Valve train for an internal combustion engine, method for a valve train of an internal combustion engine and method for a valve lash compensating element of a valve train

Abstract

Valve train (1) for an internal combustion engine (3), comprising a valve control (12, 13, 24) and a valve (5) for opening and closing a flowable channel (4), wherein the valve (5) and the channel (4) are arranged in a cylinder head (2) of the internal combustion engine (3), and wherein the valve control (12, 13, 24) is configured to bring about an opening and closing movement of the valve (5), and wherein the valve control (12, 13, 24) comprises an adjustable valve lash compensating element (27) for adjusting the valve clearance of the valve (5), wherein, for adjusting and monitoring the valve clearance, the valve lash compensating element (27) has an electronic expansion element (30) whose spatial extent can be changed and a pressure measuring element (31; 32), characterized in that the pressure measuring element (31; 32) is designed in the form of a strain gauge, wherein the Expansion element (30) and the pressure measuring element (31;32) are connected to a control and regulation unit (28) of the internal combustion engine.;

Description

The invention relates to a valve train for an internal combustion engine according to the preamble of claim 1. Furthermore, the invention relates to a method for a valve train of an internal combustion engine and a method for a valve lash compensating element of a valve train. Internal combustion engines comprise a crankcase with at least one cylinder in which a piston is mounted to perform an oscillating motion, known as a piston stroke. With the aid of the piston and a cylinder head located opposite the crankcase and covering the cylinder, a variable displacement volume can be created due to the piston's movement. This variable displacement volume serves, for example, to transmit the pressure of an expanding air-fuel mixture to the crankshaft of the internal combustion engine. Furthermore, this variable displacement volume serves to draw in the air-fuel mixture and to expel the combusted air-fuel mixture, the so-called exhaust gas. For the intake and exhaust cycles, the so-called charge exchange of the internal combustion engine, the cylinder head has at least one valve which, depending on the piston's movement, is also mounted in the cylinder head to perform an oscillating motion. The valve serves to open or close a flow-through opening in the cylinder head, through which the air-fuel mixture can flow into or out of the cylinder head. Generally, the cylinder head has at least two flow-through openings, one for the incoming air-fuel mixture and the other for the outgoing exhaust gas. The valve is set into oscillating motion by means of a camshaft. Since a reliable seal must be maintained between the valve and the opening during the compression phase—that is, during the piston stroke when the opening must remain closed—the valve is equipped with a clamping element that presses it against a valve seat formed in the opening during this phase. During the operation of an internal combustion engine, fluctuating temperatures, the impact of moving parts in the valve train, and the resulting wear lead to a phenomenon known as valve clearance. In other words, this means that during operation, and especially after prolonged use, the valve no longer maintains the required seal on the valve seat, resulting in leakage between the valve and the valve seat. Therefore, it is necessary to equip the valve train with a valve clearance adjuster. This ensures the required seal between the valve and the valve seat ring at all operating temperatures. Modern internal combustion engines, especially high-speed and high-revving ones, predominantly feature a hydraulic valve lash adjuster. This hydraulic system is supplied with the necessary oil via the engine's oil circuit. However, a disadvantage of this hydraulic system is its low rigidity, which can lead to oil foaming within the engine's circuit. Furthermore, unfavorable vibration characteristics, particularly when using rocker arms, can cause the hydraulic valve lash adjuster to "pump up," sometimes eliminating the valve clearance entirely and resulting in high frictional losses within the engine. Insufficient or eliminated valve clearance also leads to unpleasant, disruptive cold-start noises.Adjusting the settling rate of hydraulic valve lash adjusters is very complex. Patent application KR 10 2002 0 058 109 A discloses a device for adjusting valve clearance for an internal combustion engine, which includes a expansion element in the form of an electro-rheological fluid and a piezoelectric element for providing a voltage to control the electro-rheological fluid. The patent application JP H04-52 405 Y2 discloses a piezoelectric element which is arranged between a cam and a valve of the internal combustion engine. German patent application DE 20 38 675 A discloses an electrically heated expansion element intended as a valve clearance compensating element for an internal combustion engine. A heating device regulates the expansion of the element depending on operating conditions to provide the necessary valve clearance. From the patent application EP 3 144 491 A1, a valve train for an internal combustion engine is known, wherein a valve lash adjustment element is designed in the form of a piezoelectric stepper motor. The object of the present invention is to provide an improved valve train for an internal combustion engine. Further objects are to provide a method for a valve train of an internal combustion engine and a method for a valve lash compensating element of a valve train. The object of the invention is achieved by a valve train for an internal combustion engine with the features of claim 1. The further objects of the invention are achieved by a method for a valve train of an internal combustion engine with the features of claim 9 and a method for a valve lash compensating element of a valve train with the features of claim 15. