EP2550455B1 - Method for regulating a compressor - Google Patents

Description

The invention relates to a method for controlling a compressor of a compressed air supply system, wherein the compressor is switched on and off depending on a determined by means of a temperature calculation method limit temperature of one or more components of the compressed air supply system, wherein the determination of the respective limit temperature for switching on or off the temperature calculation method is dependent on one or more of the system pressure, ambient temperature, and run time of the compressor.

Such methods for controlling compressors in motor vehicles are known and are intended to substantially avoid overheating of the devices due to overloading. A stronger heat development is z. As in a compressor for a vehicle with air suspension system during normal driving less fear, as usually done in this state, fewer level changes. In level changes in the state, with constant leveling due to manual operation or changing load, for fast off-road vehicles in the field, or even with a strong encapsulation of the compressor or compressor drive by insulating materials (noise damping), a stronger warming is not uncommon.

The DE 196 21 946 C1 discloses for this purpose an air suspension with a demand-dependent and intermittently operating in normal operation compressor, which is turned on and off by a control unit depending on the estimated temperature, wherein the estimated temperature is calculated as currently existing operating temperature. If the calculated "estimated temperature" exceeds a threshold value, the compressor is switched off.

This eliminates the need for any temperature sensors to monitor the compressor and therefore no additional signal inputs to the controller.

The disadvantage here is that even and just in the also disclosed with each new switching of the compressor provided jumpwise increase of the "estimated value" of the compressor with increasing temperature more frequently and within shorter time intervals on and off, without achieving the desired pressure increase in the system ,

From the EP 1 961 960 A2 a method for controlling a compressor is known in which a temperature is determined by means of a simulation or a model as a size, in dependence of which the compressor can be switched off, the size being determined as a function of an efficiency of the compressor. In addition to the efficiency, further parameters such as the ambient temperature, the backpressure, the operating voltage or the runtime of the compressor are taken into account for determining the temperature. For the variable "temperature", the temperatures of different components are used, for example a pressure valve, a piston ring or the electric motor. The disadvantage here, however, is that this control always considers only the temperature of a component in the simulation or the temperature model and thus the temperatures ignore other components.

In the case of vehicle level controls, the temperature limits for switching the compressor on and off are usually designed such that when the compressor is switched back on, a predefined level change can be carried out while the vehicle is fully loaded. However, a full load is not available in most cases, which unnecessarily limits the availability of the compressor.

The object of the invention is therefore to provide a method in which an overload or overheating of the compressor and or the compressor drive is particularly avoided and the availability of the compressor advantageously further increased, and in which it succeeds in all operating conditions, the necessary changes in the air flow in the system perform.

This object is achieved by the features of the main claim. Advantageous developments are contained in the subclaims.

In this case, the determination of the respective limit temperature for switching on or off, i. the on or off temperature of the compressor with the temperature calculation method depending on one or more of the parameters system pressure, ambient temperature and run time of the compressor.

According to the invention, the temperature of the component is determined by correlation between the adjacent components by heat transfer mutual Temperaurabhängigkeit existing.

As a heat transfer both heat dissipation and heat supply is understood, which can be done for example by radiation, convection or heat transfer. Correlation in this case means that the influence of mutual Heat transfer between neighboring components resulting increase in temperature of the considered component or the resultant by mutual heat dissipation between adjacent components temperature reduction of the considered component is included in its temperature calculation.

While previous practice has been to consider only individual component-dependent shutdown temperatures of a compressor, which were calculated by mathematical models on a controller in a pneumatic vehicle powered vehicle, it requires the further development of materials and components and changing the operating conditions, for more than just a critical component to define a shutdown temperature.

For example, the previous shutdown temperature of 180 ° C to protect the sleeve of the compressor piston in the past sufficient. The extension of the compressor run time required for some vehicles until reaching a switch-off temperature of 200 ° C necessitates the redefinition of a switch-off temperature taking into account further critical components of the electric motor and taking into account the sealing material.

Thus, while in the previous versions of the compressor as for a closed level control system only a shutdown temperature for the protection of the compressor was taken into account before thermal damage, the use of new components means that other components of the compressor, such as. the temperature of a brush bridge of the electric motor provided as the drive, the temperature of a arranged on a compressor piston sleeve or the temperature of a cylinder tube must also be taken into account so as not to damage the compressor prematurely.

The switch-off temperatures of 180 ° C and 200 ° C are exemplified here as a numerical value. These values may vary depending on the design and availability of the product Compressors fluctuate and are often higher in compressors for air suspension of trucks, namely between 220 ° C and 250 ° C.

Advantageously, the compressor is therefore switched on and off depending on the limit temperature of a piston sleeve of the compressor piston, wherein the temperature of the piston sleeve is determined by correlating the heat transfer existing mutual Temperaurabhängigkeit between the cylinder tube of the compressor and the piston sleeve.

