Steering angle detection device

Abstract

The present invention provides a steering angle detection device that enables the calculation of the absolute steering angle even if one of the two detection units installed in the steering angle sensor for detecting the relative steering angle fails. When the self-diagnosis unit (21) determines that the absolute steering angle θf is not output from the absolute steering angle calculation unit (11c), it checks which of the main detection unit (11a) and the sub-detection unit (11b) has failed, and adds the relative steering angle (θp or θs) output from the normal detection unit to the latest absolute steering angle θf(n-1) to calculate the current absolute steering angle θf (θf←θf(n-1)+(θp or θs)), and uses this absolute steering angle θf to update the latest absolute steering angle θf(n-1) (θf(n-1)←θf).

Description

Technical Field

[0001] The present invention relates to a steering angle detection device that can determine the absolute steering angle based on the relative steering angle detected by the other relative steering angle detection unit even if one of the two relative steering angle detection units used for detecting the absolute steering angle fails. Background Technology

[0002] As is well known, a steering angle sensor that measures the tire steering angle of a steering wheel, for example as disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2006-322794), has two relative steering angle detection units that detect relative steering angles, and detects the absolute steering angle from the difference between the relative steering angles of different phases detected by the two relative steering angle detection units, and outputs the signal to each system.

[0003] Therefore, since the absolute steering angle cannot be detected when a relative steering angle detection unit fails, a signal representing that absolute steering angle cannot be output. As a result, driver assistance control systems, such as VDC (Vehicle Dynamics Control), which uses this absolute steering angle to assist the driver's driving operations, cease to function.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-322794 Summary of the Invention

[0007] Technical issues

[0008] However, if one of the two relative steering angle detection units located in the steering angle sensor fails, the output of the signal representing the absolute steering angle immediately stops, making it impossible to measure the tire steering angle of the steering wheel (actual steering angle). As a result, driver assistance based on the driver assistance control system becomes impossible.

[0009] Therefore, in the past, two steering angle sensors were used to build a redundant system. Even if one steering angle sensor failed, the other steering angle sensor could still detect the absolute steering angle and continue driver assistance control. However, installing two steering angle sensors has the disadvantage of increased cost.

[0010] In view of the above, the present invention aims to provide a steering angle detection device that reduces costs by not using two steering angle sensors to build a redundant system, and can determine the absolute steering angle even if one of the two relative steering angle detection units provided in the steering angle sensor fails, thereby enabling continued driving assistance.

[0011] Technical solution

[0012] The present invention comprises a steering angle sensor having two relative steering angle detection units that detect relative steering angles from rotation of the steering shaft using different phases, an absolute steering angle calculation unit that calculates the absolute steering angle from the phase difference of the relative steering angles detected by the two relative steering angle detection units, and a diagnostic unit that checks whether an angle signal representing the absolute steering angle is output from the absolute steering angle calculation unit. The diagnostic unit comprises: an absolute steering angle holding unit that holds the latest absolute steering angle; a relative steering angle output detection unit that, if it is determined that no angle signal representing the absolute steering angle is output from the absolute steering angle calculation unit, checks which of the two relative steering angle detection units outputs the relative steering angle; and a failure-time absolute steering angle calculation unit that, if the relative steering angle output detection unit determines that the relative steering angle is output from one of the two relative steering angle detection units, adds the output relative steering angle to the latest absolute steering angle held in the absolute steering angle holding unit to update the latest absolute steering angle.

[0013] Invention Effects

[0014] According to the present invention, when it is determined that no angle signal representing the absolute steering angle is output from the absolute steering angle calculation unit of the steering angle sensor, the latest absolute steering angle is updated by adding the relative steering angle output from one of the two relative steering angle detection units to the latest absolute steering angle. Therefore, even if one of the two relative steering angle detection units provided in the steering angle sensor fails, the absolute steering angle can still be calculated. As a result, driving assistance can continue, and costs can be reduced without constructing a redundant system using two steering angle sensors. Attached Figure Description

[0015] Figures 1A to 1B The first embodiment is shown. Figure 1A This is a diagram showing the main components of a driver assistance control system with a steering angle detection device. Figure 1B This is an explanatory diagram showing how the absolute steering angle is calculated based on the phase difference between two relative steering angles.

