System for ensuring a desired defrosting process for vehicle windows

Abstract

System for ensuring a desired defrosting process for vehicle windows with simulation modules (3, 5, 6, 7) for modeling an air conditioning unit, an air conditioning duct, a vehicle interior and a window structure, as well as with an electronic computing unit (1) for carrying out a transient heat transport study of the model formed, wherein - given thermal output-related boundary conditions (MS, T_a, T_i, T_b) are input variables of the electronic processing unit (1), - an ice layer with a defined thickness (d_E) is simulated as part of the window structure and - the electronic computing unit (1) comprises a sub-module (8) for modelling the phase transition from ice to water taking into account the melting heat capacity (Cp (melting)).

Description

[0001] The invention relates to a system for ensuring a desired defrosting process for vehicle windows, in particular for electrified vehicles.

[0002] A predefined windshield defrosting process is one of the legally relevant vehicle functions on which the vehicle's type approval depends. Furthermore, the side window defrosting function is subject to relatively strict internal criteria set by the applicant. To validate this function, extensive defrosting tests are conducted on real prototype vehicles in various development phases at ambient temperatures of -20°C in the climate tunnel.

[0003] The basis of every defrosting process is a heating and / or air conditioning system in a vehicle, which preferably has its own control element for selecting its own automatic defrosting program ("Defrost"). Such a heating and / or air conditioning system is described by way of example in DE 3606591 A1 and is described with reference to Fig. 11 to illustrate the basic functioning of air conditioning units is explained below: Accordingly, an air conditioning unit 1 (heating and / or cooling unit) contains, in an air duct 2, a fresh air / recirculating air fan 4, an air / refrigerant heat exchanger 5, and an air / coolant heat exchanger 6, arranged one after the other in the air flow direction 3. Between the two heat exchangers 5 and 6, an air outlet opening 7 is arranged, which can be controlled by means of a changeover flap 8. In the air flow direction 3, downstream of the air / coolant heat exchanger 6, heated air ducts 9 lead to the footwell of the vehicle interior and 10 to defrost vents in the area of ​​the vehicle's windshield.

[0004] The heated air duct 9 to the footwell contains a control flap 11, which is adjustable and closable by means of a servomotor 12. The heated air duct 10 to the defrost vents can be connected by means of a further servomotor 13 via the switchover flap 8, optionally to the outlet opening 7 or the warm air duct 14, or to the outlet side of the air / coolant heat exchanger 6. Intermediate positions of the switchover flap 8 are also possible. The settings of the fan speed 4 and the switchover and control flaps 8 and 11 are determined by the control device 15, which allows the vehicle occupants to make the adjustments using rotary and slide controls and actuates the servomotors 12 and 13 using electro-electronic control elements. The heat exchangers 5 and 6 are supplied with refrigerant or coolant via the refrigerant lines 16 and coolant lines 17, respectively.The coolant flow is determined by a coolant heating valve 18 adjustable on the control device 15, whereby the heating output of the air / coolant heat exchanger 6 can be controlled depending on the valve setting and the coolant temperature. The heating valve 18 can also be designed as a conventional electronically controlled timing valve, whose opening time intervals determine the coolant volume flow. The coolant lines 17 are connected to the usual cooling circuit of the vehicle drive motor 19 with radiator 20. The refrigerant flow through the air / refrigerant heat exchanger 5, and thus both the cooling output during cooling operation and the heating output during heating operation of the refrigerant circuit, is determined by the operation of the refrigerant compressor 21, which is driven by the motor 19 via a conventional clutch (not shown). The refrigerant compressor 21 has different switch-on times depending on the cooling output requirement and setting.

[0005] To switch from cooling to heating mode, a four-way switching valve 22 is installed in the refrigerant line 16. This valve switches between cooling and heating depending on the setting of the control device 1. The flow direction in the refrigerant lines 16 is indicated by solid arrows for the heating mode shown overall in the drawing and by broken arrows for the cooling mode. In heating mode, the refrigerant flows from the outlet of the compressor 21 through the four-way switching valve 22 to the air / refrigerant heat exchanger 5, which acts as a condenser and dissipates the heat generated in the compressor to the heating air. The return line contains a pressure-maintaining valve 24 in a parallel line 23 and leads via another air / refrigerant heat exchanger 25, which acts as a heating evaporator, and through the four-way switching valve 22 back to the inlet of the compressor 21.

