Systems and methods for windshield deicing.

(54) Title: WINDSHIELD DEFROST SYSTEMS AND METHODS. (54) Title: SYSTEMS AND METHODS FOR WINDSHIELD DEICING.

(57) Summary

Systems and methods are described for rapid windshield de-icing, which are efficient in cost and light; systems use boost converters and inverters, or dual-voltage batteries, to provide a high enough voltage to defrost a windshield in less than 30 seconds.

(57) Abstract

Cost efflclent, llghtwelght and rapld wlndshleld delclng systems and methods are dlsclosed. The systems utlllze stepup converters or inverters, or dual-voltage batterles, to provlde a voltage high enough to delee a wlndshleld ¡n less than thlrty seconds.

WINDSHIELD DEFROST SYSTEMS AND METHODS

BACKGROUND OF THE INVENTION

Clear windshields for various vehicles, such as cars, rail vehicles that include trains, modern trams and locomotives, snowmobiles, planes, helicopters, and marine vessels, must be thawed or thawed using the available on-board power. Thawing or defrosting is usually done by blowing air heated by the vehicle's engine onto the windshield. However, especially since the engine initially cools at start-up, defrost / defrost takes a considerable time.

To thaw a windshield in less than thirty seconds, a high voltage (typically more than 100V) and high power (typically more than 3kW) must be applied to an electrically heated windshield. Common 12V DC power sources, found in most commercial and passenger vehicles, are capable of supplying up to 10kW of power but only at extremely low resistance loads such as 0.01 ohms. A conductive film windshield heater, to be transparent enough, must have a resistance of more than 1 ohm. In this way, traditional 12V power sources are not able to meet the requirements of a fast windshield defrost system with a transparent windshield heater.

Previous attempts to increase the on-board voltage have involved either disconnecting an alternator from a battery and increasing the idle rotation speed (see for example US Patent No. 4,862,055) or supplying a step-up transformer with a rectified AC current from a alternator ( see for example, US Patent No. 5,057,763). In both cases, the output power was limited by the size of the alternator so that the voltage required for rapid windshield defrost could not be achieved without significant resizing of the alternator. Also, because an alternator generates low-frequency power, a step-up transformer of sufficientoutput power is heavy and expensive to manufacture.

BRIEF DESCRIPTION OF THE INVENTION

The instrumentation means described anticipate the art by providing cost-effective, lightweight, and fast windshield de-icing systems and methods.

In one embodiment, a windshield de-icing system includes: a low-voltage power source to provide low-voltage power;

a step-up DC-DC converter to transform low-voltage power into high-voltage DC power; an activating device to enable the booster DC-DC converter; a windshield heater; and a switch between the boost DC-DC converter and the windshield heater, the windshield heater heats resistively when the switch is closed and the high voltage DC power is conducted through the windshield heater.

In one embodiment, a windshield de-icing system includes:

a low-voltage power source to provide low-voltage DC power; a step-up DC-AC inverter to transform low-voltage DC power into high-voltage AC power; an activating device for the lifting DC-AC inverter; a windshield heater; and a switch between the riser DC-AC inverter and the windshield heater, the windshield heater heats resistively when the DC-AC inverter is active and the switch closes and the high-voltage AC power is conducted through the windshield heater.

In one embodiment, a windshield de-icing system includes: a dual-voltage battery to provide high-voltage DC power in a low-voltage mode and high-voltage DC power in a high-voltage mode; a first switch arranged between the dual voltage battery and additional electrical components of a vehicle, the first switch closes when the dual voltage battery is in the low voltage mode; and a second Switch arranged between the dual voltage battery and a windshield heater, the second Switch closes and the first switch opens when the dual voltage battery is in the high voltage mode. An alternative form of dual voltage battery has multiple low voltage sections, for example 12 volts. These sections are coupled in parallel for high current low voltage applications such as vehicle starting. When high voltage is required, the sections of the battery couple together, but one section remains coupled to low-voltage loads to dampen alternator breakouts and low-power current loads such as electronic engine controls.

