FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] VEHICLE CONTROL APPARATUS MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. DESCRIPTION Technical Field [0001] The present invention relates to a vehicle control apparatus 5 automatically controlling driving of a vehicle. Background Art [0002] Various types of electronic apparatuses are mounted on an in-vehicle system. An in-vehicle control apparatus, which is referred to as an electronic control unit (ECU) for controlling these electronic apparatuses, mounted on a vehicle increases in number in accordance with multifunctionality and diversification of electronic apparatus in recent years. Particularly, in an automatic drive system in which a research development is accelerated recently, designed is a system of achieving an advanced automatic driving by coordinating engine control, brake control, and steering control of a vehicle. [0003] In an electronic power steering control device (steering control device) used for the automatic driving, when a failure occurs in a part of a system, an fail operation needs to be achieved. When the fail operation is also hardly performed, fail-safe needs to be achieved by a minimum function other than a function in which the failure occurs. [0004] A function of limiting control of a steering control device is mounted in some cases to prevent an unintended steering operation in a case where an abnormality occurs in a steering control device. For example, Patent Document 1 obtains road information of a travel route of a subject vehicle obtained from a navigation device, thereby providing a limitation on a targeted steering angle in accordance with the road information. Patent Document 2 discloses a method of detecting output current of an actuator calculated in a steering control device to detect an abnormal output. Prior Art Documents Patent Documents [0005] Patent Document 1: International Publication No. 2017/077807 Patent Document 2: Japanese Patent Application Laid-Open No. 2015-209140 Summary Problem to be Solved by the Invention [0006] Patent Document 1 provides the limitation on the targeted steering angle to prevent the unintended steering operation, however, considered is a possibility that an unintended output is performed regardless of the targeted steering angle if a calculation part itself calculating an operation amount of the actuator of the steering control device breaks down. In Patent Document 2, the output current of the actuator calculated in the steering control device is compared with a threshold value, thus a state where the output current is too large can be detected as an abnormal state. However, when the automatic driving is highly developed, use cases requiring various sizes of steering operations, such as a case of turning right and left in a general road and parking in addition to a traveling of a straight road such as an express way, are needed occur, thus there is a problem that appropriate control cannot be performed if a fixed threshold value is used. Furthermore, in Patent Document 2, an upper limit of the output current is monitored, however, there is no description of a monitoring of a lower limit, thus there is also a problem that such a configuration cannot cope with a state where a steering is suspended during traveling along a curved road, for example. [0007] The present invention therefore has been made to solve problems as described above, and it is an object of the present invention to provide a vehicle control apparatus capable of appropriately setting a threshold value of a steering control amount. Means to Solve the Problem [0008] A vehicle control apparatus according to the present invention includes: an automatic driving control device determining a travel route at a time of executing an automatic driving based on surrounding environment information and position information of a vehicle, and outputting a control target value corresponding 5 to the travel route; and a steering control device calculating a steering control amount based on the control target value, and performing steering control of the vehicle based on the steering control amount, wherein the automatic driving control device dynamically determines a control amount threshold value for regulating a limit of the steering control amount based on automatic driving control information indicating a control state in an automatic driving of the vehicle, and provides the steering control device with the control amount threshold value, and the steering control device changes the control amount not to exceed the control amount threshold value when the steering control amount exceeds the control amount threshold value. Effects of the Invention [0009] According to the vehicle control device of the present invention, the control amount threshold value of the steering control can be appropriately set, and both an expansion of functionality and safety in the automatic driving can be achieved. Brief Description of Drawings [0010] Fig. 1 is a function block diagram illustrating a configuration of a vehicle control apparatus of an embodiment 1 according to the present invention. Fig. 2 is a flow chart illustrating a determination operation of a control amount threshold value of the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 3 is a drawing for describing a transition example of a control state in the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 4 is a drawing illustrating an example of a table for determining the control amount threshold value of the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 5 is a drawing for describing a condition of correcting 5 the control amount threshold value in the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 6 is a drawing for describing a condition of correcting the control amount threshold value in the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 7 is a drawing for describing