JP3286417B2 - Vehicle steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering apparatus for a vehicle, and more particularly to a steering apparatus for changing a steering gain of a variable gear ratio device of a front wheel steering system when a tire pressure is reduced.

[0002]

2. Description of the Related Art Since it is not preferable to run a vehicle with the air pressure of tires of a vehicle lowered more than a certain level, various tire pressure alarm devices (tire pressure judgment devices) have been proposed. For example, an air pressure sensor that detects a tire air pressure of a wheel, and detects a tire air pressure by an air pressure sensor including a transmission unit attached to the wheel side and a reception unit provided on the vehicle body side, and detects any one of the wheels. 2. Description of the Related Art Tire air pressure alarm devices that output an alarm when the air pressure drops are in practical use. On the other hand, when tire pressure drops,
Since the number of rotations of the wheel with reduced air pressure increases, 4
There have been proposed, for example, ones provided with wheel speed sensors for detecting the wheel speeds of the wheels, and determining a decrease in tire air pressure based on the wheel speeds detected by the wheel speed sensors.

For example, Japanese Patent Application Laid-Open No. Sho 63-305011 discloses that the output of a wheel speed sensor of four wheels is used to calculate the sum of the wheel speeds of a pair of wheels on a diagonal line and the sum of the wheel speeds on another diagonal line. When the difference from the sum of the wheel speeds of a certain pair of wheels is equal to or greater than a predetermined value, it is determined that the air pressure of any one of the pair of wheels having the larger total wheel speed has decreased, and When the larger one of the wheel speeds of the wheels is larger than the average value of the wheel speeds of the four wheels by a predetermined value or more, it is determined that the air pressure of the wheel has decreased, and the determination result is warned. A configured tire pressure warning device is described.

On the other hand, a variable gear ratio device (commonly called VGR) capable of changing the gear ratio of the front wheel steering system changes the gear ratio (this corresponds to the steering gain) by controlling the electric actuator. This type of gear ratio variable device is conventionally known.

[0005]

Heretofore, no technique has been proposed for changing the steering gain of the variable gear ratio device when the tire pressure of any of the wheels has decreased. However, when the tire pressure is significantly reduced, at a vehicle speed other than low speed, even a small steering angle has a large effect on the behavior of the vehicle, so that the steering stability is significantly reduced. Steering performance deteriorates due to poor cutting performance. On the other hand, when the tire pressure of the front wheels decreases, the tire lateral force of the front wheels decreases and the vehicle tends to understeer, and the steering performance decreases.On the other hand, when the tire pressure of the rear wheels decreases, the rear wheels decrease. However, since the tire lateral force decreases, there is a problem that the vehicle tends to oversteer and steering stability decreases. An object of the present invention is to prevent a decrease in steering stability and secure steering performance when a tire air pressure decreases in a front wheel steering device having a variable gear ratio device.

[0006]

According to a first aspect of the present invention, there is provided a vehicle steering system including a tire air pressure judging device for judging a decrease in tire air pressure of a wheel, and a gear ratio variable device interposed in a front wheel steering system. In the vehicle, when the tire pressure determination device determines that the tire pressure has decreased, the steering angle of the wheel with respect to the steering of the steering wheel is changed by changing the gear ratio of the gear ratio variable device as compared with the case where the tire pressure is normal. A steering gain changing means for changing the steering gain to a smaller value is provided. Here, a vehicle speed detecting means for detecting a vehicle speed of the vehicle is provided,
A configuration in which the steering gain changing unit changes the gear ratio of the gear ratio variable device so that the steering angle of the wheel becomes smaller with respect to the steering of the steering wheel as the vehicle speed increases, based on the vehicle speed detected by the vehicle speed detecting unit. (Claim 2 dependent on Claim 1)
May be adopted.

[0007]

According to a third aspect of the present invention, there is provided a steering apparatus for a vehicle, comprising: a tire pressure judging device for judging a decrease in tire pressure of a wheel; and a gear ratio variable device interposed in a front wheel steering system. The air pressure determining means includes a rear wheel tire pressure determining means for determining a decrease in the rear tire pressure, and when the rear tire pressure determining apparatus determines that the rear tire pressure is low, the tire pressure is normal. And a steering gain changing means for changing the gear ratio of the variable gear ratio device so that the turning angle of the wheel becomes smaller with respect to the steering of the steering wheel.

