Patent Description:
The teachings of the present disclosure can be applied in heavy-duty vehicles, such as trucks, buses, construction equipment, trains and trams. Although the disclosure will mainly be described with respect to a heavy-duty vehicle, the general concept is not restricted to this particular vehicle, but may also be used in other vehicles such as cars.

Compressors are well known in vehicles and are installed for providing compressed air to various parts of the vehicles, such as to service brakes, parking brakes, air suspensions, trailers and pneumatic auxiliaries. Compressors suck atmospheric (ambient) air and increase the pressure of the air. Atmospheric air contains water vapour. The vapour contained in the atmospheric air is converted into liquid water (condensation) inside the compressor if the compressed air temperature (temperature of the air after compression) is below the so called pressure dew point (Tdpres), i.e. air dew point temperature after compression. When the compressed air temperature becomes strictly higher than Tdpres, liquid water (which was formed when compressed air temperature was below Tdpres) is vaporized and can be released from the compressor as vapour in air flow.

Some compressors are oil lubricated. Oil is used for lubrication, sealing and dissipation of the heat due to the compression process. If the compressor duty cycle is too low, the compressor will not have time to heat and the compressed air temperature will stay below Tdpres. Vapour condenses and is converted into liquid water that stays in the compressor. Liquid water accumulation inside the compressor can lead to corrosion of internal parts and compressor failure. In case of oil lubricated compressors, the liquid accumulation may lead to oil degradation.

In view of the above, it would thus be desirable to avoid liquid water accumulation inside the compressor. A control strategy could be to run the compressor for a predetermined time period in order to increase the chances of the compressed air temperature reaching and staying above Tdpres so that accumulated liquid inside the compressor is vaporized. However, such a control strategy has the disadvantage that if the predetermined time period is too short, then condensed liquid will remain inside the compressor, and if the predetermined time period is too long, then too much energy will be wasted. Thus, there is a need for a control strategy which counteracts liquid accumulation inside the compressor in an energy efficient manner.

<CIT> discloses an air compressor. An oil supply port supplies a lubricating oil to a compression chamber. An oil separator separates compressed air discharged from the compression chamber and the lubricating oil from each other. Oil temperature adjustment means adjusts temperature of the lubricating oil supplied to the oil supply port. Control means control the oil temperature adjustment means. Sucked-in air temperature detection means detecting temperature of the sucked-in air. Sucked-in air humidity detection means detecting humidity of the sucked-in air. The oil temperature adjustment means is controlled on the basis of detection information of the sucked-in air temperature detection means and of the sucked-in air humidity detection means.

<CIT> discloses an electronic control device for a component of compressed-air generation, compressed-air processing, compressed-air storage, and/or compressed-air distribution. The electronic control device falls back upon one or more models, which, as component-related models, contain information relevant to the structure, or the behavior of the component.

An object of the present disclosure is to provide a method which at least partly alleviates the drawbacks discussed above. This and other objects, which will become apparent in the following discussion, are achieved by a method as defined in the accompanying independent claim <NUM>. Some non-limiting exemplary embodiments are presented in the dependent claims.

The general concept is based on the realization that by monitoring the absolute humidity of the atmospheric (ambient) air entering the compressor as well as the absolute humidity of the compressed air exiting the compressor, it is possible to calculate a liquid water mass formed or evaporated inside the compressor, and to calculate how such formation or evaporation affects the cumulated liquid water mass inside the compressor. Hereby, it is possible to determine when the cumulated liquid water mass has returned to zero, and at that time allowing the compressor to be stopped (unless the compressor is still needed in case of compressed air request from the vehicle, in which case the compressor may continue to run). Thus, by monitoring the development of the cumulated liquid water mass, it is possible to stop the compressor in a timely manner without unnecessary energy consumption. In other words, the compressor may run for a long enough time to evaporate the cumulated liquid water mass inside the compressor, and a short enough time to avoid wasting energy.

According to a first aspect of the present disclosure, there is provided a method of controlling an air compressor of a vehicle, comprising:.

By repeatedly calculating the liquid water mass inside the compressor, it will be possible to determine that the cumulated liquid water mass has returned to zero, i.e. that water formed in the compressor has evaporated. Thus, if there is no demand from other parts of the vehicle for the compressor to provide compressed air, the compressor may be stopped when the zero liquid water mass has been acknowledged. In this way the compressor does not need to run longer than necessary for achieving the evaporation, while still making sure that the compressor has run long enough for the evaporation to have occurred. Of course, it should be understood that if other parts of the vehicle are still in need of compressed air from the compressor, and therefore the control unit still receives such compressed air request, the compressor will not be stopped even though the cumulated liquid water mass is zero.

