CN113063386B - Angle measuring method of EPS system angle sensor - Google Patents

Abstract

The invention relates to the technical field of automobile steering systems, and provides an EPS system angle sensor angle measurement method, which comprises the following steps: step 1, establishing an angular difference rule of a P signal section and an S signal section in an output signal of an angle sensor; step 2, acquiring a P signal and an S signal output by an angle sensor, and obtaining an actual angle of a P signal section, an actual angle of an S signal section and an actual angle difference value by using the P signal and the S signal; step 3, determining the P signal section number and the standard angle difference value of the current angle measurement point according to the angle difference rule of the P signal section and the S signal section established in the step 1; and 4, calculating to obtain a measurement angle according to the obtained P signal section number and the actual angle of the P signal section calculated in the step 2. The invention can improve the efficiency and reliability of angle measurement.

Description

Angle measuring method of EPS system angle sensor

Technical Field

The invention relates to the technical field of automobile steering systems, in particular to an angle measuring method for an angle sensor of an EPS system.

Background

An electric power steering system (EPS for short) is very popular in modern automobiles, and the system can make a driver conveniently operate and steer, can timely and accurately execute steering operation instructions, and can correctly feed back road surface information, so that the driver can timely master the driving state of the automobile so as to judge and make appropriate steering operation instructions. The EPS system mainly comprises a torque corner sensor, an Electronic Control Unit (ECU), a steering power-assisted motor (EPS motor), a worm and gear speed reducing mechanism and the like. When the steering is carried out, the ECU judges the steering state of the automobile according to signals of the torque and the angle of the steering wheel, the speed of the automobile, the terminal voltage and the current of the motor and the like, then sends out a control command to drive the EPS motor, so that the motor generates the required power-assisted torque or the relevant compensation torque according to the rotating speed and the rotating direction of the steering wheel, and pushes wheels to steer through the mechanical steering gear after the power-assisted torque or the relevant compensation torque is amplified by the worm and gear speed reducing mechanism, thereby assisting a driver to carry out steering operation.

The angle sensor is used as one of core components of the EPS system, whether angle measurement is accurate and reliable or not, the performance of the system is directly influenced, an angle signal of the angle sensor is indispensable for realizing functions such as active return correction, even chassis electric control systems such as an ESP (electronic stability program) need to share the angle signal with the EPS to finish respective control functions, and therefore integrated control of the chassis is realized. The angle sensor of the EPS system adopts a non-contact type mostly, the output angle signal also adopts a duty ratio PWM form, and an ECU in the EPS system is required to sample and identify the angle and calculate the angle (also called measuring angle) through a proper algorithm. The angle value must be correct and reliable to be applied by the relevant functions such as the EPS system.

Since the angle sensor is affected by some factors, an angle signal sampling error will be generated, and the validity of the angle measurement result will be affected. For example, a gap exists between the meshing of the magnetic pinion built in the angle sensor, a gap also exists between other mechanical matching parts, and even vibration, a sampling circuit and other factors can cause signal sampling errors. At present, the method generally adopted in the industry is as follows: a vernier algorithm program is embedded in the ECU to complete angle measurement, and the algorithm is protected by foreign intellectual property rights, so that the domestic application of domestic EPS system manufacturers is limited, and the cost control is not facilitated; meanwhile, when the angular velocity of the steering wheel is high, the angle measurement result obtained by the cursor algorithm is not credible and even wrong.

Disclosure of Invention

The invention mainly solves the problems that the angle measurement is finished by a vernier algorithm in the prior art, the domestic application of domestic EPS system manufacturers is limited, and the cost control is not facilitated; meanwhile, when the angular speed of the steering wheel is high, the technical problem that the angle measurement result obtained by a vernier algorithm is not credible is solved, the angle measurement method of the angle sensor of the EPS system is provided, the P signal and the S signal output by the angle sensor are sampled according to the ECU, the regularity of the angle difference of the two angle signals is utilized and embedded into an ECU program to complete the angle measurement function, and the angular speed is used as an additional judgment condition to evaluate whether the measurement result is effective or not.

The invention provides an angle measurement method of an angle sensor of an EPS system, which comprises the following processes:

step 1, establishing an angular difference rule of a P signal section and an S signal section in an output signal of an angle sensor;

step 2, acquiring a P signal and an S signal output by an angle sensor, and obtaining an actual angle of a P signal section, an actual angle of an S signal section and an actual angle difference value by using the P signal and the S signal;

step 3, determining the P signal section number and the standard angle difference value of the current angle measurement point according to the angle difference rule of the P signal section and the S signal section established in the step 1;

and 4, calculating to obtain a measurement angle according to the obtained P signal section number and the actual angle of the P signal section calculated in the step 2.

Further, step 1, establishing an angular difference law of a P signal section and an S signal section in an output signal of the angle sensor, includes steps 101 to 103:

step 101, determining a standard angle difference value of a P signal section and an S signal section under an ideal state, and further determining a corresponding relation between the standard angle difference value and a P signal section number;

102, in an actual state, determining an actual angle difference value of the P signal section and the S signal section, and further determining a corresponding relation between the actual angle difference value and a P signal section number i and a corresponding relation between the actual angle difference value and a standard angle difference value;

step 103, utilizing the standard angle difference delta theta _psi Corresponding relation with P signal section number i and actual angle difference delta theta _ps Difference delta theta from standard angle _psi To obtain the actual angle difference delta theta _ps Mapping relation with P signal section number i and actual angle difference delta theta _ps Difference delta theta from standard angle _psi The mapping relationship of (2).

