ITTO970225A1 - VOLTAGE REGULATOR DEVICE FOR ALTERNATORS, ESPECIALLY FOR MOTOR VEHICLES. - Google Patents

Description

DESCRIPTION

The present invention relates to voltage regulating devices for power generation and power supply systems for motor vehicles including an alternator with a field winding and an armature winding connected by means of a rectifier circuit to a battery and to selectively switched on and off electrical loads.

More specifically, the invention relates to a voltage regulator device comprising detection means for acquiring the value of a voltage monitored in the system, such as the voltage at the output of the rectifier or the voltage on the battery;

a driving circuit connected to the field winding of the alternator and adapted to modify the current flowing in this winding, and

an electronic control unit, connected to said detecting means and to the driving circuit and arranged to control, by means of the driving circuit, the current flowing in the field winding of the alternator as a function of the value of the monitored voltage.

The object of the present invention is to provide an improved voltage regulator device adapted to maintain substantially constant and stable the voltage at the output of the rectifier or the voltage on the battery as the rotation speed of the alternator rotor varies and in the face of variations in the electrical loads inserted, and capable of avoiding, or at least drastically limiting, sudden increases in the resistant torque that the alternator applies to the motor vehicle engine when inserting electrical loads that require high power supply currents.

This and other objects are achieved according to the invention with a voltage regulator device whose main characteristics are defined in the attached claim 1.

Further characteristics and advantages of the invention will appear from the following detailed description, carried out purely by way of non-limiting example, with reference to the attached drawings, in which:

Figure 1 is a partially block diagram of a power generation and power supply system of a motor vehicle including a voltage regulator device according to the invention;

Figure 2 is a block diagram of a circuit for acquiring a monitored voltage in the generation plant according to Figure 1;

Figure 3 is a flow diagram relating to an operating mode of the circuit according to Figure 2;

Figure 4 is a block diagram showing the structure of a driving circuit comprised in the voltage regulator according to Figure 1; Figure 5 is a flow diagram illustrating the operation of a voltage device according to the invention, e

Figure 6 is a diagram which qualitatively shows, as a function of the time t reported in the abscissa, an exemplary trend of the monitored voltage in the system shown in Figure 1.

In Figure 1, 1 generally indicates a power generation and power supply system on board a motor vehicle.

This system comprises an alternator, indicated as a whole with 2, including a field winding 3 and a polyphase armature or stator winding 4. The latter in the embodiment illustrated in Figure 1 is of the three-phase type and comprises three windings connected to each other in a star shape. .

The armature winding 4 of the alternator 2 is connected to a rectifier circuit 5 of a per se known type, comprising a plurality of diodes 6 connected in such a way as to form a three-phase bridge.

The rectifier 5 has two output terminals 5a and 5b, connected by conductors 7 to the two poles 8a and ab, respectively positive and negative, of an accumulator battery 8, for example of the lead-acid type.

Generally connected to the battery 8 is a plurality of electrical loads which can be selectively switched on and off. In figure 1 these loads are represented as a single variable load 9, which can be switched on and off by means of a switch 10.

A voltage regulator device, indicated as a whole with VR in Figure 1, is associated with the power generation and power supply system 1.

The voltage regulator device VR essentially comprises a circuit 11 for acquiring the value of a monitored voltage in the generation plant 1. The monitored voltage can be, for example, the output voltage of the rectifier 5 or the voltage on the battery 8.

The circuit 11 is connected to an input of an electronic control unit ECU comprising for example a microprocessor and associated memory devices.

The control unit ECU is connected to a driving circuit 12 whose output is connected to one end of the field winding 3. In the embodiment illustrated by way of example in Figure 1, the other end of the field winding 3 is connected to the terminal output 5a of the rectifier circuit 5.

In a nutshell, and in a generally known way, the control unit ECU is arranged to control, through the driving circuit 12, the intensity of the current flowing in operation in the basin winding 3 of the alternator 2, in function of the value of the voltage monitored and acquired through the circuit 11.

