JPH0146341B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Industrial Field of Application The present invention relates to a method for preventing wheel lock in a vehicle, in which the slip rate of the wheel is added to the control factors as well as the acceleration/deceleration of the wheel. It is something.

(2) Prior Art When a vehicle suddenly brakes, if the braking input to the wheels is too large, the wheels lock and the braking efficiency decreases.

In order to prevent such a situation, when there is a risk of wheel locking, it is necessary to keep the wheel slip rate within an appropriate range, for example around 15 to 25%, regardless of the braking input by the driver. It is known that the braking torque of the wheels can be automatically controlled so that it is within the range of .

Therefore, various antilock brake devices have been proposed as devices for automatically controlling the braking torque of wheels.

(3) Problems to be Solved by the Invention None of the conventional antilock brake devices can be said to be satisfactory in terms of performance, reliability, economy, etc.

In addition, conventional anti-lock brake systems detect wheel acceleration and deceleration, which is negative acceleration, and determine whether there is a risk of wheel locking based on the magnitude of wheel acceleration or deceleration. The braking torque is controlled, but if the control method is based only on wheel acceleration/deceleration, it is not possible to control the braking torque so that the wheel slip rate is within an appropriate range under all possible conditions. Since this is difficult, it is desirable to add the wheel slip rate to the control factor in some way.

Here, the wheel slip rate λ is defined as λ=1-Vw/V, where Vw is the circumferential speed of the wheel and V is the vehicle body speed.As is clear from this equation, the slip rate of the wheel is There is no direct relationship between λ and the wheel acceleration, that is, the differential value V〓w of the wheel peripheral speed Vw. Therefore, in order to detect the slip rate of the wheels during braking, it is first necessary to detect the vehicle speed at that time.

Traditional methods for detecting vehicle speed include (1)
(2) A method in which a non-braking wheel is specially installed and the vehicle speed is detected from the circumferential speed of that wheel; (3)
Methods have been proposed in which the acceleration and deceleration of the vehicle body is detected and the vehicle speed is calculated from the integral value, but these conventional methods have complicated structures and
It is not easy to obtain a vehicle body speed detection device that is technically and economically satisfactory due to insufficient accuracy and reliability, or because the number of parts and the number of processing and assembly steps are large.

In view of the above circumstances, the present invention adds the slip rate of the wheel as well as the acceleration/deceleration of the wheel to the control factors, thereby controlling the braking so that the slip rate of the wheel falls within an appropriate range during braking. The object of the present invention is to provide a method for preventing wheels from locking in a vehicle, such that the torque can be controlled.

B. Structure of the Invention (1) Means for Solving the Problems In order to achieve the above object, the present invention detects the circumferential speed of a wheel and extracts it as a wheel speed signal, and also detects the vehicle body speed and outputs the wheel speed. A reference wheel speed signal that takes into account a predetermined slip rate of the wheel is set in a form that can be compared with the signal, and an acceleration signal of the wheel is derived from the wheel speed signal and can be compared with the acceleration signal. A reference wheel deceleration signal is set, and a low reference wheel speed signal is derived based on the vehicle body speed so as to be at a lower level than the reference wheel speed signal, and when braking, the wheel speed signal and the reference The wheel speed signal and the low reference wheel speed signal are compared, and the wheel acceleration signal and the reference wheel deceleration signal are compared, and the value of the wheel speed signal is smaller than the value of the reference wheel speed signal, and reducing the braking torque of the wheel whenever the value of the wheel acceleration signal is smaller than the value of the reference wheel deceleration signal or whenever the value of the wheel speed signal is smaller than the value of the low reference wheel speed signal; Further, when the value of the wheel speed signal is larger than the value of the reference wheel speed signal and the value of the wheel acceleration signal is smaller than the value of the reference wheel deceleration signal, the braking torque of the wheel is not reduced. , each of which controls a braking device.

(2) Effect According to the above configuration, since the slip rate of the wheel is added to the control factors as well as the acceleration/deceleration of the wheel, the braking torque can be controlled so that the slip rate is always within an appropriate range.

