Method and control device for operating electrically driven fluid pump of motor vehicle

Abstract

The invention relates to a method and a control device for operating an electrically driven fluid pump of a motor vehicle. The method comprises at least the following steps: specifying a target volume flow to be provided by the fluid pump. A first target rotational speed of a motor driving the fluid pump is determined as a function of the target volumetric flow to be provided, such that the fluid pump delivers the target volumetric flow if the motor is operating at the first target rotational speed constantly. The first target rotational speed is compared to a rotational speed boundary. And when the first target rotating speed is greater than the rotating speed boundary or equivalent to the rotating speed boundary, the motor operates at the first target rotating speed in the constant operation mode. When the first target rotational speed is less than a rotational speed boundary, the motor is operated in a pulse operating mode having a first time period within which the motor is operated and operated at a second target rotational speed, and a second time period within which the motor is shut down, the second target rotational speed of the electric machine is at least as large as the rotational speed boundary.

Description

Technical Field

[0001] The invention relates to a method and a control device for operating an electrically driven fluid pump of a motor vehicle. Background Art

[0002] Fluid pumps are installed in motor vehicles. These fluid pumps are used to convey liquid fluids in the direction of consumer devices. Thus, the fluid pump can be, for example, an oil pump in order to provide an oil flow for cooling and / or lubrication to the consumer device. In addition, the fluid pump can also be a water pump.

[0003] The fluid pump is typically driven electrically with the aid of an electric motor. When the fluid pump is to provide a defined target volume flow, the electric motor driving the delivery pump is operated at a constant target speed for this purpose. The target speed of the electric motor, via which the desired target volume flow can be provided to the delivery pump, can be determined, for example, with the aid of a characteristic curve or characteristic curve.

[0004] Electric motors without rotor position sensors are increasingly being used. Although such motors are cheap, they do not operate as accurately as electric motors with rotor position sensors, especially at low rotational speeds. Therefore, for such motors and other electric motors used to drive fluid pumps, a minimum rotational speed is predetermined. Below the minimum rotational speed, it is not permitted to drive the fluid pump via the electric motor, since the fluid pump cannot be driven with sufficient accuracy via the electric motor. The operating range of the fluid pump is limited by the minimum rotational speed of the electric motor. Therefore, there is a need to expand the operating range of fluid pumps driven by electric motors.

[0005] DE 10 2021 208 713 A1 discloses a device for oil supply, which has a pump and an electric motor for driving the pump. The device has a rotation speed sensor, a pressure sensor and a temperature sensor for detecting the rotation speed of the electric motor, wherein the pressure sensor and the temperature sensor are arranged in the outflow opening of the pump. Depending on the measurement signals of the rotation speed sensor, the pressure sensor and the temperature sensor, at least one operating condition of the electric motor is changed in order to obtain a desired output. Summary of the invention

[0006] The object of the present invention is to provide a method and a control device for operating an electrically driven fluid pump of a motor vehicle, which method and control device allow the operating range of the electrically driven fluid pump to be expanded, more precisely in the direction of lower rotational speeds of the electric motor and thus of the fluid pump. This object is achieved by a method according to claim 1 and a control device according to claim 8.

[0007] The method for operating an electrically driven fluid pump of a motor vehicle according to the present invention comprises at least the following steps: predetermining a target volume flow to be provided by the fluid pump. Determining a first target rotational speed of an electric motor driving the fluid pump so that if the electric motor is constantly running at the first target rotational speed, the fluid pump delivers the target volume flow. Comparing the first target rotational speed with a rotational speed limit. When the first target rotational speed is greater than the rotational speed limit or is equivalent to the rotational speed limit, operating the electric motor at the first target rotational speed in a constant operating mode. When the first target rotational speed is less than the rotational speed limit, operating the electric motor in a pulse operating mode having a first time period and a second time period, wherein in the first time period, the electric motor is running and running at the second target rotational speed, and in the second time period, the electric motor is stopped, wherein in the first time period, the second target rotational speed of the electric motor is at least as large as the rotational speed limit.

