EP2693001A1 - Method for regulating a heat recovery system in a motor vehicle - Google Patents

Abstract

The invention relates to a method for controlling a heat recovery system in a motor vehicle with an internal combustion engine, in particular in a commercial vehicle, with a heat recovery circuit (1) as a working cycle, which has a storage tank (VR) with a working medium over a feed pump (SP) is connected to at least one control valve (V1, V2), to each of which a heat exchanger (AGR-WT, AG-WT) is assigned as an evaporator. The working cycle further comprises an at least one heat exchanger (AGR-WT, AG-WT) downstream expansion machine (E), to which a capacitor (K) with a connection via a Kondensatorenabsaugpumpe (KP) to the storage tank (VR) follows. The at least one heat exchanger (EGR-WT, AG-WT) is flowed through both by a working medium mass flow and by a heating medium mass flow of a heat source. According to the invention, when the heating medium mass flow and predetermined heating medium temperature are preset to a predetermined steam temperature set value and / or phase state for the working medium, the mass flow through the at least one heat exchanger / evaporator is varied by adjusting the control valve passage (V1, V2). regulated.

Description

The invention relates to a method for controlling a heat recovery system (WRG system) in a motor vehicle with an internal combustion engine, in particular in a commercial vehicle.

A well-known heat recovery system has a heat recovery circuit (WRG circuit) as a working circuit containing a storage tank with a working fluid, which is connected via a feed pump with at least one control valve, each associated with a heat exchanger as an evaporator is. The working cycle further includes a, at least one heat exchanger downstream expansion machine to which a capacitor with a connection via a condenser suction pump to the storage tank follows. The heat exchanger is flowed through in the vehicle operation both by a working medium mass flow and by a heating medium mass flow of a vehicle heat source in countercurrent. After a warm-up (liquid state of the working medium) and a subsequent evaporation process (working fluid partially liquid and partially vaporous) follows an overheating process (working medium in vapor form over saturated steam temperature), wherein after switching to expander operation of the working medium vapor of the expansion machine is supplied to the drive.

In known heat recovery systems, various heat sources can be used on the internal combustion engine to vaporize a working medium. In particular, the engine coolant, the charge air or preferably the exhaust gas can be used as heat sources or heating media. The energy contained in the working medium vapor is converted into mechanical energy in the expansion machine and fed back to the internal combustion engine, so that the overall efficiency can be increased.

The object of the invention is to propose a method for controlling such a heat recovery system, with the efficiency optimal and safe operation of such a system is feasible.

This object is achieved in that at predetermined by the vehicle operation Heizmedium mass flow and predetermined heating medium temperature to a predetermined temperature setpoint and / or phase state for the working fluid by varying the working medium mass flow through the at least one heat exchanger / evaporator by means of adjustment of the control valve passage is regulated.

In order to exploit the heating energy which is fully available from the heat sources on the internal combustion engine in the heating medium mass flow, the temperature and, in particular in the evaporation process, the phase state of the working medium is regulated here by regulation of the working medium mass flow.

For a defined admission of the at least one heat exchanger / evaporator with a defined working medium mass flow, a control valve is preferably used as a proportional control valve, which is controlled via a pulse-width-modulated signal (PWM signal). An exact assignment of the working medium mass flow actual value for control valve position or the PWM signal is not immediately possible because of the varying pressure gradient across the control valve. It is therefore proposed that the exact working medium mass flow actual value through the at least one control valve using the valve map taking into account the current valve position or the PWM signal, the current (measured) pressure drop across the control valve and the current working fluid temperature at the control valve to calculate.