[0009]

In the vehicle steering apparatus according to the first aspect, the steering gain changing means determines whether the tire pressure is lower than the normal tire pressure when the tire pressure determination device determines that the tire pressure has decreased. The gear ratio of the variable ratio device
As the steering angle of the wheel is reduced with respect to the steering of the steering wheel
To change. Therefore, it is possible to prevent a decrease in steering stability due to a decrease in tire pressure of any of the wheels. In particular, when the tire air pressure is significantly reduced, the behavior of the vehicle may fluctuate greatly even with a small steering angle, but this phenomenon can be reliably prevented.

Here, in the second aspect, the steering gain changing means changes the gear ratio of the gear ratio variable device to a smaller value as the vehicle speed increases, so that the operation and effect of the first aspect can be enhanced.

[0011]

In the vehicle steering apparatus according to the third aspect, the steering gain changing means may determine that the tire pressure of the rear wheel is normal when the rear tire pressure determining apparatus determines that the tire pressure of the rear wheel has decreased. The gear ratio of the gear ratio variable device is changed so that the steering angle of the wheel becomes smaller with respect to the steering of the steering wheel than in the case. When the tire pressure of the rear wheel decreases, the lateral force of the rear tire decreases and the vehicle tends to oversteer.However, by reducing the gear ratio of the variable gear ratio device, it is possible to prevent a decrease in steering stability. it can.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. This embodiment is an embodiment in which the present invention is applied to a steering device of a riding rear-wheel drive type automobile equipped with an anti-skid brake device and a tire pressure determination device. As shown in FIG. 1, in this vehicle, left and right front wheels 1 and 2 are driven wheels, left and right rear wheels 3 and 4 are driving wheels, and an output torque of an engine 5 is transmitted from an automatic transmission 6 to a propeller shaft 7, The transmission is transmitted to the left and right rear wheels 3 and 4 via the differential device 8 and the left and right drive shafts 9 and 10.

A steering system of a steering device for steering the front wheels 1 and 2 of the vehicle is provided with a steering force transmitting device 60 including a variable gear ratio mechanism as described below.
As shown in FIGS. 2 to 4, the steering force transmission mechanism 60
A handle shaft 62 having one end fixed to the center of a steering handle 61 (hereinafter, referred to as a handle) is disposed in parallel with the handle shaft 62 and operatively connected to the handle shaft 62 via a pair of input gears 63 and 64. An input shaft 65;
An output shaft 66 arranged coaxially with the input shaft 65;
It comprises a planetary gear type differential gear mechanism 67 provided between the input shaft 65 and the output shaft 66.

The output shaft 66 is connected to left and right front wheels 1 and 2 via a steering gear device (not shown) and a link mechanism including a tie rod and the like. The differential gear mechanism 67 includes a sun gear 68 fixed to the input shaft 65, a ring gear 69 fixed to the output shaft 66, and both gears 68,6.
9, three planetary pinions 70 (70a, 70b, 70c) arranged at 120-degree angular intervals
5 and a pinion carrier 72 which is rotatably fitted to the outside and carries pinions 70 via pinion shafts 71 respectively. A sector gear 73 is provided integrally with the pinion carrier 72, and a pinion 74 fixed to a rotation shaft of a stepping motor 75 is engaged with the sector gear 73.

Further, the steering force transmitting device 60 is provided with a motor control device 76 for controlling a stepping motor 75. The motor control device 76 includes a steering angle sensor 47.
From the control unit 50, the wheel speed signals of the wheel speed sensors 51 to 54, the flag signal, and the like are supplied from the control unit 50. Is stored.

Further, one end of the steering force transmitting device 60 is connected to one end of the pinion carrier 72 of the differential gear mechanism 67.
Tension spring 7 hooked on one pinion shaft 71 and the other end hooked on a pin 77 protruding from a fixed portion as appropriate.
The spring 78 urges the pinion carrier 72 to the neutral position shown in FIGS. 2 to 4 by its elastic force. The urging force of the spring 78 allows the stepping motor 75 to rotate the pinion carrier 72 around the axis, and also allows the motor 75 to rotate the pinion carrier 72.
Is set so as to restrict the unrestricted turning operation of the carrier 72 when the restraining force is lost.

