System to detect the absolute error of a vehicle steering angle sensor

Abstract: A system for detecting an absolute error of a steering wheel sensor for a vehicle includes a steering wheel sensor, a lateral acceleration sensor, a vehicle speed sensor, a parameter determination device for determining the parameters dependent on a detection value determined in the third sensor, a calculating device for calculating an overall deviation generated due to errors in outputs from the first and second sensors, an accumulating device for accumulating the overall deviation as well as the output from the parameter determination device at the time when the overall deviation has been calculated, and an error calculating device for calculating errors in outputs from the first and second sensors.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a system for detecting an absolute error included in an output from a sensor for a vehicle by use of a response characteristic of the vehicle, so as to correct such absolute error. DESCRIPTION OF THE PRIOR ART There are conventionally known systems for correcting an error in output from a sensor for a vehicle, including (1) a system designed such that an error is estimated using a sensor different from a sensor desired to be corrected, e.g., a system for correcting an output (δ deg.) from a steering angle sensor incapable of detecting an absolute angle, wherein, when the yaw rate of a vehicle body obtained from a wheel speed sensor or a yaw rate sensor has reached 0 (zero) deg/sec, an output δ is estimated to be equal to 0 (zero) (for example, see Japanese Patent Application Laid-open No.41979/90); (2) a manually correcting system, e.g., a system in which a gyro-sensor is corrected by inputting a now location in a navigation system; and (3) a system in which an error of mounting of a sensor or an error of the sensor itself have been previously taken into consideration and corrected uniformly. When the correction is conducted using another sensor as in the above prior art, however, an error is certainly included even in an output from the other sensor, thereby bringing about a reduction in accuracy for a sensor for a precise control of movement of a vehicle. In addition, it is necessary to confirm the stability of the other sensor and, hence, a stability conforming means is required separately, and moreover, the correction is possible, only when the movement of the vehicle has entered a certain stable region, resulting in a lot of time required for the correction. When the manual correction is conducted, a human error, such as, a mis-correction, and a losing of a correction operation is unavoidable. Further, when the error is set uniformly, it is necessary to improve a processing accuracy, or to improve the degree of skill of an assembling worker, in order to minimize the sensor-assembling error, leading to an increase in cost. In addition, there is a possibility that the assembling accuracy is different for every vehicle, or type of vehicle, to which the sensor is to be assembled, resulting in a variability of performance. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a system for detecting an absolute error of a sensor for a vehicle, wherein errors in outputs from two sensors which are in a linear response relationship can be detected simultaneously, thereby overcoming the above problems. To achieve the above object, according to the present invention, there is provided a system for detecting an absolute error of a sensor for a vehicle, comprising: a first sensor for detecting a first physical quantity; a second sensor for detecting a second physical quantity having a linear response relationship with the first physical quantity; at least one third sensor for detecting a movement condition of the vehicle, which varies parameters of a linear response function established between the first and second physical quantities; parameter determination means for setting the parameters in correspondence to a value detected by the third sensor; calculating means for calculating, from the linear response function, an overall deviation generated due to errors in outputs from the first and second sensors, on the basis of an output from the first sensor, an output from the parameter determination means, and an output from the second sensor corresponding to these outputs; accumulating means for accumulating the overall deviation