A VOLTAGE REGULATOR FOR ALTERNATORS, PARTICULARLY FOR MOTOR VEHICLES

Abstract: The voltage regulator (VR) comprises an electronic control unit (ECU) connected to a circuit (11) for detecting a controlled voltage and to a circuit (12) for driving the field winding (3) of the alternator (2). The unit (ECU) is arranged to calculate successive values (E(n)) of an error quantity (E) representative of the difference between a target value (XREF) of the controlled voltage and the instantaneous value (X) of this voltage and to calculate successive values of a control quantity (Y) corresponding to the intensity of the current to be caused to flow in the field winding (3) in dependence on preceding values (Y(n-1); Y(n-2)), of this control quantity (Y) and on the instantaneous and preceding values (E(n), E(n-1)) of the error quantity (E). The current flowing in the field winding (3) of the alternator (2) is controlled in dependence on the values of the error quantity (E) or of the increments of the control quantity (Y).

Description: A voltage regulator for alternators, particularly for motor vehicles The present invention relates to a voltage regulator for voltage-generating and -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 connectible and disconnectible electrical loads . More specifically, the subject of the invention is a voltage regulator comprising: detector means for acquiring the value of a voltage controlled in the system, such as the voltage at the output of the rectifier or the voltage in the battery, a driver circuit connected to the field winding of the alternator for modifying the current flowing in this winding, and an electronic control unit connected to the detector means and to the driver circuit and arranged to control the current flowing in the field winding of the alternator, by means of the driver circuit, in dependence on the controlled voltage value . The object of the present invention is to provide an improved voltage regulator which can keep the voltage at the output of the rectifier or the voltage in the battery substantially constant with variations in the speed of rotation of the alternator rotor and upon variations in the electrical loads connected, and which can prevent or at least greatly curtail abrupt increases in the resisting torque which the alternator applies to the engine of the motor vehicle when electrical loads which require high-intensity supply currents are connected. This and other objects are achieved, according to the invention, by a voltage regulator, the main characteristics of which are defined in appended Claim 1. Further characteristics and advantages of the invention will become clear from the following detailed description given purely by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 is a diagram, partially in block form, of a voltage- generating and -supply system of a motor vehicle, including a voltage regulator according to the invention, Figure 2 is a block diagram of a circuit for acquiring a voltage controlled in the generating system according to Figure 1, Figure 3 is a flow chart relating to a method of operation of the circuit according to Figure 2, Figure 4 is a block diagram showing the structure of a driver circuit included in the voltage regulator according to Figure 1, Figure 5 is a flow chart showing the operation of a voltage regulator according to the invention, and Figure 6 is a graph showing, qualitatively and by way of example, a curve of the voltage controlled in the system shown in Figure 1, as a function of the time t given on the abscissa. In Figure 1, a voltage-generating and -supply system in a motor vehicle is generally indicated 1. The system comprises an alternator, generally indicated 2, including a field winding 3 and a multi-phase armature or stator winding 4. In the embodiment shown in Figure 1, the latter is a three-phase winding and comprises three windings connected to one another in a star arrangement . The armature winding 4 of the alternator 2 is connected to a rectifier circuit 5 of known type, comprising a plurality of diodes 6 connected so as to form a three-phase bridge. The rectifier 5 has two output terminals 5a and 5b connected by means of conductors 7 to the two poles 8a and 8b, that is, the negative pole and the positive pole, respectively, of a storage battery 8, for example, a lead-acid battery. A plurality of selectively connectible and disconnectible electrical loads is generally connected to the battery 8. In Figure 1, these loads are represented by a single variable load 9 which can be connected and disconnected by means of a switch 10. A voltage regulator, generally indicated VR in Figure 1, is associated with the voltage-generating and -supply system. The voltage regulator VR comprises essentially a circuit 11 for acquiring the value of a voltage controlled in the generating system 1. The controlled voltage may, for example, be