JP7743812B2 - Vehicle Brake Systems - Google Patents

Description

The present invention relates to a vehicle brake system, and more particularly to a mechanical brake system equipped with a brake booster.

Vehicle braking systems include mechanical systems that use a brake booster, and by-wire systems that convert the stroke input into the brake pedal into an electrical signal to activate the brakes.

However, conventional vehicle brake systems have had the problem of not being able to provide the driver with an operation feeling that matches human sensibilities due to a mismatch between the break point in the force-stroke characteristic and the rise point of deceleration G. Specifically, as shown in the force-stroke characteristic in Figure 9(a), when the driver depresses the brake pedal, the gap between the brake rotor and brake pads simply narrows up to a predetermined stroke ST _C , and once the stroke ST _C is exceeded, the frictional force of the brake pads actually acts on the brake rotor, causing deceleration G (arrow E1).

In contrast, as shown in FIG. 9(b), the output hydraulic pressure of the brake booster rises suddenly when a predetermined pedal force _FP is applied. This point is called the jump-up point _PJU . In a conventional brake system, a difference occurs between the hydraulic pressure P91 at the break point _PC in FIG. 9(a) and the hydraulic pressure P92 at the jump-up point _PJU in FIG. 9(b) (indicated by arrow E2). This difference may cause a sudden deceleration G when the driver applies pedal force and reaches the jump-up point, requiring a correction operation. For this reason, it has been difficult for a conventional brake system to ensure an operating feel that matches human senses.

Patent Document 1 discloses a configuration for a by-wire brake system in which the break point _PC in FIG. 9( a) coincides with the time when deceleration G begins to occur when the brake pedal is depressed.

Patent No. 6573220

By-wire brake systems require additional compensation measures in the event of an electrical failure and hydraulic generators in place of brake boosters, which increases manufacturing costs, so many vehicles also use mechanical brake systems with brake boosters. Even with these mechanical brake systems, there is a demand to ensure an operating feel that matches the human senses.

The present invention seeks to solve the above-mentioned problems by providing a vehicle brake system that employs a mechanical configuration with a brake booster while still providing an operating feel that matches human senses.

A brake system for a vehicle according to one aspect of the present invention comprises a brake pedal, a brake booster, a master cylinder, and a brake. The brake pedal is supported by a pivotal support and is configured to rotate around the pivotal support. The brake booster is connected to the brake pedal and multiplies the pedal force input to the brake pedal and outputs the result. The master cylinder is connected to the brake booster and increases the pressure of the hydraulic fluid in accordance with the output of the brake booster. The brake comprises a brake piston connected to the master cylinder and actuated by the increased pressure of the hydraulic fluid, a brake rotor that rotates together with the vehicle's wheels, and a pad that is pressed against the brake rotor by the operation of the brake piston, generating friction between the brake rotor and the brake piston.

In this aspect, the brake booster has a characteristic that there is a jump-up point at which it begins to output a predetermined first pressure to the master cylinder as an output start pressure once the pedal force reaches a predetermined pressure. The brake also has a characteristic that frictional force begins to be generated between the brake rotor and the pad once the hydraulic fluid pressure reaches a predetermined second pressure. The master cylinder has a cylinder diameter set so that the first pressure at the jump-up point in the brake booster and the second pressure at which frictional force begins to be generated in the brake are approximately equal.

The vehicle brake system according to the above aspect employs a master cylinder with a cylinder diameter set so that the first pressure at the jump-up point of the brake booster and the second pressure at which frictional force in the brakes begins to be generated are approximately equal, thereby achieving an operational feel that matches the driver's senses in a mechanical brake system. In other words, in the vehicle brake system according to the above aspect, the cylinder diameter of the master cylinder is set so that the first pressure and the second pressure are approximately equal. Therefore, even when the driver depresses the brake pedal and reaches the jump-up point, there is no sudden deceleration G as in conventional brake systems, and no corrective action is required. Therefore, the vehicle brake system according to the above aspect can provide the driver with an operational feel that matches the driver's sense of depressing the brake pedal.