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the respective dependent claims. A valve train according to the invention for an internal combustion engine comprises a valve control unit and a valve for opening and closing a flow-through channel, wherein the valve and the channel are arranged in a cylinder head of the internal combustion engine. The valve control unit is configured to bring about an opening and closing movement of the valve and has an adjustable valve lash compensator for setting the valve clearance. For setting and monitoring the valve clearance, the valve lash compensator has an electronic expansion element whose spatial dimensions can be varied and a pressure measuring element. The pressure measuring element is designed in the form of a strain gauge, wherein the expansion element and the pressure measuring element are connected to a control unit of the internal combustion engine.The advantage is that the valve lash adjuster is designed as an electronic component, thus eliminating all the disadvantages of a hydraulic valve lash adjuster, such as inflation or settling. Furthermore, it offers complete controllability and diagnostic capabilities. The complete controllability offers the further advantage of enabling virtually backlash-free operation of the valve train. In other words, the valves do not open their assigned ports outside of their predetermined opening and closing times. This, in turn, leads to higher efficiency of the internal combustion engine and lower exhaust emissions. According to the invention, the pressure measuring element is designed in the form of a strain gauge. The advantage over a conventional pressure sensor is its compact, space-saving design. Furthermore, the strain gauge is more cost-effective than a conventional pressure sensor. Another advantage of the valve train according to the invention is the low frictional power, since no surface pressure is generated on the camshaft in its base circle. Advantageously, the expansion element incorporates a piezoelectric element. The advantage lies in the simple adjustment of the valve clearance, since applying an electrical voltage causes the piezoelectric element to perform a mechanical movement in the form of expansion or contraction. This means that when a specific voltage is applied to the expansion element, the valve clearance is adjusted based on the mechanical movement of the element. In a further embodiment, the expansion element is designed in the form of a piezoelectric stack, consisting of a plurality of piezoelectric elements. This makes it possible to achieve a larger working stroke of the expansion element. By coupling the majority of the piezoelectric elements in parallel, the spatial extent or extension of the valve lash adjuster can be changed very quickly, as the piezoelectric elements react immediately to the application of a voltage. Due to the parallel coupling, each individual piezoelectric element reacts simultaneously with the others. Advantageously, the pressure sensor is located on an outer surface of the piezoelectric element. This makes it possible to retain the potentially functional piezoelectric element when replacing the pressure sensor, and only the pressure sensor needs to be replaced. If the pressure measuring element is formed inside the piezoelectric element, the pressure measuring element is protected against damage from the outside, e.g. during installation. According to the invention, the expansion element and the pressure measuring element are connected to a control unit of the internal combustion engine. An advantage is that the expansion element can be directly controlled by the control unit of the internal combustion engine. This reduces the valve clearance adjustment time. A further advantage is that the pressure at the camshaft can be continuously measured, the valve clearance checked, and adjusted as needed. Advantageously, the valve control includes a rocker arm, since when the valve is actuated using the rocker arm, the valve lash compensating element itself performs virtually no further movement. In a further embodiment, the expansion element has a working stroke that lies within a range of 0.3 mm to 0.4 mm. This allows for quick adjustment of the valve clearance. The second aspect of the invention relates to a method for a valve train of an internal combustion engine, wherein the internal combustion engine has a valve train according to any one of claims 1 to 8. Input variables are used to determine characteristic values, and with the help of