Patent Grant
9347717
This application is based upon and claims the benefit of priority from prior German Patent Application No. 10 2012 206 119.3, filed Apr. 13, 2012, the entire contents of which
are incorporated herein by reference in their entirety.
The invention relates to a method for operating a circuit having a heat accumulator, in particular as per the method for operating a circuit having a heat accumulator, having a coolant circuit, having a heat accumulator in a line of the circuit and having at least one valve and one pump, wherein, when the valve is open, the heat accumulator can be charged with coolant from the coolant circuit by means of the pump, or coolant can be discharged from the heat accumulator into the coolant circuit, wherein the charging or discharging of the heat accumulator takes place in an open-loop-controlled or closed-loop-controlled manner as a function of a temperature of the coolant in the circuit and/or a temperature of the coolant in the heat accumulator and/or a temperature difference therebetween and/or in a time-dependent manner.
In motor vehicles, the fuel consumption of an internal combustion engine is generally also dependent on the operating temperature of the internal combustion engine, or the temperature of the coolant. Here, the operating temperature of the coolant is generally between 80° C. and 110° C. In the time taken for the operating temperature to be reached, also referred to as the warm-up phase, the fuel consumption is, for various reasons, increased in relation to the fuel consumption when the engine is at operating temperature. One reason for this is the increased friction of all the moving parts of the internal combustion engine itself, and the friction of the components of the entire drivetrain of the motor vehicle. The initially cold combustion environment in the cylinder head however also adversely influences the fuel consumption.
The heat energy stored in the mass of the engine during the operation of the internal combustion engine, which heat energy is at a very high temperature level, is lost during the time period in which the internal combustion engine is shut down. Here, the main effect responsible for the heat energy loss is free convection.
One known measure is the provision of a heat accumulator in which thermal energy is stored in the form of warm liquid which can be supplied to the circuit again when required.
DE 103 44 018 A1 describes a method for the filling and emptying of a device for storing hot cooling liquid for the purpose of shortening the warm-up phase of an internal combustion engine. Here, all of the coolant from the circuit is pumped into a hot-water accumulator and stored there, wherein the coolant is pumped back into the circuit when required. As a result of the improved thermal insulation in the hot-water accumulator, the coolant does not cool down as quickly, such that it can be pumped back into the circuit in a warmer state than it would be in if it remained in the circuit. This leads to a faster warm-up of the internal combustion engine, such that the warm-up phase is reduced. Here, however, the energy stored in the mass of the engine is lost and is not available for a later engine start or warm-up and thus for a possible reduction of the time of the warm-up. It is thus necessary for fuel to be expended again for the warm-up, and increased fuel consumption is encountered during the warm-up phase.
In the method specified in DE 103 44 018 A1, an exchange of the fluid between the internal combustion engine and heat accumulator is provided. As a result of the extraction for example of the coolant from the engine, problems arise with regard to corrosion in the coolant jacket of the engine. Also, upon the starting of the engine, relatively fast refilling of the engine is required in order to avoid local component overheating. The ventilation, required for this purpose, of the engine coolant jacket is not solved.
The problem addressed by the invention is that of providing a method for operating a circuit having a heat accumulator, which ensures an improved yield of the thermal energy of the coolant than in the prior art. Here, it is particularly advantageous for the duration of the warm-up of the internal combustion engine to be further reduced in order to be able to operate the internal combustion engine more efficiently and, in the process, reduce fuel consumption and wear.
This is achieved by means of the features of a method for operating a circuit having a heat accumulator, having a coolant circuit, having a heat accumulator in a line of the circuit and having at least one valve and one pump, wherein, when the valve is open, the heat accumulator can be charged with coolant from the coolant circuit by means of the pump, or coolant can be discharged from the heat accumulator into the coolant circuit, wherein the charging or discharging of the heat accumulator takes place in an open-loop-controlled or closed-loop-controlled manner as a function of a temperature of the coolant in the circuit and/or a temperature of the coolant in the heat accumulator and/or a temperature difference therebetween and/or in a time-dependent manner.