In particular, under conditions where the value of the wheel speed signal is smaller than the value of the reference wheel speed signal and the value of the wheel acceleration signal is smaller than the value of the reference wheel deceleration signal, that is, under conditions where the risk of wheel lock is imminent. However, even if the value of the wheel acceleration signal is smaller than the value of the reference wheel deceleration signal, the braking torque is reduced under the condition that the value of the wheel speed signal is larger than the value of the reference wheel speed signal. Since the braking torque is not reduced, the braking torque is determined to start decreasing at the point at which the risk of wheel locking is imminent, while taking into account the magnitude relationship between the wheel speed signal and the reference wheel speed signal, that is, the actual slip situation of the wheels. Therefore, while avoiding wheel lock, strong braking torque can be continuously and effectively applied to the wheels until the very moment when the risk of wheel lock approaches.

Furthermore, even under conditions where the value of the wheel speed signal is smaller than the value of the low reference wheel speed signal, it is not affected by the magnitude relationship between the wheel acceleration signal and the reference wheel deceleration signal or the control state of the braking torque. Since the braking torque is constantly reduced, when the vehicle suddenly enters from a road surface with a high friction coefficient (such as a dry paved road surface) to a road surface with a low friction coefficient (such as an icy road surface) during braking, the control system Even if the wheels lock momentarily due to a delay in response, the lock can always be released instantaneously.

(3) Embodiment An embodiment of the present invention will be described below with reference to the drawings. First, in FIG. 1, a brake pedal 1 is operatively connected to a master cylinder 2, and a driver presses the brake pedal. 1, the master cylinder 2 generates braking oil pressure. The master cylinder 2 is connected via an oil passage 3 to a brake oil chamber 11 formed between a pair of pistons 7 and 8 in a wheel cylinder 6 mounted on the vehicle body.
is connected to. Rod 9 of each piston 7,8,
Each of the rods 9 and 10 extends outwardly through the end wall of the wheel cylinder 6, and the outer end of each rod 9, 10 generates braking torque by coming into frictional contact with the brake drum 4 mounted on the wheel. They are respectively connected to a pair of brake shoes 5 and 5'. Therefore, when the master cylinder 2 generates braking oil pressure when the brake pedal 1 is depressed, this braking oil pressure passes through the oil passage 3 to the brake oil chamber 11.
As a result, the pistons 7 and 8 are pushed away from each other, and accordingly, the brake shoes 5 and 5' are pushed toward the friction surface of the brake drum 4. It works with the brake to generate braking torque to the wheels.

If the brake oil pressure in the brake oil chamber 11 is too large, the braking torque generated between each brake shoe 5, 5' and the brake drum 4 will be too large, resulting in the wheels being locked. In order to prevent this dangerous situation, a pair of control oil chambers 12, 12' are provided between each piston 7, 8 and the end wall of the wheel cylinder 6.
are formed, and these control oil chambers 12, 1
By controlling the control oil pressure in the brake oil chamber 11, when the brake oil pressure in the brake oil chamber 11 is too large and there is a possibility or danger of wheel locking, the movement of each piston 7, 8 by the brake oil pressure is suppressed. is configured to do so.

Therefore, a control device for controlling the braking oil pressure in the control oil chambers 12, 12' will be explained below.
The pressurized control oil sucked up from the oil tank T by the pump P passes through the oil passage 15 and the pressure accumulator 13, and is sent to the inlet side port of the inlet valve 14, which is switched and controlled by the electromagnetic coil 20. The outlet side port of the inlet valve 14 is connected to the control oil chamber 12 via the oil passage 16.
Furthermore, the oil passages 17 communicate with a control oil chamber 12'. Further, the control oil chamber 12 is connected to an outlet valve 19 via an oil passage 16, an oil passage 17, and an oil passage 18, and the control oil chamber 12' is connected to an outlet valve 19 via an oil passage 18, each of which is switched and controlled by an electromagnetic coil 21. The outlet port of the outlet valve 19 communicates with the oil tank T.

The inlet valve 14 is normally held in the right position in FIG. 1, and in this state, each control oil chamber 12, 12'
is isolated from pump P and pressure accumulator 13. When the electromagnetic coil 20 is activated by a signal sent to the electromagnetic coil 20, the inlet valve 14 is switched to the left position in FIG. 13, through the inlet valve 14, into each control oil chamber 12, 12', and press each piston 7, 8 toward each other against the braking oil pressure in the brake oil chamber 11.

