Abstract:
A friction compensation logic of an MDPS (motor driven power steering) system to receive and to process a column torque signal and to output a friction compensation torque comprises: an accumulation speed adjusting portion to adjust an accumulation speed of a compensation section information set in the column torque signal; and a compensation amount adjusting portion in accordance with a vehicle speed to control so that the accumulation speed adjusting portion adjusts the accumulation speed of the compensation section information fast or slow in accordance with the vehicle speed, to adjust a compensation amount gain small or large in accordance with the vehicle speed, and to output a friction compensation torque.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority under 35 U.S.C. §119(a) to Korean patent application number 10-2014-0128086, filed on Sep. 25, 2014, in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    Embodiments relate to a friction compensation logic of a motor driven power steering (MDPS) system and a method thereof, and more particularly, to a friction compensation logic and method of an MDPS system wherein a slope of a friction compensation is adjusted according to the amount of a friction compensation, a stable friction compensation is provided and a vibration induced to an MDPS system is improved. 
         [0004]    2. Related Art 
         [0005]    Generally, an electric power steering (for example, MDPS) system is not a system that a power pump is driven and the oil is circulated and a power steering wheel is operated, but one that a steering motor is additionally installed in the lower portion of an axis of a steering wheel and the steering motor is operated when a vehicle is driven and the power steering wheel is operated. 
         [0006]    The background technology is disclosed in Korean Laid-open Patent Publication No. 10-2012-0053300 (published on May 25, 2012, title of invention: a control device and method of a vehicle MDPS). 
       SUMMARY 
       [0007]    Various embodiments are directed to a friction compensation logic and method of an MDPS system. An aspect of the invention provides a friction compensation logic and method of an MDPS system wherein a slope of a friction compensation is adjusted according to the amount of a friction compensation, a stable friction compensation is provided and a vibration induced to an MDPS system is improved. 
         [0008]    In a friction compensation logic of an MDPS system according to an embodiment, a friction compensation logic in an MDPS system to receive and process a column torque signal, and output a friction compensation torque comprises: an accumulation speed adjusting portion to adjust a speed of accumulating a compensation section information which is set in the column torque signal; and a compensation amount adjusting portion in accordance with a vehicle speed to control so that the accumulation speed adjusting portion adjusts the accumulation speed in the compensation section information fast or slow in accordance with the vehicle speed, to adjust a compensation amount gain small or large in accordance with the vehicle speed, and to output a friction compensation torque. 
         [0009]    In an embodiment, a compensation amount adjusting portion in accordance with a vehicle speed controls so that the accumulation speed adjusting portion adjusts an accumulation speed of a compensation section information fast and adjusts a compensation amount gain small if the vehicle speed is fast. 
         [0010]    In an embodiment, the a compensation amount adjusting portion in accordance with a vehicle speed controls so that the accumulation speed adjusting portion adjusts an accumulation speed of a compensation section information slow and adjusts a compensation amount gain large if a vehicle speed is slow. 
         [0011]    In an embodiment, the friction compensation logic in an MDPS system further comprises a decouple gain adjusting portion to output a compensation amount gain in accordance with the torque only if a torque in accordance with a user&#39;s steering intention is generated, to provide a friction compensation only if a user&#39;s steering intention exists. 
         [0012]    In an embodiment, the decouple gain adjusting portion outputs a compensation amount gain in accordance with a torque by using a column torque/gain information which is stored in advance in a form of a look up table. 
         [0013]    In an embodiment, the friction compensation logic in an MDPS system further comprises a compensation amount gain synthesizing portion to synthesize a compensation amount gain outputted from the compensation amount adjusting portion in accordance with a vehicle speed and a compensation amount gain outputted corresponding to a torque generated in accordance with the user&#39;s steering intention from the decouple gain adjusting portion, and to output a resultant friction compensation torque. 
