CAMSHAFT ADJUSTER WITH RESET FUNCTION

Description

[0001] The invention relates to a hydraulic camshaft adjuster for adjusting the phase position of a camshaft relative to a crankshaft in a motor vehicle drive train, comprising a stator, in particular one that is rotationally coupled to the crankshaft, a rotor that is rotatable relative to the stator within a limited angular range, in particular one that is rotationally coupled to the crankshaft, and a hydraulic supply with two working channels and a (first) switching valve. The two working channels can be connected to a pump for pressurizing or to a reservoir for pressure relief to adjust the rotor relative to the stator in two opposite directions of action, depending on the switching position of the switching valve. Hydraulic camshaft adjusters are known, for example, from JP H11 - 13 429 A or DE 196 04 865 A1.

[0002] Hydraulic camshaft adjusters require a rest position in the depressurized state, which is actively moved to when the pressure is off. For example, it is common for the rotor and stator to be adjusted to a defined position relative to each other when the pressure is off, such as a center position, from which the vehicle can be started. The return to the rest position is also referred to as a fail-safe function.

[0003] Known hydraulic camshaft adjusters usually have an integrated spring mechanism to reset the rotor relative to the stator into the defined position / end position, by whose (mechanical) restoring force the rotor is set into the defined position in the pressure-free state.

[0004] However, the prior art has the disadvantage that such spring mechanisms result in additional costs and additional weight for the spring mechanism itself and the components that accommodate the spring mechanism. Furthermore, axial and radial installation space is required to accommodate the spring mechanism. Therefore, the integration of a spring mechanism counteracts the requirement for a camshaft adjuster that is as compact as possible, particularly axially narrow, and does not collide with a central magnet. Furthermore, the provision of such a spring mechanism has the disadvantages of a risk of spring failure during operation due to material failure, and that the spring tension acting on the rotor in one of the two adjustment directions exerts a counter-torque on the rotor, which can lead to different adjustment speeds in one or the other adjustment direction.

[0005] It is therefore the object of the invention to avoid or at least reduce the disadvantages of the prior art and to provide a camshaft adjuster in which the above-described return to a defined position / rest position (fail-safe function) is realized and which, at the same time, is constructed in a particularly cost-effective and weight-saving manner without restricting the functionality of the camshaft adjuster.

[0006] The object of the invention is achieved by a camshaft adjuster having the features of patent claim 1. Advantageous further developments are claimed in the subclaims.

[0007] Accordingly, the object of the invention is achieved in a generic camshaft adjuster in that the hydraulic supply has a reset pump which can be actuated by a displacement of the switching valve between its switching positions and by the actuation of which one of the two working channels can be pressurized to return the rotor to a predetermined position.

[0008] This means that the object of the invention is achieved by a hydraulic camshaft adjuster, for example of the vane cell type, which has a first working chamber formed between the stator and the rotor, which can be pressurized with hydraulic fluid / hydraulic medium / oil via a first working channel for adjusting the rotor relative to the stator in one effective direction, and a second working chamber formed between the stator and the rotor, which can be pressurized with hydraulic fluid / hydraulic medium / oil via a second working channel for adjusting the rotor relative to the stator in the other effective direction, wherein the pressurization of the working chambers is controlled via the switching valve. In normal adjustment operation, one of the working chambers is always connected to the pump for pressurization, while the other of the working chambers is connected to the reservoir for pressure relief.According to the invention, the switching valve is designed such that it has a pumping function (i.e., forms the return pump) in that, through clocked switching of the switching valve (and thus through a longitudinal movement of the switching valve (i.e., the switching adjustment movement)), hydraulic fluid / oil is sucked from a pressureless reservoir and supplied to one of the working chambers. In other words, the supply of hydraulic fluid to one of the working chambers results in the camshaft adjuster being returned to a predetermined position in the pressureless state, thus realizing an electrohydraulic return function.

[0009] According to a preferred embodiment, the hydraulic supply can have a second switching valve which, in a first switching position, connects one of the two working channels (e.g. the second working channel) to the reset pump and, in a second switching position, connects the two working channels to the pump or to the reservoir, depending on the switching position of the (first) switching valve. This means that in the second switching position, normal operation of the adjustment takes place, in which the working channels are switchably pressurised and depressurised, and in the first switching position, a reset function takes place, in which fluid is pumped into one working chamber (e.g. the second working chamber) via the reset pump and fluid is discharged from the other working chamber (e.g. the first working chamber) until the predetermined position is reached. This has the advantage that it is possible to switch between the normal function and the reset function.