In the vehicle brake system according to the above aspect, the master cylinder may have a cylinder diameter set within the range of 26.5 mm or more and 32.0 mm or less.

The vehicle brake system according to the above aspect uses a master cylinder with a cylinder diameter of 26.5 mm or greater, which allows the output (hydraulic pressure) from the master cylinder at the jump-up point to be kept lower than conventional systems, effectively ensuring that the first pressure and the second pressure are approximately equal.

Furthermore, the vehicle brake system according to the above aspect uses a master cylinder with a cylinder diameter of 32.0 mm or less, which prevents situations where the required output (hydraulic pressure) is not obtained, and is ideal for providing the driver with a high level of operating feel.

In the vehicle brake system according to the above aspect, the master cylinder may have a piston that reciprocates within the cylinder in the axial direction, and the brake booster may have a plunger connected to the brake pedal and that moves along the axis as the brake pedal rotates, a push rod connected to the piston of the master cylinder, and a reaction disc joined to the end of the push rod opposite to the end to which the piston is connected, and the plunger and the reaction disc may be spaced apart until the pedal force reaches a predetermined force, and the jump-up point may be the point at which the plunger and the reaction disc come into contact when the pedal force reaches the predetermined force.

In the vehicle brake system according to the above aspect, the jump-up point is the point at which there is no gap between the plunger and the reaction disc in the brake booster. As described above, a master cylinder is used with a cylinder diameter set so that the first pressure and the second pressure are approximately equal, ensuring that the driver has a highly accurate operational feel that matches human senses.

In the vehicle brake system according to the above aspect, the brake pedal may further include a rod connection portion that connects to the brake booster and a tread portion that is depressed by the driver, and the distance from the pivot support portion to the tread portion in the longitudinal direction of the brake pedal may be set within a range of 3.5 to 4.7 times the distance from the pivot support portion to the rod connection portion.

In the vehicle brake system according to the above aspect, the ratio of the distance from the journal support to the rod connection on the brake pedal to the distance from the journal support to the tread surface (pedal ratio) is set to 3.5 or greater and 4.7 or less. Therefore, even if a master cylinder with a larger cylinder diameter than conventional master cylinders is used, the driver does not need to apply excessive force to the brake pedal. This also makes it possible to provide an operating feel that matches the driver's intuition.

In the vehicle brake system according to the above aspect, the second pressure may be approximately 0.2 MPa.

After extensive research, the inventors of the present application have determined that the second pressure at the point when the pads come into contact with the brake rotor and frictional force begins to be generated is approximately 0.2 MPa. Based on these findings, by adopting a master cylinder whose cylinder diameter is set so that the first pressure is approximately equal to the second pressure, it is possible to provide an operating feel that matches human senses, as described above.

In the vehicle brake system according to the above aspect, the vehicle may be a passenger car.

The vehicle brake system according to the above aspect is a brake system used in passenger cars. Passenger cars strongly require an operating feel that matches the driver's senses, and the vehicle brake system according to the above aspect can achieve this.

The vehicle brake systems according to the above aspects employ a mechanical configuration equipped with a brake booster, while still ensuring an operational feel that matches human senses.

1 is a schematic diagram showing a configuration of a brake system according to an embodiment. FIG. 2 is a cross-sectional view showing a part of the configuration of the brake booster. FIG. 2 is a cross-sectional view showing the configuration of a master cylinder. FIG. 2 is a cross-sectional view showing the configuration of a disc brake. FIG. 4 is a characteristic diagram showing the relationship between pedal stroke and hydraulic pressure. FIG. 10 is a diagram for explaining a method for determining a master cylinder diameter. FIG. 4 is a characteristic diagram showing the relationship between pedal pressure and brake fluid pressure. FIG. 4 is a characteristic diagram showing the relationship between the diameter of the master cylinder and the jump-up hydraulic pressure. 1A is a characteristic diagram showing the force-stroke characteristics of a brake, and FIG. 1B is a characteristic diagram showing the relationship between pedal depression force and brake fluid pressure in a conventional brake system.

