JPS63203472A - Electric power steering device for vehicle - Google Patents

Abstract

PURPOSE:To reduce the electric power consumption by providing a means to determine the target steering force based on the signal of a steering force detecting means and a means determine the upper limit steering auxiliary force based on the signal of a vehicle speed detecting means and selecting the smaller one between the upper limit steering auxiliary force and the target steering auxiliary force. CONSTITUTION:A target steering force determining means determines the target steering force on the output signal of a steering force detecting means. On the other hand, an upper limit value determining means determines the upper limit steering auxiliary force based on the output signal of a vehicle speed detecting means. These data are inputted to an auxiliary force limiting means, the smaller steering auxiliary force is selected between the upper limit steering auxiliary force and the target auxiliary force by the target steering force determining means, and the current corresponding to it is fed to a motor. Accordingly, the steering auxiliary force is limited to the upper limit steering auxiliary force corresponding to the vehicle speed or less, thus the electric power consumption of the motor can be reduced at the time of a turn with the minimum turning radius.

Description

[Detailed description of the invention] (A field of application) This invention relates to an electric power steering device for a vehicle,
Specifically, the present invention relates to an electric power steering device that limits the upper limit of the steering assist force generated by the electric motor according to the vehicle speed, thereby reducing power consumption and heat generation of electric circuit elements without impairing steering feel.

(Conventional technology) The yaw acceleration of the vehicle body during steering is affected by the vehicle speed.
The driver feels that the steering wheel does not have a sense of stability when driving at high speeds. For this reason, even among electric power steering devices in which the electric motor generates steering assist force, there are vehicle speed-sensitive types that control the current flowing to the electric motor according to the vehicle speed, with the aim of improving the steering feeling when driving at high speeds. Various proposals have been made.

Conventionally, such vehicle speed-sensitive electric power steering devices generally detect the vehicle speed as well as the manual steering force that the driver applies to the steering wheel as a steering reaction force, and detect the amount of power that the electric motor should output in response to this manual steering force. The steering assist force is determined according to the vehicle speed and the electric motor is energized. Such an electric power steering device controls the steering assist force to be outputted by the electric motor, that is, the current applied to the electric motor, to be small at high vehicle speeds, thereby imparting a large steering reaction force to the driver.

(Problems to be Solved by the Invention) However, in such conventional electric power steering devices, the control range of the steering assist force that the electric motor can output, in other words, the control range of the steering assist force that the electric motor can output is limited. The maximum value is constant regardless of the vehicle speed, and the maximum value of the steering assist force that can be output by this electric motor is set to a large value in order to easily perform stationary steering. Therefore, in this electric power steering device, when driving while maintaining the maximum steering angle such as in steady circular turning with the minimum turning radius, the electric motor is energized with the same current as during stationary steering. There is a problem in that the power consumption and heat generation of electrical equipment such as There is a problem in that when a disturbance occurs, the steering assist force fluctuates greatly and the steering feeling is impaired.

The present invention was made in view of the above-mentioned problems, and provides an electric power steering device for a vehicle that limits the maximum value of steering assist force that an electric motor can output according to vehicle speed, and reduces power consumption. The aim is to reduce the amount of heat generated by the electric circuit elements, and also to improve the steering feel.

(Means for Solving the Problems) As shown in the configuration diagram of FIG. In an electric power steering device for a vehicle that controls an electric motor based on an output signal of a force detection means and a vehicle speed detection means that detects the vehicle speed of the vehicle, a target steering force that determines a target steering force based on an output signal of the steering force detection means. a determining means, an upper limit determining means for determining an upper limit steering assist force based on an output signal of the vehicle speed detecting means, and an upper limit steering assist force determined by the upper limit determining means or an upper limit steering assist force determined by the target steering force determining means. assisting force limiting means for selecting the smaller one of the target steering assisting forces; The gist is to include: energizing means for generating the steering assist force selected by the assist force limiting means;

(Function) According to the electric power steering device for a vehicle according to the present invention, since the steering assist force generated by the electric motor is limited to the upper limit steering assist force depending on the vehicle speed, during steady circular turning at the minimum turning radius. It is possible to reduce the amount of heat generated by the electric motor, etc. by reducing the electric power consumed by the electric motor, etc., and it is also possible to reduce fluctuations in steering force when signal disturbance occurs, thereby preventing deterioration of steering feeling.