these characteristic values, an output variable is determined as a function of the valve lash adjustment element of the valve train. In one embodiment of the method according to the invention, a signal from the pressure measuring element of the valve lash adjuster is used to determine the output variable. The advantage is that the pressure measuring element provides a reliable pressure signal with respect to the pressure on the camshaft in the region of a base circle of the camshaft, which extends over at least 180° of the circumference of the camshaft. When determining the current valve clearance, the output value serves as a reference value for the voltage to be applied to the valve clearance compensation element of the valve train. If the initial value is used as a reference for wear of valve train components, the advantage is that information about the condition of the valve train components can be obtained without potentially destructive disassembly of the internal combustion engine. This information can, for example, be displayed to a driver during operation of the internal combustion engine in a motor vehicle or read out via the control unit during a check in a workshop. Advantageously, the output variable can be used as a reference for determining the position of a cam in the valve train. Since the pressure at the camshaft is continuously measured by the pressure sensor, information about the current valve lift switching position is available. This allows, for example, monitoring of the valve lift switching position, which is usually controlled by the engine control unit, to prevent damage to the internal combustion engine due to an incorrect valve lift at a specific operating point. Valve lift switching is typically used to increase the efficiency of the internal combustion engine at specific operating points. This means that operating point parameters, such as fuel quantity, injection timing, and ignition timing, are calculated based on the corresponding valve lift and stored in maps of the control unit. If an incorrect valve lift setting does not match the other operating point parameters, the result is at least poor efficiency and consequently high fuel consumption. This, in turn, leads to high exhaust emissions, which this method aims to prevent. The input variables are measured or calculated operating point data as well as design data of the internal combustion engine and property data of the valve lash adjuster, wherein these are property data of the expansion element and a current signal of the pressure measuring element during the operation of the internal combustion engine. A third aspect of the invention relates to a method for a valve lash adjuster of a valve train, wherein the valve train is configured according to any one of claims 1 to 8, and wherein the expansion element and / or the pressure measuring element are tested. This allows the functionality of the valve lash adjuster to be monitored. This testing is relevant with regard to current country-specific and future general emission standards. If the valve lash adjuster can no longer reliably perform its function, this can lead, for example, to high fuel consumption due to insufficient compression or to exhaust gas leakage from the combustion chamber during operation of the internal combustion engine. This, in turn, leads to an increase in exhaust emissions. In particular, the expansion element and / or the pressure measuring element are checked for signal plausibility and / or short circuit and / or MIN / MAX error and / or for being swapped. Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. Identical or functionally equivalent elements are assigned identical reference numerals. The drawings show: Fig. 1 a semi-schematic representation of a valve train according to the invention, Fig. 2 a process diagram for determining a voltage necessary for valve clearance compensation of the valve train according to the invention, Fig. 3 a process diagram for determining wear of components of the valve train according to the invention, and Fig. 4 a process diagram for determining a cam position of a cam of the valve train according to the invention with a valve lift switching device. A valve train 1 according to the invention is designed as shown in Fig. 1. The valve train 1 is associated with a cylinder head 2 of an internal combustion engine 3, which is designed as a reciprocating piston engine. The internal combustion engine 3 has a crankcase (not shown in detail) to which the cylinder head 2 is rigidly connected. The cylinder head 2 has flow-through channels 4, at least one intake channel and one exhaust channel, through which a fresh air mixture and exhaust gas can be drawn in and expelled, respectively, during a so-called charge exchange phase of the internal combustion engine 3. Figure 1 shows the intake channel 4 of the cylinder head 2. A valve 5 is arranged in the cylinder head 2, which opens or closes an opening 6 of the intake port 4. The opening 6 faces a combustion chamber 7 of the internal combustion engine 3. To open the valve 5, a moving device 8 of the valve train 1 pushes it at least partially into the combustion chamber 7, whereby a valve disc 9 of the valve 5 lifts off a valve seat 10 formed at the opening 6, thus exposing a flow cross-section 