The following describes an embodiment of the present invention with reference to the drawings. Note that the embodiment described below is merely an example of the present invention, and the present invention is not limited to the embodiment described below except for its essential configuration.

1. Schematic Configuration of Brake System 1 A schematic configuration of a brake system 1 according to this embodiment will be described with reference to Fig. 1. The brake system 1 according to this embodiment is, as an example, a brake system applied to a passenger vehicle.

As shown in FIG. 1, the brake system 1 includes a brake pedal 10, a brake booster 11, a master cylinder 12, hydraulic lines 13 and 14, disc brakes 15 and 16, and a reservoir tank 17. The brake pedal 10 has a pivotal support portion 101, which is a portion that is pivotally supported on the vehicle body, at one end of a pedal body 100, and is configured to be rotatable around the pivotal support portion 101. The brake pedal 10 also has a tread portion 102, which is the area where the driver presses down, at a location on the pedal body 100 away from the pivotal support portion 101. Furthermore, the pedal body 100 of the brake pedal 10 has a rod connecting portion 103 to which an operating rod 110 of the brake booster 11 is connected.

Here, in the brake system 1 according to this embodiment, the ratio (pedal ratio) of the distance L0 from the pivot support portion 101 to the tread portion 102 to the distance L1 from the pivot support portion 101 to the rod connecting portion 103 in the longitudinal direction of the pedal body 100 is set to 4.0.

The brake booster 11 is a device that multiplies the pedal force input via the operating rod 110 and outputs the result to the master cylinder 12. The master cylinder 12 is connected to the brake booster 11 and increases the pressure of the hydraulic fluid (brake oil) according to the output of the brake booster 11.

The first hydraulic line 13 is connected to the caliper 150 of the disc brake 15 attached to the front wheel of the vehicle. The second hydraulic line 14 is connected to the caliper 160 of the disc brake 16 attached to the rear wheel of the vehicle.

The disc brakes 15, 16 have calipers 150, 160 with brake pistons that are actuated by hydraulic fluid pressurized by the master cylinder 12, and brake rotors 151, 161 that rotate with the wheels. In this embodiment, floating-type disc brakes 15, 16 are used as an example.

2. Configuration of Brake Booster 11 The configuration of the brake booster 11 will be described with reference to Fig. 2. Note that Fig. 2 shows only a portion of the configuration of the brake booster 11.

As shown in FIG. 2, the brake booster 11 has, in addition to the operating rod 110, a plunger 111, a reaction disc 112, and a push rod 113. The plunger 111 is joined to the end of the operating rod 110 opposite the end connected to the rod connecting portion 103 of the brake pedal 10.

The push rod 113 is arranged to extend toward the side of the brake booster 11 where the master cylinder 12 is attached. The reaction disc 112 is a disc-shaped member located between the plunger 111 and the push rod 113, and is made of rubber, for example.

As shown in the enlarged portion of Figure 2, when the driver is not depressing the brake pedal 10 or when the pedal force is less than a predetermined value, a gap G1 is left between the front end face 111a of the plunger 111 and the receiving surface 112a of the reaction disc 112. Gap G1 narrows as the driver increases the pedal force, and when a predetermined pedal force is applied, the front end face 111a of the plunger 111 and the receiving surface 112a of the reaction disc 112 come into contact. In the brake booster 11, the point at which gap G1 disappears is the jump-up point, and the pressure output from the push rod 113 to the master cylinder 12 at that time is the jump-up amount (first pressure).

In the brake booster 11, the gap G1 cannot be eliminated due to structural variations in the components, and a jump-up point is always present.

3. Configuration of Master Cylinder 12 The configuration of the master cylinder 12 will be described with reference to Fig. 3. Note that Fig. 3 shows the configuration of the master cylinder 12 in a schematic manner, with some components omitted.

