JP2019137163A - Slip rate calculation device - Google Patents

Abstract

To calculate an accurate slip rate in a four-wheel drive vehicle.SOLUTION: An ECU 12 has: front wheel friction coefficient calculation means 24 that calculates front wheel friction coefficient μf; rear wheel friction coefficient calculation means 26 that calculates a rear wheel friction coefficient μr; front rear wheel speed difference calculation means 28 that calculates a front rear wheel speed difference ΔN; and slip rate calculation means 30 that calculates respective slip rates S of the front and rear wheels on the basis of the front wheel friction coefficient μf, the rear wheel friction coefficient μr, and the front rear wheel speed difference ΔN. When the front wheel friction coefficient μf is greater than the rear wheel friction coefficient μr, the slip rate calculation means 30 calculates the slip rate S by using μr×ΔN/(μf-μr)+ΔN. When the rear wheel friction coefficient μr is greater than the front wheel friction coefficient μf, the slip rate calculation means calculates the slip rate S by using μf×ΔN/(μr-μf)+ΔN.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a slip ratio calculating device that calculates a slip ratio of front and rear wheels in a vehicle.

  In the control of the vehicle drive system, for example, when performing traction control, it is necessary to obtain the slip ratio of the drive wheels. In Patent Document 1, for a two-wheel drive vehicle, the driven wheel speed Vf is calculated in proportion to the rotational speed of the driven wheel, and the driving wheel speed Vr is calculated in proportion to the rotational speed of the driving wheel. The slip ratio of the drive wheel is calculated according to the speed difference. That is, since slip does not occur in the driven wheel, Vf can be regarded as the vehicle speed, and the slip ratio is calculated based on this.

JP 7-218519 A

  Since the vehicle targeted in Patent Document 1 is a two-wheel drive vehicle, the slip ratio of the drive wheel is calculated on the assumption that no slip occurs in the driven wheel. However, in the case of a four-wheel drive vehicle, the front and rear wheels are calculated. In both cases, a driving force is applied and slipping may occur. For this reason, it is difficult to accurately calculate the slip ratio.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a slip ratio calculation apparatus that can accurately determine a slip ratio in a four-wheel drive vehicle.

  In order to solve the above-described problems and achieve the object, a slip ratio calculating device according to the present invention includes a front wheel friction coefficient calculating means for calculating a front wheel friction coefficient, and a rear wheel friction coefficient calculating means for calculating a rear wheel friction coefficient. Front and rear wheel speed difference calculating means for calculating front and rear wheel speed differences; front wheel friction coefficient calculated by front wheel friction coefficient calculating means; rear wheel friction coefficient calculated by the rear wheel friction coefficient calculating means; and Slip ratio calculating means for calculating the slip ratio of the front and rear wheels based on the front and rear wheel speed difference calculated by the front and rear wheel speed difference calculating means, wherein the slip ratio calculating means has the front wheel friction coefficient as the When the rear wheel friction coefficient is larger than the rear wheel friction coefficient, the slip ratio S is calculated by using rear wheel friction coefficient x front and rear wheel speed difference / (front wheel friction coefficient-rear wheel friction coefficient) + front and rear wheel speed difference. But Serial When greater than the front wheel friction coefficient, the front-wheel friction coefficient × the front and rear wheel speed difference / slip ratio S - and calculates using (rear wheel friction coefficient front wheel friction coefficient) + the front and rear wheel speed difference.

  In the slip ratio calculating apparatus according to the present invention, the slip ratio can be accurately obtained in a four-wheel drive vehicle using the front wheel friction coefficient, the rear wheel friction coefficient, and the front and rear wheel speed differences.

FIG. 1 is a side view of a vehicle equipped with an ECU that is a slip ratio calculating apparatus according to the present embodiment. FIG. 2 is a block diagram showing an ECU that is a slip ratio calculating apparatus according to the present embodiment and its connection elements. FIG. 3 is a flowchart showing the processing contents in the ECU. FIG. 4 is a graph showing the relationship between the slip ratio and the friction coefficient for each road surface condition. FIG. 5 is a graph in which a part of the range in which the slip ratio in FIG. 4 is very small is enlarged.