The voltage regulator device VR may further comprise a circuit 13, having the input connected to an output of the unit ECU for driving an indicator lamp L. In the exemplary embodiment of Figure 1, the lamp L is arranged between the output of the circuit 13 and the positive pole of the battery, in series with a switch 14, incorporated for example in the ignition and starter switch of the motor vehicle and operable by means of a key K.

For the reasons which will be described more clearly in the following, the voltage regulator VR can conveniently comprise a further input circuit 15, connected to a phase of the armature winding 4 of the alternator, to supply a further input of the ECU control a signal Φ indicative of the rotation speed of the alternator rotor. The input circuit 11 of the VR regulator, intended to acquire the instantaneous value of the voltage monitored in the generation plant, can be realized for example in the way that will now be described with reference to Figures 2 and 3.

The input circuit 11 of Figure 2 comprises a selection circuit 16, such as for example an analog multiplexer, with two inputs 16a and 16b selectively usable to acquire, as monitored voltage, the output voltage of the rectifier circuit 5 and, respectively, the voltage on battery 8.

The V0 signal at the output of the selection circuit 16 corresponds to the voltage at the output of the rectifier circuit 5, or to the voltage on the battery 8, depending on the level of a logic control signal SEL, supplied to the circuit 16 by the control unit ECU.

The output of the selection circuit 16 is coupled to the input of an analog / digital converter 17, by means of an anti-noise filter 18. The output of the converter 17 is connected to the control unit ECU.

The control unit ECU controls the converter 17 in such a way as to acquire from the latter, with a predetermined frequency, successive digital signals X {n) representative of the actual instantaneous value of the monitored voltage.

As mentioned above, the input circuit 11 described above can be used to monitor the voltage at the output of the rectifier circuit 5, or alternatively the voltage on the battery 8. In the first case, the input 16a of the selection circuit 16 it must be connected to the positive pole 8a of the battery 8, while in the second case the input 16b of said circuit must be connected to the output terminal 5a of the rectifier circuit 5.

The electronic unit ECU is conveniently arranged to automatically recognize one or the other connection condition of the input circuit 11, in the way that will now be described with reference to the flow chart of Figure 3.

In order to recognize whether the operative input of the selection circuit 16 is the input 16a or the input 16b, the control unit ECU is arranged to carry out a routine according to the flow chart of Figure 3. This routine, after the start indicated with 50 in figure 3, provides that the unit ECU, at a subsequent step 51, sends to the circuit 16 a signal SEL (for example SEL = ■ <»> i») whose state or level corresponds to acquisition of the signal (possibly) present at input 16a. The unit ECU then acquires (step 52 in Figure 3) the corresponding digital signal X and then checks (step 53) whether this signal is included in a predetermined range. If this is the case, this means that the operative input of the selection circuit 16 is the input 16a, and therefore the connection between the input 16b and the battery is present (step 54 in Figure 3). If this is not the case, the unit ECU changes the state or level of the signal SEL (step 56), so that the signal acquired at input 16b is then forwarded to the output of the circuit 16.

The driving circuit 12 can be realized for example in the schematic way illustrated in Figure 4. In this embodiment, the circuit 12 comprises a generator circuit for a driving signal with fixed frequency and variable duty-cycle (PWM) indicated with 19, whose output is connected to the input of the power driving stage 20, realized for example with the use of a transistor of the MOSFET type, connected to the field winding 3 of the alternator.

The input circuit 15 can comprise, for example, a squaring circuit, to convert the phase signal taken from one of the armature windings into a square wave signal whose frequency is proportional to the rotation speed of the alternator rotor and therefore to the speed of rotation of the internal combustion engine of the vehicle.

Whatever the voltage monitored in the generation plant 1, the voltage regulator VR operates in the manner which will now be described with reference to the flow diagram of Figure 5.

The control program foresees a start-up phase (block 100 in figure 5), which is followed by the acquisition, by the ECU, of the phase signal Φ and the current digital value X (n) of the monitored voltage (block 101 ).

