Method and control unit for determining the oil service life of oil used to lubricate a shaft or rotor

Abstract

Method for determining the oil lifetime or a quantity corresponding to the oil lifetime of oil used for the lubrication of a shaft or rotor, wherein an oil damping or a quantity corresponding to the oil damping is determined depending on an oil temperature of the oil, and wherein the oil lifetime or the quantity corresponding to the oil lifetime is determined depending on the oil damping or the quantity corresponding to the oil damping, wherein the oil damping or the quantity corresponding to the oil damping is determined depending on a rotational speed of the shaft or rotor, depending on a rotational speed gradient of the shaft or rotor, depending on a moment of inertia of the shaft or rotor, and depending on a torque applied to the shaft or rotor.

Description

The invention relates to a method for determining the oil lifespan, or a quantity corresponding to the oil lifespan, of oil used to lubricate a shaft or rotor. The invention further relates to a control unit for determining the oil lifespan, or a quantity corresponding to the oil lifespan, of oil used to lubricate a shaft or rotor. Numerous applications in automotive engineering utilize oil lubrication for shafts or rotors. For example, oil-lubricated shafts are found in automotive transmissions. Similarly, the rotor of an electric motor, such as one used as a drive unit in a vehicle, is lubricated and cooled by oil. To ensure the proper operation of the oil-lubricated shaft or rotor, and thus of the device containing the shaft or rotor, the oil must provide adequate lubrication. If the oil loses its lubricating properties, for example due to age, an oil change is necessary. DE 10 2006 015 678 A1 discloses a method for determining the timing of a required oil change during the operation of a drive unit. For this purpose, a service life characteristic curve for the oil is specified, the oil temperature is monitored during operation, and the duration of each temperature reading is aggregated as individual damage to form a total damage value. Based on this, an oil change can be initiated. DE 10 2006 059 071 A1 discloses a method for determining the oil quality in an oil supply line to an engine and / or consumer. DE 10 2011 082 674 A1 discloses a method for determining the time of a change of an operating component of a unit, in particular a hydraulic fluid of a transmission device. DE 10 2019 002 381 A1 discloses a method for determining the oil change time of engine oil during the operation of an internal combustion engine. There is a need for a simple method to determine the oil lifespan or a quantity of oil corresponding to the oil lifespan, which serves to lubricate and, if necessary, cool a shaft or rotor. Based on this, the invention aims to create a novel method and control device for determining the oil lifespan or a quantity corresponding to the oil lifespan of the oil used to lubricate a shaft or rotor. This problem is solved by a method according to claim 1. According to the invention, depending on an oil temperature, an oil damping or a quantity corresponding to the oil damping is determined, wherein, depending on the oil damping or the quantity corresponding to the oil damping, the oil service life or the quantity corresponding to the oil service life is determined. According to the invention, depending on the oil temperature of the oil used to lubricate a shaft or rotor, particularly when the oil temperature lies within a defined temperature range or corresponds to a defined temperature, the oil damping or the quantity corresponding to the oil damping is determined in order to determine the oil service life or the quantity corresponding to the oil service life. The invention is based on the understanding that the oil damping of oil, like the oil viscosity, changes with age and is dependent on the oil temperature. By determining the oil damping or the quantity corresponding to the oil damping, the oil service life or the quantity corresponding to the oil service life can be determined simply and reliably. Oil damping, or the quantity corresponding to oil damping, is determined as a function of the rotational speed of the shaft or rotor, the rotational speed gradient of the shaft or rotor, the moment of inertia of the shaft or rotor, and the torque applied to the shaft or rotor. Based on these parameters, the oil damping, or the quantity corresponding to oil damping, and thus ultimately the oil life, or the quantity corresponding to oil life, can be determined simply and reliably. The rotational speed of the shaft or rotor, as well as the rotational speed gradient of the shaft or rotor, can be measured or calculated. The moment of inertia and the torque acting on the shaft or rotor are known from the control side. Preferably, the oil damping is determined according to the formula: where d is the oil damping, T is the oil temperature, nR is the rotational speed of the shaft or rotor, ṅR is the rotational speed gradient of the shaft or rotor, JR is the moment of inertia of the shaft or rotor, and MR is the torque applied to the shaft or rotor. This allows for a particularly reliable determination of the oil damping. Depending on the oil damping determined in this way, the oil service life can then be easily calculated. The relationship between the oil damping and the oil service life can be represented, for example, by a function such as a linear relationship, or by a characteristic curve, or, depending on the oil temperature, by a characteristic map. Preferably, the torque MR applied to the shaft or rotor depends at least on a bearing torque of the shaft or rotor. Bearing torques are known from the control system. Bearing torques are stored in the control system and can be determined in advance, for example, via parameter identification or empirically. In particular, the shaft or rotor is not actively driven or braked during the execution of the method; rather, the shaft or rotor preferably coasts freely. In this case, the torque Mran of the shaft or rotor depends solely on the bearing torque. A braking torque is then zero. Whenever there is no drive torque and no braking torque applied to the shaft or rotor, and the shaft or rotor coasts freely, the oil damping can be determined particularly easily and reliably, ultimately allowing the oil service life to be calculated. Preferably, the lower the measured oil damping or the measure corresponding to the oil damping, the lower the oil service life or the measure corresponding to the oil damping. A corresponding