In addition, the outlet valve 19 is normally the first
It is maintained in the left-hand position in the figure, and in this state, each control oil chamber 12,
12' is connected to the oil tank T via the outlet valve 19.
open inside. When the electromagnetic coil 21 is actuated by a signal sent to the electromagnetic coil 21, the outlet valve 19 is switched to the right position in FIG. be cut off from.

Therefore, the first operating state is a state in which the inlet valve 14 is switched to the right position and the outlet valve 19 is switched to the left position;
That is, considering a state in which no signal is sent to either of the electromagnetic coils 20, 21, in this state, each control oil chamber 12, 12' is open into the oil tank T, so each piston 7, 8 is pressed and moved depending only on the brake oil pressure in the brake oil chamber 11, and as a result, the braking torque during braking can be freely increased depending on the driver's braking operation.

Next, considering a second operating state in which the outlet valve 19 is switched to the right position, that is, a signal is sent to the electromagnetic coil 21, in this state, each control oil chamber 12, 1
2' is isolated from the oil tank T, and each control oil chamber 12, 1
Since the control oil in 2' is in a locked state,
Each piston 7, 8 is prevented from further movement even if the brake oil pressure in the brake oil chamber 11 continues to increase. As a result, the braking torque during braking remains constant regardless of the driver's braking action, so that this second operating state is suitable in the event of a possible wheel lock.

As a third operating state, consider a state in which the inlet valve 14 is switched to the left position and the outlet valve 19 is switched to the right position, that is, a state in which signals are sent to both electromagnetic coils 20 and 21. In this state, the control oil sent from pump P is pressurized into each control oil chamber 12, 12' via pressure accumulator 13 and inlet valve 14, and each control oil chamber 12, 12' is Since they are cut off from the oil tank T, the pistons 7 and 8 are pushed toward each other against the braking oil pressure in the braking oil chamber 11. As a result, the braking torque during braking is reduced independently of the driver's braking action, so that this third operating state is suitable when there is a risk of wheel locking.

By the way, in order to determine the slip rate of the wheels, it is first necessary to estimate the vehicle speed, so a specific example of a practical vehicle speed estimating device 32 for this purpose will be described below according to FIGS. 2 and 3. explain. First, in FIG. 2, each wheel is equipped with wheel speed detection devices 22, 23, 24, and 25 that individually detect the circumferential speed of the corresponding wheel, and each wheel speed detection device 22, 23, 24, and 25 has a corresponding one. Wheel speed signals having values proportional to the circumferential speed of the wheels are generated as frequency signals f ₁ , f ₂ , f ₃ and f ₄ . Each wheel speed frequency signal f ₁ , f ₂ , f ₃ , f ₄ is
For conversion into an easily handled signal form, they are immediately sent to frequency-to-voltage converters 26, 27, 28 and 29, respectively, where voltage signals Uw ₁ , Uw ₂ , Uw ₃ are respectively proportional to the circumferential speed of each wheel. and
Converted to Uw ₄ . FIG. 3 exemplarily shows how the values of the wheel speed voltage signals Uw ₁ , Uw ₂ , Uw ₃ and Uw ₄ change over time when the skid prevention device is activated.

Referring again to FIG. 2, each frequency-voltage converter 2
The wheel speed voltage signals Uw ₁ , Uw ₂ , Uw ₃ , and Uw ₄ which are the output signals of 6, 27, 28, and 29 are subsequently sent to the high select circuit 30, respectively. The high select circuit 30 selects only the signal that always has the maximum value among the wheel speed voltage signals Uw ₁ , Uw ₂ , Uw ₃ , and Uw ₄ received as input signals, and selects only the signal that always has the maximum value, and selects only the signal that always has the maximum value, and selects only the signal that always has the maximum value, and selects only the signal that always has the maximum value. , the maximum wheel speed voltage signal Uwmax is generated as an output signal.

