Abstract:
The present invention relates to a low-cost windshield wiper control system which can be readily incorporated into existing vehicle systems, particularly into an operator-accessible windshield wiper control unit assembly ( 100 ). The windshield wiper control assembly ( 100 ) is selectively operable as an intermittent wiper control system, or as a rain sensing windshield wiper control system without the need for microprocessors or multiplex circuitry.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a windshield wiper control system for a vehicle. More particularly, the present invention relates to a low-cost windshield wiper control system which may be configured in a plurality of ways. 
         [0002]    In recent years, it has been increasingly common for motor vehicles to incorporate rain sensing wiper control systems that adjust the speed of the wipers in response to the accumulation of water on the outside surface of the windshield. This is especially true of luxury motor vehicles. Most commonly, these systems employ an optical rain sensor to detect the presence of water on the windshield glass. The presence of rain or snow on the outside surface of the windshield disrupts light beams emitted by the optical sensor, and the rain sensor detects such disruptions to determine an appropriate speed for the vehicle wipers. A practical implementation of such a system was taught by Teder in U.S. Pat. No. 5,059,877. The rain sensor taught in U.S. Pat. No. 5,898,183 to Teder shows a rain sensor may be made in a very compact and inexpensive form. 
         [0003]    The sensor, however, represents only part of a complete rain sensing windshield wiper control system. The sensor must be operatively connected to a windshield wiper motor which, in turn, is connected to a wiper linkage that runs the wipers to keep the windshield clear of water. In most modern rain sensing wiper systems, communication from the sensor is typically done in digital form over a multiplexed system such as a Local Interconnect Network (“LIN”) or Controller Area Network (“CAN”) bus. Indeed, the trend in most vehicle wiring has been towards more use of such multiplexed systems for a variety of purposes. These allow for greater system integration and intercommunication, improved system diagnostics, as well as other advantages. Many luxury vehicles use these multiplexed systems in almost all systems and subsystems. It is no surprise, therefore, that almost all currently produced factory-installed rain sensing windshield wiper systems are built around the CAN and LIN bus architectures. 
         [0004]    With all the advantages of multiplexed systems noted above, a critical disadvantage is the cost of such systems. Cost, typically is the single biggest driver as to whether or not a particular convenience feature is included as a standard feature or offered as an option on any particular vehicle. As result, there are currently no low-cost cars sold in North America that offer rain sensing windshield wipers, even as part of an option package. 
         [0005]    One lower cost alternative to a LIN or CAN based system is to put an interface module between the wiper motor and the switch, for example as taught by Teder in U.S. Pat. No. 5,239,244. An interface module may include relays that directly supply current to the wiper motor. A similar device is sold by Opto-Electronic Design under the trademark “Rain Tracker.” This approach is markedly less expensive than a CAN approach, but the interface module still has the expense of a plastic housing, relays, etc. Also, there is reluctance on the part of the vehicle manufacturer to proliferate ever more small control modules under the dashboard. 
         [0006]    Alternatively, manufacturers may integrate a computer-based rain sensor interface, with or without CAN communications, directly into the wiper motor housing. This has been done, for example, in many production General Motors vehicles sold in the mid-1990&#39;s with rain sensing windshield wiper control systems. The control circuit was enclosed in a suitable weatherproof enclosure for the electronic circuitry, as the under-hood environment of the wiper motor can be quite harsh. The electronic circuitry must thus also be designed to withstand an extended temperature range. Also, the connection to the sensor must be made through the vehicle firewall. This approach works well, but is not low cost. 
         [0007]    It is a common configuration in currently produced low-cost cars to include a simple intermittent wiper control system built into the windshield wiper operation switch instead of the wiper motor. The general trend has been away from such systems, partly because the space for the wiper switch is crowded by the need for a large airbag assembly built into the steering wheel hub. One such system is taught by Uchiayama in U.S. Pat. No. 5,708,242. This system does not accept a rain sensor input, however, and the physical size limits imposed upon the wiper switch would make it difficult to increase the complexity of the system. 
