Patent ID: 12194799

MODES FOR CARRYING OUT THE INVENTION

In the following, some preferred embodiments of the disclosure are described in detail with reference to the accompanying drawings. Throughout the present description and the drawings, elements having substantially the same function and configuration are denoted with the same reference numerals to avoid any redundant description.

<1. Configuration of Vehicle>

A description is given first of an example of a configuration of a vehicle to which a force sensor diagnosis apparatus according to an embodiment of the disclosure is applicable.

FIG.1is a schematic diagram illustrating a configuration example of a vehicle1including a force sensor diagnosis apparatus50according to the present embodiment. The vehicle1illustrated inFIG.1is a four-wheeled vehicle including four wheels3. The vehicle1is not limited to the four-wheeled vehicle, and may be another vehicle, for example, a two-wheeled vehicle or a commercial vehicle such as a bus or a truck.

InFIG.1, the four wheels3and suspensions10disposed for the respective wheels3, for example, are denoted by the reference numerals having additional characters LF (left front), RF (right front), LR (left rear), and RR (right rear) at the ends. Further, in the following description, the additional characters LF, RF, LR, and RR are omitted as appropriate, unless a particular distinction is to be made.

The suspension10has one end coupled to a vehicle body9, and suspends the wheel3on another end side. The suspension10includes a suspension arm13, a spring15, and a damper17. The wheel3is coupled to an axle5, and is supported to be rotatable with respect to the vehicle body9. In addition, the wheel3is supported by the vehicle body9to be able to be displaced in a vertical direction with respect to the vehicle body9by the suspension arm13.

The damper17has an upper end coupled to the vehicle body9and a lower end coupled to a support supporting the axle5or to the suspension arm13. The spring15is provided between a rod and a cylinder of the damper17. The spring15suppresses transmission, to the vehicle body9, of unevenness of a road surface and impact received by the wheel3from the road surface. The damper17dampens vibration caused by the vehicle body9and the wheel3being relatively displaced vertically.

In addition, the suspension10is provided with a stroke sensor19that detects a relative displacement between the vehicle body9and the wheel3. The stroke sensor19is a mode of a displacement sensor that is provided in a part of the suspension10and detects a state quantity corresponding to a stroke displacement of the suspension10due to external force received by the wheel3from the road surface. The stroke displacement of the suspension10corresponds to the relative displacement between the vehicle body9and the wheel3. The stroke sensor19may be, for example, a sensor that detects a relative displacement between the rod and the cylinder of the damper17(a stroke). A position where the stroke sensor19is provided is not particularly limited as long as the sensor is able to detect the relative displacement between the vehicle body9and the wheel3. A sensor signal outputted from the stroke sensor19is inputted to the diagnosis apparatus50.

The wheel3is provided with a force sensor11that detects external force (tire force) applied to the wheel3. The force sensor11is configured to detect at least a force component in a vehicle-height direction (a z direction). For example, the force sensor11may be a sensor that detects force components in a vehicle-length direction (a x direction), a vehicle-width direction (a y direction), and the vehicle-height direction (the z direction) acting on the axle5supporting the wheel3, and moments about the x-direction, y-direction, and z-direction axes. The force sensor11is not limited in type. A sensor signal outputted from the force sensor11is inputted to the diagnosis apparatus50.

The diagnosis apparatus50acquires the sensor signal of the stroke sensor19and the sensor signal of the force sensor11, and executes a malfunction determination process of the force sensor11. The diagnosis apparatus50is described in detail below.

<2. Force Sensor Diagnosis Apparatus>

(2-1. Configuration of Diagnosis Apparatus)

FIG.2is a block diagram illustrating an example of a configuration of the diagnosis apparatus50. The diagnosis apparatus50includes, for example, one or more processors and one or more memories communicably coupled to the processor. Examples of the one or more processors include a central processing unit (CPU). Examples of the one or more memories include a random access memory (RAM) and a read only memory (ROM). The diagnosis apparatus50may partially or entirely be configured by updatable software such as firmware, or may be a program module to be executed in response to a command from the processor, for example.

The diagnosis apparatus50serves as an apparatus that diagnoses a malfunction of the force sensor11by the one or more processors executing a computer program. The computer program is a computer program that causes the processor to execute operation to be executed by the diagnosis apparatus50, which will be described later. The computer program to be executed by the processor may be recorded in a recording medium serving as a storage (memory)53included in the diagnosis apparatus50, or may be recorded in a recording medium built in the diagnosis apparatus50or any recording medium externally attachable to the diagnosis apparatus50.