Next, the operation of the above-described steering force transmitting device 60 will be described. Handle 61 while driving a car
, The rotation is transmitted from the handle shaft 62 to the input shaft 65 via the pair of input gears 63 and 64 to rotate the sun gear 68 in the differential gear mechanism 67. At this time, the motor 75 is rotationally driven by the motor control device 76, as shown in the gear ratio change control described later, and accordingly, the pinion carrier 72 is rotated via the pinion 74 and the sector gear 73. Therefore, the differential gear mechanism 67
At the same time, the sun gear 68 is rotated by an amount proportional to the steering amount of the steering wheel 61, and at the same time, the pinion carrier 7 is rotated.
2 is rotated in the same direction or in the opposite direction according to the rotation amount of the stepping motor 75.

Accordingly, the ring gear 69, that is, the output shaft 66 in the differential gear mechanism 67 is rotated by a rotation amount proportional to the steering amount of the handle 61, which is added or subtracted according to the rotation amount of the pinion carrier 72. . The front wheels 1 and 2 are steered via the steering gear device and the link mechanism according to the rotation amount of the output shaft 66. That is, the pinion carrier 72, the sector gear 73, and the pinion 74
And the stepping motor 75 and the motor control device 76 correspond to a variable gear ratio mechanism, and by appropriately controlling the rotation direction and the rotation amount of the motor 75, the rotation angle of the output shaft 66 with respect to the rotation angle of the handle 61 Can be controlled.

The pinion carrier 72 includes a spring 7
8, the urging force is set so as to allow the stepping motor 75 to rotate around the axis. When the pinion carrier 72 is driven by the stepping motor 75, the spring 78 is actuated. Extend as shown by the chain line in FIG. On the other hand, when the restraining force on the pinion carrier 72 by the stepping motor 75 is lost, the differential gear mechanism 67 generally cannot transmit the rotation of the sun gear 68 to the ring gear 69, but the biasing force of the spring 78 Are set so as to restrict the unrestricted rotation of the pinion carrier 72, so that the differential gear mechanism 67 is a fixed gear train transmitting rotation from the sun gear 68 to the ring gear 69 via the planetary pinion 70. Therefore, even when the stepping motor 75 fails, the steering force of the steering wheel 61 is applied to the front wheels 1 and 2.
It becomes possible to transmit to two sides.

Next, the brake control system will be described. Each of the wheels 1 to 4 receives a disk 11 to 14 which rotates integrally with the wheel, and receives a brake pressure to rotate the disks 11 to 14. Calipers 21 to 24 for braking
Brake devices 31 to 34 are provided, respectively.
A brake control system that operates these brake devices 31 to 34 is provided.

This brake control system includes a booster 2 for increasing the stepping force on the brake pedal 25 by the driver.
6 and a master silling 27 that generates a braking pressure according to the stepping force increased by the booster 26. A front-wheel braking pressure supply line 28 from the master sill 27 is branched into two paths, and these front-wheel branch braking pressure lines 29 and 30 are respectively connected to calipers 21 and 22 of brake devices 31 and 32 of the left and right front wheels 1 and 2. A first valve unit 36 is provided in one front-branch branch braking pressure line 29 that is connected and communicates with the brake device 31 of the left front wheel 1, and the other front-branch branch braking pressure line that communicates with the brake device 32 of the right front wheel 2. 30 is also provided with a second valve unit 37 similar to the first valve unit 36.

On the other hand, a third valve unit 43 similar to the first and second valve units 36 and 37 is provided on the rear wheel braking pressure supply line 40 from the master cylinder 27. The rear wheel braking pressure supply line 40 is branched into two paths on the downstream side of the third valve unit 43, and these rear wheel branch braking pressure lines 41, 42 are connected to the left and right rear wheels 3, 4.
Are connected to the calipers 23, 24 of the brake devices 33, 34, respectively. This brake control system variably controls the braking pressure of the braking device 31 of the left front wheel 1 via the first valve unit 36, and the braking pressure of the braking device 32 of the right front wheel 2 via the second valve unit 37. Of the left and right rear wheels 3 and 4 via the third valve unit 43
Third and third channels for variably controlling the braking pressure are provided, and the first to third channels are controlled independently of each other.

