JP4935573B2 - Suspension characteristics estimation device - Google Patents

Description

  The present invention relates to a suspension characteristic estimation device for estimating a suspension characteristic of a vehicle.

  In general, it is known that suspension characteristics such as “damping coefficient”, “tire friction coefficient”, and “vehicle height” are important factors for improving the steering stability and riding comfort of a vehicle. Since these suspension characteristics change depending on use conditions, conventionally, a suspension is attached to a sensor under the spring to measure each suspension characteristic.

On the other hand, devices for estimating various types of suspension characteristics based on unsprung state values have been devised. For example, in Patent Document 1, a target damping coefficient is calculated from an unsprung relative speed with respect to a sprung from a vibration component of wheel speed. Further, in Patent Document 2, in order to calculate a target damping coefficient, a sprung and a spring are calculated. Based on the relative displacement and relative speed below and the vertical acceleration on the spring, the fluctuation amount of the damping coefficient of the shock absorber and the fluctuation amount of the spring constant of the suspension due to deterioration with time are estimated.
Japanese Patent Laid-Open No. 06-048139 JP 2003-326933 A

  However, in the past, when estimating suspension characteristics, a plurality of suspension characteristics to be estimated were included, and physical quantities that these suspension characteristics influenced independently were not found. In this case, a large number of sensors must be used, which increases the cost.

  Accordingly, an object of the present invention is to provide a suspension characteristic estimation device that can estimate a plurality of suspension characteristics while reducing costs.

  Here, as a result of intensive studies, the inventors have determined from the vertical displacement under the unsprung state of the vehicle and the longitudinal force input to the unsprung state of the vehicle, from this vertical displacement to the longitudinal force. Has succeeded in deriving the transfer function of the above, and has come to the knowledge that the gain and phase in the relationship between the vertical displacement and the longitudinal force are required.

  In addition, the inventors have studied the relationship between the gain and phase and various types of suspension characteristics. As a result, the damping coefficient, the tire friction, and the vehicle height, which are suspension characteristics, are independent of the relationship between the gain and phase. Found out. Specifically, when the vehicle height changes, the phase becomes substantially constant but the gain changes, and when the damping coefficient decreases, the gain becomes substantially constant but the phase increases, and when the tire friction decreases, the gain becomes substantially constant. Found that the phase decreased.

  Furthermore, the inventors further studied the relationship between the gain and phase and various suspension characteristics. The tire friction coefficient is related to the tire friction coefficient and the phase depending on the road surface condition and the degree of tire wear. It has been found that there is a possibility of reversal, and further, it has been found that the phase difference between different vehicle speeds has different properties between the damping coefficient and the tire friction coefficient. Specifically, it has been found that the phase difference between different vehicle speeds is substantially constant even when the tire friction changes, whereas the phase difference between different vehicle speeds changes as the damping coefficient changes.

The present invention has been made on the basis of the above-mentioned findings by the inventors, and is a suspension characteristic estimation device that estimates a plurality of suspension characteristics of a vehicle. Gain and phase are obtained based on a displacement detection means, a longitudinal force detection means for detecting a longitudinal force input to the unsprung portion of the vehicle, and a transfer function from the vertical displacement to the longitudinal force. , have a, and estimating means for estimating a plurality of suspension characteristic based on the gain and the phase, said estimating means, a plurality of suspension characteristics, attenuation coefficient, to estimate the tire friction coefficient and the vehicle height Features. In the present invention, the vehicle height refers to a displacement on the spring with respect to the unsprung state, an angle at which the main shaft of the suspension tilts upward from the horizontal line in a side view of the vehicle, in addition to directly indicating the vehicle height of the vehicle.

According to the suspension characteristic estimation device, the vertical displacement under the spring and the longitudinal force input to the unsprung force are detected, so that the relationship between the vertical displacement and the longitudinal force is detected. Since gain and phase are obtained, and multiple suspension characteristics are estimated based on the gain and phase, an increase in cost due to the use of a large number of sensors can be prevented, and multiple suspension characteristics can be estimated while reducing costs. be able to. Furthermore, according to this suspension characteristic estimation device, these suspension characteristics can be estimated without using sensors for measuring the damping coefficient, the tire friction coefficient, and the vehicle height.

  Further, the estimation means estimates a vehicle height based on the gain, and estimates an attenuation coefficient based on the phase when the phase increases from a predetermined set value, and reduces the phase from a predetermined set value. Preferably, the tire friction coefficient is estimated based on the phase. According to this suspension characteristic estimation device, the vehicle height, the damping coefficient, and the tire friction coefficient, which are suspension characteristics, have independent characteristics in relation to the gain and phase, respectively. By estimating the high, damping coefficient, and tire friction coefficient, the reliability of the estimation of the suspension characteristics can be further improved.