As shown in FIG. 3, the master cylinder 12 is a tandem-type master cylinder and includes a cylinder body 120 and a piston 121. The cylinder body 120 has pressure chambers 120a and 120b defined by the piston 121. The cylinder body 120 also has four connection portions 120c to 120f. Connection portions 120c and 120e are connected to the pressure chamber 120a. Connection portion 120c connects the pressure chamber 120a to the reservoir tank 17 (arrow A2). Connection portion 120e is connected to the first hydraulic path 13 and connects the pressure chamber 120a to the caliper 150 (arrow A4).

Connections 120d and 120f are connected to pressure chamber 120b. Connection 120d connects pressure chamber 120b to reservoir tank 17 (arrow A3). Connection 120f is connected to second hydraulic path 14 and connects pressure chamber 120b to caliper 160 (arrow A5).

The piston 121 has a first piston portion 121a and a second piston portion 121b that are spaced apart from each other in the axial direction of the cylinder body 120. The piston 121 is capable of reciprocating in the axial direction of the cylinder body 120 (arrow A1).

In this embodiment, the cylinder diameter _DMC of the master cylinder 12 is, for example, 28.57 mm.

4. Internal Configuration of Calipers 150, 160 of Disc Brakes 15, 16 The internal configuration of the calipers 150, 160 of the disc brakes 15, 16 will be described with reference to Fig. 4. Note that Fig. 4 illustrates the internal configuration of the caliper 150 of the disc brake 15, but the internal configuration of the caliper 160 of the disc brake 160 is the same.

As shown in Figure 4, pads 152 and 153, a brake piston 154, and a piston seal 155 are arranged within the caliper 150. Pads 152 and 153 are arranged opposite each other with the rotor 151 in between. Brake piston 154 is arranged so that it can press against pad 153. Piston seal 155 is arranged to provide a liquid-tight seal between the outer periphery of brake piston 154 and the inner wall surface of the caliper 150.

When hydraulic pressure is applied to the brake piston 154 via the first hydraulic path 13 (arrow B1), the brake piston 154 moves toward the rotor 151 as indicated by arrow B2. As the brake piston 154 moves, the pad 153 also moves as indicated by arrow B3. Before the brake piston 154 moves, there is a gap G3 between the main surface 151b of the rotor 151 and the pad 153. However, as the hydraulic pressure to the brake piston 154 increases, the pad 153 comes into contact with the main surface 151b of the rotor 151 (gap G3 = 0).

If the hydraulic pressure continues to rise while the pad 153 is in contact with the main surface 151b of the rotor 151, the caliper 150 moves as shown by arrow B4, and the pad 152 moves accordingly as shown by arrow B5. When the hydraulic pressure to the brake piston 154 reaches a predetermined value, the pad 152 comes into contact with the main surface 151a of the rotor 151 (gap G2 = 0), and the pad 153 comes into contact with the main surface 151b of the rotor 151, generating a frictional force. The hydraulic pressure of the working fluid at which the pads 152 and 153 come into contact with the rotor 151 and begin to generate a frictional force corresponds to the second hydraulic pressure.

When the oil pressure drops, the brake piston 154 retracts due to the restoring force of the rubber piston seal 155, releasing the pads 152 and 153 from contact with the rotor 151.

5. Relationship Between Pedal Stroke and Fluid Pressure The relationship between the pedal stroke by the driver and the fluid pressure (hydraulic pressure) applied to the brake pistons 154 in the disc brakes 15, 16 will be described with reference to FIG.

