Brake Systemlink
Last updated: October 20, 2023
Overviewlink
The Model Y brake system is a hydraulic based brake system, consisting of 4 brake calipers actuated by an electromechanical brake booster and an Electronic Stability Program (ESP) system. The rear brake calipers have an integrated Electronic Park Brake (EPB) motor mounted to each caliper for the electronically actuated parking brake.
Depending on the configuration, the brake system will have the following:
Base Package:
- Brembo front brake calipers with Mando rear brake calipers
- Grey calipers
- Internally-ventilated cast iron rotors
Performance Package:
- Brembo front and rear brake calipers
- Red calipers
- Lightweight two-piece rotors for enhanced performance and thermal capacity
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| 1. ESP Unit Assembly 2. Brake Fluid Reservoir 3. Electromechanical Brake Booster 4. Brake Pedal Assembly 5. EPB Motor 6. Rear Brake Caliper 7. Rear Brake Rotor 8. Rear Hydraulic Brake Lines 9. Front Brake Caliper 10. Front Brake Rotor 11. Wheel Speed Sensor |
| Brake System, Overview |
Brake System Overviewlink
Front Brake Caliperslink
The front brake system uses a mono-block aluminum four-piston design fixed caliper with dual bleed nipples.
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| 1. Brake Fluid bleed nipples 2. Brake Pad 3. Brake Caliper Body 4. Brake Pad anti-rattle clip 5. Brake Rotor 6. Hub (incorporates Wheel Speed Sensor Tone Ring) 7. Brake Piston (x4) 8. Brake Flexible Pipe connection |
Rear Brake Caliperslink
Mando Rear Brake Caliperslink
The Mando rear brake system uses a single piston sliding caliper with integrated EPB with single bleed nipple.
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| 1. Brake Rotor 2. Electronic Park Brake (EPB) 3. Single Bleed Nipple 4. Brake Caliper Body 5. Brake Caliper Carrier 6. Brake Pad 7. Hub (incorporates Wheel Speed Sensor Tone Ring) |
Brembo Rear Brake Caliperslink
The Brembo rear brake system uses a single piston sliding caliper with integrated EPB and single bleed nipple.
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| 1. Brake Rotor 2. Electronic Park Brake (EPB) 3. Single Bleed Nipple 4. Brake Caliper Body 5. Brake Caliper Carrier 6. Brake Pad 7. Hub (incorporates Wheel Speed Sensor Tone Ring) |
Brake Padslink
The brake pads consist of non-asbestos organic friction material bound to a steel backing plate located between the caliper pistons and the rotor. They are equipped with wear indicators which is a thin metal strip attached to the brake pad that squeals as it rubs against the rotor when the pad wears down. This squealing sound indicates that the brake pads have reached the end of their service life and require replacement.
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| 1. Brake Pad 2. Wear Indicator |
Brake Rotorslink
The brake rotors are of a single piece internally-ventilated cast iron structure treated with a hardening process to improve corrosion protection and wear resistance, because of this these items are non-serviceable. There is a minimum thickness level, please check the latest release of the Workshop Manual for specifications.
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| Cut-away showing internal ventilation |
Electronic Park Brakelink
The Electronic Park Brake (EPB) system is integrated into the rear foundation brake calipers and is not separately serviceable.
It is comprised of an EPB drive unit, brake caliper, piston assembly, brake pad assembly, and two electronic control units. The EPB control units are integrated into the left vehicle control unit (VCLEFT) and right vehicle control unit (VCRIGHT) which control the corresponding EPB motor.
The parking brake can be engaged by multiple methods: - Navigating to Controls > Safety & Security > Parking Brake and following the on-screen instructions. - Automatically when the driver exits while the vehicle in Neutral or Drive. - By pressing and holding the button on the end of the drive stalk (for longer than 800 ms) while in Park.
If either of the following happens, the RED parking brake will light up on the touchscreen: - The parking brake is applied using the touchscreen. - The button on the end of the drive stalk is pressed and held in Park mode.
Note
The EPB will be applied but the RED parking brake indicator will NOT light up on the touchscreen when the button on the end of the drive stalk is short pressed.
If a fault has been detected with the EPB, the YELLOW parking brake lights on the touchscreen with a fault message.