  On the other hand, it is preferable that the estimation means estimates the suspension characteristics based on the gain, the phase, and the phase difference obtained between different vehicle speeds. According to this suspension characteristic estimation apparatus, in addition to the gain and phase in the relationship between the vertical displacement z and the longitudinal force Fx, the suspension characteristic is estimated in consideration of the phase difference obtained between different vehicle speeds. Further, the reliability of estimation of suspension characteristics can be further improved.

  In this case, the estimation means compares the gain, the phase and the phase difference with a predetermined set value, estimates the vehicle height based on the gain, and increases or decreases the phase from the predetermined set value. When the phase difference increases or decreases from a predetermined set value, an attenuation coefficient is estimated based on the phase, and when the phase increases or decreases from a predetermined set value, the phase difference is substantially equal to a predetermined threshold value. In the same case, it is preferable to estimate the tire friction coefficient based on the phase. According to this suspension characteristic estimation device, the vehicle height, the damping coefficient, and the tire friction coefficient, which are suspension characteristics, have independent characteristics in relation to the gain, phase, and phase difference. When the vehicle height, the damping coefficient, and the tire friction coefficient are estimated based on the relationship with the difference in the difference between the damping coefficient, the tire friction coefficient, and the phase depending on the road surface condition, the degree of tire wear, etc. Even so, it is possible to further improve the reliability of the estimation of the suspension characteristics.

  According to the present invention, it is possible to estimate a plurality of suspension characteristics while reducing costs.

  Hereinafter, a preferred embodiment of a suspension characteristic estimation device according to the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

[First Embodiment]
FIG. 1 is a diagram schematically illustrating a suspension characteristic estimation apparatus according to the first embodiment, and FIG. 2 is a diagram illustrating a functional configuration of the suspension characteristic estimation apparatus according to the present embodiment. As shown in the figure, the suspension characteristic estimation device 1 of the present embodiment is mounted on a vehicle 2. The unsprung portion of the vehicle 2 includes a shock absorber 3 to which a spring (not shown) is attached, and a trailing arm 4. And a trailing arm type suspension.

  The vehicle 2 includes a vehicle speed sensor 5 that measures the vehicle speed of the vehicle 2 by detecting the rotational speed of each wheel, a vertical acceleration sensor 6 that measures an unsprung vertical acceleration, and an unsprung longitudinal sensor. A longitudinal acceleration sensor 7 that measures acceleration and an ECU 8 that performs various controls of the vehicle and estimates suspension characteristics are provided. The vertical acceleration sensor 6 and the longitudinal acceleration sensor 7 are attached to the same place on the suspension.

  Further, the vehicle speed sensor 5, the vertical acceleration sensor 6 and the longitudinal acceleration sensor 7 are each connected to the ECU 8, and each measurement result is transmitted to the ECU 8.

  The ECU 8 determines suspension characteristics based on the vehicle speed transmitted from the vehicle speed sensor 8, the unsprung vertical acceleration transmitted from the vertical acceleration sensor 6, and the unsprung longitudinal acceleration transmitted from the longitudinal acceleration sensor 7. presume. For example, the vertical displacement and the longitudinal force input to the unsprung force are obtained from the vertical acceleration and the unsprung longitudinal acceleration, and the unsprung vertical displacement and unsprung force are input. It is preferable to estimate the suspension characteristics from the gain and phase in relation to the longitudinal force. Specifically, it is preferable to determine a suspension by obtaining a transfer function from an unsprung vertical displacement to a longitudinal force input to the unsprung mass, obtaining a gain and a phase from the transfer function. The ECU 8 is mainly configured by a computer including a CPU, a ROM, and a RAM, for example.

  Also, the ECU 8 estimates the suspension characteristics, the gain and phase in the relationship between the unsprung vertical displacement and the longitudinal force input to the unsprung, the suspension characteristics such as vehicle height, damping coefficient, and tire friction. It holds a map showing the relationship with the coefficients. 3 to 5 show the structure of the map. 3A shows the vehicle height-gain map A, and FIG. 3B shows the vehicle height-phase map B. 4A shows an attenuation-gain map C, and FIG. 4B shows an attenuation-phase map D. 5A shows a tire friction-gain map E, and FIG. 5B shows a tire friction-phase map F.

  Here, a method for deriving the gain and phase indicated by each map will be described.