A method according to the invention advantageously provides a method for operating a circuit having a heat accumulator, having a coolant circuit, having a heat accumulator in a line of the circuit and having at least one valve and one pump, wherein, when the valve is open, the heat accumulator can be charged with coolant from the coolant circuit by means of the pump, or coolant can be discharged from the heat accumulator into the coolant circuit, wherein the charging or discharging of the heat accumulator takes place in an open-loop-controlled or closed-loop-controlled manner as a function of a temperature of the coolant in the circuit and/or a temperature of the coolant in the heat accumulator and/or a temperature difference therebetween and/or in a time-dependent manner.
Here, it is advantageous for the temperature of the coolant in the coolant circuit to be a coolant temperature in the internal combustion engine or at the inlet or outlet of the internal combustion engine.
It is also advantageous for the temperature of the coolant in the heat accumulator to be a coolant temperature in the heat accumulator or at the inlet or outlet of the heat accumulator.
According to the invention, it is expedient for discharging of the heat accumulator into the cooling circuit to take place when the temperature of the coolant in the heat accumulator exceeds the temperature of the coolant in the cooling circuit by a first predefinable value.
It is also advantageous for discharging of the heat accumulator into the cooling circuit to take place in a time-dependent manner in a predefinable chronological sequence, or in a manner dependent on the most recent charging process and/or on the coolant temperature in the circuit.
It is also advantageous for the discharging of the heat accumulator into the cooling circuit to be ended when the temperature of the coolant in the heat accumulator exceeds the temperature of the coolant in the cooling circuit by less than a second predefinable value.
It is advantageous for discharging of the heat accumulator to take place only once or multiple times per driving cycle. If only one discharge is permitted per cycle, it is achieved that the coolant temperature is at its highest at the end of a driving cycle. If discharging is performed multiple times in the cycle, the coolant temperature can be optimized during the cycle.
It is also expedient for charging of the heat accumulator from the cooling circuit to take place when the temperature of the coolant in the cooling circuit exceeds the temperature of the coolant in the heat accumulator by a first predefinable value or the temperature of the coolant has reached a first predefinable value and/or in a time-dependent manner.
It is also advantageous for the temperature of the predefinable value to increase from one charging process to the next, preferably by 5 K or 10 K after each charging process.
It is also advantageous for the charging of the heat accumulator from the cooling circuit to be ended when the temperature of the coolant in the cooling circuit exceeds the temperature of the coolant in the heat accumulator by less than a second predefinable value or a predefinable time duration for the charging process has expired.
It is furthermore expedient for the charging of the heat accumulator from the cooling circuit to be ended when the temperature of the coolant in the cooling circuit exceeds the temperature of the coolant in the heat accumulator by less than a second predefinable value or a predefinable time duration for the charging process has expired.
It is also advantageous for charging of the heat accumulator to take place only when the coolant temperature in the cooling circuit has exceeded a predefinable threshold value. The threshold value is advantageously 60° C. or higher.
It is also advantageous for charging of the heat accumulator to take place as a function of the temperature difference of the coolant temperature in the cooling circuit minus the temperature of the coolant in the heat accumulator or as a function of the absolute value of the temperature of the coolant in the cooling circuit, wherein the charging also takes place multiple times per driving cycle. Here, open-loop control may be performed as a function of the temperature, such that activation takes place at predefinable temperatures, such as for example 60° C., 70° C., 80° C., 90° C., etc. It is also possible for smaller or greater temperature intervals to be selected, such as 60° C., 65° C., 70° C., etc, or 60° C., 75° C., 90° C., etc. It is for example possible for 60° C. to be selected as a starting value and for further charging to then take place at the starting value plus ΔT, where ΔT=5° C., 7.5° C., 10° C. or 15° C. or more.
It is also advantageous for no discharging of the heat accumulator to take place in overrun operation phases of the internal combustion engine of the vehicle.
By means of the method according to the invention, it is possible to achieve a reduction of the CO2 emissions and a reduction in fuel consumption.
As a result of the pre-heating of the internal combustion engine, specifically of the cylinder head or of the combustion chamber, a decrease in CO2 emissions is achieved as a result of the reduced heat dissipation into the internal combustion engine owing to the thermal mass and as a result of the reduction of friction losses.