11 of the opening 6. The fresh air mixture can flow into the combustion chamber 7 through this flow cross-section 11. It is also possible that during a charge exchange phase of the internal combustion engine 3, exhaust gas flows through the opening 6 and is drawn back in, or that fresh air flows into the exhaust port 7 through a further opening associated with the exhaust port (not shown) to scavenge the combustion chamber 7. The valve train 1 comprises, in addition to the valve 5, a camshaft 12 with a cam 13. The movement of the valve 5 depends on the position of the cam 13, which is fixedly connected to the camshaft 12. During operation of the internal combustion engine 3, the camshaft 12 rotates about its axis of rotation 14. In this embodiment, the camshaft 12 is designed as an overhead camshaft. The valve 5 has a valve stem 15 which is connected to the valve head 9. The valve 5 is usually formed in one piece. The valve stem 15 is arranged on a valve surface 16 of the valve head 9, which faces away from the combustion chamber 7. The valve stem 15 extends through the channel 4 and the cylinder head 2, being axially movably received in a receiving opening 17 in the cylinder head 2 along its longitudinal axis 18. A valve spring 20 is received at a valve stem end region 19 of the valve stem 15, which faces away from the valve head 9, and the valve spring 20 is supported at its spring end 21, which faces the valve head 9, against a cylinder head housing 22 of the cylinder head 2. A lower valve spring retainer could also be arranged between the cylinder head housing 22 and the valve spring 20. To create preload, an upper valve spring retainer 23 is fixed to the valve stem 15 at the upper end 21 of the spring. The valve spring 20 is also under tension when the opening 6 is closed. This tension is increased as soon as the valve 5 is pressed towards the combustion chamber 7 by means of the cam 13 via a rocker arm 24. The rocker arm 24 is in contact with the valve stem 15 at its first end 25, which faces the valve stem 15, or it rests on a valve stem surface 26 also facing the rocker arm 24. The valve train 1 has a valve lash compensating element 27 to compensate for valve clearance occurring during the operation of the internal combustion engine 3, which is connected to a control and regulation unit 28 of the internal combustion engine 3. At its second end 29, which faces away from the valve stem 15, the rocker arm 24 is connected to the valve lash adjuster 27, hereinafter referred to as the adjuster. The adjuster 27 serves to achieve a complete seal of the opening 6 by means of the valve head 9 during a compression and combustion phase of the internal combustion engine 3, in which both the openings 6 of the intake and exhaust ports are closed by their respective valves 5. The compensating element 27 has an expansion element 30 as well as a first pressure measuring element 31 and a second pressure measuring element 32. Alternatively, it could have only one pressure measuring element. This depends on the type of pressure measuring element. In this embodiment, the expansion element 30 is configured as a so-called piezo stack, in which a specific number of piezo elements are coupled in parallel. The pressure measuring elements 31, 32 are designed as strain gauges. The strain gauges 31, 32, also called strain gauges or simply strain gauges, are attached to the outer surface of the piezo stack 30 in an orthogonal direction to each other. The strain gauges 31, 32 and the piezo stack 30 are connected to the control unit 28. The cam 13 has a so-called base circle 33, a so-called leading ramp 34 and a falling ramp 35. In operation of the internal combustion engine 3, the cam 13 with its base circle 33 rotates above the rocker arm 24. At the beginning of a valve opening phase and up to the maximum valve lift Hmax of the valve 5, the cam 13 with its leading ramp 34 is positioned above the rocker arm 24. As soon as the maximum valve lift Hmax is reached, the cam 13 with its falling ramp 35 is positioned above the rocker arm 24, and a valve closing phase follows the valve opening phase, continuing until the valve 5 has completely closed the opening 6. Between the end of the valve closing phase and the beginning of the valve opening phase, the cam 13 with its base circle 33 is positioned above the rocker arm 24. Due to the cam profile of cam 13, the pressure exerted by cam 13 on the rocker arm 24 varies. This pressure is determined using strain gauges 31, 32 and transmitted as a pressure value to the control unit 28. A calculation model stored in the control unit 28 determines whether the valve clearance has changed impermissibly and needs to be corrected. Furthermore, the system determines the extent to which the piezoelectric stack 30 must expand or contract to achieve the correct valve clearance. If necessary, a specific voltage is applied to excite the piezoelectric stack 30, thereby setting the correct or required valve clearance. The compensating element 27 can have different functions in conjunction with the control unit 28. In other words, this means that it can be used for various model-based diagnoses or investigations. Figures 2, 3 to 4 show procedure diagrams for determining reference values ​​for adjusting the valve clearance, wear of