Electromechanical Brake Booster (iBooster)link
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| 1. Brake Fluid Reservoir 2. Tandem Master Cylinder (TMC) 3. Booster Powerpack ECU 4. Booster Gear Housing Assembly 5. Input Rod |
The electromechanical brake booster is the 2nd generation iBooster. This iBooster has reduced box volume with a more compact design and reduced weight by use of plastic material and simplified gear housing. The iBooster is a vacuum-free electromechanical actuated system which is an integral part of the brake system.
If the iBooster suffers an irrecoverable fault, such as disruption of supply-power, the driver can still brake unhindered; the driver's brake energy is transmitted mechanically through the booster to the tandem master cylinder. The ESP system detects a booster fault, and generates additional brake force to aid the driver by using its own hydraulic pump (normally used for stability and traction control events). The brake force is metered proportional to the measured upstream hydraulic pressure from the tandem master cylinder, to allow reasonable modulation of brake force by the driver. During this time, pumping noise and pedal pulsations will be felt through the brake pedal by the driver. This is the intended back-up operating mode, and allows a much greater vehicle deceleration to be achieved than by the driver’s muscular energy alone. This function is called Hydraulic Brake Boost (HBB).
Brake Fluid Reservoirlink
The brake fluid reservoir, mounted on top of the Tandem Master Cylinder (TMC), is a specially-formed clear plastic fluid container designed to fill to the necessary brake fluid volume. The brake fluid reservoir houses a fluid level indicator which will set a RED warning light on the Touch Screen and will log an Alert in log data if the brake fluid level is too low.
Warning
Only Tesla-approved brake fluid is permitted in the brake system. The use of any other unapproved fluid may result in performance degradation or component damage. Do not use fluid from unsealed containers, as it might have absorbed moisture from the atmosphere.
Booster Assemblylink
Warning
No 3rd-party modification of this is permissible. Foreign magnetic fields MUST be kept away from the electronic control unit (ECU) at all times. All parts are non-serviceable.
The booster assembly itself can be broken down to several key functional areas to aid service and troubleshooting discussions:
Powerpacklink
Consists of the ECU and motor housing. All of the electronic controls are located within the black plastic ECU housing. The housing is permanently attached to the booster motor housing, and is non-serviceable. The 12V-brushless DC motor is located in the cylindrical steel housing fastened to the booster assembly. Motor rotation is measured using a rotational hall-effect sensor. There is one electrical interface on the ECU housing to connect to the vehicle.
Gear Housinglink
The primary booster mechanical components are located inside the steel housing. The internal components are physically separate from the master cylinder and brake fluid volume, as well as the external environment. This is a clean zone – no foreign contaminants, such as dirt, liquid, or any solvents or lubricants are permitted to enter the housing. Translation of the motor shaft rotation to linear motion is done by a gear-set inside this housing. A mechanical device to enable the driver to modulate brake force is packaged with the transmission. Located in the gear housing is the Differential Travel Sensor (DTS). The steel gear housing helps shield the DTS from magnetic interference.
Input Rodlink
The input tie-rod is the mechanical link between the brake pedal arm and the booster internal mechanism. It is connected to the pedal arm by a clevis and pin, and enters the booster housing through a rubber bellows, this is extended through the entire booster via another tie-rod to rigidly couple with the Tandem Master Cylinder. The input tie-rod is very sensitive to all mechanical loading while not mounted. Extreme care should be taken when handling the booster while not fully-assembled in the vehicle, to avoid permanently damaging the booster mechanism.
Electronic Stability Program Unitlink
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| 1. ESP ECU housing the processor and valve driver electronics 2. Valve block, containing the hydraulic valves and accumulators 3. ESP pump motor |
Normal Brakinglink
The iBooster detects the driver’s brake request by an integrated Pedal Travel Sensor and this information is sent to the integrated control unit. The control unit operates the electric motor, while a 2 stage gear unit converts the motor torque into the necessary longitudinal boost force. The force supplied by the booster and the driver is converted into hydraulic pressure in a conventional tandem master brake cylinder, this is the farthest upstream element of the “wet” hydraulic system, this is then distributed into the rest of the hydraulic system via the ESP unit.
The tandem master cylinder consists of two floating hydraulic pistons in series. There are two hydraulic inlets, one for each piston, from the brake fluid reservoir, and two hydraulic outputs, one for each piston, routed to the ESP unit.
