Method and control device for operating an electric motor-driven fluid pump of a motor vehicle

Abstract

Method for operating an electric motor-driven fluid pump (1) of a motor vehicle, comprising at least the following steps: specifying a target volume flow to be provided by the fluid pump (1). Operating an electric machine (2) driving the fluid pump (1) in a pulse operating mode with first time periods in which the electric machine (2) runs at a first target speed, and with second time periods in which the electric machine (2) is stopped or runs at a second target speed, such that the fluid pump (1) delivers the target volume flow on average with optimal efficiency.

Description

The invention relates to a method and a control device for operating an electric motor-driven fluid pump of a motor vehicle.Fluid pumps are installed in a motor vehicle. The fluid pumps serve for conveying a liquid fluid in the direction of a consumer. Thus, a fluid pump can be, for example, an oil pump in order to provide a consumer with an oil flow for cooling and / or lubrication. Further, the fluid pump may be a water pump.Fluid pumps are typically driven by electric motor using an electric machine. If a defined setpoint volume flow is to be provided by the fluid pump, the electric machine which drives the feed pump is operated at a constant setpoint rotational speed for this purpose. That setpoint rotational speed of the electric machine, via which the feed pump can provide the desired setpoint volumetric flow, can be ascertained, for example, with the aid of a characteristic diagram or a characteristic curve. Depending on the required setpoint volume flow, an electric machine operated at a constant setpoint rotational speed may be operated only with a low degree of efficiency. This is disadvantageous in order to operate an electric motor-driven fluid pump with the lowest possible energy requirement and thus the lowest possible electrical power consumption.DE 10 2021 208 713 A1 discloses an apparatus for supplying oil, which comprises a pump and an electric motor for driving the pump. The device has a rotational speed sensor for detecting the rotational speed of the electric motor, a pressure sensor and a temperature sensor, wherein the pressure sensor and the temperature sensor are arranged in the outlet opening of the pump. Depending on the measurement signal of the speed sensor, the pressure sensor and the temperature sensor, at least one operating condition of the electric motor is changed in order to achieve a desired output.The object of the present invention is to provide a method and control device for operating an electromotively driven fluid pump of a motor vehicle, which allow an electromotively driven fluid pump to be operated in an optimum efficiency.This object is achieved by a method for operating an electromotively driven fluid pump of a motor vehicle according to patent claim 1 and by a control device for operating an electromotively driven fluid pump of a motor vehicle according to patent claim 8.The method according to the invention for operating an electric motor-driven fluid pump comprises at least the following steps: Predefined a setpoint volume flow to be provided by the fluid pump. operating an electric machine driving the fluid pump in a pulse operating mode with first time periods in which the electric machine runs at a first setpoint rotational speed and with second time periods in which the electric machine is stopped or runs at a second setpoint rotational speed, so that the fluid pump delivers the setpoint volumetric flow on average in an optimal efficiency manner.The present invention proposes operating the electric machine of an electric motor-driven fluid pump in a pulse operating mode in order to provide a setpoint volume flow. The efficiency of an electric motor-driven fluid pump can be increased thereby; in particular, it is possible to provide different setpoint volumetric flows in an optimum manner for efficiency.Such a pulse operating mode can be used in particular when the setpoint volume flow is not required continuously or when a storage device is arranged between the fluid pump and a fluid consumer which is to be supplied with the volume flow.The method according to the invention preferably has the following steps: Depending on the setpoint volume flow to be provided, determining a third setpoint rotational speed for the electric machine driving the fluid pump, in such a way that, when the electric machine is operated constantly at the third setpoint rotational speed, the fluid pump delivers the setpoint volume flow. determining an efficiency of the fluid pump or of the electric machine driving the fluid pump, said efficiency depending on the third setpoint rotational speed. comparing the efficiency with a limit value. Then, if the determined efficiency is greater than or corresponds to the limit value. operating the electric machine in a constant operating mode at the third setpoint rotational speed. Then, if the determined efficiency is less than the limit value, operating the electric machine in the pulse operating mode. This embodiment of the invention is particularly preferred in order to