[0016] Figure 2 The first embodiment is shown as a flowchart illustrating a self-diagnostic routine.

[0017] Figure 3 The first embodiment is shown as a flowchart illustrating the absolute steering angle calculation routine when the sensor fails.

[0018] Figure 4This is a diagram showing the main components of a driver assistance control system having a steering angle detection device according to the second embodiment.

[0019] Symbol Explanation

[0020] 1: Electric Power Steering (EPS)

[0021] 1a: Steering shaft

[0022] 1b: Steering wheel

[0023] 1c: Main gear

[0024] 1d: Secondary gear

[0025] 11: Steering angle sensor

[0026] 11a: Main Inspection Department

[0027] 11b: Sub-Inspection Department

[0028] 11c: Absolute steering angle calculation unit

[0029] 11d: Interface circuit

[0030] 21, 31a: Self-diagnosis section

[0031] 31: Driver Assist Control Unit

[0032] 32: Alarm Unit

[0033] Fθp: Main failure criterion

[0034] Fθs: Secondary failure criterion

[0035] θf: Absolute steering angle

[0036] θp: Main steering angle

[0037] θs: Secondary steering angle Detailed Implementation

[0038] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0039] [First Implementation Method]

[0040] Figure 1~ Figure 3 The first embodiment of the present invention is shown. Figure 1A The symbol 1 represents the main part of the electric power steering (EPS) device, with a driver-operated steering wheel 1b fixedly mounted at the base of the steering shaft 1a. It should be noted that, although not shown in the figure, a steering gearbox with a gear and rack steering gear mechanism and an electric motor are connected to the front end of the steering shaft 1a.

[0041] The steering shaft 1a has a central axis for a main gear 1c and a secondary gear 1d, both formed in an annular shape. These two gears 1c and 1d are components of the steering angle sensor 11 (described later) and are positioned close to each other. Furthermore, target teeth are formed on the outer periphery of each gear 1c and 1d. In this embodiment, when the number of teeth on the main gear 1c is set to N, the number of teeth on the secondary gear 1d is set to one less (N-1).

[0042] Furthermore, the main detection unit 11a and the auxiliary detection unit 11b, which are components of the steering angle sensor 11, are located close to each of the gears 1c and 1d. These two detection units 11a and 11b are detection units that detect the rotation angle respectively, facing the target tooth surfaces of each gear 1c and 1d, and correspond to the relative steering angle detection unit of the present invention. Further, the steering angle sensor 11 is provided with an absolute steering angle calculation unit 11c and a self-diagnosis unit 21.

[0043] Furthermore, the self-diagnostic unit 21, the driver assistance control unit 31 (which serves as the driver assistance control unit), and the alarm unit 32 are connected via an in-vehicle communication line (e.g., CAN: Controller Area Network) in a free bidirectional communication manner. It should be noted that the self-diagnostic unit 21, and each of the units 31 and 32, are composed of known integrated circuits equipped with a CPU, RAM, ROM, non-volatile memory, and other peripheral devices, and the ROM pre-stores programs executed by the CPU and / or fixed data such as tables and mappings.

[0044] The driver assistance control unit 31 is a unit that assists the driver in operating the vehicle. A representative control method is VDC (Vehicle Dynamics Controller), which aims to suppress vehicle sideslip and improve vehicle stability. Furthermore, the alarm unit 32 is a unit that notifies the driver of alarms visually (warning lights, monitor) or audibly (speaker).

[0045] If the steering shaft 1a rotates, the main gear 1c and the secondary gear 1d of the steering angle sensor 11 will rotate together. Each detection unit 11a, 11b detects the passage of the target teeth formed on the gears 1c, 1d using magnetic or optical methods, and its waveform (sine wave output waveform) is as follows: Figure 1B The waveform is shaped in a predetermined manner and output as an angle signal representing the relative steering angles, namely the main steering angle θp and the secondary steering angle θs.

[0046] Furthermore, in this embodiment, when the number of target teeth formed on the main gear 1c is set to N, the number of target teeth formed on the secondary gear 1d is set to (N-1). Therefore, the main steering angle θp is detected in the main detection unit 11a with a phase of 360 [deg] / N. In contrast, the secondary detection unit 11b detects the secondary steering angle θs with a phase of 360 [deg] / (N-1).

