Camshaft adjuster

Abstract

The invention relates to a camshaft adjuster (1) for rotating a camshaft (2) relative to a crankshaft, the camshaft adjuster comprising: a stator (3) and a rotor (4) which can be rotated about an axial axis (a) relative to the stator (4); two oppositely acting working chambers (A, B) which can be filled with oil; a front cover (5) and a rear cover (6) which axially enclose the working chambers (A, B); a control valve (7) by means of which the working chambers (A, B) can be pressurised with oil; a reservoir (8) for the oil; and an oil drain channel (9) which guides leakage oil escaping between the rotor (4) and the front cover (5) to the reservoir (8), wherein an additional oil drain channel (10) guides further leakage oil to the reservoir (8).

Description

[0001] Camshaft adjuster

[0002] Camshaft adjusters are used in internal combustion engines to vary the timing of the combustion chamber valves. This allows the phase relationship between the crankshaft and the camshaft to be varied within a defined angular range, between a maximum advance and a maximum retardation position. Adapting the timing to the current load and engine speed reduces fuel consumption and emissions. For this purpose, camshaft adjusters are integrated into a drivetrain, through which torque is transferred from the crankshaft to the camshaft. This drivetrain can be designed, for example, as a belt, chain, or gear drive.

[0003] In a hydraulic camshaft adjuster, the output element and the drive element form one or more pairs of opposing pressure chambers, which can be pressurized with hydraulic fluid. The drive element and the output element are arranged coaxially. The filling and emptying of individual pressure chambers generates a relative movement between the drive element and the output element. The spring, acting rotationally between the drive element and the output element, urges the drive element relative to the output element in a direction of advantage. This direction of advantage can be parallel to or opposite to the direction of rotation.

[0004] One type of hydraulic camshaft adjuster is the vane-type adjuster. The vane-type adjuster has a stator, a rotor, and a drive gear with external teeth. The rotor, as the output element, is usually connected to the camshaft in a rotationally fixed manner. The drive element includes the stator and the drive gear. The stator and the drive gear are connected to one another in a rotationally fixed manner or, alternatively, are formed as one piece. The rotor is arranged coaxially to the stator and within the stator. The rotor and the stator, with their radially extending vanes, form opposing oil chambers that can be pressurized with oil and enable relative rotation between the stator and the rotor. Another type of hydraulic camshaft adjuster is the axial piston adjuster.In this case, a sliding element is moved axially via oil pressure, which generates a relative rotation between a drive element and an output element via helical gears.

[0005] Another type of camshaft adjuster is the electromechanical camshaft adjuster, which features a three-shaft gear, such as a planetary gear or a strain wave gear. One of the shafts forms the drive element, and a second shaft forms the output element. Rotational energy can be supplied to or removed from the system via the third shaft using an actuating device, such as an electric motor or a brake, to initiate an adjustment. A spring can also be arranged to support or reverse the relative rotation between the drive element and the output element.

[0006] DE 10 2009 042 202 A1 shows a device for the variable adjustment of the control times of gas exchange valves of an internal combustion engine with a hydraulic phase adjustment device and at least one volume accumulator, wherein the phase adjustment device can be brought into drive connection with a crankshaft and a camshaft and has at least one advance adjustment chamber and at least one retardation chamber, to which pressure medium is supplied or discharged via pressure medium lines.can be discharged from these, wherein by supplying pressure medium to the advance adjustment chamber with simultaneous pressure medium discharge from the retardation chamber a phase position of the camshaft relative to the crankshaft can be adjusted in the direction of earlier control times, wherein by supplying pressure medium to the retardation chamber with simultaneous pressure medium discharge from the advance adjustment chamber a phase position of the camshaft relative to the crankshaft can be adjusted in the direction of later control times, wherein pressure medium can be supplied to the volume accumulator(s) during operation of the internal combustion engine.

[0007] DE 10 2010 019 530 A1 discloses a camshaft adjuster of vane-type construction having a stator and a rotor rotatable relative to the stator, as well as at least two pressure chambers formed between the stator and the rotor, which are separated from one another by a radially oriented vane of the rotor, wherein a pressure medium can be supplied alternately to the pressure chambers, wherein the vane has a radial surface and two side surfaces directed toward the pressure chambers, and wherein the radial surface is sealed by a U-shaped sealing element having a base leg and two side legs resting against the side surfaces. Check valves are formed on the side legs, and outlets for the pressure medium, to which the check valves are assigned, are formed on the side surfaces of the vane.In particular, a volume reservoir for the pressure medium is formed in the rotor, so that this arrangement of the volume reservoir maintains the pressure buildup during adjustment of the camshaft adjuster. From there, the oil is introduced into the interior of the vane via the pressure medium channels and then fed into one of the chambers via an outlet on the corresponding side surface of the vane when the pressure in the chamber is below the volume reservoir.

