranged externally with respect to the camshaft adjuster.
In known internal combustion engines, the camshaft by means of which the valve movement of the inlet and outlet valves of the internal combustion engine is controlled is movement-coupled to the crankshaft of the machine via a control chain or a control belt, that is to say the camshaft is driven via the crankshaft. In order to allow the operating time of the inlet and/or outlet valves to be adjusted as a function of the operating situation, so that the valves open somewhat earlier or later in time with respect to the respective operating cycle, camshaft adjusters are integrated, via which the relative angle which the camshaft assumes with respect to the crankshaft can be adjusted. This means that the two shafts can be rotated somewhat relative to one another, with the consequence that the operating time of the valves which are operated via the camshaft is varied.
known camshaft adjusters are, for example, in the form of vane cell adjusters and have a rotor, which is connected to the camshaft such that they rotate together, and a stator, which is coupled to the crankshaft via the control chain or the control belt. Vanes which project radially outwards are provided on the rotor and engage between stops which project radially inwards on the stator, on the one hand limit the rotation movement and on the other hand form chamber walls. The chambers are bounded by the respective side of a rotor-side vane and by the sides of the stator-side stops. In order to rotate the rotor with respect to the stator and thus with respect to the angled setting, a hydraulic fluid is now forced into or drawn out of these chambers—a plurality of chamber pairs are in each case provided depending on the number of vanes—with a control valve being used for this purpose, generally a 4/3-way valve. Operating connections A and B are provided on this valve and respectively lead to a chamber A and a chamber B of a respective chamber pair. In the camshaft adjuster embodiment under discussion, the control valve is itself in the form of a central valve, that is to say it is inserted centrally, in the middle, in the camshaft adjuster or in its rotor and is connected to the camshaft, that is to say the control valve thus rotates with the adjuster and the rotor.
A valve piston is integrated in the control valve itself and moves axially, with its movement being controlled via a pulling or pushing magnet which is positioned externally with respect to the camshaft adjuster and, for example, is arranged on a motor or other third object. In this embodiment, the magnet is thus not integrated in the adjuster. Depending on the position of the valve piston, one or the other of the operating connections A or B is now coupled to the pressure connection P, so that hydraulic fluid is passed into the associated chamber A or B, while the respective other chamber is connected to the valve-side outlet connection, so that the fluid located in the chamber to which no pressure is applied can be drawn out towards the tank via the outlet connection. This allows the rotor to be rotated hydraulically with respect to the stator. In order to hold a rotation angle that has been set between the stops, the valve piston can also virtually close both operating connections A and B, and thus the associated chambers.
In known camshaft adjusters with the control valve under discussion, the pressure connection P is provided on the valve body, with its end aligned with the valve longitudinal axis. The hydraulic fluid, which is supplied under pressure, presses against an end surface of the frequently hollow-cylindrical valve body, before passing into the respective operating connection A or B, depending on the piston position. This leads to a considerable force being exerted on the piston, as a result of the fluid supply, which the external control magnet has to overcome in order to move the valve piston in an opposite direction. The magnetic force counteracts the spring acting on the valve piston and, when no current is flowing through the electromagnet, moves the valve piston to its basic position (P-B-A-T). The spring is matched to the system (magnetic force, flow and pressure forces of the hydraulics, piston movement, piston friction, etc). If the fluid-dependent force acting in the opposite direction now also has to be overcome in addition, this can lead in the worst case, when the applied fluid pressure is high, to the magnetic force that is acting not being strong enough to move the valve piston or to the valve piston not completely covering the movement distance associated with the electrical power applied to the magnet.
The invention is based on the object of specifying a camshaft adjuster which allows reliable positioning of the valve piston even when the applied fluid pressure is high.
In order to solve this problem for a camshaft adjuster of the type mentioned initially, the invention provides that the fluid distribution area in the control valve, that is to say in the valve body or the valve piston or between the two—is designed in such a manner that the hydraulic fluid acts on surfaces of the valve piston which point essentially in mutually opposite directions, so that local forces, which are essentially in opposite directions to one another, act on the valve piston.
In the camshaft adjuster according to the invention, the fluid path for the hydraulic fluid, as soon as it enters the valve body and before it passes to one of the operating connections A or B, is designed such that the valve piston is loaded by the fluid on two surfaces which point in mutually opposite directions, so that this directional load results in forces which project in the opposite direction, act on the valve piston and at least partially compensate for one another. As a result of this flow guidance, the total force which results from the fluid supply and acts on the valve piston is in consequence considerably reduced in comparison to the embodiments according to the prior art, which means that the force to be exerted by the external control magnet on the valve piston or on its extended control rod which points towards the magnet is considerably reduced. This means that any pressure surges in the supply of hydraulic fluid can never have any disadvantageous effect on the valve control.
It is expedient if the mutually opposite forces which are produced by the application of pressure to a surface according to the invention are essentially of equal magnitude, for which purposes the areas to which pressure is applied should expediently also be essentially of the same magnitude.
According to a first refinement of the invention, the pressure connection P may be at right angles to the valve axis and may open into an annular channel which is formed between the valve piston and the valve body, can be connected to the operating connection A as a function of position, and leads into the hollow-cylindrical valve piston, which is closed at both ends and whose cavity can be connected as a function of position to the operating connection B, with pressure being applied to the end cavity surfaces via the hydraulic fluid. The surfaces via which the forces in opposite directions are introduced into the valve piston are in this embodiment the end surfaces which bound the cavity at the end. Assuming that this is a hollow-cylindrical piston part with a constant cavity diameter, the areas are also in consequence essentially of the same magnitude, so that this also results in forces essentially of the same magnitude acting in opposite directions.