provide a setpoint volume flow in an efficiency-optimized manner. Depending on the efficiency that can be provided to the electric machine in a constant operating mode with constant rotational speed, the electric machine driving the fluid pump is operated either in the constant operating mode with constant setpoint rotational speed or in the pulse operating mode.Preferably, for the pulse operating mode, a length of the first time periods, a length of the second time periods, the first setpoint rotational speed and optionally the second setpoint rotational speed are determined such that the fluid pump delivers the setpoint volume flow in an optimum efficiency manner. By means of a corresponding determination of the lengths of the first and second time periods and amounts of the first and second setpoint rotational speeds, the setpoint volume flow can be conveyed in an optimum manner with regard to efficiency on average.In the pulse operating mode, the first setpoint rotational speed of the electric machine in the first time periods is preferably greater than the second setpoint rotational speed of the electric machine in the second time periods and / or greater than the third setpoint rotational speed. In the pulse operating mode, the length of the first time periods is greater or less than the length of the second time periods; alternatively, in the pulse operating mode, the length of the first time periods corresponds to the length of the second time periods.Preferred refinements emerge from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawings, without being restricted thereto. The following shows: FIG. 1 is a schematic illustration of an electric motor-driven fluid pump of a motor vehicle, FIG. 2 is a timing diagram for illustrating the invention, FIG. 3 shows an efficiency characteristic diagram of an electric machine for the purpose of illustrating the invention,FIG. 1 shows a highly schematic view of a detail from a motor vehicle in the region of a fluid pump 1, which is driven by means of an electric machine 2. The electric machine 2 drives a shaft 3 and, via the shaft 3, the fluid pump 1. Between the shaft 3 and the electric machine 2 a transmission or reduction stage 4 can optionally be connected. The fluid pump 1 can be, for example, an oil pump with which a setpoint oil volume flow is to be conveyed in the direction of a consumer. This setpoint oil volume flow can be used, for example, in a transmission or in a final drive for cooling and / or lubricating assemblies. Furthermore, the fluid pump 1 can be a water pump in order to make water available to a consumer for cooling. As already explained, a desired volume flow of the fluid conveyed by the fluid pump 1 is to be provided to a consumer by means of the fluid pump 1. In this case, the setpoint volume flow which the fluid pump 1 is intended to deliver is typically predefined or requested on the control side.In order to provide a setpoint volume flow requested or specified on the control side via the fluid pump 1 driven by the electric machine 2, it is proposed to operate the electric machine 2 driving the fluid pump 1 in a pulse operating mode with first time periods, in which the electric machine 2 runs at a first setpoint rotational speed, and with second time periods, in which the electric machine 2 is either stopped or runs at a second setpoint rotational speed, namely in such a way that the fluid pump 1 delivers the setpoint volume flow on average in an optimum efficiency manner.Such a non-constant setpoint volume flow, which changes with the setpoint rotational speed, can be used in particular when the consumer to be supplied by the fluid pump 1 does not continuously require the setpoint volume flow, as is the case in particular with cooling and / or lubrication, and when a reservoir is connected between the fluid pump and the consumer.Preferably, a third setpoint rotational speed for the electric machine 2 driving the fluid pump 1 is determined as a function of the setpoint volume flow to be provided, in such a way that, when the electric machine 2 is operated constantly at the third setpoint rotational speed, the fluid pump 1 delivers the setpoint volume flow. For this third setpoint rotational speed, an efficiency of the fluid pump 1 or of the electric machine 2 driving the fluid pump 1 is determined. Accordingly, that efficiency which would be established if the electric machine 2 were operated at the third setpoint rotational speed in the constant operating mode is determined. This determined efficiency is compared with a limit value.Then, if the efficiency determined is greater than the limit value or corresponds to the limit value, the electric machine 2 is operated at the third setpoint rotational speed in the constant operating mode. If, on the other hand, the determined efficiency is less than the limit value, the electric machine 2 is operated in the pulse operating mode, with first time periods in which the electric machine 2 runs at the first setpoint rotational speed, and with the second time periods in which the electric machine 2 is stopped or runs at a second setpoint rotational speed, so that the fluid pump 1 delivers the setpoint