The heat recovery cycle has the following function: the feed pump removes the working fluid from the storage tank, which is routed via the proportional control valve to the heat exchanger and evaporated in it. When using two heat exchangers, the working fluid from the feed pump is distributed to two associated proportional control valves. The heat exchanger draws its heat from the likewise conducted mass flow of heating medium, in particular from the exhaust gas of an internal combustion engine, preferably a recirculated exhaust gas and an exhaust gas which is supplied to the environment after exhaust aftertreatment, respectively a heat exchanger / evaporator with associated control valve and associated control is supplied ,

After the at least one heat exchanger, a direct flow path to the expansion machine or a flow path via a throttle valve can be switched by means of a switching valve. Is in front of the expansion machine while warming up yet no steam and In the subsequent evaporation process, only steam together with liquid is available, the working medium is passed through the throttle valve flow path. Only when reaching a certain superheat temperature above the saturated steam temperature, the working medium is passed by switching to the expander operation directly to the expansion machine. In the condenser, the remaining working medium vapor is then returned to the liquid state and further transported via the condenser suction pump and a filter back to the storage tank.

In principle, in pure expander operation, a pure temperature control to an optimum steam temperature setpoint of the working medium would be possible. Since, however, under changing conditions, for example, a speed change of the expansion machine, the working medium-steam mass flow through the expander and thus the temperature and pressure conditions vary, a working medium temperature control with a subordinate working medium mass flow controller is advantageous because it faster than changes can be reacted with a pure, relatively sluggish temperature control.

A further improvement of the control quality with respect to the response and transient response is achieved in that the working medium mass flow setpoint is additionally corrected by a pilot control, which responds to changes in the heating medium side, wherein as a correction parameter in particular the heating medium mass flow and / or the Heating medium inlet temperature at the heat exchanger and / or the working medium pressure are evaluated before the expansion machine in such a feedforward control for a correction. In the case of several heat exchangers / evaporators, the above temperature control must be carried out separately for each heat exchanger with a lower-level working medium mass flow controller and if necessary the pilot control.

A further increase in effectiveness is achieved when a proportional-integral controller (PI controller) or proportional-integral-derivative controller (PID controller) is used as the working medium mass flow controller and the local integrator depending on the circumstances with an additional manipulation value is applied, whereby a working medium mass flow maximization is possible.

This will be explained below using an example when exhaust gas is used as the heating medium: since the exhaust gas temperature is then less than the maximum component temperature at the exhaust gas heat exchanger in each possible operating state, practically always one becomes possible regulated high steam temperature. Since in this case the required mass flow in order to represent the corresponding steam temperature, due to a saturation behavior is not unique, is intervened before the integrator with the manipulation value, so that really the maximum mass flow is adjusted with the required temperature. This manipulation value depends on the exhaust gas temperature at the evaporator inlet, the current steam temperature after the evaporator and the current mass flow of the steam medium. If a steam temperature required close to the gas inlet temperature is reached, but the mass flow through the heat exchanger / evaporator is relatively small, the evaporator is operated in saturation and a higher mass flow rate at the same steam temperature is possible. Therefore, an additive, positive value at the integrator input should increase the mass flow, whereby this manipulation value should decrease again with increasing mass flow. If the steam temperature falls below the setpoint temperature, the manipulation value is set to zero, now the higher-level temperature controller regulates the required steam temperature and a maximum mass flow is achieved at this temperature with the highest achievable amount of steam. If (for numerical reasons, for example) the mass flow setpoint and thus the current mass flow decreases, the manipulation value becomes active again and the mass flow increases again. However, care must be taken that the manipulation value is chosen small enough for the temperature controller to be able to adjust the setpoint.

Another rapid intervention in the control can optionally be achieved in that wall temperatures are measured at the heat exchanger evaporator, if necessary to quickly determine a liquid / vapor limit, so that a decrease in the working fluid outlet temperature below the saturated steam temperature can be counteracted quickly. Such an intervention may be advantageous if, for example, the evaporator outlet temperature drops at a very high gradient, whereby, without this intervention, the relatively slow temperature control is no longer able to maintain the temperature above the saturated steam temperature. For the determination of the liquid / vapor limit, the wall temperature in the vicinity of the media inlet, in the middle between medium inlet and medium outlet and in the vicinity of the medium outlet can be measured, so that premature reaction to a decrease in the outlet temperature. This assumes that the wall temperature can be concluded with the least possible delay on the internal temperature conditions.