(Example) Embodiments of the present invention will be described below based on the drawings.

2 to 4 show an embodiment of the electric power steering system for a vehicle according to the present invention, in which FIG. 2 is an overall longitudinal sectional view, FIG. 3 is a block diagram, and FIG. 4 is a flowchart.

In Fig. 2, (11) is a gear case constructed by joining a plurality of members through seals, and this gear case (
11) is supported by a vehicle body (not shown). This gear case (11) has a pinion shaft (12) connected to a steering handle (not shown) on the right side of the figure, and bearings (13), (1
4) and (15) are rotatably supported. The pinion shaft (12) is composed of an upper shaft (12a) whose upper end is connected to the steering handle, and a lower shaft (12b) connected to the lower shaft (12b) for elastic relative rotational displacement by a torsion bar (not shown). 12b) and the first pinion gear (16
) is permanently installed. This first pinion gear (16)
is the first rack tooth (1) formed on the rack shaft (17).
7a) meshes with In addition, (18) is a seal interposed between the pinion shaft (12) and the upper part of the gear case (11), and (19) is the upper end of the gear case (11) from which the pinion shaft (12) protrudes. It is a dust cover.

The rack shaft (17) is supported by the gear case (11) so as to be slidable in the axial direction, and the ends protruding from both left and right ends of the gear case (11) are connected to steering wheels (not shown) via steering linkages, etc. Connected to the knuckle arm.

The rack shaft (17) has the aforementioned first rack teeth (17a) formed on the right side in FIG. 1 that mesh with the first pinion gear (16) of the pinion shaft (12), and Second rack teeth (17b) are formed on the back side on the left side in FIG. The second rack teeth (17b) mesh with a second pinion gear (20) connected to an electric motor, which will be described later.

Further, within the gear case (11), an electric motor (21) configured coaxially with the rack shaft (17) is arranged approximately at the center. The electric motor (21) includes a field magnet (22) fixed to the inner wall surface of the gear case (11), and this field magnet (22).
and a rotor (23) rotatably disposed between the rack shaft (17) and the rack shaft (17). The rotor (23) has a bearing (2
4).

(25) has a cylindrical output shaft (26) rotatably supported by the gear case (11).
) A laminated iron core (27) having a skew groove on the outer periphery and a multi-wound armature winding (28) are fixed coaxially and integrally. The armature winding (28) is connected to the output shaft (26)
It is connected to a drive circuit (32) to be described later through a commutator (29) fixedly attached to the commutator (29) and a brush (31) housed in a holder (30) and connected to and disconnected from the commutator (29).

Further, in the gear case (11), the pinion shaft (33) on the left side in FIG. 2 of the electric motor (21) is attached to a bearing (34),
A second pinion gear (20) rotatably supported by (35) and fixed to this pinion shaft (33) meshes with the second rack teeth (17b) of the rack shaft (17). There is. The pinion shaft (33) is connected to the electric motor (21)
The output shaft (26) is arranged at a position that is not parallel to and does not intersect with the output shaft (26), and a staggered gear mechanism (ske
wbevel gear) (36) so that disconnection force can be transmitted. The staggered gear mechanism (36) is a first gear mechanism fixed to the left end of the output shaft (26) of the electric motor (21).
and a second staggered bevel gear (38) fixed to the lower side of the second pinion gear (20) of the pinion shaft (33). As is well known, these staggered bevel gears (37) and (38) have tooth traces formed in the direction of the mother ship with part of the hyperboloid of rotation as the pitch plane. In addition, (39) is a spring for removing backlash of the staggered gear mechanism (36), (
40) is a rack guide mechanism that eliminates backlash between the second rack tooth (i7b) and the second pinion gear (20), and the spring (39) is a lower part that supports the pinion shaft (33). The second retainer is compressed between the retainer (41) engaged with the outerless of the bearing (35) and the adjustment bolt (42) screwed onto the gear case (11).
The staggered bevel gear (38) is connected to the first staggered bevel gear (3
7) is being pressed.

