The invention is based on a heatable washer system according to the preamble of claim 1.
Windshield washer systems for vehicles are usually used in conjunction with windshield wipers. They are actuated when the moisture from precipitation is not sufficient to clean the vehicle windshield. They contain a reservoir, spraying nozzles, and a water pump that delivers washer fluidxe2x80x94to which cleaning and antifreeze additives are possibly addedxe2x80x94with pressure from the reservoir via water lines to the spraying nozzles. The spraying nozzles are usually secured to a part of a vehicle body, e.g., to an engine hood, a window frame or the like. To prevent the spraying nozzles from freezing at temperatures below the freezing point, heating elements are integrated in the spraying nozzles that are connected to a power supply via outboard connector plugs. The heating elements require a relatively high manufacturing expenditure for the spraying nozzles and a large installation expenditure in order to lay the electrical cables and contact the connector plugs. Moreover, the highly volatile antifreeze additives evaporate quickly and the residues cause the nozzle openings to clog.
It has already been made known in DE 198 15 171 A1 to secure spraying nozzles as additional elements to the wiper blade, as the mounting element, and therefore to distribute the sprayed water directly onto the wiped area with streams of short length. Since the sprayed water is concentrated in an area in the vicinity of the wiper blade and is wiped away very quickly by the wiping motion, the view is obscured only briefly by the sprayed water used. A disadvantage of such systems, however, is that weathering influences, in particular hail and extreme effects of the sun, strongly influence the flexible parts of this arrangement, which are required to bridge the hinged regions between wiper arm and wiper blade. Moreover, the spraying nozzles and water linesxe2x80x94which are exposed to the air streamxe2x80x94quickly freeze shut at temperatures below the freezing point if an insufficient quantity of antifreeze additive is added to the water. It usually takes a great deal of effort to thaw out the frozen water lines and spraying nozzles.
In order to prevent freezing of the spraying nozzles secured to the wiper arm or wiper blade, and the connected water line, a heating cable is provided in the water line. This is particularly important for wipers having larger wiper blade lengths and a plurality of spraying nozzles. Because, in this case, the spraying nozzles are located on the wiper blade at a certain distance next to each other and they are exposed to the ambient temperature just like the connecting water line.
The older patent application DE 199 13 193 describes a washer system, the spraying nozzles of which have an uninterrupted water passage that comprises, on its ends, a coupler to the continuing water line. This leads to a further spraying nozzle or the reservoir. A cap plug that closes the water passage is clipped on the coupler at the last spraying nozzle. In order to adjust the spraying nozzles and the water lines well to the respective mounting elements, the couplers of the spraying nozzles have a straight or angled form as necessary.
The nozzle body of the spraying nozzle is made out of plastic and is clipped into a housing. A connecting passage branches off from the continuous water passage of the spraying nozzle, and leads to a spraying passage with a nozzle opening. When pressure builds up in the water pump, washer fluid is pushed out of the reservoir through the lines of the system to the nozzle opening and then moves through the nozzle opening into the open. One variant proposes a non-return valve so that washer fluid does not flow back in the unpressurized state, so that the lines are partially emptied. A diaphragm thereby closes the connecting passage in the unpressurized state. This can lie close to the nozzle opening, so that only a small volume of water is stored between the diaphragm and the nozzle opening and can flow out or evaporate in uncontrolled fashion.
The diaphragm is designed as a rubber-elastic hose diaphragm that has beads on its ends. These are embedded in ring grooves of the nozzle body. When the washer fluid flows through the connecting passage, a ring space on the circumference of the nozzle body is filled and the diaphragm is expanded. The diaphragm is thereby supported externally on the housing and clears the outlet openings of the connecting passage and the spray passage on the circumference of the nozzle body.
Washer systems are also on the market in which a heating element is located in the reservoir for the washer fluid. Although the warmed washer fluid improves the cleaning force of the spraying nozzles, the spraying nozzles cannot be prevented from freezing if frost develops during breaks in operation without additional heating elements.
