JP3286414B2 - Tire pressure warning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire pressure warning device, and more particularly to a device capable of determining a decrease in tire pressure of all wheels in addition to a decrease in tire pressure of some wheels.

[0002]

2. Description of the Related Art Since it is not preferable to run a vehicle with the tire pressure of a vehicle lowered to a certain degree or more, various tire pressure alarm devices have been proposed. For example, when the tire pressure is detected by a sensor to determine a decrease in the tire pressure, or when the tire pressure decreases, the number of rotations of the wheel with the decreased pressure increases, so that the wheel speeds of the four wheels are respectively adjusted. There has been proposed a device provided with a wheel speed sensor for detecting, and determining a decrease in tire air pressure based on the wheel speed detected by the wheel speed sensor.

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.

[0004]

The conventional tire pressure alarm system basically detects a decrease in air pressure using wheel speed data in a steady running state in which the vehicle travels straight at a substantially constant speed. Therefore, when the air pressures of all the wheels are reduced, there is a problem that the decrease in the tire pressure cannot be detected reliably. An object of the present invention is to provide a tire pressure alarm device that can determine not only a decrease in tire pressure of some wheels but also a decrease in tire pressure of four wheels.

[0005]

According to a first aspect of the present invention, there is provided a tire pressure judging device for detecting a decrease in tire air pressure by using detection signals of four wheel speed sensors of a vehicle and outputting an alarm. A wheel speed sensor for respectively detecting the wheel speeds of four wheels of the vehicle, acceleration / deceleration detection means for detecting a predetermined acceleration / deceleration state of the vehicle, and a wheel acceleration / deceleration state detected by the acceleration / deceleration detection means. Based on the output from the speed sensor , the front and rear wheel speed ratio on the left and the front and rear wheels on the right
A wheel speed ratio, and a tire pressure determining means for determining a decrease in tire air pressure using these front and rear wheel speed ratios.
Setting each value as the initial value in the serial predetermined deceleration state
The initial value of the front and rear wheel speed ratios on the left and right sides, and the tire pressure is determined by comparing the front and rear wheel speed ratios on the left and right sides, respectively. Things.

[0006]

According to a second aspect of the present invention, there is provided a tire pressure warning device for detecting a decrease in tire pressure using a detection signal of a wheel speed sensor of four wheels of a vehicle and outputting a warning. A wheel speed sensor for detecting a wheel speed, turning detection means for detecting a predetermined turning speed state of the vehicle, and a front wheel based on an output from the wheel speed sensor in a predetermined turning state detected by the turning detection means. Side
Left and right wheel speed ratios, a right and left wheel speed ratio on the rear wheel side, and a pneumatic pressure determining means for determining a decrease in tire air pressure using these right and left wheel speed ratios, the right and left wheels on the front and rear sides when the tire air pressure is normal In the predetermined turning state of the speed ratio
That an initial value is provided an initial value setting means for obtaining respectively, the air pressure determination unit, said initial value of the front and rear side of the left and right wheel speed ratio, determining a tire pressure by respectively comparing the both front and rear sides of the left and right wheel speed ratio It is configured so that

[0008]

[0009]

In the tire air pressure warning device according to the first aspect, the air pressure judging means includes a front and rear left and right wheel based on an output from the wheel speed sensor in a predetermined acceleration / deceleration state detected by the acceleration / deceleration detecting means. Wheel speed ratio and right and left vehicle
A wheel speed ratio is obtained, and a decrease in tire air pressure is determined using these front and rear wheel speed ratios. At this time, the initial value setting means,
When the tire pressure is normal, the front and rear wheel speed ratio
Each set of values in the predetermined deceleration state as an initial value
Constant, and the air pressure determination means, and the initial value of the front and rear wheel speed ratio between the left and right sides, so determining the tire air pressure by husband and actual longitudinal wheel speed ratio between the left and right sides at the time of running people compared, with high precision An air pressure determination can be made. Thus, after seeking initial values before and after the wheel speed ratio of the left and right sides at a normal tire pressure, left at a predetermined acceleration or deceleration
Since the tire air pressure is determined using the front and rear wheel speed ratios on both right sides, it is possible to reliably detect a decrease in the air pressure of all the wheels as well as a decrease in the air pressure of some of the wheels.

