Abstract:
A vehicle height controlling suspension apparatus having a signal-freeze determining function includes a plurality of vehicle height sensors to measure the height of a vehicle. Vehicle height adjusting actuators are driven to adjust the height of the vehicle. An electronic control unit (ECU) is configured to perform adjustment of the height of the vehicle by the actuators by calculating a vehicle height variation value from vehicle height signals of the plurality of vehicle height sensors and compare the calculated vehicle height variation value with a reference value to determine whether the signals are frozen.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a vehicle height controlling suspension apparatus having a signal-freeze determining function and a vehicle height control method thereof, and more particularly, to a vehicle height controlling suspension apparatus having a signal-freeze determining function and a vehicle height control method thereof, wherein the height of a vehicle is controlled by determining whether a signal from a vehicle height sensor is frozen, thereby securing handling stability of the vehicle and preventing an excessive operation of a suspension system.  
         [0002]     Initially, a vehicle suspension apparatus was based on only the concept of simply supporting a vehicle body. However, it recently is being developed to improve ride comfort by maintaining vehicle height against the weight of a vehicle body and with respect to a road surface and absorbing shocks transmitted from the road surface to the vehicle body, and to improve handling stability of the vehicle by maintaining the vehicle body in an attitude suitable for driving.  
         [0003]     Generally, damping force exhibits opposing properties in view of ride comfort and handling stability, and thus, there are many difficulties in determining the damping force. Accordingly, there have been recently conducted many studies on dynamic design and driving dynamics analysis in consideration of the ride comfort and handling stability of the suspension apparatus.  
         [0004]     As a result of those studies, there has been developed a suspension apparatus capable of actively correcting changes in the attitude of a vehicle body depending on road surface conditions, driving conditions or vehicle conditions to improve driving performance, handling stability, and ride comfort of a vehicle.  
         [0005]     A vehicle height controlling suspension apparatus has been developed in such a context. The vehicle height controlling suspension apparatus can maintain a vehicle body at a certain height depending on fluctuations of load and changes in a road surface and further may have a vehicle height varying function performed by a driver&#39;s simple operation and/or a speed-sensitive vehicle height changing function of changing vehicle height depending on changes in vehicle speed.  
         [0006]     Various types of vehicle height controlling suspension apparatuses are being developed, implemented or studied. Among them, an air suspension apparatus for controlling vehicle height using changes in internal pressure of an air spring based on vehicle height information measured by vehicle height sensors has been widely known.  
         [0007]     Such an air suspension apparatus is constructed such that vehicle height sensors are installed at least one of front and rear wheel sides of a vehicle and the height of the vehicle is controlled by driving air springs installed at respective wheels, based on signals received from the respective vehicle height sensors.  
         [0008]     In the vehicle suspension apparatus provided with such vehicle height sensors, it is determined whether signals from the vehicle height sensors, which are affected by structural or electrical defects caused by external environments, are in a normal range, and the control of the height of the vehicle is stopped if the signals are out of the normal range. That is, cases where the control of the height of a vehicle is stopped include a short circuit of a power line, an open circuit, and a ground (GND) short circuit.  
         [0009]     However, apart from the cases where normal signals are not outputted, such as a short circuit of a power line, an open circuit and a GND short circuit. if the vehicle height sensors are in a signal-freeze (fixed output) state due to the breakdown of the sensors in which they cannot output normal signals, it is difficult to determine the signal-freeze state. Therefore, the height of a vehicle is controlled even when the sensor signals are frozen, resulting in degradation of the stability of the vehicle.  
         [0010]     For example, if the voltage level of a vehicle height sensor is in the range of 0V to 5V, a signal of 0V to 0.5V is outputted in case of a short circuit or a GND short circuit, a signal of 0.5V to 1.9V is outputted in a case where a signal from the sensor is out of the normal range, a signal of 1.9V to 3.1V is outputted in a case where the sensor operates normally, a signal of 3.1V to 4.5V is outputted in a case where a signal from the sensor is out of the normal range, and a signal of 4.5V to 5V is outputted in case of an open circuit or a short circuit of a power line.  