In one embodiment, a method of de-icing windshields includes supplying low-voltage power to a vehicle's electrical components, transforming low-voltage power into high-voltage power, and supplying high-voltage power to a windshield heater for heating. resistive the windshield heater and thaw a surface of the windshield.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an exemplary embodiment of the windshield de-icing system having a booster DC-DC converter;

Figure 2 illustrates an exemplary circuit of the booster DC-DC converter of Figure 1;

Figure 3 illustrates an exemplary embodiment of the windshield de-icing system having a lift DC-AC inverter;

Figure 4 illustrates an exemplary embodiment of the windshield de-icing system having a dual voltage battery;

Figure 5 illustrates exemplary circuit systems of the dual voltage battery of Figure 4;

Figure 6A shows an exemplary configuration of a

Switch between batteries used in the double voltage battery of figure 4;

Figure 6B shows another exemplary configuration of a

Switch between batteries used in the double voltage battery of figure 4;

Figure 7 shows a cross-sectional view of an exemplary embodiment of a windshield having windshield heaters disposed on outer surfaces of glass layers of the windshield;

Figure 8 shows a cross-sectional view of an exemplary embodiment of a windshield having windshield heaters disposed between a layer of butylral pollvlnll (PVB) and glass layers of the windshield; and

Figure 9 shows a cross-sectional view of an exemplary embodiment of a windshield incorporating features of both Figure 7 and Figure 8.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the terms thaw and thaw will be used interchangeably to refer to a procedure that removes frozen water from a surface. Frozen water can be in any form. For example, frozen water may be present as a solid layer of ice or as ice crystals attached to the surface.

The windscreen de-icing systems described herein provide a high density of heating power (W / m²), which allows quick defrost and energy saving. Rapid heating ensures that only a thin layer of ice (for example, less than 1 cm, or less than

0.5 cm, or between 1 pm and 1 mm) at the ice / windshield interface to heat to the ice melting point. Thus, the remote parts of the windshield and ice do not necessarily heat up, and minimal energy is lost in the surrounding environment. This concept is further described in the patents of

USA No. 6,870,139 and 7,034,257, each incorporated by reference herein. As shown in these patents, the higher the heating density, the less energy is needed to defrost.

Figure 1 shows a windshield de-icing system 100 including an alternator 10, a battery 12, a booster DC-DC converter

15, a windshield heater 17, and switches 13, 14, and 16. In normal vehicle operation, switch 13 closes and switches 14 and

16. During defrost, switch 13 can be either opened or closed and switches 14 and 16 are closed. In the defrost configuration, the boost DC-DC converter 15 converts low-voltage direct current (DC) power (eg 12V DC) from battery 12, or battery 12 and alternator 10, into high DC power voltage (typically 70V to 300V, or 40V to 1000V). The high voltage is used to activate the windshield heater 17, which generates heat due to electrical resistance, R.

In an alternative embodiment, switch 14 is replaced with a high current fuse. In modes having switch 14, closing switch 14 activates the DC-DC converter. In modes without switch 14, a control input is provided in the converter

DC-DC 15 which, in one state, enables the DC-DC converter, and in another state disables the internal interrupting transistors of an input DC-AC section of the DC-DC converter, thereby preventing the DC-DC converter from battery power.

An advantage of system 100 is that battery 12 alone, or in conjunction with an alternator 10, can supply heater 17 with more power than alternator 10 alone. A typical 12V battery, such as a car-equipped one, is capable of supplying 7kW to 10kW for up to approximately thirty seconds without damage. Thirty seconds of 7kW power is enough to defrost a windshield, and battery 12 can be recharged by alternator 10 between such defrost events.