1. a) Aufwärmvorgang (Arbeitsmedium flüssig)
   Der Aufwärmvorgang erfolgt temperaturbasiert und temperaturgeregelt, indem die Arbeitsmedium-Solltemperatur stufenweise oder kontinuierlich je nach der Heizmedium-Eintritttemperatur am Wärmetauscher und dem Heizmedium-Massenstrom bis zur Sattdampftemperatur erhöht wird.
2. b) Verdampfungsprozess
   Im Verdampfungsprozess ist das Arbeitsmedium (nach dem Wärmetauscher) teilweise gasförmig und teilweise flüssig bei jeweils gleicher Sattdampftemperatur, so dass hier keine temperaturbasierte Regelung eingesetzt werden kann. Die Sattdampftemperatur ist grundsätzlich eine Funktion des Drucks und kann leicht ermittelt werden. Der Verdampfungsprozess wird daher nur durch eine Arbeitsmedium-Massenstrom-Regelung geführt. Der Verdampfungszustand wird durch den vorhergehenden, temperaturgeregelten Aufwärmvorgang erreicht, wobei der Arbeitsmedium-Massenstrom der Temperaturregelung zum Zeitpunkt des Umschaltens auf die reine Massenstromregelung als Sollwert übernommen wird. Durch Anpassung an die sich ständig verändernden Betriebsparameter, beispielsweise von Abgaseintrittstemperaturen und eines Abgasmassenstroms, soll über Kennfelder sichergestellt werden, dass der Arbeitsmedium-Kreislauf nicht wieder in den einphasigen, flüssigen Zustand zurückfällt. Dann wird durch zeitlich gesteuertes, stufenweises Absenken des Arbeitsmedium-Massenstroms die Überhitzungsphase eingeleitet und der Überhitzungsprozess erreicht. Fällt aber die Temperatur wieder unter die Sattdampftemperatur, so wird wieder auf die Temperaturregelung des Aufwärmvorgangs umgeschaltet, wobei der Temperaturregler so initialisiert wird, dass der zum Zeitpunkt des Umschaltens vorherrschende Massenstrom eingestellt wird.
3. c) Überhitzungsprozess
   Die Arbeitsmedien-Dampftemperatur wird über die Sattdampftemperatur temperaturgeregelt bis zu der für den Expanderbetrieb vorgegebenen Arbeitsmedium-Dampftemperatur erhöht.
4. d) Expanderbetrieb
   Es erfolgt eine Umschaltung auf den Expanderbetrieb in Verbindung mit einer Regelung, wie sie vorstehend in Verbindung mit dem Expanderbetrieb erläutert wurde.

The above statements relate essentially to a regulated expander operation with a desired steam temperature regulated above the saturated steam temperature. In order to achieve this desired state as quickly and efficiently as possible in a start-up process, the following method steps are proposed:

1. a) warm-up process (liquid working fluid)
   The warm-up process is temperature-based and temperature-controlled by the working medium target temperature is gradually or continuously increased depending on the heating medium inlet temperature at the heat exchanger and the heating medium mass flow to the saturated steam temperature.
2. b) evaporation process
   In the evaporation process, the working medium (after the heat exchanger) is partially gaseous and partly liquid at the same saturated steam temperature, so that no temperature-based control can be used here. The saturated steam temperature is basically a function of pressure and can be easily determined. The evaporation process is therefore performed only by a working medium mass flow control. The evaporation state is achieved by the previous, temperature-controlled warm-up process, wherein the working medium mass flow of the temperature control is taken over at the time of switching to the pure mass flow control as the setpoint. By adapting to the ever-changing operating parameters, for example of exhaust gas inlet temperatures and an exhaust gas mass flow, it is intended to ensure via maps that the working medium circuit does not fall back into the single-phase, liquid state. Then the overheating phase is initiated by timed, stepwise lowering of the working medium mass flow and the overheating process is achieved. However, if the temperature falls below the saturated steam temperature again, the temperature control of the warm-up process is switched over, the temperature controller being initialized in such a way that the mass flow prevailing at the time of switching over is set.
3. c) overheating process
   The working medium steam temperature is increased in temperature controlled manner via the saturated steam temperature up to the working medium steam temperature specified for the expander operation.
4. d) expander operation
   There is a switch to the expander operation in conjunction with a scheme, as has been explained above in connection with the expander operation.