  First, an equation of motion is derived so as to include the following specifications (see FIG. 6). Then, this equation of motion becomes as shown in Equation (1) and Equation (2).

m: unsprung weight z: unsprung vertical displacement Ktz: vertical stiffness of tire C: shock absorber damping coefficient Ks: spring constant of spring Fx: longitudinal force input to unsprung α: shock absorber in side view of vehicle Forward tilt angle in which the vehicle tilts forward from the vertical line β: Front / rear main axis rebound angle (vehicle height) in which the suspension main shaft tilts upward from the horizontal line in a side view of the vehicle
Kx: Front and rear rigidity of suspension W: Vehicle weight U: Vehicle speed u: 1 / f Road surface input P: Driving stiffness (tire friction coefficient)
ω: wheel rotation angular velocity ε: tire dynamic load radius change / tire static load change ro: tire radius Iw: wheel inertia moment Ktx: tire longitudinal rigidity

Next, the transfer function G (jω) from the unsprung vertical displacement z to the longitudinal force Fx is obtained from the equations of motion shown in equations (1) and (2). Then, the transfer function G (jω) becomes as shown in Expression (3). By obtaining the gain | G (jω) | and the phase ∠G (jω) of this transfer function G (jω), Gain and phase are derived in the relationship between the displacement and the longitudinal force input to the unsprung mass.

  Each of the maps shown in FIGS. 3 to 5 is generated by performing a parameter study on the relationship between the vehicle height, the damping coefficient, and the tire friction coefficient for the gain and phase thus derived.

  The characteristics of each map will be described. As can be seen from the vehicle height-gain map A and the vehicle height-phase map B, the gain changes when the vehicle height changes, but the phase becomes substantially constant even when the vehicle height changes. As can be seen from the attenuation-gain map C and the attenuation-phase map D, the phase increases as the attenuation coefficient decreases, but the gain remains substantially constant even when the attenuation coefficient changes. As can be seen from the tire friction-gain map E and the tire friction-phase map F, the phase decreases when the tire friction coefficient decreases. That is, it can be seen from these maps that the vehicle height has changed when the gain changes, the damping coefficient has decreased when the phase has increased, and the tire friction coefficient has decreased when the phase has decreased.

  Next, the suspension characteristic estimation processing operation of the suspension characteristic estimation apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing the operation of the ECU.

  First, when the suspension characteristic estimation apparatus 1 is started, the vehicle speed, the unsprung vertical acceleration, and the unsprung longitudinal acceleration, which are the measurement results, are sent to the ECU 8 from the vehicle speed sensor 5, the vertical acceleration sensor 6, and the longitudinal acceleration sensor 7, respectively. Sent.

When the ECU 8 detects the unsprung vertical acceleration (step S1), the ECU 8 calculates the unsprung vertical displacement from the unsprung vertical acceleration (step S2). Note that when the unsprung vertical acceleration is az, the unsprung vertical displacement z is calculated by the equation (4).

Further, when detecting the unsprung longitudinal acceleration (step S3), the ECU 8 calculates the longitudinal force input to the unsprung from the unsprung longitudinal acceleration (step S4). When the unsprung longitudinal acceleration is ax and the unsprung weight is m, the longitudinal force Fx input to the unsprung mass is calculated by the equation (5).

  Then, the ECU 8 uses the above equation (3) to calculate the longitudinal force Fx from the vertical displacement z based on the vertical displacement z calculated in step S2, the longitudinal force Fx calculated in step S4, and the vehicle speed of the vehicle 2. Transfer function G (jω) up to (step S5), and gain | G (jω) | of the transfer function G (jω) at a predetermined frequency (here, 16 Hz which is the unsprung resonance frequency is used) and The phase ∠G (jω) is calculated (step S6). The transfer function G (jω) has a substantially constant value when the vertical displacement z, the longitudinal force Fx, and the vehicle speed U are determined. Therefore, the transfer function G (jω) can be calculated by determining the vertical displacement z, the longitudinal force Fx, and the vehicle speed U.

  The ECU 8 refers to the vehicle height-gain map A to obtain the vehicle height corresponding to the gain calculated in step S6 (step S7), and compares the phase calculated in step S6 with the set value. Whether the phase increases or decreases is determined (step S8). The gain and phase setting values are the gain and phase at the time of shipment, and α1 to α3 in FIGS. 3 to 5 are gain setting values, and β1 to β3 in FIGS. The phase is set.

  If it is determined in step S8 that the phase has increased (step S8: YES), the ECU 8 refers to the attenuation-phase map D and obtains an attenuation coefficient corresponding to this phase (step S9). On the other hand, if it is determined that the phase has not increased (step S8: NO) and the phase has decreased (step S10: YES), the ECU 8 refers to the tire friction-phase map F and corresponds to this phase. The obtained tire friction coefficient is obtained (step S11). If it is determined that the phase has not increased or decreased (step S8: NO, step S10: NO), the ECU 8 determines that neither the damping coefficient nor the tire friction coefficient has changed, and it is not necessary to estimate. The process is terminated.