Examples of the recording medium that records the computer program include: a magnetic medium such as a hard disk, a floppy disk, or a magnetic tape; an optical recording medium such as a compact disk read only memory (CD-ROM), a digital versatile disk (DVD), or Blu-ray (registered trademark); a magneto-optical medium such as a floptical disk: a memory such as a RAM or a ROM: a flash memory such as a universal serial bus (USB) memory: and another medium that is able to store a program.

The force sensor11and the stroke sensor19provided for each of the wheels3are coupled to the diagnosis apparatus50. The force sensor11and the stroke sensor19are coupled to the diagnosis apparatus50via a dedicated line or a communication bus such as a controller area network (CAN).

The diagnosis apparatus50includes a processor51and the storage53. The processor51includes a vehicle-height direction force component detection unit61, a vehicle-height direction force component estimation unit63, and a diagnosis unit65. The processor51is one or more processors such as a CPU. The units of the vehicle-height direction force component detection unit61, the vehicle-height direction force component estimation unit63, and the diagnosis unit65are functions implemented by execution of the computer program by the processor. Note that the vehicle-height direction force component detection unit61, the vehicle-height direction force component estimation unit63, and the diagnosis unit65may partially be configured by an analog circuit.

The storage53includes one or more memories such as a RAM or a ROM, or a storage device such as a hard disk drive (HDD) or a solid state drive (SSD). The storage53stores a program to be executed by the processor51, various parameters to be used for executing the program, acquired data, and data on a calculation result, for example.

The following briefly describes the functions of the units of the processor51, and then describes specific processing operation of the processor51.

(2-1-1. Vehicle-Height Direction Force Component Detection Unit)

The vehicle-height direction force component detection unit61acquires, on the basis of the sensor signal of the force sensor11, a vehicle-height direction force component detection value Fz_det that is a force component in a height direction of the vehicle1, of external force applied to the wheel3. For example, in a case where the force sensor11is a sensor configured to detect six force components of force components in the x direction, the y direction, and the z direction and moments about the respective direction axes, the vehicle-height direction force component detection unit61acquires at least an output of the force component in the z direction as the vehicle-height direction force component detection value Fz_det.

(2-1-2. Vehicle-Height Direction Force Component Estimation Unit)

The vehicle-height direction force component estimation unit63calculates a vehicle-height direction force component estimation value Fz_est on the basis of the sensor signal of the stroke sensor19. Specifically, the vehicle-height direction force component estimation unit63obtains the vehicle-height direction force component estimation value Fz_est by calculation, on the basis of a stroke S detected on the basis of the sensor signal of the stroke sensor19and vehicle data recorded in the storage53in advance. The stroke is dependent on displacements of the spring15and the damper17. The displacements of the spring15and the damper17differ depending on an installation position of the stroke sensor19and a structure of the suspension10. Therefore, the vehicle-height direction force component estimation unit63converts the stroke S detected by the stroke sensor19into the force component in the z direction by using the vehicle data.

The vehicle data recorded in the storage53includes, in accordance with specifications of each vehicle1, a first map that converts the stroke S into a displacement Da of the spring15depending on the installation position of the stroke sensor19, and a second map that converts the stroke S into a displacement db of the damper17depending on the installation position of the stroke sensor19. Relationships between the stroke S detected by the stroke sensor19and the displacement Da of the spring15and the displacement db of the damper17may each be obtained in advance from the structure of the suspension10.

In a case where the relationships between the stroke S detected by the stroke sensor19and the displacement Da of the spring15and the displacement db of the damper17exhibit linearity, conversion formulas represented by the following expressions (1) and (2) may be recorded in place of the first map and the second map.

Da=α×S(1)Db=β×S(2)

In the expressions (1) and (2), α and β are conversion factors for conversion of the stroke S into the displacement Da of the spring15and the displacement db of the damper17respectively.

In addition, the vehicle data includes data on a spring constant ks of the spring15and a damping coefficient C of the damper17. The data on the spring constant ks of the spring15and the damping coefficient C of the damper17are identified by specifications of the spring15and the damper17that are used. In a case where the vehicle1includes a stabilizer, the vehicle data includes data on a spring constant kp at an installation position of the stabilizer. The spring constant kp at the installation position of the stabilizer may be obtained in advance from the structure of the suspension10. The vehicle data also includes data on a steering angle of the wheels3(the steered wheels3LF and3RF) with respect to an orientation (the vehicle-length direction) of the vehicle1, detected by an unillustrated steering angle sensor while the vehicle1is traveling. The vehicle-height direction force component estimation unit63calculates, by using the vehicle data, the vehicle-height direction force component estimation value Fz_est from the stroke S detected by the stroke sensor19.