         [0014]    In an embodiment, a friction compensation method in an MDPS system to receive and process a column torque signal, and output a friction compensation torque comprises: adjusting by an accumulation speed adjusting portion a speed of accumulating a compensation section information which is set in the column torque signal; controlling by a compensation amount adjusting portion in accordance with a vehicle speed so that the accumulation speed adjusting portion adjusts the accumulation speed in the compensation section information fast or slow in accordance with the vehicle speed, adjusting a compensation amount gain small or large in accordance with the vehicle speed, and outputting a friction compensation torque. 
         [0015]    In an embodiment, in outputting the friction compensation torque, the a compensation amount adjusting portion in accordance with the vehicle speed controls so that the accumulation speed adjusting portion adjusts an accumulation speed of a compensation section information fast and adjusts a compensation amount gain small if the vehicle speed is fast. 
         [0016]    In an embodiment, in outputting the friction compensation torque, the a compensation amount adjusting portion in accordance with a vehicle speed controls so that the accumulation speed adjusting portion adjusts an accumulation speed of a compensation section information slow and adjusts a compensation amount gain large if the vehicle speed is slow. 
         [0017]    In an embodiment, the method further comprises outputting a compensation amount gain corresponding to a torque in accordance with a user&#39;s steering intention by a decouple gain adjusting portion only if a torque in accordance with a user&#39;s steering intention is generated. 
         [0018]    In an embodiment, in outputting the compensation amount gain corresponding to the torque in accordance with the user&#39;s steering intention, the decouple gain adjusting portion outputs the compensation amount gain in accordance with the torque by using a column torque or gain information which is stored in advance in a form of a look up table. 
         [0019]    In an embodiment, the method further comprises synthesizing by a compensation amount gain synthesizing portion a compensation amount gain outputted from the compensation amount adjusting portion in accordance with a vehicle speed and a compensation amount gain outputted corresponding to a torque generated in accordance with the user&#39;s steering intention from the decouple gain adjusting portion, and outputting a resultant friction compensation torque. 
         [0020]    In an embodiment, a friction compensation slope is adjusted in accordance with a friction compensation amount so that a stable friction compensation is provided, a vibration induced to an MDPS system is improved, and therefore a vibration is not generated in an MDPS system although an amount of a friction compensation torque is increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is an example shown in a graph depicting the phenomena that a vibration is generated in accordance with an increase of an amount of a conventional friction compensation torque command. 
           [0022]      FIG. 2  is a sample drawing of a schematic configuration of a friction compensation logic of an MDPS system according to an embodiment. 
           [0023]      FIG. 3  is a sample graph of a performance evaluation result after a friction compensation logic of an MDPS system according to an embodiment is applied. 
           [0024]      FIG. 4  is a sample graph of steering hysteresis before and after the compensation of a friction compensation torque. 
           [0025]      FIG. 5  is a flow chart showing a method of compensating a friction of an MDPS system according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Hereinafter, embodiments will be described below with reference to the accompanying drawings through various examples. 
         [0027]    While various embodiments have been described below, it will be understood to those skilled in the art that the embodiments described are by way of example only. Accordingly, the device or equipment described herein should not be limited based on the described embodiments. 
         [0028]    In a motor driven power steering (MDPS) system, the MDPS system calculates a motor torque command by reflecting a friction compensation torque command for a smooth operation. The reason is that, in an MDPS system, if a steering motor cannot generate an auxiliary steering power to the required extent due to a friction which is generated when each steering component is driven, the driving of a steering wheel by the steering motor is not easy and a steering feeling or an initial build-up feeling is not good, and therefore a driver feels a difference in steering. 
         [0029]    In addition, the friction compensation torque command is outputted as a shape close to a step to compensate the friction of the mechanism. The larger the friction compensation torque command is, the more abrupt the change of the value of the command is. Therefore, a vibration may be generated in an MDPS system, as shown in a graph in  FIG. 1 . 
         [0030]    That is, if the amount of a friction compensation torque command is large, a vibration may be induced in an MDPS system because the amount of the compensation is abruptly changed. 
