Method for controlling the operation of a compressor

Abstract

In a method for controlling the operation of a compressor, the compressor is switched off by a controller in order to prevent thermal damage if an estimated temperature value calculated by the controller exceeds an upper threshold value. The controller calculates a cooling function as a state variable utilizing the estimated temperature value, the cooling function representing the chronological course of the cooling of the compressor. The controller determines the cooling function based on at least one first and one second estimated temperature value which are associated with points of the compressor that are at spatial distances to each other. The calculation of the cooling function is based on a temperature difference between the first and second estimated temperature values.

Claims

1. A method of controlling an operation of a compressor, the method to be executed by a controller connected to the compressor, the method which comprises: with the controller, determining at least a first estimated temperature value associated with a first location on the compressor as a first state variable and a second estimated temperature value associated with a second location on the compressor as a second state variable, the second location being disposed at a spacing distance from the first location, and determining a temperature difference between the first estimated temperature value and the second estimated temperature value; with the controller, calculating a cooling function of the compressor on a basis of the temperature difference, the cooling function representing a course over time of a cooling of the compressor after the compressor has been switched off; and with the controller, utilizing the cooling function to determine whether or not the compressor may be switched back on.

2. The method according to claim 1, wherein the second location on the compressor that is spatially associated with the second estimated temperature value is located closer to a region that is at ambient temperature than the first location spatially associated with the first estimated temperature value.

3. The method according to claim 1, wherein the first estimated temperature value is associated with a location on the compressor at which the compressor heats up relatively quickly in operation.

4. The method according to claim 3, wherein the second estimated temperature value is associated with a location on the compressor at which the compressor heats up relatively slowly in operation.

5. The method according to claim 1, wherein the second estimated temperature value is associated with a location on the compressor at which the compressor heats up relatively slowly in operation.

6. The method according to claim 1, wherein the first estimated temperature value is associated with a location that is arranged in a region of a discharge valve or a piston seal of the compressor.

7. The method according to claim 1, wherein the second estimated temperature value is associated with a location at an outer surface of a housing of the compressor.

8. The method according to claim 7, wherein the second estimated temperature value is associated with a location on a cylinder head of the compressor.

9. The method according to claim 1, which comprises determining the cooling function with the controller while taking account further state variables.

10. The method according to claim 9, which comprises selecting the further state variables from the group consisting of an ambient temperature and/or a compressor voltage and/or an admission pressure and/or back pressure of the compressor.

11. A method of controlling an operation of a compressor, the method to be executed by a controller connected to the compressor, the method which comprises: with the controller, determining at least a first estimated temperature value associated with a first location on the compressor as a first state variable and a second estimated temperature value associated with a second location on the compressor as a second state variable, the second location being disposed at a spacing distance from the first location, and determining a temperature difference between the first estimated temperature value and the second estimated temperature value; with the controller, calculating a cooling function of the compressor on a basis of the temperature difference, the cooling function representing a course over time of a cooling of the compressor after the compressor has been switched off, and utilizing the cooling function to determine whether or not the compressor may be switched back on; and after the controller had been switched off and then switched back on, determining with the controller, while taking account of the cooling function and a time elapsed between the switching off and the switching on of the controller, a time at which the temperature has fallen below a lower threshold value and at which the compressor can be switched back on.

12. A method of controlling an operation of a compressor, the method to be executed by a controller connected to the compressor, the method which comprises: with the controller, determining at least a first estimated temperature value associated with a first location on the compressor as a first state variable and a second estimated temperature value associated with a second location on the compressor as a second state variable, the second location being disposed at a spacing distance from the first location, and determining a temperature difference between the first estimated temperature value and the second estimated temperature value; with the controller, calculating a cooling function of the compressor on a basis of the temperature difference, the cooling function representing a course over time of a cooling of the compressor after the compressor has been switched off, and utilizing the cooling function to determine whether or not the compressor may be switched back on; and after the controller had been switched off and then switched back on, determining the cooling function based on the estimated temperature values at the time when the controller was switched off, and taking into account a time elapsed between the switching off and the switching back on of the controller.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The soul drawing FIGURE is a block diagram illustrating steps of the method