Note that, in a case where the vehicle1includes an air suspension that adjusts the displacement between the vehicle body9and the wheel3, the vehicle-height direction force component estimation unit63calculates the vehicle-height direction force component estimation value Fz_est by using a value from which a stroke displacement due to a function of the air suspension, independent of external force received by the wheel3from the road surface, is subtracted.

(2-1-3. Diagnosis Unit)

The diagnosis unit65performs the malfunction determination process of the force sensor11by comparing the vehicle-height direction force component detection value Fz_det detected by the force sensor11and the vehicle-height direction force component estimation value Fz_est estimated on the basis of the sensor signal of the stroke sensor19. In the present embodiment, the diagnosis unit65obtains delay time elapsed after external force received by the wheel3from the road surface is detected by the force sensor11until the external force appears in the stroke S detected by the stroke sensor19. In addition, the diagnosis unit65performs malfunction determination of the force sensor11by comparing the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est obtained on the basis of the sensor signals reflecting the same external force received by the wheel3at a given time.

(1-2-3. Operation)

A description is given next, along flowcharts, of a specific operation example of the diagnosis apparatus50for the force sensor11according to the present embodiment.FIG.3is a flowchart illustrating a diagnosis process to be executed by the diagnosis apparatus50. Note that the diagnosis process described below may be executed at all times while a vehicle-mounted system is in operation, or may be set to be executed at appropriate timing, such as for each predetermined travel distance or each predetermined travel time.

First, the processor51of the diagnosis apparatus50acquires each of the sensor signal of the force sensor11and the sensor signal of the stroke sensor19(step S11). Specifically, the processor51acquires the sensor signal of the force sensor11and the sensor signal of the stroke sensor19in every predetermined processing cycle. The processor51records, as time-series data, each of the acquired sensor signals in the storage53together with data on a time.

Thereafter, the vehicle-height direction force component detection unit61of the processor51detects the vehicle-height direction force component detection value Fz_det on the basis of the sensor signal of the force sensor11(step S13). For example, in a case where the force sensor11is the above-described sensor that detects the six force components, the vehicle-height direction force component detection unit61obtains a sensor value (e.g., a voltage value) indicating the force component in the z direction, out of sensor values indicating the six force components included in the sensor signal. In addition, the vehicle-height direction force component detection unit61records the force component in the z direction indicated by the sensor value of the force sensor11acquired in every predetermined processing cycle, as the vehicle-height direction force component detection value Fz_det, in the storage53in association with data on the sensor value and the time. At this time, the vehicle-height direction force component detection unit61may perform a filtering process on the detected sensor value or the vehicle-height direction force component detection value Fz_det. The filtering process may be, for example, performed by using a moving-average filter or a low-pass filter, or performed by using another appropriate filter.

Thereafter, the vehicle-height direction force component estimation unit63of the processor51calculates the vehicle-height direction force component estimation value Fz_est on the basis of the sensor signal of the stroke sensor19(step S15). For example, the vehicle-height direction force component estimation unit63calculates, on the basis of S indicated by the sensor signal of the stroke sensor19, the vehicle-height direction force component estimation value Fz_est by using the following expression (3).

Fz_est=ks×D⁢a+C×(dDb/dt)+k⁢p×D⁢p(3)Fz_est: the vehicle-height direction force component estimation valueks: the spring constant of the spring15kp: the spring constant at the installation position of the stabilizerC: the damping coefficient of the damper17Da: the displacement of the spring15db: the displacement of the damper17Dp: a displacement due to torsion of the stabilizer (an expansion or contraction amount of the stabilizer)t: the time

The displacement Da of the spring15and the displacement db of the damper17may be calculated on the basis of the stroke S detected by the stroke sensor19, by using the first map and the second map or the above expressions (1) and (2) recorded in the storage53in advance. The displacement Dp due to the torsion of the stabilizer may be calculated on the basis of the stroke S, by using a map or a conversion formula similar to the first map and the second map described above or the above expressions (1) and (2) and stored in advance in accordance with the structure of the suspension10. Note that, in a case where the vehicle1does not include the stabilizer, the term “kp×Dp” of the above expression (3) is set to zero or omitted.