Further, on the right side in FIG. 2 inside the gear case (11), a torque sensor (43) is installed around the pinion shaft (t2).
A control circuit (44), a constant voltage circuit (45), etc. are arranged, and the aforementioned drive circuit (45) is arranged below the rack shaft (17).
32), a current detector (46), etc. are arranged.

The torque sensor (43) includes a substantially cylindrical movable iron core (47) through which the pinion shaft (12) is inserted, and a movable iron core (47).
It has a differential transformer (48) arranged around the .

The movable iron core (47) is connected to the vertical shaft (12a) of the torsion shaft (12) by the aforementioned torsion bar.

(12b) are connected to each other via a cam mechanism, and the vertical shaft (12a) is formed by elastic torsional deformation of a torsion bar.

(12b) is displaced in the axial direction according to the relative rotational displacement, that is, the steering torque. The differential transformer (48) has a control circuit (
44), and receives a pulse signal from the control circuit (44) and outputs a front signal indicating the displacement of the movable iron core (47), that is, the direction and magnitude of the steering torque, to the control circuit (44).

The control circuit (44) includes a one-chip microcomputer, etc., and is connected to the drive circuit (32) via a flexible circuit (49). In addition, the control circuit (44
), as shown in Fig. 3, the warning lamp (50) and the vehicle speed sensor (
51) and is operated by being supplied with constant voltage power from the constant voltage circuit (45). This control circuit (44) includes the aforementioned torque sensor (43) and vehicle speed sensor (51).
, current detector (46), etc. according to a predetermined program stored in a ROM etc., and outputs a pulse width modulated drive signal (PWM) to the drive circuit (32) according to the processing result.
signal) h, t, j, k and alarm lamp (
50) Turn on the power and turn it on. The drive circuit (32) has a switch circuit etc. in which four field effect transistors (FETs) are connected in a bridge shape, and is connected to the battery (53) through a pair of lead wires (54) and to the motor (21). They are connected via a line (55). This drive circuit (32
), a PWM signal is applied to the gates of the four FETs of the switch circuit, i, j, and k are manually operated, and the FETs are selectively and intermittently driven by these PWM signals, and the electric motor (21) is powered from the battery (53). supply power to As will be described in detail later, this drive circuit (32) is driven by two FETs when the signal j is received, and the current of the duty factor of the signal j is passed through the motor (21) in the negative direction. The other two FETs are driven by the signal 1+J and the electric motor (2
1) Pass the current of the duty factor of the signal in the other direction. The current detector (46) detects a current value supplied to the electric motor (21), and outputs a detection signal representing this current value to the control circuit (44). Note that (52) is a cover, and (56) is a ground wire, and the cover (52) is connected to the aforementioned vehicle speed sensor (51), warning lamp (50), and battery (53).

The specific configuration of the above-mentioned control circuit (44), drive circuit (32), etc. is described in the patent application filed in 1986 by the applicant.
Since it is described in detail in the specification of No. 1-93950, etc., the following explanation will be omitted.

Next, the operation of this embodiment will be explained with reference to the flow chart of FIG.

In this electric power steering device, when the ignition key is turned on, the microcomputer of the control circuit (44) executes a series of processes shown in the flowchart of FIG. 4 to control the drive of the electric motor (21).