The brake control system is provided with a control unit 44 for controlling the first to third channels. The control unit 44 includes a brake switch 4 for detecting ON / OFF of the brake pedal 25.
6, a steering angle signal from a steering angle sensor 47 for detecting the steering angle of the steering wheel, and wheel speed signals from wheel speed sensors 51 to 54 for detecting the rotation speed of each wheel. The braking pressure control signals corresponding to the signals
By outputting the signals to the third valve units 36, 37, and 43, respectively, braking control (ABS control) for the slip of the left and right front wheels 1, 2 and the rear wheels 3, 4 is performed in parallel for each of the first to third channels. .

Next, the tire pressure judging device will be described. The tire pressure determination device includes four wheel speed sensors 51 to 54, an initial setting switch 55 for instructing initial setting of tire pressure determination (this is attached to an instrument panel), and an instrument. A warning lamp 56 attached to the panel, a control unit 50, and the like are provided. The control unit 50 is supplied with signals from the wheel speed sensors 51 to 54 and the initial setting switch 55, and outputs the warning lamp 56
Is driven and controlled by the control unit 50. Each of the wheel speed sensors 51 to 54 detects 48 detection units formed on the disks 21 to 24 or formed on a detection disk (not shown) provided adjacent to the disks 21 to 24 by an electromagnetic pickup. This is a configuration of

The control unit 50 includes a filter for filtering detection signals from the wheel speed sensors 51 to 54, and a circuit for shaping the waveform of the detection signal filtered by the filter.
AD converter for A / D converting various analog detection signals,
Input / output interface, CPU, ROM and RAM
In the ROM, a control program for tire pressure determination control described later is previously input and stored, and in the RAM, various memories (buffers, memories, flags, and the like) necessary for the control are stored. Counter or the like). The filter has a variable time constant, and its time constant is set to a large value in order to prevent a decrease in accuracy during high-speed running, and is set to a small value in low-speed running because accuracy is obtained.

The tire pressure determination control executed by the control unit 50 will be described below with reference to FIGS. This tire pressure determination control is for setting an initial value D0 of a later-described determination variable and an initial value H0 of a wheel speed ratio when the tire pressure is normal, such as when the tire is replaced or when the vehicle is started to be used. And an air pressure determination process for determining a decrease in tire air pressure during actual running.

Next, an initial value setting process for setting the initial value D0 of the judgment variable and the initial value H0 of the wheel speed ratio will be described.
This will be described with reference to FIG. In the figure, reference symbol Si (i = 3)
0, 31,...) Indicate each step. This initial value setting process is performed after the initial setting switch 55 is turned ON.
This is a process executed while the vehicle is running. First, it is determined whether or not the initial setting switch 55 is ON (S30). Next, when the determination is Yes, various signals such as wheel speed signals are transmitted in S31. Is read. Next, a determination is made as to whether or not the vehicle is on a low μ road (low friction road surface) (S32), a determination as to whether or not the road is rough (S33), and a determination as to whether or not the vehicle is traveling straight ahead (S34). The process shifts to S35 only when the vehicle is not traveling on a μ road, not on a rough road, and is in a straight running state. The determination of the low μ road and the determination of the bad road will be described later with reference to FIGS. 8 and 9. However, the determination as to whether or not the vehicle is in the steady traveling straight state is based on the wheel speed signals from the wheel speed sensors 51 and 52. Obtained driven wheels 1, 2
Is determined based on the wheel speed of the vehicle.

Next, in S35, wheel speed signals for 400 rotations of the wheels are read from the wheel speed sensors 513 to 54, and then the four wheels 1 to 4 are used by using the wheel speed signals.
4, the wheel speeds Vw1, Vw2, Vw3, Vw4 are calculated and stored in the memory (S36). Next, in S37, the initial value D0 of the determination variable is calculated by the illustrated formula and stored in the memory. Next, in S38, when the initial value H0 of the wheel speed ratio of the front wheel speed to the rear wheel speed is calculated by the illustrated formula and stored in the memory, the initial value setting process ends.