         [0011]     Such voltage sections (0.5V to 1.9V and 3.1V to 4.5V) out of the normal range appear when the sensor mounted between the vehicle body and a vehicle axle deviates from displacement that may be physically caused by relative motions of the vehicle body and the vehicle axle.  
         [0012]     Such voltage sections out of the normal range may occur if the sensor is damaged and stuck, a sensor mounting part (a fixing screw) is loosened and drooped down by gravity, or a rotating portion of the sensor does not move.  
         [0013]     If a sensor value deviates from the normal signal range due to such reasons, it can be easily detected. However, if a sensor signal is frozen within the normal range (1.9V to 3.1V) and does not vary, it is difficult to determine whether the signal is normal.  
         [0014]     That is, it is difficult to distinguish whether an output value of a vehicle height sensor is frozen due to the breakdown of the vehicle height sensor or an output value of the vehicle height sensor is frozen since the vehicle is actually maintained at a certain vehicle height.  
         [0015]     Accordingly, even when a sensor signal is frozen within a normal range and does not vary, the vehicle suspension apparatus controls the height of a vehicle, resulting in a risk of the breakdown of a suspension system due to excessive use of the system.  
       SUMMARY OF THE INVENTION  
       [0016]     An embodiment of the present invention provides a vehicle height controlling suspension apparatus having a signal-freeze determining function and a vehicle height control method thereof, wherein the height of a vehicle is controlled by determining whether a signal from a vehicle height sensor is frozen, thereby improving stability of the vehicle and preventing the breakdown of a suspension system due to excessive use of the system.  
         [0017]     In one embodiment, a vehicle height controlling suspension apparatus having a signal-freeze determining function includes a plurality of vehicle height sensors for measuring the height of a vehicle; vehicle height adjusting actuators driven for adjusting the height of the vehicle; and an electronic control unit (ECU) for performing adjustment of the height of the vehicle by the actuators by calculating a vehicle height variation value from vehicle height signals of the plurality of vehicle height sensors and comparing the calculated vehicle height variation value with a predetermined reference value to determine whether the signals are frozen.  
         [0018]     The ECU may comprise a calculating section for calculating a maximum vehicle height variation value from the vehicle height signals of the plurality of vehicle height sensors for a predetermined time period; a suspect flag setting section for comparing the maximum vehicle height variation value calculated by the calculating section with the reference value and setting a state flag of a vehicle height sensor satisfying a predetermined reference condition to a suspect flag; a determination section for determining the vehicle height sensor satisfying the predetermined reference condition to be in a signal-freeze state if the number of sensors set to the suspect flag is not greater than a half of the total number of vehicle height sensors; an abnormal flag setting section for setting the state flag of the vehicle height sensor to an abnormal flag according to the determination of the determination section; and a vehicle height adjustment processing section for stopping vehicle height control of an actuator positioned to correspond to the vehicle height sensor if the state flag is set to the abnormal flag by the abnormal flag setting section.  
         [0019]     The ECU may further comprise an alarm processing section for outputting a predetermined alarm signal if the state flag is set to the abnormal flag by the abnormal flag setting section.  
         [0020]     The vehicle height adjustment processing section may output a predetermined alarm signal and stop the vehicle height control if the abnormal flag is set and initialized repeatedly as many as a predetermined number of times.  
         [0021]     In another embodiment, a vehicle height control method of a vehicle height controlling suspension apparatus having a signal-freeze determining function includes the steps of receiving vehicle height signals from a plurality of vehicle height sensors for measuring the height of a vehicle; and performing vehicle height control by calculating a vehicle height variation value from the received vehicle height signals and comparing the calculated vehicle height variation value with a predetermined reference value to determine whether the signals are frozen.  