It is also possible to achieve a reduction of untreated emissions during a cold start. As a result of a pre-heated combustion chamber, less untreated emissions (HC, CO, NOx, . . . ) are generated during a cold start of the engine.
It is also possible to attain an increase in comfort. The stored thermal energy permits a more spontaneous response of the vehicle heating arrangement, and an increased heating power as a result of the temperature increase during the warm-up phase. In vehicles with a start-stop function, stop phases can be bridged without a loss of heating comfort. Further advantageous refinements are described in the following description of the figures and in the subclaims.
The invention will be explained in more detail below on the basis of at least one exemplary embodiment and with reference to the drawings, in which:
If the coolant flows through the line 9 to the thermostat 10, said thermostat 10 can perform the distribution of the coolant either to the coolant cooler 12 via line 13 or to the bypass 14. Downstream of the coolant cooler 12, the coolant flows again through the line 15 to the merging point 16 with the bypass 14, and from there through the line 17 back to the pump 4.
If the valve 11 is open, coolant can also flow into the heat accumulator 2. This preferably takes place when the thermostat 10 closes the line 9. The coolant stored in the heat accumulator can also be pumped out of said accumulator again when the line 14 is opened by the thermostat and the pump 4 then pumps the coolant out.
Here,
For efficient operation of a heat accumulator 2, it is advantageous for the thermodynamic characteristics thereof and/or the thermodynamic characteristics of the cooling circuit 1 to be taken into consideration. Furthermore, it is advantageous for the effects of the heat accumulator 2 on the cooling circuit 1 and/or the effects of the cooling circuit 1 on the heat accumulator 2 to be taken into consideration in a suitable manner.
For open-loop or closed-loop control, a unit 21 is provided which receives and processes the sensor signals from the temperature sensors 19, 20 at the inlet and/or outlet of the heat accumulator 2 in order to activate the valves 10, 11 and, if appropriate, activate the pump 4. The open-loop control unit 21 can also receive external signals 22, such as a temperature of the coolant in the internal combustion engine, via a data bus or in some other way.
Here, an operating method for the heat accumulator 2 in a cooling circuit 1 can advantageously be divided into phases, wherein said operating method can advantageously be divided into three phases. In other exemplary embodiments, the definition and number of the phases may also differ.
A first phase is the charging phase:
in the charging phase, warm or hot coolant is stored in the heat accumulator 2.
A first charging process is started when a minimum coolant temperature Tmin, which is optionally a function of the ambient temperature Tmin=f(Toutside), is reached in the cooling circuit 1 or in the internal combustion engine 2. For this purpose, coolant is preferably pumped or conducted by means of the pump 4 into the heat accumulator 2 via the open valve 11. That is to say, up to a certain coolant temperature Tmin, flow does not pass through the coolant path 18 in which the heat accumulator 2 is arranged. The valve 11 is opened only at temperatures above Tmin, that is to say when the minimum coolant temperature required has been reached.
The charging process, that is to say the filling of the heat accumulator 2 with at least warm coolant, may preferably be open-loop-controlled in a time-dependent manner. The charging may also be closed-loop-controlled in a temperature-dependent manner. For the open-loop control or closed-loop control of the charging, it is therefore advantageous in any case for the coolant temperature of the internal combustion engine to be known. Said coolant temperature can preferably be measured by means of a sensor or read out from open-loop control units which have already detected or determined said temperature or to which data are provided via a data bus, for example the CAN bus.
The time-dependent charging of the heat accumulator takes place as a function of the fill volume of the heat accumulator VWSP plus the dead volume Vdead in the hoses and also as a function of the coolant volume flow per unit of time into the heat accumulator. Since the physical relationships between coolant volume and coolant volume flow change only slightly with coolant temperature and ambient temperature, the charging process can be performed on the basis of only one item of temperature information. The item of temperature information regarding the coolant temperature may be used from a coolant temperature sensor for example of the internal combustion engine.
Here, the following definitions apply:
TKM is the coolant temperature (of the internal combustion engine).
tCharging is the charging time, that is to say the time taken for the heat accumulator to be completely charged starting from an unfilled heat accumulator.
