EP1644640B1 - Method for controlling operation of a compressor - Google Patents

Abstract

In a method for controlling operation of a compressor, the compressor is shut off by a control device in order to prevent thermal damages when an estimated temperature value Ts calculated by said control device exceeds an upper threshold value Tmax while the compressor remains on or is allowed to be turned on when there is a need for compression and a lower threshold value Tmin is not reached. In order to be able to more accurately estimate the estimated temperature and increase the thermal availability of the compressor, the estimated temperature value Ts is indirectly and cyclically determined by means of a mathematical-physical model that characterizes the cooling and heating properties of the compressor.

Description

It is well known that compressors are used in motor vehicles, with which a gaseous or liquid medium can be brought to a pressure which is above the ambient pressure. This gaseous or liquid medium is often used as a control pressure medium, for example, actuators such as piston-cylinder arrangements can be acted upon directly or via a pressure fluid reservoir.

An application in motor vehicles results from the necessity of supplying the air springs of a level control system with compressed air in such a way that they can move the vehicle to a road-surface-appropriate distance from the road surface. Since such a level control system does not constantly provide a height adjustment of the vehicle, a belonging to such a system compressor is required only ever put into operation when the need to do so. Such compressors are usually designed as electromotive piston operated compressors.

In an effort to minimize the cost of compressors, increasingly small compressors are used, in which possibly longer-lasting operation thermal problems can occur because its components can heat up excessively during prolonged operation. In such cases, the damage usually takes place first on the outlet valve or on the piston seal of a reciprocating compressor, which can ultimately lead to failure of the compressor and thus of the level control system.

To avoid such operational damage exists, for example, according to DE 15 03 466 A1, DE 19 43 936 A1 and EP 12 53 321 A2 the ability to directly measure the temperature of the compressor in the range of said components and in case of thermal overload, switch off the compressor for cooling.
However, this construction has the disadvantages that the necessary temperature sensors are comparatively expensive and, in the case of small compressors, they are often difficult to accommodate in the area of interest due to the limited installation space. Although EP 12 53 321 A2 indicates that the control of the compressor operation can also take place without temperature sensors on the basis of a thermal model, the content of such a measurement or control method is not defined.

Moreover, it is known from DE 39 19 407 A1 and DE 40 30 475 A1, to determine the thermal load of such a compressor on the electrical power consumption and / or the operating time of belonging to the compressor electric motor. In a similar direction, the proposal has become known from DE 43 33 591 A1 to influence the control of a compressor by summing up its individual switch-on times and individual switch-off times, which can be regarded as a factor of many influencing factors for the thermal loading of the compressor.

Another approach is disclosed by DE 198 12 234 C2, according to which a compressor is operated variable in terms of its on and off times. The respective current duty cycle should be adapted to the current operating conditions of the compressor. As a parameter, depending on the duty cycle of the compressor is varied, serve the heat transfer conditions that prevail between the compressor and the surrounding air.

In this case, the duty ratio may be varied, for example, depending on the air temperature and the air flow velocity prevailing in the compressor environment such that the duty ratio is shortened as the compressor ambient temperature increases and is prolonged as it decreases. The compressor ambient temperature can be determined based on a model calculation from the current vehicle exterior air temperature and / or the Fahrzeugmotoransauglufttemperatur. A disadvantage of this method is that this, like all switch-on methods, is consistently inaccurate because of its thermodynamic properties not considered by the compressor itself. The controller therefore does not influence, for example, in which temperature band the compressor is ultimately operated.

Finally, DE 196 21 946 C2 discloses a method for temperature-controlled control of a compressor for air suspension of a motor vehicle, which is designed as an estimation method and manages without a separate temperature sensor on the compressor. For this purpose, it is provided that the compressor is switched off by a control unit when a temperature estimate calculated by the latter exceeds an upper threshold value, or is switched on or is allowed to be switched on if a lower threshold value is undershot. For this purpose, the respective last temperature estimated value is increased by a certain temperature jump when the compressor is switched on, the extent of which depends on the height of the last estimated value.

