EP1644640A1

EP1644640A1 - Method for controlling operation of a compressor

Info

Publication number: EP1644640A1
Application number: EP04726849A
Authority: EP
Inventors: Kai Sorge
Original assignee: Continental AG
Current assignee: Continental AG
Priority date: 2003-07-04
Filing date: 2004-04-10
Publication date: 2006-04-12
Anticipated expiration: 2024-04-10
Also published as: ATE357597T1; WO2005003561A1; DE502004003291D1; US8152475B2; DE10330121A1; US20070098564A1; EP1644640B1

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

Continental Aktiengesellschaft

description

Method for controlling the operation of a compressor

It is generally 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 with which actuators such as piston-cylinder arrangements can be acted upon directly or via a pressure medium reservoir.

One application in motor vehicles results from the need to supply the air springs of a level control system with compressed air in such a way that they can move the vehicle at a distance from the road surface that is appropriate to the driving situation. Since such a level control system does not constantly provide for a height adjustment of the vehicle, a compressor belonging to such a system is only put into operation as required when the need for it exists. Compressors of this type are generally designed as electric motor-operated piston compressors.

In order to minimize the costs for compressors, small compressors are increasingly being used, which may cause thermal problems during their longer operation, since their components can heat up to an unacceptably high level during longer operation. In such cases, the damage usually occurs first on the outlet valve or on the piston seal of a piston compressor, which can ultimately lead to a failure of the compressor and thus of the level control system.

In order to avoid such operational damage, for example according to DE 15 03 466 A1, DE 19 43 936 A1 and EP 12 53 321 A2, it is possible to measure the temperature of the compressor directly in the area of the components mentioned and switch off the compressor to cool down in the event of thermal overload.

However, this structure has the disadvantages that the temperature sensors required for this purpose are comparatively expensive and, in the case of small compressors, are often difficult to accommodate in the area of interest due to the cramped installation space. Although EP 12 53 321 A2 indicates that the compressor operation can also be controlled without temperature sensors on the basis of a thermal model, the content of such a measuring or control method is not defined.

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

Another approach is disclosed by DE 198 12 234 C2, according to which a compressor is operated variably with regard to its on and off times. The current duty cycle should be adapted to the current operating conditions of the compressor. The heat transfer conditions between the compressor and the air surrounding it serve as parameters, depending on which the duty cycle of the compressor is varied.

The duty cycle can be varied, for example, depending on the air temperature and air flow velocity in the compressor environment such that the duty cycle is shortened when the compressor ambient temperature increases and is lengthened when it decreases. The compressor ambient temperature can be determined using a model calculation from the current vehicle outside air temperature and / or the vehicle engine intake air temperature. The disadvantage of this method is that, like all duty cycle methods, it is consistently imprecise because it has the thermodynamic properties of the compressor itself is not taken into account. The control therefore has no influence, for example, on the temperature band in which the compressor is ultimately operated.

Finally, DE 19621 946 C2 discloses a method for temperature-based control of a compressor for air suspension in a motor vehicle, which is designed as an estimation method and does not require 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 it exceeds an upper threshold value, or is switched on or is allowed to be switched on when a lower threshold value is undershot. For this purpose, the respective last temperature estimate is increased by a certain temperature jump when the compressor is switched on, the extent of which depends on the level of the last estimate.

The estimated value is increased by a predetermined positive gradient during compressor operation and decreased by a predetermined negative gradient when the compressor is at a standstill. It is disadvantageous that the linear relationships on which this method is based do not exist in reality, since with large temperature differences the temperature changes are greater than with small temperature differences. In addition, the temperature jump does not take place instantaneously in reality, so that the control-technical availability of the compressor is also disadvantageously reduced in this area.

Against this background, the object of the invention is to present a method with which the current temperature at a component of a compressor which is at risk of damage can be estimated more accurately than previously without using a temperature sensor built into the compressor, so that such a compressor is longer than before when component temperatures rise is possible to operate.