[0010]

In the tire pressure warning device according to the second aspect , the air pressure determining means, in a predetermined turning state detected by the turning detecting means, is based on the output from the wheel speed sensor and the right / left wheel speed ratio on the front wheel side. The right and left wheel speed ratios on the wheel side are obtained, and a decrease in tire air pressure is determined using these right and left wheel speed ratios. At this time, the initial value setting means performs the predetermined rotation of the right and left wheel speed ratios on the front and rear sides when the tire pressure is normal.
The initial value in the turning state is obtained respectively, and the air pressure determining means
Since the tire pressure is determined by comparing the initial values of the front and rear left and right wheel speed ratios with the front and rear left and right wheel speed ratios during actual running, respectively, it is possible to perform the air pressure determination with high accuracy. it can. As described above, after determining the initial value of the right and left wheel speed ratio when the tire air pressure is normal, the tire air pressure is determined using the right and left wheel speed ratio in a predetermined turning state. Naturally, a decrease in air pressure of all wheels can be reliably detected.

[0012]

[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 tire pressure warning device for a rear-wheel-drive type automobile equipped with an anti-skid brake 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. Each wheel 1-4
Has disks 11 to 14 that rotate integrally with the wheels,
Brake devices 31 to 34 including calipers 21 to 24 for braking the rotation of the disks 11 to 14 in response to the supply of the braking pressure are provided, respectively, and a brake control system for operating these brake devices 31 to 34 is provided. Have been.

This brake control system includes a booster 2 for increasing the depression force of 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 in 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, a tire pressure warning device unique to the present invention will be described. This tire pressure determination device is capable of
Two wheel speed sensors 51 to 54 and an initial setting switch 55 for instructing initial setting of tire pressure determination (this is
A warning lamp 56 attached to the instrument panel), a warning lamp 56 attached to the instrument panel,
A longitudinal acceleration sensor 57 for detecting a longitudinal acceleration G acting on the vehicle body, a yaw rate sensor 58 for detecting a yaw rate ψv acting on the vehicle body, a control unit 50, and the like. The control unit 50 includes wheel speed sensors 51 to 54, Signals from the longitudinal acceleration sensor 57, the yaw rate sensor 58, the initial setting switch 55, and the like are supplied, and the warning lamp 56
Drive control is performed at 0.

Each of the wheel speed sensors 51 to 54 electromagnetically connects 48 detecting portions formed on the disks 21 to 24 or formed on a detecting disk (not shown) provided adjacent to the disks 21 to 24. This is a configuration for detecting by a pickup. The control unit 50 includes: a filter that filters detection signals from the wheel speed sensors 51 to 54; and a circuit that shapes 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.

Hereinafter, the tire pressure determination control executed by the control unit 50 will be described with reference to FIGS. This tire pressure determination control, such as when the tire is replaced or when starting to use the car,
The process includes an initial value setting process for setting an initial value of a wheel speed ratio, which will be described later, when the tire air pressure is normal, and an air pressure determination process for determining the tire air pressure during actual running. In the tire pressure determination control, basically, the front and rear wheel speed ratio between the front wheel speed and the rear wheel speed during deceleration, and the left and right wheel speed of the left wheel speed and the right wheel speed during turning. Using the ratio, the tire pressure is determined.

First, the initial value setting process will be described with reference to FIGS. 2 and 3. In FIG.
.. = 10, 11...) Indicates each step. This initial value setting process is started in response to the ON operation of the initial setting switch 55. First, it is determined whether the initial setting switch 55 has been turned ON (S10), and the determination is Ye.
At s, various signals (signals such as wheel speed, longitudinal acceleration, yaw rate, etc.) are read (S11), and it is then determined whether or not the vehicle is in a deceleration state based on a detection signal from the longitudinal acceleration sensor 57 (S12). In the state, in S13, it is determined whether or not the longitudinal acceleration G is substantially equal to -G0 (G0 is a positive predetermined value) based on the detection signal from the longitudinal acceleration sensor 57.