Next, a description will be given, with reference to FIGS. 6 and 7, of an air pressure judgment process executed during use of the automobile.
Note that reference numerals Si (i = 40, 41,...) In the figure indicate each step. After the start of the process, first, various signals (wheel speed signal, initial value D0 of determination variable, initial value H0 of wheel speed ratio, signal of flag, etc.) are read (S40), and then, whether or not the road is a low μ road is determined. (S41) and whether the road is rough (S4)
2) and a determination as to whether or not the vehicle is traveling straight ahead (S43) is executed. If the vehicle is not traveling on a low μ road, is not on a bad road, and is traveling on a steady straight road, the process proceeds to S44. The determinations in S41 and S42 will be described later with reference to FIGS. 8 and 9 in the same manner as in the above-described initial value setting processing. However, the determination in S43 is also similar to that in the initial value setting processing. , 2 wheel speeds Vw1, V
Determined based on w2. Next, in S44, the wheel speed signals for 400 rotations of the wheels are output from the wheel speed sensors 51 to 54.
Then, using the wheel speed signals, the wheel speeds Vw1, Vw2, Vw3, Vw4 of the four wheels 1 to 4 are calculated and stored in the memory (S45). The variable D is calculated by the equation shown.

Next, at S47, the judgment variable D
And the initial value D0 of the determination variable obtained by the initial value setting process and stored in the memory, the absolute value of (D−D0) is determined to be a predetermined value Δ (for example, Δ is 0.02 to 0.05). Value), and if the determination is No,
In S48, it is determined that the tire air pressure is normal, and in S40
And if the determination in S47 is Yes,
This is the case where any of the tire pressures has decreased. In this case, the process proceeds to S49 in FIG.

Here, when the tire pressure is normal,
The determination variable D is substantially equal to its initial value D0. For example, when the tire pressure of the left front wheel 1 decreases, the moving radius of the left front wheel 1 decreases, so that the wheel speed Vw1 increases and the determination variable D increases. When the tire pressure of the right front wheel 2 decreases, the wheel speed Vw2 similarly increases, and the determination variable D
Decrease. The same applies to the left and right rear wheels 3 and 4. By comparing the absolute value of (D-D0) with a predetermined value Δ, a decrease in tire air pressure can be detected.

If the determination in S47 is Yes, S49 in FIG.
, The wheel speed ratio H of the front wheel speed to the rear wheel speed
Is calculated as H = (Vw1 + Vw2) / (Vw3 + Vw4). Then, in S50, the wheel speed ratio H and the initial value H0 of the wheel speed ratio obtained in the initial value setting process and stored in the memory are used. Then, it is determined whether (H−H0) is equal to or greater than a predetermined value δ. If the determination is Yes, it is determined in S51 that the tire air pressure of the driven wheels 1 and 2 has decreased, and if the determination in S50 is No, , S53, it is determined that the tire air pressure of the driving wheels 3 and 4 has decreased.

In S52 following S51, the flag Fd indicating the driving wheel is reset to 0, and the flag Fj indicating the driven wheel is set to 1. Then, in S55, the driver is notified of a decrease in tire air pressure. Warning lamp 56 is turned on for a predetermined time (for example, 5 seconds)
Then return. In S54 following S53,
The flag Fd is set to 1 and the flag Fj is reset to 0, and thereafter, the flow shifts to S55.

Next, the low μ road determination processing in S32 and S41, which is executed by interruption processing, will be described with reference to FIG. First, a predetermined number of wheel speeds and wheel speeds are read (S110),
Next, in S111, the front wheel speeds Vw1 and Vw2 are calculated based on the wheel speed signals of the front wheels 1 and 2, respectively, and the rear wheel speed Vw is calculated based on the wheel speed signals of the rear wheels 3 and 4.
3 and Vw4 are calculated respectively, and the vehicle speed V (body speed) is calculated as an average value of the front wheel speeds Vw1 and Vw2. next,
In S112, the slip ratio SL3 of the rear wheel 3 = (Vw
3-V) / V, and the slip ratio SL4 of the rear wheel 4 = (Vw4
−V) / V is calculated.

