METHOD FOR OPERATING A HEATING APPARATUS, CONTROL DEVICE AND MOTOR VEHICLE

Abstract

A method for operating a heating apparatus for a viewing surface, in particular an external viewing device of a motor vehicle, such as in the form of an external rearview mirror, in which a heating current of at least one heating element of the heating apparatus is measured and taken as basis for an input variable for a Mealy machine for controlling the heating capacity of the heating device. A control device which is designed to carry out such a method, and a motor vehicle having such a control device.

Claims

1. A method for operating a heating apparatus for an external viewing device of a motor vehicle such as an external rearview mirror, the method comprising: measuring a heating current of at least one heating element of the heating apparatus; and using the measured heating current as a basis for an input variable for a Mealy machine for controlling a heating capacity of the heating apparatus.

2. The method according to claim 1, further comprising: determining a temperature of the at least one heating element from the measured heating current; and using the determined temperature as the input variable.

3. The method according to claim 1, further comprising: measuring at least one of a resistance and the heating current in the at least one heating element repeatedly while the Mealy machine is running; and adjusting the heating current based on this repeated measurement.

4. The method according to claim 3, further comprising accessing a table, using the Mealy machine, which represents a relationship between the resistance of the at least one heating element and a resultant setpoint heating current.

5. The method according to claim 4, further comprising specifying a value for the heating current, the Mealy machine, according to the setpoint heating current determined from the table; and feeding a heating current of the specified value into the at least one heating element.

6. The method according to claim 4, wherein a pulse width-modulated heating current is used, and a duty factor of the heating current is adapted in the event of deviation of the measured heating current from the setpoint heating current.

7. The method according to claim 6, further comprising reducing the duty factor of the heating current in response to the setpoint heating current being exceeded by the measured heating current, or increasing the duty factor of the heating current in response to the measured heating current falling below the setpoint heating current.

8. The method according to claim 1, further comprising using a LIN bus for communication between a control device, on which the Mealy machine is implemented, and the heating apparatus.

9. A control device, which is set up to carry out a method according to claim 1.

10. A motor vehicle having a control device according to claim 9.

Description

DETAILED DESCRIPTION

[0023] The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the systems, apparatuses and/or methods described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness.

[0024] The state diagram shown in FIG. 1 illustrates the five possible states S0 . . . S4 of a Mealy machine suitable for use in an exemplary embodiment of the method. The states are shown here as circles (nodes of the state diagram). Arrows (edges of the state diagram) characterize possible transitions between states S0 . . . S4.

[0025] In a Mealy machine, transition between two states proceeds as a function of an input. At the same time, an output is generated which is dependent both on the respective state S0 . . . S4 and on the input.

[0026] For use for controlling a heating apparatus, a measured value for the current through at least one heating element of the heating apparatus serves as an input value for the Mealy machine shown. The current actually flowing through the heating element is namely proportional to the resistance of the heating element, which is turn dependent on the temperature of the heating element due to its temperature coefficient. The Mealy machine thus indirectly receives as input an item of information about the temperature of the at least one heating element.

[0027] The output value represents the duty factor of a pulse width-modulated heating current which is fed into the at least one heating element. The duty factor of a pulse width-modulated signal corresponds to the ratio between pulse width and period of the signal. More energy is thus fed into the at least one heating element per unit time in the case of a higher duty factor than in the case of a lower duty factor.

[0028] Overall, therefore, control of the heating capacity may thus be realized as a function of the temperature of the at least one heating element and it may thus be ensured that predetermined nominal temperatures may be complied with.

[0029] A method according to the invention may proceed as follows:

[0030] Upon switching on of the heating apparatus, first of all a test pulse is output to the at least one heating element and the resultant current flow through the at least one heating element is recorded. Since, before it is switched on, the heating element is in thermal equilibrium with the surrounding environment, this current flow is thus dependent on the ambient temperature.

[0031] The ambient temperature thus serves as an initial input for the Mealy machine. This is in state S0 when the heating apparatus is switched on and then takes the heating current respectively desired on the basis of the temperature from a table reproducing an accurately calculated interrelationship between the temperature or the internal resistance of the at least one heating element and an associated setpoint heating current. The heating current selected in this way is then applied to the at least one heating element.

[0032] In other words, on the basis of the initial input, the respectively relevant heating program is thus determined for the heating apparatus, compliance with which is then monitored and ensured by the Mealy machine.

[0033] During further operation of the heating apparatus, the current flow is then measured periodically by the at least one heating element. Providing this continues to correspond to the setpoint input, the Mealy machine remains in state S0 and controls the heating apparatus according to the table setpoint value.

[0034] If the measured current flow is too high, the Mealy machine transitions into state S1 and then state S2. As an output, the Mealy machine then generates a reduced duty factor for the heating current, such that less energy is supplied to the heating apparatus and it cools down accordingly. The machine remains in these states until a new input, i.e. a new measured current flow through the at least one heating element, is present which corresponds to the setpoint value in the table. As soon as this is the case, the Mealy machine returns to the base state S0.

[0035] Similarly, the Mealy machine transitions to state S3 and then state S4 if the measured current flow is too low. As an output, the Mealy machine then generates an increased duty factor for the heating current, such that more energy is supplied to the heating apparatus and it heats up accordingly. The machine then remains in these states again until a new input, i.e. a new measured current flow through the at least one heating element, is present which corresponds to the setpoint value in the table. As soon as this is the case, the Mealy machine returns to the base state S0.

[0036] Overall, therefore, the heating capacity and thus the temperature of the heating apparatus is thus kept stably at the specified setpoint according to the table and the ambient temperature determined by the initial test pulse. Since every state change of a Mealy machine is directly concomitant with an output, control is additionally very rapid and thus avoids overdrive, as may occur with more sluggish open- or closed-loop control systems. The Mealy machine shown may additionally be simply implemented in existing control devices, such that all that may be needed to equip an older system is a software update.

[0037] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that the invention disclosed herein is not limited to the particular embodiments disclosed, and is intended to cover modifications within the spirit and scope of the present invention.

REFERENCE LIST

[0038] S0 . . . S4 States of the Mealy machine