When the brake pedal is released, the springs in the master cylinder return the master cylinder pistons to the rest position. Brake system pressure is relieved, the caliper pistons retract, and the brake pads no longer apply a braking force to the rotors.
Electronic Stability Programlink
The ESP hydraulic control unit is separate from the iBooster and the calipers in the hydraulic circuit. This allows for the control unit to serve as a redundant brake actuation system in case of iBooster faults.
The ESP function assists the driver in maintaining control of the vehicle during cornering. ESP differs from conventional ABS/TC Systems by using yaw rate and acceleration sensor information in addition to the four wheel speed sensors (hall-effect sensors), located on the four wheel hubs which provide the wheel speed signal for each wheel.
ESP calculates the intended path of the vehicle based on the driver’s inputs (from a steering angle sensor) and compares it to the measured rate of turn of the vehicle from the yaw rate sensor.
ESP monitors for under-steer or over-steer events during cornering. In the case of understeering, braking the rear inside wheel results in a positive yaw torque that helps the vehicle turn into the corner. During oversteering, braking the front outside wheel results in a negative yaw torque that steers the vehicle out of the corner and helps the rear axle regain traction. If the vehicle path deviates from the driver’s path, ESP briefly applies the brakes at individual wheels to help steer the vehicle back to the intended path. ESP also controls and limits motor power to the extent necessary to support lateral tire grip during cornering.
ESP works on all road surfaces and weather conditions to help utilize all available road force to keep the vehicle stable. However, ESP cannot evade the laws of physics, and does not prevent loss of control if a driver carries excessive speed into a corner. Furthermore, ESP only assists the vehicle to follow the path the driver is steering. ESP does not prevent the driver from steering a vehicle off the road.
The ESP also operates a function commonly known as ABS (Anti-lock Brake System) this adjusts the maximum brake pressure transmitted to the wheels preventing loss of road-holding under all tire and road conditions caused by wheel locking. The system has been designed to integrate, but not replace, the normal mechanical braking system.
The ESP controller constantly monitors and compares signals received from the 4 speed sensors. When the brake is applied and a wheel is detect decreasing speed in relation to the other wheels and that it is about to lock, the ESP modulator reduces the brake pressure at the that wheel enough to prevent wheel locking, this alteration of brake pressure can be felt as a pulsing sensation through the brake pedal. This demonstrates that the ESP is operating and is not a cause for concern. As soon as the wheel speed becomes stable, the ESP controller increases brake pressure, thereby maintaining optimal braking force at all times. The ESP control system performs these adjustments several hundred times per second on each wheel independently. This enables the driver to achieve the highest brake force physically possible, while maintaining vehicle stability and steering over any road surface.
The ABS indicator briefly flashes yellow on the touchscreen when the vehicle switches on. If this indicator lights up at any other time, during the drive cycle, an ESP fault has occurred and the ESP is not operating. The braking system remains fully operational and is not affected by an ESP malfunction. However, braking distances may increase.
Traction Controllink
The traction control system constantly monitors the speed of the front and rear wheels. If a loss of traction is detected by analysis of the wheel speed sensors, the system minimizes wheel spin by controlling brake pressure using ESP and motor torque using the drive inverter. By default, the traction control system is on. Under normal conditions, it should remain on to ensure maximum control of the vehicle.
The yellow indicator flashes on the touchscreen whenever the traction control system is actively controlling brake pressure and motor power to minimize wheel spin. If the indicator stays on, a fault is detected with the traction control system.
Hydraulic Fade Compensationlink
Hydraulic Fade Compensation is a function that increases the braking pressure when brake fade is detected by the ESP system. It looks at the pressure in the brake master cylinder, compares this to what is happening at the wheel, and uses the ESP pump to actively build pressure in the system up to ABS initiation levels. HFC will normally trigger when there is not enough friction between brake pad and rotor due to overheated or wet/iced brake pads.
Alert ESP_a118_hfcActive will be recorded in log data if Hydraulic Fade Compensation was active.
Emergency Brakinglink
The Emergency Brake or Dynamic Brake can be actuated by holding pressed the Gear Selector Parking Brake Button, the touchscreen displays a visual warning and sounds a chime.