[0006] For cooling operation, the four-way valve 22 is switched by means of the control device 15. The refrigerant flows as shown by the broken arrows through the refrigerant lines 16, the further air / refrigerant heat exchanger 25 acting as a cooling condenser, the further parallel line 26 with the one-way valve 27 and expansion valve 28 contained therein and through the air / refrigerant heat exchanger 5 acting as a cooling evaporator in the heating and cooling device 1 back to the one-way valve 22 and to the inlet of the compressor 21. In addition to the usual mechanical, pneumatic, electromagnetic or electromotive actuators for flaps, valves and switches as well as temperature sensors for controlling or regulating the heating and cooling device, the control device 15 is provided with a further temperature sensor 29 for the ambient temperature at the air inlet of the fan 4 or 30 for the coolant temperature in the engine cooling circuit.These sensors 29 and 30 can also be components of the aforementioned control and regulation of the heating and cooling device and can be used multiple times. The temperature values ​​of these sensors 29 and 30 cause the heating mode in the control device 15 to be automatically switched on and off via the refrigerant circuit in the illustrated settings of the rotary and slide controls on the control device 15, to the illustrated switching positions of the changeover and control flaps 8 and 11, respectively, and to heating mode and fan mode according to the usual defrost settings of such heating and cooling devices.

[0007] For further information on the state of the art, please refer to DE 10 2014 000 825 A1, DE 10 2014 215 471 A1 and DE 10 2016 210 038 A1.

[0008] The object of the invention is to develop a system that simulates the defrosting process by means of a heating and / or air conditioning system in a realistic manner in order to reduce hardware and / or test costs.

[0009] This problem is solved by the features of independent claim 1. The dependent claims represent advantageous developments of the invention.

[0010] The invention relates to a system for ensuring a desired defrosting process for vehicle windows with simulation modules for modeling the air conditioning unit, the air conditioning duct, the vehicle interior and the window structure as well as with an electronic computing unit for carrying out a transient heat transport analysis of the model formed, wherein - given thermal output-related boundary conditions are input variables of the electronic processing unit, - an ice layer with a defined thickness is simulated as part of the window structure and - the electronic computing unit includes a sub-module for modelling the phase transition from ice to water, taking into account the melting heat capacity.

[0011] The invention is based on the following considerations: The system according to the invention for securing a desired defrosting process for vehicle windows represents, so to speak, a possibility for virtual safeguarding of the defrosting.

[0012] In light of the electrification of vehicles, where the energy available for defrosting is very limited, an efficient design of the defrosting system is becoming increasingly important. The system according to the invention enables optimal estimation of the required energy quantity and its temporal distribution to meet defrosting requirements, particularly in BEV or PHEV vehicles. Practical experience in this area of ​​application is currently lacking. State of the art:

[0013] Defrosting safety is currently performed exclusively through hardware tests. The defrosting system is designed using steady-state isothermal simulations, with the focus solely on flow analysis at the windshield. Technical problem:

[0014] The hardware tests required to validate the defrosting function are very complex. Efficient design of defrosting systems is virtually impossible using steady-state and isothermal simulations or flow analysis, especially for electric vehicles, because many physical parameters and phenomena, such as timing, heat transfer mechanisms, material properties, ambient conditions, etc., cannot currently be captured. Furthermore, there is a lack of experience with the defrosting process in BEV or PHEV vehicles with low heat output. Basic principle of the invention:

[0015] The hardware test for functional validation is replaced by a physically and thermodynamically accurate simulation (virtual investigation) of the defrosting process, which can significantly reduce costs. The aim is to realistically simulate the defrosting test in the air conditioning tunnel.

[0016] In addition, the issue of efficient defrosting, especially in electric vehicles, can be addressed and the energy balance of these vehicles can be positively influenced. This simulation approach enables various parameter studies, which allow conclusions to be drawn about the minimum energy requirement.

[0017] According to the invention, in particular the existing layer of ice is considered a material just like all other materials in a vehicle window structure. The key influencing parameters of the material properties for a given window structure are included in a material simulation module of an electronic processing unit, which represents a core component of the system according to the invention. The inventors recognized that in the simulation module for material properties, the most important influencing parameter to be taken into account for an ice layer as the material to be considered is the melting heat capacity during the phase transition from ice to water; this requires a comparatively very high energy input. This means that the material “ice-water in phase transition” is viewed as an independent material for which the thermodynamic properties are redefined.