The control unit ECU then (block 102) calculates the instantaneous value E (n) of an error quantity E representative of the difference between a predetermined target value X ^ p for the monitored voltage, and the actual instantaneous value X (n) of this voltage:

The control unit also calculates the instantaneous value Y (n) of a control quantity Y corresponding to the intensity of current to be made to flow in the field winding 3 of the alternator, as a function of previous values of this magnitude of control and of the instantaneous and previous value of the error magnitude E. The calculation of Y (n) conveniently takes place according to the following equation

(l) In the above equation alf a2, b0 and bx are predetermined control coefficients based on the alternator used in system 1. Furthermore, Y (n-l) and Y (n-2) represent the two previous values (stored ) of the control quantity Y. E (n) is the present value of the error quantity E, while E (n-1) is the immediately preceding value calculated for the error quantity E.

The control coefficients aA and bA are predetermined in such a way that the control equation (1) allows to obtain a desired behavior of the alternator, i.e. in such a way as to keep its output voltage substantially constant and stable. on the battery, as the electrical loads and the motor rotation speed vary.

The predetermined values of these coefficients, as well as the target voltage value are stored in memory devices included in the control unit ECU.

In a first embodiment, the control unit ECU is arranged to compare the calculated instantaneous value E (n) of the error quantity with an associated predetermined threshold value Ech (block 103 in Figure 5).

In a second and alternative embodiment, the control unit ECU is set up to check if the last increment of the control quantity Y, i.e. the difference Y (n) -Y (n-1), exceeds a threshold value Ych is predetermined, as is also indicated in block 103 of Figure 5.

In both cases, if E (n) is lower than the associated threshold Eth, or if Y (n) -Y (n-1) is lower than the relative threshold Yth, the control unit ECU transfers a signal corresponding to the calculated present value Y (n), as indicated at block 105 in figure 5, and then acquires the subsequent values of the phase signal Φ and of the monitored voltage X (blocks 106, 101 and following, in figure 5) .

As long as E (n) or Y (n) -Y (n-1) remain below the respective thresholds, the operation of the VR regulator continues according to the cycle described above. The driving circuit 12 receives from the control unit ECU a signal corresponding to the value calculated from time to time of Y (n), corresponding to a determined value of the duty cycle of the signal applied to the power driver 20 (figure 4), which controls the current flow in the field winding 3 of the alternator 2.

In the operating cycle described above, a control over the period (T) of the signal Φ indicated at block 107 of Figure 5 can be conveniently introduced: if this period becomes lower than a predetermined threshold value, the comparison of E (n) or Y ( n) -Y (n-1) with the relative thresholds is "skipped", and the control unit ECU in any case determines the application to the driving circuit 12 of a signal corresponding to the value of Y (n).

The threshold Tth is chosen so that it corresponds to a certain rotation speed of the internal combustion engine of the motor vehicle, for example 2,800 rpm of the alternator rotor, above which a sudden increase in the current absorption from however, part of the electrical loads inserted in the system 1 is not likely to cause heavy repercussions on the rotation speed of this motor.

The control functions provided downstream of block 107 of Figure 5 are instead implemented when the internal combustion engine of the motor vehicle rotates at a rotation speed lower than the threshold corresponding to the period T ^, of the phase signal, i.e. essentially at low speeds. of rotation, in which a sudden increase in the current absorption in the system 1 can have serious repercussions on the rotation speed of the combustion engine. The peculiarities of the VR voltage regulator according to the invention relate precisely to its operation in such conditions.

Let us therefore suppose that the internal combustion engine, and therefore the rotor of the alternator 2, rotates at a relatively low speed, in any case lower than the value corresponding to the threshold set for the period T of the phase signal Φ. If in these conditions the calculated value E (n) becomes at a certain instant greater than the associated threshold Eth, or the difference Y {n) -Y (n-l) becomes greater than the associated threshold Ych, the control unit ECU passes to implement a different strategy for controlling the current in the field winding 3 of the alternator (block 108 and following in Figure 5).

