Camshaft adjuster

Abstract

The invention relates to a camshaft adjuster (2) for relative rotation between a camshaft (7) and a crankshaft, the camshaft adjuster comprising: a stator and a rotor (5) which form two working chambers acting in opposite directions; a hydraulic valve (15) by means of which hydraulic medium pressure can be applied to the working chambers to enable relative rotation; a volume accumulator (4) which is arranged in the camshaft adjuster (2) and collects leakage losses of the hydraulic medium; and a hydraulic medium line (8) which supplies pressurised hydraulic medium to the volume accumulator (4) from a pressurised hydraulic medium connection (6) via the external surface (14) of the hydraulic valve (15).

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, via 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 designed to be non-rotatably connected to the camshaft. The drive element contains the stator and the drive gear. The stator and the drive gear are non-rotatably connected to one another or, alternatively, are formed as a single piece. The rotor is arranged coaxially to the stator and within the stator. The rotor and stator, with their radially extending vanes, form opposing oil chambers which can be pressurized with oil and enable relative rotation between the stator and the rotor. The vanes are either designed as a single piece with the rotor or stator, or are arranged as “inserted vanes” in designated slots in the rotor or stator.The vane cell adjusters also feature various sealing covers. The stator and the sealing covers are secured together by several screw connections.

[0005] Another type of hydraulic camshaft adjuster is the axial piston adjuster. In this case, a sliding element is axially displaced by oil pressure, which generates a relative rotation between a drive element and an output element via helical gears.

[0006] Another type of camshaft adjuster is the electromechanical camshaft adjuster, which features a three-shaft gear (e.g., a planetary gear or a wave gear). One of the shafts forms the input 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 adjustment. A spring can also be installed to support or reverse the relative rotation between the input element and the output element.

[0007] 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 adjustment 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.DE 10 2010 019 530 A1 discloses a camshaft adjuster in vane-type construction with 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. A pressure medium can be supplied alternately to the pressure chambers. The vane has a radial surface and two side surfaces directed toward the pressure chambers, and the radial surface is sealed by a U-shaped sealing element with 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 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 by a switchable lever when braking is required. A camshaft adjuster ensures the correct control timing of the engine valves during braking mode, thus setting the desired braking performance.

[0010] Typically, in DOHC engines, the exhaust camshaft is advanced using an exhaust camshaft adjuster, and then the brake cam lever is engaged. 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.

[0011] The camshaft adjustment system formed by the two camshaft adjusters must meet a certain control quality and, to achieve this, must oscillate only to a limited extent in the controlled positions. However, in braking mode, very large camshaft torques arise when the exhaust valves open, as the exhaust valves must be opened against very high cylinder pressure. Furthermore, the camshaft torques generated in this way are highly asymmetrical, and their average value depends on load and engine speed.

[0012] Therefore, the mean torque cannot be compensated and balanced across the entire operating range with a spring built into the camshaft adjuster. If the camshaft adjuster is to be held in a specific position, a balance of the torque must be created with the hydraulic force of the camshaft adjuster. 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.

[0013] However, if the piston position in the control valve deviates too much from a middle piston position, one set of chambers (A or B) of the camshaft adjuster is supplied with too little oil from the oil gallery.

[0014] To solve this problem, reservoirs are known from which the chambers can be supplied with additional oil and which are intended to always ensure sufficient hydraulic clamping. A reservoir normally refills itself through system leaks. This refilling is crucial for the correct functioning of the system. However, not all system leaks can be completely absorbed in the reservoir, so that at certain operating points it runs dry because more oil is required by the adjuster than is available for refilling. In such a case, the system will fail immediately. As a result, the oscillations increase significantly and exceed the permissible oscillation limit.

[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, an additional oil supply is created for the volume accumulator, also referred to as the reservoir. This ensures that the reservoir is not only refilled through leakage losses, but is supplied with a sufficient amount of oil at every operating point of the engine. For this purpose, a hydraulic fluid path from the oil gallery directly to the reservoir of the camshaft adjuster is implemented in the form of a direct connection. This means that the reservoir is not only filled through accumulated leakage losses, but can also be supplied with pressurized fluid directly from the pressurized oil gallery. This ensures that the volume accumulator integrated in the camshaft adjuster is not dependent solely on leakage losses or a supply via a (depressurized) tank connection for filling.Rather, filling can be ensured in all operating conditions by connecting the external hydraulic fluid supply through the constantly pressurized oil gallery.

[0019] Preferably, the pressure is reduced to a level appropriate for the volume accumulator by appropriate throttle points in the hydraulic fluid path. The invention proposes that the outer surface of the hydraulic valve, which supplies the working chambers with hydraulic fluid, forms part of the hydraulic fluid path. This largely eliminates the need for drilling holes in components of the camshaft adjuster.

[0020] In one embodiment of the invention, the hydraulic valve has a cylindrical outer surface into which a longitudinal groove is formed. The longitudinal groove forms part of the axial hydraulic fluid path.

[0021] Additionally or alternatively, the rotor of the camshaft adjuster can be provided with an axial feedthrough. Preferably, the hydraulic fluid for the axial feedthrough is collected in an annular channel in the rotor.

[0022] The volume accumulator is integrated into the camshaft adjuster and thus located between the two side covers. Preferably, there is only a single volume accumulator, which is integrated, for example, into a front spring cover.

[0023] The hydraulic fluid path is preferably formed outside the rotor feedthrough and any potential camshaft feedthrough along component boundaries. This allows it to be created without the need for tools, and additional holes are largely avoided.