the output voltage of the rectifier 5 or the voltage in the battery 8. The circuit 11 is connected to an input of an electronic control unit ECU comprising, for example, a microprocessor and associated storage devices . The control unit ECU is connected to a driver circuit 12 the output of which is connected to a terminal of the field winding 3. In the embodiment shown by way of example in Figure 1, the other terminal of the field winding 3 is connected to the output terminal 5a of the rectifier circuit 5. Extremely briefly, and in generally known manner, the control unit ECU is arranged to control, by means of the driver circuit 12, the intensity of the current flowing in the field winding 3 of the alternator 2 in operation, in dependence on the controlled voltage value acquired by means of the circuit 11. The voltage regulator VR may also comprise a circuit 13 having its input connected to an output of the unit ECU for driving an indicator lamp L. In the embodiment shown by way of example in Figure 1, the lamp L is disposed 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 below, the voltage regulator VR may advantageously comprise a further input circuit 15 connected to one phase of the armature winding 4 of the alternator in order to supply to a further input of the control unit ECU a signal Φ indicative of the speed of rotation of the alternator rotor. The input circuit 11 of the regulator VR which is intended to acquire the instantaneous value of the voltage controlled in the generating system may be formed, for example, in the manner which 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 analogue multiplexer with two inputs 16a and 16b usable selectively to acquire, as the controlled voltage, the output voltage of the rectifier circuit 5 and the voltage in the battery 8, respectively. The signal V 0 at the output of the selection circuit 16 corresponds to the output voltage of the rectifier circuit 5 or to the voltage in the battery 8, according to 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 connected to the input of an analogue/digital converter 17 via 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 so as to acquire therefrom, at a predetermined frequency, successive digital signals X(n) representative of the actual instantaneous value of the voltage controlled. As stated 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 in the battery 8. In the latter case, the input 16a of the selection circuit 16 must be connected to the positive pole 8a of the battery 8, whereas in the former case, the input 16b of the circuit must be connected to the output terminal 5a of the rectifier circuit 5. The electronic unit ECU is advantageously arranged to recognize automatically one or other connection state of the input circuit 11 in the manner which 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 implement a routine in accordance with the flow chart of Figure 3. After the start , indicated 50 in Figure 3, this routine provides for the unit ECU, in a subsequent step 51, to send to the circuit 16 a signal SEL (for example SEL = "1") the state or level of which corresponds to the acquisition of the signal (if any) present at the input 16a. The unit ECU then acquires the corresponding digital signal X (step 52 in Figure 3) and then checks (step 53) whether this signal is within a predetermined range. If this is the case, this means that the operative input of the selection circuit 16 is the input 16a and a connection is therefore present between the input 16a and the battery (step 54 in Figure 3) . If the signal is not within the predetermined range, the unit ECU changes the state or level of the signal SEL (step 56) , so that the signal acquired at the input 16b is then sent to the output of the circuit 16. The driver circuit 12 may be formed, for example, in the manner shown schematically in Figure 4. In this embodiment, the circuit 12 comprises a circuit, indicated 19, for generating a driver signal with a fixed frequency and a variable duty-cycle (PWM) , the output of this circuit being connected to the input of a power driver stage 20 formed, for example, with the use of a MOSFET transistor connected to the field winding 3 of the alternator. The input circuit 15 may comprise, for example, a squaring circuit for converting the phase signal taken from one of the armature windings into a square-wave signal the frequency of which is proportional to the speed of rotation of the alternator rotor and hence to the speed of rotation of the internal combustion engine of the motor vehicle. Whichever voltage is controlled in the generating system 1, the voltage regulator VR operates in the manner which will now be described with reference to the flow chart of Figure 5. The control program provides for a "start" step (box 100 in Figure 5) followed by the acquisition by the unit ECU of the phase signal Φ of the digital value X(n) , at