As shown in Figure 5, as the driver depresses the brake pedal 10, the hydraulic pressure gradually increases. The relationship between pedal stroke and hydraulic pressure is represented by an exponential curve _LFS . When a tangent line LLS is drawn to the curve _LFS at the point where the pedal stroke is "0" and a tangent line _LU is drawn at the point where the hydraulic pressure is "1.0 MPa," the intersection point _PC between _the tangent lines _LLS and _LU is located near a hydraulic pressure of 0.2 MPa. That is, in the disc brakes 15 and 16, when the hydraulic pressure exceeds 0.2 MPa (arrow C), the gaps G2 and G3 between the rotors 151 and 161 and the pads 152 and 153 disappear, generating frictional force.

The intersection point _PC in FIG. 5 corresponds to the "break point" of the force-stroke characteristic diagram.

6. Setting of Cylinder Diameter _DMC of Master Cylinder 12 Setting of the cylinder diameter _DMC of the master cylinder 12 will be explained using Figure 6. In Figure 6, the first quadrant shows the relationship between the pedal force and the input to the brake booster 11, the second quadrant shows the relationship between the input and output of the brake booster 11, the third quadrant shows the relationship between the input and output of the master cylinder 12, and the fourth quadrant shows the relationship between the output (hydraulic pressure) of the master cylinder 12 and the deceleration G of the disc brakes 15, 16. In Figure 6, the thick dashed line shows the characteristics of a comparative example.

The cylinder diameter _DMC of the master cylinder 12 is set on the premise that the required deceleration G is realized when the driver depresses the brake pedal 10 with a predetermined depression force.

As shown in Figure 6, a perpendicular line is drawn from point P0, where the required deceleration G can be achieved, to the fourth quadrant characteristic line L1 (a characteristic line showing the relationship between hydraulic pressure in the disc brakes 15, 16 and deceleration G), and the intersection point P1 between the perpendicular line and characteristic line L1 is obtained. When trying to achieve the required deceleration G in this embodiment, it can be seen that the required output (hydraulic pressure) of the master cylinder 12 is F1.

In the case of a comparative example employing a master cylinder with a cylinder diameter _DMC of 22.22 mm, the intersection of the characteristic line L12 of the master cylinder according to the comparative example and the hydraulic pressure F1 is P12.

On the other hand, in the present embodiment in which the master cylinder 12 has a cylinder diameter _DMC of 28.57 mm, the intersection point P2 is between the characteristic line L2 of the master cylinder 12 and the hydraulic pressure F1. The input value to the master cylinder 12 (the output value of the brake booster 11) at the intersection point P2 is larger than that at the intersection point P12.

As shown in the second quadrant of Figure 6, the brake booster 11 has a jump-up amount F2, where the output does not change with respect to the input. This jump-up amount F2 is due to the gap G1 described above. Furthermore, on the characteristic line L3, which shows the relationship between the input and output of the brake booster 11, the input and output have a roughly linearly proportional relationship from the jump-up point P5 onwards.

Here, if a perpendicular line L5 is dropped from jump-up point P5 into the third quadrant, the intersection with characteristic line L12 is P16, and the intersection with characteristic line L2 is P6. The output (hydraulic pressure) of the master cylinder 12 at intersection point P16 is 0.4 MPa, while the output (hydraulic pressure) of the master cylinder 12 at intersection point P6 is 0.2 MPa. That is, in the comparative example, the hydraulic pressure (oil pressure) does not coincide with the break point _PC in Figure 5 at jump-up point P5, whereas in this embodiment, the hydraulic pressure (oil pressure) at jump-up point P5 approximately coincides with the break point _PC in Figure 5 at 0.2 MPa.

Next, if a perpendicular line is drawn from intersection P12 to characteristic line L3, intersection P13 is obtained on characteristic line L3. Conversely, if a perpendicular line is drawn from intersection P2 to characteristic line L3, intersection P3 is obtained on characteristic line L3. As shown in Figure 6, intersection P3 has a higher input to the brake booster 11 than intersection P13 in the comparative example.