a condition of correcting the control amount threshold value in the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 8 is a drawing for describing a condition of correcting the control amount threshold value in the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 9 is a drawing illustrating a relationship between a berm width and a correction coefficient. Fig. 10 is a drawing illustrating a relationship between a road surface friction coefficient and a correction coefficient. Fig. 11 is a drawing illustrating a relationship between a vehicle speed and a correction coefficient. Fig. 12 is a block diagram illustrating a hardware configuration of an automatic driving ECU of the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 13 is a block diagram illustrating a hardware configuration of the automatic driving ECU of the vehicle control apparatus of the embodiment 1 according to the present invention. Fig. 14 is a function block diagram illustrating a configuration of a vehicle control apparatus of an embodiment 2 according to the present 5 invention. Fig. 15 is a flow chart illustrating a determination operation of a control amount threshold value of the vehicle control apparatus of the embodiment 2 according to the present invention. Fig. 16 is a flow chart illustrating an operation at a time of detecting an abnormality in a limit determination part in a vehicle control apparatus of a modification example according to the present invention. Fig. 17 is a flow chart illustrating an operation of an automatic driving control part after receiving a notification of detecting the abnormality in the vehicle control apparatus of the modification example according to the present invention. Description of Embodiment(s) [0011] Fig. 1 is a function block diagram illustrating a configuration of a vehicle control apparatus 100 of an embodiment 1 according to the present invention. As illustrated in Fig. 1, the vehicle control apparatus 100 includes a plurality of surrounding environment information acquisition parts 30, 31, and 32 mounted on a vehicle and acquiring information of a surrounding environment of the vehicle, an automatic driving ECU (automatic driving control device) controlling an automatic driving based on surrounding environment information and subject vehicle position information being output from a subject vehicle position information acquisition part 40 acquiring the subject vehicle position information, a steering control device 50 controlled by the automatic driving ECU 20, a brake control device 60, and an accelerator control device 70. [0012] The surrounding environment information acquisition parts 30 to 32 and the subject vehicle position information acquisition part 40 are connected to the automatic driving ECU 20 via a network 80, and the steering control device 50, 5 the brake control device 60, and the accelerator control device 70 are connected to the automatic driving ECU 20 via a network 81. [0013] Examples of the surrounding environment information acquisition parts 30 to 32 include various types of sensors such as a camera, a millimeter wave radar, a sonar and a vehicle-to-vehicle and road-to-vehicle communication module, for example. Fig. 1 exemplifies the three surrounding environment information acquisition parts 30 to 32, however, the number of surrounding environment information acquisition parts is not limited thereto. Examples of the subject vehicle position information acquisition part 40 include a receiving device of a global positioning system (GPS) signal and a receiving device of a high accuracy map information having an absolute position accuracy with centimeter precision. [0014] The automatic driving ECU 20 includes an information acquisition part 21, an automatic driving control part 22, and a limit determination part 23. The information acquisition part 21 acquires the surrounding environment information and the subject vehicle position information from the surrounding environment information acquisition parts 30 to 32 and the subject vehicle position information acquisition part 40, respectively, via the network 80, and collects information. The collected information is input to the automatic driving control part 22. [0015] The automatic driving control part 22 determines a travel route along which the subject vehicle intends to travel at a time of executing an automatic driving based on the input information, calculates a target steering angle corresponding to the travel route as an output of the automatic driving ECU , and inputs the target steering angle to the steering control device 50. The steering control device 50 calculates a steering control amount (torque amount) for operating a steering actuator 53 based on the input target steering angle. In order to achieve the automatic driving, a target braking 5 amount and a target acceleration amount are also transmitted from the automatic driving ECU 20 to the brake control device 60 and the accelerator control device 70. Each of the brake control device 60 and the accelerator control device 70 performs the actuator control to achieve the automatic driving. The target steering angle, the target braking amount, and the target acceleration amount being output from the automatic driving ECU 20 become a control target value for achieving the automatic driving. [0016] The limit determination part 23 acquires road information and obstacle information around the subject vehicle from the information acquisition part 21, and further acquires information indicating how the subject vehicle is controlled by the automatic driving from the automatic driving control part 22. This information is referred to as the automatic driving control information. The automatic driving control information generated in the automatic driving control part 22 includes state information for determining a control state such as a state of traveling along a