Next, in S113, the slip ratio SL
3 and SL4 are both determined to be equal to or greater than a predetermined value SL0, and if yes, it is determined that the vehicle is traveling on a low μ road, and the flag F
When μ is set to 1 and the processing is ended, and when the determination result in S113 is No, it is determined that the vehicle is traveling on the high μ road in S115, the flag Fμ is set to 0, and the processing is ended. S3
2 and S41 are determined based on the flag Fμ.

Next, the rough road determination processing for determining whether or not the vehicle is traveling on a rough road in S33 and S42 will be described with reference to FIG. This process is executed by an interrupt process every predetermined short time. First, in S120 and S121, the wheel speeds Vw1 to Vw4 of the four wheels are calculated in the same manner as in S110 and S111, and the front wheel accelerations AVw1 and AVw2 are calculated from the change rates of the wheel speeds Vw1 and Vw2. It is determined whether or not the vehicle is in the acceleration / deceleration state based on the average wheel speeds of the four wheels (S122). When the vehicle is in the acceleration / deceleration state, the process returns to S120. Is done.

When the flag Fa is 0, the counters M and N are set to 0 in S124, the timer Tc is started after reset, and then the flag Fa is set to 1
Is set (S125), and the routine goes to S126. still,
If the determination in S123 is Yes, S123 to S12
Move to 6. In S126, it is determined whether the absolute value of the wheel acceleration AVw1 of the front wheel 1 is equal to or greater than a predetermined value Ao,
If the determination is Yes, the flow shifts to S127, where the counter M is incremented. In S128,
It is determined whether or not the absolute value of the wheel acceleration AVw2 of the front wheel 2 is equal to or greater than a predetermined value Ao. If the determination is Yes, S129
Then, the counter N is incremented.

Next, in S130, it is determined whether or not the counted time Tc of the timer Tc has become equal to or longer than a predetermined time T0. Until the predetermined time T0 elapses, the return from S130 to S120 is repeated. Predetermined time T0
Then, the process proceeds from S130 to S131, and proceeds to S13.
At 1 the flag Fa is reset to 0, then at S1
At 32, it is determined whether the count value M of the counter M is equal to or less than the predetermined value m and the count value N of the counter N is equal to or less than the predetermined value m.

When the determination in S132 is Yes, S13
4, the flag Fak is set to 0 and the process is terminated. If the determination in S132 is No, the process proceeds to S4.
At 133, the road is determined to be a bad road, the flag Fak is set to 1, and the process ends. In other words, in consideration of the fact that the wheel speeds of the driven wheels 1 and 2 tend to fluctuate when traveling on a rough road, the number of times the wheel acceleration or deceleration of each of the left and right front wheels 1 and 2 becomes abnormally large within the predetermined time T0 is determined. Counting is performed, and a rough road traveling state is determined from the count values M and N. The determinations in S33 and S42 are executed based on the flag Fak.

Next, the gear ratio change control executed by the motor control device 76 will be described with reference to FIGS. This gear ratio change control is performed when a tire air pressure drops, and the gear ratio of the variable gear ratio mechanism (that is, the steering gain) is compared with when the tire air pressure is normal.
Is a control for changing

The routine of the gear ratio change control will be described with reference to FIG. 10, but reference numeral Si (i = 60, 61,
...) show each step. While the vehicle is running, this control is always performed. First, various signals (wheel speed signal, steering angle signal, flag signal, etc.) are read (S6).
0) Next, the wheel speeds Vw1 and Vw2 of the front wheels 1 and 2 are calculated (S61). Next, the vehicle speed V is calculated as an average value of the wheel speeds Vw1 and Vw2 (S62). The steering gain Gs is calculated by applying the vehicle speed V and the steering angle θh to a map M1 shown in FIG.

The map M1 is obtained by setting the steering gain Gs (corresponding to the gear ratio of the variable gear ratio device) using the steering angle θh and the vehicle speed V as parameters when the tire pressure is normal. gain when the corner (gear ratio) Han
As the steering angle of the wheel is reduced against the dollar of the operation,
The gain (gear ratio) when the large steering angle steering handle
The turning angle of the wheels is set to be large with respect to the operation, and the gain is set so as to approach 1.0 as the vehicle speed V increases. For example, the characteristic line a is 40 km
/ H or less, and the characteristic line b is 40 to 8
It is applied to the vehicle speed range of 0 km / h, and the characteristic line c is 80 km / h
This applies to the above vehicle speed range.