volumetric flow on average in an optimum efficiency manner. For the pulse operating mode, a length of the first time periods, the first setpoint rotational speed for the first time periods, a length of the second time periods and the second setpoint rotational speed for the second time periods, which is zero when the electric machine 2 is stopped in the second time periods, are determined such that the fluid pump delivers the setpoint volumetric flow on average, specifically with optimum efficiency.FIG. 2 shows speed curves 5 and 6 for setpoint speeds over time t. The rotational speed profile 5 corresponds to the third setpoint rotational speed, which would be required in order to provide a requested setpoint volume flow via the feed pump 1 when the electric machine 2 is operated constantly at the third setpoint rotational speed 5 in a constant operating mode. This third setpoint rotational speed does not, however, allow optimum operation of the electric machine 2 and thus of the fluid pump 1 driven by the electric machine 2, it being assumed by way of example that the efficiency η that can be provided at the setpoint rotational speed 5 corresponds to the efficiency η5 drawn in FIG. 3.In FIG. 3, both characteristic curves for a power consumption P and characteristic curves for the efficiency η of the electric machine 2 are plotted against the rotational speed n and a torque M.Since the efficiency η5of the constant operating mode is too low, i.e. is less than a limit value, the electric machine 2 of the feed pump 1 is not operated at the third setpoint rotational speed 5 in the constant operating mode, but rather in a pulse operating mode with the first time periods Δt 1, in which the electric machine runs at a first setpoint rotational speed, and with the second time periods Δt 2, in which the electric machine 2 is stopped or runs at a second setpoint rotational speed. If the electric machine 2 is stopped, the second setpoint rotational speed is zero. FIG. 3 shows the efficiency η6for the rotational speed n6, which means that the electric machine 2 is operated with a higher efficiency in pulse operation than in the constant operating mode, so that the requested setpoint volume flow is accordingly provided in an optimum manner for efficiency by the pulse operating mode. In the pulse operating mode, the first setpoint rotational speed of the electric machine 2 in the first time periods Δt 1 is preferably greater than the third rotational speed in the constant operating mode and also greater than the second setpoint rotational speed in the second time periods Δt 2. In the pulse operating mode, the length of the first time periods Δt 1 may be greater than or less than the length of the second time periods Δt 2, alternatively, the lengths of the first time periods Δt 1 may also correspond to the lengths of the second time periods Δt 2.The invention is therefore based on the idea that an efficiency of an electric machine 2 driving a fluid pump 1 changes as a function of its rotational speed, and that the optimum operating point of an electric machine 2 driving a fluid pump 1 is generally at higher rotational speeds and higher loads. Therefore, if the efficiency provided in a constant operating mode is too low, the electric machine 2 of the fluid pump 1 is then no longer operated in a constant operating mode but in a pulse operating mode in order to provide the requested setpoint volume flow on average in an optimum efficiency manner.The invention further relates to a control device for operating an electric motor-driven fluid pump 1 of a motor vehicle, which is configured to execute the method described above on the control side. The control unit operates a fluid pump 1, namely an electric machine 2 driving the fluid pump 1, depending on a setpoint volume flow predefined for the fluid pump 1, in a pulse operating mode with the first time periods and the second time periods, wherein the electric machine 2 runs at the first setpoint rotational speed in the first time periods, and wherein the electric machine 2 is stopped or runs at the second setpoint rotational speed in the second time periods. Thus, on average, the setpoint volume flow can be delivered by the fluid pump 1 in an optimum efficiency manner.The control device is preferably an electronic control device, for example a transmission control device. Such an electronic control device has hardware-side means and software-side means for carrying out the method according to the invention. The hardware-side means include data interfaces in order to exchange data with the modules involved in executing the method according to the invention, for example an interface via which the control device controls the electric machine 2. The hardware-side means also include a processor for data processing and a memory for data storage. Software-side means include program modules which are implemented in the control device for carrying out the method according to the invention.Reference numerals denote reference numerals1 Fluid pump 2 Electric machine 3 Shaft 4 Transmission or reduction stage 5 Speed profile 6 Speed profileReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 208 713 A1