straight road, traveling along a curved road, changing lane, turning right and left, and self-parking, for example. The automatic driving control information may include a control target value of the target steering angle, the target braking amount, and the target acceleration amount, for example. The limit determination part 23 determines a future target steering angle of the subject vehicle based on the above control information, and determines a control amount threshold value of regulating an upper limit value and a lower limit value of the steering control amount calculated in the steering control device 50 in accordance with the target steering angle. The limit determination part 23 inputs the determined control amount threshold value to a steering limiter 52 in the steering control device 50. This control amount threshold value is a threshold value for a steering control amount (torque amount) of the steering actuator 53. For example, when a current value of a motor driving an actuator corresponds to steering control amount (torque amount), 5 the control amount threshold value is a threshold value for the current value of the motor. [0017] The steering control device 50 includes a steering ECU 51, the steering limiter 52, the steering actuator 53, and a steering mechanism 54. The steering control device 50 calculates a steering control amount (torque amount) for driving the steering actuator 53 in the steering ECU 51 based on a control target value (target steering angle) being input from the automatic driving ECU 20, and inputs the steering control amount to the steering limiter 52 and the steering actuator 53. [0018] The steering limiter 52 detects whether or not the steering control amount (torque amount) of the input steering actuator 53 exceeds the control amount threshold value being input from the limit determination part 23, and when the steering control amount exceeds the control amount threshold value, the steering limiter 52 changes the steering control amount to fall within a range not exceeding the control amount threshold value. For example, the steering control amount is changed to a value corresponding to the control amount threshold value. Then, the steering actuator 53 is driven with motor current corresponding to the changed steering control amount (torque amount), and functions as a steering torque of the steering mechanism 54 mechanistically connected to the steering actuator 53 to be used for steering control. Accordingly, dangerous control performed by the vehicle can be prevented. [0019] When the steering control amount (torque amount) of the steering actuator 53 does not exceed the control amount threshold value, the steering actuator 53 is driven with the motor current corresponding to the steering control amount (torque amount) being directly input from the steering ECU 51 to the steering actuator 53. When the steering control amount (torque amount) is input from both the steering ECU 51 and the steering limiter 52, the steering actuator 53 selects the steering control amount (torque amount) being input from the steering limiter 52. Herein, the steering 5 control amount is exemplified as the torque amount, however, the steering control amount may be the motor current. [0020] Fig. 2 illustrates a flow chart of an operation of the limit determination part 23 determining the control amount threshold value. This flow is executed with a certain period, but may also be executed in conformity to an execution period of the automatic driving control part 22. Herein, the certain period described above indicates a period during which the automatic driving control part 22 transmits the target steering angle, the target braking amount, and a target acceleration amount to the steering control device 50, the brake control device 60, and the accelerator control device 70, and the execution period of the automatic driving control part 22 indicates a period of determining one target steering angle. [0021] As illustrated in Fig. 2, the limit determination part 23 firstly acquires the surrounding environment information, the subject vehicle position information, and the automatic driving control information from the information acquisition part 21 and the automatic driving control part 22 in Step S101 to confirm a surrounding state and current and future subject vehicle control state and subject vehicle speed. [0022] Next, in Step S102, the limit determination part 23 determines whether there is a change in any of the surrounding state and the control state of the subject vehicle and the subject vehicle speed associated with the change in a threshold value described below. When it is determined that there is a change, the limit determination part 23 selects the control amount threshold value (upper limit value and lower limit value) in Step S103, and the process proceeds with Step S104. The selection method is determined by referring to a table described below. In the meanwhile, when it is determined that there is no change, the control amount threshold value is maintained and a series of operations is finished. [0023] In Step S104, the control amount threshold value selected in Step S103 is corrected in accordance with the surrounding state and the travel speed of the subject vehicle. The correction method is described below. [0024] Next, in Step S105, the steering limiter 52 is notified of the corrected control amount threshold value. The correction in Step S104 is not a necessary process, thus when Step S104 is not provided, the steering limiter 52 is notified of the control amount threshold value selected in Step S103. [0025] Fig. 3 illustrates a transition example of the control state. As illustrated in Fig. 3, the control state is broadly classified as a parking state C1, a manual travel state C2, a self-parking state C3, and an automatic travel state C4. [0026] At a time when an ignition (IG) is turned on (ON), the