Further, the standard angle difference of the P signal section and the S signal section is determined using the following formula:

Δθ _psi ＝θ _sj-i -θ _p ……………………………………………………………(1)

the PWM _ P value is in 37 sections, and S signal points corresponding to the same angular position are set as S _j-i Will S _j-i The lowest point of PWM _ S angle of the section j where the signal point is located is far away from the S _j-i The angle of the signal point is defined as S signal section standard angle and is represented as theta _sj-i (ii) a The angle between the PWM _ P sampling point and the PWM _ P angle lowest point of the i section is defined as the standard angle of the P signal section and is represented as theta _p In each P signal section, [ theta ] _p Are all the same; delta theta _psi Representing the standard angle difference of the P signal section and the S signal section;

standard angle difference delta theta _psi The correspondence relationship with the P signal segment number i is as follows:

further, the actual angle difference between the P signal section and the S signal section in the actual state is determined using the following formula:

Δθ _ps ＝θ _s -θ _p ……………………………………………………………(2)

wherein, Delta theta _ps Representing the actual angular difference, θ, of the P and S signal sections in the actual state _s Representing the S signal actual sector angle.

Further, the actual angle difference Δ θ _ps Mapping relation [ Delta theta ] with P signal zone number i _ps →i]And the actual angle difference Δ θ _ps Difference delta theta from standard angle _psi Mapping of [ Delta theta ] _ps →Δθ _psi ]As in the following table:

i	15	30	8	23	1	16	31
								Δθ psi (°)	-32	-24	-16	-8	0	8	16
Δθ ps (°)	-36≤Δθ ps <-28	-28°≤Δθ ps <-20	-20°≤Δθ ps <-12	-12≤Δθ ps <-4	-4≤Δθ ps <4	4≤Δθ ps <12	12≤Δθ ps <20
								i	9	24	2	17	32	10	25
Δθ psi (°)	24	32	40	48	56	64	72
								Δθ ps (°)	20≤Δθ ps <28	28≤Δθ ps <36	36≤Δθ ps <44	44≤Δθ ps <52	52≤Δθ ps <60	60≤Δθ ps <68	68≤Δθ ps <76
i	3	18	33	11	26	4	19
								Δθ psi (°)	80	88	96	104	112	120	128
Δθ ps (°)	76≤Δθ ps <84	84≤Δθ ps <92	92≤Δθ ps <100	100≤Δθ ps <108	108≤Δθ ps <116	116≤Δθ ps <124	124≤Δθ ps <132
								i	34	12	27	5	20	35	13
Δθ psi (°)	136	144	152	160	168	176	184
								Δθ ps (°)	132≤Δθ ps <140	140≤Δθ ps <148	148≤Δθ ps <156	156≤Δθ ps <164	164≤Δθ ps <172	172≤Δθ ps <180	180≤Δθ ps <188
i	28	6	21	36	14	29	7
								Δθ psi (°)	192	200	208	216	224	232	240
Δθ ps (°)	188≤Δθ ps <196	196≤Δθ ps <204	204≤Δθ ps <212	212≤Δθ ps <220	220≤Δθ ps <228	228≤Δθ ps <236	236≤Δθ ps <244
								i	22	37	15	30	8	23	—
Δθ psi (°)	248	256	264	272	280	288	—
								Δθ ps (°)	244≤Δθ ps <252	252≤Δθ ps <260	260≤Δθ ps <268	268≤Δθ ps <276	276≤Δθ ps <284	284≤Δθ ps ≤292	—

further, step 2, acquiring a P signal and an S signal output by the angle sensor, and obtaining an actual angle theta of a P signal section by using the P signal and the S signal _p And S signal section actual angle theta _s And the actual angle difference Δ θ _ps The method comprises the following steps:

calculating the actual angle of the P signal segment using the following formula:

θ _p ＝(PWM_P-12.5)×40/75……………………………………………(5)

calculating the actual angle of the S signal section by using the following formula:

θ _s ＝(PWM_S-12.5)×296/75……………………………………………(6)

calculating the actual angle difference of the P signal and the S signal by using the following formula:

Δθ _ps ＝θ _s -θ _p ……………………………………………………………(2)。

further, in step 4, the measured angle is calculated by using the following formula:

θ＝(i-1)×40+θ _p ………………………………………………………(7)

where θ represents the measured angle of the angle sensor, θ _p Denotes the P-signal segment actual angle, and i denotes the P-signal segment number.

Further, after the step 4, the method further comprises the following steps:

step 5, calculating the reliability of the measuring angle;

and 6, evaluating the validity of the measured angle result according to the reliability of the measured angle and the angular speed of the steering wheel.

Further, step 5, calculating the reliability of the measured angle, including the following processes:

step 501, calculating the actual angle deviation of the S signal by using the following formula:

Δθ _s ＝|Δθ _ps -Δθ _psi |…………………………………………………………(8)

wherein, Delta theta _s Representing the actual angular deviation, Δ θ, of the S signal _ps Representing the actual angular difference, Δ θ _psi Represents the standard angle difference;

step 502, calculating the reliability of the measurement angle by using the following formula:

Rel＝100×(1-Δθ _s /4)……………………………………………………(9)

where Rel represents confidence.