The compressor will oftentimes be started after the control unit receives a compressed air request, however, as will be explained below, in certain situations the compressor may be started without the control unit receiving a compressed air request. This may be the case, for example, when the vehicle has been turned off and parked before all condensed water has been evaporated from the compressor. In such case, next time the vehicle is started, the control unit will know that there remains cumulated liquid water mass inside the compressor, and may restart the compressor in order to evaporate the cumulated liquid water mass. In other instance, the case may be that the ambient temperature is at such level that the Tdpres cannot be reached. In such case, the control unit may turn off the compressor as soon as no compressed air request is received, and when temperature conditions are such that Tdpres can be reached, the control unit may restart the compressor to evaporate the condensed liquid water inside the compressor.

The method according to the present disclosure may suitably be a computer-implemented method. Suitably, the implementation may be embodied in a control unit, such as the above-discussed control unit.

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where it includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

According to at least one exemplary embodiment, said formation or evaporation of liquid water mass is calculated for a series of consecutive periods of time, wherein the start of a next period of time in said series coincides with the end of the previous period of time in said series, wherein the cumulated liquid water mass inside the compressor is calculated by summarizing the calculation for said series of consecutive periods of time.

By doing the calculations "back-to-back" for consecutive periods of time, no formation or evaporation of liquid is overlooked, nor is any formation or evaporation calculated twice. As a consequence, a high accuracy is attainable for the repeated calculation of the cumulated liquid water mass.

According to at least one exemplary embodiment, the method comprises storing the most recently calculated value of the cumulated liquid water mass in an electronic memory. This is advantageous as it not only allows facilitates updating when the compressor is running and new calculations are made, but also in case the cumulated liquid has not been evaporated since the last time the compressor was stopped, for whichever reason. An example of such a reason will be discussed below. The electronic memory may suitably be accessible by the control unit, either in the form of an internal memory in the control unit or an external memory with which the control unit can communicate by wire or wirelessly.

According to at least one exemplary embodiment, the method comprises, when the vehicle is turned on after having been turned off:.

Thus, by having stored in the electronic memory the cumulated liquid water mass until the vehicle was turned off, the calculations and updating may continue when the vehicle is turned on again and the compressor is restarted.

Similarly to the previous example of restarting the compressor when the vehicle has been turned off, in at least some other exemplary embodiments, the method comprises, when the compressor has been stopped before the cumulated liquid water mass has returned to zero:.

This exemplary embodiment reflects a situation in which the control unit may determine that the compressor will, under the present conditions, not be able to evaporate the condensed liquid water inside the compressor, and therefore stops the compressor when there is no compressed air request from other parts of the vehicle. Hereby, it can be avoided that the cumulated liquid water mass keeps increasing even when there is no compressed air request. When the control unit determined that the conditions are again favourable for evaporation, the control unit may once again start the compressor and calculate the change in cumulated liquid water mass in accordance with the above described control strategy.

According to at least one exemplary embodiment, said step of calculating a liquid water mass formed or evaporated inside the compressor for a defined period of time comprises determining the flow rate through the compressor for said defined period of time, wherein the formed or evaporated liquid water mass is calculated based on the determined flow rate during the defined period of time. For instance, in a simplified case, if the values Habs,atm and Habs,comp are constant and the flow rate Q is constant, then the liquid water mass during a time t, can simply be calculated as: <MAT>.

If the result is positive, this mass is liquid water mass formed.

If the result is negative, this mass is liquid water mass vaporized into vapour.

According to at least one exemplary embodiment, the liquid water mass formed or evaporated in the compressor for said defined period of time is calculated using the formula: <MAT> where.

The calculations may suitably be made by the control unit.

According to at least one exemplary embodiment, the cumulated liquid water mass at time tn is calculated using the formula: <MAT> Where.

According to at least one exemplary embodiment, the step of determining the flow rate comprises measuring the compressor speed and determining the flow rate based on the measured compressor speed. This is a convenient way to determine the flow rate as the compressor speed is generally easily acquired and known from the compressor itself (a compressor ECU may generally be sending its actual speed via a CAN bus).

According to at least one exemplary embodiment, said step of determining the value Habs,atm of the absolute humidity for the atmospheric air entering the compressor, comprises:.

Additionally, the determination of the value Habs,atm may suitably also be based on the atmospheric pressure.