Unit time dt used in obtaining a derivative value dDb of the displacement db of the damper17is a time interval of the processing cycle in which the sensor signal of the stroke sensor19is acquired. The vehicle-height direction force component estimation unit63stores the vehicle-height direction force component estimation value Fz_est estimated on the basis of a sensor value of the stroke sensor19acquired in every predetermined processing cycle in the storage53in association with data on the sensor value and the time. At this time, the vehicle-height direction force component estimation unit63may perform a filtering process on the detected sensor value or the vehicle-height direction force component estimation value Fz_est. The filtering process may be, for example, performed by using a moving-average filter or a low-pass filter, or performed by using another appropriate filter.

Thereafter, the diagnosis unit65executes a delay time calculation process (step S17). The delay time calculation process is a process that makes it possible to perform the malfunction determination of the force sensor11by comparing the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est obtained on the basis of the sensor signals reflecting the same external force received by the wheel3at the same time. The diagnosis unit65calculates the delay time elapsed after external force received by the wheel3at the same time is detected by the force sensor11until the same external force appears in the stroke S detected by the stroke sensor19.

FIG.4toFIG.6are explanatory diagrams illustrating a process of calculating the delay time.

FIG.4illustrates the force component in the z direction detected by the force sensor11and the stroke S detected by the stroke sensor19, respectively converted into the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est. In two regions where peak values appear inFIG.4, comparison of times t at which the respective peak values are detected indicate occurrence of delay time Δt after the peak value appears in the sensor value of the force sensor11until the peak value appears in the sensor value of the stroke sensor19. Consequently, to determine whether the sensor value of the force sensor11is adequate data, it is necessary to resolve a sensor value discrepancy corresponding to the delay time.

FIG.5is a flowchart illustrating the process of calculating the delay time.

First, the diagnosis unit65calculates a derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det (step S31). The diagnosis unit65calculates the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det, for example, by subtracting, from each vehicle-height direction force component detection value Fz_det calculated in the predetermined processing cycle and recorded in the storage53, the vehicle-height direction force component detection value Fz_det calculated in the immediately preceding processing cycle. The derivative value dFz_d/dt of each vehicle-height direction force component detection value Fz_det is recorded in the storage53in association with data on the sensor value, the vehicle-height direction force component detection value Fz_det, and the time.

Thereafter, the diagnosis unit65calculates a derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est (step S33). As in step S31, the diagnosis unit65calculates the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est, for example, by subtracting, from each vehicle-height direction force component estimation value Fz_est calculated in the predetermined processing cycle and recorded in the storage53, the vehicle-height direction force component estimation value Fz_est calculated in the immediately preceding processing cycle. The derivative value dFz_e/dt of each vehicle-height direction force component estimation value Fz_est is recorded in the storage53in association with data on the sensor value, the vehicle-height direction force component estimation value Fz_est, and the time.

Thereafter, the diagnosis unit65determines whether the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det and the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est are each equal to or greater than a differentiation threshold dF_th set in advance (step S35). Here, the differentiation threshold dF_th is provided for the derivative values dFz_e/dt and dFz_d/dt of the respective values to allow the delay time Δt to be obtained only in a case where a rate of increase in the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est per unit time dt is equal to or greater than a predetermined threshold. The differentiation threshold dF_th may be set to any value. For example, the differentiation threshold dF_th may be set in consideration of the sensor value detected or a value reached by the force component in the z direction when the vehicle1decelerates suddenly.

FIG.6is an explanatory diagram illustrating an example of setting of the differentiation threshold dF_th.FIG.6illustrates changes over time in a brake pressure P_b applied to a wheel cylinder of the wheel3, a vehicle speed V, the vehicle-height direction force component detection value Fz_det, and the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det. In the example illustrated inFIG.6, a brake operation is performed at a time t0to cause the brake pressure P_b to increase abruptly, and the vehicle1starts deceleration. Accordingly, the vehicle-height direction force component detection value Fz_det detected by the force sensor11also increases abruptly, and the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det exceeds 5000. In this case, the differentiation threshold dF_th is set to, for example, 5000.

The delay time Δt is obtained by using the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est in a case where apparent peaks as illustrated inFIG.6appear. This makes it is possible to prevent burden on the processor from becoming too large by the number of calculations of the delay time Δt becoming too large. It is also possible to prevent a decrease in accuracy of a calculation result of the delay time Δt, consequently in accuracy of a malfunction detection result of the force sensor11, due to a decrease in accuracy of matching between the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est to be compared, out of the vehicle-height direction force component detection values Fz_det and the vehicle-height direction force component estimation values Fz_est recorded in the storage53.

