Method for Controlling a Waste Heat Utilization System for an Internal Combustion Engine

Abstract

The invention relates to a method for controlling a waste-heat utilization system (20) for an internal combustion engine (10) of a vehicle, wherein the waste-heat utilization system (20) has at least one expander (22), which can transmit torque to the internal combustion engine (10) and which can be bypassed by means of a bypass flow path (25), at least one evaporator (21), and at least one pump (24) for an operating medium, and wherein at least the evaporator (21) is arranged in the region of the exhaust gas system (11) of the internal combustion engine (10). The expander (22), which can be operated in several operating modes, has a driving connection to a secondary drive shaft (19) of the internal combustion engine in at least one operating mode. An operating mode of the waste-heat utilization system (20) is selected by a control device (30) on the basis of at least one input variable and the waste-heat utilization system (20) is operated in said operating mode. The input variable is selected by the control device (30) from the group consisting of expander rotational speed (n), gear information (GI), coasting information (CI), and pressure (p.sub.1, p.sub.2) and temperature (T.sub.1, T.sub.2) of the operating medium upstream or downstream of the expander (22). A first operating mode (1) is associated with a warm-up phase of the expander (22) and a second operating mode (2) is associated with a normal operating phase of the expander (22). In the first operating mode, the bypass flow path (25) is opened and the expander (22) is not connected to a secondary drive shaft (19) of the internal combustion engine (10). In the second operating mode, the bypass flow path (25) is closed and the expander (22) is connected to the internal combustion engine (10). The second operating mode (2) is selected if the pressure (p.sub.2) and/or the temperature (T.sub.2) of the operating medium downstream of the expander (22) exceeds a defined value.

Claims

1. Method for controlling a waste heat utilization system (20) for an internal combustion engine (10) of a vehicle, wherein the waste heat utilization system (20) comprises at least one expander (22) which can transmit a torque to the internal combustion engine (10) and which can be bypassed via a bypass flow path (25), at least one evaporator (21) and at least one pump (24) for an operating means, in particular ethanol, and wherein at least the evaporator (21) is disposed in the region of the exhaust gas system (11) of the internal combustion engine (10), wherein the expander (22) which can be operated in several operating modes is drive-connected in at least one operating mode to an auxiliary drive shaft (19) of the internal combustion engine and on the basis of at least one input quantity, in each case one operating mode is selected from at least two operating modes (1, 2, 3, 4, 5) of the waste heat utilization system (20) by a control device (30) and the waste heat utilization system (20) is operated in this operating mode preferably by triggering at least one bypass valve (26) of the expander (22) disposed in the bypass flow path (25) of the expander (22), wherein the input quantity is selected from the group expander speed (n), gear information (GI), coasting information (CI), pressure (p1) and temperature (T1) of the operating means upstream of the expander (22) and/or pressure (p2) and temperature (T2) downstream of the expander (22) by the control device (30), wherein a first operating mode (1) is assigned to a warm-up phase of the expander (22) and a second operating mode (2) is assigned to a normal operating phase of the expander (22), wherein in the first operating mode (1) the bypass flow path (26) is opened and the expander (22) is not connected to an auxiliary drive shaft (19) of the internal combustion engine (10) and wherein in the second operating mode the bypass flow path (25) is closed and the expander (22) is connected to the internal combustion engine (10), wherein the second operating mode (2) is selected when the pressure (p2) and/or the temperature (T2) of the operating means exceeds a defined value downstream of the expander (22).

2. The method according to claim 1, wherein a change is made from the second operating mode into the first operating mode when the pressure (p1) and/or the temperature (T1) of the operating means upstream of the expander (22) exceeds a defined value.

3. The method according to claim 1, wherein the waste heat utilization system (20) is operated in a third operating mode (3) during at least one gear change.

4. The method according to claim 3, wherein during at least one shift-down process a bypass flow path (25) of the expander (22) is closed and the auxiliary drive shaft (19) is driven by the expander (22).

5. The method according to claim 3, wherein during at least one shift-up process a bypass flow path (25) of the expander (22) is opened and/or the expander (22) is separated from the auxiliary drive shaft (19).