         [0008]    The trend in vehicle wiring systems and rain sensing wiper control systems is thus towards greater complexity, and this will likely evolve over time to become affordable. Today, however, in order to provide the convenience of rain sensing wipers for low-cost cars and vehicles sold in emerging markets, a truly simple and inexpensive complete rain sensing wiper system is needed. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is directed to a low-cost windshield wiper control system which is readily incorporated into existing vehicle systems and is, in particular, operatively connected to/integrated into the operator-accessible windshield wiper control unit assembly, and is selectively operable as a conventional intermittent windshield wiper control system, or as a rain sensing windshield wiper control system. When a rain sensor is part of the windshield wiper control system, the rain sensor is capable of producing varying control voltage outputs, each of which has an associated rain sensor output electrical resistance. Preferably, integrated into the control circuit of the operator accessible windshield wiper control unit, the present wiper control system has an intermittent operation mode wipe timing network which has a timing network resistance. The resistance of the intermittent operation mode wipe timing network is high relative to the rain sensor output resistance so that when a rain sensor is present, and all required elements are operatively connected, the present windshield wiper control system operates in a rain sensing mode, but when the rain sensor is not operatively connected, the high resistance value of the intermittent operation mode timing network causes the present windshield wiper control system to operate as a conventional intermittent wiper system. Such variable mode windshield wiper control operation is accomplished without the need for expensive integrated circuitry and/or micro-processors. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above, as well as other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description when considered in light of the accompanying drawings in which: 
           [0011]      FIG. 1  shows an embodiment of the rain sensing wiper control system according to the present invention, in perspective view. 
           [0012]      FIG. 2  is a schematic diagram of a preferred control circuit for the rain sensing wiper control system according to the invention. 
           [0013]      FIG. 3  presents a graph of the rain sensor voltage output against a slow (on the order of seconds) time scale. 
           [0014]      FIG. 4  is a schematic diagram of a high speed wiper control and automatic headlamp control which are within the scope of certain embodiments of the invention. 
           [0015]      FIG. 5  shows an alternative embodiment of the invention using comparators connected to a divider array to analyze the control voltage signal from the rain sensor. 
           [0016]      FIG. 6  presents a graph of the rain sensor output voltage of the invention compared to fast (order of microseconds) time scale, showing how a pulsatile data signal may be superimposed upon the control voltage signal from the rain sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    A preferred embodiment of the present windshield wiper control system of the invention is shown in  FIG. 1 . The major components of the system comprise a wiper driver motor assembly  10  with integrated cam assembly, an operator accessible windshield wiper control unit  100 , and a rain sensor assembly  60 . Wiper driver motor assembly  10  is connected to control unit assembly  100  with a wiring harness  50 , which also provides power and ground to the system from a vehicle in which the wiper control system is installed. A sensor cable  52  connects the control unit assembly  100  to rain sensor  60 , which is mounted on a windshield (not shown). 
         [0018]    Wiper driver motor assembly  10  is of a conventional type, and is the kind most commonly used in motor cars. It is comprised of a motor  12 , gear drive  14  for driving a wiper arm linkage, and mechanically driven cam/switch  16  for sensing a wiper home position. Cam  16  and gear drive  14  are enclosed in a waterproof assembly  18 , with electrical connections  20  provided. A schematic for wiper driver motor assembly  10  is included in an overall system schematic circuit diagram presented in  FIG. 2 . Cam  16  is disposed to ground a cam output  22  when the wipers are in a home position, and provide 12V electrical power (alternatively called B+) when the wipers are in clearing operation on the windshield, away from a home or rest position. The purpose of cam  16  is to return the wipers to the home position at the end of each wipe cycle. 