oil service life can be assigned to each measured oil damping value via a simple linear relationship or a simple characteristic curve. Preferably, an oil change is performed when the oil life, or the oil damping, or the oil damping, falls below a certain threshold. If the oil life is too short, an oil change is performed to prevent damage. The control unit according to the invention is defined in claim 7. Preferred embodiments are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. Figure 1 shows a block diagram of a powertrain of a vehicle designed as an electric vehicle. Fig. 1 shows a highly schematic diagram of a drive train 1 of a motor vehicle designed as an electric vehicle, wherein the drive train 1 of Fig. 1 has an electric machine 2 as a drive unit and a transmission 3 connected between the electric machine 2 and an output 4. The operation of the transmission 3 is controlled and / or regulated by a transmission control unit 5, for which purpose the transmission control unit 5 exchanges data with the transmission 3 in the direction of the double arrow shown. The operation of the electric machine 2 is controlled and / or regulated by an engine control unit 6, for which purpose, as shown in Fig. 1, the engine control unit 6 exchanges data with the electric machine 2. Furthermore, the engine control unit 6 and the transmission control unit 5 exchange data with each other. Both the electric machine 2 and the gearbox 3 contain a rotor or shaft that is lubricated by oil. The rotor or runner of an electric machine is thus lubricated and cooled by oil. Shafts in gearboxes are also oil-lubricated and, if necessary, oil-cooled. The invention relates to a method for determining the oil lifespan, or a quantity corresponding to the oil lifespan, of oil used to lubricate a shaft or rotor, wherein oil lifespan is understood to mean the remaining lifespan of the oil, i.e., the lifespan that the oil is still available for proper operation. If the oil lifespan is zero, an oil change is mandatory. In accordance with the present invention, it is proposed that, depending on the oil temperature, particularly when the oil temperature is within a defined temperature range or has a defined temperature, an oil damping or a quantity corresponding to the oil damping is determined, wherein, depending on the oil damping or the quantity corresponding to the oil damping, the oil service life or the quantity corresponding to the oil service life is determined. The invention is based on the finding that oil damping is particularly suitable for determining oil service life simply and reliably. The oil damping, or the quantity corresponding to oil damping, can be determined as a function of the rotational speed of the shaft or rotor, a rotational speed gradient of the shaft or rotor, a moment of inertia of the shaft or rotor, and a torque applied to the shaft or rotor. The rotational speed can be measured. The rotational speed gradient can be calculated based on the measured rotational speed. The moment of inertia and the torque acting on the shaft or rotor are known from the control side. The oil damping is preferably determined according to the following formula: where d is the oil damping, T is the oil temperature, nR is the rotational speed of the shaft or rotor, ṅR is the rotational speed gradient of the shaft or rotor, JR is the moment of inertia of the shaft or rotor, MR is the torque acting on the shaft or rotor. The above formula is based on the following equation of motion for the shaft or rotor: from which it follows Furthermore, where ωR is the angular velocity of the shaft or rotor, and ω̇R is the angular acceleration of the shaft or rotor. Preferably, the torque MR applied to the shaft or rotor is a loss torque which depends on a bearing torque and, if applicable, a braking torque of the shaft or rotor. Braking torque and bearing torque are known from the control system. Bearing torques may have been determined empirically beforehand through measurement or via parameter identification. This method is particularly advantageous when the shaft or rotor is not actively driven or braked, but rather coasts freely. In this case, the torque MR applied to the shaft or rotor corresponds to the bearing torque. The braking torque is then zero. The bearing torque can be assumed to be constant. Simply by measuring the rotational speed and determining the rotational speed gradient of the shaft or rotor, the damping as a function of the oil temperature can then be determined easily and reliably. Preferably, the oil service life, i.e., the remaining service life of the oil, is determined based on the oil damping. This can be done via a linear relationship or based on characteristic curves. The oil damping can also be used directly as the parameter corresponding to the oil service life. Then, if the oil lifespan or the quantity corresponding to the oil lifespan or the oil damping or the quantity corresponding to the oil damping is less than a limit value, an oil change is initiated by the control system. The more aged the oil is, the lower its damping capacity within the same temperature range. If the oil damping capacity is lower than the limit at a given oil temperature or within a temperature range, an oil change is required. The invention further relates to a control unit configured to automatically execute the inventive method described above. The control unit can be either an engine control unit or a transmission control unit. The control unit is designed to automatically determine the oil damping or the quantity corresponding to the oil damping in the manner described above, depending on the oil temperature, especially when the oil temperature is within a defined temperature range or corresponds to a defined temperature, and to determine the oil life or the quantity corresponding to the oil life accordingly. The control unit is an electronic control unit that has hardware and software components for carrying out the method according to the invention. The hardware components include data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention, for example, with a temperature sensor for determining the oil temperature and a speed sensor for determining the rotational speed of the shaft or rotor. Furthermore, the hardware components include a processor for data processing and a memory for data storage. The software components include program modules that are implemented in the control unit for carrying out the method according to the invention. Reference sign 1 Drivetrain 2 Electric machine 3 Transmission 4 Output 5 Transmission control unit 6 Engine control unit

