camshaft adjuster

Abstract

A camshaft adjuster (1) of an internal combustion engine (10) comprises an electric motor (2), an actuator (3), and a control device (8) for controlling the electric motor (2), which is designed to determine operating parameters of the electric motor (2) as a function of changing operating parameters of the internal combustion engine (10) after the engine has started, while permanently maintaining adjustment possibilities.

Description

[0001] The invention relates to a camshaft adjuster intended for use in an internal combustion engine, which can be in different operating states or operating ranges, in particular before, during and after the start of the internal combustion engine.

[0002] German patent application DE 10 2019 116 653 A1 relates to a wave gear designed for use in a camshaft adjuster. In this case, a flexible gear element of the wave gear is cup-shaped. DE 10 2019 116 653 A1 specifically addresses the stiffness of the gear, i.e., the wave gear. It specifically discusses the approach to a stop position in a fail-safe scenario. The stop position is considered the standard or emergency running position of the gear.

[0003] German patent DE 10 2018 126 439 A1 also addresses a fail-safe position of a wave gear, in this case with a simple flex ring as the elastic gear element. Thanks to the gear's design as a negative gear, a fail-safe position is predefined in the "early" setting.

[0004] A wave gear disclosed in DE 10 2018 128 028 B3 for an electromechanical camshaft adjuster is also designed as a negative gear. In this case, a spring element exists which acts between a housing element and an output element of the wave gear.

[0005] Another electromechanical camshaft adjuster and a method for operating a camshaft adjuster are the subject of DE 10 2021 105 281 A1. In this case, there are several fail-safe positions of an output element in relation to the drive element of the camshaft adjuster.

[0006] DE 100 80 467 B4 discloses an electro-hydraulic valve train system that is controlled depending on the temperature of the engine oil. A camshaft adjuster with two different sets of control coefficients is known from DE 10 2005 023 537 A1.

[0007] The invention is based on the objective of further developing a camshaft adjuster for an internal combustion engine compared to the prior art, whereby special provisions for adjustments to changing operating conditions, in particular in a first operating phase after the start of the internal combustion engine, are to be provided.

[0008] This problem is solved according to the invention by a camshaft adjuster having the features of claim 1. Likewise, the problem is solved by a method for operating a camshaft adjuster designed according to claims 3 or 6. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the device, i.e., the camshaft adjuster, and vice versa.

[0009] The camshaft adjuster intended for use in an internal combustion engine, in particular in a vehicle, comprises an electric motor, an actuator, and a control device for controlling the electric motor, which is designed to determine operating parameters of the electric motor as a function of changing operating parameters of the internal combustion engine after the engine has started, while permanently maintaining adjustment possibilities.

[0010] In contrast to unclaimed concepts that provide for a fixed angular relationship between the crankshaft and the camshaft after engine start, the solution according to the invention thus offers possibilities for adjusting the camshaft immediately after starting the internal combustion engine, and optionally also before starting the engine. However, these initial adjustment possibilities differ from the full range of possibilities for phase adjustment of the camshaft relative to the crankshaft that become available later, at the latest after the warm-up phase of the internal combustion engine. The camshaft can be either an intake or an exhaust camshaft. The actuator of the camshaft adjuster is in an arbitrary position when the internal combustion engine is started, in particular in a position that deviates from a fixed end position.

[0011] The operating parameters that determine the adjustment range of the camshaft adjuster include, in particular, the engine oil temperature, the coolant temperature, and the time elapsed since the engine was started. A limitation of the adjustment range can depend on a single one of these parameters or on a combination of several parameters.

[0012] Regarding the type of adjustment restrictions, various options are possible. For example, the adjustment speed of the camshaft adjuster is initially limited before, during, and after the engine starts, whereas the adjustment range—that is, the possible range of the angular relationship between the camshaft and crankshaft—is fully usable from the outset. This means that the camshaft adjuster's end positions can be reached even during the warm-up phase, although not at the maximum adjustment speed compared to later operation. This significantly contributes to protecting the mechanical components of the combustion engine, especially the camshaft adjuster, during phases in which the engine has not yet reached full operating temperature.

[0013] The difference between the speed of the electric motor at which no change in the angular ratio between the crankshaft and camshaft occurs, and the speed of the electric motor selected during adjustment operation of the camshaft adjuster, determines the adjustment speed of the camshaft adjuster. The maximum adjustment speed can depend on the crankshaft speed of the internal combustion engine. This applies particularly to the warm-up phase, i.e., the phase in which not all adjustment options are yet available. Optionally, a relationship between the crankshaft speed and the maximum possible adjustment speed can also exist when the internal combustion engine is warm.

[0014] In addition to or as an alternative to limiting the adjustment speed, the available adjustment range of the camshaft adjuster can be limited during the operating phase that begins with the engine start. In particular, such a limitation can be designed so that the camshaft adjuster does not reach a stop position during the corresponding operating phase.