vehicle is in the parking state C1. The automatic travel state C4 is classified as a state of traveling along a straight road (curvature Fig. 14 is a function block diagram illustrating a configuration of a vehicle control apparatus 200 of an embodiment 2 according to the present invention. The vehicle control apparatus 200 illustrated in Fig. 14 and the vehicle control device 100 illustrated in Fig. 1 are different from each other in that information is input from only the automatic driving control part 22 to the limit determination part 23 in the automatic driving ECU 20. That is to say, in the vehicle control apparatus 200 of the embodiment 2, the determination of the control amount threshold value performed 5 by the limit determination part 23 is determined by a control target value being output by the automatic driving control part 22 as the automatic driving control information. [0062] Fig. 15 illustrates a flow chart of an operation of the limit determination part 23 determining the control amount threshold value. This flow is executed with a certain period, but may also be executed in conformity to an execution period of the automatic driving control part 22. [0063] As illustrated in Fig. 15, firstly in Step S201, the limit determination part 23 acquires the target steering angle (the control target value) calculated by the automatic driving control part 22 and being input to the steering control device 50 as the automatic driving control information. [0064] The limit determination part 23 have the target steering angle (the control target value) of a previous period in advance, and calculates a difference value with the target steering angle of the previous period in Step S202, thereby being able to determine the steering control amount (the torque amount) of the steering actuator 53 which needs to be generated in accordance with the difference value. For example, a value which is ten percent larger than the determined steering control amount is calculated as the upper limit value of the control amount threshold value, and a value which is ten percent smaller tha that is calculated as the lower limit value of the control amount threshold value. The ratio described above is one example, thus the ratio for determining the value is not limited thereto. [0065] Next, the steering limiter 52 is notified of the control amount threshold value in Step S203. [0066] As described above, in the vehicle control apparatus 200 of the embodiment 2 according to the present invention, the control amount threshold value of the steering control device 50 is dynamically determined based on the target steering 5 angle being input to the steering control device 50, thus the automatic driving corresponding to various situations can be achieved compared with a case where the control amount threshold value is fixed. The control amount threshold value is set, thus safety in a failure of the steering ECU 51 can also be secured. [0067] In the embodiment 1 and the embodiment 2 described above, the limit determination part 23 transmits the dynamically generated control amount threshold value to the steering limiter 52, thus the steering limiter 52 detects whether or not the steering control amount (torque amount) of the steering actuator 53 exceeds the control amount threshold value, and changes the steering control amount to fall within the range not exceeding the control amount threshold value when the steering control amount exceeds the control amount threshold value. In addition, included in the present modification example is a function that, even in the case where the steering control amount is changed to fall within the range not exceeding the control amount threshold value, when the steering limiter 52 detects the motor current value exceeding the range of the control amount threshold value, the automatic driving control part 22 is notified that the steering limiter 52 detects the abnormality. [0068] Fig. 16 illustrates a flow chart of an abnormality detection performed by the steering limiter 52. As illustrated in Fig. 16, when the steering limiter 52 detects in Step S301 that the motor current value of the steering actuator 53 exceeds the control amount threshold value, the steering limiter 52 determines that the abnormality is detected, and the process proceeds with Step S302. In the meanwhile, when the steering control amount (torque amount) of the steering actuator 53 is smaller than the control amount threshold value, the series of processing is finished. [0069] In Step S302, the automatic driving control part 22 is 5 notified that the abnormality is detected, and the series of processing is finished. [0070] Considered as the case where the motor current value exceeding the range of the control amount threshold value is detected is a case where data of a control target value provided by the automatic driving ECU 20 is lost or changed due to an electrical noise, for example, or a case where the steering ECU 51 breaks down such as a case where a memory in the steering ECU 51 is broken, for example. [0071] Fig. 17 is a flow chart illustrating an operation of the automatic driving control part 22 after receiving the notification of the abnormality detection from the steering limiter 52. As illustrated in Fig. 17, the automatic driving control part 22 receiving the notification of the abnormality detection confirms the surrounding state based on the surrounding environment information being input from the information acquisition part in Step S401, and determines the target steering angle, the target braking amount, and the target acceleration amount for securing the safety of the subject vehicle in Step S402. [0072] The target steering angle, the target braking amount, and the target acceleration amount serve as the control target value for achieving an operation of stopping by applying a brake and an operation of stopping control of the