In the comparative example, by employing a brake pedal 10 having a pedal ratio R _P of 2.7 (brake pedal having characteristic line L14), the input to the brake booster corresponding to the intersection P13 (the pedal force at intersection P14) is realized with the above-mentioned predetermined pedal force. In contrast to this, in the present embodiment, by employing a brake pedal 10 having a pedal ratio R _P of 4.0 (brake pedal having characteristic line L4), the input to the brake booster corresponding to the intersection P13 (the pedal force at intersection P4) is realized with the above-mentioned predetermined pedal force.

7. Jump-Up Point As described above, the hydraulic pressure is 0.2 MPa at the break point in the force-stroke characteristic, and the relationship between this hydraulic pressure and the jump-up amount (hydraulic pressure at the jump-up point) will be explained using Figure 7. In the graph of Figure 7, the dashed characteristic line L16 is a comparative example, and the solid characteristic line L6 is for the brake system 1 according to this embodiment.

As shown by the dashed line in Fig. 7, in the characteristic line L16 of the comparative example, the hydraulic pressure suddenly rises to 0.4 MPa (jump-up amount) when the pedal depression force reaches a predetermined value. The hydraulic pressure value of 0.4 MPa at the jump-up point P17 of the comparative example is higher than the hydraulic pressure of 0.2 MPa at the break point _PC in Fig. 5, and does not match.

On the other hand, in the characteristic line L6 of the brake system 1 according to this embodiment, the jump-up amount (hydraulic pressure) is 0.2 MPa when the pedal force reaches a predetermined value. The hydraulic pressure of 0.2 MPa at the jump-up point P7 is the same as the hydraulic pressure of 0.2 MPa at the break point _PC in Figure 5. As described above, the brake system 1 according to this embodiment employs a master cylinder 12 with a cylinder diameter _DMC of φ28.57 mm, which is larger than conventional master cylinders, making it possible to make the hydraulic pressure at the break point _PC in the force-stroke characteristic and the hydraulic pressure at the jump-up point P7 equal or approximately equal.

8. Range of Cylinder Diameter _DMC of Master Cylinder 12 The brake system 1 according to this embodiment employs the master cylinder 12 having a cylinder diameter _DMC of φ28.57 mm. The range of the cylinder diameter DMC that allows the hydraulic pressure at the break point _PC in the force-stroke characteristics to approximately match the hydraulic pressure at the jump-up point _P7 will be described with reference to FIG. 8.

First, the inventors of the present application conducted extensive research into what range of jump-up amount (hydraulic pressure at jump-up point P7) would provide an operating feel that matches human senses, and found that a range of ±0.05 MPa relative to the hydraulic pressure (0.2 MPa) at the break point _PC in the force-stroke characteristics (in other words, a range of ±25% relative to the hydraulic pressure at the break point _PC in the force-stroke characteristics) would be sufficient. In other words, in this specification, "substantially the same" refers to a range of ±25%.

As shown in Figure 8, the horizontal axis represents the cylinder diameter _DMC of the master cylinder 12, and the vertical axis represents the jump-up amount. In this case, the larger the cylinder diameter _DMC of the master cylinder 12, the more gradually the jump-up amount (hydraulic pressure) decreases. To keep the jump-up amount within the range of 0.2 MPa ± 0.05 MPa (the range indicated by arrow D1), it is necessary to set the cylinder diameter _DMC to a range of φ26.5 mm or more (the range indicated by arrow D2).

Regarding the upper limit of the cylinder diameter _DMC , in order to obtain the target hydraulic pressure (hydraulic pressure required to achieve deceleration G to stop the vehicle), the cylinder diameter _DMC needs to be φ32.0 mm or less.

Furthermore, if an existing master cylinder is to be used, the diameter must be set within the range of φ26.99 mm or more and φ31.75 mm or less. In this case, there is no need to use a custom-made master cylinder, which helps prevent increases in vehicle manufacturing costs.