[0010] According to a further development of the preferred embodiment, the second switching valve can be designed to be (oil / fluid) pressure-dependently pilot-controlled, wherein the second switching valve is in the first switching position when the pump is depressurized and in the second switching position when pressure is built up at the pump. In particular, the second switching valve is controlled via a control line connected to the pump, by means of which the second switching valve is moved into its unactuated first switching position by the restoring force of a spring when there is no pressure in the control line and, when pressure is present in the control line, into its actuated second switching position against the restoring force of the spring. This ensures that in normal operation, in which pressure is built up at the pump, the second switching valve is in the second switching position, and in the depressurized state it is automatically in the first switching position.This allows for particularly simple control of the second switching valve.

[0011] According to a further development of the preferred embodiment, the hydraulic supply can have a neutral line that connects the reset pump to the reservoir in the second switching position of the second switching valve to form a neutral circuit separate from the working channels. This has the advantage that the reset pump cannot influence the adjustment function during normal operation.

[0012] According to a further development of the preferred embodiment, another of the two working channels (e.g., the first working channel) can be connected, in the first switching position of the second switching valve, via a throttle to a first line and, preferably unthrottled, to a second line. Depending on the switching position of the (first) switching valve, the first line and the second line connect that working channel (e.g., the first working channel) to the pump or to the reservoir. The throttling can provide a sufficiently large differential pressure for the second switching valve.

[0013] According to a further development of the preferred embodiment, the second switching valve can be designed as a sleeve structure arranged coaxially around the switching valve. This has the advantage that the second switching valve can be integrated into existing camshaft adjusters in a cost-effective and space-saving manner.

[0014] According to a preferred embodiment, a pump piston of the reset pump can be integrally formed by a switching valve armature / switching valve spool of the (first) switching valve. According to an alternative preferred embodiment, a pump piston of the reset pump can be connected in series with a switching valve armature / switching valve spool of the (first) switching valve. This means that the longitudinal movement of the switching valve armature is directly coupled to the pump piston, so that a clocked switching of the (first) switching valve actuates the reset pump and thus resets the rotor. Thus, the previously used return spring for returning the rotor to the predetermined position can be replaced by existing components.

[0015] According to a preferred embodiment, the return pump can be connected to a pressureless reservoir via a suction line, wherein the reservoir is formed in a cavity in the camshaft adjuster. This has the advantage that the suction line can be relatively short, for example.

[0016] According to a preferred embodiment, the reset pump can be designed such that its volume flow is greater than 1.2 l / min. This allows the required volume flow to be provided for resetting the rotor.

[0017] In other words, in the camshaft adjuster according to the invention, the reset functionality is not realized by a spring mechanism as in known camshaft adjusters, but by components or subsystems already present in the camshaft adjustment system. Thus, the camshaft adjuster differs from known camshaft adjusters in that the reset is achieved by clocked switching of the modified, electro-hydraulic switching valve instead of being spring-driven, with the modification consisting of an additional pumping function during the longitudinal movement of the switching valve armature. The pumping function can be formed, for example, by a series-connected design or, preferably, an integral design by the switching valve armature of the pump piston. Alternatively, other pump concepts, such as diaphragm pumps, are also conceivable.In a first operating state, the camshaft adjuster is in a pressure-free state, which occurs, for example, when the engine is switched off, since the lubricating oil pump is then unable to build up supply pressure. By cycling the switching valve, initiated by the ECU (control unit), oil is sucked in from a pressure-free reservoir, e.g. a cavity in the camshaft adjuster, and fed to the camshaft adjuster via a pressure line and a directional control valve piloted by the engine oil pressure, in order to move the latter into a predetermined position / its preferred position. The directional control valve can preferably be a sleeve structure arranged coaxially around the switching valve, which is axially displaced by the engine oil pressure against a return spring and accordingly opens / closes the required oil paths. In a second operating state, e.g. after the engine has started or when engine oil pressure is present, a standard adjustment function of the camshaft adjuster is ensured.In addition, a slight throttling of the oil flow may be necessary to ensure sufficient differential pressure for the pilot-operated directional control valve. Furthermore, a neutral circuit may be provided for the pump function, which prevents any influence on the switching behavior of the electrohydraulic switching valve in this operating state.

[0018] The invention is explained below with the aid of drawings. They show: Fig. 1 a schematic representation of a camshaft adjuster according to the invention in a first operating state, and Fig. 2 a schematic representation of the camshaft adjuster according to the invention in a second operating state.

[0019] The figures are merely schematic in nature and serve solely to facilitate understanding of the invention. The same elements are provided with the same reference numerals. The features of the individual embodiments can be interchanged.

