JP3719022B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus that assists steering by a motor.
[0002]
[Prior art]
The electric power steering apparatus detects steering torque by a torque sensor, and performs steering assist by driving a motor according to the steering torque. Here, the torque sensor detects the steering torque from the torsion amount of the torsion bar disposed between the input shaft connected to the steering steering of the vehicle and the output shaft connected to the steering mechanism. Then, the control device for the electric power steering device drives the motor to assist the steering in accordance with the detected steering torque.
[0003]
In the control of such a control device, when the steering torque is smaller than a predetermined value, a “dead zone” is generally provided so that motor control according to the steering torque is not performed. In other words, by providing a dead zone, a feeling of rigidity in the vicinity of the steering neutral at the time of middle and high speed driving (hereinafter simply referred to as “neutral rigidity”) is enhanced, and the steering feeling is enhanced.
[0004]
On the other hand, in the control device, when steering is performed by weighting the steering assist amount according to the vehicle speed, the steering is light at low speed, and on the contrary, the steering is heavy at high speed. FIG. 7A shows a control system for switching the control amount according to the setting of the above-described dead zone and the vehicle speed. The command torque map 120 is searched according to the steering torque Ts from the torque sensor, and the command torque Tm is determined and output to the node 124. Here, a dead zone is set in the command torque map 120. When the steering torque Tsa is smaller than the dead zone width, the command torque Tm is output as zero. On the other hand, the vehicle speed value from the vehicle speed sensor is weighted with reference to the weighting map 122 and output to the node 124. For example, “1” is output when the vehicle speed is 0 km / h, and “0.2” is output when the vehicle speed is 100 km / h. Then, both values are multiplied and integrated at a node 124 to obtain a command torque Tm ′ to the motor, and the motor is controlled based on this value.
[0005]
The relationship between the motor command torque Tm and the control system steering torque Ts is shown in the graph of FIG. In the graph, a vehicle speed of 0 km / h (so-called stationary) and a vehicle speed of 100 km / h are shown. As can be understood from the graph, within the dead zone, even if the steering torque Ts increases, the command torque Tm is maintained at 0 regardless of the vehicle speed. Then, after the steering torque Ts exceeds the dead zone, the command torque Tm is gradually increased. When the steering torque Ts exceeds the set value (e in the figure), the command torque Tm is increased according to the steering torque Ts.
[0006]
[Problems to be solved by the invention]
Here, the above-described dead zone width is determined based on the contradictory elements of neutral rigidity and steering feeling. In other words, if the dead zone width is increased, the neutral rigidity increases, and the steering is stabilized when traveling straight at medium and high speeds. On the other hand, when steering is performed, for example, in the case of a lane change, the steering assist is suddenly performed after the steering is started. As a result, the driver feels uncomfortable with the steering being caught. On the other hand, when the width of the dead zone is small, the neutral rigidity becomes low during high-speed driving, and the assist is started even with a small steering torque, so that the driver feels that the steering is unstable.
[0007]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power rudder that can immediately perform steering assist when assist is required while maintaining neutral rigidity of the steering. It is to provide a take-off device.
[0009]
[Means for Solving the Problems]
An electric power steering apparatus according to claim 1 , a motor for assisting steering,
A torque sensor for detecting steering torque;
An initial value holding means for holding an initial value for defining a dead zone width of the steering torque;
Motor command value storage means for storing a dead zone width and a motor command torque value for a steering torque exceeding the dead zone width;
Correction means for correcting the dead zone width of the motor command value storage means from the detected steering torque and the initial value of the steering torque;
Based on the corrected dead zone width and motor command torque value, a motor command torque corresponding to the steering torque is obtained, and a motor control means for controlling the motor, an electric power steering apparatus comprising:
The correction means narrows the dead zone width when the detected steering torque exceeds the initial value of the steering torque,
When the detected steering torque falls below the initial value of the steering torque, the dead zone width is widened.