[0047] Then, the absolute steering angle calculation unit 11c calculates the absolute steering angle θf based on the neutral point of the steering shaft 1a based on the phase difference between the steering angles θp and θs output from each detection unit 11a and 11b.

[0048] The self-diagnostic unit 21 receives steering angles θp and θs, representing relative steering angles, and absolute steering angle θf. Then, the self-diagnostic unit 21 monitors whether an absolute steering angle θf is output from the absolute steering angle calculation unit 11c, and if an absolute steering angle θf is output, it determines that it is normal and directly inputs the absolute steering angle θf to the driving assistance control unit 31, etc.

[0049] On the other hand, if the self-diagnosis unit 21 determines that the absolute steering angle θf is not output from the absolute steering angle calculation unit 11c, and detects any steering angle θp or θs, the absolute steering angle θf is calculated based on the detected steering angle θp or θs.

[0050] The self-diagnostic processing performed by the self-diagnostic unit 21 and the absolute steering angle calculation processing when the sensor fails are specifically performed according to... Figure 2 The self-diagnosis routine shown, and Figure 3 The absolute steering angle calculation routine shown is used when the sensor fails.

[0051] exist Figure 2 In the self-diagnostic routine shown, firstly, in step S1, it is checked whether an angle signal representing the absolute steering angle θf is output from the absolute steering angle calculation unit 11c. Then, if the absolute steering angle θf is output, the steering angle sensor 11 determines that it is normal and proceeds to step S2, outputs the absolute steering angle θf, and exits the routine.

[0052] On the other hand, if the output of the absolute steering angle θf is not detected, proceed to step S3, and in steps S3 and S5, check which of the main detection unit 11a and the sub-detection unit 11b has failed based on which angle signal of the main steering angle θp and the sub-steering angle θs is output.

[0053] Then, if the output of the main steering angle θp is detected, it is determined that the secondary detection unit 11b has failed, and the process proceeds from step S3 to step S4, where the secondary failure determination flag Fθs is set (Fθs←1), and then proceeds to step S7.

[0054] On the other hand, if the output of the secondary steering angle θs is detected, it is determined that the main detection unit 11a has failed, and the process proceeds from step S5 to step S6, where the main failure determination flag Fθp is set (Fθp←1), and then proceeds to step S7. It should be noted that the initial values ​​of the two failure determination flags Fθp and Fθs are 0. Furthermore, the processing in steps S3 to S6 corresponds to the relative steering angle output detection unit of the present invention.

[0055] Then, if the process proceeds from step S4 or step S6 to step S7, the latest absolute steering angle θf(n-1) calculated by the absolute steering angle calculation unit 11c is stored in a memory such as RAM. It should be noted that the symbol (n-1) represents the most recent value. That is, the latest absolute steering angle θf(n-1) stored in step S7 becomes the most recent absolute steering angle θf output from step S2 when the initial routine after a failure is executed. Furthermore, the memory location storing the latest absolute steering angle θf(n-1) in step S7 corresponds to the absolute steering angle storage unit of the present invention. Moreover, in the self-diagnosis unit 21, this latest absolute steering angle θf(n-1) can be maintained and updated regardless of which detection unit 11a or 11b fails.

[0056] Next, proceed to step S8, output an alarm command, and end the routine. If the alarm unit 32 receives an alarm command from the self-diagnostic unit 21, it activates the warning lights, monitor, and / or speaker to notify the driver of the failure of the steering angle sensor 11. It should be noted that at this time, the upper limit of vehicle speed can also be limited.

[0057] Furthermore, if neither of the two steering angles θp nor θs is detected, a steering angle fault is determined, and the process branches to step S9, setting the two failure determination flags Fθp and Fθs (Fθp, Fθs←1), and proceeding to step S10. In step S10, a fault notification command is output, and the routine ends.

[0058] If the alarm unit 32 receives a fault notification command from the self-diagnostic unit 21, it activates the warning lights, monitor, and / or speaker to notify the steering angle sensor 11 of a fault, and informs the driver of a system stoppage related to driver assistance control (fail-safe mode). As a result, in the electric power steering system, electric assistance becomes zero, and the driver performs steering operations mechanically.