Further, in step 6, the angle measurement result is evaluated for validity by the following formula:

wherein ω represents angular velocity, TRUE represents valid measurement, and flag represents invalid measurement;

when the measured angle is judged to be invalid by equation (10), a following algorithm is used to measure the angle.

Compared with the prior art, the angle measurement method of the angle sensor of the EPS system has the following advantages that:

1. according to the angle difference rule of the P signal section and the S signal section of the angle sensor of the EPS system, two kinds of array mapping relations are found to calculate and obtain the measured angle, the angle measuring function of the EPS system is completed, the efficiency and the reliability of the measured angle are improved, the foreign intellectual property limit is avoided, the domestic application and popularization of the EPS system sensor can be realized, and the cost control is facilitated.

2. The angular velocity is used as an additional judgment condition, and whether the angle measurement result is effective or not is evaluated in combination with the reliability, so that the misapplication of an EPS system due to the measurement error caused by the overhigh angular velocity can be avoided.

3. The method of the invention adopts two kinds of array mapping relation ([ delta theta ] _ps →i]And [ Delta theta ] _ps →Δθ _psi ]) The method replaces the modes of logic conversion, rounding calculation and table look-up of the conventional algorithm in the industry, can use conditional statements to be embedded into an ECU program for operation, occupies less IC resources, can improve the operation efficiency, and has low requirement on the IC capability of the ECU.

Drawings

FIG. 1 is a graph showing a characteristic curve of an angle signal output from an angle sensor in an EPS system to which the present invention is applied;

FIG. 2 is a flow chart of an implementation of the method for measuring an angle of an angle sensor of an EPS system according to the present invention;

FIG. 3 shows the section standard angle θ of the present invention at the same PWM _ P value under ideal conditions _p And theta _sj-i A schematic diagram;

FIG. 4 is a graph of angular velocity versus angular error for the present invention;

FIG. 5 is a graph of the characteristic of the sampled angle signal at an angular velocity of 800 °/s according to the present invention;

FIG. 6 is a graph of the actual angle and measured angle characteristics for an angular velocity of 800/s according to the present invention;

FIG. 7 is a graph of confidence of an angular difference algorithm at an angular velocity of 800 °/s according to the present invention;

FIG. 8 is a graph of the characteristic of the sampled angle signal at an angular velocity of 600 °/s according to the present invention;

FIG. 9 is a graph of the actual angle versus measured angle characteristic for an angular velocity of 600 °/s according to the present invention;

FIG. 10 is a graph of the reliability of the angular difference algorithm at an angular velocity of 600 °/s according to the present invention;

fig. 11 is a graph of angular velocity versus angular deviation and confidence for the present invention.

Table 1: physical parameter definitions and terminology

Detailed Description

In order to make the technical problems solved, technical solutions adopted and technical effects achieved by the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some but not all of the relevant elements of the present invention are shown in the drawings.

The angle measuring method of the angle sensor of the EPS system provided by the embodiment of the invention is applied to the EPS system of a vehicle, and the angle sensor is used as one of core components of the EPS system. The output signals of the angle sensor comprise a P signal and an S signal which are output by a built-in IC chip, the P signal and the S signal adopt a duty ratio form, the P signal is represented as PWM _ P, and the S signal is represented as PWM _ S. The PWM _ P signal used in current EPS systems is 40 ° per cycle, with a total of 37 cycle segments, and the segment number is i (i ═ 1, 2, … …, 36, 37). The PWM _ S signal used by current EPS systems is 296 ° per cycle, for a total of 5 cycle segments, with segment number j (j ═ 1, 2, 3, 4, 5).

The PWM _ P and PWM _ S variation in each cycle section is in linear relation with the angle variation, the effective pulse width modulation value ranges are 12.5% -87.5%, and the comprehensive angle measurement range is 1480 degrees. The angular signal characteristic shown in fig. 1 is a curve that extends rightward with the lowest point of the angle as a zero point, and the lowest point of the angle is 12.5%, that is, PWM _ P is 12.5%, and it can be understood that any one segment of the curve in an angular range of 1480 ° is cyclically repeated when the segments are connected end to end. In any section of 1480 °, if the angle scale from 0 ° to 1480 ° is divided, there is a unique combination of PWM _ P and PWM _ S at any angle point corresponding to the angle scale, that is, the measurement angle θ is equal to f (PWM _ P, PWM _ S), and if the angle scale is out of the 1480 °, a repeated signal combination appears. Therefore, the angle recognized by the electronic control unit ECU through the angular difference algorithm is a relative angle, and is effective only in the range of 1480 °.

Based on the application background and the angle signal characteristics of the angle sensor, as shown in fig. 2, the method for measuring the angle of the angle sensor of the EPS system according to the embodiment of the present invention includes the following steps:

step 1, establishing an angular difference rule of a P signal section and an S signal section in an output signal of an angle sensor.

Step 101, in an ideal state, determining a standard angle difference value of the P signal section and the S signal section, and further determining a corresponding relationship between the standard angle difference value and the P signal section number.