[0018] It was also recognized that for an accurate simulation, it is not sufficient to use a model of the windshield structure alone. While this model is the core of the overall system, additional modeling of the air conditioning unit, the air conditioning duct, and the vehicle interior is necessary to realistically define the boundary conditions of the windshield structure (including the ice layer). Otherwise, a model analysis would be too inaccurate and would not correspond to the tests.

[0019] The system according to the invention comprises, in particular, simulation modules for modeling the air conditioning duct, the air conditioning unit, the interior, and the window structure, as well as an electronic computing unit for transiently investigating the resulting model using a known method for dynamically examining heat transport mechanisms, for example, known as the "Conjugate Heat Transfer Method" (CHT analysis). Such a method is also described, for example, in DE 10 2015 217 177 A1. A CHT analysis enables the calculation of heat flows and their spatial orientation during transient system operation.

[0020] Input variables of the electronic processing unit are also given boundary conditions, such as in this invention in particular the mass flow of the air conditioning unit, the outside temperature (corresponds to the temperature of the air conditioning duct in test operation), the temperature of the interior, the outlet temperature of the air flow in the interior near the window (panels) and a predetermined thickness of an ice coating on the window, which preferably has to have melted at the latest within a defined period of time.

[0021] Finally, within the framework of the simulation of the material properties of the disk structure, a sub-module for modeling the phase transition – as mentioned above – is provided in the electronic processing unit. It is assumed that the phase transition occurs between -1 and +1 °C (ΔT=2 K) and that the ice behaves like a virtual material whose heat capacity can be calculated as follows: Cp(melting)=Δh(heat of fusion)ΔT

[0022] The heat capacity Cp of a body is the ratio of the heat supplied to it to the resulting temperature increase ΔT.

[0023] In addition to heat capacity, the density and thermal conductivity of ice can be considered as material properties. Preferably, the heat capacities of ice, water, and phase transitions are considered.

[0024] The invention will be explained in more detail using an exemplary embodiment. It shows Fig. 1 a schematic overview of examples of essential components of the entire system according to the invention, Fig. 2 a characteristic map for describing thermal performance-related boundary conditions, in particular temperature boundary conditions, Fig. 3 a visualized data result of a climate channel simulation module, Fig. 4 a visualized data result of a vehicle interior simulation module, Fig. 5 a visualized data result of a disk structure simulation module, Fig. 6 a sub-module for simulating the phase transition from ice to water, Fig. 7 an output unit for visually displaying the progress of the transient examination for a windscreen, Fig. 8 an output unit for visually displaying the progress of the transient examination for a side window, Fig. 9 a comparison of the virtual examination with a real examination for an early point in time, with the photo of a real vehicle shown on the left and the corresponding representation of the simulation on the right, and Fig. 10 a comparison of the virtual examination with a real examination for a late time point, with the photo of a real vehicle shown on the left and the corresponding representation of the simulation on the right.

[0025] The system according to the invention for ensuring a desired defrosting process for vehicle windows according to Fig. 1 comprises simulation modules for modeling the air conditioning unit, the air conditioning duct, the vehicle interior, and the window structure, as well as an electronic processing unit 1 for conducting a transient heat transport analysis of the resulting model. A simulation module 3 can be provided for constructing an air conditioning unit submodel, a simulation module 5 for constructing an air conditioning duct submodel, a simulation module 6 for constructing a vehicle interior submodel, and a simulation module 7 for constructing a window structure submodel. Such simulation modules are already known. According to the invention, however, the simulation module 7 also takes into account the material properties of a given ice layer with a defined thickness d_E on the window.

[0026] By means of the simulation module 3 and / or by measurements, thermal output-related boundary conditions, in particular the delivered mass flow MS of the air conditioning unit, the outside temperature T_a, the temperature T_i of the vehicle interior and the blow-out temperature T_b at the window diaphragm in the vehicle interior, are recorded and made available as input variables to the electronic processing unit 1.

[0027] The electronic processing unit 1 also includes a sub-module 8 for modelling the phase transition from ice to water taking into account the melting heat capacity Cp (melting) (see also Fig. 6).