If the determination in S13 is Yes, in S14, wheel speed signals for five rotations of the wheels are read from the wheel speed sensors 51 to 54, and then the wheel speed signals of the wheels 1 to 4 are read using the wheel speed signals. Wheel speeds Vw1 to Vw4 are calculated (S1
5) Then, in S16, the front / rear wheel speed ratio Vw1 / Vw3 = HL0 of the left front wheel 1 and the rear wheel 3 and the front / rear wheel speed ratio Vw2 / Vw4 = HR0 of the right front wheel 2 and the rear wheel 4 are calculated. And stored in memory. Next, in S17, the counter I
Is incremented. Then, in S18, the count value I of the counter I is increased to a predetermined value I0 (for example, I0 is 5 to 1).
It is determined whether or not the value is equal to or greater than 0). If the determination is No, the number of data is not sufficient, so the process returns to S11, and the steps from S11 are repeated.
Proceeding to S19, the front / rear wheel speed ratio HL0 for the I0 times,
The average values HL0m and HR0m of the wheel speed ratio HR0 are calculated and stored in the memory. Next, in S20, the flag F1 is set to 1
Is set, and then the process proceeds to S30.

On the other hand, when the determination in S12 is No, the process proceeds to S21 in FIG. 3, and it is determined whether or not the vehicle is turning right based on the detection signal from the yaw rate sensor 58.
If Yes, it is determined in S22 whether the yaw rate レ イ v is substantially equal to the predetermined value ψv0, and the determination is Ye.
In the case of s, the wheel speed signals for five rotations of the wheels are read in S23, and the wheel speeds Vw1 to Vw4 of the wheels 1 to 4 are calculated using the wheel speed signals (S2).
4) Next, in S25, the left / right wheel speed ratio Vw1 / Vw2 = HF0 of the left front wheel 1 and the right front wheel 2 and the left rear wheel 3
And the right / left wheel speed ratio Vw3 / Vw4 = HB0 of the right rear wheel 4 is calculated and stored in the memory.

Next, in step S26, the counter J is incremented. In step S18, it is determined whether the count value J of the counter J is equal to or greater than a predetermined value J0 (for example, J0 is a value of about 5 to 10). When the determination is No, the number of data is not enough, so the process returns to S11,
S11 and subsequent steps are repeated, and when J becomes J0 or more, S2
8, the average value HF0m and HB0m of the left and right wheel speed ratios HF0 and HB0 for the J0 times are calculated and stored in the memory. Then, in S29, the flag F2 is set to 1
Is set, and then the process proceeds to S30. Next, S30
In the above, it is determined whether the flag F1 is 1 and the flag F2 is 1, and when the determination is No, S1
1 and when the determination is Yes, the initial value setting process ends.

Next, the air pressure judging process will be described with reference to FIGS. 4 and 5, and reference symbol Si (i = 40,
41) indicate each step. This air pressure determination process is always performed while the vehicle is running. First, various signals (signals such as wheel speed, longitudinal acceleration, and yaw rate) are read (S40), and then detection from the longitudinal acceleration sensor 57 is performed. It is determined whether the vehicle is in the deceleration state based on the signal (S4).
1) In the deceleration state, it is determined in S42 whether or not the longitudinal acceleration G is substantially equal to -G0 (G0 is the same predetermined value) based on the detection signal from the longitudinal acceleration sensor 57.

If the determination in S42 is Yes, in S43, the wheel speed signals for five rotations of the wheels are read from the wheel speed sensors 51 to 54, and then the wheel speed signals of the wheels 1 to 4 are read using the wheel speed signals. The wheel speeds Vw1 to Vw4 are calculated (S4
4) Then, in S45, the front / rear wheel speed ratio Vw1 / Vw3 = HL of the left front wheel 1 and the rear wheel 3 and the front / rear wheel speed ratio Vw2 / Vw4 = HR of the right front wheel 2 and the rear wheel 4 are calculated. And stored in memory. Next, in S46, the counter K
Is incremented, and in S47, the count value K of the counter K is increased to a predetermined value K0 (for example, K0 is 5 to 1).
It is determined whether or not it is greater than or equal to 0). If the determination is No, the number of data is not sufficient, so the process returns to S40, and the steps from S40 onward are repeated.
The process proceeds to S48, and the front and rear wheel speed ratio HL for the K0 times,
Average values HLm and HRm of the front-rear wheel speed ratio HR are calculated and stored in the memory.

Next, the front-rear wheel speed ratio HL, the front-rear wheel speed ratio H
Using the average values HLm and HRm of R, the front-rear wheel speed ratio HL0, and the average values HL0m and HR0m of the front-rear wheel speed ratio HR0 calculated in the initial value setting process and stored in the memory,
The absolute value of (HLm−HL0m) is equal to or greater than a predetermined value α, or
Rm−HR0m) is determined to be equal to or greater than a predetermined value α,
If the determination is No, in S50, it is determined that the tire air pressure is normal, and the process returns to S40.
If the determination at 49 is Yes, the process proceeds to S51, where it is determined that the tire air pressure has decreased. Then, at S52, the warning lamp 56 is turned on for a predetermined time (for example, 5 seconds), and the process returns to S40.