Another advantage of system 100 is that, due to the use of high voltage and high power, the defrost duration is short (for example, less than thirty seconds at T> -10 ° C), compared to most other systems. thawing of the prior art. The booster DC-DC converter 15 can then be smaller in size and lower in cost than similar converters designed for continuous operation at the same power level.

For example, the transformer and its windings within the booster DC-DC converter 15 may be smaller in size, lower grade magnetic materials may be used, and larger losses in semiconductor devices such as diodes and MOSFET switches may be allowed, used to rectify the high voltage current of the converter

DC-DC elevator. Similarly, in semiconductor devices smaller heatsinks and smaller and smaller cooling devices such as cooling fans can be used compared to what would be required for continuous operation.

An additional advantage of the defrost system 100 is that the battery 12 and DC-DC converter 15 can be electrically separated from the alternator 10 and other electrical components of the vehicle by opening switch 13. Opening the switch 13 can thus prevent damage to vehicle electronics when power is drawn from battery 12 and the high-frequency harmonic that can be generated through the DC-DC converter 15.

For illustrative purposes, Figure 2 shows an exemplary circuit.

200 of the riser DC-DC converter 15 of Fig. 1. Circuit 200 is a full-bridged DC-DC converter, but other types of riser DCDC converters, such as a half-bridged DC-DC converter, can be used in system 100 .

It will be appreciated that switches 13, 14, and 16 may be mechanical, electromagnetic, solid state semiconductor switches, or a combination thereof. Furthermore, Switches 13, 14 and 16 can be replaced by short circuits without departing from the scope of this. Without switches 14 or 16, other methods must be used to activate or deactivate the DC-DC converter such as an electronic control signal to the DC-DC converter control circuitry to activate the heating pulse.

In one embodiment, the DC-DC converter 15, or DC-AC inverter (Figure 3) operates at full power for initial defrosting of the windshield. Once the windshield is defrosted, the DC-DC converter 15, or DC-AC inverter 35 operates in a reduced power output mode to keep the windshield in a defrosted condition. This reduced power output mode is a reduced voltage output operation, or a pulsed operation. For example, a windshield heater that absorbs 1 kilowatt at 500 volts will absorb only 250 watts at 250 volts, similarly, the same windshield heater that operates through a converter that supplies 1 kilowatt for only a quarter of every second will absorb an average power of only 250 watts.

FIG. 3 shows an exemplary windshield de-icing system 300 including an alternator 30, a battery 32, a DCAC boost inverter 35, a windshield heater 37, and switches 33, 34 and 36. During normal vehicle operation, the Switch 33 closes and switches 34 and 36 open. During defrost, Switch 33 can either be opened or closed and Switches 34 and 36 close. For defrost operation, the booster DC-AC inverter 35 inverts low-voltage DC power (for example, 12V) drawn from battery 32, or battery 32 and alternator 30, into high-voltage AC power (typically 70V to 300V, or 40V to 1000V) to activate the windshield heater 37, which produces heat due to electrical resistance, R. A typical AC frequency range for system 300 is approximately 50Hz to approximately 150 kHz.

As noted above with reference to the DCDC 15 converter, another circuitry can be used to enable the DCAC inverter 35 in place of the switch 34.

An advantage of system 300 is that the battery 32 alone, or in conjunction with an alternator 30, can supply the windshield heater 37 with more power than the alternator 30 alone. A regular 12V battery is capable of supplying 7kW to 10 kW for up to approximately 30 seconds without damage. 30 seconds is sufficient to defrost a windshield, and battery 32 can be recharged by alternator 30 between defrost events.

Another advantage of system 300 is that due to the use of high voltage, the defrost duration is short (eg less than 30 seconds at T> 10 ° C). The elevator DC-AC inverter 35 can then be smaller in size and less expensive than similar inverters designed for continuous operation at the same power level. For example, the transformer and its windings within the DC-AC 35 inverter may be smaller in size, lower grade magnetic materials may be used for its step-up transformer, and larger losses in semiconductor devices such as diodes and switches may be allowed MOSFET, used to rectify the high-voltage current of the DC-AC inverter.