         [0031]      FIG. 2  is a sample drawing of a schematic configuration of a friction compensation logic of an MDPS system according to an embodiment. 
         [0032]    As shown in  FIG. 2 , a friction compensation logic of an MDPS system according to an embodiment includes a compensation section selecting portion  110 , a compensation section accumulating portion  120 , an accumulation speed adjusting portion  130 , an accumulation limiting portion  140 , a compensation amount adjusting portion  150  in accordance with a vehicle speed, a decouple gain adjusting portion  160 , and a compensation amount gain synthesizing portion  170 . 
         [0033]    The compensation section selecting portion  110  selects a compensation section by a band pass filter (BPF) which passes a limited range of frequency band in a column torque signal inputted from a column torque. For example, when a driver tries to rotate a steering wheel, a band pass filter (BPF) filters the timing of the change, that is, the timing that the frequency is changed from f 1  to f 2 . 
         [0034]    The compensation section accumulating portion  120  accumulates the information of a compensation section (for example, frequency) outputted from the compensation section selecting portion  110 . According to the accumulation of the compensation section information, it is possible to determine whether the driver tries to rotate the steering wheel to the left, or to the right. That is, the compensation section accumulating portion  120  accumulates the information of the compensation section and it is possible to determine the direction of the compensation. 
         [0035]    The accumulation speed adjusting portion  130  adjusts the speed of accumulating the information of the compensation section. 
         [0036]    That is, when a driver tries to rotate a steering wheel, it is adjusted whether the direction by the driver to rotate is determined rapidly or slowly. If a fast determination is required, an accumulating speed is adjusted fast. If a slow determination is required, an accumulating speed is adjusted slow. 
         [0037]    The accumulation limiting portion  140  limits the amount of accumulation when the compensation section information is accumulated. If a compensation section information is unlimitedly and continuously accumulated, the timing to determine the compensation directions is delayed. Therefore, while the compensation section information is accumulated, it is limited to the extent that the compensation direction is determined thereby determining the compensation direction rapidly. 
         [0038]    However, if the accumulating speed of a compensation section information is fast, that is, if the determination of a compensation direction is fast, or if a compensation amount is large, a vibration may be generated in an MDPS system occurs. If a vibration is generated, a mechanism of an MDPS system is damaged by a mechanical friction. 
         [0039]    Accordingly, the compensation amount adjusting portion  150  in accordance with a vehicle speed controls so that the accumulation speed adjusting portion  130  adjusts the accumulation speed of a compensation section information fast and instead adjusts a compensation amount gain K small if a vehicle speed is fast. If a vehicle speed is slow, it controls so that the accumulation speed adjusting portion  130  adjusts the accumulation speed of a compensation section information slow and instead adjusts a compensation amount gain K large. 
         [0040]    The decouple gain adjusting portion  160  accomplishes a friction compensation (that is, the decouple gain adjusting portion  160  outputs a compensation amount gain in accordance with a torque) only if a driver operates a steering wheel by his/her driving intention. If the driver release the steering wheel, the decouple gain adjusting portion  160  does not accomplish a friction compensation because the driver&#39;s intention does not exist. That is, if a torque which controls a steering wheel based on the driver&#39;s driving intention does not exist, a compensation amount gain becomes the minimum (for example, zero). 
         [0041]    The compensation amount gain synthesizing portion  170  synthesizes a compensation amount gain outputted from the compensation amount adjusting portion  150  in accordance with a vehicle speed and a compensation amount gain outputted from the decouple gain adjusting portion  160 , and outputs a resultant friction compensation torque command. 
         [0042]    Therefore, in an embodiment, a compensation amount gain is adjusted to be small even if an accumulation speed of a compensation section information is fast so that a vibration is not generated in an MDPS system. An accumulation speed of a compensation section information is adjusted to be slow even if a compensation amount is adjusted to be large so that a vibration is not generated in an MDPS system. 