Before describing this field current control mode, it is noted that the condition E (n)> Eth means, from a physical point of view, that the monitored voltage has dropped beyond a certain extent with respect to the target value X ^.

Conversely, the condition Y (n) -Y (n-1)> Yth means that to keep the monitored voltage substantially at the target value, the field current needs to be increased beyond a predetermined measure.

Both the above conditions are therefore indicative of the fact that the electrical loads 9 connected to the power generation and power supply system 1 require the supply of a very high current, which corresponds to a potentially dangerous increase in the resistant torque that the alternator 2 applies. to the internal combustion engine.

When one or the other of the above conditions occurs, the control unit ECU applies to the driving circuit 12 a signal which does not simply correspond to the last calculated value of Y (n), but to this value added by a constant predetermined increment ΔΥ, as indicated at block 108 in Figure 5.

Figure 6 qualitatively shows, as a function of the time t reported in the abscissa, the trend of the monitored voltage V0 in the system 1, the subsequent values X (n) of which are periodically sampled and acquired by the control unit ECU.

In the graph of Figure 6 the voltage level νΜΡ represents the target value at which the monitored voltage must be substantially maintained; this target value corresponds to the digital value X ^.

In the same graph, the voltage threshold Vth represents the value to which the monitored voltage falls when the value of the error quantity E (n) becomes equal to the threshold value Eth, or to the value of the monitored voltage when the difference Y (n) - Y (n-1) becomes equal to the threshold value Yth. The instant in which the monitored voltage V0 crosses the threshold Vth is indicated with t1.

Starting from the instant t ^ the control unit ECU instead of driving the current in the field winding 3 of the alternator on the basis of the value Y (n) calculated on the basis of the equation (1) reported above, drives this current by successive constant increments according to the equation

(2),

as indicated at block 108 in Figure 5. The subsequent increases in the field current correspond to a gradual increase in the monitored voltage V0 {X), as qualitatively indicated in the graph of Figure 6 after the instant tj.

The monitored voltage increases until it again approaches the target value νΜΡ, and in particular reaches the value of a further threshold Vth0 (figure 6) at a subsequent instant t2.

The threshold is much closer to the target V ^ p than the Vch threshold.

When the monitored voltage V0 crosses and exceeds the threshold the error quantity E (n) equals and then becomes lower than a threshold value E0.

Correspondingly, in the time interval between t2 and ta, the control unit ECU, after having implemented the increase in the field current, checks whether the error E (n) has become less than E0 (block 109 in figure 5) . If this is not the case, the unit proceeds to cause a further increase in the field current (block 110 and then 108 in Figure 5).

As soon as the monitored voltage crosses and exceeds the threshold Vth0, and therefore the error E (n) becomes less than E0, the control unit ECU recognizes that the phase of abrupt lowering of the monitored voltage has expired and then resumes checking the field current in the manner implemented before the instant tlf, that is, by resuming control starting from block 101 of Figure 5 described previously.

The threshold V ^, that is the corresponding threshold E ^ or Yth, can be of a constant predetermined value.

However, it has been found that the extent of the decrease in the monitored voltage following a certain increase in the supplied current required by the loads inserted varies according to the number of revolutions of the alternator rotor. In other words, with the same request for increasing the delivered current, the monitored voltage undergoes a more marked decrease when the alternator rotor rotates at low speed than when it rotates at a relatively higher speed.

In view of the above, for a more reliable and precise control of the field current, the aforementioned thresholds are preferably not constant, but are rather dynamically modified, according to a predetermined function, as a function of the rotation speed. For this purpose, the control unit ECU can be easily arranged to adopt a threshold Eth or a threshold Yth increasing as the rotation speed increases, this rotation speed being inferable from the control unit ECU for example by means of a simple measurement of the period. or the frequency of the phase signal Φ.