6. The method according to claim 1, wherein the waste heat utilization system (20) is operated in a fourth operating mode (4) during at least one coasting mode of the vehicle, during at least one warm-up mode of the internal combustion engine (10) and/or at least one engine braking mode of the internal combustion engine (10), wherein the bypass flow path (25) is preferably closed in the fourth operating mode (4).

7. The method according to claim 6, wherein in the fourth operating mode the expander (22) is separated from the auxiliary drive shaft (19), wherein preferably the expander (22) is only separated from the auxiliary drive shaft (19) when the torque of the expander (22) falls below a defined value.

8. The method according to claim 1, wherein the waste heat utilization system (20) is operated in a fifth operating mode (5) during at least one starting phase of the expander (22), wherein the expander (22) is started by activating a starting device (27) connected to the expander (22).

9. The method according to claim 1, wherein the expander (22) is separated from the auxiliary drive shaft (19) in the first operating mode (1) and/or when the waste heat utilization system (20) is inactive.

10. The method according to claim 1, wherein the bypass flow path (25) of the expander (22) is closed when the operating means of the waste heat utilization system (20) is in an overheated state.

11. The method according to claim 1, wherein the expander (22) is drive-connected to the auxiliary drive shaft (19) when the operating means of the waste heat utilization system (20) downstream of the expander (22) is in an overheated state and/or when the expander speed (n) exceeds a defined value and/or the speed of the internal combustion engine (10) exceeds a defined value.

12. The method according to claim 1, wherein expander (22) is separated from the auxiliary drive shaft (19) when the operating means of the waste heat utilization system (20) upstream of the expander (22) is in a non-overheated state or when the internal combustion engine (10) is stopped.

13. Waste heat utilization system (20) for a vehicle driven by an internal combustion engine (10) via a drive train (13), comprising a control device (30) for controlling the waste heat utilization system (20), wherein the waste heat utilization system (20) comprises at least one expander (22) which can transmit a torque to the internal combustion engine (10) and which can be bypassed via a bypass flow path (25), at least one evaporator (21) and at least one pump (24) for an operating means, in particular ethanol, and wherein at least the evaporator (21) is disposed in the region of the exhaust gas system (11) of the internal combustion engine (10), wherein the expander (22) which can be operated in several operating modes can be drive-connected in at least one operating mode to an auxiliary drive shaft (19) of the internal combustion engine (10) and on the basis of at least one input quantity, in each case one operating mode can be selected from at least two operating modes (1, 2, 3, 4, 5) of the expander (22) by the control device (30) and the expander (22) can be operated in this operating mode preferably by triggering at least one bypass valve (26) of the expander (22) disposed in the bypass flow path (25) of the expander (22), wherein the input quantity can be selected from the group expander speed (n), gear information (GI), coasting information (CI), pressure (p1) and temperature (T1) of the operating means upstream of the expander (22) and/or pressure (p2) and temperature (T2) downstream of the expander (22) , wherein a first operating mode (1) is assigned to a warm-up phase of the waste heat utilization system (20) and a second operating mode (2) is assigned to a normal operating phase of the expander (22), and in at least one operating mode the expander (22) can be separated from the auxiliary drive shaft (19), wherein in the first operating mode (1) the bypass flow path (25) is opened and the expander (22) is separated from the auxiliary drive shaft (19) and in the second operating mode the bypass flow path (25) is closed and the expander (22) is connected to the internal combustion engine (10), and wherein in at least one operating mode the expander (22) can be separated from the auxiliary drive shaft (19) and wherein the second operating mode (2) can be selected when the pressure (p2) and/or the temperature (T2) of the operating means exceeds a defined value downstream of the expander (22).

14. The waste heat utilization system (20) according to claim 13, wherein a third operating mode (3) is assigned to at least one gear change phase.

15. The waste heat utilization system (20) according to claim 13, wherein a fourth operating mode (4) is assigned to at least one coasting mode of the motor vehicle, at least one warm-up mode of the internal combustion engine (10) and/or at least one engine braking mode of the internal combustion engine (10), wherein preferably in the fourth operating mode (4) the bypass flow path (25) can be closed.

16. The waste heat utilization system (20) according to claim 13, wherein in in the fourth operating mode (4) the expander (22) can be separated from the auxiliary drive shaft (19).

