EP1598555B1 - Motor pump unit having means to limit the pressure of the hydraulic fluid which is being pumped by said pump - Google Patents

Description

The invention relates to an electro-pump unit system, of the type comprising an electric motor, a hydraulic pump driven by the electric motor and intended to provide hydraulic power, and means for limiting the pressure of the hydraulic fluid in the circuit. hydraulic.

In electropump systems of this type, which are known, the function of the pressure limitation is accomplished by a mechanical pressure limiter in the form of a safety valve provided with a spring-loaded relief valve. prestressing adjustable according to the maximum permissible pressure for a given application. As we see on the figure 1 which shows a known electropump system for a motor vehicle where the pump is intended to provide assistance to the steering of the vehicle and indicates in 1 generally the electric pump unit, in 2 the electric motor, in 3 the pump hydraulic, in 4 the cylinder device fed with hydraulic fluid by the pump 3, in 5 the wheels of the vehicle, in 6 the flywheel, in 7 the steering column, the pressure limiter noted 8 is disposed between the pump and the cylinder 4. In the event of suppression, the valve indicated schematically at 9 of the limiter 8 opens a bypass lane 10 which is connected to the tank 11 of the liquid intended to be sucked by the pump 3. It should also be noted that the figure 1 illustrates at 12 the electric power supply battery of the electric pump unit 1. The figure still shows that the electric pump unit 1 receives the information on the speed of rotation of the steering wheel, denoted V _VO and the information on the vehicle speed V _VEH .

The use of the mechanical pressure limiter 8 in the known system has many major disadvantages. Indeed, it causes an additional cost, is cumbersome, can cause states of instability, generates acoustic noise related to its opening and, by constituting a specific mechanical part, decreases the reliability of the system

The document EP 0 574 623 mentions an electro-pump system equipped with pressure regulating means using a multitude of sensors to define an optimal pressure (pump speed, pressure, temperature) generating additional costs.

The object of the present invention is to propose an electro-pump group system which overcomes the drawbacks inherent in the known system.

To achieve this goal, the system according to the invention is characterized in that the pressure limiting means are implemented as electronic management means, the limitation of the pressure being effected by setting the maximum limiting current I _LIM. to send to the drive motor of the pump.

• la figure 1 est une vue synoptique en forme d'un schéma bloc d'un système de groupe électro-pompe selon l'état de la technique ;
• la figure 2 est une vue synoptique, similaire à la figure 1, d'un système d'électro-pompe selon l'invention ;
• la figure 3 montre le schéma synoptique du calculateur contrôleur 13' du groupe électro-pompe selon la figure 2 ;
• la figure 4 est un schéma synoptique illustrant la mise en oeuvre des opérations effectuées par le calculateur 13' de la figure 3 ;
• les figures 5 et 6 sont des schémas synoptiques similaires à la figure 4 et illustrent deux autres versions de mise en oeuvre du calculateur/contrôleur 13' d'un groupe électro-pompe selon l'invention.

The invention will be better understood, and other objects, features, details and advantages thereof will appear more clearly in the explanatory description which follows, with reference to the attached schematic drawings given solely by way of example illustrating two modes of embodiment of the invention and in which:

• the figure 1 is a schematic view in the form of a block diagram of an electro-pump system according to the state of the art;
• the figure 2 is a synoptic view, similar to the figure 1 of an electro-pump system according to the invention;
• the figure 3 shows the block diagram of the control computer 13 'of the electric pump group according to the figure 2 ;
• the figure 4 is a block diagram illustrating the implementation of the operations performed by the computer 13 'of the figure 3 ;
• the figures 5 and 6 are synoptic diagrams similar to the figure 4 and illustrate two others implementation versions of the computer / controller 13 'of an electric pump unit according to the invention.

Referring to the figure 2 , which gives the block diagram of a steering assistance system of a motor vehicle, using an electropump according to the invention, it is found that the latter differs from the electropump known in the state of the technique, represented on the figure 1 by the fact that the pressure limiter is removed and that the function performed in the system known by the limiter is accomplished by means electronic pressure limiters which are part of the calculator / controller 13 'and are indicated by the shaded area 15 of the rack representing this calculator. On the figure 2 , we use the same reference as on the figure 1 for identical elements.

It should be noted that, in a set of electro-pump units, the pump converts the speed of rotation of the electric motor 3 into hydraulic flow in the hydraulic circuit, namely the cylinder 4. The resisting torque exerted on the engine corresponds to the sum of the resistance torque due to the pressure in the hydraulic circuit and the resisting torque specific to the pump, the resisting torque linked to the motor can be considered negligible. Therefore, limiting the pressure in the hydraulic circuit is equivalent to limiting the torque provided by the engine. Thus, it has been found possible within the scope of the invention to obtain the limitation of the pressure in the hydraulic circuit by limiting the maximum current to be sent to the electric motor 2 for driving the pump 3.

