METHOD FOR CONTROLLING THE START-UP OF AN OIL PUMP

Abstract

A method controls the start-up of an oil pump of a gearbox by a brushless electric motor that has no position sensor. The stator coils are powered from the off mode in a constant-current open-loop control sequence until the pump reaches a speed threshold at which speed regulation switches over to closed-loop control on a setpoint corresponding to the lubrication flow rate required to ensure the reliability of the gearbox, but without in so doing exceeding a current threshold indicative of pump seizure, at which point motor control switches back over to the constant-current open-loop control sequence. The open-loop current setpoint is higher than the threshold for switching over to closed-loop control so that in the open-loop control mode the motor torque available at the pump is higher than in the closed-loop control mode.

Claims

1. A method for controlling the start-up of a gearbox oil pump by a brushless electric motor, without position sensor, comprising: powering the stator coils from the off mode according to a constant-current open-loop control sequence until the pump reaches a speed threshold at which the speed regulation switches over to closed-loop control on a setpoint corresponding to the lubrication flow rate necessary to ensure the reliability of the gearbox, but without exceeding a current threshold detecting seizure of the pump at which the motor control switches back over to the constant-current open-loop control sequence, wherein the open-loop current setpoint is higher than the threshold for switching over to closed-loop mode, so as to have, in open-loop mode, a motor torque on the pump that is higher than in closed-loop mode.

2. The method for controlling the start-up of an oil pump as claimed in claim 1, wherein, upon detection of seizure of the pump in closed-loop mode, the GMP computer switches over the pump speed regulation to open-loop mode for a calibrated period.

3. The method for controlling the start-up of an oil pump as claimed in claim 2, wherein the open-loop mode pump control sequence comprises a sequence of oscillations of the rotor.

4. The method for controlling the start-up of an oil pump as claimed in claim 2, wherein, at the end of the calibrated period, the GMP computer sends a speed setpoint to the pump corresponding to closed-loop mode operation.

5. The method for controlling the start-up of an oil pump as claimed in claim 4, wherein the GMP computer returns the open-loop control sequence each time the seizure detection threshold is exceeded in closed-loop mode.

6. The method for controlling the start-up of an oil pump as claimed in claim 4, wherein the control of the current remains in closed-loop mode on the setpoint corresponding to the lubrication flow rate necessary to ensure the reliability of the gearbox, when the temperature of the oil has increased sufficiently for this setpoint to remain under the seizure detection threshold in closed-loop mode.

Description

[0012] The present invention will be better understood on reading the following description of a nonlimiting embodiment thereof, with reference to the attached drawings, in which:

[0013] FIG. 1 is a simplified control diagram.

[0014] FIG. 2 illustrates the brushless motor.

[0015] FIG. 3 reproduces the typical profile of the signals analyzed.

[0016] FIG. 4 shows the trend of the oil temperature.

[0017] In FIG. 1, a gearbox 1 is schematically represented transmitting the torque C.sub.m from a motor to the wheels (torque at the wheels C.sub.r), on different transmission ratios. The oil pump 3, placed under the bottom of the box enclosing the lubrication oil h, supplies an external lubrication circuit 2, by which the oil is reintroduced into the upper part of the box, to ensure the lubrication of the parts. In this example, the pump has a brushless and temperature-sensorless motor (not represented), communicating with the controller of the power train 4.

[0018] FIG. 2 shows a diagram of a motor with three wound stators S, the windings of which are connected to an electronic switch (not represented). When two of the three stators are powered electrically, the rotor creates, in the third, a back-electromotive force, or back-EMF. A brushless and current-sensorless motor is controlled by a current regulator, usually of PID type.

[0019] In a gearbox lubrication pump, it is known practice to calibrate the current for an efficient start-up, for example from a gearbox oil temperature of 20° C. The control is provided either in open-loop (BO) mode according to determined constant-current sequences, or in closed-loop (BF) mode on current setpoints that are variable as a function of the speed, reached by the motor and by the pump. To start up the pump cold, the usual method is to power the rotor coils according to a first determined constant-current sequence, which starts from the off mode of the motor and of the pump (zero speed) to a pre-established speed threshold of the motor. From this threshold, the motor switches over to a second control mode, in closed-loop mode, on a pump speed setpoint. This setpoint corresponds to the lubrication flow rate necessary to ensure the reliability of the gearbox.

[0020] When controlling the start-up of a gearbox oil pump by a brushless and position-sensorless electric motor, it is advantageously powered, from off, according to an open-loop mode computer control sequence. In this first sequence, the control is performed at constant current, until the pump reaches a speed threshold. The regulation then switches over to a closed-loop control, on a speed setpoint corresponding to the lubrication flow rate necessary to ensure the reliability of the gearbox. However, in closed-loop mode, the current cannot exceed a diagnostic threshold, by which the seizure of the pump is detected. If this threshold is reached, the computer requires the control of the motor to switch back over to the constant-current open-loop control sequence.