The maximum wheel speed voltage signal Uwmax generated by the high select circuit 30 is then sent to a storage circuit 31 having a constant current discharge characteristic commensurate with standard vehicle deceleration during braking. The memory circuit 31
As shown by the chain line in the figure, an estimated wheel speed voltage signal U, which is an attenuated signal having a gradient determined by the discharge characteristics of the maximum wheel speed voltage signal Uwmax, which is the input signal, is generated as an output signal.

Vehicle speed voltage signal U estimated in this way
is sent to the reference wheel speed setting circuit 33 as shown in FIG. Reference wheel speed setting circuit 33
is a circuit that sets the wheel speed such that a predetermined slip rate λo is achieved with respect to the estimated vehicle speed voltage signal U, and is composed of a divided circuit, and U _R =(1−λo)U. Set the reference wheel speed voltage signal U _R.

Since the reference wheel speed is set as described above, only specific examples of the method and device for adding the wheel slip rate to the control factor in the anti-skid device will be described below.

In FIG. 4, the circumferential speed of a wheel whose braking torque is to be controlled is first detected by a wheel speed detection device 34 attached to the wheel.
The wheel speed detection device 34 generates a wheel speed frequency signal fi proportional to the wheel speed as its output signal, but this signal is immediately converted into a wheel speed voltage signal proportional to the wheel speed by the frequency-voltage converter 35. Converted to Uwi. This wheel speed voltage signal
In order to obtain Uwi, each wheel speed detecting device 22, 23, 24, 25 constituting the vehicle speed estimating device 32 shown in FIG. The frequency-voltage converters 26, 27, 28, 29 can be used for each wheel.

The wheel speed voltage signal Uwi is subsequently applied to the comparator circuit 3.
6, sent to the differentiation circuit 37 and comparison circuit 50. The comparison circuit 36 compares the wheel speed voltage signal Uwi and the reference wheel speed voltage signal U _R , which is the output signal of the reference wheel speed setting circuit 33, so that the value of the wheel speed voltage signal Uwi is equal to that of the reference wheel speed voltage signal U _R. It is configured to generate an output signal only when the value is smaller than the value, that is, when Uwi< _UR .

Differentiating circuit 37 differentiates wheel speed voltage signal Uwi and generates wheel acceleration voltage signal U〓wi as an output signal. Then, this wheel acceleration voltage signal U〓wi is immediately sent to comparison circuits 40, 41 and 42.

Here, the comparison circuit 40 outputs the wheel acceleration voltage signal
U〓wi is compared with the reference wheel deceleration voltage signal -V〓wo indicating a preset negative reference wheel acceleration, and the value of the wheel acceleration voltage signal U〓wi is the reference wheel deceleration voltage signal -V〓wo. When it is smaller than the value of , i.e.
It is configured to generate an output signal only when U〓wi＜−V〓wo.

The comparison circuit 41 also outputs a wheel acceleration voltage signal.
U〓wi is compared with a preset first reference wheel acceleration voltage signal _V〓w1 , and the value of the wheel acceleration voltage signal U〓wi is larger than the value of the first reference wheel acceleration voltage signal _V〓w1 . The output signal is generated only when V〓w ₁ <U〓wi.

Furthermore, the comparison circuit 42 outputs the wheel acceleration voltage signal
U〓wi is compared with a preset second reference wheel acceleration voltage signal _V〓w2 having a value larger than the first reference wheel acceleration voltage signal _V〓w1 , and the wheel acceleration voltage signal U〓wi is The value is the second reference wheel acceleration voltage signal V〓w ₂
It is configured to generate an output signal only when V〓w ₂ <U〓wi. The output side of this comparison circuit 42 is connected to the input side of an inversion circuit 45, and while the comparison circuit 42 is generating an output signal, the inversion circuit 45 cancels the signal and produces no output signal. However, while the comparison circuit 42 is not generating an output signal, it is configured to always generate an output signal. That is, the inversion circuit 45 functions to invert the output signal of the comparison circuit 42.