First, in step P1, the microcomputer is initialized, data stored in internal registers is erased, addresses are specified, etc. Subsequently, in step P2, initial failure diagnosis is performed according to a subroutine defined elsewhere, and the process advances to step P3 only when everything is functioning normally.

In step P3, the output signal of the vehicle speed sensor (51) is read, and then, in step P4, a failure diagnosis of the vehicle speed sensor (51) is performed according to a subroutine defined elsewhere. Then, in step P4, the vehicle speed sensor (51
) is determined to be functioning normally, the process proceeds to the next step P5. In step P5, the vehicle speed V is calculated from the read output signal of the vehicle speed sensor (51), and a signal representing this vehicle speed (hereinafter referred to as vehicle speed V) is generated.

Next, in step P6, a map is searched for 1 in the vehicle speed correction component using the vehicle speed V as an address from the data table (1) shown in FIG. ) is generated. Similarly, in the following step P7, a map search of 2 for the upper limit steering assist force is performed using the vehicle speed V as an address from the data table (2) shown in FIG. The auxiliary force (referred to as 2) is generated.

Next, in step P8, the torque sensor (43)
Read the output signal of Then, in the next step P9, a failure diagnosis of the torque sensor (43) is performed according to a subroutine defined elsewhere, and only when it is determined that the torque sensor (43) is functioning normally, step P9 is performed.
Process O. In step P1G, a steering torque T, which is a manual steering force applied to the steering wheel, is calculated from the read output signal of the torque sensor (43), and a signal representing this steering torque T (hereinafter referred to as steering torque T) is calculated. generate.

This steering torque T can be positive or negative depending on the direction of action, and its absolute value represents the magnitude of the torque. Next, step p
At H, it is determined whether the steering torque T is positive or negative, and if the steering torque T is O or positive, the flag F for sign determination is set to O in step P12, and if the steering torque T is negative, step P13 In step P14, the flag F is set to 1, and the sign of the steering torque T is reversed to convert it into a positive value (absolute value).

Next, in step P15, a map search is performed for the frictional resistance component OF using the steering torque T as an address from the data table (3) shown in FIG. 8, and a signal representing the frictional resistance component DF (hereinafter referred to as the frictional resistance component DF) generate. This frictional resistance component OF corresponds to the frictional resistance of the steering force transmission system, etc., and represents the steering assist force that the electric motor (21) should output against this frictional resistance. Subsequently, in step P16, the steering torque T is corrected by the vehicle speed V by subtracting 1 from the vehicle speed correction component from the steering torque T. Then, it is determined whether the steering torque T corrected in step P17 is positive or negative, and if the steering torque T is negative, the steering torque T is determined in step P18.
is set to 0 and the process proceeds to step P19. In step P19, the steering torque T is calculated from the data table (4) shown in FIG.
A map search is performed for the road surface load component DT using the address as the signal representing this road surface load component DT (hereinafter referred to as road surface load component D).
(referred to as T). This road surface load component 1)T corresponds to the road surface resistance to the steering of the steering wheels, and represents the steering assist force that the electric motor (21) should output in response to this road surface resistance. Note that the road surface load component DT in this embodiment corresponds to the target steering force in the claims.

Subsequently, in step P20, the road surface load component DT
Determine whether the value obtained by subtracting 2 from the upper limit steering assist force is positive or negative, that is, the magnitude of the road load component DT and the upper limit steering assist force by 2,
If this value is positive, that is, the road load component DT is larger than the upper limit steering assist force by 2, then in step P21 the road load component (I
Set T as the upper limit steering assist force to 2 and proceed to step P22.
That is, this road surface load component DT is regulated by the upper limit steering assist force determined in accordance with the vehicle speed V with an upper limit of 2, and does not exceed the upper limit steering assist force of 2.