as well as the output from the parameter determination means at the time when the overall deviation has been calculated; and error calculating means for calculating errors in outputs from the first and second sensors on the basis of the overall deviation and parameters accumulated in the accumulating means. With the above construction, it is possible to simultaneously detect the errors in outputs from the first and second sensors by use of the linear response relationship between the physical quantities detected by the sensors, and to detect absolute errors in outputs from the sensors promptly and with an excellent accuracy. The above and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a block diagram illustrating a relationship between input and output into and from a system; Fig.2 is a block diagram illustrating a construction according to a preferred embodiment of the present invention; Fig.3 is a graph for explaining an interpolation of parameters; and Fig.4 is a flow chart illustrating a processing procedure. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described by way of a preferred embodiment in connection with the accompanying drawings. Referring first to Fig.1, a steering angle δ, as a first physical quantity, is inputted into a vehicle movement system. A lateral acceleration G as a lateral momentum of a second physical quantity, which permits a linear response function S to be established between the steering angle δ, is outputted from the vehicle movement system . Parameters A₁, A₂, B₁ and B₂ of the linear response function S are varied by a vehicle speed V as a movement condition of a vehicle. If a real value and a detection value of steering angle are represented by δ and δ', respectively, a deviation between the real value δ and the detection value δ' is by Δδ; a real value and a detection value of lateral acceleration are by G and G', respectively; and a deviation between the real and detection values G and G' is by ΔG, these deviations Δδ and ΔG are detected using a response characteristic of a vehicle by a system according to the present invention. Referring to Fig.2, the system according to this embodiment comprises a first sensor 1 for detecting the steering angle to deliver a detection value of steering angle δ', a second sensor 2 for detecting the lateral acceleration to deliver a detection value of lateral acceleration G', and a third sensor 3 for detecting the vehicle speed V. The parameters A₁, A₂, B₁ and B₂ are determined in a parameter determination means 4 in accordance with the vehicle speed V detected in the third sensor 3. Outputs from the first and second sensors 1 and 2 are accumulated in a first accumulating means 5. An overall deviation ΔH, generated on the basis of errors in outputs from the first and second sensors 1 and 2, is determined in a calculating means 6 by applying, to the linear response function S, output hysteresis δ' t-1 , δ' t-2 from the first sensor 1 which have been obtained from the first accumulating means 5 and outputs A₁, A₂, B₁ and B₂ from the parameter determination means 4 as well as output hysteresis G', G' t-1 and G' t-2 from the second sensor 2 which have been obtained from the first accumulating means 5 in correspondence to δ' t-1 , δ' t-2 , A₁, A₂, B₁ and B₂. The overall deviation Δ H and the outputs A₁, A₂, B₁ and B₂ from the parameter determination means 4 at the time when such overall deviation ΔH has been calculated, are accumulated in a second accumulating means 7. The errors in outputs from the first and second sensors 1 and 2 are calculated in an error calculating means 8 on the basis of the overall deviation ΔH and parameters A₁, A₂, B₁ and B₂ accumulated in the second accumulating means 7. In a relationship between input and output into and from the system as shown in Fig.1, the linear response function S can be assumed according to a following first equation (1) using a Z-conversion: S = G/δ = (b₁Z⁻¹ + b₂Z⁻²)/(1 + a₁Z⁻¹ + a₂Z⁻²) From this first equation (1), a following equation is given: (1 + a 1 Z -1 + a 2 Z -2 ) G (t) = (b 1 Z -1 + b 2 Z -2 ) δ (t) If G (t) = G t (Δt = 1) , a following equation is given: G t = -a 1 G t-1 - a 2 G t-2 + b 1 δ t-1 + b 2 δ t-2 If -a 1 = A 1 , -a 2 = A 2 , b 1 = B 1 and b 2 = B 2 , a following equation (2) is given: G t = A 1 G t-1 + A 2 G t-2 + B 1 δ t-1 + B 2 δ t-2 Here, G t = G t ' + ΔG, and δ t = δ t ' + Δ δ, and therefore, the