Patent Publication Number: US-2004059485-A1

Title: Vehicle operation control method and vehicle operation control apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001] The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. JP2002-203420. The contents of these applications are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to a vehicle operation control method and vehicle operation control apparatus for controlling an actual steering angle of a driven wheel based on a steering angle of a steering wheel and vehicle velocity.  
       [0004] 2. Description of Related Art  
       [0005] As a vehicle operation control apparatus including a transmission ratio changing mechanism for changing the transmission ratio by driving a motor, provided halfway of a steering transmission system which connects a steering wheel to driven wheels, a vehicle operation control apparatus  100  which comprises a steering wheel  21 , a first steering shaft  22 , a second steering shaft  23 , an EPS actuator  24 , a rod  25 , a steering angle sensor  26 , a vehicle velocity sensor  27 , a torque sensor  28 , an EPS ECU  30 , a gear ratio changing mechanism  32  (transmission ratio changing mechanism), a VGRS ECU  40  and the like, as shown in FIG. 1, is available. In the meantime, such “a transmission ratio changing mechanism for changing a transmission ratio by driving an electric motor, located halfway of a steering transmission system which connects the steering wheel to the driven wheels” is sometimes called variable gear ratio system (referred to as VGRS, hereinafter) depending on a case.  
       [0006] That is, an end of the first steering shaft  22  is connected to the steering wheel  21  and an input side of the gear ratio changing mechanism  32  is connected to the other end side of this first steering shaft  22 . This gear ratio changing mechanism  32  comprises a motor, a reduction gear and the like. An end side of the second steering shaft  23  is connected to this output side of the gear ratio changing mechanism and an input side of the EPS actuator  24  is connected to the other end side of the second steering shaft  23 . The EPS actuator  24  is an electric type powered steering system, which is capable of converting a rotary motion inputted by the second steering shaft  23  through a rack and pinion gear (not shown) to a motion in the axial direction of the rod  25  and outputting it. Further, this EPS actuator  24  generates an assist force depending on a steering condition by means of an assist motor which is controlled by the EPS ECU  30  so as to assist steering by a driver. In the meantime, this rod  25  is mounted on driven wheels FR, FL.  
       [0007] A rotation angle (steering angle) of the first steering shaft  22  is detected by a steering angle sensor  26  and inputted to the VGRS ECU  40  as a steering angle signal. A steering torque by the second steering shaft  23  is detected by a torque sensor  28  and inputted to the EPS ECU  30  as a torque signal. Further, a vehicle velocity is detected by a vehicle velocity sensor  27  and inputted to the EPS ECU  30  and VGRS ECU  40  as a vehicle velocity signal. Additionally, the EPS actuator  24  contains a tire angle sensor (not shown) capable of detecting a tire angle (actual steering angle) from a moving amount of the rod  25 .  
       [0008] With such a structure, ratio between input gear and output gear is changed depending on vehicle velocity at real time by means of a motor and reduction gear in the gear ratio changing mechanism  32  and VGRS ECU  40  so as to change a ratio of output angle of the second steering shaft  23  relative to the steering angle of the first steering shaft  22 . The EPS actuator  24  and the EPS ECU  30  generate an assist force for assisting steering of the vehicle driver by means of an assist motor depending on vehicle driver&#39;s steering condition and vehicle velocity detected by means of the torque sensor  28  and the vehicle velocity sensor  27 .  
       [0009] Consequently, the steering gear ratio corresponding to the vehicle velocity can be set. For example, an output angle to a second steering shaft  23  by the gear ratio changing mechanism  32  can be set to be increased with respect to the steering angle of the steering wheel at the time of vehicle stop or traveling at a low velocity. Further, the output angle of the gear ratio changing mechanism  32  can be set to be decreased with respect to the steering angle of the steering wheel at the time of traveling at a high velocity. Meanwhile, an appropriate assist force corresponding to the vehicle velocity can be generated by means of an assist motor.  