[0008] The present invention proposes to determine the first target speed of the motor driving the fluid pump as follows, depending on the target volume flow to be provided by the fluid pump: when the motor is constantly running at the first target speed, the target volume flow can be provided by the fluid pump. The first target speed is compared with the speed limit. The speed limit can be equivalent to the lowest speed of the motor driving the fluid pump. When the first target speed is greater than the speed limit or is equivalent to the speed limit, the motor is operated at the first target speed in a constant operation mode, that is, it is operated at the target speed constantly or continuously or uninterruptedly. On the contrary, when the first target speed is less than the speed limit, the motor driving the fluid pump is not operated in the constant operation mode, but in the pulse mode, wherein the motor will alternately operate or stop at the second target speed with a predetermined beat or cycle. The second target speed when the motor is running in the pulse mode is at least as large as the speed limit. What can be achieved by the present invention is that the operating range of the electrically driven fluid pump is expanded. If the first target speed of the target volume flow caused by the motor driving the fluid pump in the constant operation mode is too small due to the predetermined target volume flow, that is, less than the speed limit, the motor is alternately connected and disconnected in the pulse mode. This makes it possible to provide relatively small target volume flows with sufficient accuracy. Ultimately, the operating range is extended in electrically driven fluid pumps.

[0009] Preferably, for the pulse operating mode, the length of the first time period, the length of the second time period and the second target rotational speed of the motor in the first time period are determined so that the fluid pump delivers the target volume flow rate on average or on average. This can particularly advantageously expand the operating range of the electrically driven fluid pump in the direction of a smaller target volume flow rate.

[0010] In the pulse operating mode, the second target speed of the electric machine in the first time period corresponds to the speed limit. Alternatively, in the pulse operating mode, the second target speed of the electric machine in the first time period is greater than the speed limit. With both variants, the operating range of the electrically driven fluid pump of the motor vehicle can be particularly preferably expanded in the direction of a smaller target volume flow.

[0011] In the pulse operating mode, the length of the first time period is greater than the length of the second time period. Alternatively, in the pulse operating mode, the length of the first time period corresponds to the length of the second time period. It is also possible that in the pulse operating mode, the length of the first time period is less than the length of the second time period. With these variants, the operating range of the electrically driven fluid pump of the motor vehicle can also be particularly advantageously expanded in the direction of a smaller target volume flow (which cannot be provided with sufficient accuracy in the constant operating mode). BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Preferred improvements are obtained from the dependent claims and the following description. The embodiments of the present invention are further described in conjunction with the accompanying drawings, but are not limited thereto. In the drawings:

[0013] Figure 1 A schematic diagram of an electrically driven fluid pump of a motor vehicle is shown,

[0014] Figure 2 A timing diagram for illustrating a first variant of the present invention is shown.

[0015] Figure 3 A timing diagram is shown for explaining a second variant of the present invention. DETAILED DESCRIPTION

[0016] Figure 1 A section of a motor vehicle is shown very schematically in the region of a fluid pump 1 which is driven with the aid of an electric motor 2. The electric motor 2 drives a shaft 3 and drives the fluid pump 1 via the shaft 3. A step-up or step-down ratio 4 can optionally follow between the shaft 3 and the electric motor 2.

[0017] The fluid pump 1 can be, for example, an oil pump, with which a target oil volume flow is to be delivered in the direction of the consumer. This target oil volume flow can be used, for example, in a transmission or an axle drive for cooling and / or lubricating components. Furthermore, the fluid pump 1 can also be a water pump in order to supply water to the consumer for cooling.

[0018] As already mentioned above, the fluid pump 1 is to provide a consumer with a target volume flow of the fluid delivered by the fluid pump 1. In this case, the target volume flow to be delivered by the fluid pump 1 is typically predetermined or required on the control side.

[0019] Depending on the predetermined or required target volume flow, a first target rotational speed of the electric motor 2 driving the fluid pump 1 is determined, and the fluid pump 1 delivers or provides the target volume flow if the electric motor 2 is operated constantly or uninterruptedly or continuously at this first target rotational speed.

[0020] The first target speed is determined depending on the predetermined or required target volume flow, for example, based on a characteristic curve or a corresponding characteristic curve stored on the control side, which reflects the first target speed of the motor 2 depending on the target volume flow and, if necessary, the temperature of the fluid.

[0021] A first target rotational speed determined for the constant operating mode of the electric motor 2 and thus of the fluid pump 1 in order to provide a target volume flow is compared with a rotational speed limit.

[0022] The speed limit may be a so-called minimum speed of the electric machine 2. The speed limit may also be greater than the minimum speed.

[0023] When the first target speed of the motor 2 is greater than the speed limit or is equivalent to the speed limit, the motor 2 operates in a constant operating mode, more specifically, operates constantly or uninterruptedly or continuously at a first target speed that is greater than the speed limit or is equivalent to the speed limit, more specifically, for providing a target volume flow through the fluid pump 1 in the constant operating mode of the motor 2.

