Patent Application
20170211430
The present invention relates to a vane-type camshaft adjuster, including a rotor, which has radially projecting vanes, the rotor, together with a stator rotatably accommodating the rotor, forming vane cells, each of which is divided by a vane into two adjustable chambers provided for accommodating hydraulic fluid.
Camshaft adjusters of this type are used in valve train assemblies of internal combustion engines, as known, for example, from DE 102 39 748 A1. Camshaft adjusters as valve timing control units are also known from the prior art, for example US 2008/0173267 A1 or U.S. Pat. No. 7,182,052 B2 or DE 10 2008 000 083 A1. In these publications, a valve timing control unit controls a valve timing of an inlet/outlet valve of an internal combustion engine. The device includes a housing which is rotated with the aid of a drive shaft. The housing has a chamber space which accommodates a vane rotor, which is rotatable toward a retard and an advance side relative to the housing with the aid of a driven shaft, in that a hydraulic pressure is applied thereto in a retard and advance chamber in the chamber space. A filter is provided in a fluid channel for removing foreign substances, which extends from a sliding section between the driven shaft and a bearing to both the housing and the vane rotor through a connected section between the driven shaft and the vane rotor. The filter is provided on the side of both the housing and the vane rotor with respect to the sliding section.
Camshaft adjusters are furthermore known from the publications U.S. Pat. No. 7,245,077 B2, U.S. Pat. No. 7,318,401 B2 and U.S. Pat. No. 7,000,580 B1. Slide valve devices for a camshaft adjuster including integrated check valves are described therein.
The present invention is in the field of accumulators and additional control functions in the switching valve. It therefore relates to pressure-driven adjusters, which are also known as oil pressure-activated (OPA) adjusters.
At excessively high torsional moments, an underpressure currently occurs periodically on the pump side in a camshaft adjuster. This results in dynamic problems and in additional air intake due to suction from leakage gaps and/or a degassing of a hydraulic fluid, such as a hydraulic liquid, e.g., oil, such as pressure oil/motor oil.
An object of the present invention is to avoid these disadvantages, to provide a particularly dynamically optimized camshaft adjuster and to eliminate or at least mitigate the disadvantages known from the prior art.
The present invention provides that a hydraulic fluid control device/hydraulic fluid regulating device is situated and/or connected between the chambers for conducting hydraulic fluid in such a way that a pressure drop, preferably below a predetermined limit pressure in the chambers, caused or amplified by camshaft alternating torques occurring during operation, is used to open the hydraulic fluid control device so that fluid flows therethrough.
The pressure at which the system begins to suck in air, or at which oil begins to degas, may be understood to be the critical pressure, in certain situations equal to a limit pressure. A limit pressure is understood to be the pressure which is the pressure set via the spring pretension and piston active surface.
It is advantageous if the hydraulic fluid control device includes at least one bypass line closing device or preferably two bypass line closing devices. In this way, hydraulic fluid may be transported both from the one chamber into the other chamber during a pressure drop and from the other chamber into the one chamber. An optimization in both adjusting directions of the camshaft adjuster is then achievable.
If the two bypass line closing devices are situated in parallel to each other in a fluid conducting manner, the reaction times may be minimized.
A particularly efficient camshaft adjuster optimization is achieved if the bypass line closing device includes a valve, such as a 2/2-way valve, and a spring acting thereupon, such as a pressure or tension spring. In this case, two open/close valves may be situated on/in the camshaft adjuster, which are actuated when the pressure in the first chamber falls. The actuated valve then opens a channel to allow oil to flow from the other chamber to the first chamber.
If the spring pretensions the valve into a position in which the hydraulic fluid flow is prevented, simple means may be used to facilitate a complex actuation.
A hydraulic fluid control unit is thus proposed, which connects chambers A and B, i.e., a first chamber and a second chamber, only when the pressure in one chamber falls below the pressure (pkrit) set via a controller/switch. A pressure compensation between the chambers may then take place. In this process, the pressure gradient between the chambers is utilized, which is induced in any case by the (camshaft) alternating torques.