the time in question, of the voltage controlled (box 101) . The control unit ECU then provides for the calculation (box 102) of the instantaneous value E(n) of an error quantity E representative of the difference between a predetermined target value for the voltage controlled and the actual instantaneous value X(n) of this voltage: E(n) = X REP - X(n) The control unit also provides for the calculation of the instantaneous value Y(n) of a control quantity Y corresponding to the intensity of the current to be caused to flow in the field winding 3 of the alternator, in dependence on preceding values of this control quantity and on the instantaneous and preceding values of the error quantity E. Y(n) is advantageously calculated in accordance with the following equation: Y(n) = a 1 Y(n-l)+a 2 Y(n-2)+b 0 E(n)+b 1 E(n-l) (1) In the equation given above a 1# a 2 , b 0 and b x are control coefficients predetermined on the basis of the alternator used in the system 1. Moreover, Y(n-l) and Y(n-2) represent the two preceding (stored) values of the control quantity Y. E(n) is the value of the error quantity E at the time in question, and E(n-l) is the immediately preceding value calculated for the error quantity E. The control coefficients a-_ and b ± are predetermined in a manner such that the control equation (1) enables the desired behaviour of the alternator to be achieved, that is, in a manner such as to keep its output voltage or the voltage in the battery substantially constant and stable with variations in the electrical loads and in the speed of rotation of the engine . The predetermined values of these coefficients, as well as the target voltage value X REF , are stored in storage 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 E th (box 103 in Figure 5) . In a second and alternative embodiment, the control unit ECU is arranged to check whether the last increment of the control quantity Y, that is, the difference Y(n)-Y(n-1) exceeds a predetermined threshold value Y th , as also indicated in box 103 of Figure 5. In either case, if E(n) is below the associated threshold E th or if Y(n)-Y(n-1) is below the respective threshold Y th , the control unit ECU transmits to the driver circuit 12 a signal corresponding to the value Y(n) calculated at the time in question, as indicated in box 105 of Figure 5, and then acquires the subsequent values of the phase signal Φ and of the controlled voltage X (boxes 106, 101 and subsequent boxes in Figure 5) . As long as E (n) or Y(n)-Y(n-1) remains below the respective threshold, the operation of the regulator VR continues in accordance with the cycle described above. The driver circuit 12 receives from the control unit ECU a signal corresponding to the value of Y(n) calculated at the time in question and corresponding to a certain value of the duty-cycle of the signal applied to the power driver 20 (Figure 4) which controls the flow of current in the field winding 3 of the alternator 2. A check on the period (T) of the signal Φ, indicated in box 107 of Figure 5, may advantageously be introduced into the operating cycle described above; if this period becomes less than a predetermined threshold value T th the comparison of E(n) or of Y(n)-Y(n-1) with the respective thresholds is "skipped" and the control unit ECU in any case causes a signal corresponding to the value of Y(n) to be applied to the driver circuit 12. The threshold T th is selected so as to correspond to a certain speed of rotation of the internal combustion engine of the motor vehicle, for example, 2,800 revolutions/minute of the alternator rotor, above which a sudden increase in the absorption of current by electrical loads connected in the system 1 is not in any case liable to have serious effects on the speed of rotation of the engine. The control functions provided for downstream of box 107 in Figure 5, however, are implemented when the internal combustion engine of the motor vehicle is rotating at a speed below the threshold corresponding to the period T th of the phase signal, that is, essentially at low rates of rotation at which an abrupt increase in the absorption of current in the system 1 may seriously affect the speed of rotation of the combustion engine. The distinctive features of the voltage regulator VR according to the invention actually relate to operation in these conditions . It is thus assumed that the internal combustion engine, and hence the rotor of the alternator 2, is rotating at relatively low speed, in any case below the value corresponding to the threshold T th set for the period T of the phase signal Φ. If, in these conditions, at a certain moment, the calculated value E (n) becomes greater than the associated threshold E th or the difference Y(n)-Y(n-1) becomes greater than the associated threshold Y th , the control unit ECU changes to the implementation of a different strategy for controlling the current in