       [0010] For example, if a vehicle is stopped or traveling at a low velocity, the steering gear ratio by the gear ratio changing mechanism  32  is set low and an assist force is intensified by an assist motor, so that the driven wheels can be steered largely even with a light steering operation. This facilitates the steering operation of a vehicle driver. On the other hand, if the vehicle is traveling at a high velocity, the assist force by the assist motor drops and the steering ratio by the gear ratio changing mechanism  32  is set high. Consequently, the steering operation becomes heavy and even if the steering wheel  21  is turned largely, it comes that the driven wheels are steered a little. Consequently, it can be expected that vehicle control stability is further improved.  
       [0011] However, such a vehicle operation control apparatus  100  changes the steering gear ratio corresponding to the vehicle velocity as described above. Thus, if the vehicle is accelerated or decelerated suddenly when the vehicle is swirling with the steering wheel maintained at a specific steering angle, the steering gear ratio is changed corresponding thereto. That is, under-steer or over-steer sometimes occurs although the steering wheel is maintained at a specific angle by the vehicle driver, thereby possibly providing the vehicle driver with a feeling of disharmony.  
       SUMMARY OF THE INVENTION  
       [0012] The present invention has been accomplished to solve the above-described problem and therefore, an object of the present invention is to provide a vehicle operation control method and vehicle operation control apparatus which protects a vehicle driver from a feeling of disharmony in his steering operation.  
       [0013] In order to achive the above object,according to the present invention, a vehicle operation control method for controlling an actual steering angle of driven wheels based on a steering angle of a steering wheel and a vehicle velocity, comprising:  
       [0014] a first step of obtaining a change amount in the steering angle by the steering wheel;  
       [0015] a second step of controlling a variable gain based on the vehicle velocity;  
       [0016] a third step of multiplying the change amount in the steering angle obtained in the first step with the variable gain controlled in the second step;  
       [0017] a fourth step of integrating results of multiplications in the third step; and  
       [0018] a fifth step of controlling the actual steering angle of the steering wheel based on a result of the integration in the fourth step.  
       [0019] Further, in order to achive the above object, according to the present invention, a vehicle operation control apparatus for controlling an actual steering angle of driven wheels based on a steering angle of a steering wheel and a vehicle velocity, comprising:  
       [0020] a steering angle change amount obtaining means for obtaining a change amount in the steering angle by the steering wheel;  
       [0021] a variable gain control means for controlling a variable gain based on the vehicle velocity;  
       [0022] a multiplying means for multiplying the change amount in the steering angle obtained by the steering angle change amount obtaining means with the variable gain controlled by the variable gain control means;  
       [0023] an integrating means for integrating results of multiplications by the multiplying means; and  
       [0024] an actual angle controlling means for controlling the actual steering angle of the driven wheels based on a result of the integration by the integrating means.  
       [0025] According to the present invention, the variable gain controlled based on a vehicle velocity is multiplied with a change amount in the steering angle, the multiplication results are integrated and then, an actual steering angle of driven wheels is controlled based on the integration result. Consequently, because if the steering angle by the steering wheel changes, a change amount in the steering angle is generated corresponding to that change, the change amount is multiplied with the variable gain controlled based on the vehicle velocity. The actual steering angle of the driven wheel is controlled based on the integration result integrated the multiplication results. That is, the actual steering angle of the driven wheel can be controlled based on the steering angle and the vehicle velocity. On the other hand, because the change amount in the steering angle becomes zero when the steering wheel is maintained at a specific angle, a result of multiplication with the variable gain also becomes zero. Further, because a result of integration of the multiplication results does not change when the steering wheel is maintained at a specific angle, no changes occur in the actual steering angle of the driven wheels controlled based on the integration result. Therefore, because when the steering wheel is maintained at a specific angle, the actual steering angle of the driven wheels is not affected even if the vehicle velocity changes, over-steer characteristic and under-steer characteristic due to a sudden change in the vehicle velocity can be improved, thereby protecting the vehicle driver from a feeling of disharmony in this steering operation.  