9. Effects The brake system 1 according to this embodiment employs the master cylinder 12 having a cylinder diameter DMC set so that the hydraulic pressure (first pressure) at the jump-up point _P7 in the brake booster 11 and the hydraulic pressure (second pressure) at which frictional force begins to be generated in the disc brakes 15, 16 are approximately equal. This makes it possible to achieve an operation feel that matches the driver's sense in the mechanical brake system 1. That is, in the brake system 1, the cylinder diameter _DMC of the master cylinder 12 is set so that the hydraulic pressure at the jump-up point P7 and the hydraulic pressure at which frictional force begins to be generated in the disc brakes 15, 16 are approximately equal to each other. Therefore, when the driver depresses the brake pedal 10 and reaches the jump-up point P7, a sudden deceleration G is not applied as in the conventional brake system, and no corrective operation is required. Therefore, the brake system 1 can provide the driver with an operation feel that matches the driver's sense of depressing the brake pedal 10.

Furthermore, the brake system 1 according to this embodiment employs a master cylinder 12 having a cylinder diameter _DMC in the range of 26.5 mm or more, so that the output (hydraulic pressure) from the master cylinder 12 at the jump-up point P7 can be kept smaller than in the past, which is effective in roughly matching the hydraulic pressure (first pressure) at the jump-up point P7 in the brake booster 11 with the hydraulic pressure (second pressure) at which frictional force begins to be generated in the disc brakes 15, 16.

Furthermore, the brake system 1 employs a master cylinder 12 having a cylinder diameter _DMC of 32.0 mm or less, which can avoid situations where the required output (hydraulic pressure) is not obtained, and is suitable for providing the driver with a high level of operating feeling.

Furthermore, in the brake system 1 according to this embodiment, the jump-up point P7 is determined by the gap G1 between the plunger 111 and the reaction disc 112 in the brake booster 12. However, the master cylinder 12 is used, which has a cylinder diameter _DMC that is set so that the hydraulic pressure at the jump-up point P7 (first hydraulic pressure) and the hydraulic pressure at which frictional force begins to be generated in the disc brakes 15, 16 (second hydraulic pressure) are approximately equal. This ensures that the driver has an excellent operating feel that is in line with human senses.

Furthermore, in the brake system 1 according to this embodiment, the pedal ratio of the brake pedal 10 is set to 3.5 or more and 4.7 or less (for example, 4.0), so even if the master cylinder 12 has a larger cylinder diameter _DMC than conventional ones, the driver does not need to apply an excessively large force to depress the brake pedal 10. This also makes it possible to provide an operation feeling that matches the driver's senses.

As a result of extensive research, the inventors of the present application have determined that the hydraulic pressure at the point where the pads 152, 153 come into contact with the brake rotors 151, 161 and frictional force begins to be generated is approximately 0.2 MPa (0.2 MPa ±0.05 MPa ₎ . Based on these results, by employing a master cylinder 12 with a cylinder diameter _DMC set so that the hydraulic pressure at jump-up point P7 approximately matches the hydraulic pressure at which frictional force begins to be generated in the disc brakes 15, 16, it is possible to provide an operation feeling that matches human senses.

The brake system 1 according to this embodiment is a brake system used in passenger cars. Passenger cars strongly require an operating feel that matches the driver's senses, and brake system 1 can achieve this.

As described above, the brake system 1 according to this embodiment employs a mechanical configuration including a brake booster 11, while still ensuring an operational feel that matches human sensibilities.

[Modification]
In the above embodiment, the master cylinder 12 has a cylinder diameter _DMC set in the range of φ26.5 mm to φ32.0 mm, but the present invention is not limited to this. That is, it is sufficient to use a master cylinder whose cylinder diameter is set so that the hydraulic pressure at the jump-up point (first pressure) and the hydraulic pressure at which frictional force in the disc brake begins to occur (second pressure) are approximately equal.

In the above embodiment, the jump-up amount was caused by the gap G1 between the plunger 111 and the reaction disc 112 in the brake booster 11. However, in the present invention, the jump-up amount may also be caused by variations in other components of the brake booster.

