Method for controlling the operating speed of an electric oil pump by cold time

Abstract

This method for controlling the operating regime of an electric oil pump in a lubrication and / or cooling circuit includes the following steps: - Estimation of the oil temperature in the lubrication and / or cooling circuit (step E1); and - Starting up the pump (step E2) at an operating regime for which the oil outlet flow rate and the pump supply current are maximized with regard to the oil viscosity at the estimated temperature.

Description

technical field

[0001] The present invention relates to the control of the operating regime of an electric oil pump of a lubrication and / or cooling circuit.

[0002] In particular, the present invention relates to controlling the operating regime of such a pump under temperature conditions for which the viscosity of the oil increases and risks damaging the pump or forcing it to stop.

[0003] In general, the invention applies to any oil pump operating in an environment where the temperature may vary, for example in a motor vehicle. Previous techniques

[0004] An electric oil pump for an electric motor is used to lubricate and / or cool the motor with oil. The control of such a pump is achieved, according to current best practices, by defining an operating regime directly proportional to the oil flow rate at the pump outlet, based on the oil temperature.

[0005] In the case of low or even negative oil temperature in °C, for example during the first morning start of a motor vehicle in negative temperatures, the sizing of the electric pump is essential.

[0006] Indeed, during an initial morning start-up in sub-zero temperatures, the oil pump must perform the following priority functions in order of priority: 1) a minimum flow rate for lubrication; 2) as much flow rate as possible for cooling.

[0007] However, the lower the oil temperature, the more viscous the oil, and the more power the pump must deliver to achieve the same flow rate. Therefore, for more viscous oil, the pump's supply current must be higher to generate greater resistive torque for an equivalent oil flow rate at the pump outlet.

[0008] The viscosity of the oil increases exponentially when cold, and also increases due to its aging.

[0009] Since the exact temperature of the oil in a lubrication and / or cooling circuit can never be precisely known, it is necessary to oversize the power capacity of the oil pump to be sure of having the desired oil flow in all cases.

[0010] Indeed, if the pump is undersized, there is a risk of the oil pump stopping when the temperature is too low, the oil being too viscous, and the supply current required to pump the oil to the desired flow rate being too high. In the latter case, the pump may have a protection mechanism and stop completely, or the pump may lack such a mechanism, and starting it with an excessively high supply current leads to reliability issues, such as bearing or seal problems, in addition to overheating and / or insufficient lubrication of the electric motor.

[0011] Conversely, if the pump is oversized, it will not be possible to take advantage of it for nominal use.

[0012] Currently, in order to avoid installing an oversized pump, a precise oil temperature sensor for the circuit is used, reducing uncertainty about the actual viscosity of the oil, but significantly increasing production costs.

[0013] In other words, the less accurate the sensor, the more the pump needs to be oversized. For example, if the temperature sensor is accurate to + / -6°C when cold and indicates an oil temperature of -30°C, then the actual oil temperature could be -36°C with a viscosity much higher than that of -30°C. Consequently, if a flow rate of 0.5 liters per minute (L / min) is required at an actual temperature of -30°C, then the pump must be sized to deliver 0.5 L / min with an oil viscosity corresponding to that of an oil at -36°C. If the sensor is more accurate, with an uncertainty of + / -3°C, for example, the pump must be sized to deliver 0.5 L / min with an oil viscosity corresponding to that of an oil at -33°C. Description of the invention

[0014] The present invention therefore aims to overcome the aforementioned disadvantages and to provide a method for controlling the operating regime of an electric oil pump of a lubrication and / or cooling circuit allowing a proper balance in the sizing of the oil pump and not using a temperature sensor that is too precise and expensive.

[0015] The present invention relates to a method for controlling the operating mode of an electric oil pump in a lubrication and / or cooling circuit, said method comprising the following steps: Estimation of the oil temperature in the lubrication and / or cooling circuit; and Starting the pump at an operating speed for which the oil output flow rate and / or the pump supply current are maximized with respect to the oil viscosity determined by the estimated temperature.

[0016] Thus, this process allows the optimization of the pump sizing and the systematic achievement of the maximum possible pump flow rate for low temperatures, without needing precise temperature information.

[0017] Advantageously, the pump start-up step is carried out at an operating regime for which the oil output flow rate and / or the pump supply current are maximized with respect to the oil viscosity at the estimated temperature only when the estimated oil temperature is less than or equal to a predetermined temperature threshold.