         [0022]     The step of performing the vehicle height control may comprise the steps of calculating a maximum vehicle height variation value from the vehicle height signals of the plurality of vehicle height sensors for a predetermined period of time; comparing the calculated maximum vehicle height variation value with the reference value and setting a state flag of a vehicle height sensor satisfying a predetermined reference condition to a suspect flag; determining the vehicle height sensor satisfying the predetermined reference condition to be in a signal-freeze state if the number of sensors set to the suspect flag is not greater than a half of the total number of vehicle height sensors; setting the state flag of the vehicle height sensor to an abnormal flag according to the determination; and stopping vehicle height control of an actuator positioned to correspond to the vehicle height sensor if the state flag is set to the abnormal flag.  
         [0023]     The step of performing the vehicle height control may further comprise the step of outputting a predetermined alarm signal if the state flag is set to the abnormal flag.  
         [0024]     The step of stopping the vehicle height control may comprise the steps of outputting a predetermined alarm signal if the abnormal flag is set and initialized repeatedly as many as a predetermined number of times; and stopping the vehicle height control. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a diagram schematically showing a vehicle height controlling suspension apparatus having a signal-freeze determining function according to an embodiment of the present invention;  
         [0026]      FIG. 2  is the block diagram specifically illustrating an ECU shown in  FIG. 1 ; and  
         [0027]      FIG. 3  is a flowchart illustrating a vehicle height control method of the vehicle height controlling suspension apparatus having the signal-freeze determining function according to an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]      FIG. 1  is a diagram schematically showing a vehicle height controlling suspension apparatus having a signal-freeze determining function according to an embodiment of the present invention.  
         [0029]     As shown in  FIG. 1 , the vehicle height controlling suspension apparatus having a signal-freeze determining function according to the present embodiment comprises a plurality of vehicle height sensors  12 L,  12 R,  22 L and  22 R for measuring the height of a vehicle, a plurality of vehicle height adjusting actuators  10 L,  12 R,  20 L and  20 R driven for adjusting the height of the vehicle, and an ECU  30  for controlling the height of the vehicle adjusted by the actuators according to signals received from the plurality of vehicle height sensors  12 L,  12 R,  22 L and  22 R.  
         [0030]     The vehicle height sensors include front wheel-side sensors  12 L and  12 R installed in the vicinity of front left and right wheels FL and FR, and rear wheel-side sensors  22 L and  22 R installed in the vicinity of rear left and right wheels RL and RR.  
         [0031]     In this embodiment, the vehicle height sensors  12 L,  12 R,  22 L and  22 R detect relative distances between a vehicle body and vehicle axles (i.e., vehicle height), and the most typical one in which two rotating levers are respectively mounted on the vehicle body and the vehicle axle to sense a distance therebetween by detecting a relative angle of the two levers with respect to linear displacement are employed as the vehicle height sensor.  
         [0032]     The actuators  10 L,  10 R,  20 L and  20 R (hereinafter, referred to as “air springs”) are also positioned to correspond respectively to the aforementioned vehicle height sensors  12 L,  12 R,  22 L and  22 R. Such air springs include front wheel-side left and right air springs  10 L and  10 R, and rear wheel-side left and right air springs  20 L and  20 R.  
         [0033]     The ECU  30  receives vehicle height signals from the vehicle height sensors  12 L,  12 R,  22 L, and  22 R at the positions of respective wheels and substantially controls the height of the vehicle based on the signals.  
         [0034]     In the embodiment of the present invention, the ECU  30  controls the front wheel-side air springs  10 L and  10 R and rear wheel-side air springs  20 L and  20 R based on the vehicle height signals received from the respective vehicle height sensors.  
         [0035]     The ECU  30  drives, with a certain control value, a compressor (not shown) and a pneumatic circuit (not shown) including the compressor.  