[0010]
According to a second aspect of the present invention, the electric power steering apparatus according to the first aspect is characterized in that, in the first aspect , the correction means increases the dead band width after a certain delay time when the dead band width is increased.
[0011]
According to a third aspect of the present invention, the electric power steering apparatus according to the first aspect is characterized in that, in the first aspect , the correction means gradually widens the dead zone width when the dead zone width is increased.
[0012]
According to a fourth aspect of the present invention, there is provided an electrical power steering apparatus according to any one of the first to third aspects, wherein the correction means gradually narrows the dead band width when the dead band width is narrowed.
[0013]
According to the first aspect of the present invention, since the correction means corrects the dead band width of the motor command value storage means from the steering torque and the initial value of the steering torque, the dead band width can be adjusted to an optimum value according to the steering state. For this reason, when assist is required while maintaining neutral rigidity during steering, it is possible to immediately perform steering assist.
[0014]
According to the first aspect of the present invention, when the detected steering torque exceeds the initial value of the steering torque, the dead zone width is narrowed. Therefore, the steering assist can be started immediately when the steering is turned off and the assist is required. On the other hand, when the detected steering torque falls below the initial value of the steering torque, the dead zone width is widened. Therefore, when returning the steering, the neutral rigidity in the vicinity of the steering neutral can be immediately increased.
[0015]
According to the second aspect of the present invention, when the dead zone width is widened, it is widened after a certain delay time. Therefore, when returning the steering, the steering assist amount does not change suddenly and does not give the driver an uncomfortable feeling.
[0016]
According to the third aspect of the present invention, since the dead zone width is gradually increased, the steering assist amount does not change suddenly when returning the steering, so that the driver does not feel uncomfortable.
[0017]
In the invention of claim 4 , since the dead zone width is gradually narrowed, the steering assist amount does not change suddenly at the start of turning of the steering, and the steering person does not feel uncomfortable.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a control configuration of the electric power steering apparatus of the first embodiment. The electric power steering apparatus includes a torque sensor 12 for detecting steering torque, and a control apparatus 20 that calculates a motor command torque (steering assist amount) based on the steering torque from the torque sensor 12 and the vehicle speed from the vehicle speed sensor 14. And a motor drive circuit 30 that controls the motor M in accordance with the motor command torque from the control device 20.
[0019]
The torque sensor 12 detects a steering torque from the torsion amount of a torsion bar disposed between an input shaft connected to the steering steering of the vehicle and an output shaft connected to the steering mechanism. The control device 20 includes a CPU 22 and an interface 24 for connecting the CPU 22 to the torque sensor 12 and the vehicle speed sensor 14.
[0020]
The control system of the control device 20 and the motor drive circuit 30 is shown in the block diagram of FIG. The output (steering torque: voltage value) from the torque sensor 12 is output to the phase compensation means 44 via the filter circuit 42 that removes noise and performs A / D conversion. The phase compensation means 44 advances the phase by differentiating the detected value to compensate for the steering assist delay. That is, if the command value is calculated based on the detected value, it takes a certain time to complete the calculation, and this fixed time is a delay of the command value with respect to the detected value. The steering assist cannot be properly controlled. For this reason, the phase compensation means 44 advances the phase of the steering torque Ts.
[0021]
On the other hand, the vehicle speed value from the vehicle speed sensor is waveform-shaped by the vehicle speed pulse detecting means 60 and weighted according to the vehicle speed by the weighting function by the vehicle speed weight function determining means 62. That is, the weighting function map 62A shown in FIG. 5A is stored in the ROM or the like of the CPU 22, and by searching the stored map according to the vehicle speed, for example, when the vehicle speed is 0 km / h. “1” is output, and “0.2” is output at 100 km / h.
