Abstract:
Disclosed herein are an apparatus for controlling a solenoid valve and a control method thereof. The apparatus for controlling the solenoid valve, which controls the solenoid valve including a solenoid coil, includes a switching part configured to switch a current supplied to the solenoid coil; a pre-driver configured to output a driving signal for driving the switching part; and a microcontroller unit (MCU) configured to control the pre-driver so that a frequency of the driving signal output from the pre-driver to the switching part is randomly varied.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2014-0060649, filed on May 21, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated in its entirety herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to an apparatus for controlling a solenoid valve and a control method thereof, and more particularly, to an apparatus for controlling a solenoid valve, which is capable of reducing an operation noise of the solenoid valve, and a control method thereof. 
     2. Description of the Related Art 
     In general, a solenoid valve is installed at each inlet and outlet side of four wheels in a vehicle having an electronically-controlled brake system, e.g., an anti-lock brake system (ABS). 
     In the ABS vehicle, when a braking force exceeds a friction force between a wheel of the vehicle and a road, and the vehicle starts to be slid, the solenoid valve of the corresponding wheel is operated to reduce a pressure thereof, and then when the vehicle starts to be driven again, the solenoid valve is operated to increase the pressure. Due to such an operation of the ABS, the vehicle is not slid, and is stably braked. 
     In the electronically-controlled brake system, the solenoid valve serves to supply a brake liquid pressure to a wheel cylinder or to cut off supply of the brake liquid pressure to the wheel cylinder. 
     The solenoid valve is opened and closed by a current supplied to a solenoid coil. 
     A conventional solenoid valve controlling device includes a shunt resistance part which detects the current flowing through the solenoid coil in the solenoid valve, a switching part which switches the current flowing through the solenoid coil, a pre-driver which outputs a driving signal to the switching part so as to switch on or off the switching part, and an electronic control unit (ECU) which monitors the current flowing through the solenoid coil using the shunt resistance part and controls the switching part through the pre-driver based on a monitoring result, such that a target current flows through the solenoid coil. 
     In the conventional solenoid valve controlling device, while the current flowing through the solenoid coil arrives at the target current, the ECU outputs the driving signal having a fixed frequency to the switching part through the pre-driver. 
     Therefore, an acoustic noise having the same frequency is generated at a solenoid valve assembly. 
     SUMMARY 
     Therefore, it is an aspect of the present invention to provide an apparatus for controlling a solenoid valve, which randomly varies a frequency of a driving signal output to a switching part, when a current of the solenoid valve is controlled, and thus reduces an acoustic noise of the solenoid valve, and a control method thereof. 
     Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     In accordance with one aspect of the present invention, an apparatus for controlling a solenoid valve, which controls the solenoid valve including a solenoid coil, includes a switching part configured to switch a current supplied to the solenoid coil; a pre-driver configured to output a driving signal for driving the switching part; and a microcontroller unit (MCU) configured to control the pre-driver so that a frequency of the driving signal output from the pre-driver to the switching part is randomly varied. 
     The MCU may control the pre-driver so that, while the driving signal is output from the pre-driver to the switching part, the frequency of the driving signal is randomly varied. 
     The apparatus may further include a current detecting part configured to detect a current flowing through the solenoid coil, wherein the pre-driver may include a proportional-integral (PI) controller configured to output the driving signal for controlling the switching part so that a current value which subtracts a current value detected through the current detecting part from a target current value input from the MCU is supplied to the solenoid coil, and a frequency shifter configured to randomly vary the frequency of the driving signal output to the switching part, while the driving signal is output from the PI controller to the switching part. 
     The MCU may control the frequency shifter so that the frequency of the driving signal is randomly varied according to a number of steps of the frequency of the driving signal subdivided into a predetermined number of steps, and a frequency variable range of the driving signal set to a predetermined frequency range. 
     In accordance with another aspect of the present invention, a method of controlling a solenoid valve which includes a solenoid coil, and is opened or closed by a current supplied to the solenoid coil so as to control a brake pressure supplied to a wheel cylinder, the method including, when the current of the solenoid valve is controlled, outputting a driving signal to a switching part configured to switch the current supplied to the solenoid coil so that the current flows through the solenoid coil; detecting the current flowing through the solenoid coil; and outputting the driving signal to the switching part for allowing the detected current value of the solenoid coil to arrive at a target current value, and randomly varying a frequency of the driving signal while the driving signal is output. 
     While the driving signal is output, the randomly varying of the frequency of the driving signal may randomly vary the frequency of the driving signal according to a number of steps of the frequency of the driving signal subdivided into a predetermined number of steps, and a frequency variable range of the driving signal set to a predetermined frequency range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a hydraulic circuit diagram of an electronically-controlled brake system to which an apparatus for controlling a solenoid valve according to one embodiment of the present invention is applied; 
         FIG. 2  is a schematic control block diagram of the apparatus for controlling the solenoid valve according to one embodiment of the present invention; 
         FIG. 3  is a schematic control circuit diagram of the apparatus for controlling the solenoid valve according to one embodiment of the present invention; 
         FIG. 4  is a graph illustrating a frequency variable range of a driving signal in the apparatus for controlling the solenoid valve according to one embodiment of the present invention; and 
         FIG. 5  is a graph illustrating a scatter plot of timing and a frequency of the driving signal in the apparatus for controlling the solenoid valve according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF MAIN ELEMENTS 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 13: solenoid valve 
                 30: power source 
               
