Method and apparatus for monitoring the temperature of the coil wire of a solenoid valve

A method and an apparatus for monitoring a temperature of a coil wire of a solenoid valve are provides. An actuation signal has actuation intervals which follow one another is used in this case, wherein a start pulse, which causes an increase in current in the coil wire of the magnet coil and has a prespecified pulse duration, and a pulse sequence, which follows the start pulse and has a duty cycle, are provided in each actuation interval. The current intensity of the current flowing through the coil wire of the solenoid valve is measured at two different times during the increase in current, and the current gradient is subsequently calculated from the measured current intensities. A prespecified threshold value for the current gradient is then compared with the calculated current gradient.

TECHNICAL FIELD

The disclosure relates to a method and an apparatus for monitoring a temperature of a coil wire of a solenoid valve.

BACKGROUND

Solenoid valves are often used for regulating and controlling a volumetric flow, for example the fuel volumetric flow of a common-rail diesel injection system. During the operation of the solenoid valves, there is a risk that the temperature of the coil wire of the respective solenoid valve exceed a permissible maximum temperature. This may lead to a disturbance of the functioning of the solenoid valve and also to a destruction of the solenoid valve.

In order to avoid this, it is already known to measure a temperature value characterizing the coil temperature by means of a temperature sensor fitted on the housing of the coil of the solenoid valve.

However, one disadvantage of this procedure is that the temperature measured by a temperature sensor fitted on the housing of the solenoid valve does not correspond to the actual temperature of the coil wire. Instead, the temperature measures corresponds at most to an approximated value of the actual coil temperature.

SUMMARY

As such, it is desirable to have a method and apparatus for monitoring the temperature of a coil wire of a solenoid valve in which the actual temperature of the coil wire may be detected better than in known methods.

One aspect of the disclosure provides a method and apparatus configured to measure the temperature of the coil wire of a solenoid valve by evaluating an actuation signal having successive actuation intervals, wherein a start pulse having a predefined pulse duration, the start pulse bringing about a current rise in the coil wire of the magnet coil, and a pulse sequence succeeding the start pulse and having a duty ratio are provided in each actuation interval. This involves measuring the current intensity of the current flowing through the coil wire of the solenoid valve at a first point in time during the duration of the current rise, measuring the current intensity of the current flowing through the coil wire of the solenoid valve at a second point in time during the duration of the current rise, calculating the current gradient from the measured current intensities, comparing a predefined threshold value for the current gradient with the calculated current gradient, and reducing the current flowing through the coil wire if the calculated current gradient is less than the predefined current gradient.

Implementations of the disclosure may include one or more of the following optional features. In some implementations, reducing the current flowing through the coil wire in this way may be performed in a simple manner by changing the duty ratio of the pulses of the pulse sequence or by changing the number of pulses of the pulse sequence.

As such, the method and apparatus allow the coil wire temperature to be detected directly and thus more accurately than in known methods in which the coil wire temperature is detected by means of a temperature sensor fitted on the coil housing. By applying the method according to the disclosure, a critical limit temperature of the coil wire is prevented from being exceeded and the function of the solenoid valve is thus always ensured.

Additionally, the the technical outlay for carrying out the method is reduced as compared with known methods. The number of components needed is reduced in comparison with known methods in which temperature sensors are used. In this regard, in particular the need for a temperature sensor and also the need for electrical lines and plug connections by means of which the temperature sensor must be connected to an evaluation unit are obviated. In the method according to the disclosure, monitoring the temperature of the coil wire of a solenoid valve may be effected using the actuation equipment of the solenoid valve that is present anyway.

Furthermore, the method according to the disclosure has a higher reliability than the known methods in which temperature sensors are used, since the need for the additional components mentioned above is obviated and, consequently, the failure probability of the entire system is reduced.

A further advantage of the method according to the disclosure is that the reaction time to a change in the temperature of the coil wire that occurs during the operation of the solenoid valve is reduced.

Furthermore, costs are saved by obviating the need for the additional components mentioned above.

DETAILED DESCRIPTION

FIG. 1shows a block illustration of an apparatus for monitoring the temperature of a coil wire of a solenoid valve. The apparatus includes a voltage source1, a solenoid valve2, a control and regulating unit3and a switch4. The voltage source1, the control and regulating unit3and the switch4form an electronic control unit ECU.