accelerator when there is no obstacle around the subject vehicle, for example. When there is the obstacle around the subject vehicle, the target steering angle, the target braking amount, and the target acceleration amount serve as the control target value within a range capable of avoid the obstacle, for example, the control target value for achieving an operation of stopping by a slow brake while maintaining a distance from the subject vehicle to a preceding vehicle or a following vehicle, for example. [0073] The control target value determined in Step S402 is transmitted to the brake control device 60 and the accelerator control device 70 in Step S403 to achieve the vehicle control. [0074] As described above, the control described in the present modification example is performed, thus even if abnormality occurs in the steering ECU 51, the vehicle can be stopped while maintaining the safety. [0075] The present invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. [0076] According to the present invention, the above embodiments can be arbitrarily combined, or each embodiment can be appropriately varied or omitted within the scope of the invention. We Claim : 1. A vehicle control apparatus, comprising: an automatic driving control device determining a travel route at a time of executing an automatic driving based on surrounding environment 5 information and position information of a vehicle, and outputting a control target value corresponding to the travel route; and a steering control device calculating a steering control amount based on the control target value, and performing steering control of the vehicle based on the steering control amount, wherein the automatic driving control device dynamically determines a control amount threshold value for regulating a limit of the steering control amount based on automatic driving control information indicating a control state in an automatic driving of the vehicle, and provides the steering control device with the control amount threshold value, and the steering control device changes the steering control amount not to exceed the control amount threshold value when the steering control amount exceeds the control amount threshold value. 2. The vehicle control apparatus according to claim 1, wherein the automatic driving control information includes state information of at least an automatic travel state and a self-parking state as the control state, the state information of the automatic travel state includes state information of a state of traveling along a straight road and a state of traveling along a curved road, the state information of the state traveling along the straight road and the state of traveling along the curved road includes state information indicating whether or not a lane is changed, the state information of the self-parking state includes state information of a normal movement state and a turn-back state, and the automatic driving control device determines the control 5 amount threshold value based on a table of the control amount threshold value being set for each combination of the state information. 3. The vehicle control apparatus according to claim 1, wherein the automatic driving control device corrects the control amount threshold value based on the surrounding environment information or a travel speed of the vehicle. 4. The vehicle control apparatus according to claim 3, wherein the control amount threshold value is corrected by multiplying a correction coefficient being set in accordance with a distance to an obstacle, with which the vehicle is assumed to collide, obtained from the surrounding environment information to the control amount threshold value. 5. The vehicle control apparatus according to claim 4, wherein the correction coefficient is set to increase the control amount threshold value when the distance to the obstacle is large and reduce the control amount threshold value when the distance to the obstacle is small. 6. The vehicle control apparatus according to claim 3, wherein the control amount threshold value is corrected by multiplying a correction coefficient being set in accordance with a road surface friction coefficient obtained from the surrounding environment information to the control amount threshold value. 7. The vehicle control apparatus according to claim 6, wherein the correction coefficient is set to increase the control amount 5 threshold value when the road surface friction coefficient is relatively large and reduce the control amount threshold value when the road surface friction coefficient is relatively small. 8. The vehicle control apparatus according to claim 3, wherein the control amount threshold value is corrected by multiplying a correction coefficient being set in accordance with the travel speed to the control amount threshold value. 9. The vehicle control apparatus according to claim 7, wherein the correction coefficient is set to increase the control amount threshold value when the travel speed is relatively high and reduce the control amount threshold value when the travel speed is relatively low. 10. The vehicle control apparatus according to claim 1, wherein the automatic driving control information includes the control target value, the automatic driving control device determines the control amount threshold value based on the control target value, and provides the steering control device with the control amount threshold value, and the steering control device changes the steering control amount not to exceed the control amount threshold value when the steering control amount exceeds the control amount threshold value. 11. The vehicle control apparatus according to Wherein the steering control device notifies the automatic driving abnormality is detected when the steering control amount exceeds the control amount threshold value, and the automatic driving control device contro the vehicle is stopped when