Under an ideal state that the angle signals output by the angle sensor are not influenced by any factors, the output signals PWM _ P and PWM _ S of the angle sensor are both standard signals without errors. The PWM _ P value is in 37 sections, and the S signal point corresponding to the same angular position is set as S _j-i Will S _j-i The lowest point of PWM _ S angle of the section j where the signal point is located is far away from the S _j-i The angle of the signal point is defined as S signal section standard angle and is represented as theta _sj-i (ii) a The angle between the PWM _ P sampling point and the PWM _ P angle lowest point of the i section is defined as the standard angle of the P signal section and is represented as theta _p In each P signal section, θ _p Are all the same. In this embodiment, the minimum angle point of PWM _ S is a point PWM _ S of 12.5%, and the minimum angle point of PWM _ P is a point PWM _ P of 12.5%.

As shown in fig. 3. Ideally, the standard angle difference of the P signal segment and the S signal segment is determined using the following equation:

Δθ _psi ＝θ _sj-i -θ _p ………………………………………………………...…(1)

wherein, Delta theta _psi Indicating the standard angle difference of the P signal section and the S signal section.

Obtaining the standard angle difference Delta theta according to the rule shown in figure 3 _psi The correspondence relationship with the P signal segment number i is shown in table 2.

Table 2: standard angle difference delta theta _psi List of values and P signal segment numbers i

i	1	2	3	4	5	6	7
								Δθ psi (°)	0	40	80	120	160	200	240
i	8	8	9	10	11	12	13
								Δθ psi (°)	280	-16	24	64	104	144	184
i	14	15	15	16	17	18	19
								Δθ psi (°)	224	264	-32	8	48	88	128
i	20	21	22	23	23	24	25
								Δθ psi (°)	168	208	248	288	-8	32	72
i	26	27	28	29	30	30	31
								Δθ psi (°)	112	152	192	232	272	-24	16
i	32	33	34	35	36	37	—
								Δθ psi (°)	56	96	136	176	216	256	—

The standard angle difference Δ θ in Table 2 _psi In ascending order, the corresponding P signal segment numbers i also correspond, as shown in table 3.

Table 3: standard angle difference delta theta _psi List of ascending sequence and corresponding P signal segment number i

i	15	30	8	23	1	16	31
								Δθ psi (°)	-32	-24	-16	-8	0	8	16
i	9	24	2	17	32	10	25
								Δθ psi (°)	24	32	40	48	56	64	72
i	3	18	33	11	26	4	19
								Δθ psi (°)	80	88	96	104	112	120	128
i	34	12	27	5	20	35	13
								Δθ psi (°)	136	144	152	160	168	176	184
i	28	6	21	36	14	29	7
								Δθ psi (°)	192	200	208	216	224	232	240
i	22	37	15	30	8	23	—
								Δθ psi (°)	248	256	264	272	280	288	—

As can be seen from table 3, in the four P signal sections with section numbers i of 8, 15, 23 and 30, the S signal cyclic section switching phenomenon occurs in each section, so that the standard angle difference Δ θ is equal to _psi Two different standard angle difference values occur, and the standard angle difference values in other numbers are constant; for the standard angle difference delta theta in table 3 _psi Also, it was found that the new i-value was transformed every 8 deg. interval.

The conclusion is that: standard angle difference delta theta _psi The mapping relationship with directivity corresponds to the P signal segment number i, that is: mapping relation array [ Delta theta ] _psi →i]The corresponding relation of (2) conforms to the rule shown in figure 3, and has deviation fusion capability of +/-4 degrees.

Step 102, in an actual state, determining an actual angle difference value between the P signal section and the S signal section, and further determining a corresponding relationship between the actual angle difference value and the P signal section number i, and a corresponding relationship between the actual angle difference value and the standard angle difference value.

In the actual state that the signal output by the angle sensor is affected by some factors, angle signal sampling errors are generated, and in order to reduce the influence of the errors on the angle measurement effectiveness as much as possible, the errors of the PWM _ P and the PWM _ S are respectively treated. Because the P signal is less influenced, the measuring accuracy can be enhanced on the basis of the angle measuring method, and the PWM _ P error becomes a main influence factor of the angle measuring precision in an actual state; however, since the S signal is influenced by many factors, in the angle measurement method in the actual state, the S signal is used as an auxiliary signal only for transition calculation, and the reliability rel (reliability) is calculated to evaluate whether the angle measurement result is valid.

In an actual state, output signals of a group of angle sensors are obtained by ECU sampling: PWM _ P and PWM _ S. Because the P signal is affected by a few factors and has a small error, the default state is consistent with the ideal state, and the actual angle of the P signal section calculated by the current sampling can be still consistent with the code of the standard angle, that is: theta _p . Because the S signal is influenced by more factors and has a larger error, the error between the actual section angle of the S signal calculated by the current sampling and the standard section angle is larger, and the actual angle difference between the P signal section and the S signal section in the actual state is determined by using the following formula:

Δθ _ps ＝θ _s -θ _p ………………………………………………………...…(2)

wherein, Delta theta _ps Representing the actual angular difference, θ, of the P and S signal sections in the actual state _s Representing the S signal actual sector angle.