[0022]
The assist torque determination means 46 determines the assist amount by the motor M from the steering torque Ts from the phase compensation means 44 and the weight value Wa from the vehicle speed weight function determination means 62. That is, the assist torque determining means 46 has a function of a steering torque Ts-motor command torque Tm map 62A and a node 46B shown in FIG. 5A and corresponds to the inputted steering torque Ts. The motor command torque Tm is obtained by searching the map, and at the node 46A, the searched motor command torque Tm and the weight value Wa from the vehicle speed weight function determining means 62 are integrated, that is, the motor command torque Tm is corrected by the vehicle speed. The corrected motor command torque Tm ′ is output. As will be described later, in the present embodiment, unlike the prior art described above with reference to FIG. 7B, the assist torque determination means 46 enables optimal control by changing the dead zone. .
[0023]
The current command determining unit 48 determines a current command value for causing the motor M to generate the motor command torque Tm ′ from the assist torque determining unit 46. This current value is output to the amplifying means 50 via a node 49 that feeds back the motor current. The amplification means 50 amplifies the input value and outputs it to the PWM circuit 52. The PWM circuit 52 performs PWM control for turning on and off a current from a battery (not shown) according to the value output from the amplifying means 50, generates torque according to the motor command torque Tm ', and performs steering. Assist.
[0024]
1 functions as the filter circuit 42, the phase compensation means 44, the assist torque determination means 46, the vehicle speed pulse detection means 60, and the vehicle speed weight function determination means 62 described above, and the current command determination means 48. The motor drive circuit 30 includes a node 49, an amplification unit 50, and a PWM circuit 52.
[0025]
Subsequently, the calculation processing of the motor command torque by the CPU 22 of the control device 20 will be described with reference to the flowcharts of FIGS. 3 and 4 and FIG. FIG. 5B shows only the first quadrant of the map 46A in FIG. 5A in an enlarged manner.
[0026]
FIG. 3 shows an initial setting process when the CPU 22 starts up. First, the steering torque default value Ts1 ′ of the dead zone width of the steering torque Ts is stored (S10). Here, the range from 0 to b shown in FIG. 5B is read as the dead zone width Ts1, and this value is stored as the default value Ts1 ′ = Ts1. To be precise, the default value on the third quadrant side of the map 46A shown in FIG. 5A is also stored, but for convenience of explanation, only the right-hand steering is described. Subsequently, the dead zone change amount Tsd is read (S12). Here, the dead zone change amount Tsd indicates a change amount when changing the width of the dead zone, as shown in FIG. Therefore, the dead zone change amount Tsd is larger than 0 and smaller than the above-mentioned dead zone width default value Ts1 ′ = Ts1.
[0027]
Next, the calculation processing of the motor command torque Tm ′ at the normal time by the CPU 22 will be described with reference to the flowchart of FIG.
First, the CPU 22 reads the steering torque Ts from the torque sensor 12 (S22). Next, it is determined whether the steering torque Ts exceeds the dead zone width Ts1 ′ (S24). Here, as long as the steering is not cut and the steering torque Ts does not exceed the dead zone width Ts1 ′ (No in S24), the process proceeds to step 28 through the process of step 32 and the determination of step 34: No. The motor command torque Tm is calculated from the steering torque Ts by the map processing of the map 46A shown in FIG. Here, “0” is calculated because it is within the dead zone. Then, the value of “0” is weighted according to the vehicle speed with reference to the map 62A having the contents shown in FIG. 5A, that is, according to the motor command torque Tm and the vehicle speed calculated in step 28. The motor command torque Tm ′ is calculated by multiplying the weighting value Wa. Here, when driving straight, the width of the dead zone is maintained wide, so that the motor assist is neglected, the neutral rigidity at the time of middle and high speed driving is increased, and the steering feeling is improved.
