JP2943273B2 - Electric power steering device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus, and more particularly, to an assist motor (electric motor) in an automobile according to an output of a torque sensor for detecting a steering torque. The present invention relates to an electric power steering apparatus that controls the output of (1) and performs power assist according to the steering torque by the motor.

(Background technology)

2. Description of the Related Art Conventionally, in an automobile, in order to reduce steering operation at the time of turning, the motor current of an assist motor is increased or decreased according to the steering torque and the vehicle speed at the time of turning, or on / off control is performed. A relatively large number of so-called vehicle speed-sensitive electric power steering devices that perform power assist in a steering direction according to a steering torque have been developed and put into practical use.

FIG. 4 shows a simplified configuration of this type of electric power steering apparatus.

In FIG. 4, the steering torque input to the steering handle 51 can be detected by a torque sensor 52 attached to a steering shaft (not shown) that is a rotation shaft of the steering handle. The output of the torque sensor and the output of the vehicle speed sensor 53 are input to a controller 55 that controls the assist motor 54. The torque of the assist motor 54 is transmitted to the reduction gear via the clutch 56.
The transmission is transmitted to a torque transmission shaft (not shown) connected to the steering gear portion 58 via a universal joint (not shown). Here, the assist motor, the clutch, and the reduction gear are actually mounted on a steering column that supports the steering shaft.

On the other hand, the steering torque of the steering handle 51 is transmitted to a torque transmission shaft (not shown) via a steering shaft (not shown). Further, the torque and the steering torque of the assist motor 54 transmitted to the torque transmission shaft are transmitted to the steering gear unit 58. This steering gear part 58
Is usually provided at the center of a tie rod connected to the left and right front wheels, and is configured by a mechanism for converting the rotational movement of the torque transmission shaft into a left and right reciprocating movement of the tie rod, for example, a rack and pinion mechanism. The tie rods are driven left and right by the transmitted torque of the motor and steering torque of the steering wheel, and the wheels (left and right front wheels) 59 are steered.

With such a configuration, by performing control in accordance with the measurement values of the torque sensor and the vehicle speed sensor, the motor current of the assist motor is increased / decreased or turned on / off to perform required power assist. The steering wheel is made larger so that light steering can be performed, the auxiliary steering force is gradually reduced as the vehicle speed increases, and the steering becomes manual at a certain speed or higher, so that stable steering performance can be obtained.

[Problems to be solved by the invention]

However, in the above-mentioned conventional example, since the command current-torque sensor output map is single as shown in FIG. 5, the force (torque) necessary for the driver's steering operation differs depending on the number of occupants. Had become.

That is, as shown in FIG. 5, the force required for steering by the driver when the number of occupants is one is T ₁ −K _T I ₁ , and the force required for steering by the driver when the number of occupants is four is: T ₂ −K _T I ₂ . Where _KT is the motor torque constant. In the conventional device, since T ₁ −K _T I ₁ −T ₂ −K _T I ₂ , the force required by the driver for steering varies depending on the number of occupants, and the steering wheel operation feeling differs. .

[Object of the invention]

The present invention has been made in view of the problems of the related art, and has an object to make the driver's steering feeling substantially the same even if the weight of the front wheels varies depending on the number of occupants and the presence or absence of luggage. It is an object of the present invention to provide an electric power steering device capable of performing the above.

[Means for solving the problem]

The present invention relates to a torque sensor for detecting a steering torque at the time of turning operation of a steering wheel, a vehicle speed sensor for detecting a vehicle speed, and increasing / decreasing or turning on / off a motor current of an assist motor according to output values of both sensors. An electric power steering apparatus having a main control unit for controlling the vehicle and performing power assist in a steering direction according to a steering torque by an output of an assist motor. A height sensor, a main controller controls a road frictional resistance estimating function for estimating a vehicle weight and a road frictional resistance applied to a front wheel based on a predetermined reference based on an output of the vehicle height sensor; Map selection for selecting a map corresponding to the road frictional resistance estimated from the torque sensor output-command current map group for each road frictional resistance value that satisfies the relationship And a target current determination function unit that determines a command current value of the assist motor based on the map selected by the vehicle speed sensor, the torque sensor, and the map selection function unit. to degrees each consisting, work and road surface frictional resistance estimation function unit and the map selection function unit, and the predetermined _{relationship, K = {(Moμθ a '} -T 0) / (Mμθ a' -T 0)} k _{+ (M-Mo) μθ a} '/ {K T (Mμθ a' -T 0)} ( where, M: vehicle weight corresponding to the output value of the vehicle height sensor, Mo: vehicle weight as a reference, K: Slope of the slope linear portion of the torque sensor output-command current map at vehicle weight M;
k: slope of the slope linear portion of the torque sensor output-command current map at vehicle weight Mo, μ: assumed road surface frictional resistance, K _T :
The motor torque constant, θ _a ': differential value of the tire steering angle with time, T ₀ : output of a torque sensor at which a command current starts flowing). This aims to achieve the above-mentioned object.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows an overall circuit configuration of an embodiment of the present invention.