In at least some exemplary embodiments, instead of using a humidity sensor, an alternative is to estimate the relative humidity. For instance, the relative humidity may instead be estimated. In other exemplary embodiments, instead of making an estimation, the relative humidity may simply be determined to be <NUM>%, thereby applying a worst case scenario for determining the absolute humidity for the atmospheric air.

According to at least one exemplary embodiment, said steps of determining the value Habs,atm further comprises:.

This provides a simple way to estimate that atmospheric pressure for determining the value Habs,atm. However, as indicated previously, an alternative is to use a pressure sensor, and another alternative is to use <NUM> bar as the value of the atmospheric air pressure when determining the value Habs,atm of the absolute humidity for the atmospheric air.

According to at least one exemplary embodiment, said step of determining the value Habs,comp of the absolute humidity for the compressed air exiting the compressor, comprises.

According to at least one exemplary embodiment, the second temperature sensor is placed in the coldest area of the compressor. This is advantageous since the coldest area presents the highest risk of condensation. However, if it is not practically possibly to place the second temperature sensor in the coldest area of the compressor, for example because of limitations due to the design of the compressor, a delta temperature ΔT may be taken between the measured temperature with the second sensor and the temperature used for calculation so that the coldest area is covered in the calculations.

So, Tca/culation = Tmeasured - ΔT. The selected value of ΔT depends on the actual location of the second temperature sensor and should be defined to cover the coldest area of the compressor.

According to at least one exemplary embodiment, the method comprises:.

This is advantageous as it avoids unnecessary power consumption. Thus, the above exemplified embodiment not only allows the compressor to stop in time, i.e. not running the compressor when no longer needed for evaporating the condense liquid water, but also finds a balance for the actual evaporation process so that the temperature increase is at an energy efficient pace.

All references to "a/an/the part, element, apparatus, component, arrangement, device, means, step, etc." are to be interpreted openly as referring to at least one instance of the part, element, apparatus, component, arrangement, device, means, step, etc., unless explicitly stated otherwise.

The embodiments are provided by way of example so that this disclosure will be thorough and complete.

<FIG> illustrates a vehicle <NUM> according to at least one exemplary embodiment, for which the method of the present disclosure may be implemented. In this example, the vehicle <NUM> is a heavy-duty vehicle in the form of a tractor unit. However, the teachings of the present disclosure may also be implemented in other types of vehicles which use an air compressor for providing compressed air to various other parts of the vehicle.

<FIG> illustrates schematically an example of components that may be used for carrying out the method of the present disclosure. An air compressor <NUM> is provided for sucking ambient air <NUM> and to increase the pressure of the air. Compressed air <NUM> leaves the compressor <NUM> and may be provided to other parts of the vehicle, such as to a service brake, a parking brake, air suspensions, a connected trailer, auxiliaries, etc. The compressor <NUM> may be operated in response to control signals <NUM> from a control unit <NUM>. Thus, the control unit <NUM> controls the operation of the compressor <NUM>. The control unit <NUM> can turn the compressor <NUM> on and off. Furthermore, the control unit <NUM> can control the rotational speed of the compressor <NUM>. The control unit <NUM> may be used for implementing the method of this disclosure. As such, the method of the present disclosure may be a computer-implemented method performed by the control unit <NUM>. The control unit <NUM> may receive various sensor signals <NUM> from different sensors <NUM> and may process the sensor signals <NUM> to determine appropriate controlling of the air compressor <NUM>. Furthermore, the control unit <NUM> may receive request signals <NUM> from various other parts or subsystems of the vehicle that demand compressed air to be provided from the compressor <NUM>. In the present illustration a pressurized air tank <NUM> is illustrated as sending a request signal <NUM> to the control unit <NUM>. For instance, the tank <NUM> may act as a storage for pressurized air to be distributed to other components, and when the pressure is low, a request signal <NUM> may be sent to the control unit <NUM>. However, it is conceivable to allow the control unit <NUM> to receive request signals <NUM> from other parts of the vehicle as well. Furthermore, although three sensors <NUM> are illustrated, it should be understood that this is just made for explanatory purposes, and it should be understood that the specific number of sensors <NUM> may be varied according to the desired implementation of the method disclosed in here and its various exemplary embodiments. Examples of sensors <NUM> include temperature sensors, humidity sensors, pressure sensors, flow sensors, etc. Further details of the control unit <NUM> will be briefly discussed later in connection with <FIG>.