  In this way, by determining the vehicle height, the damping coefficient, and the tire friction coefficient, the suspension characteristic estimation device 1 estimates the vehicle height, the damping coefficient, and the tire friction coefficient, which are suspension characteristics.

As described above, according to the suspension characteristic estimation apparatus 1 according to the first embodiment, the vertical displacement z under the spring is detected from the vertical acceleration az, and the longitudinal direction input from the longitudinal acceleration ax to the unsprung direction is detected. By detecting the force fx, the gain and phase in the relationship between the vertical displacement z and the longitudinal force Fx are obtained, and the damping coefficient, tire friction coefficient, and vehicle height are estimated based on the gain and phase. Therefore, it is possible to prevent an increase in cost by using sensors that respectively measure the damping coefficient , the tire friction coefficient, and the vehicle height, and reduce the damping coefficient, the tire friction coefficient, and the vehicle height, which are suspension characteristics, while reducing the cost. Can be estimated.

  Furthermore, since the vehicle height, the damping coefficient, and the tire friction coefficient have independent characteristics in relation to the gain and the phase, respectively, the vehicle height, the damping coefficient, and the tire friction coefficient are estimated based on the relation to the gain and the phase. As a result, the reliability of the estimation of the suspension characteristics can be improved.

[Second Embodiment]
Next, a second embodiment will be described. The suspension characteristic estimation apparatus 11 according to the second embodiment is the same as the configuration of the suspension characteristic estimation apparatus 1 according to the first embodiment, and only the suspension characteristic estimation processing operation performed by the ECU 8 is different.

  That is, depending on the road surface condition and the degree of tire wear, the relationship between the tire friction coefficient and the phase may be reversed, and the phase may increase due to a decrease in the tire friction coefficient. Therefore, in the suspension characteristic estimation device 11 according to the second embodiment, when the phase increases or decreases (increases), the damping coefficient changes (decreases) or the tire friction coefficient changes (decreases) compared to the set value. Thus, the suspension characteristics are estimated.

  FIG. 8 is a flowchart showing the operation of the ECU. As shown in the figure, the suspension characteristic estimation device 11 according to the second embodiment performs steps S1 to S6 in the same manner as in the first embodiment, and performs a predetermined frequency (here, the unsprung resonance frequency). The gain | G (jω) | and the phase ∠G (jω) of the transfer function G (jω) are calculated (step S6). In the second embodiment, Steps S1 to S6 are performed twice to calculate phases between different vehicle speeds (100 km / h and 120 km / h). Then, the ECU 8 refers to the vehicle height-gain map A and obtains the vehicle height corresponding to the gain calculated in step S6 (step S7).

  Thereafter, in the second embodiment, the phase calculated in step S6 is compared with the set value, and an increase or decrease in this phase is determined (step S21). Note that the set values of the second embodiment are set to the gain and phase at the time of shipment, similarly to the set values of the first embodiment.

  If it is determined in step S21 that the phase is substantially the same as the set value (step S21: NO), the ECU 8 determines that neither the damping coefficient nor the tire friction coefficient has changed, and there is no need for estimation, and processing is performed. Exit. On the other hand, if it is determined in step S21 that the phase has changed (step S21: YES), the ECU 8 further determines whether or not the phase difference obtained between different vehicle speeds has changed (step S22). .

  Here, with reference to FIG.9 and FIG.10, the difference of the phase calculated | required between different vehicle speeds is demonstrated. FIG. 9A is a diagram showing the relationship between the damping coefficient and the phase when the vehicle 2 travels at 100 km / h and 120 km / h, and FIG. 9B shows the phase in FIG. It is the figure which showed the difference. FIG. 10A is a diagram showing the relationship between the attenuation coefficient and the phase when the vehicle 2 travels at a speed of 100 km / h and a speed of 120 km / h, and FIG. 10B is a diagram in FIG. It is the figure which showed the difference of a phase. When the damping coefficient shown in FIG. 9 and the tire friction coefficient shown in FIG. 10 are compared, the damping coefficient changes in phase between different vehicle speeds, whereas the tire friction coefficient differs between different vehicle speeds. It can be seen that the phase difference is substantially constant.