[0004]

Claims

Method for operating an electric motor-driven fluid pump (1) of a motor vehicle, having at least the following steps: Presetting a setpoint volume flow to be provided by the fluid pump (1), operating an electric machine (2) driving the fluid pump (1) in a pulse operating mode having first time periods in which the electric machine (2) runs at a first setpoint rotational speed, and having second time periods in which the electric machine (2) is stopped or runs at a second setpoint rotational speed, such that the fluid pump (1) delivers the setpoint volume flow in an optimum efficiency average.Method according to Claim 1, characterized bythe following steps: determining, as a function of the setpoint volume flow to be provided, a third setpoint rotational speed for the electric machine (2) driving the fluid pump (1), in such a way that, if the electric machine (2) is operated constantly at the third setpoint rotational speed, the fluid pump (1) delivers the setpoint volume flow, ascertaining an efficiency of the fluid pump (1) or of the electric machine driving the fluid pump (1) which efficiency is dependent on the third setpoint rotational speed, comparing the efficiency with a limit value, if the ascertained efficiency is greater than the limit value or corresponds thereto, operating the electric machine (2) in a constant operating mode at the third setpoint rotational speed, if the ascertained efficiency is less than the limit value, operating the electric machine ( 2) in the pulse operating mode.Method according to Claim 1 or 2, characterized in that, for the pulse operating mode, a length of the first time periods, a length of the second time periods, the first setpoint rotational speed and, if appropriate, the second setpoint rotational speed are determined in such a way that the fluid pump (1) delivers the setpoint volumetric flow in an optimum efficiency manner on average.Method according to one of Claims 1 to 3, characterized in thatthe first setpoint rotational speed of the electric machine (2) in the first time periods is greater than the second setpoint rotational speed of the electric machine (2) in the second time periods and / or greater than the third setpoint rotational speed in the pulse operating mode.Method according to one of Claims 1 to 4, characterized in that, in the pulse operating mode, the length of the first time periods is greater than the length of the second time periods.Method according to one of Claims 1 to 4, characterized in that, in the pulse operating mode, the length of the first time periods corresponds to the length of the second time periods.Method according to one of Claims 1 to 4, characterized in that, in the pulse operating mode, the length of the first time periods is less than the length of the second time periods.Control device for operating an electric motor-driven fluid pump (1) of a motor vehicle, wherein the control device operates an electric machine (2) driving the fluid pump (1) in a pulse operating mode with first time periods in which the electric machine (2) runs at a first desired rotational speed and with second time periods in which the electric machine (2) is stopped or runs at a second desired rotational speed, depending on a predefined desired volumetric flow to be provided by the fluid pump (1), such that the fluid pump (1) delivers the desired volumetric flow on average in an efficiency-optimized manner.Control device according to Claim 8, characterized in that the control device determines a third setpoint rotational speed for the electric machine (2) on the basis of the predefined setpoint volume flow to be provided by the fluid pump (1), in such a way that, if the electric machine (2) is operated constantly at the third setpoint rotational speed, the fluid pump (1) delivers the setpoint volume flow, the control device determines an efficiency of the fluid pump (1) or of the electric machine driving the fluid pump (1) which efficiency is dependent on the third setpoint rotational speed, wherein the control device compares the efficiency with a limit value, wherein, if the determined efficiency is greater than the limit value or corresponds to the same, the control device operates the electric machine (2) in a constant operating mode at the third setpoint rotational speed, wherein, if the determined efficiency is less than the limit value, the control device operates the electric machine (2) in a constant operating mode at the third setpoint rotational speed, the electric machine ( 2) operates in the pulse operating mode.Control device according to Claim 8 or 9, characterized in that it is designed to automatically carry out the method according to one of Claims 1 to 7.

Images