[0008] Internal combustion engines for trucks are often also used as engine brakes for the vehicle. Various engine brakes have been established, such as decompression brakes and engine exhaust brakes. The engine brake is activated when the engine is towing. The vehicle's kinetic energy is converted into heat through internal friction, as air is compressed and expanded unburned in the combustion engine.

[0009] Engine braking can be implemented using a variety of different concepts. They are generally based on compression in the fourth engine stroke and expansion of the compressed air at the end of the fourth engine stroke. Concepts are also known in which, in addition to the fourth engine stroke, the second engine stroke is also used for the expansion of the compressed air. For example, a brake cam can serve as an additional cam profile on the exhaust camshaft to open the exhaust valves in the desired position for braking. This brake cam is switched on by a switchable lever when braking is required. A camshaft adjuster ensures the correct timing of the engine valves during braking mode to achieve the desired braking performance. Normally, in DOHC engines, the exhaust camshaft is advanced using an exhaust camshaft adjuster, and then the brake cam lever is switched on.From this point on, the engine will be in braking mode. An intake camshaft adjuster then controls the braking performance by adjusting the intake camshaft adjuster to control the amount of air flowing through the engine.

[0010] The camshaft adjustment system formed by the two camshaft adjusters must meet a certain control quality and, to achieve this, must only oscillate to a limited extent in the controlled positions. However, in braking mode, large camshaft torques arise when the exhaust valves open, as the exhaust valves must be opened against high cylinder pressure. Furthermore, the camshaft torques generated in this way are highly asymmetrical, and their average value depends on load and engine speed. Therefore, the average torque cannot be compensated and balanced across the entire operating range with a spring built into the camshaft adjuster.

[0011] If a hydraulic camshaft adjuster is to be held in a specific position, a balance of torque and the hydraulic force of the camshaft adjuster must be created. For this purpose, a control valve with a magnet as an actuator can be used, whose piston is controlled to achieve the balance. Within a certain variance, the camshaft torques can thus be adequately compensated and unwanted oscillations prevented.

[0012] To prevent oscillations, reservoirs are commonly installed in camshaft adjusters. These reservoirs can supply the chambers with additional oil and are designed to ensure adequate hydraulic clamping at all times. These reservoirs fill up by catching system leaks between the rotor and the front cover of the camshaft adjuster. This refilling is necessary for the system's proper function. However, the reservoirs can run dry at certain operating points because the adjuster requires more oil than is available for refilling.

[0013] Especially during braking, the camshaft torques become asymmetrical. The piston position in the control valve then deviates significantly from a mean piston position, resulting in negative effects that can lead to system instability.

[0014] DE 10 2020 105 518 A1 , DE 10 2017 113 361 B3 and JP 2024 - 33 054 A show further camshaft adjusters.

[0015] Object of the invention

[0016] The object of the invention is to provide a camshaft adjuster which ensures a high control quality even at high camshaft torques over a longer period of time.

[0017] The object is achieved by a camshaft adjuster according to claim 1. Advantageous embodiments are the subject of the subclaims.

[0018] According to the invention, additional leaks, for example, those occurring between the stator and the rear and front covers of the camshaft adjuster, are captured and added to the adjuster's reservoir. The same applies to leaks between the rotor and the rear cover of the camshaft adjuster. This not only directs the leaks occurring between the rotor and the front cover to the reservoir, but also significantly more leakage oil.

[0019] In a first embodiment of the invention, the additional oil drain channel guides leakage oil that forms between the stator and the front cover to the reservoir. In this case, it is preferably provided to arrange the additional oil drain channel in the stator. In a further embodiment of the invention, the additional oil drain channel guides leakage oil that forms between the stator and the rear cover to the reservoir. In this case, it is also preferably provided to arrange the additional oil drain channel in the stator.

[0020] In a further embodiment of the invention, the additional oil drain channel guides leakage oil that forms between the rotor and the rear cover to the reservoir. In this case, it is preferably provided to arrange the additional oil drain channel in the rotor.

[0021] Preferably, all adjuster leaks are collected before they leave the adjuster and redirected to the reservoir. This ensures that the reservoir is filled with a sufficient amount of oil at every operating point of the engine. For this purpose, several additional oil drain channels can be provided. These can each drain separately into the reservoir or into a collecting channel leading to the reservoir.