[0015] According to one possible embodiment, the control device for the camshaft adjuster's electric motor is designed to allow for braking operation of the electric motor. Braking is achieved, for example, by short-circuiting two or three phases, provided a three-phase motor is used. If the control device includes a B6 bridge rectifier, the low side of the B6 bridge can be activated and the high side deactivated for braking purposes. During startup, the braking mode of the electric motor can generate a torque that counteracts the acceleration occurring in this case.

[0016] The braking function of the electric motor is not necessarily limited to the warm-up phase of the combustion engine equipped with the camshaft adjuster. Rather, in defined configurations, camshaft adjustment can be achieved by using the electric motor as a brake in any operating phase of the combustion engine.

[0017] The method for operating the camshaft adjuster, which comprises an electric motor and an actuator driven by the electric motor, is generally characterized by the fact that, immediately after starting the combustion engine, the camshaft adjuster operates with limited adjustment capabilities—though not completely restricted—and only later, at the latest after the combustion engine's warm-up phase, are the full adjustment capabilities of the camshaft adjuster enabled. A sensor system known in principle, such as Hall sensors, is suitable for detecting the rotational speed of the camshaft or a component of the camshaft adjuster.

[0018] The camshaft adjuster's actuator is typically a three-shaft drive, for example, in the form of a wave gear. Generally, a three-shaft camshaft adjuster has a first, driven shaft, which is usually driven mechanically, particularly via a wrap-around drive, by the crankshaft of the internal combustion engine. An output shaft of the three-shaft drive is rotationally fixed to the camshaft being adjusted. The third shaft of the three-shaft drive is an adjustment shaft driven by the electric motor. Alternative three-shaft drive designs include, for example, swashplate drives or planetary gears.

[0019] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1. Partially a schematic representation of an internal combustion engine with a camshaft adjuster, Fig. 2 in a diagram: Relationships between crankshaft speed and camshaft speed of the internal combustion engine in different operating conditions, Fig. 3 usable properties of the camshaft adjuster in a first and a second operating mode, shown in a further diagram, Fig. 4, Fig. 5 to Fig. 6 different variants of the dependence of the adjustment possibilities of the camshaft adjuster on an operating parameter of the internal combustion engine.

[0020] An internal combustion engine, designated in its entirety by reference numeral 10 and used in a vehicle, namely a single- or multi-cylinder reciprocating piston engine, for example a four-cylinder engine, comprises an electromechanical camshaft adjuster 1 for adjusting the phase position of a camshaft 11 relative to the crankshaft 10 (not shown) of the internal combustion engine.

[0021] The camshaft adjuster 1 comprises an electric motor 2 and an actuator 3. The actuator 3 is designed as a three-shaft gearbox, in this case a wave gearbox. A drive element 4, which represents one of the three shafts of the three-shaft gearbox 3, is provided with external teeth 5, making it suitable for drive by a traction element (not shown), i.e., a chain or a toothed belt. The output element, i.e., the second shaft of the three-shaft gearbox 3, is rigidly connected to a central screw 9, which is screwed into the camshaft 11. The third shaft of the three-shaft gearbox 3 is an input-side gearbox element 6, which in the exemplary embodiment is connected to or identical with an inner ring of a wave generator and is also referred to as the adjusting shaft. The gearbox element 6 is rotationally fixed to the shaft 7 of the electric motor 2.

[0022] A control device 8 is provided for controlling the electric motor 2; its characteristics will be discussed in more detail below. Electrical lines for power and / or signal transmission are generally designated by 12.

[0023] The diagram according to Fig. Figure 2 shows various possible relationships between the crankshaft speed nK and the camshaft speed nN, that is, the speed of the camshaft 11. In the operation designated NB without adjustment of the camshaft 11, the camshaft 11 rotates at half the crankshaft speed nK.

[0024] Immediately after the combustion engine 10 is started, the control device 8 operates in a mode that allows adjustment of the camshaft 11. Fig. Figure 2 shows various adjustment options, not to scale. In any case, it is possible to adjust the camshaft 11 either positively or negatively relative to the crankshaft, that is, to change the timing of the gas exchange valves, which are actuated by the camshaft 11.

[0025] During the warm-up phase of the internal combustion engine 10, limited adjustment operation is possible, the limits of which are defined in Fig. 2 through the curves Ve + and Ve - are visualized. The limitation here refers only to the speed of the adjustment, not to the maximum angular range of the adjustment. This means that the end positions of the camshaft adjuster 1 are already achievable during the warm-up phase. A fixed setting of the camshaft adjuster 1 is not predetermined at any time.

[0026] Only after the combustion engine 10 has warmed up is the full adjustment speed of the camshaft adjuster 1 enabled. Fig. 2. The curves Vm + and Vm - For adjustment operation at maximum adjustment speed in the first or second direction. In particular, the slope of the curve Vm. + is in Fig. 2 is exaggerated.

[0027] In Fig. 3 considers the operation of the internal combustion engine 10 at a constant speed nK. A possible constant speed of the camshaft 11 is denoted by nc. The camshaft speed nN deviates from this, either upwards or downwards, as soon as the camshaft 1 is adjusted. In operating mode during the warm-up phase, the camshaft speed nN remains within the range between n1 and nc. - and n1 + limited.