This object is achieved from the features of the main claim, while advantageous refinements and developments of the method can be found in the subclaims. The invention is therefore based on the knowledge 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 components which are subject to high thermal stress, if the heating and cooling behavior of the compressor can be estimated better than previously. To this end, the invention proposes, in a further development of the prior art, to determine the cooling and heating properties of the compressor in the form of mathematical-physical models, to store them in a control device and to control the operation of the compressor on the basis thereof.

In a particularly advantageous embodiment of the invention, in order to carry out this method it is provided that physical-technical influencing variables A (Tc); B (U), which influence the estimation temperature T _s , determine that at least one relative temperature Tc using the influencing variables A (Tc); B (U) is determined, which describes the thermal state of the compressor, that the influencing variables A (Tc); then to the cyclically previous value of the relative temperature Tc; B (U) are added and / or subtracted, so that the result of this calculation is a cyclically current value of the relative temperature Tc, which then calculates an estimated temperature T _s (Tc) of the compressor from this relative temperature Tc and the ambient temperature T «of the compressor which takes into account the heating and cooling behavior of the compressor, and that this cyclically determined estimation temperature T _s (Tc) finally for carrying out a limit value comparison with a lower and an upper temperature threshold value T _min ; T _{max is} used, on the basis of which the compressor operation is controlled.

The influencing variables U, which characterize the characteristic relative temperatures T in a temperature-increasing manner and are taken into account when carrying out the estimation method, include, for example, in addition to the ambient temperature T »of the compressor also the electrical voltage U _Kom p at the compressor and the back pressure P of the compression medium downstream of the compressor. With 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 U are incorporated into a heating function B (U) which describes the heating behavior of a specific compressor.

In contrast, in the method in question it is also expedient to use 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.

To carry out the calculation of a current value of the relative temperatures Tcu; Tcu suggests that from the last predetermined or calculated values of the relative temperatures Tci,; TC ₂ , M the current value of the cooling function A (Tc) is subtracted if the compressor is not in operation in the time interval under consideration, and the current value of the heating function B (U) is added if the compressor is in operation in the time interval under consideration. However, it is considered to be particularly advantageous to take the cooling function A (Tc) into account when calculating the relative temperature even during compressor operation, since the compressor naturally also emits heat to its surroundings in this operating mode.

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 (Tc) 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 (Tc) does not describe the absolute temperature of the compressor but the temperature difference compared to the temperature T »at the compressor installation location, this relative temperature T _s (Tc) can be initialized with the value zero at the beginning of the compressor control process after a long idle time of the compressor become. This procedure ensures that the temperature estimation method according to the invention delivers exactly the ambient temperature T "after a long cooling time. The rough structure of the control method according to the invention, as it is stored as software in a motor vehicle control device, for example, can be explained with the aid of the attached drawing. This shows a relative temperature module 2 in which the characteristic relative temperature Tc is stored and calculated which describes the thermal state of the compressor with sufficient accuracy. At short intervals, this relative temperature Tc, preferably two relative temperatures Tc ^ Tc ₂ , is recalculated cyclically, for example controlled by a clock generator.

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

In particular, when the compressor is in operation, it causes waste heat, which is recorded by the control device as relevant measured values via heating-specific influencing variables 7 and in a so-called heating module (working memory 5 in the control device) with the aid of a heating function B (U) stored there to a heating value are converted, which takes into account all those influencing factors in the sense of a physical model that increase the temperature of 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 a plus sign), so that a new relative temperature Tc results, which includes both cooling and all heating influence factors to be taken into account if necessary.

