Patent Application
20170159579
Camshaft adjusters of this type are used to change the timing of gas exchange valves of an internal combustion engine during engine operation for the purpose of improving the consumption values and the operating behavior of the internal combustion engine.
One specific embodiment, which has been proven and tested in practice, is a camshaft adjuster designed as a vane adjuster, including a stator and a rotor which delimit an annular space, which is divided into two working chambers by vanes. A hydraulic medium may be optionally applied to the working chambers, which is supplied to the working chambers on one side of the vanes of the rotor from a pressure medium reservoir in a pressure medium circuit via a pressure medium pump, and which is fed back into the pressure medium reservoir from the working chambers on the particular other side of the vanes. The working chambers whose volume is increased have an operating direction which is opposite the operating direction of associated opposite working chambers. Due to the operating direction, a rotation of the rotor relative to the stator may be triggered in the clockwise or counterclockwise direction. The control of the pressure medium flow, and thus the adjusting movement of the camshaft adjuster, includes a hydraulic multi-way switching valve, with the aid of which flow-through openings may be blocked or unblocked as a function of a position of a valve body.
One problem with these camshaft adjusters is that they are not yet fully filled with pressure medium in a start phase or have not yet been emptied. When the engine starts, if the oil pressure within the internal combustion engine has not yet been built up, the alternating torques applied by the camshaft may trigger uncontrolled movements of the rotor with respect to the stator, which may result in increased wear and an undesirable noise development. To avoid this problem, it is known to provide a locking device between the rotor and the stator, which locks the rotor when the internal combustion engine is turned off in a rotation angle position with respect to the stator which is favorable for startup.
Locking devices of this type preferably include spring-loaded locking pins, which successively lock into locking gates provided on the sealing cover or the stator when the rotor rotates. Before a central locking position is reached, a rotation of the rotor in the direction of the central locking device is possible, but a rotation of the rotor in the opposite direction is blocked. After the internal combustion engine has warmed up and/or the camshaft adjuster has been completely filled with pressure medium, the locking pins are forced out of the locking gates, actuated by the pressure medium, so that the rotor is subsequently able to properly rotate with respect to the stator to adjust the rotation angle position of the camshaft.
A control device assigned to the vanes is also known, whose control pins are positioned in the vane separating the working chambers. A fluidic connection of two oppositely acting working chambers may be established with the aid of this control device. The control pins are moved against a spring force by the application of pressure medium. The control pins may be arranged in such a way that a fluidic connection between the working chambers is interrupted upon an application of pressure medium. When the internal combustion engine is turned off, both the spring-loaded locking pins of the locking devices and the control pins of the control device are placed from an unlocking position into an unpressurized locking position by the spring force.
A hydraulic camshaft adjuster designed as a vane adjuster is known from the publication U.S. Pat. No. 6,684,835 B2, whose central locking action takes place when the engine is turned off. An electronic control unit detects a signal which is generated when the engine is turned off as well as signals that represent the status of the stator relative to the rotor. An electrical control valve includes five ports, of which one port accommodates the oil inflow from the lubricating oil circuit of the engine or the pressure medium pump, one port connects the solenoid valve to all locking pistons or locking pins, and two ports connect the solenoid valve to working chambers A and B of the camshaft adjuster and one tank port is provided for the oil outflow from the solenoid valve.
An object of the present invention is to provide a starting strategy for the internal combustion engine, which makes it possible to lock the camshaft adjuster in the central locking position even during an active pressure medium adjustment.
The present invention provides a starting strategy of the internal combustion engine, which provides a hydraulic circuit, in which an additional, fifth control position is provided for the switching valve. In the additional control position, a flow connection exists between the A port and the P port and consequently between the pressure pump and working chambers A. The B port communicates with the T port and consequently with the oil or pressure medium reservoir and working chambers B. The C port connects the control device of the vanes to the T port. Five control positions, which are also to be referred to as piston positions, are thus provided for the switching valve according to the present invention which includes five connections or ports. A P port, or inlet port, is connected to a pressure pump, and a T port, or outlet port, is assigned to a tank or pressure medium reservoir. The A port forms a connection for the working chambers, and the B port is in contact with the working chambers. The additional C port is designated for the control device of the vanes. The additional, second control position of the control valve follows the first control position, which is approached when the engine stops and which is situated upstream from the third control position, in which the camshaft adjuster is adjustable to ADVANCE.