[0059] Next, the self-diagnosis department will implement the 21st procedure. Figure 3The example shown is the absolute steering angle calculation routine when the sensor fails. In this routine, firstly, in step S11, the main detection unit 11a is checked for failure by referring to the value of the main failure determination flag Fθp. Then, in the case of failure (Fθp=1), the process proceeds to step S12. Furthermore, in the case of normal operation (Fθp=0), the process branches to step S13.

[0060] If step S12 is reached, the value of the secondary failure determination flag Fθs is used to check whether the secondary detection unit 11b has failed. Then, if Fθs=0, although the main detection unit 11a has failed, the secondary detection unit 11b is normal, so step S14 is reached. Furthermore, if Fθs=1, since both detection units 11a and 11b have failed, the routine is exited directly.

[0061] On the other hand, if the branch moves from step S11 to step S13, the value of the secondary failure determination flag Fθs is referenced. Then, if Fθs=1, although the secondary detection unit 11b fails, the main detection unit 11a is normal, so the process proceeds to step S15. Furthermore, if Fθs=0, since both detection units 11a and 11b are normal, the routine exits directly.

[0062] If the process proceeds from step S12 to step S14, the latest absolute steering angle θf(n-1) is read, and the secondary steering angle θs is added to this latest absolute steering angle θf(n-1) to calculate the latest absolute steering angle θf at the time of failure (θf←θf(n-1)+θs), and the process proceeds to step S16. Conversely, if the process proceeds from step S13 to step S15, the latest absolute steering angle θf(n-1) is read, and the primary steering angle θp is added to this latest absolute steering angle θf(n-1) to calculate the latest absolute steering angle θf at the time of failure (θf←θf(n-1)+θp), and the process proceeds to step S16. It should be noted that the processing in steps S14 and S15 corresponds to the absolute steering angle calculation unit at the time of failure of the present invention.

[0063] Then, if step S16 is entered, the absolute steering angle θf obtained in step S14 or step S15 is output, and step S17 is entered. The latest absolute steering angle θf(n-1) (θf(n-1)←θf) held in the storage unit is updated using the absolute steering angle θf, and the routine is exited.

[0064] However, the direction of rotation of steering shaft 1a is switched by increasing or decreasing the rotation of the steering wheel. The absolute steering angle θf increases with increasing rotation and decreases with decreasing rotation. On the other hand, hysteresis occurs on steering shaft 1a when the direction of rotation is switched.

[0065] Since this hysteresis manifests as a delay in the waveform of the sine wave detected by the normal detection unit (11a or 11b), by detecting this delay, the rotation direction (increasing rotation, decreasing rotation) of the steering angle (θp or θs) detected by the normal detection unit (11a or 11b) can be determined. Then, in the case of increasing rotation, the steering angle (θp or θs) detected by the normal detection unit (11a or 11b) is marked with a positive (+) sign, and in the case of decreasing rotation, the steering angle (θp or θs) detected by the normal detection unit (11a or 11b) is marked with a negative (-) sign. Furthermore, the absolute steering angle θf is also marked, for example, with a positive (+) sign for the tire steering direction to the left of the neutral point and a negative (-) sign for the tire steering direction to the right of the neutral point.

[0066] The absolute steering angle θf is read, for example, by a driver assistance control unit 31. The driver assistance control unit 31 uses the absolute steering angle θf to assist the driver of the vehicle in driving operations.

[0067] Thus, in this embodiment, if one of the main detection unit 11a and the auxiliary detection unit 11b provided in the steering angle sensor 11 fails, the absolute steering angle θf is calculated by adding the relative steering angle (θp or θs) detected by the other normal detection unit (11a or 11b) to the nearest previous absolute steering angle θf, thereby enabling continued driving assistance. Furthermore, since there is no need to construct a redundant system using two steering angle sensors, cost reduction is possible.

[0068] [Second Implementation]

[0069] Figure 4 The second embodiment of the present invention is shown. In the first embodiment described above, the self-diagnostic unit 21 provided on the steering angle sensor 11 monitors the failure of each detection unit 11a, 11b, and when a failure is detected, the absolute steering angle θf is calculated based on the angle signal (θp or θs) from the normal detection unit (11a or 11b).