Note that the diagnosis unit65may determine whether a combination in which the derivative value dFz_d/dt and the derivative value dFz_e/dt are each equal to or greater than the differentiation threshold dF_th set in advance is included in combinations of the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det and the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est at times within a time difference equal to or less than a maximum value of the delay time assumed in advance. This makes it possible to prevent the sensor values reflecting external force applied to the wheel3at different times from being subjected to comparison.

If at least one of the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det or the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est is not equal to or greater than the differentiation threshold dF_th (S35/No), the diagnosis unit65ends the process of calculating the delay time Δt (step S37), and returns to step S11inFIG.3. In contrast, if the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det and the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est are both equal to or greater than the differentiation threshold dF_th (S35/Yes), the diagnosis unit65calculates times t1and t2at the peaks where the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det and the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est have each become equal to or greater than the differentiation threshold dF_th (step S39).

Specifically, the diagnosis unit65identifies a maximum value of the vehicle-height direction force component detection value Fz_det in a case where the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det has become equal to or greater than the differentiation threshold dF_th, and obtains the time t1associated with the maximum value. Similarly, the diagnosis unit65identifies a maximum value of the vehicle-height direction force component estimation value Fz_est in a case where the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est has become equal to or greater than the differentiation threshold dF_th, and obtains the time t2associated with the maximum value.

Thereafter, the diagnosis unit65calculates a time difference between the calculated two times t1and t2to obtain the delay time Δt (step S41). Thus calculated is the delay time Δt elapsed after external force applied to the wheel3at the same time is detected by the force sensor11until the external force appears in the stroke S detected by the stroke sensor19.

Referring back toFIG.3, the diagnosis unit65performs time matching of the data on the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est, by shifting the time of either of the recorded vehicle-height direction force component detection value Fz_det and vehicle-height direction force component estimation value Fz_est by the delay time Δt obtained by the delay time calculation process (step S19). This brings about a state in which malfunction detection of the force sensor11is executable by using the sensor value of the force sensor11and the sensor value of the stroke sensor19reflecting the same external force applied to the wheel3at the same time.

Thereafter, the diagnosis unit65executes the malfunction determination of the force sensor11on the basis of the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est at the same time after the time matching (step S21). In the present embodiment, the diagnosis unit65calculates a difference (first difference) ΔFz_det between a vehicle-height direction force component detection value Fz_det_1before the time t1at which the vehicle-height direction force component detection value Fz_det increases abruptly and a positive peak of the derivative value dFz_d/dt appears, and a maximum value Fz_det_2of the vehicle-height direction force component detection value Fz_det that appears after the time t1. The diagnosis unit65also calculates a difference (second difference) ΔFz_est between a vehicle-height direction force component estimation value Fz_est_1before the time t2at which the vehicle-height direction force component estimation value Fz_est increases abruptly and a positive peak of the derivative value dFz_e/dt appears, and a maximum value Fz_est_2of the vehicle-height direction force component estimation value Fz_est that appears after the time t2.

In addition, the diagnosis unit65determines that the force sensor11can be malfunctioning in a case where a discrepancy ΔFz between the first difference ΔFz_det and the second difference ΔFz_est described above is equal to or greater than a predetermined measurement threshold ΔFz_th, in consideration of a detection accuracy Ea of the force sensor11and a detection accuracy Eb of the stroke sensor19. In addition, in the present embodiment, the diagnosis unit65counts up (adds 1 to) a malfunction counter Q if it is determined that the discrepancy ΔFz described above is equal to or greater than the predetermined measurement threshold ΔFz_th, whereas the diagnosis unit65resets the malfunction counter Q if it is not determined that the discrepancy ΔFz described above is equal to or greater than the predetermined measurement threshold ΔFz_th. The diagnosis unit65determines that the force sensor11is malfunctioning if the malfunction counter Q reaches a counter threshold Q_th set in advance.

FIG.7illustrates a flowchart of an example of the malfunction determination process of the force sensor11.

First, the diagnosis unit65calculates the difference (first difference) ΔFz_det between the vehicle-height direction force component detection value Fz_det_1before the time t1and the maximum value Fz_det_2of the vehicle-height direction force component detection value after the time t1(step S51). Calculated in step S51is an increase range of the vehicle-height direction force component detection value Fz_det detected by the force sensor11upon application of external force to the wheel3.