[0022] The additional oil drain channel(s) are provided in the stator of the adjuster, both circumferentially on the front (reservoir side) and on the rear, to collect the corresponding leaks. These oil drain channels are connected to one or more recesses in the stator to allow the oil to flow forward from the rear channel toward the reservoir. Furthermore, these oil drain channels are connected to the adjuster's reservoir via one or more recesses in the front cover and in the check valve plate. The oil drain channels are designed and distributed in such a way that the tightness of the adjuster is not compromised.

[0023] Alternatively or additionally, oil drainage channels or recesses are introduced into the rotor of the adjuster to redirect the leaks between the rear cover and the rotor into the adjuster reservoir.

[0024] The reservoir is a local volume storage unit integrated into the camshaft adjuster. This ensures that oil is available locally and close to the chamber, eliminating the need to transport oil from the more distant tank via pressure lines. The reservoir is preferably located between the front cover and the rotor.

[0025] In one design, the oil drainage channels are machined into the stator or rotor without the need for tools. This eliminates the need for complex, machining-related post-processing. Alternatively, they can be added later, for example, by drilling.

[0026] To collect oil leaks as evenly as possible, one embodiment provides for a portion of the oil drain channel to be formed as an annular channel. The annular channel is designed to be circumferential or partially circumferential on the stator or rotor. The leakage oil collected in the annular channel can be drained away via an axial channel.

[0027] The axial channel can open into the annular channel, which provides a particularly simple oil routing solution. However, to ensure process reliability, it is preferred to arrange the axial channel radially spaced from the annular channel and connect the two channels with a connecting channel. The axial channel, as a collecting channel, can have a larger diameter than the width of the annular channel.

[0028] The proposed camshaft adjuster is particularly suitable for internal combustion engines where engine braking is regularly used, which is especially true for trucks. However, the invention also improves control quality in the passenger car sector.

[0029] Short description of the drawings

[0030] The invention is described below using an exemplary embodiment. The figures show:

[0031] Fig. 1 shows a hydraulic camshaft adjuster in longitudinal section, Fig. 2 shows a circuit diagram for the camshaft adjuster according to Fig. 1,

[0032] Fig. 3a schematic camshaft torques in load operation,

[0033] Fig. 3b schematic camshaft torques in braking mode,

[0034] Fig. 4a is a schematic circuit diagram of the switching valve in a first switching position deviating from a central position,

[0035] Fig. 4b is a schematic circuit diagram of the switching valve in a second switching position deviating from a central position,

[0036] Fig. 5a shows a cross-section of the hydraulic camshaft adjuster according to Fig.

[0037] 1 in a front plane,

[0038] Fig. 5b shows an enlarged partial section of the camshaft adjuster according to Fig. 5a,

[0039] Fig. 6 is a perspective view of the camshaft adjuster according to Fig. 5a,

[0040] Fig. 7a shows a cross-section of the camshaft adjuster according to Fig. 1 in a rear, camshaft-side plane,

[0041] Fig. 7b schematically shows the pressure conditions of an axial channel in a camshaft adjuster according to Fig. 7a,

[0042] Fig. 8a shows a cross-section of the camshaft adjuster according to Fig. 1 in a rear, camshaft-side plane,

[0043] Fig. 8b schematically shows the pressure conditions in an annular channel of a stator of a camshaft adjuster according to Fig. 8a, Fig. 9a shows a cross section of the camshaft adjuster according to Fig. 1 in a rear, camshaft-side plane and

[0044] Fig. 9b schematically shows the pressure conditions in an annular channel of a rotor of a camshaft adjuster according to Fig. 9a.

[0045] Detailed description of the drawings

[0046] A hydraulic camshaft adjuster 1 according to Figure 1 has a stator 3 as a drive element and a rotor 4 as an output element. The rotor 4 is rotationally connected to a camshaft 2, and the stator 3 is rotationally connected to a drive gear 11, for example, a sprocket, which is rotationally fixed to the crankshaft. The stator 3 and the rotor 4 are rotatable about the common axis of rotation a. The stator 3 and the rotor 4 are axially closed by a front cover 5 and a rear cover 6. The covers 5, 6 form sealing covers.

[0047] A set of working chambers A, B is formed between the stator 3 and the rotor 4 (Fig. 2, Fig. 5a). In the present case, the camshaft adjuster 1 has three working chambers A and three working chambers B, which are hydraulically separated from one another by vanes 12 arranged in the rotor 4. Pressurizing chamber A with hydraulic oil adjusts (retards) the rotor 3 relative to the stator 4 within an adjustment range defined by end stops 13 against the circumferential direction; pressurizing chamber B causes the rotor 3 to advance relative to the stator 4.