[0024] If the first target rotational speed for the constant operating mode, which is determined as a function of the target volume flow, is less than a rotational speed limit, the electric motor 2 and thus the fluid pump 1 will not be operated in the constant operating mode but in the pulsed operating mode.

[0025] In the pulse operation mode, the motor 2 is operated in the first time period and for this purpose is operated at the second target speed, whereas the motor 2 is stopped in the second time period of the pulse operation mode. The second target speed for driving the motor 2 in the first time period of the pulse operation mode is at least as large as the speed limit, but can also be larger than the speed limit. In the pulse operation mode, the predetermined or required target volume flow is provided on average. Therefore, in the first time period of the pulse operation mode, the motor 2 is operated and operated at the second target speed. In the second time period of the pulse operation mode, the motor 2 is stopped. In other words, the third target speed of the motor 2 in the second time period of the pulse operation mode is zero.

[0026] According to the present invention, it is possible to expand the operating range of the electrically driven fluid pump 1 toward a smaller target volume flow. If the desired target volume flow cannot be provided by the corresponding first target speed in the constant operating mode because the first target speed in the constant operating mode is too low, the motor 2 and thus the fluid pump 1 are operated in the pulse operating mode.

[0027] In the pulse operating mode, the electric motor 2 is alternately switched on and off, wherein in a first time period the electric motor is running and operated at a second target rotational speed, and in a second time period the electric motor 2 is stopped.

[0028] The duration of the first time period is also referred to as the pulse duration, and the sum of the first time period and the second time period is also referred to as the cycle duration. Each first time period is followed by a second time period, and each second time period is followed by a first time period. Thus, the first time period in which the motor 2 and thus the fluid pump 1 is operated and the second time period in which the motor 2 is stopped will alternate in a beat or in a sequence.

[0029] For the pulse operation mode, the length of the first time period in which the motor 2 is operated and operates at the second target speed so that the fluid pump 1 conveys the fluid, the length of the second time period in which the motor 2 is stopped and the fluid pump 1 does not convey the fluid, and the second target speed of the motor 2 in the first time period are determined, so that the fluid pump 1 conveys the target volume flow on average in the pulse operation mode. Here, the second target speed of the motor 2 in the first time period can be equivalent to the speed limit or can also be greater than the speed limit. The length of the first time period can be equivalent to the length of the second time period. However, the length of the first time period can also be greater than or less than the length of the second time period.

[0030] exist Figure 2 , a first target speed is shown with respect to time t using a speed curve 5, which provides the required target volume flow in a constant operating mode of the motor 2 and thus of the fluid pump 1 driven by the motor 2. The first target speed 5 is Figure 2 Less than the speed limit n G .also, Figure 2 The speed curve 6 shows a target speed at which the electric machine 2 is operated in the pulsed operating mode in order to provide a desired target volume flow which must be provided via the first target speed 5 in the constant operating mode.

[0031] In the first time period Δt1, the motor 2 is operated and runs at a second target speed. Figure 2 The speed limit n G In the second time period Δt2, the motor 2 is stopped. In other words, the third target rotation speed of the motor 2 in the second time period Δt2 of the pulse operation mode is zero.

[0032] exist Figure 2 In the constant operation mode, the first target speed 5 is equal to the first time period Δt1 and the second time period Δt2. Figure 2 corresponds to 50% of the speed limit.

[0033] exist Figure 3 , the speed curves 5 and 6 are also shown with respect to the time t. Here, the speed curve 5 again corresponds to the first target speed for the constant operating mode of the motor 2 and thus the fluid pump 1, at which the motor 2 needs to be operated in the constant operating mode, so that the fluid pump 1 provides the required target volume flow. Figure 3 In the example, the first target speed is less than the speed limit n G , however, the first target speed exceeds the speed limit n G 50% of Figure 3 In the embodiment, the length of the first time period during which the motor 2 is running and the fluid pump 1 is delivering fluid is longer than the length of the second time period Δt2 during which the motor 2 is stopped and no fluid is delivered.

[0034] exist Figure 2 and Figure 3 According to the speed curve 6, the second target speed of the motor 2 when it is running in the first time period Δt1 is respectively equivalent to the speed limit n G It is possible that the motor runs at a speed greater than the speed limit n in the first time period Δt1. G In this case, the length of the first time period Δt1 is shortened.

[0035] The first target speed and the second target speed are respectively greater than zero in value.