On the other hand, if it is determined in step S41 that the vehicle is not in the deceleration state, the process proceeds to step S53, where it is determined whether or not the vehicle is turning right based on the detection signal from the yaw rate sensor 58. At S54, it is determined whether or not the yaw rate ψv is substantially equal to the predetermined value ψv0. If the determination is Yes, wheel speed signals for five rotations of the wheel are read at S55, and then these wheel speed signals are read. Are used to calculate the wheel speeds Vw1 to Vw4 of the wheels 1 to 4 (S56). Next, in S57, the left / right wheel speed ratio Vw1 / Vw2 = HF of the left front wheel 1 and the right front wheel 2 is calculated as follows:
Left and right wheel speed ratio Vw3 / Vw4 of left rear wheel 3 and right rear wheel 4
= HB and is stored in the memory.

Next, in S58, the counter L is incremented. Next, in S59, it is determined whether or not the count value L of the counter L is equal to or more than a predetermined value L0 (for example, L0 is a value of about 5 to 10). When the determination is No, the number of data is not sufficient, and the process returns to S40,
S40 and subsequent steps are repeated, and when L becomes L0 or more, S6
Then, the process proceeds to 0, and the left and right wheel speed ratios HF and the average values HFm and HBm of the left and right wheel speed ratios HB for the L0 times are calculated and stored in the memory.

Next, at S61, the left and right wheel speed ratio HF
The average values HFm and HBm of the left and right wheel speed ratios HB and the average values HF0m and H of the left and right wheel speed ratios HB0 calculated in the initial value setting process and stored in the memory.
Using B0m, the absolute value of (HFm-HF0m) is equal to a predetermined value β
It is determined whether or not the absolute value of (HBm-HB0m) is equal to or greater than a predetermined value β. If the determination is No, it is determined that the tire pressure is normal in S62, and the process returns to S40. If the answer is Yes, the program proceeds to S51, where it is determined that the tire air pressure has decreased. Then, in S52, the warning lamp 56 is turned on for a predetermined time (for example, 5 seconds).
(Seconds), and returns to S40.

Next, the operation of the tire pressure determination control will be described. If the tire pressures of the four wheels are normal when the vehicle is running, the front-rear wheel speed ratio HLm is set to its initial value HL0.
m, and the front-rear wheel speed ratio HRm is a value substantially equal to the initial value HR0m. But, for example,
If the tire pressure of the left front wheel 1 decreases, the left front wheel 1
Is reduced, the wheel speed Vw1 is increased, and the front-rear wheel speed ratio HLm and the left-right wheel speed ratio HFm are increased. Therefore, a decrease in air pressure can be determined by the determination in S49 or S61. The same applies to the case where the air pressures of the other three wheels decrease.

Although rarely actually occurring, consider the case where the air pressures of the four wheels 1-4 decrease. At the time of deceleration, the wheel loads of the front wheels 1 and 2 become larger than the wheel loads of the rear wheels 3 and 4 due to the effect of the deceleration. Even if the wheel loads of the front wheels 1 and 2 and the wheel loads of the rear wheels 3 and 4 do not change, the degree of decrease in the moving radius of the front wheels 1 and 2 due to the decrease in air pressure increases. The ratios HLm, HRm are the initial values HL0m, HR0m
Larger than each.

The same is true for turning. When turning, the wheel load of the turning outer wheel is larger than that of the turning inner wheel. Even if the degree is the same and the wheel load of the turning inner wheel and the wheel load of the turning outer wheel do not change, since the degree of reduction in the moving radius of the turning outer wheel increases due to the decrease in air pressure, the left and right wheel speed ratios HFm, HBm are: Its initial value HF0m,
Each becomes larger than HB0m. Therefore, the four wheels 1
Also in the case where the tire pressure of all of the tires 4 decreases, the decrease of the air pressure can be determined by the determination of S49 or S61.