Specifically, in the example illustrated inFIG.6, the diagnosis unit65calculates the difference ΔFz_det between the vehicle-height direction force component detection value Fz_det_1before the time t1at which the derivative value dFz_d/dt becomes equal to or greater than the differentiation threshold dF_th and the maximum value Fz_det_2of the vehicle-height direction force component detection value Fz_det after the time t1. Used as the vehicle-height direction force component detection value Fz_det_1is the vehicle-height direction force component detection value Fz_det around the time to immediately before the vehicle-height direction force component detection value Fz_det increases. Used as the maximum value Fz_det_2of the vehicle-height direction force component detection value Fz_det is the maximum value Fz_det_2of the vehicle-height direction force component detection value Fz_det detected at a time t3, in a period from the time t1at which the vehicle-height direction force component detection value Fz_det increases abruptly and the positive peak of the derivative value dFz_d/dt appears to a time t4at which the vehicle-height direction force component detection value Fz_det decreases abruptly and a negative peak of the derivative value dFz_d/dt appears.

Thereafter, the diagnosis unit65calculates the difference (second difference) ΔFz_est between the vehicle-height direction force component estimation value Fz_est_1before the time t2after the time matching and the maximum value Fz_est_2of the vehicle-height direction force component estimation value after the time t2(step S53). Calculated in step S53is an increase range of the vehicle-height direction force component estimation value Fz_est estimated on the basis of the stroke S detected by the stroke sensor19upon application of external force to the wheel3. Also in step S53, the diagnosis unit65similarly calculates the difference ΔFz_est between the vehicle-height direction force component estimation value Fz_est_1before the time t2at which the derivative value dFz_e/dt becomes equal to or greater than the differentiation threshold dF_th and the maximum value Fz_est_2of the vehicle-height direction force component estimation value Fz_est after the time t2.

Thereafter, the diagnosis unit65determines whether the discrepancy ΔFz between the first difference ΔFz_det and the second difference ΔFz_est is equal to or greater than the predetermined measurement threshold ΔFz_th (step S55). The measurement threshold ΔFz_th is set, for example, by using the following expression (4), in consideration of the detection accuracy Ea of the force sensor11and the detection accuracy Eb of the stroke sensor19.

Δ⁢Fz_th=k⁢q×(E⁢a+E⁢b)(4)

The detection accuracy Ea of the force sensor11and the detection accuracy Eb of the stroke sensor19may be set on the basis of, for example, correction amounts such as offset amounts of the sensor values obtained by diagnosis processes of the respective sensors, but a setting method is not limited to this example. A factor kq may be set freely in consideration of an allowable error, for example.

In other words, in a case where the calculated discrepancy ΔFz is equal to or greater than a predetermined level with respect to a discrepancy (Ea+Eb) assumed on the basis of the detection accuracy Ea of the force sensor11and the detection accuracy Eb of the stroke sensor19, the diagnosis unit65determines that the force sensor11can be malfunctioning.

If the discrepancy ΔFz between the first difference ΔFz_det and the second difference ΔFz_est is less than the predetermined measurement threshold ΔFz_th (S55/No), the diagnosis unit65resets the malfunction counter Q (step S57), and returns to step S13inFIG.3. In contrast, if the discrepancy ΔFz between the first difference ΔFz_det and the second difference ΔFz_est is equal to or greater than the predetermined measurement threshold ΔFz_th (S55/Yes), the diagnosis unit65counts up (adds 1 to) the malfunction counter Q, and updates the malfunction counter Q (step S59).

Thereafter, the diagnosis unit65determines whether the malfunction counter Q has reached the counter threshold Q_th set in advance (step S61). The counter threshold Q_th is also used to guarantee a diagnosis system against an erroneous determination, together with the above-described measurement threshold ΔFz_th. For example, in a case where there is a possibility that the malfunction determination process using the measurement threshold ΔFz_th makes an erroneous determination about once out of five times of measurement, the counter threshold Q_th is set to “5”. Thus, in a case where the discrepancy ΔFz between the first difference ΔFz_det based on the sensor value of the force sensor11and the second difference ΔFz_est based on the sensor value of the stroke sensor19becomes equal to or greater than the measurement threshold ΔFz_th five times in a row, it is finally determined that a malfunction has occurred.