This embodiment is generally configured in the same manner as the above-described conventional example, but is characterized in that the outputs of the vehicle height sensors 11A and 11B are connected to the control unit 10.

These vehicle height sensors 11A and 11B detect variations in vehicle height and output voltage signals corresponding to the detected values, respectively, and are actually mounted on the left and right front wheels, respectively.
Outputs of these vehicle height sensors 11A and 11B are output from a torque sensor 12 for detecting a steering torque input to a steering shaft.
Is input to the input circuit 3 of the main control unit 1 via the A / D converter 2. Further, an output signal of the vehicle speed sensor 13 is also input to the input circuit 3. These signals are input to the input circuit 3
Are subjected to desired processing and input to the main control unit 1.

Although the main control unit 1 is shown in FIG. 1 as a functional block for convenience of explanation, it is actually configured by a microcomputer or the like. The main control unit 1 estimates a vehicle weight including an occupant and luggage on the front wheels based on outputs of the vehicle height sensors 11A and 11B by a method described later, and a road surface friction resistance estimating function unit 1A for estimating a road surface friction resistance. A map selection function unit 1B for selecting a map corresponding to road surface frictional resistance from a torque sensor output-command current map group described later based on the estimation result,
Vehicle speed sensor 13, torque sensor 12, and map selection function unit 1B
And a target current determination function unit 1C that determines the command current value of the assist motor 14 based on the map selected in the step (1).

Then, according to the command current value of the assist motor 14 determined by the target current determination function unit 1C, the output circuit 4 of the next stage is used.
The following control is performed via the.
That is, the command current value signal output via the output circuit 4 is converted to a pulse width modulation circuit (PWM circuit) via the D / A converter 5.
The pulse width extending circuit 15 controls the duty of the assist motor 14 via a forward / reverse drive circuit 17 in accordance with a detection current of a current sensor 16 provided in the assist motor 14. When the command current value output from the main control unit 1 is substantially zero (see FIG. 2), the output circuit outputs a signal for turning off the electromagnetic clutch 18. As a result, the electromagnetic clutch 18 is turned off,
This is what is called manual steering. Further, the output circuit 4 sends a forward / reverse rotation to the forward / reverse drive circuit 17 according to the command current value.
A reverse rotation command signal is output.

Next, the principle of the estimation of the vehicle weight and the estimation of the steering wheel operating resistance using the vehicle height sensor, which are the features of the present invention, and the principle of the motor control based thereon will be described.

Here, as the vehicle height sensor value, an average value of the output values of the vehicle height sensors 11A and 11B of the left and right front wheels is used.

First, the relationship between the vehicle height sensor value and the vehicle weight M including the occupant on the front wheels and the luggage is checked by an experiment in advance, and this relationship is created on a map.

Assuming that the road friction resistance μ is a constant value, the road friction resistance D is estimated as D = μM.

When most of the steering resistance is assumed to be the road surface frictional resistance, steering resistance T _n can be expressed by T _n ≒ μMdθ / dt ....... Here, θ is the tire steering angle.

_Assuming that this T _n is equal to the torque sensor output,
The purpose of the present invention is to control the motor current of the assist motor so that the driver's steering force is kept constant irrespective of the variation in the vehicle weight applied to the front wheels.

For example, the vehicle weight applied to the front wheels is 35
Consider the case of 0kg and 450kg (light car).

FIG. 2 shows a torque sensor output-command current map when the vehicle weight applied to the front wheels is 350 kg by a solid line, and a torque sensor output-command current map when the vehicle weight applied to the front wheels is 450 kg by a dotted line. I have.

For 350 kg, the torque sensor output T _a is a _{T a = 350 × μdθ a /} dt = 350 × μθ a '....... Assist torque due to the command current I _a is a _{T a '= K T I a} ....... However, mu is assumed road surface friction resistance, K _T is a motor torque constant, the theta _a tire turning angle is _{θ a '= dθ a / dt} .