For the standard angle difference delta theta in table 3 _psi It is also observed that if the actual angle difference Δ θ is measured _ps Comparing the closest standard angle difference delta theta in the table _psi And all fall within the standard angle difference Delta theta _psi In this way, the actual angle difference Δ θ can be made _ps Has definite attribute and is unique, and the allowable deviation is controlled within +/-4 degrees, so that the deviation fusion capability of the angle signal characteristic is met, and further the deviation fusion capability is obtainedActual angle difference Δ θ _ps Difference delta theta from standard angle _psi The corresponding relationship of (1).

Step 103, utilizing the standard angle difference delta theta _psi Corresponding relation with P signal section number i and actual angle difference delta theta _ps Difference delta theta from standard angle _psi To obtain the actual angle difference value delta theta _ps Mapping relation with P signal section number i and actual angle difference delta theta _ps Difference delta theta from standard angle _psi The mapping relationship of (c).

Specifically, this step is combined with table 3 to determine the actual angle difference Δ θ _ps Also included therein is the actual angle difference Δ θ _ps Mapping relation [ Delta theta ] with P signal section number i _ps →i]And the actual angle difference Δ θ _ps Difference value delta theta from standard angle _psi Is [ Delta theta ] of _ps →Δθ _psi ]As shown in table 4.

Table 4: array [ Delta theta ] _ps →i]And [ Delta theta ] _ps →Δθ _psi ]Mapping relation table

i	15	30	8	23	1	16	31
								Δθ psi (°)	-32	-24	-16	-8	0	8	16
Δθ ps (°)	-36≤Δθ ps <-28	-28°≤Δθ ps <-20	-20°≤Δθ ps <-12	-12≤Δθ ps <-4	-4≤Δθ ps <4	4≤Δθ ps <12	12≤Δθ ps <20
								i	9	24	2	17	32	10	25
Δθ psi (°)	24	32	40	48	56	64	72
								Δθ ps (°)	20≤Δθ ps <28	28≤Δθ ps <36	36≤Δθ ps <44	44≤Δθ ps <52	52≤Δθ ps <60	60≤Δθ ps <68	68≤Δθ ps <76
i	3	18	33	11	26	4	19
								Δθ psi (°)	80	88	96	104	112	120	128
Δθ ps (°)	76≤Δθ ps <84	84≤Δθ ps <92	92≤Δθ ps <100	100≤Δθ ps <108	108≤Δθ ps <116	116≤Δθ ps <124	124≤Δθ ps <132
								i	34	12	27	5	20	35	13
Δθ psi (°)	136	144	152	160	168	176	184
								Δθ ps (°)	132≤Δθ ps <140	140≤Δθ ps <148	148≤Δθ ps <156	156≤Δθ ps <164	164≤Δθ ps <172	172≤Δθ ps <180	180≤Δθ ps <188
i	28	6	21	36	14	29	7
								Δθ psi (°)	192	200	208	216	224	232	240
Δθ ps (°)	188≤Δθ ps <196	196≤Δθ ps <204	204≤Δθ ps <212	212≤Δθ ps <220	220≤Δθ ps <228	228≤Δθ ps <236	236≤Δθ ps <244
								i	22	37	15	30	8	23	—
Δθ psi (°)	248	256	264	272	280	288	—
								Δθ ps (°)	244≤Δθ ps <252	252≤Δθ ps <260	260≤Δθ ps <268	268≤Δθ ps <276	276≤Δθ ps <284	284≤Δθ ps ≤292	—

The contents of Table 4 are written in the form of expressions based on the actual angle difference Delta theta of Table 4 _ps Mapping relation array [ Delta theta ] with P signal zone number i _ps →i]The assignment expression of the P signal segment number i is:

actual angle difference Δ θ _ps Difference delta theta from standard angle _psi Is [ Delta theta ] of _ps →Δθ _psi ]The expression of (c) is:

the ellipses in the above two formulas also represent the calculation relationships, which can be mapped according to the mapping relationship array shown in Table 4, and the mapping relationship [ Delta theta ] is _ps →i]And [ Delta theta ] _ps →Δθ _psi ]Has directivity.

Step 2, acquiring a P signal and an S signal output by the angle sensor, and obtaining the actual angle theta of a P signal section by using the P signal and the S signal _p And S signal section actual angle theta _s And the actual angle difference Delta theta _ps 。

Specifically, the P signal segment actual angle is calculated by using the following formula:

θ _p ＝(PWM_P-12.5)×40/75……………………………………………(5)

calculating the actual angle of the S signal segment by using the following formula:

θ _s ＝(PWM_S-12.5)×296/75……………………………………………(6)

calculating the actual angle difference of the P signal and the S signal by using formula (2):

Δθ _ps ＝θ _s -θ _p ……………………………………………………………(2)

step 3, determining the number i of the P signal section and the standard angle difference value delta theta of the current angle measuring point according to the angle difference rule of the P signal section and the S signal section established in the step 1 _psi 。

In step 1, the actual angle difference Δ θ is obtained _ps Mapping relation [ Delta theta ] with P signal zone number i _ps →i]And the actual angle difference Delta theta _ps Difference delta theta from standard angle _psi Mapping of [ Delta theta ] _ps →Δθ _psi ]. Therefore, at the actual angle difference Δ θ _ps After determination, the P signal segment number i and the standard angle difference value delta theta of the current angle measurement point can be determined _psi 。

Step 4, according to obtainingThe obtained P signal section number i is combined with the P signal section actual angle theta calculated in the step 2 _p And calculating to obtain a measurement angle by using the following formula:

θ＝(i-1)×40+θ _p ……………………………………………………(7)

where θ represents the measurement angle of the angle sensor.