       [0026] Further, in accordance with the more preferred teaching of the present invention, a transmission ratio changing mechanism f or changing a transmission ratio by a drive of a motor is provided half way of a steering transmission system connecting the steering wheel with the driven wheels,  
       [0027] the variable gain controlled in the second step being a transmission ratio attained by the transmission ratio changing mechanism.  
       [0028] Still further, in accordance with the more preferred teaching of the present invention, a transmission ratio changing mechanism for changing a transmission ratio by a drive of a motor is provided halfway of a steering transmission system connecting the steering wheel with the driven wheels,  
       [0029] the variable gain controlled by the variable gain control means being a transmission ratio attained by the transmission ratio changing mechanism.  
       [0030] In accordance with the more preferred teaching of the present invention, a transmission ratio changing mechanism for changing the transmission ratio by a drive of a motor is provided halfway of steering transmission system which connects the steering wheel with the driven wheels, the transmission ratio is controlled based on the vehicle velocity, and this transmission ratio is multiplied with the change amount in the steering angle. Further, the multiplication results are integrated and the actual steering angle of the driven wheel is controlled based on the integration result. Consequently, because if the steering angle by the steering wheel changes, a change amount in the steering angle is generated corresponding to that change, the change amount is multiplied with the transmission ratio of the transmission ratio changing mechanism controlled based on the vehicle velocity. The actual steering angle of the driven wheel is controlled based on the integration result integrated the multiplication results. That is, the actual steering angle of the driven wheel can be controlled based on the steering angle and the vehicle velocity. On the other hand, because the change amount in the steering angle becomes zero when the steering wheel is maintained at a specific angle, a result of multiplication with the transmission ratio of the transmission ratio changing mechanism also becomes zero. Further, because a result of integration of the multiplication results does not change when the steering wheel is maintained at a specific angle, no changes occur in the actual steering angle of the driven wheels controlled based on the integration result. Therefore, because when the steering wheel is maintained at a specific angle, the actual steering angle of the driven wheels is not affected even if the vehicle velocity changes, over-steer characteristic and under-steer characteristic due to a sudden change in the vehicle velocity can be improved, thereby protecting the vehicle driver from a feeling of disharmony in this steering operation.  
       [0031] In order to achive the above object, according to the present invention, a vehicle operation control method for controlling an actual steering angle of driven wheels based on a steering angle of a steering wheel and a vehicle velocity, wherein  
       [0032] if information that the steering wheel is not being turned or information that the steering wheel is being turned without affecting the steering of the driven wheels is obtained based on the change amount in the steering angle by the steering wheel, changes in the actual steering angle of the driven wheels is restricted.  
       [0033] Further, in order to achive the above object, according to the present invention,a vehicle operation control apparatus for controlling an actual steering angle of driven wheels based on a steering angle of a steering wheel and a vehicle velocity, further comprising a control means which if information that the steering wheel is not being turned or information that the steering wheel is being turned without affecting the steering of the driven wheels is obtained based on the change amount in the steering angle by the steering wheel, restricts changes in the actual steering angle of the driven wheels.  