VTotal=VWSP+Vdead−total volume=volume of the heat accumulator+dead volume (hoses)
To store the highest possible coolant temperature in the heat accumulator, the charging process is repeated when predefined temperature levels are reached. For example, the charging process may take place when further temperature intervals T=Tmin+ΔT are reached, wherein ΔT may for example be a predefinable value of 5 K, 7.5 K or 10 K, until the operating temperature of the internal combustion engine and thus the operating temperature TOperating of the coolant has been reached. Here, Tmin is advantageously 60° C. or higher.
Furthermore when a predefinable average speed of the vehicle is undershot, the frequency of the charging may be increased, such that for example ΔT is reduced from 10 K to 5 K or from 5 K to 3 K. This results in more frequent charging of the heat accumulator 2.
For a charging of the heat accumulator in the closed-loop control method, the charging may however also be performed in a temperature-dependent manner as a function of the coolant temperature TKM.
The start signal for the charging comes from the coolant temperature TKM of the internal combustion engine. The charging process starts when the coolant temperature in the heat accumulator TWSP lies in a predefinable range of for example 5 K to 10 K below the coolant temperature TKM of the internal combustion engine.
The charging process continues until the temperature difference between the coolant entering and exiting the heat accumulator falls below a predefinable threshold value of for example 3 K.
To store the highest possible coolant temperature TWSP in the heat accumulator, the charging process is started again as a function of the most recently encountered coolant temperature TKM with a defined hysteresis, that is to say a temperature offset (TOffset). For example, for the activation of the next charging process, a coolant temperature may have been reached which is 6K higher than that in the case of the most recent charging process. This means that, if the most recent charging process took place at TKM=70° C., the next charging process will take place at TKM=76° C. This is however expedient only when the coolant temperature is rising. This can be identified if the gradient of the coolant temperature is evaluated as a time-dependent function.
The charging process is ended when the temperature difference between the inlet temperature and the outlet temperature falls below the threshold value TThreshold of for example 3 K. The charging process is repeated until the operating temperature TOperating of the internal combustion engine reaches a predefinable value in the range from 80 to 110° C.
This means that the difference in temperature in the heat accumulator is the difference of the coolant temperature at the heat accumulator inlet minus the coolant temperature at the heat accumulator outlet.
A second phase is the discharging:
During the discharging, warm or hot coolant is discharged from the heat accumulator 2 into the cooling circuit 1.
During a driving cycle, it is advantageously the case that only one discharging process is performed, said discharging process being carried out, in the open-loop-controlled version, in a time-dependent and if appropriate time-dependent and parameterizable manner. Here, time-dependent and parameterizable means that the time dependency can be varied by means of parameters.
In the closed-loop-controlled method variant, the discharging may take place in a temperature-dependent manner.
A first discharging process is started when the coolant temperature of the cooling circuit or of the internal combustion engine is considerably lower than the coolant temperature in the heat accumulator.
The time-dependent discharging takes place as a function of the fill volume of the coolant volume, which is to be exchanged, of the respective cooling circuit, as a function of the available coolant volume of the heat accumulator, and as a function of the coolant volume flow. Since the physical relationships between coolant volume and coolant volume flow vary only slightly with coolant temperature and ambient temperature, the discharging process can be performed in a time-dependent manner on the basis of only one item of temperature information.
A first discharging process is started when the coolant temperature of the cooling circuit or of the internal combustion engine is considerably lower than the coolant temperature prevailing in the heat accumulator. Here, a required temperature difference of for example 5 K to 10 K may be taken as a basis.
The first discharging process of the heat accumulator preferably takes place before the starting of the internal combustion engine after a relatively long standstill period t>x h, where x is in the range from 0.5 to 24, has taken place.
It is thus possible for complete preheating of the cooling circuit and of the internal combustion engine to be achieved, and thus for the maximum advantage to be attained. The discharging process may for example take place already upon the unlocking of the vehicle or during a corresponding initialization by means of a vehicle key or the like. The discharging process ends when the temperature difference between the coolant outlet temperature at the heat accumulator and the coolant temperature of the internal combustion engine is lower than a predefinable value, such as for example 3 K.