the field winding 3 of the alternator (box 108 and subsequent boxes in Figure 5) . Before this method of controlling the field current is described, it is pointed out that the condition E(n) > E th means, from a physical point of view, that the voltage controlled has fallen by more than a predetermined amount relative to the target value X REF . The condition Y(n)-Y(N-1) > Y th , on the other hand, means that, in order to keep the voltage controlled substantially at the target value, the field current needs to be increased by more than a predetermined amount. Both of the above-mentioned conditions are therefore indicative of the fact that the electrical loads 9 connected to the voltage-generating and -supply system 1 require the delivery of a very high current which corresponds to a potentially dangerous increase in the resisting torque which the alternator 2 applies to the internal combustion engine. When one or other of the aforementioned conditions occurs, the control unit ECU applies to the driver circuit 12 a signal which corresponds not simply to the last value of Y(n) calculated, but to that value increased by a predetermined constant increment ΔY, as indicated in box 108 of Figure 5. Figure 6 shows qualitatively the curve of the voltage V 0 controlled in the system 1, the successive values X(n) of which are sampled and acquired periodically by the control unit ECU, as a function of time t given on the abscissa. In the graph of Figure 6, the voltage level V^p represents the target value at which the voltage controlled is substantially to be kept; this target value corresponds to the digital value X REP . In the same graph, the voltage threshold V th represents the value to which the voltage controlled falls when the value of the error quantity E(n) becomes equal to the threshold value E th , or to the value of the voltage controlled when the difference Y(n)-Y(n-1) becomes equal to the threshold value Y th . The moment at which the voltage V 0 controlled crosses the threshold V th is indicated t x . Starting from the moment t x , 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 equation (1) given above, the control unit ECU drives this current by means of successive uniform increments in accordance with the equation Y(n) = Y(n) + ΔY (2) as indicated in box 108 of Figure 5. The successive increments of the field current cause a corresponding gradual increase in the voltage V 0 (X) controlled, as indicated qualitatively in the graph of Figure 6 after the moment t x . The voltage controlled increases until it is brought to the vicinity of the target value V^p and, in particular, until it reaches the value of a further threshold V th0 (Figure 6) at a subsequent moment t 2 . The threshold V th0 is much closer to the target value V^p than the threshold V th . When the voltage V 0 controlled crosses and exceeds the threshold V th0 , the error quantity E(n) equals and then becomes less than a threshold value E 0 . Accordingly, during the period of time between and t 2 , after implementing the increment of the field current, the control unit ECU checks whether the error E(n) has become less than E 0 (box 109 in Figure 5) . If this is not the case, the unit brings about a further increase in the field current (box 110 and then box 108 in Figure 5) . As soon as the controlled voltage crosses and exceeds the threshold V th0 and the error E(n) thus becomes less than E 0 , the control unit ECU recognizes that the stage of abrupt lowering of the controlled voltage has finished and therefore resumes control of the field current in the manner implemented before the moment t 1# that is, it resumes control starting from box 101 of Figure 5, described above. The threshold V th , or the corresponding threshold E th or Y th , may have predetermined constant values . It has been found, however, that the magnitude of the reduction in the voltage controlled as a result of a certain increase in the current supply required by connected loads varies according to the rate of revolution of the alternator rotor. In other words, for a given increased current-output requirement, the voltage controlled undergoes a more marked drop when the rotor of the alternator is rotating at a slow speed than when it is rotating at a relatively faster speed. In view of the foregoing, for a more reliable and precise control of the field current, the thresholds mentioned above are preferably not constant but are modified dynamically in accordance with a predetermined function, in dependence on the speed of rotation. For this purpose, the control unit ECU can easily be arranged to adopt a threshold E th or a threshold Y th which increases as the speed of rotation increases, the speed of rotation being deducible by the control unit ECU, for example, simply by a measurement of the period or of the frequency of the phase signal Φ. Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims .

Claims: CLAIMS 1. A voltage regulator (VR) for a voltage-generating and - supply system (1) of a motor vehicle, including an alternator (2) with a field winding (3) and an armature winding (4) connected, by means of a rectifier circuit (5) , to a battery (8) and to selectively connectible and disconnectible electrical loads (9) , the voltage regulator (VR) comprising: detector means (11) for acquiring the value (X) of a voltage (V 0 ) controlled in the system, such as the voltage at the output of the rectifier (5) or the voltage in the battery (8) , a driver circuit (12) connected to the field winding (3) of the alternator (2) for modifying the current flowing in this winding (3) , and an electronic control unit (ECU) connected to the detector means (11) and to the driver circuit (12) and arranged to control the current flowing in the field winding (3) of the alternator, by means of the driver circuit (12) , in dependence on the controlled voltage value, the voltage regulator being characterized in that the control unit (ECU) is arranged: - to calculate and store successive values (E (n) ) of an error quantity (E) representative of the difference between a target value (X REF ) of the voltage controlled and the actual instantaneous value (X) of this voltage, - to calculate and store successive values of a control quantity (Y) corresponding to the intensity of the current to be caused to flow in the field winding (3) in dependence on preceding values (Y(n-l); Y(n-2)) of the control quantity (Y) and of the instantaneous value (E(n)) and a preceding value (E(n-l)) of the error quantity (E) , - to control the current flowing in the field winding (3) of the alternator (2) in accordance with a normal procedure such that the current corresponds to the instantaneous calculated value (Y(n)) of the 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 preceding value (Y(n-l)) of the control quantity (Y) , is below a respective predetermined threshold value (E th ; Y th ) , - to control the current flowing in the field winding (3) in accordance with a special procedure such that the current corresponds to the instantaneous calculated value (Y (n) ) of the control quantity (Y) increased by a predetermined increment (ΔY) when the instantaneous value (E(n)) of the error quantity (E) or, alternatively, the difference between the instantaneous value (Y(n)) and the preceding value (Y(n- 1) ) of the control quantity (Y) exceeds the respective predetermined threshold value (E th ; Y th ) and for as long as the value of the error quantity (E) remains above a predetermined reference value (E 0 ) . 2. A voltage regulator according to Claim 1, characterized in that the threshold values (E th ; Y th ) are constant. 3. A voltage regulator according to Claim 1, characterized in that it also comprises further detector means (15) for supplying to the control unit (ECU) signals (Φ) indicative of the speed of rotation of the rotor (3) of the alternator (2) , and in that the threshold values (E th ; Y th ) are variable in a predetermined manner in dependence on the speed of rotation of the rotor, these values increasing with increases in the speed of rotation. 4. A voltage regulator according to any one of the preceding claims, comprising further detector means (15) for supplying to the control unit (ECU) signals (Φ) indicative of the speed of rotation of the rotor (3) of the alternator (2) , the regulator being characterized in that the control unit (ECU) is arranged to control the field current only in accordance with the normal procedure when the speed of rotation of the rotor is greater than a predetermined value . 5. A voltage regulator according to Claim 3 or Claim 4 , characterized in that the further detector means comprise a squaring circuit (15) connected to a phase winding of the armature winding (4) of the alternator (2) . 6. A voltage regulator according to any one of the preceding claims, in which the means for detecting the controlled voltage have two inputs (16a, 16b) connectible to the battery (8) and to the output of the rectifier (5) , respectively, the inputs (16a, 16b) being connectible selectively to an input of the control unit (ECU) in dependence on a selection control signal (SEL) . 7. A voltage regulator according to Claim 6, characterized in that the control unit (ECU) is arranged to implement an automatic procedure for recognizing the input (16a; 16b) of the detector means (16) which is operatively connected to the voltage-generating and -supply system (1) .

Inventors: ORLANDI GIANCARLO, QUADRELLI CLAUDIO, SALUSSOLIA PIER LUIGI, ORLANDI, GIANCARLO, QUADRELLI, CLAUDIO, SALUSSOLIA, PIER, LUIGI
Applicants: MAGNETI MARELLI SPA, ORLANDI GIANCARLO, QUADRELLI CLAUDIO, SALUSSOLIA PIER LUIGI, MAGNETI MARELLI S.p.A., ORLANDI, GIANCARLO, QUADRELLI, CLAUDIO, SALUSSOLIA, PIER, LUIGI
Application year: 1998
Main classification: H02P9
IPC codes: H02J7, H02P9