As long as the pressure in the relevant chamber is above the critical pressure (limit pressure), the relevant controller/switch ensures a blocking of the short-circuit between the chambers. Each path A or B having the particular connected chambers requires a separate control unit, which varies the pressure in the corresponding path or opens the bypass to the other chamber if the pressure falls below the critical pressure in the one chamber. The pressure difference between the chambers is not an issue. It is additionally possible that a bypass/bypass line is opened when the pressure falls below a level set via the control unit (limit pressure). An overflow through this bypass line then occurs. The pressure level is not “equalized,” but instead the camshaft adjuster takes in the additional oil available to it (i.e., the oil “that it can get”) and thus increases the speed of its adjusting movement.
It is desirable if the bypass line closing device is preset in such a way that, when the pressure in a first of the chambers falls below a limit pressure (pkrit), a switching position of the bypass line closing device is forced, in which the hydraulic fluid enters the one, first chamber from the other, second chamber through a bypass line.
It is advantageous if the spring is adapted to the limit pressure/the pressure (pkrit) set via the controller. This precise limit pressure is set with the aid of the spring, the area ratios and/or the active surfaces on the piston.
It is also advantageous if the hydraulic fluid conducting device is integrated or built into a vane. In this way, a very compact camshaft adjuster may be achieved.
It is advantageous if the bypass line closing device includes a pilot line, which establishes a pressure-transmitting connection between the first chamber and a closing element, the spring, in its basic position, forcing the closing element into the bypass line connecting the two chambers in a hydraulic fluid-suppressing manner and, in an activating position, opening the bypass line, when the pressure in the first chamber reaches and/or falls below the limit pressure.
One advantageous exemplary embodiment is also characterized in that two pistons, which are movable toward and away from each other, are situated in a channel, the pistons being situated in such a way that they are activated only by the pilot line assigned to them. The two pistons are thus hydraulically controllable separately from each other. A pressure-impermeable separation is thus to be maintained in the channel, which may be designed in the manner of a bore. In this way, a specific embodiment in a vane may be used as an insertion element which includes two separate chambers and pistons/cups. The insertion element may be provided with two sections having bores in a sleeve. Internally, the spring-loaded pistons or cups close the bores in a basic position, the pressure in both chambers being above the critical pressure. If the pressure in one of the two chambers falls below the critical pressure, the piston located on this chamber side moves, whereby the piston exposes a bore, and an overflow into the chamber having the lower pressure from the other chamber occurs via the bypass line.
A camshaft adjuster of this type may also be refined in that the switching area is the area of the shared pilot line which ensures a hydraulic fluid-permeable connection between the two bypass lines in a pressure difference-/pressure drop-dependent displacement of one of the pistons.
It should be noted that it is possible to provide the springs on the two slide valves with tensile or pressure pretensioning or to eliminate them altogether, depending on how the critical pressure level is to be set, at which the slide valve is to be deflected out of its initial position (closed without pressure). For example, no spring is necessary if the slide valve is to open upon falling below 0 bar, the underpressure in the chamber connected to the corresponding port “pulling open” the slide valve.
A spring having pressure pretensioning is sensible if the slide valve is to be moved only starting at a certain underpressure, e.g., at a pilot pressure of −0.1 bar. A tensile pretensioning is theoretically also conceivable if the slide valve is to open the bypass upon falling below a certain positive pressure, such as above 0 bar. A pilot pressure would then be detectable, e.g., at 0.1 bar. However, this design is risky, because both slide valves are set to “through-flow” upon the startup of the internal combustion engine, i.e., they are open without pressure, and are thus able to generate an undesirable short circuit via the two slide valves. One may try to compensate for this state with the aid of additional switching elements. This design is still technically very critical, since there is the risk of the bypass unintentionally opening or being open in the first place with each torque zero crossing/alternating torque, causing a backflow of the fluid. The variant without a spring is also critical, since the indifferent position of the cups/pistons/slide valves may also cause the wrong bypass to open unintentionally. From a technical perspective, therefore, the variant with spring pretensioning is sensible and preferred, because it permits a defined basic position of the valve, and a secure sealing against chamber pressures may thus occur.