In order to fully understand the method of the present invention, the codes of the angle measurement method in this embodiment are schematically as follows:

θ _p (PWM _ P-12.5)% 40/75%% assigns the actual angle of the P signal segment according to the PWM _ P sample value

θ _s (PWM _ S-12.5) × 296/75%% assigns an actual angle to the S signal segment based on the PWM _ S sample value

Δθ _ps ＝θ _s -θ _p % according to the obtained theta _p And theta _s To calculate the actual angular difference

% according to Δ θ obtained _ps The value is assigned to the P signal segment number i according to the mapping relation of Table 4

IfΔθ _ps >＝-36andΔθ _ps <-28Then

i＝15

End If

IfΔθ _ps >＝-28andΔθ _ps <-20Then

i＝30

End If

……

IfΔθ _ps >＝276andΔθ _ps <284Then

i＝8

End If

IfΔθ _ps >＝284andΔθ _ps <＝292Then

i＝23

End If

θ＝(i-1)*40+θ _p % based on i and θ obtained _p Calculating the measurement angle

And 5, calculating the reliability of the measurement angle.

Through the analysis, the angle signal characteristics have the deviation fusion capacity of +/-4 degrees, which is also the total deviation requirement caused by all factors of the S signal output by the angle sensor. When the angular deviation of the S signal exceeds the range of ± 4 °, an angular measurement error may occur, and even if the required range is not exceeded, when the deviation limit is approached, there is a risk of a measurement error. Therefore, a confidence index is introduced to evaluate whether the measurement result is at risk or not so as to avoid misuse by the EPS system.

Step 501, calculating the actual angle deviation of the S signal by using the following formula:

Δθ _s ＝|Δθ _ps -Δθ _psi |…………………………………………………………(8)

wherein, Delta theta _s Representing the actual angular deviation, Δ θ, of the S signal _psi Expressing the standard angle difference value, according to the mapping relation array [ Delta theta ] of Table 4 _ps →Δθ _psi ]It evaluates the expression as in equation (4).

Step 502, calculating the reliability of the measurement angle by using the following formula:

Rel＝100×(1-Δθ _s /4)……………………………………………………(9)

where Rel represents confidence.

The angle sensor is assembled in an EPS system, the calibrated reliability is also calculated and evaluated according to the formula (9), in the static detection of an actual product, Rel can reach more than 62.5 percent, and the actual angle deviation of an S signal can be controlled within the range of +/-1.5 degrees. The P signal represents the angle measurement accuracy, typically the PWM _ P static deviation is ± 0.03%, and the static accuracy affecting the angle measurement is: + -0.016 deg.

In order to fully understand the method of the present invention for those skilled in the art, the codes for calculating the confidence level in the present embodiment are schematically shown as follows:

% Delta Theta obtained as described above _ps Values, as mapped in Table 4, for the standard angular difference Δ θ _psi Assignment of value

IfΔθ _ps >＝-36andΔθ _ps <-28Then

Δθ _psi ＝-32

End If

IfΔθ _ps >＝-28andΔθ _ps <-20Then

Δθ _psi ＝-24

End If

……

IfΔθ _ps >＝276andΔθ _ps <284Then

Δθ _psi ＝280

End If

IfΔθ _ps >＝284andΔθ _ps <＝292Then

Δθ _psi ＝288

End If

Δθ _s ＝|Δθ _ps -Δθ _psi % according to Δ θ obtained _ps And Δ θ _psi Calculating the actual angle deviation of the S signal

Rel＝100*(1-Δθ _s /4)%% based on Δ θ obtained _s Calculating the reliability of the angular difference algorithm

And 6, evaluating the validity of the measured angle result according to the reliability of the measured angle and the angular speed of the steering wheel.

Step 5 is to evaluate in a static state, and when the EPS system executes a steering action, the angular signal of the angle sensor is inevitably in a dynamic state, particularly the rotating angular speed of the steering wheel, which has a great influence on the measured angle reliability Rel and the index of the angle measurement precision. Since the frequency of the P signal is 1000Hz, one signal period is 1ms, the frequency of the S signal is 200Hz, and one signal period is 5ms, this means that the corresponding signal values are not updated in their signal periods. Thus, when the steering wheel is turned rapidly, angular errors will be generated within their respective signal periods and not reflected by the angular signals, with the dynamic angular error versus angular velocity relationship shown in FIG. 4. The manual limit rotational angular speed for steering wheel operation is 1000 °/S, whereby the P signal angle error is ± 1 ° and the S signal is ± 5 ° as shown in fig. 4. Therefore, the P signal is selected as the main angle signal to carry out angle measurement of the angle difference algorithm, so that the reliability is high, and the dynamic accuracy of the angle measurement is +/-1 degrees.

The angle measurement is based on the sampled value with a period of 1 ms: and obtaining the measured angle through an angle difference algorithm by PWM _ P and PWM _ S, wherein the P signal is updated once every 5 times because of different frequencies of the two signals, so that the reliability Rel is reduced, and even an angle measurement error occurs. The limit of angular velocity for turning the steering wheel by a normal person is typically 800 °/s, and when driving a vehicle, it is generally not more than 600 °/s due to safety awareness, and the influence of angular velocity on the angular difference algorithm is analyzed by taking two typical angular velocities as examples and taking an angle of 15 ° as a starting point.