       [0034] According to the present invention, if information that the steering wheel is not being turned or information that the steering wheel is being turned without affecting the steering of the driven wheels is obtained based on the change amount in the steering angle by the steering wheel, changes in the actual steering angle of the driven wheels is restricted. Thus, even if when the vehicle driver maintains the steering wheel at a specific angle, the actual steering angle of the driven wheels is controlled based on the steering angle by the steering wheel and the vehicle velocity, changes in the actual steering angle of the driven wheels is restricted. Consequently, even if the vehicle velocity changes when the steering wheel is maintained at a specific angle, the actual steering angle of the driven wheels is not affected. Therefore, over-steer characteristic and under-steer characteristic due to a sudden change in the vehicle velocity can be improved, thereby protecting the vehicle driver from a feeling of disharmony. In the meantime, those informations may be obtained based on the steering angle velocity instead of the change amount in the steering angle by the steering wheel and in this case, the same operation and effect are produced. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0035]FIG. 1 is an explanatory diagram showing an outline of the structure of a vehicle operation control apparatus;  
     [0036]FIG. 2 is a functional block diagram showing vehicle operation control processing by means of the EPS ECU and VGRS ECU of the vehicle operation control apparatus of this embodiment;  
     [0037]FIG. 3 is a functional block diagram showing a basic functional configuration of the vehicle operation control processing applied to the VGRS control processing of this embodiment;  
     [0038]FIG. 4 is a functional block diagram showing a specific functional configuration of the vehicle operation control processing applied to the VGRS control processing of this embodiment; and  
     [0039]FIG. 5 is aflow chart showingaflowof the vehicle operation control processing of this embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0040] Hereinafter, the embodiment of the vehicle operation control apparatus which the vehicle operation control method and vehicle operation control apparatus of the present invention are applied to will be described with reference to the accompanying drawings. Meanwhile, because the vehicle operation control apparatus  20  of this embodiment is not different from the vehicle operation control apparatus  100  in terms of mechanical structure, the vehicle operation control apparatus  20  ( 100 ) shown in FIG. 1 will be described.  
     [0041] As shown in FIG. 1, a vehicle operation control apparatus  20  comprises a steering wheel  21 , a first steering shaft  22 , a second steering shaft  23 , an EPS actuator  24 , a rod  25 , a steering angle sensor  26 , a vehicle velocity sensor  27 , a torque sensor  28 , an EPS ECU  30 , a gear ratio changing mechanism  32 , a VGRS ECU  40  and the like. Because its mechanical and electrical connections have been already described, description thereof is omitted here. FIG. 2 shows a functional block diagram showing vehicle operation control processing by means of the EPS ECU  30  and VGRS ECU  40  of the vehicle operation control apparatus  20  of this embodiment.  
     [0042] As shown in FIG. 2, in the vehicle operation control apparatus  20  of this embodiment, two processings, that is, an EPS control processing  30   a  by the EPS ECU  30  and VGRS control processing  40   a  by the VGRS ECU  40  are carried out by an electronic control unit (ECU). That is, the vehicle operation control apparatus  20  has a function for controlling the steering gear ratio by means of the gear ratio changing mechanism  32  according to VGRS control processing  40   a  with the VGRS ECU  40 , depending on the vehicle velocity. Further, it has a function of assisting steering by the vehicle driver by generating an assist force depending on steering condition by means of the EPS control processing  30   a  with the EPS ECU  30 .  
     [0043] Thus, in the VGRS control processing  40   a,  a rotation angle instruction value of the motor  32   m  of the gear ratio changing mechanism  32 , which is automatically determined corresponding to the vehicle velocity, is determined from a motor rotation angle map (not shown) when the steering angle signal by the steering angle sensor  26  and the vehicle velocity signal by the vehicle velocity sensor  27  are inputted to the VGRS ECU  40 . Then, a motor voltage corresponding to the determined rotation angle instruction value is supplied to the motor  32   m  through a motor drive circuit. Consequently, the gear ratio changing mechanism  32  and the VGRS ECU  40  change a ratio of an output gear to an input gear by means of the motor  32   m  and the reduction gear  32   g  corresponding to the vehicle velocity at real time, so that a ratio Gv of an output angle of the second steering shaft  23  to a steering angle of the first steering shaft  22  is changed.  
     [0044] In the EPS control processing  30   a,  if a steering torque signal by the torque sensor  28  and a vehicle velocity signal by the vehicle velocity sensor  27  are inputted to the EPS ECU  30 , a current instruction value of the assist motor  24   m  of the EPS actuator  24 , which is automatically determined depending upon the vehicle velocity, is determined from a motor current map(not shown). A motor voltage corresponding to the determined current instruction value is supplied to the motor  24   m  by the motor drive circuit. Consequently, the EPS actuator  24  and the EPS ECU  30  generate an assist force for assisting steering of a vehicle driver by means of the assist motor  24   m,  corresponding to the steering condition by the vehicle driver and vehicle velocity detected by the torque sensor  28  and the vehicle velocity sensor  27  through the EPS control processing  30   a.    