above equation (2) is transformed into a following third equation (3): G t ' - A 1 G' t-1 + A 2 G' t-2 - B 1 δ' t-1 - B 2 δ' t-2 = (A 1 + A 2 - 1)ΔG + (B 1 + B 2 ) Δ δ In the above third equation (3), the left side can directly be calculated by only the values detected by the first and second sensors, and the right side is indicative of an overall deviation based on the deviations ΔG and Δ δ. Here, if the directly calculatable left side is replaced by the overall deviation ΔH, a following equation (4) is given: ΔH = (A 1 +A 2 - 1)ΔG+(B 1 +B 2 ) Δ δ Thus, a relationship represented by the equation (4) is always established in a scope of linear movement in the system shown in Fig.1. The parameters A₁, A₂, B₁ and B₂ can previously be set in the first and second sensors 1 and 2 by an experiment, or the like in accordance to the movement condition of the vehicle. Unknown quantities in the equation (4) are only ΔG and Δ δ and hence, the ΔG and Δ δ can be determined by solving simultaneous equations provided by determining A₁, A₂, B₁, B₂ and ΔH in the equations (4) in different movement conditions of the vehicle, i.e., at different vehicle speeds V₁ and V₂. More specifically, if the overall deviation ΔH and parameters A₁, A₂, B₁ and B₂ at a vehicle speed equal to V₁, are represented by ΔH₁, A₁₁, A₂₁, B₁₁ and B₂₁, respectively, and the overall deviation ΔH and parameters A₁, A₂, B₁ and B₂ at a vehicle speed equal to V₂ are represented by ΔH₂, A₁₂, A₂₂, B₁₂ and B₂₂, respectively, following simultaneous equations (5) and (6) are established: ΔH 1 = (A 11 + A 21 - 1) ΔG + (B 11 + B 21 ) Δ δ ΔH 2 = (A 12 + A 22 - 1) ΔG + (B 12 + B 22 ) Δ δ Here, assuming that α 1 = A 11 + A 21 - 1, α 2 = A 12 + A 22 - 1, β 1 = B 11 + B 21 , and β 2 = B 12 + B 22 , and if α ₁, α ₂, β ₁ and β ₂ are put into the equations (5) and (6), following equations (7) and (8) are given: ΔH 1 = α 1 ΔG + β 1 Δ δ ΔH 2 = α 2 ΔG + β 2 Δ δ If these equations (7) and (8) are solved, following equations (9) and (10) are obtained: ΔG = ( ΔH 1 β 2 - ΔH 2 β 1 )/(α 1 β 2 - α 2 β 1 ) Δ δ = (ΔH 2 α 1 - ΔH 1 α 2 )/(α 1 β 2 - α 2 β 1 ) The system according to the present embodiment as shown in Fig.2 is based on the above-described principle. The parameter determination means 4 determines the parameters A₁, A₂, B₁ and B₂ dependent on the vehicle speed V determined in the third sensor 3, but in determining the parameters A₁, A₂, B₁ and B₂, they are set for every different preset movement conditions of the vehicle, i.e., every preset vehicle speeds. When the vehicle speed V, detected by the third sensor 3, is between the adjacent preset vehicle speeds, the parameters A₁, A₂, B₁ and B₂ are determined by a linear interpolation. For example, for determination of the parameter A₁, values of the A₁ have been previously determined, for example, at every vehicle speeds 15, 25, 35, 45 km/hr, --- set at intervals of 10 km/hr, as shown in Fig.3. When a vehicle speed V is between two adjacent vehicle speeds and if the lower preset vehicle speed is represented by V L ; the preset parameter corresponding to the lower preset vehicle speed is by A 1L ; the higher preset vehicle speed is by V H ; and the preset parameter corresponding to the higher preset vehicle speed is by A 1H , an interpolation value A₁' of the parameter A₁ is calculated according to following equations (11) and (12): V' = (V - V L )/10 A 1 ' = A 1L + V' × (A 1H - A 1L ) Even for the other parameters A₂, B₁ and B₂, an interpolation similar to that described above is carried out, thereby giving interpolation values A₂', B₁' and B₂'. This is represented by following equations: A 2 ' = A 2L + V' × (A 2H - A 2L ) B 1 ' = B 1L + V' × (B 1H - B 1L ) B 2 ' = B 2L + V' × (B 2H - B 2L ) The preset parameters B₁ and B₂ on the output side of the second sensor 2 have been obtained by an experiment using the second sensor 2 alone at every preset vehicle speeds. In carrying out the interpolation in association with the first sensor 1, it is necessary to conduct an interpolating calculation in consideration of the fact that a control gain G AIN does not depart from a range in which a control system is stable. Thereupon, the control gain G AIN is defined to be represented by G AIN = (B 1 + B 2 ) / (1 - A 1 - A 2 ) and if a control gain corresponding to a lower value in a region of vehicle speeds V is represented by G AINL , and a control gain corresponding to