         [0043]    In  FIG. 3 , comparing with a conventional graph in  FIG. 1 , a vibration is not generated even if an amount of a compensation torque A 1  is increased corresponding to a column torque A 2 . 
         [0044]      FIG. 3  is a sample graph of a performance evaluation result after a friction compensation logic of an MDPS system according to an embodiment is applied. 
         [0045]      FIG. 4  is a sample graph of steering hysteresis before and after the compensation of a friction compensation torque. As shown in the simulation result in  FIG. 4 , values of the initial driving torque decrease gradually in the order of a driving torque B 1  before a friction compensation torque is applied, a driving torque B 2  after a friction compensation torque of 0.4 Nm is applied, a driving torque B 3  after a friction compensation torque of 0.8 Nm is applied. 
         [0046]      FIG. 5  is a flow chart showing a method of compensating a friction of an MDPS system according to an embodiment. Referring to  FIG. 5 , the detailed operation is described. 
         [0047]    In a method of compensating a friction generated in an MDPS system according to an embodiment, a column torque signal inputted from a column torque is filtered by a band pass filter so that only an information (for example, frequency band) which is selected in a compensation section can be passed (S 101 ). 
         [0048]    Next, a compensation section information which is filtered by the band pass filter is accumulated by the compensation section accumulating portion  120  so that a column torque signal which passed the band pass filter can be used in determining a friction compensation direction (S 102 ). 
         [0049]    The accumulation speed of the compensation section information is adjusted by the accumulation speed adjusting portion  130  so that a speed of determining a direction of a friction compensation can be adjusted in accordance with a vehicle speed (S 103 ). 
         [0050]    If a fast determination is required, an accumulation speed is adjusted fast. If a slow determination is required, an accumulation speed is adjusted slow. 
         [0051]    In accumulating the compensation section information, the accumulation amount is limited by the accumulation limiting portion  140  (S 104 ). 
         [0052]    The reason is that the timing to determine a compensation direction may be delayed if a compensation section information is unlimited and continuously accumulated. Therefore, while a compensation section information is accumulated, it is limited so that a compensation direction may be determined (for example, ±1). Accordingly, a compensation direction may be determined rapidly. 
         [0053]    The compensation amount adjusting portion  150  in accordance with a vehicle speed controls so that the accumulation speed adjusting portion  130  adjusts an accumulation speed of a compensation section information fast and adjusts a compensation amount gain K small if a vehicle speed is fast. 
         [0054]    The compensation amount adjusting portion  150  in accordance with a vehicle speed controls so that the accumulation speed adjusting portion  130  adjusts an accumulation speed of a compensation section information slow and adjusts a compensation amount gain K large if a vehicle speed is slow (S 105 ). 
         [0055]    A friction compensation is not accomplished if a user&#39;s steering intention does not exist, for example, a user releases a steering wheel. A friction compensation is accomplished only if a user&#39;s steering intention exists. For this, the decouple gain adjusting portion  160  outputs a compensation amount gain in accordance with a torque (S 106 ). 
         [0056]    The decouple gain adjusting portion  160  may output a compensation amount gain in accordance with a torque by using a column torque/gain information which is stored in advance in a form of a look up table. 
         [0057]    Finally, a compensation amount gain outputted from the compensation amount adjusting portion  150  in accordance with a vehicle speed and a compensation amount gain outputted from the decouple gain adjusting portion  160  are synthesized and a resultant friction compensation torque command is outputted (S 107 ). 
         [0058]    As described above, in this embodiment, a vibration is not generated in an MDPS system even if an accumulation speed of a compensation section information is fast or if a compensation amount is large. Therefore, a mechanism in an MDPS system is prevented to be damaged by a mechanical friction. 
         [0059]    While various embodiments have been described above, it will be understood to those skilled in the art that the embodiments described are by way of example only. Accordingly, the device described herein should not be limited based on the described embodiments.