17. The waste heat utilization system (20) according to claim 13, wherein the expander (22) can be separated from the auxiliary drive shaft (19) in the first operating mode and/or when the waste heat utilization system (20) is inactive.

18. The waste heat utilization system (20) according to claim 13, wherein the expander (22) is at least connected to a starting device (27), wherein in a fifth operating mode assigned to at least one starting phase of the expander (22) the expander (22) can be started by activating the external starting device (27). (FIG. 3, 4)

19. The waste heat utilization system (20) according to claim 13, wherein the expander (22) can be connected to the auxiliary drive shaft (19) or separated from this by means of at least one disengageable clutch (28).

20. The waste heat utilization system (20) according to claim 13, wherein the expander (22) can be connected to the auxiliary drive shaft (19) by means of at least one overrunning clutch (29a) wherein at least one centrifugal force braking device (29b) is preferably disposed between the overrunning clutch (29a) and the expander (22).

Description

[0019] The invention is described in detail hereinafter with reference to the non-restrictive figures. In the figures schematically:

[0020] FIG. 1 shows a waste heat utilization system for an internal combustion engine with a control device according to the invention in a first embodiment;

[0021] FIG. 2 shows the operating modes of this control device;

[0022] FIG. 3 shows a waste heat utilization system for an internal combustion engine with a control device according to the invention in a second embodiment; and

[0023] FIG. 4 shows the operating modes of this control device.

[0024] In the embodiments shown, components having the same function are provided with the same reference numbers.

[0025] FIG. 1 and FIG. 3 each show an internal combustion engine 10 with an exhaust gas system 11 in which an exhaust gas after-treatment device 12for example a diesel oxidation catalyst 12, a diesel particle filter 12b and an SCR catalyst 12c (SCRselective catalytic reduction)is arranged. The internal combustion engine 10 has a drive train 13 with a crank shaft 14, a disengageable clutch 15 and a (manual) transmission 16 which acts on the drive shaft 17 of the drive wheels 18.

[0026] The internal combustion engine 10 further has a waste heat utilization system 20 for utilizing the exhaust gas values of the exhaust gas system 11 of the internal combustion engine 10. The waste heat utilization system 20 has an evaporator 21 which is arranged downstream of the exhaust gas after-treatment device 12 in the region of the exhaust gas system 11. The waste heat utilization system 20 which functions for example according to the organic Rankine cycle (ORC) comprises, downstream of the evaporator 21 in the operating medium circuit, an expander 22 and a condenser 23, as well as a pump 24 for the operating medium. For example, ethanol can be used as operating medium. In order to bypass the expander 22, a bypass line 25 with a bypass valve 26 is provided. The evaporator 21 can be bypassed on the exhaust gas side via a bypass line 36 and a bypass valve 37 if the exhaust gas heat is too high for the evaporator 21 or the system pressure exceeds a defined value or the cooling system is excessively loaded or the waste heat utilization system 20 is in an error mode or in pure engine mode, without engine braking. The bypass valve 37 is triggered depending on at least one of the operating parameters from the group of fan power, system pressure, system temperature and mass flow of the operating medium.

[0027] A control device 30 is provided for controlling the waste heat utilization system 20, which has a program logic 31 which is configured to select the most suitable operating mode from the plurality of operating modes 1 to 4 or 1 to 5 for operation of the waste heat utilization system 20. The selection of the most suitable operating mode is made on the basis of at least one of the input variables of the control device 30, namely: expander rotational speed n, gear information GI, coasting information CI, pressure p.sub.1, temperature T.sub.1 of the operating medium upstream of the expander 22 as well as the pressure p.sub.2 and the temperature T.sub.2 of the operating medium upstream of the expander 22. Pressure sensors 32, 33 and temperature sensors 34, 35 are provided upstream and downstream of the expander 22 in the operating medium circuit of the waste heat utilization system 20 to record the parameters pressures p.sub.1, p.sub.2 and temperatures T.sub.1, T.sub.2. The pressure sensors 32, 33 and temperature sensors 34, 35 are connected to the control device 30. The gear information GI and coasting information CI are provided, for example by suitable sensors in the transmission 16 of the control device 30.