<FIG> illustrates schematically a method <NUM> in accordance with at least one exemplary embodiment of the present disclosure. More specifically, <FIG> illustrates a method <NUM> of controlling an air compressor of a vehicle. The method <NUM> comprises:.

Step <NUM> may, for instance, be initiated by a compressed air request from another part of the vehicle. For example, as illustrated in <FIG>, the compressed air request may come as a request signal <NUM> from a tank <NUM>. However, Step <NUM> may also be initiated if the control unit knows that there is condensed liquid in the compressor, i.e. without a compressed air request having been received. For instance, the control unit may access an electronic memory which stored the latest calculated cumulated liquid water mass before the compressor was shut off. The fact that the compressor was shut off before all liquid had evaporated may be because the vehicle was turned off, or it may be because there was no compressed air request and that the conditions were not adequate for enabling the compressed air temperature to exceed the pressure dew point (Tdpres).

Steps <NUM> and <NUM>, i.e. determining the absolute humidity of the atmospheric air (Habs,atm) and the absolute humidity of the compressed air (Habs,comp) may be accomplished by using the following general method to calculate absolute humidity Habs [g/m<NUM>]:.

A first temperature sensor may be used to measure the temperature of the atmospheric air, for determining/calculating the absolute humidity of the atmospheric air. A second temperature sensor provided inside the compressor may be used to measure a temperature of the compressed air, the for determining/calculating the absolute humidity of the compressed air.

RH is the relative humidity of the atmospheric air. This may, for instance, be measured by means of a humidity sensor.

Continuing with the method of <FIG>, the step S4, i.e. calculating by means of a control unit a liquid water mass formed or evaporated inside the compressor during a defined period of time, may be accomplished by using the below formula, which has already been discussed and explained previously in this disclosure.

As the compressor is running the above determinations/calculations are repeated (step S5) and the cumulated liquid water mass is calculated in connection with each repetition (step S6). The cumulated liquid water mass may be calculated by using the below formula, which has already been discussed and explained previously in this disclosure.

When the sum of the above formula results in zero, and the control unit (e.g. the control unit in <FIG>) does not receive a compressed air request, then in accordance with step S7, the control unit may stop the compressor.

<FIG> illustrates schematically a graphical representation of the implementation of at least one exemplary embodiment of the method of the present disclosure. The solid black line shows how the compressor air temperature increases after the compressor has been started (i.e. at time zero). The dotted line shows the pressure dew point temperature (Tdpres), which in this example is approximately <NUM>. After compression, if the compressed air temperature is below Tdpres, air becomes saturated (RH = <NUM>%). In other words, as long as the compressed air temperature is below Tdpres, the water vapour in the air condenses into liquid water inside the compressor. However, when the compressed air temperature exceeds Tdpres, then the liquid water inside the compressor is vaporized and can be released from the compressor as vapour in the air flow. In the example in <FIG>, the solid line representing the compressed air temperature crosses the dotted line representing Tdpres at approximately <NUM>. When this happens, the dashed line, representing the cumulated liquid water mass, turns downwardly, i.e. the cumulated liquid water mass is steadily decreased as the liquid water evaporates. As indicated by the arrow, at approximately <NUM>, the cumulated liquid water mass has returned to zero. Unless the control unit still receives a compressed air request, it can now stop the compressor. Hereby, the liquid water has been successfully evaporated without running the compressor for longer than necessary, thereby saving energy.

In at least some exemplary embodiments, the control unit may suitably calculate the pressure dew point Tdpres when starting the compressor. This may be based on ambient air temperature, relative humidity, ambient air pressure and compressed air pressure. Furthermore, the control unit may know, or may determine, the maximum temperature, Tmax, that can be reached uniformly and steadily by the air during the compression in the compressor.

If Tmax > Tdepres, then the control unit may control the compressor according to the above control strategy.

However, if Tmax ≤ Tdepres, then there are two different cases, which will here be referred to as Case <NUM> and Case <NUM>.

Case <NUM>: Actual relative humidity is known from humidity sensor or other means, (the control strategy of Case <NUM> can also be used if worst case <NUM>% RH is assumed).

If Tmax ≤ Tdepres, this means that no matter for how long time the compressor is running, the compressed air temperature will never exceed Tdpres, so there is no possibility to evaporate liquid water and condensation will occur during all the time that the compressor is running. In this case, the control unit may suitably limit the running time of the compressor to what is needed by the vehicle, and avoid any extra time, as Tdpres cannot be passed and condensation is occurring. Thus, the control unit may suitably stop the compressor when the vehicle no longer needs any more compressed air, i.e. no compress air request received. Accordingly, in this Case <NUM>, the control unit stops the compressor even though there is liquid water, simply because not stopping the compressor would increase the accumulation of liquid water.