               
                   
                 40: switching part 
                 50: current detecting part 
               
               
                   
                 60: pre-driver 
                 61: PI controller 
               
               
                   
                 62: frequency shifter 
                 70: MCU 
               
               
                   
                 71: frequency variable logic part 
               
               
                   
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The exemplary embodiments described below are provided as examples to sufficiently transfer the spirits of the invention to those skilled in the art. Accordingly, the present invention is not limited to those embodiments described below and can be embodied in different forms. In addition, in the drawings, explanatorily irrelevant portions are omitted to clearly describe the present invention, and the width, the length and the thickness of an element could be exaggerated for convenience. Throughout the disclosure, like reference numerals refer to like parts throughout the various figures and embodiments of the present invention. 
       FIG. 1  is a hydraulic circuit diagram of an electronically-controlled brake system to which an apparatus for controlling a solenoid valve according to one embodiment of the present invention is applied. 
     Referring to  FIG. 1 , the electronically-controlled brake system includes a brake pedal  10  which is operated by a driver when braking, and a booster  11   a  and a master cylinder  11   b  which amplify a force transmitted from the pedal  10  and generate a brake pressure. 
     Also, the electronically-controlled brake system further includes first and second solenoid valves  13   a  and  13   b  which supply a brake liquid pressure generated through the booster  11   a  to a wheel cylinder  12 , a low pressure accumulator (LPA)  15  which temporarily stores a brake liquid discharged from the wheel cylinder  12 , and a motor  16  and a pump  17  which pump and return the brake liquid stored in the LPA  15  to the master cylinder  11   b  or the wheel cylinder  12 , and these elements are compactly installed at a modulator block. 
     The first and second solenoid valves  13   a  and  13   b  are respectively installed at inlet and outlet sides of the wheel cylinder  12  to introduce or discharge the brake liquid pressure generated from the master cylinder  11   b  and supplied to the wheel cylinder  12 . The first solenoid valve  13   a  is a normally-opened (NO) valve which is opened in an off state, and the second solenoid valve  13   b  is a normally-closed (NC) valve which is closed in the off state. 
     When an anti-lock brake system (ABS) is operated, the first and second solenoid valves  13   a  and  13   b  are opened or closed, and thus the brake pressure in the wheel cylinder  12  is reduced, maintained or increased so as to brake a vehicle. 
     When the brake pressure is increased, the second solenoid valve  13   b  is closed, and the first solenoid valve  13   a  is opened, and thus the brake liquid pumped by the motor  16  and the pump  17  is supplied to the wheel cylinder  12 . 
     Also, when the brake pressure is reduced, the first solenoid valve  13   a  is closed, and the second solenoid valve  13   b  is opened, and the brake liquid of the wheel cylinder  12  is discharged to the LPA  15 , and thus the brake pressure of the wheel cylinder  12  is reduced. 
       FIG. 2  is a schematic control block diagram of the apparatus for controlling the solenoid valve according to one embodiment of the present invention, and  FIG. 3  is a schematic control circuit diagram of the apparatus for controlling the solenoid valve according to one embodiment of the present invention. 
     Referring to  FIGS. 2 and 3 , the apparatus for controlling the solenoid valve may include a power source  30 , a switching part  40 , a current detecting part  50 , a pre-driver  60 , and a microcontroller unit (MCU)  70 . 
     An electronic control unit (ECU) which performs a general braking control of the vehicle includes the pre-driver  60  and the MCU  70 . 
     The power source  30  includes a battery, and power is supplied from the battery to the solenoid valve  13 . 
     The switching part  40  serves to switch a current supplied from the power source  30  to a solenoid coil L in the solenoid valve  13 . 
     The current detecting part  50  detects the current supplied to the solenoid coil L. The current detecting part  50  may include a shunt resistor R connected to the solenoid coil L in series, and may detect a voltage applied to both ends of the shunt resistor R, and thus may detect the current supplied to the solenoid coil L. For reference, D 1  is a freewheeling diode. 