In a particularly preferred method, the heating medium is both an exhaust gas after treatment of the environment supplied exhaust (AG) from a vehicle internal combustion engine and a recirculated exhaust gas (EGR), both types of exhaust gas is assigned a separate heat exchanger with upstream control valves and each acting thereon control. Alternatively or additionally, if other heating media, such as an engine coolant and / or a charge air, are used in a heat recovery cycle, the above control methods are appropriate and adapted to the particular heating medium to be used.

dm_{air, th...}

theoretischer Luftmassenstrom

Sf_NP...

Liefergrad bei geschlossener AGR-Klappe

dm_AGR...

AGR-Massenstrom

If, for cost reasons, the mass flow for the recirculated exhaust gas can not be determined by a corresponding mass flow measurement, the following low-cost calculation is possible using an engine control unit: The engine control unit calculates based on a combination of the delivery level with fully closed or fully opened exhaust gas recirculation flap (EGR flap ) the intake air mass flow. From the engine control unit values for the theoretical air mass flow and the calculated air mass flow (dm _air ), the EGR mass flow can be represented as follows: $${\mathit{dm}}_{\mathit{AGR}}={\mathit{dm}}_{\mathit{air}.\mathit{th}}{\mathit{sf}}_{\mathit{NP}}-{\mathit{dm}}_{\mathit{air}}$$

dm _{air, th ...}

theoretical mass air flow

Sf _{NP ...}

Degree of delivery with closed EGR flap

dm _{AGR ...}

EGR mass flow

On the basis of a drawing, a method for controlling with exhaust gas as a heating medium is further explained.

Fig. 1

eine schematische Darstellung eines Wärme-Rückgewinnungs-Kreislaufs,

Fig. 2

eine Temperaturregelung mit Vorsteuerung und unterlagertem Massenstromregler, und

Fig. 3

eine Anpassung des Massenstromreglers zur Massenstrommaximierung.

Show it:

Fig. 1

a schematic representation of a heat recovery cycle,

Fig. 2

a temperature control with pilot control and underlying mass flow controller, and

Fig. 3

an adaptation of the mass flow controller for mass flow maximization.

In Fig. 1 a heat recovery circuit 1 is shown as a block diagram, being used as the working medium water / steam and as a heating medium recirculated exhaust gas AGR and after exhaust aftertreatment of the environment supplied exhaust gas AG. To the left of the dotted line (arrow 2) is the liquid area of the circuit and to the right of the dotted line (arrow 3) is the vaporous area of the circuit.

From a storage tank VR with a feed pump SP, the working medium via a manifold VT with two flow lines via associated proportional control valves V1 and V2 through an EGR heat exchanger (EGR-WT) and a parallel AG heat exchanger (AG-WT) passed. EGR exhaust gas is passed through the EGR heat exchanger in countercurrent and AG exhaust gas through the AG heat exchanger. At the inlet, both the EGR inlet temperature T1 of the EGR exhaust gas and the AG inlet temperature T3 of the EG exhaust gas are measured. The AGR-WT and the AG-WT are operated in the retracted operation as an evaporator, wherein the steam outlet temperatures T2 and T4 and after merging the steam temperature T5 are detected. In addition, the pressure P0 after the feed pump and the pressures P1 and P2 are respectively detected after the proportional control valves V1 and V2 and the pressure P6 in front of a switching valve V3. At low pressure drop Δp across the evaporators (EGR-WT, AG-WT), the measurement of the pressure P1 and / or P2 is sufficient. The working medium vapor is supplied in the retracted state with the valve V3 in the expander operation of an expansion machine E and from there into a condenser K, in which the steam to the liquid cools and by means of a condenser suction pump KP and a filter F back to the storage tank VR is supplied. If steam is not yet sufficiently available for operation of the expansion engine E, particularly in a starting state, a line is passed via a throttle valve V4.