         [0036]     According to the present invention, the ECU  30  is constructed to control the height of the vehicle by comparing a vehicle height variation value calculated from the vehicle height signals received from the plurality of vehicle height sensors  12 L,  12 R,  22 L and  22 R with a predetermined reference value, and determining whether the sensor signals are frozen. The configuration of the ECU  30  will be described below with reference to  FIG. 2 .  
         [0037]     Referring to  FIG. 2 , the ECU  30  in this embodiment determines from the freeze of a sensor signal that a sensor cannot function any more and generates a fixed output, and then stops the control of the height of the vehicle. The ECU comprises a receiving section  31  for receiving vehicle height signals, a calculating section  32  for calculating a vehicle height variation value from the received vehicle height signals, a suspect flag setting section  33  for comparing the vehicle height variation value with a predetermined reference value and setting a state flag of a sensor to a suspect flag according to whether a predetermined condition is satisfied, a determination section  34  for determining a signal-freeze state, an abnormal flag setting section  35  for setting the state flag to an abnormal flag according to the determination, a vehicle height adjustment processing section  36  for stopping vehicle height control of an air spring including a wheel on which a sensor with a state flag set to the abnormal flag is mounted, an alarm processing section  37  for notifying the breakdown of a vehicle height sensor, and a vehicle speed processing section  38  for determining whether the vehicle is in a driving state.  
         [0038]     At this time, in addition to the control of the vehicle height of the suspension apparatus, the ECU can perform overall control on the suspension apparatus and shock absorbers, and further participate in controlling other systems of the vehicle (for example, a steering system and/or a braking system). However, since the other control is not directly related to the subject matter of the present invention, detailed descriptions thereof will be omitted.  
         [0039]     The receiving section  31  receives vehicle height signals from the two vehicle height sensors  12 L and  12 R on the side of the front wheels FL and FR, and the two vehicle height sensors  22 L and  22 R on the side of the rear wheels RL and RR, and transmits the signals to the calculating section  32 .  
         [0040]     The calculating section  32  calculates a maximum vehicle height variation value from the respective vehicle height signals received by the receiving section  31  for a predetermined period of time (e.g., one minute), using the following equation 1: 
 
Δ H   l =max H   i −min H   i ,
 
i=1, . . . ,4  (1)
 
         [0041]     If the maximum vehicle height variation value calculated by the calculating section  32  is smaller than a predetermined reference value, the suspect flag setting section  33  sets a state flag of a vehicle height sensor of the vehicle height sensors that satisfies a predetermined reference condition, to a suspect flag.  
         [0042]     If the number of sensors, which are set to the suspect flag by the suspect flag setting section  33 , is smaller than a half of the total number of vehicle height sensors (i.e., two or less among the four vehicle height sensors), the determination section  34  determines the vehicle height sensor that satisfies the predetermined reference condition to be in a signal-freeze state.  
         [0043]     For example, if the state flag of the vehicle height sensor  12 L on the side of the front wheels FL and FR is set to a suspect flag, or the state flag of the vehicle height sensor  12 L on the side of the front wheels FL and FR is set to a suspect flag and the state flag of the vehicle height sensor  22 L on the side of the rear wheels RL and RR is set to a suspect flag, the vehicle height sensor are determined to be in a signal-freeze state (i.e., an abnormal state).  
         [0044]     If the vehicle height sensor is determined to be in an abnormal state as such, the abnormal flag setting section  35  sets the state flag of the vehicle height sensor to an abnormal flag.  
         [0045]     If the state flag is set to an abnormal flag, the vehicle height adjustment processing section  36  stops vehicle height control of an air spring including a wheel on which the vehicle height sensor is mounted. Here, although the present embodiment has been described in connection with the case where the vehicle height control of an air spring positioned to correspond to the sensor is stopped, it is also possible to stop vehicle height control of an air spring for a wheel in which the state flag of the vehicle height sensor is set to an abnormal flag.  