various components of the valve train 1, and position of the cam 13, provided the valve train 1 has a valve lift switching function. These investigations are to be carried out depending on the valve clearance compensating element 27, in particular with the aid of the pressure measuring elements 31, 32. These procedural schemes concern the three determinations or calculations: - Determination of the current valve clearance, - Determination of an adjustment path of the piezo stack over a specific operating time, and - Determination of a support force on the strain gauges 31; 32 during a maximum valve stroke Hmax of the valve 5. Input variables E1, E2, E3, which are determined via n-dimensional characteristic maps of the control unit 28 or are available as measurement data of the internal combustion engine 3, are operating point data as well as design data of the internal combustion engine 3 and property data of the compensating element 27. The operating point data includes engine temperature, starting temperature, ambient temperature, oil temperature, coolant temperature, and the operating mode of the internal combustion engine. Furthermore, the current crankshaft position and camshaft position are also included. Design data used in the calculation include material constants of the valve train 1 and its components, as well as the valve train 1's transmission ratio. Additionally, specific properties of the piezoelectric stack 30, such as its expansion rate as a function of an applied voltage, and the respective signals from the strain gauges 31 and 32 are used for the calculation. Naturally, other input variables can be used, or, depending on the specific calculation, one or more input variables may not be strictly necessary. The input variables E1, E2, E3 are processed using specific parameters K1, K2, K3, which are stored in the control unit 28 in the form of characteristic curves, maps, and / or constants. These parameters K1, K2, K3 are combined using mathematical and logical operators. The valve clearance is determined in principle with the camshaft 12 in a position where the cam 13 is located in its base circle 33 above the rocker arm 24 between the valve closing and opening phases. This is because, during the valve opening phase (i.e., when the leading ramp 34 is located above the rocker arm 24), the piezoelectric stack 30 remains rigid and therefore the voltage measured on it is constant. During the valve clearance determination, the piezoelectric stack 30 is energized until a pressure, determined by the strain gauges 31 and 32, is present on the camshaft 12. The valve clearance is adjusted immediately upon starting the internal combustion engine 3 during the first rotation of the camshaft 12, so that the current valve clearance can be measured and adjusted immediately at the start of operation of the internal combustion engine 3. Ideally, the so-called working path of the piezo stack 30, in other words its expansion or contraction, lies within a range of 0.3 mm to 0.4 mm. Furthermore, in the event of a defect in the compensating element 27, emergency operation with a contact speed of up to 1 m / s is possible. After determining the current valve clearance of the valve train 1 using the input variables E1 and the characteristic variables K1, the output variable A1 is a necessary voltage which is to be applied to the piezo stack 30 to compensate for the current valve clearance. Determining the adjustment path of the piezoelectric stack 30 over a specific operating time using the input variables E2 and the characteristic variables K2 results in an output variable A2, which describes a specific wear of the valve train 1 or its components. Using the signals from the strain gauges 31 and 32, as well as the voltage required to compensate for the valve clearance, it is possible to determine a specific path of the piezoelectric stack 30 using the applied calculation model and thus make a statement about the wear of the valve train 1. If the valve train 1 according to the invention has a valve lift switch, the corresponding current position of the cam 13 can be determined with its aid. For this purpose, the input variables E3 are processed in the control unit 28 using the characteristic variables K3, whereby a support force of the strain gauges 31; 32 during the maximum valve lift Hmax is calculated. The output variable A3 corresponds to the position of the valve lift switch. In a further method according to the invention, the valve lash adjustment element 27 is diagnosed or tested. The expansion element 30 and the pressure measuring element 31; 32 are each independently checked for either signal plausibility, a reversal, a short circuit, or so-called MIN / MAX errors. Depending on their design, the piezoelectric elements 30 can contract or expand when a voltage is applied. When used as a valve lash adjuster 27, the variant with a rocker arm-controlled valve train 1 would be suitable, since in this installation the valve lash adjuster 27 itself performs virtually no movement. Naturally, the valve train 1 according to the invention is independent of the type of valve actuation. In other words, the valve train 1 according to the invention can equally comprise a rocker arm or a tappet. It could also include a camshaft 12 located below.