Next, in step P22, the frictional resistance component INF
and the road surface load component [IT] to determine the target steering assist force that the electric motor (21) should output. This target steering assist force represents the duty factor of the PWM signal, that is, the current applied to the electric motor (21), and as shown in FIG. 11, the vehicle speed is 09Vl, V2. V3
(0(Vl (V2 (V3) 1.: Changes with different characteristics in the corresponding range. In other words, the maximum value that the target steering assist force can take changes depending on the vehicle speed V and becomes smaller at high vehicle speeds. Therefore, By performing post-processing, it is possible to reduce the power consumed by the electric motor (21) etc. and the amount of heat generated when the vehicle is running in a steady circular turn, and also to reduce fluctuations in steering force when disturbances occur in the electrical signal. In step P23, it is determined whether or not the target steering assist force is 0. If the target steering assist force is 0, the PWM signal is activated in step P27.

The duty factors of i, j, and all are set to O and output, and the target steering assist force D J! If l<0, the value of flag F is determined in step P24. In this step P24, if the flag F is O, step P25
The duty factor of the PWM signal, t, j, is set to 1.
．． O, D, O are set and output, and if the flag F is 1, the PWM signal is output in step P28, and the duty factor *o, 1 . Set to O, D and output. Therefore, a current of duty factor D is applied to the electric motor (21) in a direction corresponding to the acting direction of the steering torque T, and the electric motor (21) outputs the target steering assist force.

Next, in step P28, the output signal of the current detector is read, and the current supplied to the electric motor (21) is calculated from the output signal of the current detector read in step P29.

Thereafter, in step P30, a failure diagnosis of the current detector is performed according to a subroutine defined elsewhere, and only when it is determined that it is functioning normally, the process from step P3 is repeated again.

As described above, the electric power steering device in this embodiment is configured such that the upper limit of the current that can be applied to the electric motor (21), that is, the steering assist force output by the electric motor (21), is reduced at high vehicle speeds according to the vehicle speed. As a result, power consumption and heat generation during steady circular turning at the minimum turning radius can be reduced, and even when the electric signal is disturbed, the fluctuation range of the steering assist force output by the electric motor (21) can be reduced. becomes smaller, which hinders the deterioration of the steering feeling. The steering torque T, which is the manual steering force applied by the driver to the steering wheel, has characteristics as shown in FIG. 13 depending on the steering load and vehicle speed, and the steering feeling is not impaired. In particular, with this electric power steering device,
Since the upper limit value of the road surface load component DT that directly contributes to the turning of the steered wheels is limited according to the vehicle speed, a better steering feeling can be obtained.

FIG. 5 shows another embodiment of the electric power steering device for a vehicle according to the present invention. Note that in this example,
The mechanical and electrical configuration is the same in the drawings as in the previous embodiment.

This embodiment executes a series of processes shown in the flowchart of FIG. However, from step P1 to step P5, from step P7 to step P15, from step P1B, and from step P21 to step P28 in FIG.
Steps PI to P5 in FIG. 4, respectively.
Step P7 to Step P15, Step P19,
These steps are the same as steps P23 to P30, and their explanation will be omitted.

In step P6, the vehicle speed correction coefficient is set to 3 using the vehicle speed V as an address from the data table (5) shown in FIG.
is searched on the map, and a signal representing 3 as the vehicle speed correction coefficient (hereinafter referred to as 3 as the vehicle speed correction coefficient) is generated. Then, in step P17, the road surface load component DT is multiplied by the vehicle speed correction coefficient by 3, and the road surface load component DT is corrected by the vehicle speed V. Next, in step P18, the corrected road surface load component DT and frictional resistance component DF are added to calculate a target steering assist force.

In the subsequent step P19, it is determined whether the value obtained by subtracting 2 from the target steering assist force to the upper limit steering assist force is positive or negative, in other words, the magnitude of the target steering assist force and the upper limit steering assist force is 2,
If the target steering assist force is larger than the upper limit steering assist force by 2, the target steering assist force is set as the upper limit steering assist force in step P20. As shown in FIG. 12, the target steering assist force changes with respect to the steering torque T in accordance with the vehicle speed V, and its maximum value is also determined in accordance with the vehicle speed V. Then, as in the embodiment described above, an intermittent current of duty factor D is applied to the electric motor (21), and the electric motor (21) outputs the target steering assist force.