Also, since defrosting normally occurs with a cold engine idle, rapid defrosting times will help conserve fuel and minimize polluting gas emissions from the vehicle.

Still another advantage of the defrost system 300 is that the battery 32 and DC-AC inverter 35 can be electrically separated from the alternator 30 and other electrical components of the vehicle when the switch 33 is opened. The opening of the switch 33 can avoid damage to the vehicle electronics when power is drawn from the battery 32, and from the high-frequency harmonic that can be generated through the DCAC 35 inverter, especially if a suppression circuitry is provided. of discharge irruptions or auxiliary battery 38. Because abrupt disconnection of even a 12-volt battery from an alternator that charges the battery at high current can cause surges exceeding 100 volts, the suppression circuitry or auxiliary battery system is recommended.

38.

It will be appreciated that the DC-DC converter 15 (Figure 2) can be an example of a boost DC-AC inverter 35 after removal of the bridge rectifier connected between the boost winding secondary winding and windshield heater 17, 37.

It will further be appreciated that switches 33, 34, and 36 may be mechanical, electromagnetic, solid-state semiconductor switches, or a combination thereof. Furthermore, switch 34 can be replaced with a short circuit without departing from the scope of the present provided that alternative apparatus are provided to enable the system, and switches 33 and 36 can be replaced by short circuits in some embodiments.

FIG. 4 illustrates a windshield defrost system 400 having a dual voltage battery 42 to be used as a high power / high voltage source for rapid windshield defrost. System 400 includes an alternator 40, dual voltage battery 42, a windshield heater 47, and Switches 43 and 46. During normal vehicle operation, battery 42 is set in a low voltage mode (eg 12V), the switch 43 closes and switch 46 opens. During defrost, switch 43 opens, battery 42 adjusts in a high voltage mode (eg, 70V TO 300V, or 40V to 1000V), and Switch 46 closes.

Dual voltage batteries are described, for example, in US Patent Nos. 3,667,025 and 4,114,082, which are incorporated herein by reference. Typically, a dual-voltage battery is made up of a bank of smaller batteries. Figure 5 illustrates an exemplary principle circuitry of the dual voltage battery 42, which for example can provide 12V power in low voltage mode and 84V power in high voltage mode. It will be appreciated that other voltage limits can be obtained by providing different types or numbers of batteries in the bank. When the batteries are connected in parallel, the dual voltage battery 42 supplies the same voltage as each Individual battery, for example,

12V, and is capable of supplying high current. In high voltage mode, the batteries are connected in series, and the dual voltage battery 42 is capable of supplying high voltage that is approximately equal to the sum of the voltages of the individual batteries. Switching between high voltage and low voltage mode can be done by simultaneously activating Switches S53-S64. The connections shown in figure 5 correspond to the high voltage mode.

It will further be appreciated that the systems of Figures 1, 3, and 4 are capable of providing less than maximum continuous heating power by periodically switching between an off state, the low voltage setting, and the high voltage setting. Depending on a duty cycle, that average heating power can be adjusted to any desirable magnitude between 0W and maximum power, which can be provided by the high voltage setting. For example, if the high power setting supplies 5kW of peak power, when a 10% duty cycle is used (for example it is 0.1 second in high voltage mode and 0.9 second in low voltage setting over each one second period) the system will apply 0.1 * 5kW = 500W of heating power to a windshield heater.

It should be further appreciated that when said intermittent mode is used for the system of figure 4, the battery recharges between the heating work cycles from an alternator.

An advantage of the system 400 is that the dual voltage battery 42 is similar in size and weight to a regular low voltage battery, but is capable of supplying the windshield heater 47 with sufficient power to perform rapid defrosting of the windshield.