     [0045] The VGRS ECU  40  carries out the VGRS control processing  40   a  based on a steering angle signal transmitted from the steering angle sensor  26 , so that a steering gear ratio is changed corresponding to the vehicle velocity. Thus, as described in the Description of Related Art, if a vehicle is accelerated or decelerated suddenly when it swirls with a specific steering angle maintained with the steering wheel  21 , the steering gear ratio can be changed corresponding thereto.  
     [0046] Thus, in the vehicle operation control apparatus  20  of this embodiment, even if the vehicle velocity is changed with the steering wheel  21  maintained at a specific angle when the vehicle operation control processing, which is a basic functional block shown in FIG. 3, is executed by the VGRS ECU  40 , an actual steering angle θT of the driven wheels FR, FL is never affected.  
     [0047] Here, the vehicle operation control processing shown in FIG. 3 will be described.  
     [0048] As shown in FIG. 3, the vehicle operation control processing by the VGRS ECU  40  is constituted of a steering angle change amount detecting means  40   a   1 , a variable gain multiplying means  40   a   2 , an integrating means  40   a   3 , an object actual steering angle computing means  40   a   4 , a deflection amount detecting means  40   a   5 , an object steering angle computing means  40   a   6 , and a VGRS object angle computing means  40   a   7 .  
     [0049] In the vehicle operation control processing, a change amount Δθh (differential value) of the steering angle θh by the steering wheel  21  is detected by the steering angle change amount detecting means  40   a   1 , the variable gain G is controlled by the variable gain multiplying means  40   a   2  based on the vehicle velocity V by vehicle velocity sensor  27  and that controlled variable gain G is multiplied with the change amount Δθh in the steering angle. Then, the multiplication result is integrated by the integrating means  40   a   3  and further, that integration result (integrated value) is converted to the object actual steering angle θT* by the object actual steering angle computing means  40   a   4 . The deflection amount detecting means  40   a   5  obtains a deflection between an actual steering angle θT by a tire angle sensor (not shown) obtained through the EPS ECU  30  and an object actual steering angle produced by conversion by the object actual steering angle computing means  40   a   4  so as to compute an angle deflection ΔθT.  
     [0050] After such a computation, the angle deflection ΔθT is converted to an object steering angle by the object steering angle computing means  40   a   6  and further, converted to a VGRS object angle by the VGRS object angle computing means  40   a   7  so as to obtain the VGRS object angle which is outputted to the gear ratio changing mechanism  32  based on this object steering angle. In the meantime, the Gs shown in FIG. 3 indicates steering gear ratio, which is a ratio between the steering angleθh and the actual steering angle θT and Gv indicates a gear ratio of the reduction gear  32   g,  which is accommodated in the gear ratio changing mechanism  32 .  
     [0051] If the steering angle θh by the steering wheel  21  is changed in the vehicle operation control processing, an amount corresponding to that change is generated as the change amount Δθh (differential value) of the steering angle θh. Thus, the variable gain G controlled based on the vehicle velocity V is multiplied with that change amount Δθh and this multiplication result is integrated, and the actual steering angleθT of the driven wheels FR, FL is controlled based on this integration result (integrated value).  
     [0052] Because when the steering wheel  21  is maintained at a specific angle, the change amount Δθh of the steering angle θh becomes zero and therefore, a multiplication result of the variable gain G also becomes zero. Because the integration result of this multiplication result is not changed when the steering wheel  21  is maintained at a specific angle, the actual steering angle of the driven wheels FR, FL controlled based on the integration result is not changed. Therefore, even if the vehicle velocity V changes with the steering wheel  21  maintained at a specific angle, the actual steering angle θT of the driven wheels FR, FL is never affected. Thus, over-steer characteristic and under-steer characteristic by a sudden change in vehicle velocity can be adjusted to be preferable.  