In this case, the estimated value is increased during a compressor operation by a predetermined positive gradient and lowered at standstill of the compressor by a predetermined negative gradient. The disadvantage is that the linear relationships used for this method are not present in reality, since with large temperature differences, the temperature changes are greater than with small temperature differences. The temperature jump also does not take place in reality immediately, so that in this area, the control technology availability of the compressor is disadvantageously reduced.

Against this background, the object of the invention to provide a method with which the current temperature at a damaged component of a compressor without using a built-in compressor temperature sensor is more accurate than previously estimated, so that such a compressor with increasing component temperatures longer than before is possible operable.

The solution of this problem arises from the features of the main claim, while advantageous embodiments and further developments of the method are the dependent claims.

The invention is therefore based on the finding that the operating time and the availability of a compressor can be advantageously extended even without using a temperature sensor arranged in the region of the thermally heavily loaded components, if the heating and cooling behavior of the compressor can be estimated better than heretofore. The invention proposes, in a further development of the prior art, to determine the cooling and heating characteristics of the compressor in the form of mathematical-physical models, to store them in a control unit and on the basis of which to control the operation of the compressor.

It is provided according to the features of claim 1 in particular that physical-technical influencing variables are determined, which influence the estimated temperature TS (T _c ) changing that at least one relative temperature Tc ₁ ; Tc _{2 is determined} with the aid of the influencing variables, which describes the thermal state of the compressor, in addition to the previously cyclical value of the relative temperature Tc ₁ ; Tc ₂ the current influencing variables are added and / or subtracted, so that as a result of this calculation a current relative temperature Tc ₁ ; Tc ₂ yields that then from this current relative temperature Tc ₁ ; Tc ₂ and the ambient temperature T _{∞ of} the compressor a current estimated temperature T _s (Tc) is determined, which takes into account the heating and cooling behavior of the compressor, and that this cyclically determined estimated temperature T _s (T _c ) to perform a threshold comparison with a lower and an upper temperature threshold T _min ; T _{max is} used, based on the compressor operation is controlled.

Among the factors that characterize the characteristic relative temperatures Tc _i temperature increasing and will be considered in the implementation of the estimation method, is one example, in addition to the ambient temperature T _∞ of the compressor and the electric voltage U _comp at the compressor as well as the counterpressure P of the compression medium downstream of the compressor. In a closed pressure system, the pressure in front of the compressor can also be used.

In a further embodiment of the invention, these temperature-increasing influencing variables enter into a heating function B (U) which describes the heating behavior of a specific compressor.

In contrast, a temperature-reducing influencing variable A (Tc) in the form of a cooling function, which takes into account the cooling properties of the compressor and its installation environment, is usefully used in the method in question.

To carry out the calculation of a current value of the relative temperatures Tc _{1, i} ; Tc _{1, i} it is proposed that of the last given or calculated values of the relative temperatures Tc _{1, i-1} ; Tc _{2, i-1} the current value of the cooling function A (Tc) is subtracted when the compressor in the considered time interval is not in operation, and the current value of the heating function B (U) is added, if the compressor in the time interval in operation is. However, it is considered to be particularly advantageous to take account of the cooling function A (Tc) during the compressor operation during the calculation of the relative temperature, since the compressor naturally also gives off heat to its surroundings in this mode of operation.

At the start of the control process, the initial value of the relative temperatures Tc should be selected so that the estimated temperature T _s (T _c ) of the compressor corresponds to the value of the ambient temperature T _∞ at the installation location of the compressor.

Since the relative temperature T _s (T _c ) describes not the absolute temperature of the compressor but the temperature difference with respect to the temperature T _∞ at Kompressoreinbauort, this relative temperature T _s (T _c ) at the beginning of the compressor control method after a long period of inactivity of the compressor with the value Zero initialized. This procedure ensures that temperature estimation method of the invention for a longer cooling time provides just the ambient temperature T _∞.

The rough structure of the control method according to the invention, as stored for example in a motor vehicle control device as software, can be explained with the aid of the attached drawing. Therein, a relative temperature module 2 is shown, in which that characteristic relative temperature Tc is stored and calculated, which describes the thermal state of the compressor with sufficient accuracy. At short intervals of time, this relative temperature Tc, preferably two relative temperatures Tc ₁ , is cyclically controlled, for example, by a clock generator; Tc ₂ , recalculated.