The third phase is a neutral phase:
After the time functions of the closed-loop control expire or after the charging or discharging temperature conditions for the open-loop control are attained, a mode switch takes place into the neutral mode in which the accumulator is separated from the rest of the cooling circuit, that is to say is neither charged nor discharged.
Discharging of the heat accumulator takes place when the difference of the temperature of the coolant at the heat accumulator outlet is more than 6 K higher than the temperature of the coolant in the internal combustion engine, and the discharging of heat accumulator is ended when the temperature of the coolant at the heat accumulator outlet is less than 3 K higher than the coolant temperature at the internal combustion engine. Here, 6 K and 3 K are examples of two predefinable threshold values for the starting and ending of the discharging. Other values may also be used, such as for example 10 K and 5 K.
In this way, a hysteresis is defined in each case for the charging and discharging, which is highly advantageous for the closed-loop control of the method.
From the time t4 to the time t5, a charging phase takes place again. In the overrun operation phase from the time t6 to the time t7, no discharging takes place, because in this exemplary embodiment, it is defined that only a single discharge may take place while the ignition is activated, and in this exemplary embodiment this was the discharge from the time t0 to the time t1, for which reason no charging or discharging takes place between the time t5 and the time t8, and charging takes place again from the time t8 to the time t9 because, at the time t8, the coolant temperature at the outlet of the heat accumulator is again 10 K lower than the coolant temperature, wherein at the time t9, the temperature of the coolant at the outlet of the heat accumulator is only 5° C. below the coolant temperature in the internal combustion engine, for which reason the charging is ended again.
As can be seen, charging states occur when the coolant temperature at the outlet of the heat accumulator lies below the coolant temperature in the internal combustion engine by a predefined value, and the charging state is ended when a second threshold value for the coolant temperature at the outlet of the heat accumulator is exceeded, wherein in the exemplary embodiment of
Discharging takes place, as per
From t5 to t6, the temperature of the coolant at the heat accumulator outlet rises again. Subsequently, from t6 to t7, a neutral phase takes place again without charging or discharging of the heat accumulator, and charging of the heat accumulator takes place again at t7 because the temperature of the coolant in the internal combustion engine has exceeded 80° C. The charging of the heat accumulator takes place from t7 to t8 and the temperature of the coolant at the heat accumulator outlet increases again. A neutral phase takes place from t8 to t9 because the coolant temperature decreases owing to the overrun operation from t10 to t11 and only increases again thereafter from t11 to t9, and at t9, a threshold temperature of 90° C. is reached, such that charging of the heat accumulator takes place again from t9 to t10, and a neutral phase is assumed after t10.
As an alternative to the pump 4, it is also possible for an auxiliary water pump to be provided in the line 18, which auxiliary water pump serves for the admission and/or discharging of the coolant into or out of the heat accumulator.
In the case of a closed-loop-controlled embodiment by means of the temperature difference of the coolant of the internal combustion engine with respect to the temperature of the coolant of the heat accumulator, use may be made of a hysteresis for the inflow state and for the discharging process.
In a preferred embodiment, a single discharge of the heat accumulator while the ignition is activated, that is to say during one driving cycle, may be realized. This has the effect that coolant with a maximum coolant temperature can be stored.
Discharging and storing multiple times is however alternatively also possible if, for example in the event of a long period of travel in the overrun mode, the coolant temperature falls more than a predefinable value of for example 10 K in relation to the highest coolant temperature hitherto attained.
It is also possible in a further exemplary embodiment for storage of cold coolant to take place, said cold coolant being discharged by being provided in the event of an increased power demand of the internal combustion engine. This is advantageous in particular in internal combustion engines with charge air cooled by means of coolant, because it increases the cooling capacity.
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|---|---|---|---|
| 10 2012 206 119 | Apr 2012 | DE | national |
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| European Search Report, Appl. No. EP 13162995.8, Sep. 22, 2015, 6 pgs. |
| Number | Date | Country | |
|---|---|---|---|
| 20130269925 A1 | Oct 2013 | US |