         [0019]    A number of wires connect to wiper motor assembly  10  as well as to the vehicle to form wiring harness  50 . The wires include slow winding wire  24 , fast winding wire  26 , power B+, ground  28 , and cam output wire  22 . Optionally, a window wash wire  32  connects a window wash motor  30  to control unit assembly  100 . Thus, there are preferably only six wires in harness  50 , and the distance between wiper motor assembly  10  and switch assembly  100  is typically short in a small car. This keeps the wiring harness simple and inexpensive. 
         [0020]    Wiring harness  50  connects to control unit assembly  100 , which is an integrated switch/controller combination. The control unit assembly  100  includes an electrical switch  102  comprising a set of electrical contacts arranged in a conventional slide switch style of contact arrangement, operatively connected to a control arm  104 . Switch  102  may assume each of 4 positions: OFF, RS/INT, SLOW, and FAST. RS/INT means “Rain Sensor or Intermittent Mode.” Control unit assembly  100  includes a printed circuit board  106 . Electronic control circuitry  108  is disposed upon circuit board  106 . The contacts of switch  102  are integrated into circuit board  106  using rivets in a conventional manner. The single circuit board  106  thus interconnects the circuitry, supports the electrical switch  102  contacts, and provides overall mechanical structure to the control unit assembly  100 . Plastic covers for the circuitry (not shown) may protect the circuitry from mechanical damage, but there is no need for a weatherproof enclosure, as switch  102  is deployed in the passenger compartment of the vehicle. 
         [0021]    An important component of control circuitry  108  of the control unit assembly  100  is the slow relay  110  to engage the slow wiper motor winding  24 . Relay  110  is shown mechanically in  FIG. 1 , and schematically in  FIG. 2 . An electrical input analysis device, for example, a Darlington-type driver transistor  112  is utilized to activate slow relay  110 . A sensor connector  114  is connected to transistor  112  via resistors  116  and  118 . Sensor connector  114  connects to power B+, ground  28 , and a sensor output S. A long time constant, intermittent RC network  120  comprised of resistors  122  and  124 , as well as capacitor  126 , connects cam output wire-to-sensor output S. RC network  120  has a high resistance, so resistor  122  has a high resistance value. For example, resistor  122  may be ≧68K ohms, and capacitor  126  may be about 47 microfarads. A blocking diode  128  is disposed to prevent the network  120  from sending negative voltages to connection S, which could harm electrical input analysis device  112 . A diode, for example, a zener-type diode  130 , prevents inductive voltage spikes generated in slow relay  110  from reaching levels that could damage electrical input analysis device  112 . 
         [0022]    Control circuitry  108  additionally includes a monostable circuit  140 , shown in  FIG. 2 . Monostable circuit  140  is comprised of resistors  142 ,  144 , and  146 , capacitor  148 , transistor  150 , as well as diode  152 . Monostable circuit  140  is configured so as to generate a current pulse, preferably a single current, pulse, through resistor  146  when electrical switch  102  is first switched to the RS/INT position. As will be explained in detail hereafter, monostable circuit  140  does not provide any such pulse if power is applied to switch  102  with the switch already in the off position. Optionally, a MIST switch  156  may be deployed to provide momentary power to wiper motor  12  should the driver pull wiper control arm  104  towards himself or herself. A WASH switch  160  is deployed to engage a wash motor  30 . As an additional option, monostable extend wash circuitry (not shown) may be added to provide for a few follow up wipes in the event of activation of the wash circuit. Such wash circuitry is generally not needed, however, as the rain sensor will detect washer fluid sprayed at the windshield, and provide follow up wipes. This reduces or eliminates the need for wash circuitry. 
         [0023]    Operation of several embodiments of the windshield wiper control system of the present invention will now be described. The present wiper control system is designed so that the vehicle manufacturer may install the system in a vehicle in two configurations: conventional intermittent or rain sensing. The intermittent system is identical to the rain sensing system, except that it lacks rain sensor  60  and sensor cable  52 . Thus, the vehicle manufacturer enjoys the low cost of commonality of most components. 