[0048] To pressurize the working chambers A, B with hydraulic oil, the camshaft adjuster 1 has a control valve 7 with a piston 17 in a valve sleeve 18 that can be moved by an actuator 19. Due to its arrangement on the axis of rotation a, the control valve 7 is also referred to as a central valve. As is clear from the circuit diagram in Figure 2, the working chambers A, B are supplied with oil from a reservoir 8, which is designed as a local volume accumulator arranged in the camshaft adjuster 1. As can be seen from Fig. 7b, for example, the reservoir 8 borders on the front cover 5 and is closed at the front by a spring cover 15. Spring-loaded check valves 14 prevent the oil from flowing back into the reservoir 8. The reservoir 8 serves as an intermediate storage device and is connected to an external volume accumulator 16 of an internal combustion engine via a tank connection T.The reservoir 8 is initially filled from the camshaft adjuster 1 via the tank connection T of the control valve 7. The cover 5 additionally accommodates a torsion spring (not shown) as a return spring, which clamps the rotor 4 and the stator 3 together in a circumferential direction.

[0049] During operation of the camshaft adjuster 1, hydraulic fluid from the control valve 7 is captured by a funnel-shaped design of the front cover 5 and, due to centrifugal force, collected in the reservoir 8 at its radially outer inner edge. As soon as a certain fill level in the reservoir 8 is exceeded, a portion of the collected hydraulic fluid can be supplied to the desired working chamber A, B via the corresponding check valve 14 or is sucked into the working chamber B, A by the negative pressure caused by camshaft alternating torques.

[0050] Figures 3a and 3b show camshaft alternating torques plotted against the camshaft angle. Figure 3a illustrates load operation. It can be seen that – apart from friction-related flank stretching – the camshaft torques are symmetrical. In particular, the maximum amplitude in the advanced direction 20 is comparable to the maximum amplitude in the retarded direction 21 during load operation. In braking operation, as shown in Figure 3b, the camshaft torques shift and become asymmetrical, so that the maximum amplitude in the retarded direction 23 is significantly greater than the maximum amplitude 22 in the advanced direction. In this position, in a prior-art camshaft adjuster, reservoir 8 is not sufficient to continuously supply one of the working chambers A, B with the desired amount of oil despite leakage losses. Compensation with a stronger return spring would be possible, but would have a detrimental effect on load operation.In addition, the mean camshaft torques during braking depend strongly on the speed and braking load, so that the choice of a return spring for all operating points would always represent a compromise.

[0051] Figures 4a and 4b illustrate the difficulties of controlling a hydraulic camshaft adjuster 1 with highly asymmetrical camshaft torque changes. If these occur, the controller of the control valve 7 must control the valve well outside its center position in order to hydraulically support the resulting center torque. However, the further the piston 17 of the control valve 7 is positioned off-center in the valve sleeve 18 accommodating the piston 17, the more asymmetrical the leakage compensation of one of the two working chambers A, B becomes. Figure 4a shows control of the control valve 7 with a PWM level significantly above 50%. In the position shown, a large center position compensation for the working chamber A can be achieved from a pressure port P, while almost no center position compensation can be achieved for the working chamber B. The working chamber B is therefore dependent on its leakage losses, which can occur, for example, at the leaks 25 (Fig.1 ) from reservoir 8. If this is exhausted, mid-position compensation is no longer possible, resulting in strong oscillations. The situation is reversed in Figure 4b, which shows control of control valve 7 with a PWM level of significantly below 50%. In the position shown, a large amount of mid-position compensation for working chamber B can take place from pressure port P, while almost no mid-position compensation can take place for working chamber A. Working chamber A is therefore dependent on compensating its leakage losses from reservoir 8.

[0052] Figures 5a to 9b show how a permanent filling of the reservoir 8 can be ensured. From the cross-section of the camshaft adjuster 1 shown in Figure 5a, it is clear that the rotor 4 is located at an end stop 13 of the stator 3. Sealing strips 24 seal the rotor 4 to the stator 3. To collect the leakage losses from the working chambers A, B, the stator 3 has circular grooves as annular channels 31 on both its side facing the front cover 5 and its side facing the rear cover 6. The annular channels 31 are designed to be completely circumferential with a constant groove depth. Via three connecting channels 35, the annular channels 31 are each hydraulically connected to an axial channel 33, so that the oil can be fed to one another and to the reservoir 8 via the axial channels 33.In an alternative variant not shown, several spaced-apart annular channel segments form an annular channel, with each of the annular channel segments then requiring its own return (axial channel) to the reservoir 8. Each annular channel 31, together with the connecting channel 35 and the axial channel 33, forms a further oil drain channel 10.