[0070] In contrast, in this embodiment, the self-diagnosis unit 31a, which is originally included in the driving assistance control unit 31 as a driving assistance control unit, is made to monitor the failure of each detection unit 11a, 11b installed on the steering angle sensor 11.

[0071] The driver assistance control unit 31 has various functions such as VDC control, ABS control, ALK control, and LDP control. The driver assistance control unit 31 uses the absolute steering angle θf detected by the steering angle sensor 11 to assist the driver in operating the vehicle through the aforementioned control functions.

[0072] Here, VDC (Vehicle Dynamics Control) is a function that suppresses vehicle sideslip to improve vehicle stability. ABS (Anti-lock Brake System) is a function that reduces braking pressure on wheels prone to locking to prevent them from locking. ALK (Active Lane Keep) is a steering assist function that helps the vehicle stay centered in its lane. Furthermore, LDP (Lane Departure Prevention) is a function that intervenes through steering to suppress lane departure when the system detects a tendency for the vehicle to deviate from its lane.

[0073] In addition, an interface circuit 11d is provided in the steering angle sensor 11. Through the interface circuit 11d, the angle signals of the main steering angle θp, the secondary steering angle θs, and the absolute steering angle θf detected by the detection units 11a and 11b are output to the driver assistance control unit 31 through the in-vehicle communication line.

[0074] In the self-diagnosis unit 31a of the driver assistance control unit 31, if a failure is detected in either of the detection units 11a or 11b installed in the steering angle sensor 11, similar to the first embodiment, the latest absolute steering angle θf at the time of failure is obtained by adding the steering angle θp (or θs) detected by the normal detection unit 11a (or 11b) to the latest absolute steering angle θf (n-1).

[0075] If the self-diagnostic unit 31a detects a failure in either of the two detection units 11a and 11b, the driving assistance control unit 31 executes the aforementioned control functions using the latest absolute steering angle θf obtained by the self-diagnostic unit 31a.

[0076] It should be noted that the self-diagnostic routine executed by the self-diagnostic unit 31a and the absolute steering angle calculation routine when the sensor fails are the same as those in the first embodiment described above, so detailed descriptions are omitted.

[0077] By utilizing the self-diagnostic unit 31a of the driving assistance control unit 31 to monitor the angle signals θp, θs, and θf from the steering angle sensor 11, the component configuration of the steering angle sensor 11 can be simplified accordingly. Therefore, this embodiment is also applicable to steering angle sensors that do not have self-diagnostic functions.

Claims

1. A steering angle detection device, characterized in that, have: A steering angle sensor comprising two relative steering angle detection units that detect relative steering angles from rotation of a steering shaft using different phases, and an absolute steering angle calculation unit that calculates an absolute steering angle from the phase difference of the relative steering angles detected by the two relative steering angle detection units; and The diagnostic unit checks whether an angle signal representing the absolute steering angle is output from the absolute steering angle calculation unit. The diagnostic unit includes: An absolute steering angle holding unit maintains the latest absolute steering angle; The relative steering angle output detection unit, when it determines that no angle signal representing the absolute steering angle is output from the absolute steering angle calculation unit, checks which of the two relative steering angle detection units outputs the relative steering angle; An alarm command output unit outputs an alarm command when it determines that the relative steering angle is detected by one of the two relative steering angle detection units. as well as When the absolute steering angle calculation unit fails, if the relative steering angle output detection unit determines that a relative steering angle is output from one of the two relative steering angle detection units, it adds the output relative steering angle to the latest absolute steering angle held by the absolute steering angle holding unit to update the latest absolute steering angle. The steering angle detection device further includes an alarm unit. If the alarm unit receives the alarm command, it notifies the driver and limits the vehicle speed to an upper limit.

2. The steering angle detection device according to claim 1, characterized in that, The diagnostic unit is located on the steering angle sensor.

3. The steering angle detection device according to claim 1, characterized in that, The diagnostic unit is located in a driver assistance control unit that uses the absolute steering angle to assist the driver's driving operations.

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