The characteristic curve of the sampling angle signal at an angular velocity of 800 °/s is shown in fig. 5. As shown in fig. 6 and 7, when the angular velocity is 800 °/S, in the first 5ms period of the S signal, when the P signal is sampled 1, 2, 3, 4 times, the measured angle is substantially consistent with the actual angle (within the error range), the reliability is reduced from 62.5% to 42.5%, 22.5%, 2.5%, when the P signal is sampled 5 times, the measured angle is greatly different from the actual angle, the actual angle is 18.20 ° to 18.92 °, the measured angle is 898.20 °, and the reliability is further improved from 2.5% of the 4 th sampling time to 17.5%; when the P signal is sampled at the 6 th sampling moment, the second S signal period is entered, the measurement result of the first S signal period is repeated, and the cycle is repeated. It can be seen that when the angular velocity is 800 °/s, the measurement results of the angular difference algorithm are not reliable, and if the angular velocity is increased, the phenomena that the measured angle does not conform to the actual angle and the reliability Rel is more than 25% occur more frequently, and the measurement results are not reliable.

The characteristic graph of the sampling angle signal at an angular velocity of 600 °/s is shown in fig. 8. As shown in fig. 9 and 10, when the angular velocity is 600 °/s, the above-described error does not occur, and the angle measurement result substantially matches the actual angle, but the reliability is lowered to 2.5%, and there is a certain measurement risk. When the angular velocity is high, i.e., the P signal and the S signal corresponding to the sampling timing have a chance to generate a large relative angular deviation, as shown in fig. 11, thereby causing the angular deviation to exceed the critical limit, the angle outputted by the calculation becomes unstable. In order to ensure that the measurement result of the angular difference algorithm is effective, in the actual work of the EPS system, the minimum limit value of the reliability is set to be Rel which is more than or equal to 25%, the angular measurement result which meets the requirement of the limit value is allowed to be applied by the ECU, otherwise, the measurement result is forbidden. The relationship between the angular velocity and the reliability is also shown in fig. 11.

As shown in fig. 11, when the maximum static angle deviation of P and S of the angle sensor angle signal is 1.5 ° and the current reliability Rel is 62.5%, the following three cases occur as the steering wheel rotation angular velocity increases:

the first method comprises the following steps: when the angular velocity is less than 375 DEG/s, Rel is greater than 25%, the measured angle is credible and can be applied by the ECU;

and the second method comprises the following steps: when the angular velocity is greater than 375 °/s and less than 875 °/s, Rel is less than 25%, the measured angle is not authentic and will be disabled by the ECU;

and the third is that: when the angular velocity is greater than 875 °/s, Rel is also greater than 25%, but the measured angle is erroneous and will also be disabled by the ECU.

For the first and third cases, a phenomenon that Rel is greater than 25% occurs, and an angular velocity estimation value is used as an additional judgment condition to evaluate the validity of an angle measurement result through the following formula:

wherein ω represents angular velocity, TRUE represents valid measurement, and flag represents invalid measurement; angular velocity is the average angular velocity obtained from the previous number of valid measured angles and corresponding time instants, and allows a rough estimate as long as the deviation is within ± 250 °/s.

When the angle measured by the angular difference algorithm is judged to be invalid by the formula (10), the angle cannot be applied by the EPS system, the following algorithm in the prior art is adopted to measure the angle, and the method is matched with the following algorithm in the prior art. The following algorithm measures the angle by the independent P signal sampling value according to the angle reference determined by the angular difference algorithm, thereby avoiding the influence of the angular speed on the measurement and simultaneously expanding the measurement range.

In summary, the present invention provides an angle measuring method for an angle sensor of an EPS system, wherein an ECU in the EPS system outputs a P signal and an S signal according to output signals of the angle sensor, so as to obtain an actual angle θ of a P signal segment _p And S signal section actual angle theta _s From the actual angular difference Δ θ _ps ＝θ _s -θ _p To determine the P signal segment number i and the standard angular difference Delta theta _psi The value is obtained. According to the i value and theta _p The value can be calculated to obtain the measured angle theta value according to delta theta _ps Value sum Δ θ _psi The value can be used for calculating the reliability Rel of the angular difference algorithm, and the effectiveness evaluation is carried out on the measured angle result according to the reliability Rel and the angular speed omega. The method of the invention enables the EPS system to have the capability of measuring the angle and can judge whether the angle measurement is effective or not.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: modifications are made to the technical solutions described in the foregoing embodiments, or some or all of the technical features are replaced with equivalents, without departing from the spirit of the technical solutions of the embodiments of the present invention.