         [0024]    When deployed as an intermittent system, and when switch  102  is in the OFF position, the wiper motor cam circuitry  16  returns the wipers to a home position at the base of the windshield. To accomplish this, if the wipers are not already home, cam  16  provides B+ to the cam wire  22 . This power flows through the normally closed contact of slow relay  110 , through switch  102 , and to the slow winding  24  of wiper motor  12 . The motor thus spins and moves the wipers by way of the linkage. When the wipers reach the home position, cam  16  grounds cam output  22 . This quickly stops the wiper motor  12 . For manual slow operation, slow winding connection  24  is connected to B+ through switch  102 . MIST switch  156  provides for a momentary operation of the same function. Manual fast is similar, providing B+ to fast winding connection  26  by way of switch  102 . In fast operation, slow winding  24  is disconnected from other electrical connection via switch  102  to prevent a higher voltage present through the generator effect of the motor from being shorted to B+, which would otherwise cause unnecessary wear on the wiper motor. Slow relay  110  is powered through switch  102  by conductor R, which assumes a voltage of B+ only when the switch is in the RS/INT position. 
         [0025]    When switch  102  is moved from off to intermittent, monostable circuit  140  provides a pulse of about one second to the base of transistor  112 , engaging slow relay  110 . It does this by discharging capacitor  148 , which was charged when the switch was in the off position, through transistor  150 . The normally open contact of slow relay  110  provides B+, by way of switch  102 , to slow winding  24 , and the motor spins. At the conclusion of this pulse, cam circuit  16  returns the wipers to the home position in the manner described above. If the system is powered up with switch  102  already in the off position, then  148  was never charged, and there is no monostable pulse. This is so that the system does not deliver a wipe on power-up should the driver elect to leave the switch in the RS/INT position. 
         [0026]    During the wipe, cam output  22  goes to B+, charging capacitor  126  of intermittent RC network  120 . At the conclusion of the wipe, the voltage transition from B+ down to zero volts on cam output  22  is transferred to terminal  127  of capacitor  126 , causing a negative pulse at that point. At the conclusion of the wipe, no circuit turns on either driver transistor  112  or relay  110 , so the wipers remain in the home position for a dwell period. During the dwell period of preferably about five seconds, terminal  127  of capacitor  126  charges to a positive voltage by way of resistor  124 . Note that in this configuration, the rain sensor is disconnected, so current flows freely to the base of driver transistor  112 . This turns on drive transistor  112  and relay  110 , initiating another wipe cycle. This process repeats indefinitely, thus providing the intermittent wiper function. As noted above, a vehicle may be equipped with the complete rain sensing wiper system, as shown in  FIGS. 1 and 2 . Optionally, because the switch and motor are in common with the intermittent system, the automobile dealer may install the rain sensor  60  and cable  52 . For the rain sensing system, the manual off, slow, fast, and mist control settings function just as with the intermittent system described above. 
         [0027]    When the operator switches switch  102  to rain sensor mode (RS/INT), monostable circuit  140  provides a single wipe, as described above in intermittent operation. This is the case regardless of whether or not the sensor  60  has sensed the presence of water on the windshield, because the operator would likely not be operating the switch unless the windshield needed to be cleared. If there should happen to be water on the windshield, the effect of the wipers themselves will tend to trigger the rain sensor  60 , properly affecting a rapid response within the sensor  60 . 
         [0028]    During the wipe, the intermittent circuit of the wiper switch charges capacitor  126 , just as before. However, output resistor  62  within rain sensor  60  is of a low resistance value—nominally ≧1K ohm. Such low resistance dominates the relatively high resistance of the intermittent RC network  120 , shunting any current flowing through resistor  62  to the voltage level established by a microprocessor  74  within sensor  60 . Lower resistances yet may be selected, but this would tend to require higher drive capability on the output circuitry of microprocessor  74 . Thus, the intermittent RC network  120  cannot turn on wiper relay  110 , and the intermittent function is defeated. Both sensor output resistance  62  and intermittent RC network  120  may be scaled up or down, but for the sensor to properly dominate the circuit when the sensor is connected, resistor  122  should be at least ten times the value of resistor  62 . When no water is present on the windshield, the nominal voltage from the rain sensor  60  is zero, and the wipers remain in the home position. 
         [0029]      FIG. 3  shows the output voltage of the rain sensor  60  with changing water conditions. The rain sensor  60  commands the state of the wipers by assuming a control voltage, as per the following table: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 
               