[0020] Figs. 1 and 2show a hydraulic camshaft adjuster 1 according to the invention in two different operating modes. The camshaft adjuster 1 serves to adjust the phase position of a camshaft relative to a crankshaft in a motor vehicle drive train. The camshaft adjuster 1 has a stator 2 and a rotor 3 that can be rotated / adjusted relative to the stator 2 within a limited angular range. The stator 2 is rotationally coupled to the crankshaft, and the rotor 3 is rotationally coupled to the camshaft. In the figures, the stator 2 and the rotor 3 are shown merely as examples as a double-acting hydraulic cylinder, wherein an adjustment of the hydraulic cylinder in one direction symbolizes a rotation of the rotor 3 in a first direction of action, and an adjustment of the hydraulic cylinder in the other direction symbolizes a rotation of the rotor 3 in a second direction of action opposite to the first direction of action.

[0021] To adjust the rotor 3 relative to the stator 2, the camshaft adjuster 1 has a hydraulic supply 4, which is shown in the figures in the form of a hydraulic circuit diagram. The hydraulic supply 4 has a first working channel 5, which is connected to a first working chamber formed between the rotor 3 and the stator 2, and a second working channel 6, which is connected to a second working chamber formed between the rotor 3 and the stator 2. When pressure is applied to the first working channel 5 (or the first working chamber) (and pressure is relieved from the second working channel 6), the rotor 3 is adjusted in the first effective direction (to the right in the figures). When pressure is applied to the second working channel 6 (or the second working chamber) (and pressure is relieved from the first working channel 5), the rotor 3 is adjusted in the second effective direction (to the left in the figures).

[0022] The hydraulic supply 4 has a switching valve 7, which is adjustable between a first switching position 8 and a second switching position 9. In the illustrated embodiment, the switching valve 7 is designed as a 2 / 2-way valve. In the first switching position 8, the first working channel 5 is connectable or connected to a pump 10 for pressurization, and the second working channel 6 is connectable or connected to a tank / reservoir 11 for pressure relief. In In the second switching position 9, the first working channel 5 is connectable or connected to the tank / reservoir 11 for pressure relief, and the second working channel 6 is connectable or connected to the pump 10 for pressurization. The switching valve 7 is designed as an electrohydraulic valve that can be actuated / switched by a control unit (ECU) not shown.

[0023] According to the invention, the hydraulic supply 4 has a reset pump 12. The reset pump 12 can be actuated / operated by moving the switching valve 7 between its switching positions 8, 9. This means that an additional pumping function is created during a longitudinal movement of the switching valve 7. By actuating the reset pump 12, one of the two working channels 5, 6, in the illustrated embodiment the second working channel 6, can be pressurized to reset the rotor 3 to a predetermined (rest) position.

[0024] In the illustrated embodiment, the return pump 12 has a pump piston 14 which is displaceable in a pump chamber 13 and by means of which displacement hydraulic fluid can be sucked in from the tank / reservoir 11 via a suction line 15 and introduced into the second working channel 6 via a pressure line 16. The pump piston 14 is moved by the longitudinal movement / switching movement of the switching valve 7. The pump piston 14 can, for example, reduce the size of a pressure chamber 18 connected to the suction line 15 and / or the pressure line 16 against the restoring force of a spring 17. A check valve 19 can be arranged in the suction line 15 to prevent backflow from the pressure chamber 18 into the reservoir 11 via the suction line 15. A check valve 20 can be arranged in the pressure line 16 to prevent backflow from the second working channel 6 into the pressure chamber 18 via the pressure line 16.

[0025] Preferably, the pump piston 14 can be formed integrally with a switching valve armature / switching valve spool of the switching valve 7. Alternatively, the pump piston 14 can be connected in series with the switching valve armature / switching valve spool of the switching valve 7. Further alternatively, the reset pump 12 can be formed as a diaphragm pump or the like, although this is not shown.

[0026] Between the working channels 5, 6 and the switching valve 7 or the return pump 12, a further switching valve 21 designed as a directional control valve is arranged, which can be adjusted between a first switching position 22 and a second switching position 23. The switching valve 21 is pilot-controlled as a function of the oil pressure of the pump 10. This means that the switching valve 21 is controlled via a control line 24 connected to the pump 10 and, when the pump 10 is depressurised, is in the unactuated first switching position 22 (cf. Fig. 1) and when the pressure of the pump 10 is applied, against the restoring force of a spring 25 in the actuated second switching position 23 (cf. Fig. 2 ) is.

[0027] In the first switching position 22, the first working channel 5 is connected to a line 26, which is connected to the pump 10 in the first switching position 8 of the switching valve 7, and to a line 27, which is connected to the reservoir 11 in the first switching position of the switching valve 7. In the first switching position 22, the first working channel 5 is connected to the line 26 via a throttle 28 that limits the fluid flow. The second working channel 6 is connected to the pressure line 16 in the first switching position 22. By initiating cycling of the switching valve 7, the reset pump 12 sucks fluid from the reservoir 11 and feeds it into the second working chamber via the pressure line 16 and the switching valve 21, so that the rotor 3 is moved to the predetermined (rest) position / default position. Fluid can be discharged from the first working chamber via the line 27.