a higher value is by G AINH , then an interpolation value G AIN ' is given according to a following equation (17): G AIN ' = G AINL + V' × (G AINH - G AINL ) Here, an interpolation factor K is calculated according to a following equation (18) from values A₁', A₂' and G AIN ' determined from the equations (12), (13) and (17): K = G AIN ' × {(1- A 1 ' - A 2 ') / (B 1 ' + B 2 ')} From this equation (18) and the above-described equations (14) and (15), following equations (19) and (20) are derived: B 1 '' = K × B 1 ' B 2 '' = K × B 2 ' Thus, values A₁' and A₂', determined in the equations (12) and (13) as well as values B₁'' and B₂'', determined in the equations (19) and (20) are parameters obtained after interpolation, and equations, α = A 1 ' + A 2 '-1 , and β = B 1 '' + B 2 '' , are established. The first accumulating means 5 accumulates the output δ' from the first sensor 1 and the output G' from the second sensor 2. The hysteresis δ' t-1 and δ' t-2 of outputs from the first sensor 1 and the hysteresis G', G' t-1 and G' t-2 of outputs from the second sensor 2 are applied from the first accumulating means 5 to the calculating means 6. On the basis of the output hysteresis δ' t-1 , δ' t-2 , G', G' t-1 and G' t-2 , obtained from the first accumulating means 5, as well as the parameters A₁, A₂, B₁ and B₂ obtained in the parameter determination means 4, the calculating means 6 calculates, from the linear response function S, an overall deviation ΔH generated due to errors in outputs from the first and second sensors 1 and 2, i.e., a value ( = G t ' - A 1 G' t-1 - A 2 G' t-2 - B 1 δ' t-1 - B 2 δ' t-2 ) represented by the left side of the above-described equation (3). Further, the error calculating means 8 calculates an error Δ δ in output from the first sensor 1 and an error ΔG in output from the second sensor 2 by solving the simultaneous equations (7) and (8) dependent on two different movement conditions, as represented by the equations (9) and (10), on the basis of ΔH₁, ΔH₂, α ₁, α ₂, β ₁ and β ₂ read from the accumulating means 7 in accordance with these movement conditions. A processing procedure in the system of the present invention, constructed in the above manner, will be described below with reference to Fig.4. First, a vehicle speed V is inputted at a first step S1, and then, it is judged at a second step S2 whether or not the inputted vehicle speed V is equal to the last speed. If it is equal to the last speed, the processing is returned to the first step S1, and if the inputted vehicle speed V is not equal to the last speed, the processing is advanced to a third step S3. At the third step S3, parameters A₁, A₂, B₁ and B₂, corresponding to the inputted vehicle speed V, are determined. Outputs δ' and G', from the first and second sensors 1 and 2, are inputted at a fourth step S4 and then accumulated at a fifth step S5. An overall deviation ΔH (= G t ' - A 1 G' t-1 - A 2 G' t-2 - B 1 δ' t-1 - B 2 δ' t-2 ) is calculated at a sixth step S6 on the basis of the accumulated outputs δ' and G', and then accumulated at a seventh step S7. At an eighth step S8, it is judged whether or not overall deviations ΔH₁ and ΔH₂, corresponding to different vehicle speeds V₁ and V₂, have been calculated. If they are not calculated, the processing is returned to the first step S1, and if they have been calculated, the error Δ δ in output from the first sensor 1 and the error ΔG in output from the second sensor 2 are determined at a ninth step S9 by solving the simultaneous equations. In this manner, the errors Δ δ and ΔG, in outputs from the first and second sensors 1 and 2 which are in a linear response relationship, can be detected, simultaneously, by utilizing a linear response characteristic. Therefore, as compared with a prior art system in which a correction using another sensor or a manual correction is carried out, it is possible to insure a control accuracy insufficient for a sensor for a precise control of vehicle movement, and to provide a prompt detection at a low cost, because of processing by software. The technique for definitely determining the errors Δ δ and ΔG in outputs have been described in the above embodiment, but it is difficult to perform a correction for an influence of the errors possessed by the system itself in addition to the first and second sensors 1 and 2. Thereupon, if a statistical technique is used for setting an error in a