               
                   
                   
               
               
                   
                 Function 
                 Voltage 
               
               
                   
                   
               
             
             
               
                   
                 Off 
                 0 
               
               
                   
                 Lights 
                 1.25 V 
               
               
                   
                 Slow 
                  2.5 V 
               
               
                   
                 Fast 
                   5 V 
               
               
                   
                   
               
             
          
         
       
     
         [0030]    The voltages in the Table are determined by setting the outputs of hi (5V), low (0V) or tristate (open), connected to the divider network formed by resistors  64 ,  66 , and  68 . At the beginning of the graph of  FIG. 3 , at time  80 , the rain sensor is commanding off. At a time  82 , sensor output S assumes 2.5V for 1 sec, thereby commanding a single wipe. It takes nominally 1.4 seconds for the wipers to actually complete a wipe cycle. Upon completion of the wiper command at time  84 , the rain sensor may command an optional light function. In an alternative embodiment further described later herein, the rain sensor is capable of activating vehicle headlamps. Continuing in  FIG. 3 , at time  86  the rain sensor commands steady slow, this time lasting for nominally 6 seconds, or 4 complete wipes. At time  88 , a higher flow of rainfall has justified entry into steady fast or high speed, and the sensor output commands this by assuming 5V. The sensor output subsequently decelerates through slow, and back into a dwell period with the lights on. 
         [0031]    Returning to  FIG. 2 , electrical input analysis device, also known as driver transistor  112 , is held off when the off command is given by the rain sensor  60 . As explained earlier, because the sensor has a low resistance output, this is irrespective of the state of the high resistance intermittent network  120 . At time  86 , when the rain sensor output crosses a threshold of nominally 1.8 V as set by resistors  116  and  118 , driver transistor  112  turns on, initiating a single wipe in a fashion similar to intermittent operation described earlier. Similarly, the preferred embodiment does not respond differently to a fast command. At time  88  (referring to  FIG. 3 ), it simply continues operation of the wiper at a slow speed. 
         [0032]    It may be readily seen that the only components needed to effect rain sensor  60  operation over those required for intermittent operation, are the sensor  60  and cable  52 , as well as sensor connector  114 , and a single resistor  116 . Thus, the cost penalty for an intermittent system that can be upgraded to rain sensor operation is just connector  114  and resistor  116 , representing a negligible additional cost. 
         [0033]    The embodiment of the invention thus far described provides a windshield wiper control system that may operate as an intermittent system or a rain sensing system with little increase in cost. The vehicle manufacturer may choose to implement the additional features of fast speed wiper control, as well as automatic headlamp control, retaining the same general shape of control unit assembly  100  shown in  FIG. 1 , and using the same mounting arrangement. This allows the vehicle manufacturer to provide a full range of vehicle option levels, wherein the least expensive vehicles suffer no cost penalty over more expensive vehicles. It may be noted that for the lowest possible cost system the switch may also be offered even without intermittent control in control unit assembly  100 . 
         [0034]    The windshield wiper control system of the invention may optionally be upgraded to control the wipers at high speed by adding the circuit as shown in  FIG. 4 . The circuit is added to the schematic diagram of  FIG. 2  by connecting the sensor output S as shown, as well as connecting the normally open connection P of slow relay  110 , rather than directly to B+.  FIG. 4  shows a transistor  170  disposed to turn on when sensor output S reaches a nominal threshold of 3.25V. This in turn engages a fast relay  176 , which withdraws power (B+) from the slow relay connection P, and applies power to the fast winding  26 . This causes wiper motor  12  to spin at high speed. As the system is shown, slow speed winding  24  is disconnected when fast winding  26  is engaged. Power for fast relay  176  is supplied by conductor R. Thus configured, when the sensor commands fast speed at time  88 , the wipers run fast. 
