Vehicle air-conditioning system and method of operation

Abstract

A vehicle air-conditioning system and a method for operating that vehicle air-conditioning system in dependence on the difference between the temperature of the engine coolant at the inlet into the heating heat exchanger and the temperature of the air at the outlet out of the heating heat exchanger are provided. The measured or estimated temperatures of the coolant at the inlet into the heating heat exchanger and of the air at the outlet out of the heating heat exchanger are checked to determine whether their values indicate fault states of components of the air-conditioning system.

Claims

1. A method of operating a vehicle air-conditioning system, comprising: determining a first temperature of an engine coolant at an inlet to a heating heat exchanger; determining a second temperature of air at an outlet of said heating heat exchanger; comparing said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate a fault state of a component of said vehicle air-conditioning system; and checking said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate presence of gas bubbles in the heating heat exchanger.

2. The method of claim 1, including checking said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate malfunctioning of a closing valve of said heating heat exchanger.

3. The method of claim 1, including checking said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate malfunctioning of a mixing flap of the vehicle air-conditioning system.

4. The method of claim 1, including checking said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate presence of a low engine coolant level.

5. The method of claim 1, including checking said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate incorrect concentration of antifrost agent in the engine coolant.

6. The method of claim 1, including comparing said first temperature to said second temperature to determine a difference between said first temperature and said second temperature.

7. The method of claim 1, including directly measuring said first temperature with a first sensor in order to determine said first temperature.

8. The method of claim 7, including directly measuring said second temperature with a second sensor in order to determine said second temperature.

9. The method of claim 7, including estimating said second temperature on a basis of measuring temperature of cooling fins of the heating heat exchanger.

10. The method of claim 1, further including regulating a quantity of said air flowing through said heating heat exchanger in dependence on difference between said first temperature and said second temperature.

11. The method of claim 1, further including regulating a quantity of said air flowing into said heating heat exchanger in accordance with a preset dependence based upon a temperature of said engine coolant.

12. The method of claim 1, further including regulating a quantity of said air flowing through said heating heat exchanger so that when said temperature of said engine coolant is 0° C. 40-60% of a maximum air quantity based upon fan voltage is circulated through said heating heat exchanger.

13. The method of claim 12, further including increasing said quantity of said air flowing through said heating heat exchanger substantially linearly with rising engine temperature until at an engine coolant temperature of 50-60° C. 80% of the maximum air quantity based upon fan voltage is circulated through said heating heat exchanger.

14. A vehicle air-conditioning system, comprising: a first sensor for monitoring a first temperature of an engine coolant at an inlet into a heating heat exchanger; a second sensor for monitoring a second temperature of air at an outlet out of said heating heat exchanger or an air outlet region of said heating heat exchanger; and a controller adapted to compare said first temperature and said second temperature to determine whether a fault state of a component of said vehicle air-conditioning system is indicated, the fault state comprising (a) gas bubbles are present in the heating heat exchanger or (b) an incorrect concentration of antifrost agent is in engine coolant.

15. A method of operating a vehicle air-conditioning system, comprising: determining a first temperature of an engine coolant at an inlet to a heating heat exchanger; determining a second temperature of air at an outlet of said heating heat exchanger; comparing said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate a fault state of a component of said vehicle air-conditioning system; and checking said first temperature and said second temperature to determine whether said first temperature and said second temperature indicate incorrect concentration of antifrost agent in the engine coolant.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) Exemplary embodiments will be described below on the basis of the drawings. In the drawings:

(2) FIG. 1 shows an example of a profile of the air volume flow in dependence on the current engine coolant temperature;

(3) FIG. 2 shows an example of a profile of the fan voltage in dependence on the current engine coolant temperature (ECT) and on other variables; and

(4) FIG. 3 schematically illustrates the vehicle air conditioning system.

DETAILED DESCRIPTION

(5) The air quantity flowing through the heating heat exchanger, also referred to below as air volume flow, is generally proportional to the voltage applied to the fan, which is at most slightly smaller than the maximum available voltage in the vehicle. For example, in an on-board power system of 12.8 volts, the voltage supplied to the fan can be a maximum of 12 volts.

(6) A vehicle air-conditioning system 10 is schematically illustrated in FIG. 3. That vehicle air conditioning system 10 includes a controller 12, in the form of a computing device, a first sensor 14 for monitoring a first temperature of an engine coolant at an inlet 20 to a heating heat exchanger 18 and a second sensor 16 for monitoring a second temperature of air at an outlet 22 of the heating heat exchanger.

(7) In the case of a request for maximum heating power or in defroster operating mode the air volume flow is regulated by the controller 12 of this air conditioning system 10 in a temperature-dependent manner as follows.