[0028]
Next, the flow of processing when steering is started will be described. When the steering is turned, the torsion bar connected to the steering side is twisted, and the steering torque Ts detected by the torque sensor 12 exceeds the dead band width Ts1 ′ (S24 is Yes), the process proceeds to step 26. Change (narrow) the deadband width. That is, the dead zone width Ts1 is set to a value obtained by subtracting the dead zone change amount Tsd from the default value Ts1 ′. As a result, the dead zone width Ts1 is narrowed to a range indicated by 0 to a in FIG. As a result, in step 28, the motor command torque Tm is calculated from the steering torque Ts by map processing along the broken line indicated by a-cd in FIG. Then, the calculated value is weighted according to the vehicle speed, and is output as a motor command torque Tm ′ (S30). Here, when the steering torque Ts exceeds the default value Ts1 ′ of the dead zone, the dead zone width is narrowed. Therefore, when the steering is started and the assist is required, the steering assist can be started immediately.
[0029]
Next, a process for returning the steering to the neutral position will be described. When the steering is returned, the twist of the torsion bar is returned, and the steering torque Ts does not exceed the dead band width Ts1 ′ (No in S24), the process proceeds to step 32, and reading of the counter by the timer interruption of the CPU 22 is started. Here, the CPU 22 increments by one for every 50 ms interrupt timing. Then, it is determined whether the count value has reached N (here, 10) (S34). Here, until the count value reaches N (10), that is, until the steering is returned and 500 ms elapses after the steering torque Ts decreases (No in S34), the process proceeds to step 28, and the narrow dead zone described above is reached. Continue processing at.
[0030]
On the other hand, when the steering is returned and 500 ms elapses after the steering torque Ts decreases (Yes in S34), the dead band width Ts1 (range from 0 to a in FIG. 5B) is set to the default value Ts1 ′ (from 0 in FIG. 5). (range b) (S36), the counter of the CPU 22 is reset (S38). That is, in this process, the width of the dead zone returns (expands) to the original value. In step 28, the motor command torque Tm is calculated from the steering torque Ts by map processing along the broken line indicated by bcd in FIG. Then, the calculated value is weighted according to the vehicle speed and output as a motor command torque Tm ′ (S30). When returning the steering, a neutral rigidity can be established in order to widen the dead zone width when the steering torque falls below the default value of the steering torque.
[0031]
In the first embodiment, when widening (returning) the dead zone width, the dead zone width is widened after a certain delay time. Therefore, when the steering wheel is returned, the steering assist amount changes suddenly, giving the driver a sense of incongruity. There is no.
[0032]
Next, a second embodiment of the present invention will be described. Since the second embodiment is the same except for the calculation process of the motor command torque described above with reference to FIG. 4 of the first embodiment, only the calculation process of the motor command torque will be described with reference to FIG. .
In the first embodiment described above, when the dead zone is narrowed, it is narrowed immediately, and when it is widened, it is spread after a certain delay time. On the other hand, in the second embodiment, when the width of the dead zone is changed, that is, when it is narrowed, it is gradually performed when it is widened. This process will be described.
[0033]
First, processing when the steering is started will be described. When the steering is turned off and the steering torque Ts exceeds the dead zone width Ts1 ′ (Yes in S24), the process proceeds to step 52, and it is determined whether the dead zone width Ts1 is reduced to a value obtained by subtracting the dead zone change amount Tsd from the default value Ts1 ′. to decide. Here, before narrowing to this value (No in S52), the process proceeds to step 54, and the width of the dead zone is slightly narrowed. That is, the dead zone width Ts1 is set to a value obtained by subtracting the dead zone change amount dTsd (a value about 1/10 of Tsd) from the current dead zone Ts1. Then, the process of narrowing the dead zone change amount dTsd is repeated, and when the dead zone width Ts1 narrows to a value obtained by subtracting the dead zone change amount Tsd from the default value Ts1 ′ (Yes in S52), the process immediately proceeds to step. Here, when the steering torque Ts exceeds the default value Ts1 ′ of the dead zone width, the dead zone width is gradually narrowed, so that the steering assist amount does not suddenly change at the start of turning the steering wheel, so that the driver does not feel uncomfortable. .