DETAILED DESCRIPTION OF THE INVENTION

(2) In a method according to the invention for controlling the operation of a compressor, the compressor is first subjected in a test bed assembly to various operating states, in particular with respect to the duration of its operation, to the ambient temperature, to the compressor voltage and to the admission pressure and back pressure of the compressor. In these tests the course over time of the temperature of the compressor at a first point, which in this exemplary embodiment is arranged in the region of a discharge valve of the compressor, is measured by means of a first temperature sensor and stored, in particular during cooling of the compressor in the switched-off state. In addition, the course over time of the temperature of the compressor is measured by means of a second temperature sensor at a second point, which in this exemplary embodiment is arranged in the region of the cylinder head of the compressor. The temperature curves obtained in this way for various operating states are stored and fed into a software of the controller of the compressor, so that, in the installed state of the compressor, for example on a leveling control system of a motor vehicle, estimated temperature values can be determined by the controller. No temperature sensor, or its operation, is required in the installed state of the compressor.

(3) In the installed state, the compressor is controlled by the controller in such a manner that, in order to avoid thermal damage, the controller switches off the compressor if an estimated temperature value calculated by the controller exceeds an upper threshold value.

(4) During operation of the compressor, the controller, with the aid of its software, calculates continuously over time or at intervals a first estimated temperature value, which in the exemplary embodiment is associated with a point in the region of the discharge valve of the compressor, and a second estimated temperature value, which in the exemplary embodiment is associated with a point in the region of the cylinder head of the compressor. On the basis of these estimated temperature values, the controller additionally calculates a cooling function which represents the course over time of the cooling of the compressor after it has been switched off. In this case, the controller determines the cooling function, according to the invention, on the basis of the first and the second estimated temperature values, in such a manner that the cooling function is determined on the basis of the temperature difference between the first estimated temperature value and the second estimated temperature value.

(5) If the first estimated temperature value exceeds an upper threshold value, the controller switches off the compressor in order to avoid thermal damage. If the controller remains switched on after the compressor has been switched off, it calculates, on the basis of the estimated temperature values, the cooling function from which it can be inferred at what time the compressor can be switched on again without giving rise to thermal damage in the compressor. If the temperature difference between the first and the second estimated temperature values is relatively large, this means that the compressor has heated up relatively strongly locally, above all at its discharge valve, without being heated relatively strongly throughout. This yields a cooling function corresponding to more rapid cooling, so that the temperature falls relatively quickly below a lower threshold value and, accordingly, the compressor can be switched on again relatively quickly.

(6) If, on the other hand, the controller ascertains that the temperature difference between the first and second estimated temperature values is relatively small, it follows that the compressor has heated up relatively strongly not only in the region of its discharge valve, but has heated up relatively strongly throughout.

(7) This yields a cooling function corresponding to relatively slow cooling, so that the temperature falls below the lower threshold value, at which the compressor can be switched back on, only after a relatively long time.

(8) If the controller is switched off when, or shortly after, the compressor is switched off, for example when the ignition of the motor vehicle is switched off, the cooling function is calculated, on the basis of the estimated temperature values determined for the time of switching off, as soon as the controller is switched on againthat is, for example, when the ignition of the motor vehicle is switched on. On the basis of the cooling function determined and the time which has elapsed between switching off the compressor and switching on the controller again, the controller can then ascertain the time at which the temperature of the compressor has fallen below a lower threshold value, and at which the compressor can therefore be switched on again.

(9) On the basis of the teaching according to the invention, the cooling function can be determined more precisely, since it is determined, according to the invention, not on the basis of a single estimated temperature value but on the basis of a temperature difference between two estimated temperature values.

(10) The advantages of the teaching according to the invention are already obtained if only the difference between two temperature values is determined. However, it is also possible according to the invention to determine the cooling function on the basis of at least two temperature differences from at least three estimated temperature values. According to the particular requirements, a use of two or more temperature differences makes possible still more accurate information on the spatial distribution of heat in the compressor.

(11) The sole FIGURE is a block diagram illustrating the major steps of the method 100. These steps are performed with a controller. Step 10 includes determining at least a first estimated temperature value associated with a first location on the compressor as a first state variable and a second estimated temperature value associated with a second location on the compressor as a second state variable. The second location is disposed at a spacing distance from the first location. Step 10 also includes determining a temperature difference between the first estimated temperature value and the second estimated temperature value. Step 20 includes calculating a cooling function of the compressor on a basis of the temperature difference. The cooling function represents a course over time of a cooling of the compressor after the compressor has been switched off. Step 30 includes utilizing the cooling function to determine whether or not the compressor may be switched back on.