According to the invention, the water line in a heatable washer system has two passages, one of which is connected to the pressure side of the water pump, and the other of which is connected to the reservoir and, thereby, to the suction side of the water pump. An open circulation is produced as a result, in which the water pump circulates the warmed washer fluid, supplies the washer system with heat, and therefore prevents parts of the washer system from freezing if frost develops, without additional heating elements. All spraying nozzles that are connected to the water line have pressure valves in front of their nozzle opening that are advantageously designed as non-return valves. During the circulation operation, the pressure in the water line is below the opening pressure of the pressure valves. In order to actuate the spraying nozzles, the pressure in the water line is raised above the opening pressure of the pressure valves, so that washer fluid is sprayed through the opened pressure valves and the nozzle openings onto the vehicle windshield. The spraying procedure is ended by reducing the pressure in the water line to the circulating pressure.
The pressure in the water line can be created in different fashions. According to one embodiment of the invention, a two-step water pump is provided. In the first step, it produces the operating pressure for the circulation operation, while, in the second step, it is designed for the spraying pressure. By switching from one step to the next, the washing function is activated or ended. A steplessly variable [water pump] can be used instead of a two-step water pump. This is advantageously controlled below the opening pressure of the pressure valve as a function of temperature, so that the circulation performance and, therefore, the energy consumption of the water pump, can be adapted to the respective requirements. Furthermore, unnecessary evaporation of washer fluid at the spraying nozzlesxe2x80x94which can result in the formation of depositsxe2x80x94is prevented.
Using a constantly-delivering water pump, the pressure in the water line can be controlled by means of a controllable pressure limiting valve. This can be located basically on the suction side or the pressure side of the water pump. If the pressure limiting valve lies on the pressure side, it is practical to provide a pressure valve opening in the delivery direction and designed as a non-return valve parallel to the pressure limiting valve. If a spraying pressure is controlled at the pressure limiting valve, the pressure valve opens, in order to make larger delivery quantities available quickly.
A further possibility for pressure control lies in the fact that an adjustable restrictor is provided in the water line. Depending on the control of the nozzle, the flow rate through the water line increases, which, with a positioning in the inlet, leads to a pressure increase and, with a positioning in the return, leads to a pressure reduction. A temperature-dependent control of the circulation quantity is possible hereby as well.
According to one embodiment, the heating element located in the reservoir can be controlled as a function of the external temperature, independently of the flow rate of washer fluid, so that the temperature of the washer fluid is kept within a desired temperature range in accordance with the external temperature. It is hereby sufficient when the washer fluid in the reservoir is only heated below +5xc2x0 C.
All variants represent simple embodiments of a heatable washer system, because additional heating cables in the water lines up to the spraying nozzles are eliminated. Additionally, additional contacts required for electrical heating elements located at the spraying nozzles can be eliminated. In advantageous fashion, electrical contact sites are provided only at the reservoir, which can also be used simultaneously for the heating device and the water pump, if necessary.
In order to make an optimal heating of the complete system possible with minimal use of energy, the invention provides that the washer system comprises a washer module with integrated water pump, heating device, and electronics that processes input signals, such as the external temperature or the actuation of the switch on the steering column, for example, into an output signal for heating or changing the flow rate of the washer fluid. In a variant of the invention, the washer module is controlled by means of external vehicle or wiper electronics. The proposed means of attaining a heatable washer system should be used mainly in systems having spraying nozzles integrated on the wiper arm or wiper blade. Due to the simple and variable embodiment, however, it also functions with spraying nozzles positioned on the vehicle hood.
In order to make a flexible manufacture of a washer system according to the invention possible, it is provided, according to one embodiment of the invention, that the washer system be composed of different functional parts, such as spraying nozzles, connecting pieces, distributor elements, washer module, and the like. Couplers are thereby provided at the junction points, that connect the parts of the water line tightly to each other. In a water line having two passages that are separated from each other by means of a common dividing wall, the dividing wall is designed as a coupling in the connecting region by an extension of a dividing wall gripping in a gap on the face of the contiguous dividing wall of an adjacent functional part. An absolute tightness between the passages is not necessary, because small short-circuit currents can be tolerated.