Claims

Method for determining the oil lifetime or a quantity corresponding to the oil lifetime of oil used for the lubrication of a shaft or rotor, wherein an oil damping or a quantity corresponding to the oil damping is determined depending on an oil temperature of the oil, and wherein the oil lifetime or the quantity corresponding to the oil lifetime is determined depending on the oil damping or the quantity corresponding to the oil damping, wherein the oil damping or the quantity corresponding to the oil damping is determined depending on a rotational speed of the shaft or rotor, depending on a rotational speed gradient of the shaft or rotor, depending on a moment of inertia of the shaft or rotor, and depending on a torque applied to the shaft or rotor. Method according to claim 1, characterized in that the oil damping is determined using the following formula: d ( T ) = − 1 2 ∗ π ∗ n R ( JR ∗ 2 ∗ π ∗ n ˙ R + MR ) where d the oil damping is, T is the oil temperature n R the rotational speed of the shaft or rotor is, ṅ R the speed gradient of the shaft or rotor is, J R the moment of inertia of the shaft or rotor is, M R The torque applied to the shaft or rotor. Method according to claim 2, characterized in that the torque MR acting on the shaft or rotor is dependent at least on a bearing torque of the shaft or rotor. Method according to one of claims 1 to 3, characterized in that, for carrying out the method, the shaft or rotor is not driven and not braked, but coasts freely. Method according to one of claims 1 to 4, characterized in that the oil lifetime or the quantity corresponding to the oil lifetime is lower the lower the determined oil damping or the quantity corresponding to the oil damping. Method according to one of claims 1 to 5, characterized in that an oil change is initiated when the oil life or the oil life corresponding size or the oil damping or the oil damping corresponding size is less than a limit value. Control unit for determining the oil lifespan or a quantity corresponding to the oil lifespan of oil used for the lubrication of a shaft or rotor, wherein the control unit is configured to determine an oil damping or a quantity corresponding to the oil damping depending on an oil temperature of the oil and to determine the oil lifespan or the quantity corresponding to the oil lifespan depending on the oil damping or the quantity corresponding to the oil damping, wherein the control unit is configured to execute the method according to any one of claims 1 to 6 automatically.

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