In this additional, second control position, the C port is connected to the T port or the tank, corresponding to the first control position. The locking gate of the locking device thus remains unpressurized, and at least one locking pin is able to engage with the locking gate. Deviating from the first control position of the switching valve, however, the B port is connected to the T port. The additional control position of the switching valve has a positive impact on the characteristic of the volume flow of the hydraulic medium. In the second control position, no oil or hydraulic medium yet flows into the hydraulic line connected to the C port. However, the working chamber is already connected to the T port, whereby the oil may be forced out of the working chamber. Consequently, the hydraulic pressure present in the working chamber effectuates an adjustment in the ADVANCE direction.
The starting strategy according to the present invention is advantageously characterized in that the hydraulic line connected to the C port is depressurized in the additional control position, whereby the locking pins engage into the locking gate unhindered. In addition, a disadvantageous adjustment of the camshaft adjuster past the central locking position in the ADVANCE direction is effectively prevented. With the aid of the starting strategy according to the present invention, the hydraulic camshaft adjuster may be adjusted into the central locking position and locked therein primarily during the shutdown operation of the internal combustion engine.
If the engine has stalled or if central locking is not possible for physical reasons, for example due to low ambient temperatures and the high oil viscosity associated therewith, the starting strategy according to the present invention ensures that the desired central locking action is achieved during the subsequent startup of the internal combustion engine. For this purpose, the hydraulic lines of the line system are switched in such a way that the pressure medium is able to flow out of a pressure medium chamber, which is used for acting upon the control and locking pins, into the pressure medium reservoir. In the unpressurized state of the hydraulic lines, the camshaft adjusters may be placed into the locking position and locked therein.
The starting strategy according to the present invention may be advantageously applied if the camshaft adjuster does not lock in a central locking position (CLP) in a start phase of the internal combustion engine and an angle position sets in between a RETARD end stop and the central locking position. In the start phase, the angle position of the camshaft may be determined after one camshaft revolution at the latest, for example with the aid of sensors in connection with a control unit of the internal combustion engine. For example, if the camshaft adjuster is then in the angle position between the RETARD end stop and the central locking position, the starting strategy according to the present invention is automatically initiated. A switching element, in particular an electromagnet of the switching valve, is then energized in such a way that it displaces a piston of the switching valve into the second control position.
According to the present invention, an arrangement of working ports on the switching valve is furthermore proposed, according to which the B port is placed in the center, the A port is placed on the right side and the C port is situated on the left side thereof. The port arrangement ensures an application of pressure onto the working chambers in the second control position, whereby the camshaft adjuster adjusts in the ADVANCE direction. In contrast thereto, in the previous port arrangement in connection with the four control positions of the switching valve, the camshaft adjuster adjusts to RETARD in the second control position and thus not in the direction of the central locking position.
As a measure for clearly limiting the actuations of the vane, the locking device furthermore has separate locking pins for an advance locking and for a retard locking. An inadvertent actuation of the vane into the ADVANCE working chamber as well as into the RETARD working chamber may be effectively prevented thereby.
For the operation of the locking device, it is advantageous if the locking pin designated for the advance locking disconnects a hydraulic line in a position extended from the rotor and consequently prevents a hydraulic flow in the direction of working chamber A. Accordingly, the locking pin designated for retard locking also disconnects a hydraulic line in a position extended from the rotor and thus interrupts a hydraulic flow acting upon working chamber B.
It is furthermore provided that all locking pins of the locking device are inserted in a spring-loaded manner. Pressure springs are preferably suitable therefor, whose particular spring force forces the relevant locking pin out of the rotor and into the locking gate in the absence of a counter-force. This measure ensures a failsafe adjustment of the camshaft adjuster even if the system pressure or the oil pressure is eliminated.
According to one advantageous embodiment, a first check valve is assigned to a hydraulic line assigned to a vane for the purpose of preventing a hydraulic flow from one working chamber into the additional working chamber, preferably for a hydraulic flow from the ADVANCE working chamber into the RETARD working chamber. Alternatively or additionally, a second check valve may be provided for the hydraulic line of another vane, which has a reverse operating direction from that of the first check valve. In the first of the two cases, a progression of the vane in the ADVANCE direction is achieved with the aid of the check valve, a progression in the RETARD direction being ensured in the second of the two cases.
A preferred structure of the camshaft adjuster in connection with the measure according to the present invention includes preferably four or more vanes for the purpose of achieving an optimum force distribution, which are situated on the rotor, distributed symmetrically over the circumference, and assigned to the pressure chambers.
