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Brake force and vehicle stability
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When the brake pressure is increased, wheel speed is reduced. Slip occurs between the tire and the road surface and brake force is gener-ated. The limit of this brake force is determined by the friction force between the tire and the road surface and is closely related to wheel slippage. Wheel slippage is represented by the slip ratio.
Therefore, side force is also closely related to wheel slippage. See figure И. If the brakes are applied while keeping the proper slip ratio, it is possible to obtain the maximum brake force without losing much side force.
ABS allows full use of the tire capabilities even on slippery road surfaces or less slippery road surfaces. See figure Й.
EAS00875
Wheel slip and hydraulic control
The ECU (ABS) calculates the wheel speed of each wheel according to the rotation signal received from the front and rear wheel sen-sors. In addition, the ECU (ABS) calculates the vehicle chassis speed and the rate of speed reduction based on the wheel speed values.
The difference between the chassis speed and the wheel speed calculated in the slip ratio for-mula is equal to the wheel slip. When the wheel has a tendency to lock, the wheel speed is suddenly reduced. When the wheel slip and the wheel speed reduction rate exceed the preset values, the ECU (ABS) determines that the wheel has a tendency to lock.
If the slip is large and the wheel has a ten-dency to lock (point A in the figure), the ECU (ABS) reduces the brake fluid pressure in the brake caliper and increases the pressure of the brake fluid in the brake caliper when the tendency to lock has diminished (point B in the figure).
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FEATURES
EAS00876
GEN
INFO
| between the | Brake force | |
| surface | ||
| Friction force | tire and road | Side force |
| Slip ratio (%) | ||
ABS operation and vehicle control
If the ABS starts operating, there is a tendency of the wheel to lock, and the vehicle is approaching the limit of control. To make the rider aware of this condition, the ABS has been designed to generate a reaction-force pulsat-ing action in the brake lever.
NOTE:
When the ABS is activated, a pulsating action may be felt at the brake lever, but this does not indicate a malfunction.
The higher the cornering force on a tire, the less traction there is available for braking. This is true whether the vehicle is equipped with an ABS or not. Therefore, sudden braking while cornering is not recommended. Excessive cor-nering force, which an ABS cannot prevent, could cause the tire to slip sideways.
WARNING
The braking of the vehicle, even in the worst case, is principally executed when the vehicle is advancing straight ahead. During a turn, sudden braking is liable to cause a loss of traction of the tires. Even in vehicles equipped with an ABS, overturn-ing of the vehicle cannot be prevented if it is braked suddenly.
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The ABS functions to prevent the tendency of the wheel to lock by controlling the brake hydraulic pressure. But, if there is a tendency of the wheel to lock on a slippery road surface, due to engine braking, the ABS may not be able to prevent the wheel from locking.
WARNING
The ABS controls only the tendency of the wheel to lock caused by applying the brakes. The ABS cannot prevent wheel lock on slippery surfaces, such as ice, when it is caused by engine braking, even if the ABS is operating.
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GEN
FEATURES INFO
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EAS00878
ABS component functions
• Wheel sensors and sensor rotors
Wheel sensors 1 detect the wheel rotation speed and transmit the wheel rotation signal to the ECU (ABS).
Each wheel sensor is composed of a perma-nent magnet and a coil. The wheel sensors are installed in the sensor housing for each wheel. Sensor rotors 2 are installed inside the front and rear wheel hubs and rotate with the wheels. Each sensor rotor has 40 serrations that face the sensor housing. As the distance changes between the top and bottom of the serrations with the rotation of the wheels, inductive electromotive force is generated in the wheel sensors. Wheel rotation speed is detected based on the frequency of this alter-nating voltage.
3 At high speed
4 At low speed
5 Wheel sensor
6 Sensor rotor
| EAS00879 | |
| • Hydraulic unit | |
| The hydraulic unit 1 is composed of a hydrau- | |
| lic control valve (solenoid valve, flow control | |
| valve), a buffer chamber, and a hydraulic | |
| pump for each brake and an ABS motor. The | |
| hydraulic unit adjusts the front and rear wheel | |
| brake fluid pressure to control the wheel rota- | |
| tion speed according to signals transmitted | |
| from the ECU (ABS). |
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FEATURES INFO
• Electronic control unit (ECU)
The ECU (ABS) 1 controls the ABS and is located on the right side of the vehicle near the top of the front fork. To protect the ECU (ABS) from water damage, it is protected by a cover.
• ABS control operation
The ABS control operation performed in the ECU (ABS) is divided into the following two parts.
• Hydraulic control
• Self-diagnosis
These operations are performed once every 8/1,000 of a second. When a failure is detected in the ABS, a malfunction code is stored in the memory of the ECU (ABS) for easy problem identification and troubleshoot-ing.