[0044] In S63, as described above, is applied to the steering gain Gs is calculating the vehicle speed V and the steering angle θh in the map M1, then the flag Fd determined by the air pressure judgment control in S 64, the Fj Judge whether both are 0, and the judgment is Yes
In the case of, the tire pressure is normal (S6
5) Then, in S66, the rotation angle of the stepping motor 75 is calculated. In this case, the rotation angle of the motor 75 is calculated by applying the steering gain Gs to the map M2 shown in FIG. With respect to the vertical axis of the map M2, the rotation angle in the (+) steering angle increasing direction (the same direction) is shown.
(-) Indicates the rotation angle in the steering angle decreasing direction (reverse direction).

Next, in S67, a motor control signal is output to the drive circuit of the motor 75, and the flow returns to S60. On the other hand, when the determination in S64 is No, since the tire air pressure of any of the wheels has decreased (S68),
The coefficient k is calculated by applying the vehicle speed V to the map M3 shown in FIG. 13 (S69). Next, in S70, the steering gain GsA when the tire air pressure decreases is given by GsA = Gs
Xk is calculated, and the process proceeds to S66.

The operation of the gear ratio change control described above will be described. When the tire pressure is reduced, especially when the tire pressure is significantly reduced, the steering stability is reduced and a slight steering angle greatly affects the behavior of the vehicle. As described above, the steering gain GsA when the tire pressure does not decrease by 1.0
Since the coefficient is set by multiplying by the following coefficient k, it is possible to prevent a decrease in steering stability when the tire air pressure decreases. In particular, when the tire pressure decreases, the steering stability decreases in proportion to the increase in the vehicle speed V. However, as shown in the map M3, the coefficient k is set to decrease as the vehicle speed V increases. It is possible to reliably prevent a decrease in steering stability.

Next, two modified examples in which the gear ratio change control is partially changed will be described. The same steps as those in the flowchart of FIG. 10 are denoted by the same step numbers, and the description is omitted. 1) First Modification—See FIGS. 14 and 15 As shown in FIG. 14, when the determination in S64 is No,
Since the tire air pressure has decreased (S68), in S80, the vehicle speed V is increased to a predetermined vehicle speed V0 (for example, V0 = 40 km).
/ H) It is determined whether it is the following or not. If the determination is Yes, S
At 81, by applying the steering angle θh to the map M4 shown in FIG. 15, the steering gain GsL is calculated from the characteristic line d applied when the tire air pressure is reduced and the vehicle speed is equal to or lower than the predetermined vehicle speed. Move to S66. On the other hand, when the vehicle speed V> V0, the process proceeds to S66 via S69 and S70.

In this gear ratio change control, when the tire air pressure decreases, the turning of the steering wheel decreases at low vehicle speed and the steering performance decreases, so the map M4 is set as shown in the figure. That is, the characteristic a indicates the case where the tire air pressure is normal and the vehicle speed V indicates the steering gain Gs at or below the predetermined vehicle speed V0, and the characteristic line d of the steering gain GsL is larger than the characteristic line a. since that is set to be larger than 0, by increasing the steering gain GsL during and low speed in tire pressure drop state, as possible out to prevent deterioration in drivability.

2) Second Modification—See FIG. 16 As shown in FIG. 16, in S90 following S63 in FIG. 10, it is determined whether or not the flag Fd for the drive wheel is 1, and the determination is Yes. At this time, since the tire pressure of the rear wheel has decreased (S91), the steering gain G
sAr is set to GsAr = Gs × (1−β), and the process proceeds to S66. Here, β is a predetermined value in the range of 0 <β ≦ 1.0, whereby the steering gain when the tire pressure of the rear wheels decreases can be reduced.

On the other hand, when the determination in S90 is No, S
In 93, it is determined whether or not the flag Fj relating to the front wheel is 1; if the determination is Yes, since the tire pressure of the front wheel has decreased (S94), in S95, the steering gain GsAf becomes GsAf = Gs × (1 + α). ), And then the flow shifts to S66. Note that α is 0 <α ≦ 1.
This is a predetermined value in the range of 0, and this makes it possible to increase the steering gain when the tire pressure of the front wheels decreases.