The control unit may store in an electronic memory the cumulated liquid water mass that was created during this running phase when Tmax ≤ Tdepres. The liquid water mass may then be eliminated the next time conditions allow to have compressed air temperature greater than the pressure dew point temperature, i.e. when conditions allow Tmax > Tdepres and evaporation can occur. The compressor may be restarted to evaporate liquid water either during vehicle needs or whenever the conditions (such as relative humidity, ambient temperature) are such that Tmax > Tdepres.

Case <NUM>: Actual relative humidity is not known, and worst case scenario is assumed, i.e. <NUM>% RH. In this case the control unit may calculates the pressure dew point for worst case <NUM>% RH, Tdpres_100.

If Tmax < Tdpres_100 this means that no matter for how long time the compressor is running, the air temperature will never reach the dew point Tdpres_100 and therefore there is no possibility to evaporate liquid water inside the compressor and condensation will continue as long as the compressor is running. However, this is the worst case scenario and since the actual relative humidity (RH) is not known, the actual RH may be lower than <NUM>%.

In this case the control unit may base the anti-condensation function on the max Tdpres that can be reached by the compressor with Tdpres_max = Tmax - ΔT (where ΔT is strictly positive, e.g. <NUM>).

From Tdpres_max and the below equations and the above equations [(<NUM>) → (<NUM>) → (<NUM>) → (<NUM>) → (<NUM>)], the control unit can calculate the RH corresponding to Tdpres_max and base the ant-condensation function on this RHmax.

<MAT> where A, m and Tn are constants for calculating the dew point temperature over different temperature ranges and are listed in commercially available lookup tables.

The control unit stops the compressor when the cumulated liquid water mass (Tdepress_max; RHmax) = <NUM>. This allows to cover and avoid condensation in cases where the actual RH ≤ RHmax and actual Tdpres ≤ Tdpres_max.

In parallel, the control unit may calculate and keep in memory the cumulated liquid water mass (Tdpres_100; <NUM>%RH) as well as RHmax and the date and time that this occurs. The cumulated liquid water mass (Tdpres_100; <NUM>%RH) is incremented each time Tmax < Tdpres_100, and if it reaches a defined maximum value, the control unit can warn the driver/user with a message. The driver/user can check actual RH and reset the cumulated liquid water mass (Tdpres_100; <NUM>%RH) if actual RH < Hmax, or drain and exchange compressor oil if actual RH > RHmax.

<FIG> schematically illustrates a control unit <NUM> according to at least one exemplary embodiment of the present disclosure. In particular, <FIG> illustrates, in terms of a number of functional units, the components of a control unit <NUM> according to exemplary embodiments of the discussions herein. The control unit <NUM> may be comprised in any vehicle disclosed herein, such as the one illustrated in <FIG>, and others discussed above. Processing circuitry <NUM> may be provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium <NUM>. The processing circuitry <NUM> may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.

Particularly, the processing circuitry <NUM> is configured to cause the control unit <NUM> to perform a set of operations, or steps, such as the method discussed in connection to <FIG>, and exemplary embodiments thereof discussed throughout this disclosure. Thus, the processing circuitry <NUM> is thereby arranged to execute exemplary methods as herein disclosed.

The control unit <NUM> may further comprise an interface <NUM> for communications with at least one external device such as the compressor <NUM>, the sensors <NUM> and the tank <NUM> discussed herein. As such, the interface <NUM> may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication.

Claim 1:
A method (<NUM>) of controlling an air compressor (<NUM>) of a vehicle (<NUM>), comprising:
- starting (S1) the compressor,
- at the time of starting the compressor:
- determining (S2) , for the atmospheric air (<NUM>) entering the compressor, a value Habs,atm of the absolute humidity,
- determining (S3), for the compressed air (<NUM>) exiting the compressor, a value Habs,comp of the absolute humidity,
- based on the determined values Habs,atm and Habs,comp, calculating (S4) by means of a control unit (<NUM>) a liquid water mass formed or evaporated inside the compressor during a defined period of time,
- repeatedly performing (S5) the determining steps and the calculating step,
- for each repetition, calculating (S6) by means of the control unit a cumulated liquid water mass inside the compressor, and
- stopping (S7) the compressor when the calculated cumulated liquid water mass has returned to zero and the control unit no longer receives a compressed air request.