If the malfunction counter Q is less than the counter threshold Q_th (S61/No), the diagnosis unit65returns to step S13inFIG.3, without finally determining occurrence of a malfunction. In contrast, if the malfunction counter Q has reached the counter threshold Q_th (S61/Yes), the diagnosis unit65sets a malfunction flag (step S63), and ends the malfunction determination process.

In a case where it is determined that a malfunction has occurred in the malfunction determination process described above, if reliability of the stroke sensor19is high, a determination result by the diagnosis unit65that a malfunction has occurred may be considered as a result indicating that a malfunction has occurred in the force sensor11.

In contrast, if the reliability of the stroke sensor19is unlikely to be high, a determination result by the diagnosis unit65that a malfunction has occurred may be considered as a result indicating that a malfunction has occurred in either one or both of the force sensor11or the stroke sensor19. In this case, it is possible to estimate in which of the force sensor11or the stroke sensor19the malfunction has occurred, for example, by the following method.

In a case where deceleration operation and acceleration operation are performed in the four-wheeled vehicle, outputs of the force sensor11and the stroke sensor19as illustrated inFIG.4are obtained. In a case of the four-wheeled vehicle, in a case where the deceleration operation and the acceleration operation are performed in a state in which a steering angle of a steering wheel is zero, i.e., a state in which the vehicle1is traveling straight, outputs with symmetry may be obtained as sensor outputs at the left front wheel3LF and the right front wheel3RF and at the left rear wheel3LR and the right rear wheel3RR.

Therefore, after setting the malfunction flag in the malfunction determination process described above, the diagnosis unit65executes a process of comparing sensor values of the force sensors11LF and11RF and sensor values of the stroke sensors19LF and19RF, obtained at the left front wheel3LF and the right front wheel3RF. Similarly, the diagnosis unit65executes a process of comparing sensor values of the force sensors11LR and11RR and sensor values of the stroke sensors19LR and19RR, obtained at the left rear wheel3LR and the right rear wheel3RR.

The diagnosis unit65determines whether there is symmetry between the compared sensor values, and determines that a malfunction has occurred in, out of the left and right force sensors11or stroke sensors19determined as exhibiting no symmetry, the force sensor11or the stroke sensor19provided for the wheel3where a malfunction is determined as having occurred in the malfunction determination process described above. Thus, even in a case where the reliability of the stroke sensor19is unlikely to be high, it is possible to estimate occurrence of a malfunction of the force sensor11.

Referring back toFIG.3, if it is determined that a malfunction has occurred in the force sensor11in the malfunction determination process, the diagnosis unit65executes a process upon malfunction detection (step S23). For example, in a case where the sensor value of the force sensor11is used for vehicle dynamics control logic in the vehicle-mounted system, the diagnosis unit65executes a process of lowering a degree of reliability of an arithmetic processing result obtained by the control logic. This makes it possible to make the vehicle1less likely to enter a dangerous travel state.

For control logic using only the vehicle-height direction force component detection value Fz_det detected by the force sensor11in the vehicle-mounted system, the diagnosis unit65may substitute the sensor value of the sensor determined as exhibiting no malfunction for the sensor value of the sensor in which a malfunction is determined as having occurred in the above-described process of determining the symmetry between the sensor values detected at the left and right wheels3. In this case, the diagnosis unit65executes a process of lowering a degree of reliability of the sensor value that is substituted.

The diagnosis unit65may execute a notification process of prompting a user to bring the vehicle to, for example, a dealer or a repair shop. Further, in a case where the vehicle1includes a unit that communicates with the outside of the vehicle, the diagnosis unit65may change setting, if a limitation is imposed on arithmetic processing using the sensor value of the force sensor11, to make it possible to acquire information corresponding to a result of the arithmetic processing from the outside of the vehicle. Note that the process upon malfunction detection described above is an example, and not limited to the exemplified process. The diagnosis unit65may be configured to execute an appropriate process.

As described above, the force sensor diagnosis apparatus50according to the present embodiment calculates the vehicle-height direction force component estimation value Fz_est on the basis of the sensor signal of the stroke sensor19that is provided in a part of the suspension10of the wheel3and detects the stroke S of the suspension10due to external force received by the wheel3from the road surface. In addition, the diagnosis apparatus50performs the malfunction determination of the force sensor11by comparing the vehicle-height direction force component detection value Fz_det detected by the force sensor11and the vehicle-height direction force component estimation value Fz_est calculated on the basis of the sensor signal of the stroke sensor19. Thus, it is possible to detect a malfunction of the force sensor11by using another existing sensor mounted on the vehicle, instead of duplexing the same force sensor. Consequently, a function of detecting a malfunction of the force sensor11is achieved without causing a significant increase in cost.