Claims (9)

1. An EPS system angle sensor angle measurement method is characterized by comprising the following processes:

step 1, establishing an angular difference rule of a P signal section and an S signal section in an output signal of an angle sensor; the output signals of the angle sensor comprise a P signal and an S signal, the P signal and the S signal adopt a duty ratio form, the P signal is represented as PWM _ P, and the S signal is represented as PWM _ S;

step 2, acquiring a P signal and an S signal output by an angle sensor, and obtaining an actual angle of a P signal section, an actual angle of an S signal section and an actual angle difference value by using the P signal and the S signal;

step 3, determining the P signal section number and the standard angle difference value of the current angle measurement point according to the angle difference rule of the P signal section and the S signal section established in the step 1; the PWM _ P signal adopted by the EPS system is 40 ° per cycle, and has 37 cycle segments, where the segment number is i (i is 1, 2, … …, 36, and 37); the PWM _ S signal used by the EPS system is 296 ° one cycle, and there are 5 cycle segments, and the segment number is j (j is 1, 2, 3, 4, 5);

determining the standard angle difference of the P signal section and the S signal section using the following formula:

Δθ _psi ＝θ _sj-i -θ _p ……………………………………………………………(1)

wherein, the PWM _ P value is in 37 sections, and the S signal point corresponding to the same angular position is set as S _j-i Will S _j-i The lowest point of PWM _ S angle of the section j where the signal point is located is far away from the S _j-i The angle of the signal point, defined as S signal section standard angle, is represented as theta _sj-i (ii) a The angle between the PWM _ P sampling point and the PWM _ P angle lowest point of the i section is defined as the standard angle of the P signal section and is represented as theta _p In each P signal section, θ _p Are all the same; delta theta _psi Representing the standard angle difference of the P signal section and the S signal section;

and 4, calculating to obtain a measurement angle according to the obtained P signal section number and the actual angle of the P signal section calculated in the step 2.

2. The EPS system angle sensor angle measurement method according to claim 1, wherein step 1, establishing an angular difference law of a P signal segment and an S signal segment in an angle sensor output signal, comprises steps 101 to 103:

step 101, determining a standard angle difference value of a P signal section and an S signal section under an ideal state, and further determining a corresponding relation between the standard angle difference value and a P signal section number;

102, in an actual state, determining an actual angle difference value of the P signal section and the S signal section, and further determining a corresponding relation between the actual angle difference value and a P signal section number i and a corresponding relation between the actual angle difference value and a standard angle difference value;

step 103, utilizing the standard angle difference delta theta _psi Corresponding relation with P signal section number i and actual angle difference delta theta _ps Difference delta theta from standard angle _psi To obtain the actual angle difference value delta theta _ps Mapping relation with P signal section number i and actual angle difference delta theta _ps Difference delta theta from standard angle _psi The mapping relationship of (2).

3. The EPS system angle sensor angle measurement method according to claim 2, wherein the actual angle difference value of the P signal section and the S signal section in the actual state is determined using the following formula:

Δθ _ps ＝θ _s -θ _p ……………………………………………………………(2)

wherein, Delta theta _ps Representing the actual angular difference, theta, of the P and S signal sections in the actual state _s Representing the S signal actual sector angle.

4. The EPS system angle sensor angle measurement method of claim 3, wherein the actual angle difference Δ θ _ps Mapping relation [ Delta theta ] with P signal zone number i _ps →i]And the actual angle difference Δ θ _ps Difference delta theta from standard angle _psi Mapping of [ Delta theta ] _ps →Δθ _psi ]As in the following table:

5. the EPS system of claim 1 or 4The angle measuring method of the angle sensor is characterized in that step 2, a P signal and an S signal output by the angle sensor are obtained, and the P signal and the S signal are used for obtaining an actual angle theta of a P signal section _p And S signal section actual angle theta _s And the actual angle difference Δ θ _ps The method comprises the following steps:

calculating the actual angle of the P signal segment using the following formula:

θ _p ＝(PWM_P-12.5)×40/75……………………………………………(5)

calculating the actual angle of the S signal segment by using the following formula:

θ _s ＝(PWM_S-12.5)×296/75……………………………………………(6)

calculating the actual angle difference of the P signal and the S signal by using the following formula:

△θ _ps ＝θ _s -θ _p ……………………………………………………………(2)。

6. the EPS system angle sensor angle measurement method according to claim 5, wherein in step 4, the measurement angle is obtained by calculating using the following formula:

θ＝(i-1)×40+θ _p ………………………………………………………(7)

where θ represents the measured angle of the angle sensor, θ _p Indicates the P-signal segment actual angle, and i indicates the P-signal segment number.

7. The EPS system angle sensor angle measurement method of claim 1 or 4, further comprising, after step 4:

step 5, calculating the reliability of the measuring angle;

and 6, evaluating the validity of the measured angle result according to the reliability of the measured angle and the angular speed of the steering wheel.

8. The EPS system angle sensor angle measurement method according to claim 7, wherein the step 5 of calculating the reliability of the measurement angle comprises the following steps:

step 501, calculating the actual angle deviation of the S signal by using the following formula:

△θ _s ＝|△θ _ps -△θ _psi |…………………………………………………………(8)

wherein, Delta theta _s Representing the actual angular deviation, Δ θ, of the S signal _ps Representing the actual angular difference, Δ θ _psi Represents the standard angle difference;

step 502, calculating the reliability of the measurement angle by using the following formula:

Rel＝100×(1-△θ _s /4)…··…………………………………………………(9)

where Rel represents confidence.

9. The EPS system angle sensor angle measurement method according to claim 7, wherein in step 6, the angle measurement result is evaluated for validity by the following formula:

wherein ω represents angular velocity, TRUE represents valid measurement, and flag represents invalid measurement;

when the measured angle is judged to be invalid by equation (10), a following algorithm is used to measure the angle.

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