The heat recovery circuit 1 is controlled and / or controlled by varying the working medium passage through the proportional control valves V1, V2.

In Fig. 2 For this purpose, a temperature controller 4 with a lower-level mass flow controller (dm controller) 5 for the working medium is shown as a vapor medium. The control is shown here for the EGR-WT, wherein the same rule is also required for the AG branch. At the input of the temperature controller, the comparison is made between the steam temperature setpoint in the EGR branch and the corresponding steam temperature actual value, wherein a control deviation is output as a control signal in accordance with the applicable controller behavior. This control signal is used in the lower-level mass flow controller 5 as a mass flow setpoint for the steam medium (dm _soll ) for comparison with the corresponding mass flow actual value (dm _is ), wherein according to the set controller behavior (PI controller) of the dm controller. 5 sends a control signal to the EGR proportional control valve V1.

In order to improve the control quality, the mass flow setpoint value is also influenced and corrected here by a feedforward control 6, wherein the feedforward control 6 reacts in particular to changes in the heating medium side (EGR). In this case, the precontrol in addition to the steam temperature setpoint is the EGR inlet temperature T _AGR corresponding to T1 as a correction parameter Fig. 1 fed. Further correction parameters are the pressure before the expansion _machine P _vapor (corresponding to P6 off Fig. 1 or additionally measured directly in front of the expansion engine E), as well as the EGR mass flow dm _AGR , which is calculated for example by means of values from the engine control (EDC).

In Fig. 3 is the mass flow controller 5 (dm controller) off Fig. 2 detailed with further details. As mass flow controller 5, a proportional-integral controller is used. In order to maximize the mass flow of the vapor medium, the input of the integrator (I regulator) is subjected to a manipulation value from a mass flow adaptation unit 9.

In Fig. 3 Specifically, consider the mass flow adjustment in the control for the AG branch with the AG heat exchanger (the control in the parallel EGR branch should be carried out accordingly).

The mass flow adaptation unit 9, the gas-side AG inlet temperature T _AG and the setpoint and actual value of the working medium for the AG-WT outlet temperature are supplied. Furthermore, in the mass flow adaptation 9, the mass flow actual value for the vapor medium dm _is taken into account.

Claims (11)