  Hereinafter, an embodiment of a slip ratio calculating device according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

  As shown in FIG. 1, the embodiment of the slip ratio calculating device according to the present invention is realized as an ECU (Electronic Control Unit) 12 mounted on a four-wheel drive vehicle 10. The ECU 12 is mainly composed of a microcomputer having a CPU (Central Processing Unit), a RAM (Random Access Memory) and the like. The ECU 12 performs calculations using the input data and data and programs stored in advance, and outputs the calculation results as command signals. The ECU 12 may be realized by software, may be realized by hardware such as an IC (Integrated Circuit), or may be realized by using software and hardware in combination.

  The vehicle 10 generates driving forces for the front wheels Tf and the rear wheels Tr, respectively. Since the driving force is transmitted to the front wheel Tf and the rear wheel Tr, a slight slip occurs. For example, when the vehicle 10 performs traction control, it is necessary to obtain the slip rate S, and in order to obtain the slip rate S, an accurate vehicle speed at that time is necessary. However, since there is no driven wheel in the vehicle 10, the exact vehicle speed at that time cannot be obtained. In contrast, the ECU 12 can calculate the slip ratio S by the following means.

  As shown in FIG. 2, an acceleration sensor 14, a front wheel speed sensor 16, and a rear wheel speed sensor 18 are connected to the ECU 12. The acceleration sensor 14 detects the acceleration G of the vehicle 10. The front wheel speed sensor 16 detects the front wheel speed Nf of the front wheel Tf. The rear wheel speed sensor 18 detects the rear wheel speed Nr of the rear wheel Tr. Sensors for detecting the rotational speeds of the front wheel Tf and the rear wheel Tr may be provided for all four wheels. In addition, the engine 12 (engine) total driving force 33 and a deceleration signal 35 are input to the ECU 12. The ECU 12 is connected to the engine control unit 20, the brake control unit 22, the 4WD control unit 37, and the torque vectoring control unit 39, and performs traction control by adjusting engine output and braking force, For example, torque vectoring is performed for controlling and distributing torque to drive wheels. The sensors and control objects shown in FIG. 2 are only representative, and other sensors and control objects may be connected to the ECU 12.

  The ECU 12 includes a front wheel friction coefficient calculation means 24, a rear wheel friction coefficient calculation means 26, front and rear wheel speed difference calculation means 28, a slip ratio calculation means 30, and a traction control unit 32. The front wheel friction coefficient calculating means 24 is a part for calculating the front wheel friction coefficient μf. The rear wheel friction coefficient calculating means 26 is a part for calculating the rear wheel friction coefficient μr. The front-rear wheel speed difference calculating means 28 is a part for calculating the front-rear wheel speed difference ΔN. The slip ratio calculating means 30 calculates the slip ratio S. The traction control unit 32 performs traction control based on the slip rate S obtained by the slip rate calculating means 30. The slip ratio calculating means 30 corresponds to step S5 and step S6 described later.

  The ECU 12 calculates the slip ratio S based on the procedure shown in FIG. First, in step S1, it is checked whether or not the vehicle speed V at that time satisfies V> 0 Km / h. If V> 0 Km / h, the process proceeds to step S2, and if V = 0, step S1 is continued as it is and waits. Even if the vehicle speed V is not an accurate value to some extent, for example, a numerical value represented by a speedometer may be used.

  In step S2, it is checked whether the driving force distribution to the rear wheel Tr is larger than 0 N · m. If the driving force distribution is greater than 0 N · m, the process proceeds to step S3, and if not, the process proceeds to step S5.

  In step S3, it is checked whether the driving force coefficients of the rear wheel Tr and the front wheel Tf are larger than the driving force threshold value. If it is larger than the coefficient threshold value, the process proceeds to step S4, and if not, the process proceeds to step S5. The driving force coefficient corresponds to a rear wheel friction coefficient μr and a front wheel friction coefficient μf described later.