In addition, in the above embodiment, the pedal ratio of the brake pedal 10 was set to 3.5 or more and 4.7 or less. However, in the present invention, when a master cylinder is used whose cylinder diameter is set so that the hydraulic pressure at the jump-up point and the hydraulic pressure at which frictional force in the disc brake begins to occur are approximately equal, it is possible to adopt a pedal ratio that allows the driver to input the necessary force to the brake booster.

In addition, in the above embodiment, a master cylinder 12 is used in which the cylinder diameter DMC is set so that the hydraulic pressure at the jump-up point roughly matches the hydraulic pressure at which frictional force begins to be generated in the disc brake. In this case, "roughly matching" can mean, for example, that a range of approximately ±25% of the reference hydraulic pressure is acceptable.

Furthermore, while the brake system 1 according to the above embodiment is intended for use in passenger vehicles that are primarily used for transporting people and have a small passenger capacity (e.g., 10 or fewer), the present invention is not limited to this and can also be used in vehicles used to transport cargo.

1 Brake system 10 Brake pedal 11 Brake booster 12 Master cylinder 15, 16 Disc brake 111 Plunger 112 Reaction disc 113 Push rod 150, 160 Caliper 151, 161 Rotor 152, 153 Pad 154 Brake piston D _MC master cylinder diameter P7 Jump-up point P _C break point

Claims (6)

A braking system for a vehicle, comprising:
a brake pedal that is pivotally supported by a pivotal support portion and is configured to be rotatable around the pivotal support portion;
a brake booster connected to the brake pedal, multiplying a pedal depression force input to the brake pedal and outputting the result;
a master cylinder connected to the brake booster and increasing the pressure of hydraulic fluid in accordance with the output of the brake booster;
a brake having a brake piston connected to the master cylinder and actuated by the pressurized hydraulic fluid, a brake rotor that rotates together with a wheel of the vehicle, and a pad that is pressed against the brake rotor by actuation of the brake piston to generate a frictional force between the brake rotor and the pad;
Equipped with
the brake booster has a characteristic that there is a jump-up point at which it starts to output a first pressure, which is a predetermined pressure, to the master cylinder as an output start pressure after the pedal depression force reaches a predetermined depression force,
the brake has a characteristic that a frictional force begins to be generated between the brake rotor and the pad when the hydraulic fluid pressure reaches a second pressure, which is a predetermined pressure;
The master cylinder has a cylinder diameter set so that the first pressure at the jump-up point in the brake booster and the second pressure at which the frictional force in the brake begins to be generated are substantially equal to each other.
Vehicle braking system. 2. The vehicle brake system according to claim 1,
The master cylinder has a cylinder diameter set within a range of 26.5 mm or more and 32.0 mm or less.
Vehicle braking system. 3. The vehicle brake system according to claim 1,
The master cylinder has a piston that reciprocates in the cylinder in the axial direction,
The brake booster is
a plunger connected to the brake pedal and adapted to move along an axis in accordance with rotation of the brake pedal;
a push rod connected to the piston of the master cylinder;
a reaction disk joined to an end of the push rod opposite to the end to which the piston is connected;
and
The plunger and the reaction disc are spaced apart from each other until the pedal force reaches a predetermined value.
The jump-up point is a point at which the pedal depression force reaches the predetermined depression force and the plunger and the reaction disc come into contact with each other.
Vehicle braking system. 3. The vehicle brake system according to claim 1,
The brake pedal further includes a rod connecting portion that is a connecting portion with the brake booster, and a tread portion that is depressed by a driver,
In the longitudinal direction of the brake pedal, the distance from the pivot support portion to the tread portion is set within a range of 3.5 to 4.7 times the distance from the pivot support portion to the rod connecting portion.
Vehicle braking system. 3. The vehicle brake system according to claim 1,
The second pressure is approximately 0.2 MPa.
Vehicle braking system. 3. The vehicle brake system according to claim 1,
The vehicle is a passenger car.
Vehicle braking system.