[0028] Preferably, a further input variable of the electronic processing unit 1 is a defined period of time dt within which the ice layer must melt. This period of time dt is also specified, in particular, by legal requirements within the framework of type approval for new vehicles.

[0029] The thermal output-related temperature boundary conditions are available to the computing unit 1 in the form of a characteristic map 4 plotted over the defined time period dt. The characteristic map 4 shown was measured with a resolution in time steps of 0.05 [s]. The real time dt to be simulated here was 40 [min] with an ice thickness d_E of 0.48 [mm].

[0030] When building the model, at least one of the following prerequisites is defined: - Assumption that radiation is negligible, - Assumption that after the phase transition the melt water remains on the disc, - free convection is assumed for the climate channel, - forced convection is assumed for the vehicle interior, - When constructing the pane, only the thermal conduction of the individual material layers is taken into account.

[0031] According to Fig.1, the system according to the invention also has an output unit 2, which is connected to the computing unit 1, by means of which the progress of the transient investigation can be visually displayed (see Fig. 7 for a windscreen after 300 [s], 600 [s], 900 [s] and 1800 [s] and Fig. 8 for a side window after 300 [s], 900 [s], 1200 [s] and 1800 [s]) and / or by which a comparison with real transient investigations can be carried out (see Fig. 9 for an earlier time e.g. after 600 s and Fig. 10 for a later time, e.g. after 1200 s; on the left, the photo of a real vehicle and on the right, the corresponding representation of the simulation as proof of the correctness of the simulation).

[0032] The system according to the invention can be integrated in a single computer and contain a microprocessor and a corresponding software program as a computer program product.

[0033] Preferably considered material properties (density R, thermal conductivity k, heat capacity Cp) for ice in the context of modeling the phase transition: R (kg / m3): 918 (Ice) T<272 °K 998 (water) T>274 °K 960 (water / ice average) 272 ≤ T ≤ 274 °K k (W / (m*K)): 2.3 (ice) T<272 °K 0.6 (water) T>274 °K 1.5 (water / ice average) 272 ≤ T ≤ 274 °K Cp (J / (kg*K)): 2100 (Ice) T<272 °K 4182 (water) T>274 °K 166500 (melting) 272 ≤ T ≤ 274 °K In Fig. 6 or in sub-module 8 of the Fig. 1 shows a corresponding Cp polynomial.

Claims

[1] System for ensuring a desired defrosting process for vehicle windows with simulation modules (3, 5, 6, 7) for modeling an air conditioning unit, an air conditioning duct, a vehicle interior and a window structure, as well as with an electronic computing unit (1) for carrying out a transient heat transport study of the model formed, wherein - given thermal output-related boundary conditions (MS, T_a, T_i, T_b) are input variables of the electronic processing unit (1), - an ice layer with a defined thickness (d_E) is simulated as part of the window structure and - the electronic computing unit (1) comprises a sub-module (8) for modelling the phase transition from ice to water taking into account the melting heat capacity (Cp (melting)). [2] System according to claim 1, characterized bythat the given thermal output-related boundary conditions are the mass flow (MS) of the air conditioning unit, the outside temperature (T_a), the temperature (T_i) of the vehicle interior and the outlet temperature (T_b). [3] System according to one of the preceding claims, characterized by that a further input variable of the electronic computing unit (1) is a defined period of time (dt) within which the ice layer must have melted. [4] System according to one of the preceding claims, characterized by that the heat output-related input variables for the defined period (dt) are present in the computing unit (1) in the form of a characteristic map (4). [5] System according to one of the preceding claims, characterized by that in the simulation modules (3, 5, 6, 7, 8) at least one of the following prerequisites is defined during modeling: - radiation is neglected, - free convection is assumed for the climate channel, - forced convection is assumed for the vehicle interior, - only the heat conduction of the individual material layers is taken into account in the pane construction and / or - after the phase transition, the meltwater is assumed to remain on the disk. [6] System according to one of the preceding claims, characterized by that an output unit (2) is connected to the computing unit (1), by means of which the progress of the transient investigation can be displayed and / or by means of which a comparison with real transient investigations can be carried out. [7] System according to one of the preceding claims characterized by that the system is integrated into a single computer.

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