Method for controlling a heat recovery system (heat recovery system) in a motor vehicle with an internal combustion engine, in particular in a commercial vehicle,
with a heat recovery circuit (1) as a working cycle, which has a storage tank (VR) with a working medium, which is connected via a feed pump (SP) with at least one control valve (V1, V2), each having a heat exchanger (AGR- WT, AG-WT) is assigned as an evaporator, and the working cycle further comprises an at least one heat exchanger (AGR-WT, AG-WT) downstream expansion machine (E), to which a capacitor (K) with a connection via a Kondensatorenabsaugpumpe ( KP) to the storage tank (VR) follows, wherein the at least one heat exchanger (AGR-WT, AG-WT) is flowed through both by a working medium mass flow and by a heating medium mass flow of a heat source, such that after a warm-up (liquid state of Working medium) and a subsequent evaporation process (working medium partially liquid and partially vaporous) in an overheating process (working medium vaporous over the saturated steam emperatur) working medium vapor is supplied after a switch to expander operation of the expansion machine (E) to the drive,
characterized,
that at predetermined by the vehicle operation heating medium mass flow and predetermined heating medium temperature to a predetermined steam temperature setpoint and / or phase state for the working fluid by varying the working medium mass flow through the at least one heat exchanger / evaporator (AGR-WT, AG-WT) means Adjustment of the control valve passage (V1, V2) is regulated. A method according to claim 1, characterized in that the working medium mass flow actual value by the at least one control valve (V1, V2) by means of the valve map taking into account the current valve position, the current pressure drop across the control valve (V1, V2) and the current working medium Temperature at the control valve (V1, V2) is calculated. A method according to claim 2, characterized in that the at least one control valve (V1, V2) is a proportional control valve, which is controlled via a pulse width-modulated signal (PWM signal). Method according to one of claims 1 to 3, characterized in that after the at least one heat exchanger (AGR-WT, AG-WT) by means of a switching valve (V3) a direct flow path to the expansion machine (E) or a flow path via a throttle valve (V4) is switchable, wherein the working fluid in the warm-up and subsequent evaporation process with partially liquid and gaseous working fluid via the throttle valve flow path and only when reaching a certain superheat temperature above the saturated steam temperature by switching to the expander operation directly to the expansion machine (E) is passed. Method according to one of claims 1 to 4, characterized in that in the expander operation to an optimal steam temperature setpoint of the working medium regulating working medium temperature controller (4) is subordinate to a working medium mass flow controller (dm controller 5), wherein the working medium temperature controller Output value as working medium mass flow setpoint (dm _soll ) is applied to the input of the subordinate working medium mass flow controller (dm controller 5). A method according to claim 5, characterized in that the working medium mass flow setpoint (dm _soll ) is additionally corrected by a feedforward control (6) which responds to changes in the heating medium side, wherein as a correction parameter in particular the heating medium mass flow (dm _EGR ) and / or the heating medium inlet temperature (T _AGR ) at the heat exchanger (EGR-WT) and / or the working medium pressure (P _steam ) before the expansion machine (E) in the feedforward control (6) are evaluated for a correction. Method according to claim 5 or claim 6, characterized
in that a proportional-integral controller (PI controller) or proportional-integral-derivative controller (PID) controller is used as the working medium mass flow controller (5), and
that for the working medium mass flow maximization of the input of the integrator (8) of the PI controller or PID controller is additionally acted upon by a manipulation value, depending on the heating medium temperature (T _AG ) at the heat exchanger inlet, the current working medium steam temperature (Tp _{G medium} ) is after the heat exchanger (AG-WT) and controlled by the current working medium vapor mass flow (dm _ist ), in such a way
that upon reaching an optimum working medium vapor temperature close to the heating medium temperature at the heat exchanger inlet and a relatively small working medium mass flow, a positive manipulation value is generated. Method according to one of claims 5 to 7, characterized in that the wall temperatures at least one heat exchanger Nerdampfer (EGR-WT, AG-WT) are measured to determine if necessary quickly a liquid / vapor limit and a decrease in the working medium outlet temperature below the Saturated steam temperature to counteract quickly. Method according to one of claims 1 to 8, characterized
the following method steps are carried out to achieve a controlled expander operation: a) warm-up
The warm-up process is temperature-based and temperature-controlled by the working medium setpoint temperature is increased gradually or continuously depending on the heating medium inlet temperature at the heat exchanger (EGR-WT, AG-WT) and the heating medium mass flow to the saturated steam temperature. b) evaporation process
In the evaporation process, the working medium after the heat exchanger (EGR-WT, AG-WT) is gaseous and liquid with the saturated steam temperature and upon reaching the saturated steam temperature is switched to a working medium mass flow control, wherein by lowering the working medium mass flow by means of the control valve (V1 , V2) a temperature increase takes place, the 2-phase state is left and the overheating process is achieved. c) overheating process
The working medium steam temperature is increased in temperature controlled manner via the saturated steam temperature up to the working medium steam temperature specified for the expander operation. d) expander operation
There is a switch to the expander operation in conjunction with a control according to the claims 1 to 8. Method according to one of claims 1 to 9, characterized in that the heating medium is a after exhaust aftertreatment of the environment supplied exhaust gas (AG) and recirculated exhaust gas (EGR) from a vehicle internal combustion engine, wherein both types of exhaust gas (AG and AGR) each have their own heat exchanger ( AG-WT and AGR-WT), each with upstream control valves (V1 and V2) and each acting on it control is assigned. A method according to claim 10, characterized in that the mass flow for the recirculated exhaust gas (EGR mass flow) is derived from the calculated by the engine control unit (EDC) intake air mass flow.

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