         [0046]     In addition, if the state flag of the vehicle height sensor is set to an abnormal flag and initialized repeatedly as many as a predetermined number of times, the vehicle height adjustment processing section  36  stops the control of the height of the vehicle. That is, the vehicle height adjustment processing section  36  determines the sensor to be broken down and does not any more perform vehicle height adjustment according to a vehicle height signal from the vehicle height sensor.  
         [0047]     If the state flag of the vehicle height sensor is set to an abnormal flag, the alarm processing section  37  outputs a predetermined alarm signal. At this time, it is preferred that a user be notified of the breakdown of the sensor through a warning lamp.  
         [0048]     In addition, even when the state flag of the vehicle height sensor is set to an abnormal flag and initialized repeatedly as many as a predetermined number of times, the alarm processing section  37  also outputs an alarm signal through the warning lamp. Accordingly, the user can easily notice the breakdown of the vehicle height sensor.  
         [0049]     The vehicle speed processing section  38  determines whether the vehicle is in a driving state according to whether the speed of the vehicle measured by a vehicle speed sensor  40  for measuring the speed of a vehicle is not less than a predetermined speed (e.g., 30 kph).  
         [0050]     At this time, if the speed of the vehicle measured by the vehicle speed sensor  40  is less than a predetermined speed (e.g., 30 kph), the vehicle is determined not to be in a driving state. This case occurs when state flags of three or four vehicle height sensors are set to a suspect flag by the suspect flag setting section  33 .  
         [0051]     In this manner, it is determined whether a signal from a vehicle height sensor is frozen, so that the height of the vehicle is controlled, thereby securing the stability of the vehicle.  
         [0052]     The vehicle height control method of the vehicle height controlling suspension apparatus having a signal-freeze determining function constructed as such will be described below.  
         [0053]      FIG. 3  is a flowchart illustrating a vehicle height control method of the vehicle height controlling suspension apparatus having the signal-freeze determining function according to an embodiment of the present invention.  
         [0054]     The vehicle speed processing section  38  of the ECU  30  determines whether the vehicle is in a driving state (S 101 ). That is, it determines whether the speed of the vehicle is not less than a predetermined speed (e.g., 30 kph).  
         [0055]     If it is determined in step S 101  that the vehicle is not in a driving state, the ECU terminates the process.  
         [0056]     If it is determined in step S 101  that the vehicle is in a driving state, the receiving section  31  of the ECU  30  receives vehicle height signals from the plurality of vehicle height sensors  12 L,  12 R,  22 L and  22 R installed in the vehicle (S 102 ).  
         [0057]     Then, the calculating section  32  of the ECU  30  calculates a maximum vehicle height variation value for each of the sensors from the vehicle height signals received for a predetermined period of time (S 103 ).  
         [0058]     Next, the suspect flag setting section  33  of the ECU  30  determines whether there is at least one sensor in which the calculated maximum vehicle height variation value is smaller than a predetermined reference value (S 105 ).  
         [0059]     If it is determined in step S 105  that there is no sensor in which the calculated maximum vehicle height variation value is smaller than a predetermined reference value, the vehicle height adjustment processing section  36  of the ECU  30  performs vehicle height adjustment of an actuator positioned to correspond to the vehicle height sensor (S 106 ).  
         [0060]     Next, the vehicle height adjustment processing section  36  initializes the state flag and the number of counts of each sensor (S 108 ) and proceeds to the process of step S 101  to receive vehicle height signals.  
         [0061]     If it is determined in step S 105  that there is at least one sensor in which the calculated maximum vehicle height variation value is smaller than a predetermined reference value, the suspect flag setting section  33  sets the state flag of the vehicle height sensor to a suspect flag (S 107 ).  