The present invention is explained in greater detail below with the aid of a drawing in which four exemplary embodiments are illustrated.
The figures are only of a schematic nature and are used only for the sake of understanding the present invention. Identical elements are provided with identical reference numerals.
Features of the individual exemplary embodiments are also interchangeable with each other.
A first specific embodiment of a camshaft adjuster 1 according to the present invention is illustrated in
Rotor 2 is rotatably situated in a stator 4, which may be connected to an endless traction mechanism, such as a chain, e.g. via a gear wheel. Rotor 2 and stator 4 form vane cells 5, which are each divided into a first chamber 6 and a second chamber 7 by a vane 3. The first chamber may also be referred to as chamber A, and the second chamber may also be referred to as chamber B, and vice versa. A main shutoff/switchover valve 9 is provided in a line system 8. This main shutoff/switchover valve 9 is situated between a pump (P) 10 and a tank (T) 11. A hydraulic fluid control device 12 is additionally provided.
Hydraulic fluid control device 12 preferably includes two bypass line closing devices 13. The two bypass line closing devices 13 include a valve 14, such as a 2/2-way valve 15. This valve 14, which may also be referred to as a slide valve, is pretensioned with the aid of a spring 16.
Bypass line closing devices 13 are each situated in one bypass line 17 or situated in a shared bypass line 17. There is also a pilot line 18 for each bypass line closing device 13. Upon falling below limit pressure/critical pressure pkrit in first chamber 6, an opening action is ultimately applied to one of the two 2/2-way valves 15 via pilot line 18, so that, as illustrated in
The adjusting direction of rotor 2 relative to stator 4 is symbolized by arrow 19.
However, a variant of the specific embodiments illustrated in
The two bypass line closing devices 13, which are separated from each other, are mounted alternatingly in vane 3. Each bypass line closing device 13 includes a pilot line 18 to particular assigned first or second chamber 6 or 7, which facilitates an opening and closing of particular assigned bypass/bypass line 17 in coordination with active spring 16. Pilot line 18 may also be referred to as a pilot channel.
The arrangement is selected in such a way that the first and second chambers are hydraulically separated from each other in a valve basic position, i.e. when the pilot pressure is above the critical pressure. Neither the (over)pressure in first chamber 6 nor the pressure in second chamber 7 may cause closing element 12 to open in the manner of a piston or a cup, nor cause a pressure gradient between the two chambers 6 and 7.
A suitable recess in the sense of an indentation for the end-face accommodation of closing element 20 may support the secure closing of the closing element/valve body/cup/piston.
The pressure in both chambers is above the critical pressure, as shown in
In
If a pressure compensation occurs between the two chambers 6 and 7, valve/closing element 20 returns to its seat and closes bypass/bypass line 17. A slight recess for accommodating closing element 20 ensures a secure sealing against a laterally acting pressure from chambers 6 and 7.
The system operates like a traditional adjuster in pure OPA mode until the pressure in one chamber 6 or 7 falls as a result of the present alternating torques and critical pressure pkrit set via spring 16 and an active surface of the closing element interior or the piston surface. Up to this point, the system is operated by oil pressure control and is not dependent on “repumping” between the chambers, which has an advantageous effect on the adjusting speed or the adjusting behavior at low torsional moments.
As the moments increase, the adjustment is then additionally supported by the repumping between the chambers, in the sense of a CTA adjustment, i.e. a cam torque actuation. The pressure gradient between chambers 6 and 7 additionally helps achieve higher adjusting speeds. The potential for air intake or outgassing from the oil is minimized. Of course, this also depends on the set pilot pressure.
| Number | Date | Country | Kind |
|---|---|---|---|
| DE102014215419.7 | Aug 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2015/200356 | 6/11/2015 | WO | 00 |