The electric power steering device of this embodiment also has an electric motor (
21) Since the maximum value of the current applied to the vehicle is limited according to the vehicle speed so that it becomes smaller at high vehicle speeds, it is possible to reduce power consumption and heat generation during steady circular turning at the minimum turning radius. Furthermore, fluctuations in the output of the electric motor (21) when the electric signal is disturbed are reduced, and deterioration of the steering feeling is prevented.

In each of the embodiments described above, the target steering assist force, that is, the steering assist force output by the electric motor (21) is shown in FIGS.
Although the control is performed as shown in FIG. 2, it is also possible to control as shown in FIG. 15 or FIG. 1e. However, when the target steering assist force is controlled as shown in FIG. 16, the steering torque has the characteristics shown in FIG. 14 with respect to the steering load.

(Effects of the Invention) As explained above, according to the electric power steering device for a vehicle according to the present invention, the maximum value of the current that can be applied to the electric motor is limited according to the vehicle speed so that it becomes smaller at high vehicle speeds, so that the steady circle The power consumption of the electric motor, etc. during turning, etc. is reduced, and the amount of heat generated is also reduced.Furthermore, the fluctuation in the output of the electric motor when the electric signal is disturbed can be reduced, and the deterioration of the steering feeling can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an electric power steering device for a vehicle according to the present invention. 2 to 4 show an embodiment of the electric power steering device for a vehicle according to the present invention, in which FIG. 2 is a longitudinal sectional view of the machine, FIG. 3 is a block diagram of the electric circuit, and FIG. 4 is a flowchart. It is. FIG. 5 is a flowchart of another embodiment of the electric power steering device for a vehicle according to the present invention. FIGS. 6 to 10 are data tables used for control processing, FIGS. 11 and 12 are diagrams showing the control mode of the duty factor of the current supplied to the electric motor with respect to the steering torque, and FIGS. 13 and 14 are This figure shows the relationship between the steering load and the manual steering force, and FIGS. 15 and 16 are diagrams showing other control modes of the duty factor of the current applied to the electric motor with respect to the steering torque. 21... Electric motor 32... Drive circuit (energizing means) 43... Torque sensor (steering force detection means) 44.
...Control circuit (target steering force determining means, upper limit value determining means,
(Auxiliary force limiting means) 51...Vehicle speed sensor (vehicle speed detection means) Patent Applicant: Honda Motor Co., Ltd. Agent Patent attorney
Part 2 Patent Attorney Kuni Ohashi Patent Attorney Yuki Koyama Patent Attorney No 1) Shigeru Figure 3

Claims (1)

[Scope of Claims] An electric motor that generates a steering assist force according to an applied current is provided in a steering force transmission system, and a steering force detection means that detects the steering force of the transmission system and a vehicle speed that detects the vehicle speed. An electric power steering device for a vehicle that controls an electric motor based on an output signal of a detection means, comprising: a target steering force determining means for determining a target steering force based on an output signal of the steering force detection means; and an output signal of the vehicle speed detection means. an upper limit value determining means for determining an upper limit steering assist force based on the upper limit value determining means; and an upper limit value determining means for determining an upper limit steering assist force based on the upper limit value determining means or a target steering assist force determined by the target steering force determining means, whichever is smaller. an auxiliary force limiting means for selecting a steering auxiliary force; and a current corresponding to the steering auxiliary force selected by the auxiliary force limiting means being supplied to the electric motor to apply the steering auxiliary force selected by the auxiliary force limiting means to the electric motor. An electric power steering device for a vehicle, comprising: energizing means for generating .