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

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

In an exemplary embodiment of the invention, the control step sequence of a specific control method is presented below, which follows the inventive idea and contains some of the advantageous developments of the invention. This process is characterized by the following process steps: a) determining the operating state of the compressor (on or off), b) measuring the back pressure P of the pressure medium downstream of the compressor and / or in the case of closed systems of the upstream pressure in front of the compressor, c) measuring the current one Operating voltage U _Kom p of the compressor, d) measuring or estimating the ambient temperature T »of the compressor, e) determining the validity of the influencing variables operating voltage Uκ _om p and back pressure P or the compressor inlet pressure (admission pressure), f) calculating the current value of the heating function B (U) using heating-specific influencing variables U, g) calculating the current value of the cooling function A (Tc) using the characteristic temperatures of the last time cycle, h) calculating the characteristic relative temperatures Tc ^ Tc ₂ by adding and / or subtracting the current values of the heating function B (U) and the cooling function action A (Tc), i) calculating the estimated temperature Ts (Tc) as a function of the characteristic relative temperatures Tci; Tc ₂ , and the ambient temperature T », j) comparison of the estimated temperature Ts (Tc) with predetermined temperature threshold values T _m j _n and T _max , where T _{min is} less than T _max , k) start enable if the estimated temperature Ts (Tc) is less than or equal to T _m j _n , or permission to continue operation for the compressor if the estimated temperature Ts (Tc) is less than the temperature value T _max , I) switching off the compressor if the estimated temperature Ts (Tc) is greater than or equal to the temperature value T _max , m) save the characteristic relative temperatures Tc ^ TC ₂ for use in the next calculation run, n) waiting until the next time cycle, and o) starting the next calculation run (step a).

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

The relative temperature Tc ^ Tc ₂ and the estimation temperature Ts (Tc) for a time step i are to be calculated according to the following equations:

With the compressor switched off

and when the compressor is switched on Tc, = TCM - A Ton + B Uι (Eq. 2)

as well as for the estimation temperature where the values A to C represent matrices with constant coefficients, which characterize the compressor and the compressor environment, in particular 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 _m j _n , the compressor can be switched on if the operating time of the compressor which lasts until the upper threshold value T _{max is reached is} sufficient is to promote a quantity of pressure medium that is sufficient to fill a compressed air reservoir to a certain pressure level and / or to fill air springs of a motor vehicle by a certain filling value.

In addition, it should be mentioned that if the functions A (Tc), B (U) and Ts (Tc) have a linear character, their parameters can easily be determined and / or identified directly from sensor measured values by numerical methods. It should also be mentioned that the model calculations performed showed very good results when two characteristic model temperatures or relative temperature Tc ^ Tc ₂ were used.

The special 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 from measurements using existing numerical methods, so that Control method can be inserted very well into existing motor vehicle control devices and that more precise damage temperatures can always be calculated compared to time-of-use methods according to the prior art, and as a result a higher availability of the compressor can be achieved. LIST OF REFERENCE NUMBERS

1 estimation temperature module

2 relative temperature module 3 holding element

4 cooling module

5 heating module

6 switches

7 Warming-specific influencing variables 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) heating function

U Influencing variables that influence the relative temperature T _{c to increase the} temperature

Uκomp compressor voltage

P Back pressure of the print medium Ts (Tc) Estimation temperature

T _max Upper temperature threshold

T _m in lower temperature threshold

T-- ambient temperature at the compressor i index

Claims

claims

1. A method for controlling the operation of a compressor, in which the compressor is switched off by a control device to avoid thermal damage when a temperature estimate T _S (T _C ) calculated by the latter exceeds an upper threshold value T _max , or remains switched on or is switched on when there is a need for compression, as well as when a lower threshold T _m i _{n is} undershot, characterized in that the temperature estimated value T _S (T _C ) of the compressor is indirectly and cyclically by means of the cooling and heating properties of the Compressor characteristic mathematical-physical model is determined.

2. The method according to claim 1, characterized in that physical-technical influencing variables A (Tc); B (U) can be determined, which influence the estimation temperature TS (T _C ) by changing that at least one relative temperature Tc ^ TC ₂ with the help of the influencing variables A (Tc); B (U) is determined, which describes the thermal state of the compressor, in addition to the cyclically previous value of the relative temperature Tc ^ Tc _2, the current influencing variables A (Tc); B (U) are added and / or subtracted, so that the result of this calculation is a current relative temperature Tc ^ Tc ₂ , which then results from this current relative temperature Tci; Tc ₂ and the ambient temperature T "of the compressor, a current estimation temperature T _s (Tc) is determined, which takes into account the heating and cooling behavior of the compressor, and that this cyclically determined estimation temperature T _S (T _C ) for carrying out a limit value comparison with a lower and an upper temperature threshold T _m j _n ; T _{max is} used, on the basis of which the compressor operation is controlled.