For this purpose, first in a Abkühlsoftwaremodul 4 by means of the stored there cooling function A (Tc) and provided by the holding member 3 relative temperature Tc of the last period that Kompressorabkühlungswert calculated by the compressor since the last calculation cycle due to the characteristics of the compressor and its installation environment has cooled. This Abkühlwert is then subtracted from the previous relative temperature Tc (minus sign), so that a new value for the relative temperature Tc is formed.

In particular, when the compressor is in operation, this causes a waste heat, which are detected by the control device over heating-specific influencing variables 7 as measured values in this case and in a so-called heating module (main memory 5 in the control unit) with the aid of a heating function B (U) stored there to a heating value which, in the sense of a physical model, takes into account all influencing factors which have a temperature-increasing effect on the compressor.

The cyclically recalculated value of the heating function B (U) is added in particular, but not exclusively, to the current relative temperature Tc when the compressor is switched on (switch 6 with plus sign), so that a new relative temperature Tc results, which includes all the cooling temperatures also take into account, if applicable, factors of warming influence.

From this current value for the relative temperature Tc, the cyclically current estimated temperature Ts (Tc) can then be determined in an estimated temperature module 1 for the further operation control (on or off depending on the compression requirement and the operating temperature) of the compressor is used.

If the estimated temperature exceeds the permissible upper temperature limit, the compressor must be switched off. However, it is turned on when there is a demand for compression and the estimated temperature falls below a lower temperature limit, or when it can be expected that the cooling will be sufficiently high to complete a requested parking task (e.g., a vehicle level change) without overheating.

1. a) Feststellen des Betriebszustandes des Kompressors (An oder Aus),
2. b) Messen des Gegendrucks P des Druckmediums stromab hinter dem Kompressor und/oder bei geschlossenen Systemen des Vordrucks vor dem Kompressor,
3. c) Messen der aktuellen Betriebsspannung U_Komp des Kompressors,
4. d) Messen oder Schätzen der Umgebungstemperatur T_∞ des Kompressors,
5. e) Ermitteln der Gültigkeit der Einflussgrößen Betriebsspannung U_Komp und Gegendruck P beziehungsweise des Kompressor-Eingangsdrucks (Vordruck),
6. f) Berechnen des aktuellen Wertes der Erwärmungsfunktion B(U) unter Nutzung von erwärmungsspezifischen Einflussgrößen U,
7. g) Berechnen des aktuellen Wertes der Abkühlfunktion A(Tc) unter Nutzung von den charakteristischen Temperaturen des letzten Zeittakts,
8. h) Berechnen der charakteristischen Relativtemperaturen Tc₁; Tc₂ durch Addition und/oder Subtraktion der aktuellen Werte der Erwärmungsfunktion B(U) und der Abkühlfunktion A(Tc),
9. i) Berechnen der Schätztemperatur Ts(Tc) als Funktion der charakteristischen Relativtemperaturen Tc₁; Tc₂, und der Umgebungstemperatur T_∞,
10. j) Vergleich der Schätztemperatur Ts(Tc) mit vorbestimmten Temperaturschwellwerten T_min und T_max, wobei T_min kleiner ist als T_max,
11. k) Startfreigabe, wenn die Schätztemperatur Ts(Tc) kleiner oder gleich als T_min ist, oder Erlaubnis zum Weiterbetrieb für den Kompressor, wenn die Schätztemperatur Ts(Tc) kleiner als der Temperaturwert T_max ist,
12. l) Ausschalten des Kompressors, wenn die Schätztemperatur Ts(Tc) größer oder gleich dem Temperaturwert T_max ist,
13. m) Abspeichern der charakteristischen Relativtemperaturen Tc₁; Tc₂ zur Nutzung im nächsten Berechnungslauf,
14. n) Warten bis zum nächsten Zeittakt, und
15. o) Starten des nächsten Berechnungslaufs (Schritt a).