     [0053] Even while the vehicle driver maintains the steering wheel  21  at a specific angle, a rotation in the steering wheel  21 , which does not affect steering of the driven wheels, that is, “a play in the steering wheel  21 ” may occur due to backlash or the like generated in gears constituting the gear ratio changing mechanism  32  or a steering transmission mechanism among the steering wheel  21 , the first steering shaft  22  and the gear ratio changing mechanism  32 . Because the change amount in the steering angle θh due to the “a play in the steering wheel  21 ” does not affect the steering, that change amount Δθh is adjusted to zero by removing it by non-sensitive range processing or filter processing, which will be described later.  
     [0054] Next, a configuration example in which the basic functional block of the vehicle operation control processing shown in FIG. 3 is applied specifically to the VGRS control processing  40   a  and its processing flow will be described with reference to FIG. 4 and FIG. 5. In FIG. 4 the same reference numerals are attached to substantially the same components as the respective functions shown in FIG. 3.  
     [0055] As shown in FIG. 5, the vehicle operation control processing is computed by the VGRS ECU  40  through the VGRS control processing  40   a  and respective processings of step S 101 -step S 117  are executed successively. In the meantime, this vehicle operation control processing is carried out periodically and repeatedly by timer interruption or the like (for example, every 5 millisecond). Hereinafter, each step will be described with reference to FIGS. 4, 5.  
     [0056] (1) Step S 101   
     [0057] In this step, a processing for obtaining the steering angle θh, the vehicle velocity V and the actual steering angle θT is carried out. The steering angle θh is obtained by receiving a steering angle signal detected by the steering angle sensor  26  from the steering angle sensor  26  or other ECU. The vehicle velocity V is obtained by receiving a vehicle velocity signal detected by the vehicle velocity sensor  27  from the vehicle velocity sensor  27  or the like. Further, the actual steering angle θT is obtained by receiving an actual steering angle signal detected by the tire angle sensor accommodated in the EPS actuator  24  through the EPS ECU  30 .  
     [0058] (2) Step S 103   
     [0059] In this step, a processing of detecting the change amount Δθh in steering angle θh is carried out. That is, a steering angle Z detected previously and stored in the steering angle memory  41  is subtracted from the steering angleθh obtained in step S 101  through arithmetic operating processing by the steering angle change amount detecting means  40   a   1  shown in FIG. 4 so as to obtain a deflection between the both. Because consequently, the change amount Δθh in steering angleθh, that is, a differential value of the steering angle θh is computed, the change amount Δθh in steering angle θh is detected. In the meantime, the steering angle memory  41  is constituted of, for example, a semiconductor storage unit of the VGRS ECU  40 . Further, because the change amount (for example, ±3°) in steering angle θh due to the “play in the steering wheel  21 ” (may correspond to “rotation of steering wheel not affecting steering of driven wheels”) does not affect the steering of driven wheels, that change amount is removed through a processing for neglecting that change amount (non-sensitive range processing and filter processing). Consequently, the steering angle change amount detecting means  40   a   1  regards the change amount in the steering angleθh by the “play in the steering wheel  21 ” as zero and detects the change amount Δθh in steering angleθh which exceeds the “play in the steering wheel  21 ”.  
     [0060] (3) Step S 105   
     [0061] In this step, a processing of map-operation between the vehicle velocity and gear ratio is carried out. That is, the variable gain multiplying means  40   a   2  shown in FIG. 4 determines a gear ratio Ga (transmission ratio by the transmission ratio changing mechanism) corresponding to the vehicle velocity V according to the vehicle velocity-gear ratio map  42 , which automatically determines a transmission ratio by the gear ratio changing mechanism  32  based on the vehicle velocity V obtained in step S 101 . Meanwhile, the vehicle velocity-gear ratio map  42  is constituted of a data table stored by the semiconductor storage unit of the VGRS ECU  40 , for example.  