  In step S4, it is checked whether or not the condition that the front-rear wheel speed difference ΔN is larger than the first threshold and smaller than the second threshold is satisfied. If this condition is satisfied, the process proceeds to step S6. If not satisfied, the process proceeds to step S5.

In steps S5 and S6, the slip ratio S is calculated. In step S5, the slip ratio S is calculated. In step S6, the slip ratio S is calculated. The first calculation method performed in step S5 is the same calculation method as the conventional one, and is based on the following formula (1).
S = (front wheel rotational speed Nf−rear wheel rotational speed Nr) / front wheel rotational speed Nf (1)

  This equation (1) is a calculation performed on the assumption that there is no slip in the front wheel Tf, and is performed when the second calculation method in step S6 described below cannot be applied. The calculation accuracy of the slip ratio S is preferably performed by the second calculation method rather than the first calculation method.

  Next, the second calculation method performed in step S6 will be described. In the second calculation method, formula (2) and formula (3), which will be described later, are used. First, the basis for calculating these formula (2) and formula (3) will be described. FIG. 4 is a graph showing the relationship between the slip ratio S and the friction coefficient μ. Note that the friction coefficient μ is a parameter indicating the ratio of the driving force F to the load W, and therefore can be called a driving force coefficient. Therefore, in FIG. 4 and FIG. 5, the vertical axis indicating the friction coefficient μ is expressed as a driving force coefficient. The horizontal axis indicates the slip ratio S and increases toward the right. The vertical axis represents the friction coefficient μ and increases upward.

  As shown in FIG. 4, the relationship between the slip ratio S and the friction coefficient μ varies depending on the type of road surface on which the vehicle travels. Graph 40 is for dry asphalt, graph 42 is for asphalt wet with a thin water film, graph 44 is for asphalt wet with a thick water film, and graph 46 is for fresh snow. Graph 48 is for solid snow, and graph 50 is for smooth ice. As can be seen from FIG. 4, the range 52 in which the slip rate S is 10% or less can be regarded as a substantially linear change region in each of the graphs 40 to 50. In the present embodiment, this linear change region is a region for obtaining the slip ratio S by correction. When the slip ratio S exceeds 10%, the second calculation method in step S6 is not appropriate, and another calculation method is applied.

  FIG. 5 is an enlarged view of a part of the range 52 in FIG. Here, the slip ratio S is about 0 to 0.03, which is a sufficiently linear region. The slope of the graph 40 varies depending on the friction coefficient μ of the road surface. In the case shown in FIG. 5, when μ = 1, the slip ratio S = 0.03. Moreover, although the graph 40 in FIG. 5 is illustrated here, the same applies to the other graphs 42 to 50. In FIG. 5, Sr is the rear wheel slip ratio, Sf is the front wheel slip ratio, point Pr shows the behavior of the rear wheel, point Pf shows the behavior of the front wheel, μf shows the front wheel friction coefficient, and μr is The rear wheel friction coefficient is shown. Here, either the rear wheel slip ratio Sr or the front wheel slip ratio Sf can be expressed as a front-rear wheel speed difference ΔN with the other as a reference. Here, Sf = ΔN.

  Since the graph 40 is sufficiently linear and can be regarded as a straight line, μr: μf = Sr: (Sr + ΔN), that is, μf × Sr = μr × (Sr + ΔN) according to the similarity law. When this equation is modified, the rear wheel slip ratio Sr is expressed as Sr = μr × ΔN / (μf−μr). On the other hand, since the slip ratio S to be obtained is the sum of the rear wheel slip ratio Sr and the front wheel slip ratio Sf, S = Sr + Sf = Sr + ΔN, and the following equation (2) is established.

S = Rear wheel friction coefficient μr × Front wheel speed difference ΔN / (Front wheel friction coefficient μf−Rear wheel friction coefficient μr) + Front wheel speed difference ΔN (2)
This equation (2) is established when the front wheel friction coefficient μf is larger than the rear wheel friction coefficient μr. Conversely, when the rear wheel friction coefficient μr is larger than the front wheel friction coefficient μf, the following equation (3) is established on the same basis.