[0053] The rotor 4 also has an annular groove as an annular channel 32. The annular channel 32 is directly connected to axial channels 34. In other words, the axial channels 34 open into the annular channel 32, so that no connecting channel is required between them. In the present case, the rotor 4 has three axial channels 34, which open into the front-side reservoir 8. The annular channel 32, which is arranged on the side facing the front cover 5, forms the oil drain channel 9 or part of the oil drain channel 9. The annular channel 32, which is arranged on the side facing the rear cover 6, forms another oil drain channel 10 or part of another oil drain channel 10.

[0054] Figures 7b, 8b, and 9b illustrate the return of the leakage oil in the dashed areas of Figures 7a, 8a, and 9a. Otherwise, Figures 7a, 8a, and 9a correspond to Figure 5a.

[0055] Figure 7b shows the return of the leakage oil (dashed line) from the annular channels 31 of the stator 3 on the axial side facing the front cover 5 and thus the reservoir 8. The oil pressure Pch in the additional oil drain channel 10 is always greater than the ambient oil pressure Pu or that of the reservoir PR, so that the collected oil actually flows out due to the positive pressure difference AP2 = Pch - Pu. The same applies to the pressure difference APi = PA, B - PU as the difference between the respective chamber pressure and the channel pressure. Figure 8b shows the pressure conditions and the flow path (dashed line) of the leakage oil in the two axially opposite annular channels 31. Finally, Figure 9b shows the flow paths of the leakage oil from the annular channels 32 of the rotor. The fact that all leakage residues are collected in this embodiment ensures that the reservoir 8 cannot run dry, even over a long period of time in the braking mode of the internal combustion engine.

[0056] List of reference symbols

[0057] Camshaft adjuster

[0058] camshaft

[0059] stator

[0060] Rotor front cover rear cover

[0061] control valve

[0062] Volume storage

[0063] Oil drain channel additional oil drain channel

[0064] drive wheel

[0065] wing

[0066] End stop

[0067] Check valve

[0068] spring cap

[0069] Volume storage

[0070] Pistons

[0071] valve sleeve

[0072] Actuator

[0073] Maximum amplitude early in load operation

[0074] Maximum amplitude late in load operation

[0075] Maximum amplitude early in braking operation

[0076] Maximum amplitude late in braking operation

[0077] sealing strip

[0078] Leaks

[0079] Ring canal

[0080] Ring canal

[0081] axial channel

[0082] axial channel

[0083] Connecting channel A working chamber

[0084] B Working chamber

[0085] P pressure connection

[0086] T Tank connection a Rotation axis

Claims

Patent claims 1 . Camshaft adjuster (1 ) for the relative rotation of a camshaft (2) to a crankshaft with - a stator (3) and a rotor (4) rotatable about an axial axis (a) relative to the stator (4), - two opposing working chambers (A, B) that can be filled with oil, - a front cover (5) and a rear cover (6) which axially enclose the working chambers (A, B), - a control valve (7) through which the working chambers (A, B) can be pressurised with oil, - a reservoir (8) for the oil, characterized by - an oil drain channel (9) which leads leakage oil escaping between the rotor (4) and the front cover (5) to the reservoir (8) and through - another oil drain channel (10) which directs further leakage oil to the reservoir (8).

2. Camshaft adjuster (2) according to claim 1, characterized in that the further oil drain channel (10) is arranged in the rotor (3).

3. Camshaft adjuster (2) according to claim 1, characterized in that the further oil drain channel (10) is arranged in the stator (4).

4. Camshaft adjuster (2) according to one of the preceding claims, characterized in that the further oil drain channel (10) between the stator (3) and the front cover (5) directs leakage oil generated to the reservoir (8).

5. Camshaft adjuster (2) according to one of the preceding claims, characterized in that the further oil drain channel (10) between the stator (3) and the rear cover (6) leads leakage oil to the reservoir (8) leads.

6. Camshaft adjuster (2) according to one of the preceding claims, characterized in that the further oil drain channel (10) between the rotor (3) and the rear cover (6) directs leakage oil generated to the reservoir (8).

7. Camshaft adjuster (2) according to one of the preceding claims, characterized in that one of the oil drain channels (9, 10) has an annular channel (31, 32).

8. Camshaft adjuster (2) according to claim 7, characterized in that one of the oil drain channels (9, 10) has an axial channel (33, 34).

9. Camshaft adjuster (2) according to claims 7 and 8, characterized in that the axial channel (33, 34) is arranged radially offset from the annular channel (31, 32) and is connected to it by a connecting channel (35).

10. Internal combustion engine for a truck with a camshaft adjuster (1) according to one of the preceding claims.

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