     [0062] (4) Step S 107   
     [0063] In this step, a processing of multiplying the change amount Δθh in steering angle θh with a gear ratio Ga is carried out. That is, that change amount Δθh is multiplied with the gear ratio Ga through arithmetic operation processing by the variable gain multiplying means  40   a   2  shown in FIG. 4 and outputted to the integrating means  40   a   3  at a next stage. Because consequently, the gear ratio Ga is multiplied with only the change amount Δθh in steering angle θh, no change occurs in the steering angleθh by the steering wheel  21  and unless no change amount Δθh occurs (Δθh=0), a result of multiplication between the vehicle velocity and gear ratio becomes zero even if the gear ratio Ga corresponding to the vehicle velocity V is determined according to the vehicle velocity—gear ratio map  42  (Δθh×Ga=0). Consequently, a value outputted to the integrating means  40   a   3  becomes zero. That is, if the vehicle velocity V changes with the steering wheel  21  maintained at a specific angle, zero is outputted to the integrating means  40   a   3 . In the meantime, the case where “no change occurs in the steering angle θh of the steering wheel  21  so that the change amount Δθh is not generated (Δθh=0)” may correspond to “information that the steering wheel is not being turned”. Further, a multiplication result (Δθh×Ga=0) obtained when the information that the steering wheel  21  is not being turned (θh =0) is obtained may correspond to the “restricting changes in the actual steering angle of the driven wheel”.  
     [0064] (5) Step S 109   
     [0065] In this step, a processing of computing the object actual steering angle is carried out. That is, by integrating multiplication results by the integrating means  40   a   3  shown in FIG. 4 and then dividing that integration result by the steering gear ratio Gs by means of the object actual steering angle computing means  40   a   4 , an object actual steering angle θT* corresponding to a change in the steering angle θh by the steering wheel  21  is obtained.  
     [0066] (6) Step S 111   
     [0067] In this step, a processing of computing a deflection between the object actual steering angle θT* and the actual steering angleθT is carried out. That is, by subtracting an actual angle θT obtained in step S 101  from an object actual steering angle θT* by means of the deflection amount detecting means  40   a   5  shown in FIG. 4 through arithmetic operation, the deflection of the actual angle θT to the object actual steering angle θT*, that is, the angle deflection ΔθT, is obtained.  
     [0068] (7) Step S 113   
     [0069] In this step, a processing of computing an object steering angle is carried out. That is, by multiplying the steering gear ratio Gs with the angle deflection ΔθT obtained in step S 111  by means of the object steering angle computing means  40   a   6  shown in FIG. 4 through arithmetic operation, the actual steering angle is converted to the steering angle, thereby obtaining the object steering angle.  
     [0070] (8) Step S 115   
     [0071] In this step, a processing of computing a VGRS object angle is carried out. That is, by multiplying the object steering angle obtained in step S 113  with the gear ratio Gv of the reduction gear  32   g  in the gear ratio changing mechanism  32  by means of the VGRS object angle computing means  40   a   7  shown in FIG. 4 through arithmetic operation, the steering angle is converted to the VGRS object angle, thereby obtaining the VGRS object angle.  
     [0072] (9) Step S 117   
     [0073] In this step, a processing of memorizing the steering angle θh is carried out. That is, due to a necessity of referring to the steering angle θh obtained in step S 101  as a steering angle Z detected last upon a next processing of step S 103 , a currently obtained steering angle θh is stored in the steering angle memory  41 , so that the steering angle θh is memorized.  