(8) As shown in the graphs of FIG. 1, at engine coolant temperatures around zero ° C. the air volume flow is limited to approximately 50% and increases approximately linearly with rising engine coolant temperature until, at engine coolant temperatures of 50° C. and higher, it is approx. 80% of the maximum value.

(9) The air volume flow is expediently regulated by correspondingly setting fan voltage, as shown in the graph of FIG. 2, and specifically in the dependence, specified on the abscissa, on the current engine coolant temperature (ECT), the ambient temperature (T.sub.ambient), and the opening temperature of the thermostat (T.sub.thermostat,opening). Here, the minimum fan voltage is a fixedly predefined value, in this example 50% of the on-board power system voltage, which value permits a noise level of the fan, that is still perceivable, as an acoustic confirmation of correct functioning. The maximum fan voltage here should be approx. 80% of the on-board power system voltage. If the engine coolant temperature and thus the blowing-out temperature of the air-conditioning system reaches or exceeds a limit value, the air volume flow is limited to a corresponding maximum value.

(10) The dependence, shown in FIG. 2, of the air volume flow on the coolant temperature may be stored, for example in the form of a lookup table, by the software of the air-conditioning system.

(11) Table 1, which is reproduced below, shows calculated heating of the passenger compartment of a certain motor vehicle type having an air-conditioning system whose fan voltage is the function, shown in FIG. 2, of the current coolant temperature.

(12) TABLE-US-00001 TABLE 1 Constant fan voltage = 80% of Fan voltage the maximum value as f (ECT) Blowing- Average Blowing- Average out interior out interior temper- temper- temper- temper- ature ature ature ature Starting conditions ° C. −18.0 −18.0 −18.0 −18.0 Idle state after 5 min ° C. 12.7 −5.7 21.9 −4.7 after 10 min ° C. 20.4 0.4 31.8 1.9 50 km/h phase after 5 min ° C. 36.2 8.3 43.6 9.2 after 10 min ° C. 41.7 14.1 50.1 15.3 after 15 min ° C. 44.6 18.1 47.3 19.1 after 20 min ° C. 45.7 20.9 47.4 21.6 after 25 min ° C. 46.1 22.9 47.3 23.5 after 30 min ° C. 46.7 24.4 47.5 25.0 100 km/h phase after 10 min ° C. 66.9 39.1 67.0 39.1 Idle state after 10 min ° C. 44.5 31.6 44.3 33.6

(13) The times specified in table 1 relate to a standard test procedure of the applicant. The vehicle is firstly cooled to −18° C. in this case. Following the start of the engine, the vehicle runs firstly for 10 minutes in the idle state, then for 30 minutes at a constant 50 km/h, then for 10 minutes at a constant 100 km/h, and then for 10 minutes in the idle state again.

(14) As can be seen from table 1, the vehicle cabin can be heated up significantly more quickly in the case of temperature-dependent regulation of the fan voltage than at a constant fan voltage.

(15) Alternatively, the air volume flow is regulated in such a way that the difference between the temperature of the coolant into the heating heat exchanger 18 and the temperature of the air flowing out of the heating heat exchanger is not greater than a predefined value which may be for example 2° K. In this way too, the vehicle cabin can be heated up significantly more quickly.

(16) Thus, only the air volume flow is regulated and not the coolant mass flow which flows through the heating heat exchanger 18 of the air-conditioning system 10 and depends on parameters other than the air volume flow. In the internal combustion engine, the air volume flow is obtained substantially by the rotational speed of the engine and the function of the thermostat.

(17) In battery electric vehicles and hybrid electric vehicles, in which the method described is likewise applicable, the heating heat exchanger 18 being thermally connected to the traction current batteries and to the power electronics, the air volume flow is determined substantially by the current temperatures of the traction current batteries and of the power electronics.

(18) The methods described may also be advantageously carried out with the inclusion of a positive temperature coefficient (PTC) supplementary heating element upstream or downstream of the heating heat exchanger 18. Such a PTC supplementary heating element is often available in battery electric vehicles and hybrid electric vehicles, but may also be available in vehicles operated purely by internal combustion engines.

(19) The described air quantity regulation which is limited in a temperature-dependent manner is advantageous in particular for the following reasons. In the case of low coolant temperatures at the inlet 20 into the heating heat exchanger 18, only a very small part of the heating heat exchanger is used for heat transfer in the case of a large air quantity since the coolant is already substantially cooled down just after entering the heating heat exchanger. An ideal heat exchange would be realized if the temperature of the coolant were to reach ambient temperature just before exiting the heating heat exchanger 18. In other words, when there is a small difference between the inlet-air temperature and the inlet-coolant temperature at the heating heat exchanger 18, the air quantity could be very small (as far as zero) and increases with rising coolant temperature. However, too small an air quantity can lead to condensation in the vehicle, and so a minimum air quantity is necessary at all times for preventing or eliminating condensation, for which quantity a value of 50% of the maximum air quantity has been assumed here, this, however, depending on the design of the vehicle, of the air-guiding channels and of the air-conditioning system.