Claims

Valve train (1) for an internal combustion engine (3), comprising a valve control (12, 13, 24) and a valve (5) for opening and closing a flowable channel (4), wherein the valve (5) and the channel (4) are arranged in a cylinder head (2) of the internal combustion engine (3), and wherein the valve control (12, 13, 24) is configured to bring about an opening and closing movement of the valve (5), and wherein the valve control (12, 13, 24) comprises an adjustable valve lash compensating element (27) for adjusting the valve clearance of the valve (5), wherein, for adjusting and monitoring the valve clearance, the valve lash compensating element (27) has an electronic expansion element (30) whose spatial extent can be changed and a pressure measuring element (31; 32), characterized in that the pressure measuring element (31; 32) is configured in the form of a strain gauge, wherein the expansion element (30) and the pressure measuring element (31;32) are connected to a control and regulation unit (28) of the internal combustion engine.; Valve train (1) according to claim 1, characterized in that the expansion element (30) has a piezo element (30). Valve train (1) according to claim 1 or 2, characterized in that the expansion element (30) is designed in the form of a piezo stack consisting of a plurality of piezo elements (30). Valve train (1) according to claim 3, characterized in that the majority of the piezo elements (30) are coupled in parallel with each other. Valve train (1) according to one of claims 2 to 4, characterized in that the pressure measuring element (31; 32) is arranged on an outer surface of the piezo element (30). Valve train (1) according to one of claims 2 to 4, characterized in that the pressure measuring element (31; 32) is formed within the piezo element (30). Valve train (1) according to one of the preceding claims, characterized in that the valve control (12, 13, 24) comprises a rocker arm. Valve train (1) according to one of the preceding claims, characterized in that the expansion element (30) has a working stroke which lies in a value range between 0.3 mm and 0.4 mm. Method for a valve train (1) of an internal combustion engine (3), wherein the internal combustion engine (3) has a valve train (1) according to one of claims 1 to 8, and wherein input variables (E1, E2, E3) are used to determine characteristic variables (K1, K2, K3) and with the help of these characteristic variables (K1, K2, K3) an output variable (A1, A2, A3) is determined as a function of the valve lash compensating element (27) of the valve train (1). Method according to claim 9, characterized in that a signal from a pressure measuring element (31; 32) of the valve lash adjustment element (27) is used to determine the output variable (A1; A2; A3). Method according to one of claims 9 or 10, characterized in that the output variable (A1) is determined as a reference variable for a voltage to be supplied to the valve lash adjustment element (27). Method according to one of claims 9 or 10, characterized in that the output variable (A2) is determined as a reference variable for wear of components of the valve train (1). Method according to one of claims 9 or 10, characterized in that the output variable (A3) is determined as a reference variable for determining the position of a cam (13) of the valve train (1). Method according to one of claims 9 to 13, characterized in that the input variables (E1, E2, E3) are operating point data as well as design data of the internal combustion engine (3) and property data of the valve lash compensating element (27). Method for a valve lash adjustment element of a valve train (1), wherein the valve train (1) is designed according to one of claims 1 to 8, wherein the expansion element (30) and / or the pressure measuring element (31; 32) are tested. Method according to claim 15, characterized in that the expansion element (30) and / or the pressure measuring element (31; 32) are checked for signal plausibility and / or short circuit and / or MIN / MAX error and / or reversal.

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