It will be appreciated that the switches (43, 46, and 53-64) of Figures 5 may be mechanical, electromagnetic, solid state semiconductor switches, or a combination thereof. Two examples of possible battery switches are shown in Figures 6A and 6B. For example, the Switch shown in Figure 6A is based on an isolated raised-side FET driver, while the Switch shown in Figure 6B is based on an opto-insulating Driver.

The batteries 12, 32 and 42 of the windshield de-icing systems 100, 300 and 400 may be lead-acid batteries, Ll-lon batteries, Nl-metal hydride batteries, or any other electrochemical type of battery known in the art.

In one embodiment, the windshield heaters 17, 37, and 47 are transparent continuous film metal oxide coatings made of idlo-tin-oxide (ITO), zinc-oxide, tin-oxide, or any other transparent, electrically conductive film made of a single metal oxide or a mixed material of several metal oxides.

In another embodiment, the windshield heaters 17, 37, and 47 are thin optically transparent metal films made of silver, aluminum, gold, or the like, or of an optically transparent and electrically conductive polymeric material.

Figure 7 shows a cross-sectional view of a windshield 700. The windshield 700 comprises a break-resistant plastic layer of polyvinyl butyral (PVB) 702 laminated between two layers of glass 704. The windshield heaters 706 are then disposed on the outer surfaces 708 of the glass layers 704, and the dielectric layers 710 are arranged in the windshield heaters 706. Dielectric layers 710 increase safety as well as provide tear protection for 706 windshield heaters. Windshield heater 706 (1) defrosts windshield 700, and windshield heater 706 (2) defrosts windshield 700.

Figure 8 shows a cross-sectional view of a windshield 800. The windshield 800 comprises windshield heaters 806 arranged between a layer of break-resistant plastic of polyvinyl butyral (PVB) 802 and layers of glass 804. The windshield heater 806 (1) defrosts windshield 800, and windshield heater 806 (2) defrosts windshield 800. It is appreciated that future windshields can be made of safety glass that incorporates a layer of plastic resistant to breakage of plastics other than

PVB.

Figure 9 shows a cross-sectional view of a windshield 900 having features in common with both the 700 windshield and the 800 windshield. The 900 windshield includes a layer of polyvinyl butyral (PVB)

902, a first pair of windshield heaters 906 (1) and 906 (2), glass layers 9804, a second pair of windshield heaters 906 (3) and 906 (4), and dielectric layers 910. Windshield heaters 906 (2) and 906 (4) can be electrically connected, and operate to defrost windshield 900, while windshield heaters 906 (1) and 906 (3), which can be electrically connected, operate to defrost / defrost the windshield 900.

In one embodiment, the area of ​​a windshield may be separated into multiple sections, each section containing a windshield heater (such as windshield heaters 17, 37, 47, 706, 806, 906) that is electrically isolated from heaters / sections neighbors. Applying power to a windshield heater that has an area smaller than the total area of ​​the windshield provides the application of all of the heating power in a relatively concentrated area. The entire area of ​​the windshield can be thawed in sections one at a time.

EXAMPLE

As discussed above, the main obstacle to rapid windshield thaw using conventional systems is insufficient on-board voltage. The following calculations further illustrate this point.

Typical windshield and ice parameters are shown in Table 1.

TABLE 1

<td>Solid glass windshield coated with ITO</td><td>R₂= 10 ohms (sheet resistance)</td>

<td>Windshield area</td><td>A = 1.5 rrf</td>

<td>Windshield aspect ratio</td><td>r = 1.5</td>

<td>Ice thickness</td><td>t - (mm ice</td>

<td>Effective thickness of windshield glass</td><td>l - 5mm glass</td>

<td>Room temperature</td><td>T = -10 ° C amb</td>

<td>Ice melting point</td><td>T = 0 ° C m</td>

<td>Density of glass</td><td>P = 2500 * ^ glass s</td>

<td>Glass thermal capacity</td><td>C = 150^{Jm, e}g kg- ° C</td>

<td>Ice density</td><td>P = 920kg ice</td>

<td>Thermal capacity of ice</td><td>P = 2200 ^Jice kg ° C</td>

For a windshield with electrical connecting bars placed at the top and bottom of the windscreen, the electrical resistance of the windscreen is:

R = R / r = 6.67 ohms (1)

The heating density of the windshield, using a 12V source is;

<img file="MX2009009586A_D0001.tif" />

RA

RA

<img file="MX2009009586A_D0002.tif" />

(2) where P is the power. At that low heating power density, the windshield cannot be heated from -10 ° C to 0 ° C, even in fixed air, because a cooling convection heat transfer rate of approximately h »5^vatl0S , provides a cooling power rate of:

m - ° C

W conv h-AT «50 watts

Τ '(3) where / 17 = T_m - T_amb = 10 ° C. Therefore, the cooling power rate exceeds the heating power rate by a factor of approximately three.

Even when using transparent conductive coatings that have less resistance than ITO, for example, thin silver coatings with foil resistivity /? □ = 2 ohms, the time required to heat the glass at the melting point of ice is estimated to be :

m.

⁺ Chielo '^mice) δγ

3200y (4) where the heating power for the silver coating is equal to

P = 108W.

In reality, the thawing time (would be even longer than the one calculated by equation (4) due to the convection cooling and additional energy required to melt a layer of ice at the windshield / ice interface. When the thickness of the melted ice layer is only 100 pm, the melt time t increases an additional 400 seconds, the total melt time is therefore 3600 seconds, or 60 minutes.

According to equation (4), rapid defrost (t &lt;30s) would require an increase in heating power by a factor of approximately 100. Thus, an increased voltage of approximately 100V would be necessary for a transparent conductor based silver, and approximately 200V to 300V for a clear ITO-based conductor.

The defrost systems and methods described herein are capable of supplying voltage within the required scale.

Because the DC-DC or DC-AC converter described here to drive the transparent conductor is capable of producing high current electrical voltages that could be dangerous to human health, it is anticipated that the converter may be encapsulated with an encapsulating compound. insulation known in the art, or having a security lock on its cover. In addition, the connectors in the wiring from the converter output terminal to the windshield must be of a type that does not expose any uninsulated metal bolt 10 Regardless if one or more of the connectors are in connected or disconnected condition. In embodiments with the resistive conductive film on the outer surface of the windshield, there must also be a thin insulating coating, or dielectric layer, over the transparent conductive layer on the windshield to prevent these voltages from contacting prying fingers.

In some embodiments that have a DC-AC converter, a dual-voltage battery, or a DC-DC converter, cables of opposite polarity for attachment to opposite sides of the windshield are attached to the windshield from the converter or battery through the circuit to detect ground fault currents that can be lost through a resistive short circuit, such as a human, to the vehicle floor; when such stray current is detected, the high voltage power is immediately turned off or disconnected to interrupt the ground fault. In other embodiments, the high voltage output from the converter or battery is electrically isolated from the vehicle floor to reduce the possibility of a current through a human or other path to ground. In some of these isolated modes, an insulation monitor circuit is used to verify the integrity of the insulation and immediately turn off or disconnect the high voltage if a fault is detected. In some embodiments, the dual-voltage converter or battery is also disabled or disconnected during vehicle conditions when human contact with the windshield is particularly likely, for example when a door is opened or the engine is turned off.

Everything contained herein with reference to 12-volt systems, such as those used in current production automobiles, applies equally to 24-volt systems as frequently used in recently produced trucks and light aircraft, as well as systems using other Battery voltages such as automotive emerging 42 volt systems.

Changes may be made to the above methods and systems without departing from their scope. Therefore, it should be noted that the matter contained in the previous description or shown in the attached drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to encompass all of the generic and specific features described herein, as well as statements of the scope of the present method and system, of which it could be said that, as a matter of language, they are among them.