In the following, in an exemplary embodiment of the invention, the control step sequence of a specific control method is presented, which follows the idea of the invention and includes some of the advantageous developments of the invention. This process is characterized by the following process steps:

1. a) determining the operating state of the compressor (on or off),
2. b) measuring the backpressure P of the pressure medium downstream of the compressor and / or with closed systems of the upstream pressure upstream of the compressor,
3. c) measuring the actual operating voltage U _{Komp of} the compressor,
4. d) measuring or estimating the ambient temperature T _{∞ of} the compressor,
5. e) determining the validity of the influencing variables operating voltage U _Komp and counterpressure P or of the compressor inlet pressure (admission pressure),
6. f) calculating the current value of the heating function B (U) using heating-specific influencing variables U,
7. g) calculating the current value of the cooling function A (Tc) using the characteristic temperatures of the last time clock,
8. h) calculating the characteristic relative temperatures Tc ₁ ; Tc ₂ by addition and / or subtraction of the current values of the heating function B (U) and the cooling function A (Tc),
9. i) calculating the estimated temperature Ts (Tc) as a function of the characteristic relative temperatures Tc ₁ ; Tc ₂ , and the ambient temperature T _∞ ,
10. j) comparing the estimated temperature Ts (Tc) with predetermined temperature thresholds T _min and T _max , where T _{min is} less than T _max ,
11. k) start enable when the estimated temperature Ts (Tc) is less than or equal to T _min , or permission to continue operation for the compressor when the estimated temperature Ts (Tc) is less than the temperature value T _max ,
12. l) switching off the compressor when the estimated temperature Ts (Tc) is greater than or equal to the temperature value T _max ,
13. m) storing the characteristic relative temperatures Tc ₁ ; Tc ₂ for use in the next calculation run,
14. n) Wait until the next time clock, and
15. o) Start the next calculation run (step a).

In a further embodiment of this method can also be provided that, for example, the validity of the variables operating voltage U _Komp and back pressure P and possibly form are determined by multiplying these values with the value "one" when the compressor is in operation, or multiplied by the value "zero" when the compressor is not in operation. By means of this multiplication, it is achieved that these influencing variables, which characterize compressor heating, are included in the calculation of the estimated temperature Ts (Tc) only when the compressor is actually activated.

The relative temperature T _c1 ; Tc ₂ and the estimated temperature Ts (Tc) for a time step i are to be calculated according to the following equations:

und bei eingeschaltetem Kompressor $${\mathrm{Tc}}_{\mathrm{i}}\mathrm{=}{\mathrm{Tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}\mathrm{-}\mathrm{A}{\mathrm{Tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}+\mathrm{B}{\mathrm{U}}_{\mathrm{i}}$$

sowie für die Schätztemperatur $${\mathrm{Ts}}_{\mathrm{i}}\mathrm{=}\mathrm{C}{\mathrm{Tc}}_{\mathrm{i}}+{\mathrm{T}}_{\mathrm{\infty }}$$

worin die Werte A bis C Matrizen mit konstanten Koeffizienten darstellen, die den Kompressor sowie die Kompressorumgebung, insbesondere hinsichtlich deren thermischen Eigenschaften kennzeichnen, sowie T_∞ wie bereits erwähnt die Umgebungstemperatur des Kompressors angibt.With the compressor off $${\mathrm{tc}}_{\mathrm{i}}\mathrm{=}{\mathrm{tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}\mathrm{-}\mathrm{A}{\mathrm{tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}$$

and with the compressor on $${\mathrm{tc}}_{\mathrm{i}}\mathrm{=}{\mathrm{tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}\mathrm{-}\mathrm{A}{\mathrm{tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}+\mathrm{B}{\mathrm{U}}_{\mathrm{i}}$$

as well as for the estimated temperature $${\mathrm{ts}}_{\mathrm{i}}\mathrm{=}\mathrm{C}{\mathrm{tc}}_{\mathrm{i}}+{\mathrm{T}}_{\mathrm{\infty }}$$

wherein the values A to C represent constant coefficient matrices which characterize the compressor and the compressor environment, particularly with regard to their thermal properties, and T _∞, as already mentioned, indicates the ambient temperature of the compressor.