[0018] Advantageously, a pump start-up step is performed at an operating regime according to a secondary lookup table between the operating regime and the estimated oil temperature implemented only when the estimated temperature is above the predetermined temperature threshold, the secondary lookup table being established so that the operating regime delivers a desired oil flow rate as a function of the oil temperature.

[0019] In one implementation mode, the predetermined temperature threshold is between -10°C and 20°C, preferably between -5°C and 10°C.

[0020] In a particular implementation mode, the oil temperature estimation step includes measuring or deducing the oil temperature with an uncertainty of up to plus or minus 15°C.

[0021] Advantageously, the estimated temperature is the measured or deduced temperature minus the uncertainty of 15°C.

[0022] Advantageously, the step of starting the pump at an operating regime for which the oil outlet flow rate and / or the pump supply current are maximized with regard to the oil viscosity at the estimated temperature is implemented by starting the pump at an operating regime according to a primary lookup table obtained beforehand by a simulation or test step of the correspondence between an oil temperature and / or a limiting supply current, in particular the maximum permissible current of the pump beyond which the pump is damaged, in particular by overheating.

[0023] In one implementation mode, the primary lookup table is stored in a pump computer or in an external computer sending operating regime commands to said pump.

[0024] Advantageously, the electric oil pump is a volumetric pump whose output flow rate is proportional to the operating speed.

[0025] Advantageously, the present method is implemented for controlling the operating regime of the electric oil pump in the lubrication and / or cooling circuit of an electric motor in a motor vehicle, Brief description of the drawings

[0026] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawing in which: [ Fig 1] is a schematic view of the steps implemented in the process of controlling the operating regime of an electric oil pump according to the invention. Detailed description of at least one embodiment

[0027] We have schematically represented on the figure 1 the steps of a process for controlling the operating regime of an electric oil pump in a lubrication and / or cooling circuit.

[0028] The lubrication and / or cooling circuit is, for example, that of an electric motor in a motor vehicle.

[0029] The electric oil pump, for example, is a volumetric pump, also called a positive displacement pump, whose output flow rate is proportional to the operating speed of said pump.

[0030] In this method of controlling the operating regime of the pump, a step E1 is first carried out to estimate the temperature of the oil in the lubrication and / or cooling circuit.

[0031] Step E1 of oil temperature estimation includes measuring, for example using a temperature sensor, or deducing, for example using a temperature estimator, the temperature of the oil present in the cooling and / or lubrication circuit. The measurement or deduction is carried out with an uncertainty of up to ±15°C, preferably ±10°C.

[0032] Indeed, the present process is robust and does not require having to estimate the oil temperature precisely.

[0033] In particular, the temperature estimated during step E1 is preferably the measured or deduced temperature from which the uncertainty is subtracted, where appropriate, from 15°C or 10°C.

[0034] Then, step E2 is performed to start up the pump at an operating speed for which the pump's oil output flow rate and / or the pump's supply current are as high as possible, in other words, maximized, with regard to the oil viscosity determined by the temperature estimated in step E1. Indeed, a high oil viscosity must be taken into account in order to avoid overheating the pump with an excessive supply current.

[0035] In other words, the pump's oil output flow rate and / or the pump's supply current are maximized while ensuring that the pump cannot be damaged by the oil's viscosity at the temperature estimated in step E1. The pump is considered damaged if its operation is abnormal or if its operating parameters exceed the nominal parameters provided by the pump manufacturer for a period longer than a predetermined time, for example, 5 seconds. For instance, the pump may overheat and be considered damaged.

[0036] In a particular implementation mode, the parameter to be maximized as a priority between the pump's oil output flow rate and the pump's supply current is said pump supply current.

[0037] In a first particular implementation mode, this step E2 is carried out by a pump computer, automatically determining an operating regime for which the pump's oil output flow rate and / or the pump supply current are as high as possible, in other words maximized, without the pump being damaged by the oil viscosity at the temperature estimated in step E1.

[0038] In a second particular mode of implementation, the E2 step of starting up the pump is carried out at an operating regime according to a primary correspondence table between the operating regime and the estimated oil temperature.

[0039] The primary correspondence table is established so that the operating regime is the pump operating regime for which the pump oil output flow rate and / or the pump supply current are as high as possible, in other words maximized, without the pump being damaged by the viscosity of the oil at the corresponding temperature.