     [0074] By executing a sequence of the vehicle operation control processing from step S 101  to step S 117 , the vehicle operation control apparatus  20  detects a change amount Δθh in the steering angle of the steering wheel  21  in step S 103 , controls the vehicle velocity—gear ratio map  42  (variable gain G) based on the vehicle velocity V in step S 105 , multiplies the change amount Δθh in the steering angle with a gear ratio (variable gain G) outputted according to the vehicle velocity—gear ratio map  42  in step S 107 , integrates multiplication results in step S 109 , and controls the actual steering angle θT of the driven wheels FR, FL based on a result of integration in step S 111 . That is, a gear ratio (variable gain G) from the vehicle velocity—gear ratio map  42  controlled based on the vehicle velocity V is multiplied with the change amount Δθh in the steering angle, the multiplication results are integrated and the actual angle θT of the driven wheels FR, FL is controlled based on the integration result.  
     [0075] Because if the steering angle θh attained by the steering wheel  21  is changed, the change amount Δθh in the steering angle is generated corresponding to that change, the gear ratio (variable gain G) controlled based on the vehicle velocity V is multiplied with the change amount Δθh, so that the actual steering angle θT of the driven wheels FR, FL is controlled based on an integration result of the multiplication results. That is, the actual steering angle θT of the driven wheels FR, FL can be controlled based on the steering angle θh and the vehicle velocity V. On the other hand, when the steering wheel  21  is maintained at a specific angle, the change amount Δθh in the steering angle θh becomes zero and therefore, a result of multiplication of the variable gain G also becomes zero. Further, because the integration result of the multiplication results is never changed when the steering wheel  21  is maintained at a specific angle, no change occurs in the actual steering angle θT of the driven wheels FR, FL controlled based on the integration result. Therefore, even if the vehicle velocity V changes in the condition that the steering wheel  21  is maintained, the actual steering angle θT of the driven wheels FR, FL is never affected. Therefore, the over-steer characteristic and under-steer characteristic due to a sudden change in vehicle velocity can be controlled preferably, thereby protecting the vehicle driver from a feeling of disharmony.  
     [0076] Although in the above-described embodiment, the change amount Δθh in the steering angle θh is detected in step S 103 , for example, the step S 103  may be a processing of obtaining steering angle velocity ωh obtained by time-differentiating the steering angle θh. In this case, the steering angle velocity ωh when the steering angle velocity ωh is zero may correspond to “information that the steering wheel is not being turned” and the steering angle velocity ωh when the steering angle velocity ωh is substantially zero may correspond to “information that the steering wheel  21  is being turned without affecting the steering operation of the driven wheels” (that is, a rotation within “a play in the steering wheel  21 ”).  
     [0077] In this case, in step S 107 , a processing of multiplying the steering angle velocity ωh with the gear ratio Ga is carried out. If the steering angle velocity ωh attained by the steering wheel  21  is zero (ωh=0; may correspond to “information that the steering wheel is not being turned”) or if the steering angle velocity ωh is substantially zero (may correspond to information “the steering wheel is being turned without affecting the steering), even if the gear ratio Ga corresponding to the vehicle velocity V is determined according to the vehicle velocity—gear ratio map  42 , multiplication result of both becomes zero or substantially zero (ωh×Ga=0 or substantially 0; may correspond to “restricting changes in the actual steering angle of the steering wheel”).  
     [0078] Further, because no change occurs in a result of integration in the object actual steering angle computing processing of step S 109  when the steering wheel  21  is maintained, no change occurs in the actual steering angle θT of the driven wheels FR, FL controlled based on the integration result. Therefore, when the steering wheel  21  is maintained at a specific angle, the actual steering angle θT of the driven wheels FR, FL is not affected even if the vehicle velocity V changes. Therefore, the over-steer characteristic and the under-steer characteristic due to a sudden change in vehicle velocity can be improved through a processing of obtaining the steering angle velocity ωh by time-differentiating the steering angle θh in step S 103 , thereby protecting the vehicle driver from a feeling of disharmony.  
     [0079] Although the invention has been disclosed in the context of a certain preferred embodiments, it will be understood that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments of the invention. Thus, it is intended that the scope of the invention should not be limited by the disclosed embodiments but should be determined by reference to the claims that follow.