         [0062]     Next, the determination section  34  of the ECU  30  determines whether the number of sensors having a suspect flag set by the suspect flag setting section  33  is not greater than a half of the total number of vehicle height sensors (S 109 ). That is, if there are four vehicle height sensors, it is determined whether state flags of two or less vehicle height sensors are set to a suspect flag.  
         [0063]     Here, if the number of sensors having the suspect flag is not greater than a half of the total number of vehicle height sensors, the determination section  34  determines that the vehicle height sensor(s) is(are) in a signal-freeze state. If the number of sensors having the suspect flag is three or four, the determination section determines that the vehicle is in a stationary state.  
         [0064]     If it is determined in step S 109  that the number of sensors having the suspect flag set by the suspect flag setting section is greater than a half of the total number of vehicle height sensors, i.e., if state flags of three or four vehicle height sensors are set to a suspect flag, the ECU  30  terminates the process.  
         [0065]     The case where the state flags of three or four vehicle height sensors are set to a suspect flag occurs when the vehicle is in a stationary state.  
         [0066]     If it is determined in step S 109  that the number of sensors having the suspect flag set by the suspect flag setting section is not greater than a half of the total number of vehicle height sensors, i.e., if the state flags of one or two vehicle height sensors are set to a suspect flag, the abnormal flag setting section  35  of the ECU  30  sets the state flag of the vehicle height sensor to an abnormal flag (S 111 ).  
         [0067]     Then, the vehicle height adjustment processing section  36  temporarily stops vehicle height adjustment of an actuator positioned to correspond to the vehicle height sensor (S 112 ). At this time, it is also possible to temporarily stop vehicle height control of the actuator.  
         [0068]     Next, the vehicle height adjustment processing section  36  increases the number of counts by one (S 113 ).  
         [0069]     Then, the vehicle height adjustment processing section  36  determines whether the number of counts exceeds a predetermined number of counts (S 115 ).  
         [0070]     If it is determined in step S 115  that the number of counts does not exceed a predetermined number of counts, i.e., if setting of the state flag to an abnormal flag and initialization of the state flag are not repeated as many as a predetermined number of times, the vehicle height adjustment processing section  36  initializes the state flag of each sensor (S 116 ) and proceeds to the process of step S 101 .  
         [0071]     If it is determined in step S 115  the number of counts exceeds a predetermined number of counts, i.e., if setting of the state flag to an abnormal flag and initialization of the state flag are repeated as many as a predetermined number of times, the vehicle height adjustment processing section  36  outputs an alarm signal predetermined by the alarm processing section  37  and completely stops the vehicle height control (S 117 ).  
         [0072]     Although this embodiment has been described in connection with the case where vehicle height control is completely stopped if the state flag of the vehicle height sensor is set to an abnormal flag and initialized repeatedly as many as a predetermined number of times, the present invention is not limited thereto. Even when the vehicle height control is stopped and resumed repeatedly as many as a predetermined number of times, the vehicle height control may be completely stopped.  
         [0073]     In this manner, the height of the vehicle is controlled to improve the stability of the vehicle, and the breakdown of a sensor is identified to prevent an excessive operation of the suspension system, thereby preventing the breakdown of the system.  
         [0074]     According to the present invention described above, there is an advantage in that the height of a vehicle is controlled by determining a signal-freeze state of a vehicle height sensor, thereby improving the stability of the vehicle.  
         [0075]     Further, according to the present invention described above, there are advantages in that the breakdown of a corresponding vehicle height sensor is identified so that an excessive operation of a suspension system can be prevented and thence the breakdown of the system can be prevented.  
         [0076]     Moreover, according to the present invention described above, there are advantages in that a driver is notified of the breakdown of a vehicle height sensor, so that the driver can easily notice the breakdown of the vehicle height sensor and the worst dangerous situation can be prevented in advance.  
         [0077]     The present invention is not limited to the aforementioned embodiments, and various changes and modifications can be made thereto by those skilled in the art. The various changes and modifications fall within the spirit and scope of the present invention defined by the appended claims.