By the way, the estimated vehicle speed voltage signal U, which is the output signal of the vehicle speed estimating device 32, is also sent to a dividing circuit 49 different from the dividing circuit 33.
With the estimated vehicle speed voltage signal U as a reference,
The low reference wheel speed voltage signal U _R ' is configured to have a value smaller than the value of the reference wheel speed voltage signal U _R . This low reference wheel speed voltage signal U _R ' is sent to the comparator circuit 50 as an output signal of the dividing circuit 49, and the comparator circuit 50 compares the wheel speed voltage signal Uwi and the low reference wheel speed voltage signal U _R '. Generates an output signal only when the value of the speed voltage signal Uwi is smaller than the value of the low reference wheel speed voltage signal U _R ′ and sends it to the OR circuits 44 and 46.
I am trying to send it to. Now, each comparison circuit 36,
The output signals of 40, 41, 42, and 50 are determined through a logical decision process to the electromagnetic coil 20 for operating the inlet valve 14 and the output signal for operating the outlet valve 19 shown in FIG. This is sent to the electromagnetic coil 21 as an operation command signal, and a logic circuit device therefor will be explained below.

The output sides of comparator circuits 36 and 40 are both
It is connected to the input sides of the AND circuit 43 and the OR circuit 44, and the output sides of the comparison circuits 41 and 50 are connected to the input side of the OR circuit 44. AND circuit 4
3 and the output sides of the comparison circuit 50 are further connected to the input side of the OR circuit 46, and the output sides of the OR circuit 46 and the inversion circuit 45 are connected to the AND circuit 4.
It is connected to the input side of 7. The output side of the OR circuit 44 and the inverting circuit 45 is connected to the AND circuit 4.
It is connected to the input side of 8. The AND circuit 47 is connected to the electromagnetic coil 20, and the AND circuit 47 is connected to the electromagnetic coil 20.
7 generates an output signal, the electromagnetic coil 20 is actuated to switch the inlet valve 14 from the right position to the left position in FIG.
When the AND circuit 48 generates an output signal, the electromagnetic coil 21 is activated to switch the outlet valve 19 from the left position to the right position in FIG.

Since the logic circuit device is configured as described above, each comparison circuit 36, 40, 41, inversion circuit 45
The output signal of the pulse generator 39 is processed as follows.

First, the value of the wheel speed voltage signal Uwi is larger than the value of the low reference wheel speed voltage signal U _R ′ (U _R ′<
Uwi), the comparator circuit 50 does not generate an output signal, the value of the wheel speed voltage signal Uwi is larger than the value of the reference wheel speed voltage signal U _R , and the value of the wheel acceleration voltage signal U〓wi is the reference When the value of the wheel deceleration voltage signal −V〓wo is greater than the value of the first reference wheel acceleration voltage signal _V〓w1 , that is, U _R <Uwi and −V〓wo＜U〓wi＜V〓w ₁ , or when the value of the wheel acceleration voltage signal U〓wi is larger than the value of the second reference wheel acceleration voltage signal _V〓w2 , regardless of the value of the wheel speed voltage signal Uwi, that is, −
When V〓w ₂ <U〓wi, it is determined that there is no possibility of wheel lock, and each AND circuit 47 and 4
8 do not generate an output signal, and therefore the electromagnetic coils 20 and 21 do not operate together at this time, so the inlet valve 14 and the outlet valve 19 are placed in the first operating state, and the braking during control is performed. Torque increases freely according to the driver's braking operation.

Further, the value of the vehicle speed voltage signal Uwi is larger than the value of the reference wheel speed voltage signal U _R , and the value of the wheel acceleration voltage signal U〓wi is the reference wheel deceleration voltage signal -
When it is smaller than the value of V〓wo, that is, U _R <Uwi
and U〓wi＜−V〓wo, or regardless of the value of the wheel speed voltage signal Uwi, the wheel acceleration voltage signal
The value of U〓wi is larger than the value of the first reference wheel acceleration voltage signal _V〓w1 , and the second reference wheel acceleration voltage signal
When it is smaller than the value of V〓w ₂ , that is, V〓w ₁ <U〓wi
<V〓w ₂ , or the value of the wheel speed voltage signal Uwi is smaller than the reference wheel speed voltage signal U _R , and the value of the wheel acceleration voltage signal U〓wi is less than the reference wheel deceleration voltage signal −V〓wo. When it is significantly smaller than the second reference wheel acceleration voltage signal V〓w ₂ , that is, Uwi <
When U _R and −V〓wo＜U〓wi＜V〓w ₂ , it is determined that there is a possibility that the wheels may become locked.
AND circuit 47 does not generate an output signal, but only AND circuit 48 generates an output signal. Therefore, at this time, the electromagnetic coil 20 is not activated, but the inlet valve 14 is activated due to the electromagnetic coil 21 activated.
The outlet valve 19 is placed in the second operating state, and the braking torque during braking is kept constant so that it does not increase any further regardless of the driver's braking operation.