[0036] The invention also relates to a control device which is set up to automatically implement the method according to the invention on the control side. The control device determines a first target speed of the electric motor 2 as a function of a predetermined target volume flow to be provided by the fluid pump 1, at which the electric motor 2 needs to be operated in order to deliver the target volume flow via the fluid pump 1 in a constant operating mode. The control device compares the first target speed with a speed limit.

[0037] When the first target speed is greater than the speed limit or is equal to the speed limit, the control device operates the motor 2 at the first target speed in the constant operation mode to provide the target volume flow in the constant operation mode. In contrast, when the first target speed is less than the speed limit, the control device operates the motor 2 in the pulse operation mode, in which the motor 2 is turned on and off, that is, it is operated and stopped in sequence or in a clocked manner, wherein the target volume flow is provided on average in the pulse operation mode. When the motor 2 is operated in the pulse operation mode within the first time period, the motor is operated at the second target speed.

[0038] The control device may be a control device for a fluid pump, or may be another control device for a motor vehicle, such as a transmission control device. The control device is particularly implemented as an electronic control device and has hardware-side devices and software-side devices for executing the method according to the present invention. The hardware-side devices include a data interface to exchange data with structural components involved in executing the method according to the present invention, such as exchanging data with the motor 2. In addition, the hardware-side structural components also include a processor for data processing and a memory for data storage. The software-side devices include programmable modules implemented in the control device for executing the method according to the present invention.

[0039] Reference numerals list

[0040] 1 Fluid Pump

[0041] 2 Motor

[0042] 3 Axis

[0043] 4 speed increase or reduction ratio stages

[0044] 5 Speed ​​curve

[0045] 6 Speed ​​curve

Claims

1. A method for operating an electrically driven fluid pump (1) of a motor vehicle, the method comprising at least the following steps: predetermining a target volume flow to be provided by the fluid pump (1), determining a first target speed of an electric motor (2) driving the fluid pump (1) as a function of a target volume flow to be provided, so that if the electric motor (2) is constantly operated at the first target speed, the fluid pump (1) delivers the target volume flow, comparing the first target speed with the speed limit, When the first target speed is greater than the speed limit or equal to the speed limit, the motor (2) is operated at the first target speed in a constant operation mode, When the first target speed is less than the speed limit, the motor (2) is operated in a pulse operation mode having a first time period and a second time period, during the first time period, the motor (2) is operated and operates at the second target speed, and during the second time period, the motor (2) is stopped, wherein: During the first time period, a second target rotational speed of the electric machine (2) is at least as great as the rotational speed limit.

2. The method according to claim 1, characterized in that For the pulse operating mode, the length of the first time period, the length of the second time period and a second target rotational speed of the motor (2) within the first time period are determined so that the fluid pump (1) delivers a target volume flow on average.

3. The method according to claim 1 or 2, characterized in that: In the pulse operating mode, the second target speed of the electric machine (2) in the first time period corresponds to the speed limit.

4. The method according to claim 1 or 2, characterized in that: In the pulse operation mode, the second target rotational speed of the electric motor (2) in the first time period is greater than the rotational speed limit.

5. The method according to any one of claims 1 to 4, characterized in that In the pulse operation mode, the length of the first time period is greater than the length of the second time period.

6. The method according to any one of claims 1 to 4, characterized in that In the pulse operation mode, the length of the first time period corresponds to the length of the second time period.

7. The method according to any one of claims 1 to 4, characterized in that In the pulse operation mode, the length of the first time period is shorter than the length of the second time period.

8. A control device for operating an electrically driven fluid pump (1) of a motor vehicle, wherein: The control device determines a first target speed of an electric motor (2) driving the fluid pump (1) as a function of a predetermined target volume flow to be provided by the fluid pump (1), so that if the electric motor (2) is constantly operated at the first target speed, the fluid pump (1) delivers the target volume flow, wherein the control device compares the first target speed with a speed limit. When the first target speed is greater than the speed limit or equal to the speed limit, the control device causes the motor (2) to operate at the first target speed in a constant operation mode. When the target speed is less than the speed limit, the control device operates the motor (2) in a pulse operation mode having a first time period and a second time period, wherein the motor is operated and runs at a second target speed during the first time period, and the motor is stopped during the second time period, wherein the second target speed of the motor is at least as great as the speed limit during the first time period.

9. The control device according to claim 8, characterized in that The control device is set up to automatically carry out the method according to any one of claims 1 to 7 .

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