[0034]
Next, a process for returning the steering to the neutral position will be described. When the steering is returned and the steering torque Ts does not exceed the dead zone width Ts1 ′ (No in S24), the process proceeds to step 56, and it is determined whether the dead zone width Ts1 has increased to the default value Ts1 ′. Here, before spreading to this value (No in S56), the process proceeds to step 58, and the width of the dead zone is slightly increased. That is, the dead zone width Ts1 is set to a value obtained by adding the dead zone change amount dTsd (a value about 1/10 of Tsd) to the current dead zone value Ts1. Then, the process of increasing the dead zone change amount dTsd is repeated, and when the dead zone width Ts1 increases to the default value Ts1 ′ (Yes in S56), the process immediately proceeds to step. Here, in the electric power steering apparatus of the second embodiment, when the steering torque Ts falls below the default value Ts1 ′ of the dead band width, the dead band width is gradually widened. The amount does not change suddenly and does not give the driver a sense of incongruity.
[0035]
In the above-described embodiment, the same default value is used as a reference when the dead zone is widened or narrowed. However, it is also possible to set different default values depending on whether the dead zone is widened or narrowed.
[0036]
【The invention's effect】
As described above, according to the present invention, since the dead zone width is corrected from the initial values of the steering torque and the dead zone width, the dead zone width can be adjusted to an optimum value according to the steering state. For this reason, when assist is required while maintaining neutral rigidity during steering, it is possible to immediately perform steering assist.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a control configuration of an electric power steering apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram of a control system of a control device and a motor drive circuit.
FIG. 3 is a flowchart showing an initial setting process of a CPU.
FIG. 4 is a flowchart showing a calculation process of a motor command assist value of a CPU.
5A is an explanatory diagram showing the contents of a map held in the assist torque determining means, and FIG. 5B is a steering torque-motor command torque in FIG. 5A. It is explanatory drawing which expands and shows the 1st quadrant of a map.
FIG. 6 is a flowchart showing a calculation process of a motor command torque of a CPU of the electric power steering apparatus according to the first embodiment of the present invention.
FIG. 7 (A) is an explanatory view showing a control system for setting a dead zone and switching a control amount according to the vehicle speed of an electric power steering apparatus according to the prior art, and FIG. 7 (B). FIG. 5 is an explanatory diagram showing a relationship of motor command torque with respect to steering torque.
[Explanation of symbols]
12 Torque sensor 14 Vehicle speed sensor 20 Control device 22 CPU
30 motor drive circuit 42 filter circuit 44 phase compensation means 46 assist torque determination means 46A motor command torque value map (motor command value storage means)
48 Current command determination means 52 PWM circuit 60 Vehicle speed pulse detection means 62 Vehicle speed weight function determination means M Motor S22 Initial value holding means S26 Correction means S28 Motor control means

Claims (4)

A motor to assist steering;
A torque sensor for detecting steering torque;
An initial value holding means for holding an initial value for defining a dead zone width of the steering torque;
Motor command value storage means for storing a dead zone width and a motor command torque value for a steering torque exceeding the dead zone width;
Correction means for correcting the dead zone width of the motor command value storage means from the detected steering torque and the initial value of the steering torque;
An electric power steering apparatus comprising: motor control means for determining a motor command torque corresponding to a steering torque based on the corrected dead zone width and motor command torque value, and controlling the motor;
The correction means narrows the dead zone width when the detected steering torque exceeds the initial value of the steering torque,
Said detected when the steering torque is below the initial value of the steering torque, an electric power steering apparatus you characterized in that widening the dead zone width. Wherein the correction means, when expanding the dead zone width, the electrically-powered steering apparatus according to claim 1, characterized in that widening the dead zone width from at a predetermined delay time. 2. The electric power steering apparatus according to claim 1 , wherein the correction means gradually widens the dead zone width when the dead zone width is widened. The electric power steering apparatus according to any one of claims 1 to 3 , wherein the correction means gradually narrows the dead zone width when narrowing the dead zone width.

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