         [0035]    The alternative embodiment also includes a transistor  180  to turn on the lights when sensor output S exceeds 0.7 V. The collector  184  of transistor  180  drives a relay (not shown) operatively connected to the vehicle&#39;s headlamps through the connection labeled LIGHTS CONTROL. Thus disposed, the vehicle headlamps properly turn on when the rain sensor senses darkness, or initiates wiping. A switch may be connected in series with conductor LIGHTS CONTROL to disable automatic operation. 
         [0036]    Transistors are preferred for implementing the thresholds as required to respond to the voltage commands of the Table. The threshold response analysis may alternately be implemented using comparators  190 , such as the LM339 by National Semiconductor. This is shown at  FIG. 5 , replacing the control circuit generally of  FIG. 2 . Although not a preferred configuration, a simple microprocessor  194  may be included to accomplish the very simple timing functions of the monostable circuit  140  as well as the intermittent circuit  120 . It must be stressed that the computational requirements of the microprocessor are extremely modest; an inexpensive four-bit processor, is well up to the task. This is still within the design intent of the invention, requiring nowhere near the processing power required to implement a CAN or LIN mode. Microprocessor  194  need not analyze any digital data from the rain sensor. Optionally, a comparator section may be configured as a pulse-detector  192  to discriminate superimposed data, as described below. This embodiment thus includes a high resistance resistor  196  to pull the sensor output S to ground in the absence of a sensor  60 . Alternatively, the sensor outputs may be connected to an RC intermittent network, such as network  120  of  FIG. 2 . 
         [0037]    The rain sensor  60  of the preferred embodiment, in order to affect the basic commands required of the rain sensing system, uses a simple control voltage scheme, rather than data transfer as such. This permits the interface portion, incorporated into the switch  102  in this embodiment, to respond to the switch  102  with no need for computation. The sensor  60  preferably, however, superimposes data transfer upon the control voltage output S, in a way that does not impede operation of the invention described herein. In addition to the relatively slow (seconds time scale) control voltage outputs, the sensor  60  produces fast, short pulses. These pulses last nominally 30 microseconds, and are nominally 833 microseconds apart. This permits data transfer at a slow 1200 baud.  FIG. 6  shows a serial communications data stream  200 , internal to rain sensor  60 , as well as sensor output S. Data stream  200  represents a bit, within a register of sensor microprocessor  74 . The relays of the system ( 110 ,  176 ) respond much too slowly to be affected by the superimposed data. The 833 microsecond period is lengthened by nominally 60 microseconds for positive data transitions  202 , and shortened by 60 microseconds for negative data transitions  204 . Over time, positive and negative data transitions cancel. The graph shown at  FIG. 6  shows the rain sensor  60  commanding an off state of the wiper. For other states, such as slow, the pulses are superimposed upon the larger, slower voltages shown in  FIG. 3 . This scheme may be used for testing the rain sensor  60  during its manufacture. The scheme may also be used to test the simple existence of a sensor  60  using pulse detector  192  without fully decoding the data. This again allows for an extremely simple processor. 
         [0038]    Although the description above contains many specificities, these should not be construed as limiting the scope of the invention, but as merely providing some of the presently preferred embodiments of the invention. For example, each of the above descriptions show the wiper motor with a common ground terminal, and engaged by applying a positive voltage. Almost as common in the auto industry is ground-side switching, wherein the common terminal of the motor is connected to B+, and slow and fast windings are grounded to affect motor operation. The invention may be readily modified to accommodate ground side switching. Also, the switch assembly may be dash-mounted rather than deployed with a steering column stalk control. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.