Further, when the value of the wheel speed voltage signal Uwi is smaller than the value of the reference wheel speed voltage signal U _R and the value of the wheel acceleration voltage signal U〓wi is smaller than the value of the reference wheel deceleration voltage signal −V〓wo , that is, Uwi<
When U _R and U〓wi＜−V〓wo, it is determined that there is a risk of wheel locking, and the AND circuit 4
7 and 48 together generate an output signal. Therefore, at this time, the electromagnetic coils 20 and 21 operate together, so that the inlet valve 14 and the outlet valve 19 are placed in the third operating state, and the braking torque during braking is reduced regardless of the driver's braking operation. be done.

By the way, the circumferential speed of the wheel becomes extremely low, and the value of the wheel speed voltage signal Uwi becomes smaller than the value of the low reference wheel speed voltage signal U _R ′, that is, Uwi<
When U _R ' is reached, the comparator circuit 50 generates an output signal in response to the division circuit 49 generating an output signal. In such a case, the value of the wheel acceleration voltage signal U〓wi is the second reference wheel acceleration voltage signal V〓w ₂
Since the inverting circuit 45 is generating an output signal, the AND circuits 47 and 4
8, regardless of the output signals of the comparison circuits 36, 40 and 41, the electromagnetic coils 20 and 21 operate together only while the comparison circuit 50 generates the output signal, and the inlet valve 14 and the outlet valve 19 is placed in the third operating state, and the braking torque during braking is reduced regardless of the driver's braking operation.

The division circuit 49 and the comparison circuit 50 are configured to detect, for example, when the vehicle suddenly enters a road surface with a low friction coefficient from a road surface with a high friction coefficient while braking, the wheels momentarily lock due to a delay in response of the control system. Even if it does, it immediately releases it and acts as an additional circuit to reliably prevent continued wheel locking.

FIG. 5 shows an example of the operating mode of the anti-skid device when the logic circuit device shown in FIG. 4 is employed. In FIG. 5, the horizontal axis shows the time elapsed after the start of control, and the vertical axis shows
In the uppermost position, the estimated vehicle speed voltage signal U, the wheel speed voltage signal Uwi and the reference wheel speed voltage signal U _R are shown, and in the lower position,
The wheel acceleration voltage signal U〓wi is shown, and below it, in order, the output signal A of the comparison circuit 36, the output signal B of the comparison circuit 40, the output signal C of the comparison circuit 41, the output signal D of the comparison circuit 42, A third operating state of the inlet valve 14 and outlet valve 19, also a second operating state, also a first operating state.
The operating state of , and the braking torque T _B are shown, respectively.

Immediately after starting braking at time t=0, neither of the AND circuits 47 and 48 generates an output signal, so the hydraulic control system of the braking device
Since the vehicle is in the operating state, the braking torque T _B gradually increases, and along with this, both the wheel speed voltage signal Uwi and the wheel acceleration voltage signal Uwi gradually decrease.

When the value of the wheel acceleration voltage signal U〓wi becomes smaller than the value of the reference wheel deceleration voltage signal -V〓wo at time _t1 , the output signal B of the comparator circuit 40 is generated,
It was determined that there was a possibility of wheel locking.
The AND circuit 48 generates an output signal, but since the output signal A of the comparison circuit 36 has not yet been generated at this time, the AND circuit 47 does not generate an output signal and the hydraulic control system of the braking device is in the second operating state. At this time, the braking torque T _B is maintained approximately constant.