[0028] This defines a first adjustment range Δn1, in which only moderate rates of change in camshaft speed nN are permitted. Blocked ranges B1 and B2, which extend up to the maximum increased speed n2, + or up to the maximum reduced speed n2 - The adjustment ranges are automatically activated after the warm-up phase. This means that camshaft 11 has a second, further adjustment range Δn2 with regard to the adjustment speed.

[0029] The diagrams according to the Fig. 4, Fig. 5 to Fig. Figure 6 shows various conceivable dependencies between the state of the internal combustion engine 10 and the adjustment possibilities of the camshaft adjuster 1. In one and the same control device 8, all relationships can be shown according to the Fig. 4, Fig. 5 to Fig. 6. can be stored and activated as needed. Likewise, configurations are possible in which only one or two of the variants are used according to the Fig. 4, Fig. 5 to Fig. 6 or other variants not evident from these exemplary figures are implemented.

[0030] In each of the diagrams, according to the Fig. 4 to Fig. 5 denotes nr as a relative speed, namely the difference between the camshaft speed nN and the crankshaft speed nK. The maximum possible relative speed nr depends on a temperature T of the internal combustion engine 10, that is, an operating parameter of the internal combustion engine 10. In this case, T denotes the lubricant temperature, or alternatively, the coolant temperature.

[0031] In the Fig. In the case outlined in section 4, the relative rotational speed nr after starting the internal combustion engine 10 is initially limited to the range from -nr1 to +nr1. With increasing cooling or lubricant temperature T, after Fig. 4. A continuous widening of the speed limits up to the values ​​-nr3, +nr3 is provided. This corresponds to the complete elimination of the blocked ranges B2, B1 ( Fig. 3).

[0032] The scenario according to Fig. 5 is in contrast to the variant according to Fig. 4 is therefore simplified, as at a first temperature threshold T1 an immediate widening of the limits of the relative rotational speed nr from [-nr1; +nr1] to [-nr3; +nr3] is provided.

[0033] In the case of Fig.6. There are two temperature thresholds T1 and T2. Upon reaching the first temperature threshold T1, the range of permissible relative speed nr is initially extended to [-nr2;+nr2]. Only upon reaching the second temperature threshold T2 is the full range [-nr3;+nr3] enabled. Reference symbol list 1 Camshaft adjuster 2 electric motors 3 actuators 4 Drive element 5 External teeth 6 input-side gear element 7 Shaft of the electric motor 8 Control device 9 Central screw 10 Internal combustion engine 11 Camshaft 12 Line B1 first blocked area B2 second blocked area n1 + moderately increased speed n1 moderately reduced speed n2 + maximum increased speed n2 Maximum reduced speed NC constant speed no. relative speed No. 1 Relative speed, limited in first stage No. 2 Relative speed, limited in second stage No. 3 Relative speed, limited in third stage Δn1 first adjustment range Δn2 second adjustment range nK Crankshaft speed nN Camshaft speed NB Operation without camshaft adjustment t time Temperature T1 first temperature threshold T2 second temperature threshold Ve + Adjustment operation, restricted, adjustment in the first direction Ve Adjustment operation, restricted, adjustment in the second direction Vm + Adjustment operation, adjustment in the first direction Vm Adjustment operation, adjustment in the second direction

Claims

[1] Camshaft adjuster (1) of an internal combustion engine (10), comprising an electric motor (2), an actuating gear (3), and a control device (8) for controlling the electric motor (2), which is designed to determine operating parameters of the electric motor (2) as a function of changing operating parameters of the internal combustion engine (10) after the engine has started, while permanently maintaining adjustment possibilities, characterized by , that the control device (8) comprises a B6 bridge circuit which has an operating mode in which it acts as a brake on an input-side gear element (6) of the actuator (3). [2] Camshaft adjuster (1) according to claim 1, characterized by , that the actuating mechanism (3) is designed as a three-shaft mechanism, in particular a wave mechanism. [3] Method for operating a camshaft adjuster (1), which comprises an electric motor (2) and an actuator (3) that can be actuated by means of the electric motor (2), in an internal combustion engine (10), wherein immediately after starting the internal combustion engine (10) the camshaft adjuster (1) is operated with restricted adjustment possibilities (1) - but not restricted to zero - and only later, at the latest after the warm-up phase of the internal combustion engine (10), are the full adjustment possibilities of the camshaft adjuster (1) released, characterized by , that after the start of the internal combustion engine the adjustment range of the camshaft adjuster (1) is initially limited. [4] Method according to claim 3, characterized by , that after the start of the internal combustion engine (10) the adjustment speed of the camshaft adjuster (1) is initially limited. [5] Method according to claim 3 or 4, characterized by, that during the warm-up phase, adjustment options of the camshaft adjuster (1) are specified depending on the crankshaft speed of the internal combustion engine (10). [6] Method according to the preamble of claim 3 or according to any one of claims 3 to 5, characterized by , that at least during the warm-up phase the camshaft (11) is adjusted by braking an adjustment shaft (6) of the actuator (3) by means of the electric motor (2). [7] Method according to claim 6, characterized by , that the braking of the electric motor (2) is effected by a phase short circuit.

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