The present invention is explained in greater detail below on the basis of one preferred exemplary embodiment. Specifically:
A camshaft adjuster 1, having a known basic structure, is illustrated schematically in
The rotation angle of the camshaft with respect to the crankshaft during normal operation, e.g., in the ADVANCE direction, is adjustable by the fact that pressure medium is applied to working chambers 11, 13, 15 via hydraulic line 30, whereby their volume is increased, while the pressure medium is simultaneously forced out of working chambers 12, 14, 16 and their chamber volume is consequently reduced. In
Locking device 29 includes two locking pins 33, 34, which are also to be referred to as locking pinions, and which are linearly displaceable and inserted, spring loaded, into a receptacle 35 of rotor hub 4. Locking pins 33, 34 are arranged in the direction of a locking gate 36, spring-loaded by a spring element 43. Locking device 29 is released to facilitate the adjustment of rotor 3 with respect to stator 2. This takes place by applying pressure medium to locking gate 36, for which purpose pressure medium is supplied from C port 22 via hydraulic line 32 and another hydraulic line 37 in a corresponding control position of switching valve 17. Due to the application of pressure medium, locking pins 33, 34 are forced out of locking gate 36, so that rotor 3 is able to rotate freely with respect to stator 2.
Flow connections 38, 39, 40 are introduced into each of vanes 5, 6, 7, flow connections 38, 39 being assigned to a check valve 41, 42, which facilitates an overflow of the pressure medium or hydraulic medium from working chamber 12 into working chamber 11 or from working chamber 13 into working chamber 14. The flow of the pressure medium through flow connections 38, 39, 40 may be unblocked or blocked by switchable, control pins 44, 45, 46, to which spring force is applied. Switchable control pins 44, 45, 46, to which spring force is applied and which are assigned to control device 23, 24, 25, are each acted upon by pressure medium via hydraulic line 32 and are adjustable from a locking position into an unlocking position. In the unlocking position, the flow-through flow connection 38, 39, 40 is blocked, so that working chambers 11, 12; 13, 14 and 15, 16 are separated from each other.
According to first control position 47a of switching valve 17 illustrated in
The application of the starting strategy according to the present invention is provided for the event that camshaft adjuster 1 does not lock in a central locking position (CLP) in a start phase of the internal combustion engine. In the start phase, the controller of the internal combustion engine briefly detects the angle position of the camshaft, no later than after one revolution of the camshaft. If camshaft adjuster 1 is not locked in the central locking position (CLP) but rather, for example, in an angle position between a RETARD stop position and the central locking position, the starting strategy according to the present invention is automatically initiated. Switching valve 17 is energized in such a way that its piston approaches control position 47b, the second position. After a brief engine standstill, an oil pressure builds up relatively quickly in the internal combustion engine, so that oil as the hydraulic medium is applied to working chambers 13, 15 from P port 18 to A port 20 and via hydraulic line 30. At the same time, working chambers 14, 16 are connected to the tank or the pressure medium reservoir via hydraulic line 31, B port 21 and T port 19. Similar to control position 47c, the third piston position, camshaft adjuster 1 is adjusted into control position 47c in the direction of the arrow, i.e., in the ADVANCE direction.
In contrast to control position 47c but corresponding to control position 47a, C port 22 is connected to T port 19 in control position 47b, resulting in an unpressurized hydraulic line 32 and unpressurized locking gate 36, whereby locking pin 33 remains engaged in locking gate 36. Deviating from control position 47a, the first piston position, which provides a closed B port 21, B port 21 is also connected to the tank via T port 19 in control position 47b. In first control position 47a, B port 21 is closed, so that the oil does not flow out of camshaft adjuster 1 back into the tank in the start phase of the internal combustion engine when camshaft adjuster 1 is being filled. This results in increased pressure medium or oil leaks, which prevent a necessary, short-term pressure buildup within the internal combustion engine. Compared to previous approaches, A port 20 and the B port are reversed for the starting strategy according to the present invention, so that camshaft adjuster 2 adjusts to ADVANCE in second control position 47b of switching valve 17. In the previous circuit, camshaft adjuster 1 would have adjusted to RETARD and thus not in the direction of the central locking position (CLP).
Based on the new starting strategy, camshaft adjuster 1 is able to adjust only to up the central locking position, where it locks due to the engagement of locking pin 34. The internal combustion engine may subsequently be started up. After a long standstill time, the oil pressure buildup within the internal combustion engine may be prolonged, whereby the adjusting operation is slightly delayed. The starting strategy according to the present invention may, however, also be applied here, since a delayed oil pressure buildup does not have a negative impact on the start operation.
A flowchart for the starting strategy of an internal combustion engine according to the present invention is illustrated graphically in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 212 617.7 | Jun 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2015/200176 | 3/19/2015 | WO | 00 |