Accordingly, the torque T _d1 applied by the driver is T _d1 = T _a −T _a ′ = 350 × μθ _a ′ −K _T I _a .

In the case of 450 kg, the torque T applied by the driver
_d2 is a _{T d2 = T b -K T I} b = 450 × μθ a '-K T I b .......

Here, when the solid line slope of the second view, and _{k, T d1 = T a -T} a '= 350 × μθ a' -K T I a = 350μθ a '-K T k (350μθ a -T 0) Can be expressed as Here, I _a = k (T _a −T ₀ ).

Similarly, 'When, T _d2 = 450μθ _a' dotted slope _{k -K T k '(450μθ a} ' -T 0) and expressed. Therefore, the T _d1 = T _d2 is 'is, k' dotted slope _{k = {(350μθ a '-T} 0) / (450μθ a' -
_{T 0)} k + (100μθ} a ') / {K T (450μθ a' -T 0)} may be satisfied .... Such two torque sensor output - Using command current _{map, T a -K T I a (} D) ≒ T b -K T I b (D) ...... is established.

Similarly, the vehicle weight M of any of the front _{wheel, K = {(350μθ a '} -K O) / (Mμθ a' -T 0)}
k + (M-350) μθ a '/ {K T (Mμθ a' -T 0)} torque sensor output has an inclined linear portion of the slope K that satisfies ...... - can be determined command current map .

In this embodiment, for each vehicle weight that satisfies the condition of the above equation,
That is, it is assumed that a torque sensor output-command current map group for each road surface frictional resistance is stored in the internal memory of the main control unit 1.

Next, the control function of the main control unit 1 will be described with reference to the flowchart of FIG.

The initialization program of FIG. 3 (1) will be described.

When starting the engine, set the ignition switch to `` ON
(ON), the output signals of the vehicle height sensors 11A and 11B are input to the main control unit 1 via the A / D converter 2 and the input circuit 3 (step S101). Then, the road surface frictional resistance estimating function unit 1A of the main control unit 1 specifies the vehicle weight applied to the front wheels from the vehicle height sensor value as described above (S102), and estimates the road surface frictional resistance (S103). Next, the map selection function unit 1B of the main control unit 1 selects a map corresponding to the vehicle weight, that is, the road surface friction resistance, from a group of maps stored in the internal memory in advance (S104).

Next, the main routine of FIG. 3 (2) will be described.

When the vehicle starts running and the steering wheel is steered, the torque sensor 12 detects a steering torque (steering wheel operation resistance), and an electric signal (torque sensor output signal) corresponding thereto is sent to the main control unit 1. Entered (Step S2
01). Then, the target current determination function unit 1C of the main control unit 1 determines a command current based on the map selected in step S104 (S202), and outputs the command current to the output circuit 4 (S203). As a result, as described above, the duty control of the assist motor 14 and the on / off control of the electromagnetic clutch 18 are performed, and the power assist of the steering force of the steering wheel is performed as in the conventional case. The control operation of this main routine is repeatedly performed at every minute time Δt.

Here, when the vehicle stops and the output of the vehicle speed sensor 13 becomes zero, the interrupt start condition is satisfied, and the routine shifts to the interrupt processing subroutine shown in FIG. 3 (3).

After the start of the interruption, the output signals of the vehicle height sensors 11A and 11B are input to the main controller 1 (step S301). Then, the road frictional resistance estimating function unit 1A of the main controller 1 estimates the vehicle weight applied to the front wheels from the vehicle height sensor value (S302), and estimates the road frictional resistance (S303). Next, the map selection function unit 1B of the main control unit 1 selects a map corresponding to the vehicle weight, that is, the road surface frictional resistance from a map group stored in the internal memory in advance (S304). Then, while the interrupt condition that the output of the vehicle speed sensor 13 is zero is satisfied, the processing of steps S301 to S304 is repeated at regular intervals. Thereafter, when the vehicle starts running again and the output of the vehicle speed sensor 13 is not zero, the interruption is terminated, the process returns to the main routine, and the same control program as described above is repeated.