[0028] In the first embodiment shown in FIG. 1, the expander 22 is connected to the auxiliary drive shaft 19 of the internal combustion engine 10 via a disengageable clutch 28. The disengageable clutch 28 is controlled via the control device 30. It enables the expander 22 to start via the internal combustion engine 10 by closing the disengageable clutch 28.

[0029] The operating modes of this first embodiment are shown in FIG. 2. The following operating modes can be executed with the embodiment shown in FIG. 1:

[0030] First operating mode 1 is executed during the warm-up phase of the expander 22; in the operating mode 1 the bypass valve 26 is opened so that the operating medium is guided past the expander 22.

[0031] Second operating mode 2: this operating mode 2 is assigned to the normal operation of the expander 22. As soon as the pressure p.sub.2 and/or the temperature T.sub.2 of the operating medium downstream of the expander 22 exceed a defined value or defined values, the operating mode 2 is activated.

[0032] Third operating mode 3: this operating mode 3 is used for gear change processes of the transmission 16.

[0033] During the shift-down process the bypass valve 26 is closed. The auxiliary drive shaft 19 is driven by the expander 22 and the torque of the expander 22 is utilized whilst the rotational speed of the crankshaft 14 of the internal combustion engine 10 and the rotational speed of the transmission 16 are synchronized. The disengageable clutch 5 is opened in this case. As a result, the amount of fuel for accelerating the internal combustion engine 10 can be reduced. Furthermore, a certain engine rotational speed can be held during the switching process. Thus, the exhaust gas heat downstream of the exhaust gas after-treatment device 12 can be used to bridge torque drops during shifting pauses.

[0034] During the up-shift process the bypass valve 26 of the expander 22 is opened andin the case of the disengageable clutch 28the expander 22 is separated from the auxiliary drive shaft 19 by opening the disengageable clutch 28. This avoids the torque being transmitted from the expander 22 to the internal combustion engine 10.

[0035] Fourth operating mode 4: this operating mode 4 is used during the coasting mode, the warm-up mode and/or the engine braking mode of the internal combustion engine 10. In the coasting mode the vehicle travels without transmission of torque between internal combustion engine 10 and drive wheels 18, generally with the disengageable clutch 15 open. The bypass valve 26 is closed in the operating mode 4 in order to transmit torque from the expander 22 to the internal combustion engine 10. As a resultin particular when the disengageable clutch 15 is openthe fuel consumption during idling is reduced. When a high torque is provided by the expander 22, the disengageable clutch 15 can be closed until the torque of the expander 22 falls below a defined value.

[0036] The second embodiment shown in FIG. 3 differs from FIG. 1 in that instead of the disengageable clutch 28, an overrunning clutch 29a and a centrifugal braking device 29b are provided for connecting the expander 22 to the auxiliary drive shaft 19 of the internal combustion engine 10.

[0037] For starting the expander 22, in addition to the aforesaid operating modes 1 to 4, the control device 30 can execute a fifth operating mode 5 to start the expander 22 with an internal or external starting device 27 (see FIG. 3, FIG. 4).

[0038] In order to avoid the expander 22 being operated at excessive rotational speed and thereby being damaged, the control device 30 provides special safety measures. Thus, the bypass valve 26 is only closed when the operating medium is in an overheated state, i.e. for example when the operating medium ethanol is present in the gas phase. Another safety measure is that the bypass valve 26 is opened when a gear change to a higher gear is implemented. In particular in the embodiment with overrunning clutch 29a and centrifugal braking device 29b shown in FIG. 3, no further steps are required.

[0039] In the embodiment shown in FIG. 1 with a disengageable clutch 28, the bypass valve 26 and the disengageable clutch 28 are only closed when the operating medium is in an overheated state, i.e. for example when the operating medium ethanol is in the gas phase. In the case of a gear change to a higher gear, both the bypass valve 26 and also the disengageable clutch 28 are open.

[0040] The disengageable clutch 28 is therefore closed when the operating medium is an overheated state or when the rotational speed n of the expander 22 and/or the rotational speed of the internal combustion engine 10 lies above a defined value. The disengageable clutch 28 is therefore opened when the expander 22 is in a non-overheated state. The disengageable clutch 28 is also opened when the operating state of the internal combustion engine 10 changes from an activated to a deactivated state, that is, when the internal combustion engine 10 is turned off.