If the maximum limit temperature is e.g. increased by 20K, it turns out, however, that in these circumstances, the cuff does not protect the cuff, i. is the critical component, but the O-rings that seal the compressor unit / compressor unit at different locations. Advantageously, then the compressor is switched on and off depending on the limit temperature of an O-ring of the compressor piston, wherein the temperature of the O-ring is determined by correlating the heat transfer existing mutual Temperaurabhängigkeit between the cylinder tube of the compressor and the O-ring.

In the test series of the invention often had different O-rings are exchanged. It was noticeable that the O-rings always failed when the cylinder tube temperature was above a temperature of 160 ° C for a certain time. Surprisingly, it was found in the further development of the previous temperature model that with a suitable correlation of the temperatures of individual components that influence each other by heat transfer, such as radiation, convection or heat transfer, a temperature for the cylinder head _interior T _{ZKI could} be determined that not only one damaging overheating of z. As the PTFE (polytetrafluoroethylene) existing cuff prevented, but also provided a temperature for the cylinder tube T _ZR at the same time to protect the thermally highly stressed O-ring from a temperature failure.

$$T_{\mathit{ZR},k}=f\left(T_{\mathit{ZKI},k-1}{T}_{\mathit{ZR},k-1}\right)$$

Namely, the mathematical description of the model has a "fully coupled" dependence of the two temperatures to be calculated. This also means that the temperatures currently to be calculated at time k depend on the temperatures that were previously calculated at time k-1. $$T_{\mathit{ZKI}.k}=f\left(T_{\mathit{ZKI}.k-1}{T}_{\mathit{ZR}.k-1}\right)$$

$$T_{\mathit{ZR}.k}=f\left(T_{\mathit{ZKI}.k-1}{T}_{\mathit{ZR}.k-1}\right)$$

If a preset temperature limit is reached, i.e. a "shutdown temperature" for a particular component, the compressor is shut down to allow the component to cool again.

The brush bridge of an electric motor of a compressor is nowadays a "temperature-critical" component, since at this point plastic material is now used. As a brush bridge, and brush holder, the component is called, which carries the carbon brushes / has, which are pressed by a spring as a sliding contact on the rotor of an electric motor.

Accordingly, also with respect to this component or to the electric motor to provide a further critical shutdown, which must be specified and stored as a limit and when they are reached during compressor operation, the compressor run is stopped. Thus, a further advantageous embodiment is that a driven by an electric motor compressor is switched on and off depending on the limit temperature of the brush bridge of the electric motor, wherein the temperature of the brush bridge under correlation of existing heat transfer mutual temperature dependence between the cylinder tube of the compressor and the brush bridge is determined.

With such a method, a simple optimization of the compressor operation can be carried out, so that after switching off the compressor and a subsequent cooling the "triggering" component, which can also be calculated as well as depending on the heat transfer between the individual components, the compressor is available as soon as possible again for a pending task.

A further advantageous development is that the critical temperature limit of the component is determined depending on an instantaneous driving condition. As a result, in special situations, a higher limit temperature can be set for specific tasks at short notice. Such a higher limit temperature may be necessary if it is to be left for a "temperature reserve". A typical case is e.g. automatic level control operations that have a higher priority than manual control operations.

Claims (6)

1. Method for regulating a compressor of a pressurized air supply system of a vehicle, wherein the compressor is switched on and off in dependence on a limit temperature of one or more components of the pressurized air supply system ascertained with the aid of a temperature calculation method, wherein the respective limit temperature for switching the compressor on or off is ascertained using the temperature calculation method in dependence on one or more of the parameters: system pressure, ambient temperature, and running time of the compressor, characterized in that the temperature of the component is ascertained by correlating the reciprocal temperature dependence existing as a result of heat transfer between adjacent components.
2. Method according to Claim 1, wherein the compressor is switched on and off in dependence on a limit temperature of one or more components of the compressor.
3. Method according to Claim 2, wherein a compressor driven by an electric motor is switched on and off in dependence on the limit temperature of a brush holder of the electric motor, the temperature of the brush holder being ascertained by correlating the reciprocal temperature dependence existing as a result of heat transfer between a cylinder tube of the compressor and the brush holder.
4. Method according to any one of Claims 1 to 3, wherein the compressor is switched on and off in dependence on the limit temperature of an O-ring of a compressor piston, the temperature of the O-ring being ascertained by correlating the reciprocal temperature dependence existing as a result of heat transfer between the cylinder tube of the compressor and the O-ring.
5. Method according to any one of Claims 1 to 4, wherein the compressor is switched on and off in dependence on the limit temperature of a piston sleeve of the compressor piston, the temperature of the piston sleeve being ascertained by correlating the reciprocal temperature dependence existing as a result of heat transfer between a cylinder tube of the compressor and the piston sleeve.
6. Method according to Claim 1 or 2, characterized in that the limit temperature is defined in dependence on an instantaneous driving state.