According to one characteristic of the invention, the maximum limiting current I _LIM is determined according to three parameters, namely the supply voltage U _BAT supplied by the battery, the temperature T _MOS of the active electronic elements, namely transistors. used and the temperature T _CA of the carrier board electronic components calculator. The values of the limit current I _LIM vary according to these parameters and are taken in a calibration table made from tests. Thus each group of three battery voltage and temperature values corresponds to a limit current value I _LIM . This interdependence is represented on the figure 4 in 19a in the form of a three-dimensional diagram on the three axes of which are reported respectively the U _BAT temperatures, T _MOS active element temperatures and T _ca card temperatures, next to the table of values. From the established values the intermediate values of I _LIM are obtained by linear interpolation between the different points of the diagram and the table. As also shows figure 4 , the system according to the invention further provides a torque management in avoidance, that is to say the system allows an exceeding of the limit current I _LIM to have a better response of the system to avoid an obstacle by a quick maneuver. The avoidance current I _EV is obtained from the limit current I _LIM by multiplication according to a correction coefficient, as shown in the diagram. fig 4 box 19b representing on the ordinate axis the current I and on the abscissa axis the speed V, the vehicle speed V _VEH .

We will describe below, referring to figures 3 and 4 the manner in which the limiting current I _LIM is taken into account in the system proposed by the invention. On the figures 3 and 4 , the calculation of the maximum current limit noted I _LIM is shown in box 19, the figure 3 indicating that the calculation of the current limit itself is carried out at 19a, then corrected by the avoidance function at 19b.

As shown in the diagram of the electro-pump group 1, the figure 3 , the computer 13 comprises a microprocessor 17 which is intended to establish by calculation the engine speed reference C _RPM , that is to say the engine speed reference, from the vehicle speed V _VEH and of the speed of rotation of the steering wheel V _VO and, also by calculation, the limit current I _LIM , from the vehicle speed V _VEH and the values representative of the battery voltage U _BAT and the temperature values T _mos of the active elements of electronic devices and the temperature T _ca of the card of this device. The calculation operations of the engine speed setpoint C _RPM and the limit current I _LIM are symbolized in the figure by boxes marked 18 and 19. The values of the battery voltage and of the temperature are applied to the inputs of a circuit of formatting 20 which adapts the level of these values to the level allowable for the microprocessor 17 which performs, before using them for calculating the current I _LIM in 21 a software formatting 21.

After calculating the motor speed set point C _RPM and the current I _LIM , the microprocessor 17 calculates the motor control C _M. This calculation is symbolized by box 22. The engine control C _M is sent to the engine after having been shaped by a circuit 23 of the computer. The calculation of the motor control C _M , carried out by the microprocessor 17, again takes into account the current I _M consumed by the motor, the value of which has been shaped by the circuit 24 of the computer and software formatted in FIG. by the microprocessor.

The figure 4 shows in more detail the implementation of the operations just described. As can be seen in this figure, the result of the calculation engine speed calculation performed at 18 is subjected to a decision logic symbolized by the box 27, which is intended to let the setpoint C _RPM for a servo operation of speed, materialized by block 28 or to prohibit this passage, according to a rotation authorization signal S _AR of binary nature, which is the result of an assessment of the speed of rotation of the motor V _RPM , provided for provide protection for the pump. This operation will be described in more detail below and is designated by the reference 30.

The speed control box 28 thus receives at an input a signal which is either the engine speed set point C _RPM equal to zero, as a function of the rotation authorization signal S _AR applied to box 27. The box speed control 28 receives at a second input a signal representative of the speed of rotation of the motor, noted V _RPM and produces at its output a signal S _PWM1 to ensure the nullity of the error between the two input signals , namely the setpoint C _RPM and the speed signal V _RPM . The signal is advantageously a pulse width modulated signal. The control is effected by applying the output signal S _PWM1 to a first input of a bit comparator 31 which receives at a second input the calculated current value I _LIM and a third input the information of the motor current I _M. From the comparison operation results a signal S _PWM2 , which is either identical to the signal S _PWM1 or equal to zero, the signal is applied to a motor power control 32 applied to the motor 2.

The control loop formed by the speed control unit 28, the comparator 31, the motor power control 32 and the motor 2 is designed to ensure that the motor rotation speed V _RPM is slaved to the engine speed set point C _RPM which has been calculated in 22. As long as the consumed motor current I _M is less than the limit current value I _LIM , the comparator 31 passes the signal S _PWM1 to the motor control 32. When the current I _M is greater than the value of the limiting current I _LIM , the comparator prohibits the passage of the signal S _PWM1 , which has the consequence that the signal S _PWM2 becomes zero and the power control of the motor decreases until the current I _M consumed by the motor becomes lower than current I _LIM . This situation causes the comparator to allow again the passage of the signal S _PWM1 to the motor control 32.