In a further advantageous embodiment of the control method according to the invention, it is proposed that, even if the estimated temperature Ts (Tc) is greater than the temperature value T _min , the compressor can be switched on, if the operating time of the compressor until the upper threshold T _max is reached is sufficient, to promote a quantity of pressure medium sufficient to fill a compressed air reservoir to a certain pressure level and / or for filling air springs of a motor vehicle by a certain Befüllwert.

It should also be mentioned that if the functions A (Tc), B (U) and Ts (Tc) have a linear character, their parameters can be determined and / or identified directly from sensor measured values simply by numerical methods. In addition, it should not go unmentioned that performed model calculations showed very good results when using two characteristic model temperatures or relative temperature Tc ₁ ; Tc _{2 was} calculated.

As particular advantages of this control method are that no separate temperature sensor on or in the compressor is necessary that the thermodynamic properties of a compressor are very well taken into account by the estimation method, that the necessary calculation factors can be determined very well by existing numerical methods from measurements that the Control method is very well inserted into existing motor vehicle control devices and that over Zeiteinschaltdauerverfahren according to the prior art always more accurate damage temperatures are calculated and thereby a higher availability of the compressor can be achieved.

LIST OF REFERENCE NUMBERS

1

Estimated temperature module

2

Relative temperature module

3

retaining member

4

Abkühlmodul

5

heating module

6

switch

7

Heating-specific parameters

A

Matrix with constant coefficients

B

Matrix with constant coefficients

C

Matrix with constant coefficients

tc

Characteristic relative temperature, which describes the thermal state of the compressor with sufficient accuracy

A (Tc)

cooling function

B (U)

warming function

U

Factors influencing the relative temperature T _c temperature-increasing

U _comp

compressor voltage

P

Back pressure of the pressure medium

Ts (Tc)

estimated temperature

T _max

Upper temperature threshold

T _min

Lower temperature threshold

T _∞

Ambient temperature at the compressor

i

index

Claims (11)

1. Method for controlling the operation of a compressor, in which the compressor is switched off by a control unit to avoid thermal damage if an estimated temperature value Ts(Tc) calculated by said unit exceeds an upper threshold value T_max, or remains switched on or is switched on if there is a compression requirement and if a lower threshold value T_min is not reached, the estimated temperature value Ts(Tc) of the compressor being determined indirectly and cyclically by means of a mathematical-physical model characterizing the cooling and heating properties of the compressor, characterized in that physical-technical influencing variables, which influence the estimated temperature Ts(Tc) in a changing manner, are determined, in that at least one relative temperature Tc₁; Tc₂, which describes the thermal state of the compressor, is determined with the aid of the influencing variables, in that, for this purpose, the currently applicable influencing variables are added to or subtracted from the cyclically prior value of the relative temperature Tc₁; Tc₂, so that a currently applicable relative temperature Tc₁; Tc₂ is obtained as the result of this calculation, in that a currently applicable estimated temperature Ts(Tc), which takes into account the heating and cooling behavior of the compressor, is then determined from this currently applicable relative temperature Tc₁; Tc₂ and the ambient temperature T∞ of the compressor, and in that this cyclically determined estimated temperature Ts(Tc) is used for carrying out a limit value comparison with a lower temperature threshold value T_min and an upper temperature threshold value T_max, on the basis of which the operation of the compressor is controlled.
2. Method according to Claim 1, characterized in that, apart from other variables, the influencing variables include the electric voltage U_comp at the compressor as well as the counterpressure P of the compression medium downstream of the compressor and/or, in the case of closed pressure systems, the admission pressure of the pressure medium at the inlet of the compressor.
3. Method according to Claim 2, characterized in that the influencing variables are entered in a heating function B(U), which describes the heating behavior of a specific compressor.
4. Method according to Claim 1, characterized in that an influencing variable A(Tc) represents a cooling function which takes into account the cooling properties of a specific compressor and the surroundings in which it is installed.
5. Method according to at least one of the preceding claims, characterized in that, to calculate a current value of the relative temperatures Tc_1,i; Tc_2,i, the value of the cooling function A(Tc) is subtracted from the last predetermined or calculated values of the relative temperatures Tc_1,i-1; Tc_2,i-1 if the compressor is not in operation in the time interval considered, and the value of a heating function B(U) is added if the compressor is in operation in the time interval considered.
6. Method according to at least one of the preceding claims, characterized in that the initial value of the relative temperatures Tc is chosen such that the estimated temperature Ts(Tc) of the compressor corresponds to the value of the ambient temperature T_∞ at the installation location of the compressor.
7. Method according to Claim 6, characterized in that the initial value of the relative temperatures Tc is set to the value zero at the beginning of the compressor control method.
8. Method according to at least one of the preceding claims, characterized by the following method steps:

   a) establishing the operating state of the compressor (on or off),

   b) measuring the counterpressure P of the pressure medium downstream of the compressor and/or, in the case of closed systems, of the admission pressure upstream of the compressor,

   c) measuring the currently applicable operating voltage U_comp of the compressor,

   d) measuring or estimating the ambient temperature T∞ of the compressor,

   e) determining the validity of the influencing variables, operating voltage U_comp and counterpressure P or the compressor inlet pressure (admission pressure),

   f) calculating the current value of the heating function B(U) by using heating-specific influencing variables U,

   g) calculating the current value of the cooling function A(Tc) by using the characteristic temperatures of the last time clock,

   h) calculating the characteristic relative temperatures Tc₁; Tc₂ by addition and/or subtraction of the current values of the heating function B(U) and the cooling function A(Tc),

   i) calculating the estimated temperature Ts(Tc) as a function of the characteristic relative temperatures Tc₁; Tc₂ and the ambient temperature T_∞,

   j) comparison of the estimated temperature Ts(Tc) with predetermined temperature threshold values T_min and T_max, where T_min is less than T_max,

   k) clearance for starting the compressor if the estimated temperature Ts(Tc) is less than or equal to T_min, or authorization to continue operation if the estimated temperature Ts(Tc) is less than the temperature value T_max,

   l) switching off the compressor if the estimated temperature Ts(Tc) is greater than or equal to the temperature value T_max,

   m) storing the characteristic relative temperatures Tc₁; Tc₂ for use in the next calculation run,

   n) waiting until the next time clock, and

   o) starting the next calculation run (step a).
9. Method according to Claim 8, characterized in that the validity of the measured variables, operating voltage U_comp and counterpressure P or admission pressure, is determined by these values being multiplied by the value "one" if the compressor is in operation or multiplied by the value "zero" if the compressor is not in operation.
10. Method according to at least one of the preceding claims, characterized in that the relative temperature Tc₁; Tc₂ and the estimated temperature Ts(Tc) for a time increment i are calculated according to the following equations:

    with the compressor switched off $${\mathrm{Tc}}_{\mathrm{i}}\mathrm{=}{\mathrm{Tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}\mathrm{-}\mathrm{A}{\mathrm{Tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}$$

    

    and with the compressor switched on $${\mathrm{Tc}}_{\mathrm{i}}\mathrm{=}{\mathrm{Tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}\mathrm{-}\mathrm{A}{\mathrm{Tc}}_{\mathrm{i}\mathrm{-}\mathrm{1}}+\mathrm{B}{\mathrm{U}}_{\mathrm{i}}$$

    

    and for the estimated temperature $${\mathrm{Ts}}_{\mathrm{i}}\mathrm{=}\mathrm{C}{\mathrm{Tc}}_{\mathrm{i}}+{\mathrm{T}}_{\mathrm{\infty }}$$

    

    in which the values A to C represent matrices with constant coefficients which characterize the compressor and the compressor surroundings, in particular with regard to their thermal properties.
11. Method according to at least one of the preceding claims, characterized in that, even if the estimated temperature Ts(Tc) is greater than the temperature threshold value T_min, the compressor may be switched on if the operating time of the compressor up until the upper threshold value T_max is reached is adequate to convey an amount of pressure medium adequate for filling a compressed air accumulator to a specific pressure level and/or for filling pneumatic springs of a motor vehicle by a specific filling value.

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