  Therefore, as shown in FIG. 8, when it is determined in step S22 that the phase difference obtained between different vehicle speeds has changed (step S22: YES), the ECU 8 determines that the attenuation coefficient has changed, and the attenuation is reduced. -Referring to the phase map D, an attenuation coefficient corresponding to this phase is obtained (step S23). On the other hand, if it is determined that the phase difference obtained between different vehicle speeds is substantially the same (step S22: NO), the ECU 8 determines that the tire friction coefficient has changed, and refers to the tire friction-phase map F. A tire friction coefficient corresponding to this phase is obtained (step S24).

  In this way, by obtaining the vehicle height, the damping coefficient, and the tire friction coefficient, the suspension characteristic estimation device according to the second embodiment estimates the vehicle height, the damping coefficient, and the tire friction coefficient, which are suspension characteristics.

  Thus, according to the suspension characteristic estimation device 11 according to the second embodiment, in addition to the gain and phase in the relationship between the vertical displacement z and the longitudinal force Fx, the phase difference obtained between different vehicle speeds. In consideration of the above, by estimating the damping coefficient, the tire friction coefficient, and the vehicle height, which are suspension characteristics, the reliability of the estimation of the suspension characteristics can be further improved.

  That is, the vehicle height, damping coefficient, and tire friction coefficient have independent characteristics in relation to the gain, phase, and phase difference, respectively. By estimating the coefficient and tire friction coefficient, even if the relationship between the damping coefficient and the tire friction coefficient and the phase is similar depending on the road surface condition and the degree of tire wear, etc. The property can be further improved.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, in the above embodiment, the longitudinal force Fx input to the unsprung portion has been described as being detected by calculating the longitudinal acceleration ax measured by the longitudinal acceleration sensor 7, but for example, using a strain gauge or the like, The longitudinal force Fx may be directly measured and detected.

In the above embodiment, the ease of observing the gain and phase has been described with reference to 16 Hz, which is the unsprung resonance region, using the gain and phase. However, other frequency bands may be used.

It is the figure which showed typically the suspension characteristic estimation apparatus which concerns on 1st Embodiment. It is the figure which showed the function structure of the suspension characteristic estimation apparatus which concerns on this embodiment. (A) The figure which showed the vehicle height-gain map, (b) The figure which showed the vehicle height-phase map. (A) The figure which showed the attenuation-gain map, (b) The figure which showed the attenuation-phase map. (A) The figure which showed the tire friction-gain map, (b) The figure which showed the tire friction-phase map. It is a figure for demonstrating each item under a spring. It is a flowchart which shows operation | movement of ECU. It is a flowchart which shows operation | movement of ECU. (A) is the figure which showed the relationship between the attenuation coefficient and phase between different vehicle speed, (b) is the figure which showed the difference of the phase in (a). (A) is the figure which showed the relationship between the tire friction coefficient between different vehicle speeds, and a phase, (b) is the figure which showed the difference of the phase in (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Suspension characteristic estimation apparatus, 2 ... Vehicle, 6 ... Vertical acceleration sensor (vertical displacement detection means), 7 ... Longitudinal acceleration sensor (longitudinal force detection means), 8 ... ECU (vertical displacement detection means, longitudinal force detection means, estimation means).

Claims (4)

A suspension characteristic estimation device for estimating a plurality of suspension characteristics of a vehicle,
Vertical displacement detection means for detecting vertical displacement under the unsprung state of the vehicle;
A longitudinal force detecting means for detecting a longitudinal force input to the unsprung portion of the vehicle;
An estimation means for obtaining a gain and a phase based on a transfer function from the vertical displacement to the longitudinal force, and estimating the plurality of suspension characteristics based on the gain and the phase;
I have a,
The estimation means estimates a damping coefficient, a tire friction coefficient, and a vehicle height as the plurality of suspension characteristics . The estimating means estimates the vehicle height based on the gain, estimates the attenuation coefficient based on the phase when the phase increases from a predetermined set value, and calculates the damping factor when the phase decreases from a predetermined set value. The suspension characteristic estimation device according to claim 1 , wherein the tire friction coefficient is estimated based on the phase. The suspension characteristic estimation apparatus according to claim 1 , wherein the estimation means estimates the suspension characteristic based on the gain, the phase, and the phase difference obtained between different vehicle speeds. The estimating means compares the gain, the phase, and the phase difference with a predetermined set value, estimates the vehicle height based on the gain, and increases or decreases the phase from a predetermined set value. When the phase difference increases or decreases from a predetermined setting value, the attenuation coefficient is estimated based on the phase, and when the phase increases or decreases from the predetermined setting value and the phase difference is substantially the same as the predetermined threshold value. The suspension characteristic estimation device according to claim 3 , wherein a tire friction coefficient is estimated based on the phase.

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