  S = front wheel friction coefficient μf × front and rear wheel speed difference ΔN / (rear wheel friction coefficient μr−front wheel friction coefficient μf) + front and rear wheel speed difference ΔN (3)

  The front wheel friction coefficient μf and the rear wheel friction coefficient μr used in the expressions (2) and (3) are obtained as follows. First, a front wheel load Wf and a rear wheel load Wr (see FIG. 1) are obtained from the acceleration G. Further, a front wheel driving force Ff and a rear wheel driving force Fr are obtained. These front wheel driving force Ff and rear wheel driving force Fr are obtained as values from which inertia loss is removed.

  Further, the friction coefficient μ is obtained from the relational expression F = μW of the friction coefficient μ, the load W, and the driving force F, that is, μ = F / W. Specifically, the front wheel friction coefficient μf is determined individually as μf = Ff / Wf, and the rear wheel friction coefficient μr is determined as μr = Fr / Wr. This calculation is performed by the front wheel friction coefficient calculation means 24 and the rear wheel friction coefficient calculation means 26.

  The front and rear wheel speed difference ΔN is obtained by the front and rear wheel speed difference calculating means 28 as a difference between the front wheel speed Nf and the rear wheel speed Nr. These front wheel friction coefficient μf, rear wheel friction coefficient μr, and front and rear wheel speed difference ΔN are substituted into equations (2) and (3), and the slip ratio S is obtained. The obtained slip ratio S is used by the traction control unit 32, for example.

  As described above, according to the ECU 12 as the configured slip ratio calculating device, Expression (2) and Expression (3) are obtained by using the characteristic that the slip ratio S is proportional to the friction coefficient μ in the minute range 52. Since it is established, the slip ratio S can be accurately calculated by the equations (2) and (3). Further, according to the ECU 12, the slip ratio S can be accurately obtained even in a four-wheel drive vehicle having no driven wheel.

  The present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be freely changed without departing from the gist of the present invention.

10 Vehicle 12 ECU (slip rate calculation device)
24 front wheel friction coefficient calculating means 26 rear wheel friction coefficient calculating means 28 front and rear wheel speed difference calculating means 30 slip ratio calculating means Ff front wheel driving force Fr rear wheel driving force Nf front wheel speed Nr rear wheel speed S slip ratio Sf front wheel slip Rate Sr Rear wheel slip ratio Tf Front wheel Tr Rear wheel Vf Driven wheel speed Vr Drive wheel speed Wf Front wheel load Wr Rear wheel load μf Front wheel friction coefficient μr Rear wheel friction coefficient ΔN Front wheel speed difference

Claims (1)

Front wheel friction coefficient calculating means for calculating a front wheel friction coefficient;
Rear wheel friction coefficient calculating means for calculating a rear wheel friction coefficient;
Front and rear wheel speed difference calculating means for calculating front and rear wheel speed differences;
Based on the front wheel friction coefficient calculated by the front wheel friction coefficient calculation means, the rear wheel friction coefficient calculated by the rear wheel friction coefficient calculation means, and the front and rear wheel speed differences calculated by the front and rear wheel speed difference calculation means. Slip ratio calculating means for calculating the slip ratio of the front and rear wheels;
Have
The slip ratio calculating means includes
When the front wheel friction coefficient is greater than the rear wheel friction coefficient, the slip ratio S is calculated using the following formula: rear wheel friction coefficient × front and rear wheel wheel speed difference / (front wheel friction coefficient−rear wheel friction coefficient) + front and rear wheel speed difference. ,
When the rear wheel friction coefficient is larger than the front wheel friction coefficient, the slip ratio S is calculated using the following formula: front wheel friction coefficient × front and rear wheel wheel speed difference / (rear wheel friction coefficient−front wheel friction coefficient) + front and rear wheel speed difference. A slip ratio calculating device characterized by the above.

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