It should be noted at this point that, of course, depending on the configuration of the control valve and of the adjustment apparatus, the operating connection B may also be connected to the annular channel instead of the operating connection A, and the operating connection A may be connected to the cavity instead of the operating connection B, that is to say the respective operating connections can also be interchanged. This applies to all of the embodiments described in the following text.
In the described embodiment, it is also possible to provide that the two operating connections can be connected as a function of position to the outlet connection which is at an angle, preferably at right angles, to the valve longitudinal axis, via an annular channel which is formed between the valve piston and the valve body. Expediently, in this valve embodiment, all of the connections, that is to say both the pressure connection P and the outlet connection T and the operating connections A and B are arranged such that they run at right angles to the valve axis and in the sequence B-T-A-P or A-T-B-P, with a tension spring being used in the last-mentioned case in order to switch the valve to the basic position P-B-A-T when no current is flowing that is to say when the magnet is not active.
One alternative embodiment of a control valve provides that the pressure connection P is at an angle, preferably at right angles, to the valve axis and opens into an annular space which is formed between the valve piston and the valve body and can be connected as a function of position to the operating connection A or B, in which case the operating connections A, B can be connected as a function of position via connecting holes to the cavity in the hollow-cylindrical valve piston, and the cavity leads to the outlet connection T, which in this embodiment runs aligned axially with the valve longitudinal axis. In this case as well, the pressure connection P and the operating connections A and B can expediently be arranged such that they run at right angles to the valve longitudinal axis and in the sequence A-P-B.
A further embodiment variant provides that the pressure connection P is on the valve longitudinal axis and opens via guide channels into an annular space which is formed between the valve piston and the valve body and can be connected as a function of position to the operating connection A or B, in which case the operating connections A, B can be connected as a function of position via connecting holes to the cavity in the hollow-cylindrical valve piston, and the cavity leads to the outlet connection T.
Finally, a further valve embodiment provides that the pressure connection P runs aligned with the valve longitudinal axis and opens into the hollow-cylindrical valve piston on which radial openings are provided through which the hydraulic fluid enters the annular space which is formed between the valve piston and the valve body and is bounded by the end face of the valve piston. In this embodiment—in a similar manner to that in the prior art—the hydraulic fluid is passed axially into the hollow-cylindrical valve piston. Because of the piston openings which are provided according to the invention, the fluid emerges from the piston into the rear annular space which is formed between the piston and the valve body, or it is effectively diverted and presses against the piston outer surface, which is located opposite the cavity end wall. Thus, in this embodiment as well, the pressure acts on surfaces which are effectively mutually opposite thus resulting in local forces in opposite directions acting on the valve piston.
A plurality of different connections are provided on the valve body 2. On the one hand, an operating connection A and an operating connection B are shown, via which hydraulic fluid can be passed into corresponding chambers in the apparatus, which is in the form of a vane-cell adjustment apparatus, depending on the position of the valve piston 4. The illustration also shows a pressure connection P, via which the hydraulic fluid is supplied by a pump, which is not illustrated in any more detail. Furthermore, an outlet connection T is shown, via which hydraulic fluid to be carried away is passed to a tank, which is not shown in any more detail.
Various control edges 7a (which are associated with the operating connection A) and 7b (which are associated with the operating connection B) are provided on the valve piston 4. Depending on the position of the valve piston, the operating connections A and B are connected via these control edges either to the pressure connection P or to the outlet connection T via the channel 41, depending on whether fluid is intended to be supplied into the chambers which are associated with the operating connection A and fluid is intended to be carried away from the chambers which are associated with the operating connection B, and is intended to be passed to the tank via the outlet connection T, or vice versa. The position is controlled by the magnet, which is not shown in any more detail.
In order to prevent the hydraulic fluid, which is supplied at a relatively high pressure, from exerting a force on the valve piston which would additionally have to be overcome by the magnet which is moved against the spring force in order to move the valve piston 4, an annular channel 8 is provided in the control valve 1, and the pressure connection P opens into it. The annular channel 8—which can be connected to the operating connection A if required depending on the piston position—opens via openings 9 on the valve piston side into the cavity 10 in the valve piston 4. The cavity 10 can be connected via appropriate openings 11 to the operating connection B, when the aim is to supply the hydraulic fluid to it, depending on the piston position.
The hydraulic fluid in the cavity 10 presses against two mutually opposite end surfaces 12, 13 which bound the cavity, seen in the axial direction. This results in a force Fp1 or Fp2, which in each case acts in the direction of the valve piston, with these forces being in opposite directions to one another, as can be seen. The two forces—which in the ideal case are of equal magnitude—thus compensate for one another, so that the valve piston 4 effectively has no pressure applied to it in the ideal case, to the extent that forces act on it from the fluid supply.
Finally,
As can be seen, in this case as well, the valve piston is mounted with respect to a return spring 29. This is hollow-cylindrical, and the fluid that is supplied enters it. However, a plurality of openings 40 are provided on the opposite side so that the fluid can enter the annular space 31 which surrounds this piston end, where the fluid presses against the piston outer surface 32 which is opposite the end surface 33 in the interior of the piston. Thus, in this case as well, two surfaces which point in mutually opposite directions once again have the fluid applied to them, thus resulting in forces in mutually opposite directions acting on the valve piston 28.
Finally,
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 025 215.7 | May 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/04849 | 5/4/2005 | WO | 11/17/2006 |