Further, in consideration of the fact that the deceleration state and the turning state continue only for a relatively short time, the wheel is rotated five times (however, in both the initial value setting processing and the air pressure determination processing).
(Not limited to five revolutions) is accumulated a plurality of times, and as an average value, the initial values HL0m and HR0m of the front and rear wheel speed ratios and the initial values HF0m and HF0m of the right and left wheel speed ratios are averaged.
HB0m, front and rear wheel speed ratio HLm, HRm, left and right wheel speed ratio H
Since the configuration is such that Fm and HBm are obtained, the accuracy and reliability of air pressure determination can be improved.

Here, the above embodiment can be partially modified as follows. 1) The determinations in S12 and S41 are to determine whether the vehicle is accelerating,
Further, the determination in S13 and S42 indicates that the longitudinal acceleration is the predetermined value G0.
Is determined to be substantially equal to or not. 2) The determination in S21 and S53 is to determine whether or not the vehicle is turning left. 3) Instead of applying the yaw rate ψv as the turning degree, a lateral acceleration acting on the vehicle body detected by the lateral acceleration sensor is applied, or a product of the steering angle and the wheel is applied. 4) The longitudinal acceleration sensor 57 is omitted, and deceleration is detected from the wheel speed of the driven wheel. 5) When traveling on a low-friction road surface, the accumulation of wheel speed data is prohibited in the initial value setting process and the air pressure determination process, and when traveling on a bad road, the accumulation of wheel speed data is inhibited in the initial value setting process and the air pressure determination process. Ban.

[Brief description of the drawings]

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

FIG. 2 is a part of a flowchart of an initial value setting process of the tire pressure alarm device of FIG. 1;

FIG. 3 is the remaining part of the flowchart of the initial value setting process of the tire pressure alarm device of FIG. 1;

FIG. 4 is a part of a flowchart of a pneumatic pressure determination process of the tire pressure alarm device of FIG. 1;

FIG. 5 is the remaining part of the flowchart of the air pressure determination process of the tire air pressure alarm device of FIG. 1;

[Explanation of symbols]

 1, 2, front wheel 3, 4 rear wheel 50 control unit 51-54 wheel speed sensor 55 initialization switch 56 warning lamp 57 longitudinal acceleration sensor 58 yaw rate sensor

Continuation of front page (56) References JP-A-4-262907 (JP, A) JP-A-54-33772 (JP, A) JP-A-4-271907 (JP, A) JP-A-63-305011 (JP, A) , A) Patent 3129555 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 23/00-23/08

Claims (2)

(57) [Claims] 1. A tire pressure judging device for detecting a decrease in tire air pressure using a detection signal of a wheel speed sensor of four wheels of a vehicle and outputting an alarm, wherein a wheel speed detecting each wheel speed of the four wheels of the vehicle is provided. A sensor, acceleration / deceleration detecting means for detecting a predetermined acceleration / deceleration state of the vehicle, and a predetermined acceleration / deceleration state detected by the acceleration / deceleration detection means, based on the output from the wheel speed sensor , the front and rear left side
A wheel speed ratio, seek and right front and rear wheel speed ratio, and a pneumatic judging means for judging decrease in tire air pressure with these longitudinal wheel speed ratio, the front and rear wheel speeds of the right and left sides in the normal tire air pressure
An initial value setting unit for setting a value of the ratio in the predetermined acceleration / deceleration state as an initial value, wherein the air pressure determination unit includes an initial value of the front and rear wheel speed ratio on both the left and right sides, Wherein the tire pressure is determined by comparing the front and rear wheel speed ratios with each other. 2. A tire pressure judging device for detecting a decrease in tire air pressure using a detection signal of a wheel speed sensor of four wheels of a vehicle and outputting an alarm, wherein a wheel speed detecting each wheel speed of four wheels of the vehicle. A sensor, turning detection means for detecting a predetermined turning speed state of the vehicle, and a left and right vehicle on the front wheel side based on an output from the wheel speed sensor in a predetermined turning state detected by the turning detection means.
A wheel speed ratio, and a right and left wheel speed ratio on the rear wheel side, and air pressure determining means for determining a decrease in tire air pressure using these left and right wheel speed ratios. An initial value setting unit for obtaining an initial value of the ratio in the predetermined turning state , wherein the air pressure determining unit compares the initial value of the front and rear left and right wheel speed ratios with the front and rear both right and left wheel speed ratios. The tire pressure alarm device is configured to determine the tire pressure by performing the following.