As described above, according to this embodiment, the vehicle weight on the front wheels is estimated and the road surface frictional resistance is estimated based on the output value of the vehicle height sensor at the initial stage before the vehicle starts traveling and every time the vehicle stops after the vehicle starts traveling. Is estimated and the corresponding torque sensor output-command current map is selected, so that the steering torque required by the driver is substantially constant regardless of the number of occupants at the start of traveling and the weight of luggage. Not only is it possible to perform steering, but even if a person gets on or off the vehicle halfway after the start of traveling and unloads the luggage, the steering torque required by the driver is almost constant regardless of the number of occupants and the weight of the luggage. It can be.

In the above description, the case of a mini car has been described as an example. However, the present invention can of course be applied to an ordinary passenger car (ordinary car) and other automobiles.
The estimated weight of 350 kg in the above equation will be changed to an appropriate value. Further, in the above-described embodiment, the case where the vehicle height sensors are provided on the left and right front wheels, respectively, and the average value of the both is used as the vehicle height sensor value is exemplified. However, it is not always necessary to provide two vehicle height sensors. Three or more may be provided. Further, the same can be achieved by using the relational expression of torque sensor output-command current for each estimated vehicle weight and road surface frictional resistance instead of the torque sensor output-command current map described above.

〔The invention's effect〕

Since the present invention is configured and functions as described above, according to this, the road surface frictional resistance estimation function unit and the map selection function unit of the main control unit function each time the vehicle speed of the vehicle becomes zero. Therefore, at the initial stage before the start of traveling of the vehicle and every time the vehicle stops after the start of traveling, the estimation of the vehicle weight applied to the front wheels and the estimation of the road surface frictional resistance are performed based on the output value of the vehicle height sensor. Sensor output-command current map to be executed is selected. For this reason, the target current determination function unit determines the command current value of the assist motor based on the vehicle speed sensor, the torque sensor, and the map selected by the map selection function unit, and controls the assist motor accordingly. The steering torque required by the driver is almost constant irrespective of the number of occupants and the weight of luggage, not only at the start, but also when a person gets on and off the vehicle and loads are unloaded. Then, the assist steering force by the assist motor is increased or decreased. Therefore, it is possible to provide an unprecedented excellent electric power steering apparatus in which the operation feeling of the steering wheel of the driver can be made substantially constant regardless of the number of occupants and the weight of luggage.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a circuit section according to one embodiment of the present invention. FIG. 2 is an explanatory diagram showing a torque sensor output-command current map used in the embodiment of FIG. FIG. 4 is a flowchart showing a main control program of a main control unit shown in FIG. 1, FIG. 4 is an explanatory view showing a configuration of a conventional speed-sensitive electric power steering apparatus, and FIG. It is explanatory drawing which shows a command current map. 1 ... Main control unit, 1A ... Road surface frictional resistance estimation function unit, 1B ...
… Map selection function, 1C …… Target current determination function, 11A,
11B: Vehicle height sensor, 12: Torque sensor, 13: Vehicle speed sensor, 14: Assist motor.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 5/04 B62D 6/00

Claims (1)

(57) [Claims] A torque sensor for detecting a steering torque when a steering wheel is turned, a vehicle speed sensor for detecting a vehicle speed, and increasing / decreasing or turning on / off a motor current of an assist motor according to output values of the two sensors. An electric power steering device having a main control unit that performs off-control, and performing power assist in a steering direction according to a steering torque by an output of the assist motor. A road height sensor for detecting a vehicle height and a road surface frictional resistance based on a predetermined reference based on an output of the vehicle height sensor; A map corresponding to the road surface frictional resistance estimated from the torque sensor output-command current map group for each road surface frictional resistance value that satisfies the predetermined relationship stored in And a target current determination function unit that determines a command current value of the assist motor based on the map selected by the vehicle speed sensor, the torque sensor, and the map selection function unit. with, each time the vehicle speed of the vehicle is zero, the road surface frictional resistance estimation function unit and the map selection function unit functions, the a predetermined _{relationship, K = {(Moμθ a '} -T 0) / _{(Mμθ a '-T 0)}} k + (M-Mo) μθ a' / {K T (Mμθ a '-T 0)} ( where, M: vehicle weight corresponding to the output value of the vehicle height sensor,
Mo: reference vehicle weight, K: inclination of the slope linear portion of the torque sensor output-command current map at vehicle weight M, k: inclination of the slope linear portion of the torque sensor output-command current map at vehicle weight Mo, μ: Assumed road surface frictional resistance, K _T : motor torque constant, θ _a ': differential value of tire steering angle with time, T ₀ : torque sensor output at which command current starts to flow). apparatus.