(20) Without the air quantity limitation described or with a limitation, known per se, to 80% of the maximum air quantity, when there is a relatively high air throughput the blowing-out temperature of the air would drop, and the air would flow more quickly through the interior and also quickly exit it again.

(21) By contrast, in the case of relatively low air throughput the blowing-out temperature of the air into the interior of the vehicle rises. As a result, the residence time of the air in the interior of the vehicle is also longer, and therefore more heat can be discharged to the interior before the air exits the interior again through extractors.

(22) On account of measurement and adjustment of the inlet-air temperature and the in-let-coolant temperature into the heating heat exchanger 18, the following diagnoses can be made: Correct functioning or malfunctioning of the closing valve 26 of the heating heat exchanger Correct functioning or malfunctioning of a mixing flap 28 of the air-conditioning system in relation to the inlet-air temperature Identification of a low coolant level or of gas bubbles in the heating heat exchanger Identification of the concentration of antifrost agent in the coolant

(23) Anomalous temperatures or temperature differences indicate fault states of components of the air-conditioning system 10, and different fault states can also be distinguished from one another, in particular as follows:

(24) Malfunctioning of the Closing Valve of the Heating Heat Exchanger:

(25) The temperature of the coolant rises, the blowing-out-temperature sensors for the air out of the air-conditioning system show a rise, the temperature sensor at the inlet 20 into the heating heat exchanger 18, however, shows no rise.

(26) Malfunctioning of a Mixing Flap in Relation to Blowing-Out-Temperature Sensor(s):

(27) The temperature of the coolant rises, the blowing-out-temperature sensors for the air out of the air-conditioning system show no rise, the temperature sensor at the inlet 20 into the heating heat exchanger 18, however, shows a rise.

(28) Identification of a Low Coolant Level or of Gas Bubbles or

(29) Identification of the Concentration of Antifrost Agent in the Coolant:

(30) In the heating heat exchanger 18 of the air-conditioning system 10, the coolant heats up the air which flows into the interior of the vehicle. The exchange of heat can be described by an equation which contains only parameters which are able to be measured, calculated, or stored electronically by way of a characteristic map. It is possible to calculate from the individual values a value cps which ideally is equal to a defined thermal capacity c.sub.pc,ref (reference thermal capacity) of the coolant. The formula relationship is in this case as follows:

(31) $\mathrm{Fault}\mathrm{value}\left[\%\right]=\frac{c_{\mathrm{pc}}}{c_{\mathrm{pc},\mathrm{ref}}}=\frac{c_{pA}.Math.M_a.Math.\left(T_{A0}-T_{\mathrm{Ai}}\right)}{c_{\mathrm{pc},\mathrm{ref}}.Math.M_c.Math.\left(T_{\mathrm{ci}}-T_{\mathrm{co}}\right).Math.\phi }$

(32) Here: c.sub.pA is the thermal capacity of the air as f (T, φ, p)

(33) M.sub.a is the air mass flow as f (fan stage, vehicle speed, operating mode of the air-conditioning system, etc.)

(34) T.sub.Ai is the temperature of the air at the inlet 20 into the heating heat exchanger 18 measurement value (evaporator temperature sensor)

(35) T.sub.A0 is the temperature of the air at the outlet 22 out of the heating heat exchanger 18-->measurement value by means of new sensor (alternatively: measurement value of the blowing-out temperature sensors) c.sub.pc,ref is the reference thermal capacity of the coolant M.sub.c is the coolant mass flow, known as f (engine rotational speed, thermostat control, voltage, etc.) T.sub.ci is the temperature of the coolant at the inlet 20 into the heating heat exchanger 18 is equal to the coolant temperature in the engine, which temperature is available as a measurement value T.sub.co is the temperature of the coolant at the outlet 22 out of the heating heat exchanger 18-->is known from component tests (dependent on air mass flow, T.sub.ci, T.sub.Ai, . . . ) φ is the degree of exchange of the heat exchanger. Is determined in component tests. Can also be determined jointly with T.sub.co (in which case φ=1)

(36) The fault value is assigned here, for example, the following fault codes:

(37) TABLE-US-00002 Fault value Fault code   1 . . . 0.9 No fault 0.9 . . . 0.7 Insufficient coolant frost protection 0.7 . . . 0.2 Air in the coolant circuit 0.2 . . . 0   Critical coolant loss