[0021] The lubrication flow rate is a current regulator setting parameter, which must be adjusted as a function of the degree of viscosity of the oil, and therefore of its temperature. The issue on which the invention is based is to adjust the parameterization of the current regulator, to the oil temperature, without having any oil temperature sensor. As indicated above, the motor has a phase current monitoring system. This system monitors the passing of the current through a diagnostic threshold that makes it possible to detect that the pump is seized. In the proposed solution, it is chosen to calibrate the phase current in open-loop mode on a value above the phase current diagnostic threshold in closed-loop mode, so as to have a motor torque on the pump which is higher in open-loop mode than in closed-loop mode.

[0022] When the speed of the vehicle is positive, the computer of the power train (GMP) first sends a speed setpoint to the pump, which is above the switchover threshold between the open-loop mode and the closed-loop mode. The computer of the GMP (or the computer of the oil pump, depending on the chosen software) uses the diagnostic current threshold overshoot information to detect that the rotor is seized in closed-loop phase. The computer counts the number of seizures. When the counter exceeds a threshold n of number of seizures, it engages a phase of oscillation of the rotor (sinusoidal) called “deblocking”. This phase makes it possible to remove any possible metal particle jammed in the mechanism of the pump.

[0023] In the absence of metal particles in the oil, it is considered that the seizure of the rotor is due to the viscosity of the oil, which is too great at low temperature. The method proposed for adapting the parameters of the regulator to the temperature of the oil relies on the detection of a seizure. This event is exploited to send to the regulator a speed setpoint, such that the pump operates in open-loop mode for a calibrated period.

[0024] According to the invention, the open-loop current calibration is above the closed-loop current diagnostic threshold, so as to have, in open-loop mode, a motor torque on the pump that is higher than in closed-loop mode. The pump can thus operate at a lower speed in open-loop mode than in closed-loop mode but thus ensure a minimum lubrication of the gearbox, at low temperature. While the gearbox operates at low temperature, the shearing of the oil by the pinions (splash lubrication) and the motive power dissipated in the gearbox raises the temperature of the oil. Each time a seizure of the pump is detected in closed-loop mode, the computer of the GMP switches over the pump to open-loop mode for a calibrated period. After this calibrated time delay, the computer returns the initial closed-loop mode speed setpoint.

[0025] If the temperature of the oil has increased sufficiently for this setpoint to remain under the seizure detection threshold in closed-loop mode, the pump can then reach its speed setpoint. The pump is effectively started up.

[0026] Otherwise, the oil temperature is still too low. The resisting torque on the rotor is greater than the torque that the motor is capable of supplying in closed-loop mode. At the end of the calibrated time delay, the computer of the GMP once again controls the speed in closed-loop mode. The computer of the pump then seeks to increase the current, and exceeds the current diagnostic threshold without reaching its speed setpoint. The computer of the GMP returns the open-loop mode control setpoint each time the seizure detection threshold is exceeded in closed-loop mode. This alternation of open-loop and closed-loop control periods continues until the temperature of the oil increases sufficiently to allow the oil pump to start up in closed-loop mode.

[0027] FIG. 3 shows, overlaid, the trend over time of several signals: [0028] the speed setpoint C.sub.v of the pump in revolutions per minute, on two levels with respect to the threshold for switchover from open-loop mode to closed-loop mode BO/BF, [0029] the speed of the pump V in revolutions per minute during the open-loop and closed-loop control phases, up to effective start-up, [0030] the phase current overshoot (seizure detection) signals (bits), [0031] the signal applying oscillation (deblocking bit) of the rotor.

[0032] FIG. 4 shows the trend of the temperature θ of the oil in degrees with respect to the threshold s from which the pump can operate with a current in closed-loop mode that is lower than the seizure diagnostic current threshold (oil sufficiently hot). To sum up, the control consists in testing the viscosity of the oil and its temperature through the resisting torque at the rotor of the pump, because this torque is the image of the phase current. The value of the current is used as an estimator of the temperature of the oil. Owing to this estimation, it is not necessary to know the temperature of the oil to allow the pump to start up. By operating on the basis of tests and detection of seizures, it becomes possible to ensure an autonomous start-up of the pump, regardless of the oil temperature.

[0033] The elimination of the temperature sensor offers many advantages: [0034] reduction of costs, [0035] increased reliability, [0036] simpler development, with no mapping table between the oil temperature and the PID regulator parameters, [0037] elimination of an input on the GMP computer or on the oil pump, [0038] simplified architecture of the gearbox and of its coverless environment.

[0039] This last advantage is very beneficial, notably on a hybrid power train, where the installation of the temperature sensor on the casing, and the run of its electrical cable are problematical, because of the bulk of the sector concerned.