As stated above, the invention provides a pump protection function in the case where the rotational speed of the motor 2 is too low to ensure proper operation of the pump. This protection function is illustrated by the diagram inside box 28 of the figure 4 represents the speed of rotation V _RPM as a function of time t. When the speed of rotation has passed below a minimum speed threshold V _min , the engine is stopped after a time t1 and is then restarted after a time t2, the stopping and starting times t1 and t2 being fixed but configurable. It is also possible that the times t1 and t2 are modulated according to the accelerations and decelerations of the engine. In this case, the modulation laws of t1 and t2 are parameterizable. Depending on the rotation state of the motor, the protection function 30 of the pump applies to the decision logic 27 of the figure 4 , the aforementioned rotation authorization signal S _AR , which is of a binary nature and causes the decision logic to allow the passage of the engine speed setpoint C _RPM to the speed control box 28, as has been described above, this passage of the signal is forbidden.

The figure 5 illustrates another version of implementation of the strategy of the system according to the invention, which consists in replacing the comparator 29 of the figure 4 by a scalar controller 34, the control 32 of the motor thus becoming a scalar control which limits the torque supplied to the motor 2 by controlling the value of the phase currents and by slaving the phase difference between the field created by the power supply Bri and that Ba created by the magnets at a constant value of ± π / 2. This control is known in particular for synchronous machines in which the stator is generally provided with a three-phase winding, powered by a voltage and current system and creating in the gap a rotating induction field Bri. The Bri field tends to attract the rotor which is provided with permanent magnets producing an induction field Ba. As the rotor attracts the stator, the induction field tends to align, giving rise to an electromagnetic torque.

The figure 6 shows another version of implementation of the invention which provides a vector control of the engine and uses instead of the scalar controller 34 of the figure 5 a vector controller 35. The vector control makes it possible to limit the torque supplied to the motor by directly controlling the current vector I _{s (t)} . As is known, all the information relating to the three currents of the three phases of the motor can be combined into a single mathematical quantity, namely the current phasor which is a spatial quantity. The advantage of using a spatial phaser rather than processing scalar magnitudes is that the three information pertaining to three phase currents of the motor are combined into one complex size.

The phasor represented by the vector current I in the diagram given inside the vector controller box 35 can be decomposed, in a two-phase space system equivalent to a three-phase scalar system, according to a direct stator current component I _D carried on the X-axis and a quadrature stator current component I _Q carried on the ordinate axis. The advantage lies mainly in handling only two quantities.

Of course the invention which has just been described with reference to the figures, in its application to a motor vehicle to provide assistance to the steering thereof is not limited to this application. The latter has been indicated only as an example.

Indeed, the invention is usable in all cases where an electric pump unit is used which is intended to provide hydraulic power while providing protection against possible overpressures in the hydraulic circuit, for example in braking systems and for suspension of a motor vehicle or forklift trucks or the like.

Claims (9)

1. An electropump unit system, of the type comprising an electric motor, a hydraulic pump driven by the electric motor and intended to provide hydraulic power to a hydraulic device, and means for limiting the pressure of the hydraulic fluid sent by the pump into the hydraulic circuit, embodied as electronic management means (13', 17, 15), the limitation of the pressure being performed by establishing the limiting maximum current I_LIM to be sent to the motor (2) driving the pump (3).
2. The system according to claim 1, of the type comprising a computer for managing the operation of the system, characterized in that the computer (13') is adapted in order to provide the aforementioned electronic management.
3. The system according to claim 2, characterized in that the computer (13') includes means for computing the limiting maximum current I_LIM to be sent to the motor (2) for driving the pump (3).
4. The system according to claim 3, characterized in that the means for computing the limiting maximum current I_LIM are adapted so as to provide an increase in the limiting maximum current by multiplication by a predetermined coefficient for avoiding an obstacle during the driving of the vehicle for example.
5. The system according to claim 4, characterized in that the electronic pressure-limiting means are adapted in order to compare the motor current I_M with the aforementioned limiting maximum current I_LIM and to provide a control preventing the motor current I_M from exceeding the limiting current I_LIM.
6. The system according to claim 5, characterized in that the electronic management means are adapted in order to prevent the motor (2) from operating at low speeds of rotation which may cause inappropriate operation of the pump (3).
7. The system according to any of claims 1 to 6, characterized in that it is intended to equip a motor vehicle and to provide assistance in the steering of the latter via a hydraulic actuator device.
8. The system according to any of claims 1 to 6, characterized in that it comprises a calibration table established from tests, determining a correspondence between a group of three values of battery voltage and of temperature (U_BAT, T_MOS, T_CA) and a limiting current value (I_LIM) and in that the limiting maximum current value I_LIM to be sent to the motor stems from the calibration table.
9. The system according to claim 8, characterized in that the group of three values integrated into the calibration table are a value U_BAT of a supply voltage provided by the battery (U_BAT), a value of the temperature (T_MOS) of the active electronic components and a value of the temperature (T_CA) of the card bearing the computer's electronic components, respectively.

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