At this time, since the braking torque T _B has become excessive due to the delay in the operation of the hydraulic control system, the wheel speed voltage signal Uwi continues to decrease further, and as a result, the comparison circuit 36 generates the output signal A at time _t2 . . At this point, the output signal A of the comparison circuit 36 and the comparison circuit 4
Since output signal B of 0 is generated at the same time, it is determined that there is a risk of wheel locking.
AND circuits 47 and 48 both generate output signals, and each electromagnetic coil 20, 21 operates together, the hydraulic control system enters the third operating state, and the braking torque
T _B is reduced.

As the braking torque T _B decreases, the wheel acceleration gradually increases, so that at time t ₃ the value of the wheel acceleration voltage signal U〓wi is larger than the value of the reference wheel deceleration voltage signal −V〓wo Then, the output signal B of the comparator circuit 40 disappears, and it is determined that the risk of wheel locking disappears, and the output signal of the AND circuit 47 disappears, but the output signal A of the comparator circuit 36 disappears.
continues to occur, so the output signal of the AND circuit 48 does not disappear, so the hydraulic control system returns to the second operating state, and the braking torque T _B is held substantially constant.

At this time, the braking torque T _B has decreased too much due to the delay in the operation of the hydraulic control system, etc., so the wheel acceleration voltage signal U〓wi continues to rise and the wheel speed voltage signal Uwi starts to rise, and at time t ₄ the wheel The value of the acceleration voltage signal U〓wi becomes larger than the value of the first reference wheel acceleration voltage signal _V〓w1 , and the output signal C of the comparator circuit 41 is generated, and furthermore, at time _t5 , the value of the wheel acceleration voltage signal U〓wi When the value becomes larger than the value of the second reference wheel acceleration voltage signal _V〓w2 , the comparator circuit 4
2 output signals D are generated. As a result, it was determined that there was no possibility of the wheels locking, and the AND
Both circuits 47 and 48 produce no output signal;
Both electromagnetic coils 20, 21 are placed in an inactive state, the hydraulic control system is placed in a first operating state, and the braking torque T _B begins to increase again.

As the braking torque T _B increases, the value of the wheel acceleration voltage signal U〓wi becomes smaller than the value of the second reference wheel acceleration voltage signal V〓w ₂ at time t ₆ , and the output signal D of the comparison circuit 42 becomes Although it disappears, comparison circuit 4
Since the output signal C of 1 still remains,
It is determined that there is a possibility that the wheels may be locked, and the AND circuit 48 generates an output signal, the electromagnetic coil 21 is activated, and the hydraulic control system enters the second operating state, and the braking torque T _B becomes almost constant. Retained.

When the wheel speed voltage signal Uwi increases to the extent that a proper wheel slip rate can be maintained, the value of the wheel acceleration voltage signal U〓wi becomes lower than the value of the first reference wheel acceleration voltage signal _V〓w1 at time _t7 . As the output signal C of the comparator circuit 41 becomes smaller, the output signal C of the comparator circuit 41 disappears, and it is determined that there is no possibility of the wheels locking, so the AND circuits 47 and 48 do not generate output signals, and the electromagnetic coils 20 and 21 With both inactive, the hydraulic control system enters a first operating state and the braking torque T _B begins to increase.

Thereafter, the above process is repeated in the same way, and the vehicle speed decreases without the wheels locking.

In the above explanation, the reference wheel speed voltage signal
U _R constitutes the reference wheel speed signal of the present invention, wheel speed voltage signal Uwi constitutes the wheel speed signal of the present invention, wheel acceleration voltage signal U〓wi constitutes the wheel acceleration signal of the present invention, and further, The reference wheel deceleration voltage signal -V〓wo constitutes the reference wheel deceleration signal of the present invention.

C. Effect of the invention As described above, according to the present invention, the wheel speed signal
In addition to comparing Uwi with a reference wheel speed signal U _R determined by taking into account the wheel slip rate,
Wheel acceleration signal U〓wi and reference wheel deceleration signal −
Since the braking torque pressure reduction control timing is determined based on the magnitude relationship of the values of each signal, the braking torque pressure reduction is performed while checking both wheel speed changes and acceleration changes. Control can be performed automatically and accurately.