In this gear ratio change control, when the tire pressure of the rear wheel, which is the driving wheel, decreases, the tire lateral force of the rear wheel decreases and tends to oversteer, but as described above, the steering gain GsAr = By setting Gs × (1−β), it is possible to prevent a decrease in steering stability. Also, when the tire pressure of the front wheels decreases, the lateral force of the tires of the front wheels decreases and the vehicle tends to understeer. However, as described above, by setting the steering gain GsAf = Gs × (1 + α), the steering performance may be reduced. Can be prevented.

The above-described tire pressure determination control is merely an example, and the present invention can be similarly applied to other various types of tire pressure control.
Further, the maps M1 to M4 in the gear ratio change control.
Is merely an example, and it goes without saying that various other maps can be applied.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an automobile anti-skid brake device and a tire air pressure determination device according to an embodiment.

FIG. 2 is a cross-sectional view of the steering force transmitting device of the vehicle shown in FIG.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a flowchart of an initial value setting process of the tire air pressure determination device of FIG. 1;

FIG. 6 is a part of a flowchart of an air pressure determination process of the tire air pressure determination device of FIG. 1;

FIG. 7 is the remaining part of the flowchart of the air pressure judgment process of the tire air pressure judgment device of FIG. 1;

FIG. 8 is a flowchart of a low μ road determination process of the tire air pressure determination device of FIG. 1;

FIG. 9 is a flowchart of a rough road determination process of the tire air pressure determination device of FIG. 1;

FIG. 10 is a flowchart of a gear ratio change control of the automobile of FIG. 1;

FIG. 11 is a diagram of a map M1 in which characteristics of a steering gain are set.

FIG. 12 is a diagram of a map M2 in which a relationship between a steering gain and a motor rotation angle is set.

FIG. 13 is a diagram of a map M3 in which a coefficient k is set using a vehicle speed as a parameter.

FIG. 14 is a flowchart of gear ratio change control according to a first modification.

FIG. 15 is a diagram of a map M4 in which a steering gain applied to a first modification is set.

FIG. 16 is a flowchart of gear ratio change control according to a second modification.

[Explanation of symbols]

 1, 2, front wheel 3, 4 rear wheel 47 steering angle sensor 50 control unit 51-54 wheel speed sensor 55 initialization switch 56 warning lamp 60 steering force transmission device 72 pinion carrier 73 sector gear 74 pinion 75 stepping motor 76 motor control device

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-286632 (JP, A) JP-A-62-59169 (JP, A) JP-A-63-168163 (JP, U) JP-A-63-168163 188274 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 23/00-23/08 B62D 6/00 B62D 101: 00 B62D 105: 00

Claims (3)

(57) [Claims] 1. A vehicle comprising: a tire pressure determining device for determining a decrease in tire pressure of a wheel; and a gear ratio variable device interposed in a steering system for front wheels, wherein the tire pressure determining device reduces the tire pressure. Is determined, a steering gain changing means is provided for changing the gear ratio of the gear ratio variable device so that the turning angle of the wheel becomes smaller with respect to the steering of the steering wheel than when the tire air pressure is normal. A steering device for a vehicle, comprising: 2. A vehicle speed detecting means for detecting a vehicle speed of the vehicle, wherein the steering gain changing means handles the gear ratio of the gear ratio variable device as the vehicle speed increases, based on the vehicle speed detected by the vehicle speed detecting means. 2. The steering system according to claim 1, wherein the steering angle of the wheel is changed to be smaller for the steering operation.
A vehicle steering system according to claim 1. 3. A vehicle comprising: a tire pressure determining device that determines a decrease in tire pressure of a wheel; and a gear ratio variable device interposed in a steering system of a front wheel, wherein the tire pressure determining means includes A rear wheel tire pressure determining means for determining a decrease in tire air pressure; when the rear wheel tire pressure determining device determines that the tire pressure of the rear wheel has decreased, the gear ratio is variable as compared with a case where the tire pressure is normal. A steering apparatus for a vehicle, comprising: a steering gain changing unit that changes a gear ratio of the apparatus so that a turning angle of a wheel becomes smaller than a steering of a steering wheel.