linear response function and determining values Δ δ and ΔG, so that such error is minimal, it is possible to further improve the detection accuracy. Such technique will be described below. An error εk ( k = 1∼n) is introduced into the linear response function, as given in an equation (21), thereby determining values Δ δ and ΔG, so that such error is smallest in the sense of a square at a minimum. If this equation (21) is replaced by following equations: , then the equation H (n) =C (n) ×X+ε (n) (22) is established. An evaluation function represented by Jn is defined as Jn= 1 2 k=1 n εk 2 = 1 2 ε* (n) ×ε (n) Here, if ε* (n) = (ε 1 ∼εn) , a condition where a value Jn is minimal is as follows: ∂Jn ∂X =0 From the equations (22), (23) and (24), a following expression (25) is established: X= ΔG Δδ =(C* (n) ×C (n) ) -1 ×C*×H (n) This is a form similar to the result of the above-described definite technique. Here, if , then ΔG= ΔH 1 *×β 2 *-ΔH 2 *×β 1 * α 1 *×β 2 *-α 2 *×β 1 * Δδ= ΔH 2 *×α 1 *-ΔH 1 *×α 2 * α 1 *×β 2 *-α 2 *×β 1 * are established, so that Δ δ and Δ G can be determined, wherein α*,β* and ΔH* may be increased successively. Thus, it is possible to provide a yet highly improved accuracy by such a definite technique. Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to such embodiment, and various modification and variations in design can be made without departing from the spirit and scope of the invention defined in claims. For example, it is possible to carry out the present invention in connection with a first sensor for detecting a steering angle as a first physical quantity and a second sensor for detecting a yaw rate as a second physical quantity.

Claims: A system for detecting an absolute error of a sensor for a vehicle, comprising: a first sensor (1) for detecting a first physical quantity; a second sensor (2) for detecting a second physical quantity having a linear response relationship with the first physical quantity; at least one third sensor (3) for detecting a movement condition of the vehicle which varies parameters of a linear response function established between the first and second physical quantities, characterized by parameter determination means (4) for setting the parameters in correspondence to a value detected by said third sensor (3); calculating means (6) for calculating, from said linear response function, an overall deviation generated due to errors in outputs from the first and second sensors, on the basis of an output from the first sensor, an output from the parameter determination means, and an output from the second sensor corresponding to said outputs; accumulating means (7) for accumulating said overall deviation as well as said output from said parameter determination means at the time when said overall deviation has been calculated; and error calculating means (8) for calculating errors in outputs from the first and second sensors (1, 2) on the basis of said overall deviation and parameters accumulated in said accumulating means (7). A system for detecting an absolute error of a sensor for a vehicle according to claim 1, wherein said parameter determination means (4) sets the parameter for every different movement condition of the vehicle, and obtains a parameter corresponding to a detection value detected by the third sensor (3) from a control gain having a linear interpolation of said parameters and a linear response function when the movement condition of the vehicle detected by the third sensor (3) is between the adjacent set preset movement conditions of the vehicle. A system for detecting an absolute error of a sensor for a vehicle according to claim 1 or 2, wherein said first sensor (1) is a sensor for detecting a steering angle as the first physical quantity, said second sensor (2) is a sensor for detecting a lateral momentum as the second physical quantity, and said third sensor (3) is a sensor for detecting a vehicle speed as the movement condition of the vehicle.

Inventors: KIN KEIYU C O K K HONDA, NISHIHARA TAKASHI C O K K HOND, OHNO YASUAKI C O K K HONDA, SAKAKI YUJI C O K K HONDA, SHIRAISHI SHUJI C O K K HONDA, KIN, KEIYU, C/O K.K HONDA, NISHIHARA, TAKASHI, C/O K.K HONDA, OHNO, YASUAKI, C/O K.K HONDA, SAKAKI,YUJI, C/O K.K HONDA, SHIRAISHI, SHUJI, C/O K.K HONDA
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1993
Main classification: B62D5
IPC codes: G01D3, B62D15, G01C21, G08G1, B62D6