[0040] The primary lookup table is optionally obtained beforehand through a simulation or testing step E3, which determines the relationship between an oil temperature and / or a supply current limit beyond which pump reliability is no longer guaranteed, or the pump may even be damaged. The supply current limit is, for example, the maximum permissible current of the pump; a current exceeding this limit would result in pump damage, for example, through overheating.

[0041] According to a particular implementation method, this E2 step of starting the pump is only carried out when the estimated oil temperature is less than or equal to a predetermined temperature threshold.

[0042] The predetermined temperature threshold is for example between -10°C and 20°C, preferably between -5°C and 10°C.

[0043] Below this predetermined threshold, the pump is therefore operating at its highest possible operating speed, in other words maximized, without this speed being too high and damaging the pump.

[0044] The pump must not stop under any circumstances for any of these reasons, unless the oil temperature is below a second predetermined threshold, for example -50°C.

[0045] Thus, the pump outlet flow rate is optimized for a range of low and common temperatures. In particular, for the same supply current, the higher the oil temperature, the higher the oil pump speed, a correlation shown, for example, in the primary lookup table.

[0046] Furthermore, when the estimated temperature is higher than the predetermined temperature threshold, for example for a temperature above 20°C, an E4 step is instead performed to start the pump at an operating regime according to a secondary correspondence table between the operating regime and the estimated oil temperature.

[0047] The secondary correspondence table is established so that the operating regime delivers a desired oil flow rate as a function of the oil temperature, without any other condition since the viscosity of the oil becomes very low for high temperatures and the power that the pump can deliver, in particular in terms of resistive torque, is no longer limiting.

[0048] This secondary correspondence table is classic and is obtained for example beforehand according to the needs of the lubrication and / or cooling circuits at certain oil temperatures, the said secondary correspondence table being optionally obtained by taking into account additional parameters such as the acoustics of the electric motor, cavitation, or the mechanical reliability of a motor element for such temperatures.

[0049] In a particular mode of implementation, the primary lookup table is stored in a pump computer or in an external computer sending operating regime instructions to said pump.

[0050] The same applies to the secondary lookup table which can be stored in a pump computer or in an external computer sending operating regime instructions to said pump.

Claims

1. Method for controlling the operating mode of an electric oil pump in a lubrication and / or cooling circuit, characterized in that It includes the following steps: - Estimation of the oil temperature in the lubrication and / or cooling circuit (step E1); and - Starting up the pump (step E2) at an operating regime for which the oil output flow rate and / or the pump supply current are maximized with regard to the oil viscosity determined by the estimated temperature.

2. Method according to claim 1, wherein step (E2) of starting up the pump is carried out at an operating regime for which the pump supply current is maximized with respect to the viscosity of the oil at the estimated temperature only when the temperature of the estimated oil is less than or equal to a predetermined temperature threshold.

3. Method according to claim 2, wherein a step (E4) is performed of starting the pump at an operating regime according to a secondary lookup table between the operating regime and the estimated oil temperature, implemented only when the estimated temperature is above said predetermined temperature threshold, the secondary lookup table being established so that the operating regime delivers a desired oil flow rate as a function of the oil temperature.

4. A method according to any one of claims 2 and 3, wherein the predetermined temperature threshold is between -10°C and 20°C, preferably between -5°C and 10°C.

5. A method according to any one of claims 1 to 4, wherein the step (E1) of estimating the oil temperature includes measuring or deducing the oil temperature with an uncertainty of up to plus or minus 15°C.

6. Method according to claim 5, wherein the estimated temperature is the measured or deduced temperature less the uncertainty of 15°C.

7. A method according to any one of claims 1 to 6, wherein the step (E2) of starting the pump at an operating regime for which the oil outlet flow rate and / or the pump supply current are maximized with regard to the oil viscosity at the estimated temperature is implemented by starting the pump at an operating regime according to a primary lookup table obtained beforehand by a step (E3) of simulating or testing the correspondence between an oil temperature and / or a limiting supply current, in particular the maximum permissible current of the pump, beyond which the pump is damaged, in particular by overheating.

8. Method according to claim 7, wherein the primary lookup table is stored in a pump computer or in an external computer sending operating regime commands to said pump.

9. A method according to any one of claims 1 to 8, wherein the electric oil pump is a positive displacement pump whose output flow rate is proportional to the operating regime.

10. Method according to any one of claims 1 to 9, implemented for controlling the operating regime of the electric oil pump of the lubrication and / or cooling circuit of an electric motor of a motor vehicle.

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