Naturally, the principle of the invention remaining the same, the embodiments and details of construction may be varied widely with respect to what has been described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined. in the attached claims.

Claims (8)

CLAIMS 1. Voltage regulator device (VR) for a power generation and power supply system (1) of a motor vehicle including an alternator (2) with a field winding (3) and an armature winding (4) connected via a circuit rectifier (5) with a battery (8) and with electrical loads (9) which can be selectively switched on and off; the voltage regulator device (VR) comprising detector means (11) for acquiring the value (X) of a monitored voltage (V0) in the system, such as the voltage at the output of the rectifier (5) or the voltage on the battery (8); a driving circuit (12) connected to the field winding (3) of the alternator (2) and adapted to modify the current flowing in this winding (3), and an electronic control unit (ECU), connected to said detecting means (11) and to the driving circuit (12) and arranged to control, through the driving circuit (12), the current flowing in the field winding (3 ) of the alternator as a function of the value of the monitored voltage; the device being characterized by the fact that the control unit (ECU) is designed for: calculating and storing successive values (E (n)) of an error quantity (E) representative of the difference between a target value (X ^) of the monitored voltage and the instantaneous effective value (X) of this voltage; calculate and store successive values of a control quantity (Y) corresponding to the intensity of current to be made to flow in the field winding (3), as a function of previous values (Y (n-l); Y (n-2)) of said control quantity (Y) and of the instantaneous (E (n)) and previous (E (n-1)) value of said error quantity (E); control according to a normal procedure the current flowing in the field winding (3) of the alternator (2) in such a way that said current corresponds to the calculated instantaneous value (Y (n)) of said control quantity (Y) when the instantaneous value (E {n)) of the error quantity (E) or, alternatively, the difference between the instantaneous value (Y (n)) and the previous value (Y (n-l)) of the control quantity (Y) are lower than respective predetermined threshold values (Eth; Y ^); check according to a special procedure the current flowing in the field winding (3) in such a way that said current corresponds to the instantaneous value calculated (Y (n)) of the control quantity (Y) plus a predetermined increase (ΔΥ), when the instantaneous value (E (n)) of the error quantity (E) or, alternatively, the difference between the instantaneous value (Y {n)) and the previous value (Y (n-l)) of the control quantity (Y ) exceed said respective predetermined threshold values (Eth; Yjj,), and as long as the value of the error quantity (E) remains higher than a predetermined reference value (E0). 2. Device according to claim 1, characterized in that said threshold values (Eth; * Λ> are constant. 3. Device according to claim 1, characterized in that it also comprises further detection means (15) suitable for supplying the control unit (ECU) with signals (Φ) indicative of the rotational speed of the rotor (3) of the alternator (2 ), and by the fact that the aforesaid threshold values (Ε ^; Y ^) are variable according to predetermined methods as a function of the rotation speed of the rotor, said values increasing as said rotation speed increases. 4. Device according to any one of the preceding claims, comprising further detecting means (15) adapted to supply to the control unit (ECU) signals (Φ) indicative of the rotational speed of the rotor (3) of the alternator (2), the device being characterized in that the control unit (ECU) is arranged to control the field current only according to the aforementioned normal procedure, when the rotor rotation speed is greater than a predetermined value. 5. Device according to claim 3 or 4, characterized in that said further detector means comprise a squaring circuit (15) connected to a phase winding of the armature winding (4) of the alternator (2). Device according to any one of the preceding claims, in which said means for detecting the monitored voltage have two inputs (16a, 16b) respectively connectable to the battery (8) and to the output of the rectifier (5); said inputs (16a, 16b) being selectively coupled to an input of the control unit (ECU) as a function of a selection control signal (SEL). 7. Device according to claim 6, characterized in that the control unit (ECU) is arranged to carry out an automatic procedure for recognizing the input (16a; 16b) of said detector means (16) which is operatively connected to the power generation and power supply system (1). 8. Voltage regulator device for a power generation and power supply system for a motor vehicle, substantially as described and illustrated, and for the specified purposes.