The voltage source1provides a DC voltage at its output, the DC voltage causing a current flow through the magnet coil2aof the solenoid valve2via the switch4. The current flowing through the solenoid valve2is fed to the control and regulating unit3, in which the current is measured, the current gradient is calculated and the calculated current gradient is evaluated. The control and regulating unit3, which includes a microcomputer, makes available at its output a switch control signal s, by means of which the switch4is actuated. The actuation of the switch4is effected by means of an actuation signal, which is explained in greater detail below with reference to the further FIGS.

The apparatus described above is used in the present disclosure for carrying out a method for monitoring the temperature of the coil wire2aof the magnet coil2.

FIG. 2shows a flow diagram for elucidating the method for monitoring the temperature of the coil wire of the magnet coil of a solenoid valve. This method uses an actuation signal having successive actuation intervals. A start pulse having a predefined pulse duration, the start pulse bringing about a current rise in the coil wire of the magnet coil, and a pulse sequence succeeding the start pulse and having a duty ratio are provided in each of the actuation intervals.

A step S1involves measuring the current intensity I(t1) of the current flowing through the coil wire of the solenoid valve at a first point in time t1during the current rise.

Afterward, a step S2involves measuring the current intensity I(t2) of the current flowing through the coil wire of the solenoid valve at a second point in time t2during the current rise.

Then, a step S3involves calculating the current gradient α according to the following relationship:

A transition is then made to a step S4, in which a predefined threshold value αlim for the current gradient is compared with the calculated current gradient α.

If this comparison reveals that the calculated threshold value α is less than the predefined threshold value αlim, then a transition is made to a step S5, which involves reducing the current flowing through the coil wire2aof the magnet coil2. Reducing the current flowing through the coil wire in this way can advantageously be performed by changing the switch control signal s fed to the switch4in the sense of changing the duty ratio of the pulses of the pulse sequence of the respective actuation interval. As an alternative thereto, reducing the current flowing through the coil wire in this way may also be performed by changing the number of pulses of the pulse sequence of the respective actuation interval.

Reducing the current flowing through the coil wire of the solenoid valve in this way in step S5is followed by a return to step S1, such that steps S1to S5may be carried out again in a subsequent actuation interval.

By contrast, if the comparison carried out in step S4reveals that the calculated current gradient α is greater than the predefined threshold value αlim or equal to the predefined threshold value αlim, then proceeding from step S4a direct return to step S1is effected, such that steps S1to S5may be carried out again in a subsequent actuation interval.

The method and apparatus makes use of the fact that the current gradient decreases as the temperature of the coil wire increases. The predefined threshold value αlim for the current gradient is therefore predefined in such a way that, during the operation of the solenoid valve, it is always ensured that a permissible maximum temperature of the coil wire of the magnet coil is not exceeded. This prevents overheating of the coil wire and also destruction of the magnet coil on account of overheating of the coil wire.

FIG. 3shows a schematic diagram of one exemplary embodiment of the actuation signal used in the method according to the disclosure. In the schematic diagram, the voltage U is plotted upward and time t is plotted toward the right. It is evident that the actuation signal used has a plurality of actuation intervals A1, A2, . . . , which are respectively spaced apart from one another by a pause interval P1, P2, . . . . A start pulse SI, which brings about a current rise in the coil wire of the magnet coil, is provided in each of the actuation intervals. Furthermore, a pulse sequence IF succeeding the start pulse and having a duty ratio is provided in each of the actuation intervals. The pulse duration of the start pulse SI is greater than the pulse duration of the pulses of the pulse sequence IF. If the above-described evaluation of the current gradient reveals that the calculated current gradient is less than the predefined threshold value for the current gradient, then the duty ratio of the pulses of the pulse sequence IF may be changed for the purpose of reducing the current flowing through the coil wire2aof the magnet coil2. As an alternative thereto, the number of pulses of the pulse sequence IF may also be changed for the purpose of reducing the current flowing through the coil wire2aof the magnet coil2. This leads to a change in the duration of the respective pause interval and also to a change in the duration of an actuation interval.

FIG. 4shows a schematic diagram for elucidating various current gradients. In this case, the start pulse SI of an actuation interval is illustrated in an enlarged manner inFIG. 4. Two different current profiles SV1and SV2are illustrated within the start pulse. The progression of the current profile SV1is flatter than the current profile SV2. Consequently, the current gradient associated with the current profile SV1, α1=[I(t2)−I(t1)]/(t2−t1), is less than the current gradient associated with the current profile SV2, α1=[I′(t2)−I′(t1)]/(t2−t1).