3. The method according to claim 1 or claim 2, characterized in that for the influencing variables U, among other variables, the electrical voltage U «omp at the compressor and the back pressure P of the compression medium downstream of the grain pressors and / or in closed systems the pre-pressure of the pressure medium at the inlet of the compressor.

4. The method according to claim 3, characterized in that the influencing variables U are included in a heating function B (U) which characterizes the heating behavior of a specific compressor.

5. The method according to claim 1 or claim 2, characterized in that the influencing variable A (Tc) represents a cooling function that takes into account the cooling properties of a specific compressor and its installation environment.

6. The method according to at least one of the preceding claims, characterized in that for calculating a current value of the relative temperatures Tcu; Tcu from the last specified or calculated values of the relative temperatures Tc _{1? M} ; Tc ₂ , ι-ι the value of the cooling function A (Tc) is subtracted if the compressor is not in operation or in operation in the time interval under consideration, and the value of a heating function B (U) is added if the compressor is in the time interval under consideration in Operation is.

7. The method according to at least one of the preceding claims, characterized in that the initial value of the relative temperatures Tc is selected such that the estimated temperature T _s (Tc) of the compressor corresponds to the value of the ambient temperature T »at the installation site of the compressor.

8. The method according to claim 8, 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.

9. The method according to at least one of the preceding claims, characterized by the following method steps: a) determining the operating state of the compressor (on or off), b) measuring the back pressure P of the Duck medium downstream behind the compressor and / or with closed systems the admission pressure upstream of the compressor, c) measuring the current operating voltage U "o _m p of the compressor, d) measuring or estimating the ambient temperature T" of the compressor, e) Determine the validity of the influencing variables operating voltage U _Ko m _P and back pressure P or the compressor inlet pressure (admission pressure), f) Calculate the current value of the heating function B (U) using heating-specific influencing variables U, g) Calculate the current value of the Cooling function A (Tc) using the characteristic temperatures of the last time cycle, h) calculating the characteristic relative temperatures Tc ^ Tc ₂ by adding and / or subtracting the current values of the heating function B (U) and the cooling function A (Tc), i) Calculate the estimated temperature Ts (Tc) as a function of the characteristic relative temperatures Tc ^ Tc ₂ , and the environment t temperature T "j) comparison of the estimated temperature Ts (Tc) with predetermined temperature threshold values T _m and T _max, where T _m i _n is less than T _max, k) start enable for the compressor if the estimated temperature Ts (Tc) is less than o - which is equal to the temperature value T _m ι _n , or permission to continue operating if the estimated temperature Ts (Tc) is less than the temperature value T _max I) switching off the compressor when the estimated temperature Ts (Tc) is greater than or equal to the temperature value T _max , m) storing the characteristic relative temperatures Tc ^ Tc ₂ for use in the next calculation run, n) waiting for the next time step, and o) starting the next calculation run (step a).

10. The method according to claim 10, characterized in that the validity of the measured variables operating voltage U _Kθm p and back pressure P or _upstream pressure are determined by multiplying these values by the value "one" when the compressor is in operation, or by the The value "zero" can be multiplied when the compressor is not in operation.

11. The method according to at least one of the preceding claims, characterized in that the relative temperatures Tq and Tq and the estimation temperature TsfTc) are calculated for a time step i according to the following equations:

with compressor switched off Td = Tc _M - A Tc _M (Eq. 1)

and when the compressor is switched on Tci = TCM - A TCM + B UI (Eq. 2)

as well as for the estimation temperature

Ts, = C Tc-, + T- (Eq. 3)

where the values A to C represent matrices with constant coefficients which characterize the compressor and the compressor environment, in particular with regard to their thermal properties.

12. The 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 Tmin, the compressor can be switched on if the operating time of the. Until the upper temperature threshold value T _{max is reached} Compressor is sufficient to convey a quantity of pressure medium that is sufficient to fill a compressed air reservoir to a certain pressure level and / or to fill air springs of a motor vehicle by a certain filling value.