In particular, the value of the wheel speed signal Uwi is smaller than the value of the reference wheel speed signal U _R and the value of the wheel acceleration signal U〓wi is the reference wheel deceleration signal -
Under conditions where the value of V〓wo is smaller than the value of the wheel acceleration signal U〓wi, that is, under conditions where the danger of wheel lock is imminent, the braking torque is always reduced. Signal −V〓wo
Even if the value of the wheel speed signal Uwi is smaller than the value of the reference wheel speed signal U _R , the braking torque is not reduced under the condition that the value of the wheel speed signal Uwi is larger than the value of the reference wheel speed signal U _R . Taking into account the actual slip situation of the wheels, it is possible to postpone the point at which the braking torque starts to be reduced until the moment when the risk of wheel lock is imminent, thereby avoiding wheel lock. A strong braking torque can be continuously and effectively applied to the wheels until the very moment when the wheels are in danger of locking up, and therefore it can greatly contribute to improving the braking efficiency as a whole.

Furthermore, the wheel speed signal is lower than the value of the low reference wheel speed signal U _{R ′} , which is derived based on the vehicle speed so that the level is lower than the reference wheel speed signal U _R .
Under conditions where the value of Uwi is small, the wheel acceleration signal
Since the braking torque is constantly reduced regardless of the magnitude relationship between U〓wi and the reference wheel deceleration signal - V〓wo or the control status of the braking torque, the vehicle will experience friction during braking. When the vehicle suddenly enters a road surface with a low coefficient of friction (such as an icy road) from a road surface with a high coefficient of friction (for example, a dry paved road), even if the wheels lock up momentarily due to a delay in the response of the control system, the It can be released instantaneously, prevents the wheels from being continuously locked, and minimizes the reduction in braking efficiency that accompanies wheel locks.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional conceptual diagram of main parts showing a wheel braking device and a hydraulic control device for controlling the braking torque of the braking device, Fig. 2 is a block diagram showing an example of a vehicle speed estimating device, and Fig. 3 is a block diagram showing an example of a vehicle speed estimating device. The figure is a graph diagram for explaining an example of the operation of the vehicle body speed estimating device in Figure 2, Figure 4 is a signal processing circuit and logic circuit diagram for operating the hydraulic control device in Figure 1, and Figure 5 is a graph diagram for explaining an example of the operation of the vehicle speed estimation device in Figure 2. FIG. 5 is an explanatory diagram showing an example of the operation mode of the braking device and hydraulic control device of FIG. 1 and the signal processing circuit device and logic circuit device of FIG. 4; U _R ...Reference wheel speed signal, U _R ′...Low reference wheel speed signal, Uwi...Wheel speed signal, U〓wi...Wheel acceleration signal, -V〓wo...Reference wheel deceleration signal, λo
...Slip rate.

Claims (1)

[Claims] 1. Detecting the circumferential speed of the wheel and extracting it as a wheel speed signal Uwi, and detecting the vehicle body speed and determining a reference wheel speed that takes into account a predetermined slip rate (λo) of the wheel. Set the signal U _R , derive the acceleration signal U〓wi of the wheel from the wheel speed signal Uwi, and set the reference wheel deceleration signal −V〓wo in a form that can be compared with the acceleration signal U〓wi. and further the reference wheel speed signal
A low reference wheel speed signal U _{R '} is derived based on the vehicle body speed so as to be at a lower level than U R , and during braking, the wheel speed signal Uwi, the reference wheel speed signal U _R and the low reference wheel speed signal
In addition to comparing U _R ′, the wheel acceleration signal
The value of the wheel speed signal Uwi is smaller than the value of the reference wheel speed signal U _R and the value of the wheel acceleration signal U〓wi is compared with the reference wheel deceleration signal -V〓wo. The reference wheel deceleration signal −V〓wo
or whenever the value of the wheel speed signal Uwi is smaller than the value of the low reference wheel speed signal U _R ′, the braking torque of the wheel is reduced; When the value of the reference wheel speed signal U _R is larger than the value of the reference wheel speed signal U R and the value of the wheel acceleration signal U〓wi is smaller than the value of the reference wheel deceleration signal −V〓wo, the braking torque of the wheel is not reduced. A method for preventing wheels from locking in a vehicle, the method comprising controlling a braking device.