The force sensor diagnosis apparatus50according to the present embodiment obtains the delay time Δt elapsed after external force applied to the wheel3is detected by the force sensor11until the external force appears in the stroke S detected by the stroke sensor19, and determines a malfunction of the force sensor11by comparing the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est attributed to the same external force. This makes the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est attributed to different external forces less likely to be compared, making it possible to reduce the possibility of erroneous determination of a malfunction of the force sensor11.

The force sensor diagnosis apparatus50according to the present embodiment calculates the delay time Δt in a case where the derivative value dFz_d/dt of the vehicle-height direction force component detection value Fz_det and the derivative value dFz_e/dt of the vehicle-height direction force component estimation value Fz_est are each equal to or greater than the differentiation threshold dF_th set in advance. This makes it possible to prevent the burden on the processor from becoming too large by the number of calculations of the delay time Δt becoming too large. It is also possible to prevent a decrease in the accuracy of the calculation result of the delay time Δt, consequently in the accuracy of the malfunction detection result of the force sensor11, due to a decrease in the accuracy of the matching between the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est to be compared, out of the vehicle-height direction force component detection values Fz_det and the vehicle-height direction force component estimation values Fz_est recorded in the storage53.

The force sensor diagnosis apparatus50according to the present embodiment determines that the force sensor11is malfunctioning in a case where the discrepancy ΔFz between the difference ΔFz_det between before and after the time t1at which the vehicle-height direction force component detection value Fz_det increases and the difference ΔFz_est between before and after the time t2at which the vehicle-height direction force component estimation value Fz_est increases is equal to or greater than the predetermined measurement threshold ΔFz_th. Thus, it is possible to determine a malfunction of the force sensor11by checking for a great discrepancy between the increase ranges of the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est. This makes it possible to increase reliability of the determination result of the malfunction of the force sensor11even in a case where a variation occurs in the accuracy of the calculation result of the delay time Δt.

Although preferred embodiments of the disclosure have been described in the foregoing with reference to the accompanying drawings, the disclosure is by no means limited to such embodiments. It should be appreciated that various modifications and alterations may be made by persons skilled in the art without departing from the scope as defined by the appended claims. The disclosure is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims.

For example, the foregoing embodiment describes an example in which the diagnosis unit65performs the time matching of the data on the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est, by shifting the time of either of the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est by the delay time Δt obtained by the delay time calculation process. However, the technology of the disclosure is not limited to this example. For example, in a case where the sensor signal of the force sensor11and the sensor signal of the stroke sensor19include synchronizing signals that allow for identification of the vehicle-height direction force component detection value Fz_det and the vehicle-height direction force component estimation value Fz_est due to the same external force applied to the wheel, it is possible to execute the malfunction detection of the force sensor11by identifying the corresponding vehicle-height direction force component detection value Fz_det and vehicle-height direction force component estimation value Fz_est.

In addition, in the foregoing embodiment, the stroke sensor19that detects the relative displacement between the rod and the cylinder of the damper17is used as the displacement sensor that detects the state quantity corresponding to the stroke displacement of the suspension10. However, the technology of the disclosure is not limited to this example. The position where the stroke sensor19is provided is not particularly limited as long as the sensor is able to detect the relative displacement between the vehicle body9and the wheel3. Further, the displacement sensor may be, for example, a displacement sensor that detects an elastic deformation amount of the spring15. In a case of using a displacement sensor different from the stroke sensor19used in the foregoing embodiment, a map or a conversion formula that converts a displacement obtained from a sensor value of the displacement sensor into the displacement of the spring15and the damper17or of the stabilizer is recorded in the storage53in advance. Thus, it is possible to detect a malfunction of the force sensor11by using the sensor value of the displacement sensor, making it possible to achieve effects similar to the effects achieved by the foregoing embodiment.

DESCRIPTION OF REFERENCE NUMERALS

1Vehicle3Wheel3LF Left front wheel3RF Right front wheel3LR Left rear wheel3RR Right rear wheel5Axle9Vehicle body10Suspension11Force sensor13Suspension arm15Spring17Damper19Stroke sensor50Diagnosis apparatus51Processor53Storage61Vehicle-height direction force component detection unit63Vehicle-height direction force component estimation unit65Diagnosis unit