[0024] Alternatively and additionally, sections of the hydraulic fluid path can be formed by a bore or a recess. These can form a throttle point that is independent of component tolerances, allowing a predefined oil flow to be set in the oil path designed as an additional supply path.

[0025] The desired hydraulic fluid flow is defined by adjusting various throttling points in this additional supply path.

[0026] The hydraulic fluid in the volume accumulator is sucked in by a working chamber during an adjustment process, as a vacuum peak can occur in the working chamber to be enlarged during an adjustment process due to camshaft alternating torques. During this short time interval, this vacuum peak opens a check valve located between the working chamber and the volume accumulator, after which the hydraulic fluid stored in the volume accumulator can flow into the working chamber and compensate for the supply shortage caused by the vacuum peak. As a result, less air can enter the working chamber because the hydraulic fluid is sucked in from the volume accumulator. For this purpose, it is advantageous if the openings of the hydraulic fluid lines to the volume accumulator are covered with a level of hydraulic fluid.

[0027] In a particularly preferred embodiment, the camshaft adjuster forms a camshaft adjustment device with a camshaft supported by a rolling bearing. The rolling bearing can be located in the hydraulic fluid path and can then also be lubricated thereby or supplied with lubricant in another way.

[0028] Description of the drawings

[0029] Fig. 1 shows a camshaft adjusting device 1 with a camshaft adjuster 2 according to the invention and a camshaft 5 and a central valve 15 shown only schematically.

[0030] The camshaft adjuster 2 has a drive element with a toothed system and an output element 5, which are rotatable relative to each other. This rotatability is achieved—as is known from the prior art—by opposing working chambers formed between these two elements, which are controlled by a hydraulic valve 15 as a control valve. The camshaft adjuster 2 is bounded on one axial side by a cover 3. In this case, the cover 3 is made of sheet metal and is pot-shaped. On the camshaft adjuster side, the cover 3 forms a volume accumulator 4.

[0031] A hydraulic fluid line 8 connects the volume accumulator 4 to a pressurized oil supply, which here is designed as a pressure fluid connection 6 of the camshaft 7. The hydraulic fluid line 8 has first sections 9, which are designed as bores, and second sections 10, which are formed at the interfaces of components of the camshaft adjustment device 1. The supply of the volume accumulator 4 by absorbing leakage losses is not shown in the drawing. However, the additional oil supply via a pressurized hydraulic fluid line 8 is symbolized by arrows 11. The hydraulic fluid line 8 leads from the hydraulic fluid connection 6 of the camshaft 7 via first sections 9, which are designed as bores, and an axial groove 16 in the valve housing of the hydraulic valve 15. From there, the hydraulic fluid flows via an annular channel 12 in the rotor 5 and a through-bore in the rotor 5 to the through-bore in the spring receptacle of a return spring in the cover 3.Finally, the hydraulic fluid is pumped radially outward due to centrifugal force into the volume accumulator 4, which serves as the oil reservoir of the cover 3. The cross-sections of the first and second sections 9, 10 are used to throttle the hydraulic fluid flow. This allows for a defined additional supply depending on the hydraulic fluid pressure.

[0032] As can be seen from Fig. 2, a groove 14 forms part of the hydraulic fluid line 8. The groove 14 is axially directed and is introduced into the outer circumference, the lateral surface, of the hydraulic valve 15 designed as a central valve.

[0033] Figure 3 shows schematically the rotor 5 of the camshaft adjuster 2. As far as relevant for the invention, it has an annular channel 12 and an axial recess 13 in the form of a bore, both of which are part of the hydraulic fluid line 8.

[0034] List of reference symbols

[0035] Camshaft adjustment device

[0036] Camshaft adjuster

[0037] Lid

[0038] Volume storage

[0039] rotor

[0040] Hydraulic fluid connection

[0041] camshaft

[0042] Hydraulic fluid line

[0043] First section

[0044] Second section

[0045] Arrow

[0046] Ring canal

[0047] axial recess

[0048] lateral surface

[0049] hydraulic valve

[0050] Nut

Claims

Patent claims 1 . Camshaft adjuster (2) for relative rotation between a camshaft (7) and a crankshaft, with - a stator and a rotor (5) forming two opposing working chambers, - a hydraulic valve (15) through which the working chambers can be pressurised with hydraulic medium pressure for relative rotation, - a volume accumulator (4) arranged in the camshaft adjuster (2), which collects leakage losses of the hydraulic fluid - a hydraulic fluid line (8) which supplies pressurised hydraulic fluid to the volume accumulator (4) from a pressurised hydraulic fluid connection (6) via the outer surface (14) of the hydraulic valve (15).

2. Camshaft adjuster according to claim 1, characterized in that the hydraulic valve (15) has a groove (16) on its outer surface (14) which forms part of the hydraulic medium line (8).

3. Camshaft adjuster according to claim 1 or 2, characterized in that the rotor (5) has an annular channel (12) and an axial recess (13) opening into the annular channel (12), wherein the annular channel (12) and the axial recess (13) form part of the hydraulic medium line (8).

4. Camshaft adjuster according to one of the preceding claims, characterized in that the volume accumulator (4) is arranged in a cover (3) of the camshaft adjuster (2) designed as a spring cover.

5. Camshaft adjusting device (1) with a camshaft (7), a camshaft adjuster (2) according to one of the preceding claims, wherein the camshaft (6) forms the hydraulic medium connection (6).

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