     The pre-driver  60  outputs a driving signal for driving the switching part  40  according to a control signal of the MCU  70 . The pre-driver  60  controls the switching part  40  through a proportional-integral (PI) control, such that a current value flowing through the solenoid coil L arrives at a target current value. 
     Also, the pre-driver  60  includes a proportional-integral (PI) controller  61  and a frequency shifter  62 . 
     In general, a controller using a control technique in which a control signal is generated by multiplying an error signal as a difference between a command signal and a feedback signal by an appropriate proportional constant gain is called a proportional controller. The PI controller is a controller using a control technique in which an integral control producing the control signal by integrating the error signal is connected in parallel with a proportional control. 
     The PI controller  61  outputs the driving signal for controlling the switching part  40 , so that that a current valve which subtracts the current value detected through the current detecting part  50  from the target current value input from the MCU  70  is supplied to the solenoid coil L. 
     The frequency shifter  62  varies a frequency of the driving signal output from the PI controller  61  to the switching part  40 . 
       FIG. 4  is a graph illustrating a frequency variable range of a driving signal in the apparatus for controlling the solenoid valve according to one embodiment of the present invention. 
     Referring to  FIG. 4 , the driving signal is a signal having a frequency which is randomly varied, instead of a fixed frequency. 
     A variable frequency range is a predetermined frequency range Fx′ to Fx. 
     That is, when the current of the solenoid valve  13  is controlled, while the driving signal is output from the pre-driver  60  to the switching part  40  so that the current value detected through the current detecting part  50  arrives at the target current value, the frequency of the driving signal is randomly varied within the frequency range Fx′ to Fx. 
     Referring to  FIG. 3  again, the MCU  70  controls the frequency shifter  62  of the pre-driver  60 , such that, when the current of the solenoid valve  13  is controlled, while the driving signal is output from the pre-driver  60  to the switching part  40  so that the current value detected through the current detecting part  50  arrives at the target current value, the frequency of the output driving signal is varied. 
     Therefore, the frequency of the driving signal output to the switching part  40  is not maintained constantly, but is changed as time goes on. Thus, an acoustic noise of the solenoid valve may be reduced. 
     The MCU  70  includes a frequency variable logic part  71  which varies the frequency of the driving signal through the frequency shifter  62  of the pre-driver  60 . 
     The frequency variable logic part  71  controls so that, when the current of the solenoid valve  13  is controlled such that, while the driving signal is output from the pre-driver  60  to the switching part  40  so that the current value detected through the current detecting part  50  arrives at the target current value, the frequency of the driving signal output from the pre-driver  60  to the switching part  40  is randomly varied. 
     The frequency variable logic part  71  subdivides the number of steps of a frequency of the frequency shifter  62  of the pre-driver  60  into, e.g.,  256  steps, and randomly varies the frequency variable range within a frequency variable range of e.g., 2 to 10 kHz (or 3 to 10 kHz). 
       FIG. 5  is a graph illustrating a scatter plot of timing and the frequency of the driving signal in the apparatus for controlling the solenoid valve according to one embodiment of the present invention. 
     Referring to  FIG. 5 , in the scatter plot of the timing and the frequency of the driving signal, points indicating a frequency value and a timing value are indicated on a graph so as to show a relationship between the frequency and the timing. An X axis indicates the timing, and a Y axis indicates the frequency, and the points indicating the frequency and the timing are indicated so as to show the relationship between the frequency and the timing. 
     Assuming that the frequency of the driving signal is a value within a range of 3 to 10 kHz, and the timing is a value within a range of 0 to 250 ms, it may be understood that the scatter plot of the driving signal is randomly indicated, as the frequency of the driving signal is randomly varied. Therefore, the acoustic noise of the solenoid valve may be considerably reduced. 
     According to the present invention, while the current of the solenoid valve is controlled, when the switching part is controlled so that the current flowing through the solenoid coil arrives at the target current, the frequency of the driving signal output from the pre-driver to the switching part can be varied randomly, and thus the acoustic noise of the solenoid valve can be reduced. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.