[0028] In the second switching position 23, the first working channel 5 is connected to the line 26, which is connected to the pump 10 in the first switching position 8 of the switching valve 7 and to the reservoir 11 in the second switching position 9 of the switching valve 7. In the second switching position 22, the second working channel 6 is connected to the line 27, which is connected to the reservoir 11 in the first switching position 8 of the switching valve 7 and to the pump 10 in the second switching position 9 of the switching valve 7. In the second switching position 23, the pressure line 16 is connected to the reservoir 11 via a neutral line 29. As a result, the reset pump 12 has a neutral circulation in the second switching position 23, so that the switching behavior of the switching valve 7 is not influenced. List of reference symbols

[0029] 1 Camshaft adjuster 2 Stator 3 Rotor 4 Hydraulic supply 5 First working channel 6 Second working channel 7 Switching valve 8 First switching position 9 Second switching position 10 Pump 11 Reservoir 12 Reset pump 13 Pump chamber 14 Pump piston 15 Suction line 16 Pressure line 17 Spring 18 Pressure chamber 19 Check valve 20 Check valve 21 Second switching valve 22 First switching position 23 Second switching position 24 Control line 25 Spring 26 First line 27 Second line 28 Throttle 29 Neutral line

Claims

1. A hydraulic camshaft adjuster (1) for adjusting the phase position of a camshaft relative to a crankshaft in a motor vehicle drivetrain, having a stator (2), a rotor (3) rotatable relative to the stator (2) within a limited angular range, and a hydraulic supply (4) having two working channels (5, 6) and a shift valve (7), wherein the two working channels (5, 6), for adjusting the rotor (3) relative to the stator (2) in two opposite directions of action, can be connected to a pump (10) for pressurisation or to a reservoir (11) for pressure relief, depending on the shift position (8, 9) of the shift valve (7), characterized in that the hydraulic supply (4) has a reset pump (12) which can be actuated by a displacement of the shift valve (7) between its shift positions (8, 9) and by the actuation of which, one of the two working channels (6) can be pressurised for resetting the rotor (3) into a predetermined position.

2. The camshaft adjuster (1) according to claim 1, characterized in that the hydraulic supply (4) has a second shift valve (21) which, in a first shift position (22), connects one of the two working channels (6) to the reset pump (12) and, in a second shift position (23), connects both the working channels (5, 6) to the pump (10) or to the reservoir (11), depending on the shift position (8, 9) of the shift valve (7).

3. The camshaft adjuster (1) according to claim 2, characterized in that the second shift valve (21) is designed to be pilot-controlled as a function of pressure, wherein the second shift valve (21) is in the first shift position (22) when the pump (10) is depressurised and is in the second shift position (23) when pressure is built up at the pump (10).

4. The camshaft adjuster according to claim 2 or 3, characterized in that the hydraulic supply (4) has a neutral line (29) which connects the reset pump (12) to the reservoir (11) in the second shift position (23) of the second shift valve (21) to form a neutral circulation separate from the working channels (5, 6).

5. The camshaft adjuster (1) according to one of claims 2 to 4, characterized in that another of the two working channels (5) in the first shift position (22) of the second shift valve (21) is connected via a throttle (28) to a first line (26) and to a second line (27), wherein the first line (26) and the second line (27) connect the working channel (5) to the pump (10) or to the reservoir (11), depending on the shift position (8, 9) of the shift valve (7).

6. The camshaft adjuster (1) according to one of claims 2 to 5, characterized in that the second shift valve (21) is designed as a sleeve structure which is arranged coaxially around the shift valve (7).

7. The camshaft adjuster (1) according to one of claims 1 to 6, characterized in that a pump piston (14) of the reset pump (12) is integrally formed by a shift valve armature of the shift valve (7).

8. The camshaft adjuster (1) according to one of claims 1 to 6, characterized in that a pump piston (14) of the reset pump (12) is connected in series with a shift valve armature of the shift valve (7).

9. The camshaft adjuster (1) according to one of claims 1 to 8, characterized in that the reset pump (12) is connected to an unpressurized reservoir (11) via a suction line (15), wherein the reservoir (11) is formed in a cavity in the camshaft adjuster (1)10. The camshaft adjuster (1) according to one of claims 1 to 9, characterized in that the reset pump (12) is designed such that its volume flow is greater than 1.2 l / min.