NOTE:
Some types of failures are not recorded in the memory of the ECU (ABS) (e.g., a drop in bat-tery voltage).
1 Software operation flow
2 Set the main switch to “ON”.
3 Initialize
4 Self-diagnosis (when static)
5 Self-diagnosis (when riding)
6 Receive signals
7 Control operation
8 Depressurize/pressurize
И 8/1,000 of a second
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1 
• Fail-safe relay
The fail-safe relay controls the power supply of the hydraulic unit and is located upper the ECU (ABS).
1 Fail-safe relay
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FEATURES
Composition and operation
GEN
INFO
The fail-safe relay is composed of the solenoid relay 1 and ABS motor relay 2. The solenoid relay is activated (continuous) by signals transmitted from the ECU (ABS). As a result, the solenoid valve 3 can be operated.
If a malfunction occurs in the circuit, the solenoid relay is deactivated and it becomes impossible for the solenoid valve to reduce the hydraulic pressure of the brake fluid and normal braking is resumed.
The ABS motor relay is also activated by signals transmitted from the ECU (ABS) and operates simultaneously when the ABS starts to reduce the hydraulic pressure of the brake fluid.
If the solenoid relay is turned off, the motor relay is also deactivated and the motor stops operating if there is a malfunction.
| 1 Solenoid relay | 6 Pump motor monitor | A Power |
| 2 ABS motor relay | 7 ABS warning light | B Fail-safe relay |
| 3 Solenoid valve | 8 Fail-safe relay coil | C Hydraulic unit |
| 4 ECU (ABS) | 9 Rear solenoid | |
| 5 Pump motor relay coil | 0 Front solenoid |
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FEATURES
ABS operation
GEN
INFO
The ABS hydraulic circuit consists of two systems: the front wheel and rear wheel. The following describes the front system only.
• Normal braking (ABS not activated)
When the ABS is not activated port D A of the solenoid valve is closed because a control signal has not been transmitted from the ECU (ABS) and port A 7 and port B 9 of the flow control valve are open. Therefore, when the brake lever is squeezed, the hydraulic pressure in the brake master cyl-inder increases and the brake fluid is sent to the brake caliper via port A and port B.
At this time, the inlet and outlet check valves of the pump close the lines and brake fluid is not sent. As a result, the brake master cylinder directly pressurizes the brake caliper during normal braking. When the brake lever is released, the brake fluid in the brake caliper returns to the brake master cyl-inder via port A and port B.
1 Brake master cyl- A Port D
inder B Solenoid valve
2 Brake light switch C Port C
3 ABS motor D Brake caliper
4 Pump E ECU (ABS)
5 Buffer chamber F ABS warning light
6 Flow control valve G Brake fluid pres-
7 Port A sure
8 Spool H Time
9 Port B I Repressurizing
0 Orifice
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FEATURES
• Emergency braking (ABS activated)
GEN
INFO
1) Depressurized state
When the front wheel is about to lockup, port D A of the solenoid valve is opened by the “depres-surization” signal transmitted from the ECU (ABS). When this occurs, the spool of the flow control valve compresses the return spring to close port B 9. Brake fluid that has entered through port A 7 is restricted by the orifice 0 and the brake fluid is sent to the brake caliper via port C C and port D A, and the buffer chamber. As a result, the hydraulic pressure in the brake caliper is reduced.
The brake fluid stored in the buffer chamber is pumped back to the brake master cylinder by the fluid pressure pump linked to the pump motor.
1 Brake master cyl- A Port D
inder B Solenoid valve
2 Brake light switch C Port C
3 ABS motor D Brake caliper
4 Pump E ECU (ABS)
5 Buffer chamber F ABS warning light
6 Flow control valve G Brake fluid pres-
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7 Port A sure
8 Spool H Time
9 Port B I Repressurizing
0 Orifice
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FEATURES INFO
2) Pressurized state
Port D A is closed by the “pressurization” signal transmitted from the ECU (ABS). Before this occurs, the spool of the flow control valve has compressed the return spring to close port B 9. Brake fluid that has entered through port A 7 is further restricted by the orifice 0 and the brake fluid is sent to the brake calipers via port A 7 and port C C. At this time, the brake is pressurized at a constant speed regardless of the brake fluid pressure level since restriction of port A 7 changes so that a constant pressure difference is maintained between chamber A J and cham-ber B K of the flow control valve.
1 Brake master cyl- B Solenoid valve
inder C Port C
2 Brake light switch D Brake caliper
3 ABS motor E ECU (ABS)
4 Pump F ABS warning light
5 Buffer chamber G Brake fluid pres-
6 Flow control valve sure
7 Port A H Time
8 Spool I Repressurizing
9 Port B J Chamber A
0 Orifice K Chamber B
A Port D
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FEATURES INFO
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