This is used in emergency situations in the event of the normal braking system encountering a malfunction i.e. total brake fluid loss.
The Gear Selector Parking Brake Button will need to pressed until the desired reduction of speed has been obtained or until a complete stop.
An Emergency Brake request will cause the EPB to apply while the vehicle is moving.
Alerts EPBR_a180_dynamicActive and/or EPBL_a180_dynamicActive will be recorded in log data if emergency braking was active.
Automatic Emergency Brakinglink
Warning
Automatic Emergency Braking is designed to reduce the severity of an impact. It is not designed to avoid a collision.
Warning
The brake pedal moves downward abruptly during automatic braking events. Always ensure that the brake pedal can move freely.
When Automatic Emergency Braking applies the brakes, the touchscreen displays a visual warning and sounds a chime. The driver may also notice an abrupt downward movement of the brake pedal. The brake lights turn on to alert other road users that the vehicle is slowing down.
Automatic Emergency Braking logic is performed by the Driver Assistance System. For more details on how this feature operates, see the Automatic Emergency Braking section of the Driver Assistance System Hardware 3.1 Theory of Operation.
Automatic Emergency Braking does not apply the brakes, or stops applying the brakes, when:
- The driver turns the steering wheel sharply.
- The driver presses and releases the brake pedal while Automatic Emergency Braking is applying the brakes.
- The driver accelerates hard while Automatic Emergency Braking is applying the brakes.
- The obstacle is no longer detected ahead.
Automatic Emergency Braking is automatically enabled. To disable it for your current drive, use the touchscreen:
Controls > Autopilot > Automatic Emergency Braking
Vehicle Holdlink
Vehicle Hold can continue to apply the brakes even after the foot brake has been released. After coming to a complete stop, press the brake pedal again until the touchscreen displays the Vehicle Hold indicator light to enable Vehicle Hold.
The driver can then release the brake pedal and remain stopped, even on a hill. This indicator displays on the touchscreen whenever Vehicle Hold is actively braking.
To disengage Vehicle Hold, press the accelerator pedal or press and release the brake pedal. Shifting into Neutral also disengages the Hill Hold Function.
Note
Vehicle Hold shifts into Park after approximately 10 minutes of use or detection of Driver Leaving the vehicle.
Slip Startlink
To allow the wheels to spin at a limited speed, the driver can enable Slip Start. Slip Start can be enabled at any speed, however it is less effective at higher speeds.
Under normal conditions, Slip Start default is off. Enable it only in circumstances when deliberate wheel spin is required:
- Starting on a loose surface, i.e. gravel/snow.
- Driving in deep snow, sand or mud.
- Rocking out of a hole or deep rut.
To activate Slip Start, use the touch screen menu:
Controls > Driving > Traction Control > Slip Start
The touchscreen displays an alert message when Slip Start is enabled.
Slip Start is not available whilst using Traffic Aware Cruise Control. If Traffic Aware Cruise Control is activated whilst in Slip Start the system will revert back to normal traction control conditions.
Note
Slip Start is automatically disabled the next time start cycle.
Off-Road Assistlink
In addition to allowing the wheels to spin, Off-Road Assist balances the torque between the front and rear motors to optimize traction vs range. Off-Road Assist improves traction on rough and soft surfaces where one side of the vehicle may lose traction while the other side still has traction. With Off-Road Assist enabled, the accelerator pedal provides more gradual torque, which is useful for crawling at low speeds (for example, over rocky surfaces).
To activate Off-Road Assist, use the touch screen menu
Controls > Driving > Traction Control > Off-Road Assist
The touchscreen displays an alert message OFF_ROAD above the Speedometer and the TC Off symbol when Off-Road Assist is enabled.
Off-Road Assist is not available whilst using Traffic Aware Cruise Control. If Traffic Aware Cruise Control is activated whilst in Off-Road Assist the system will revert back to normal TC conditions.
Note
Off-Road Assist is automatically disabled the next time start cycle.
Note
AEB and Lane Departure Avoidance do not operate in Off-Road Assist.
Wheel Speed Sensorlink
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| 1. Wheel Speed Sensor (WSS) 2. Sensor tone ring integrated into wheel bearing 3. Hub |
The wheel speed sensors provide the digital wheel speed signals to the ESP modulator. A wheel speed sensor is installed in each wheel hub unit. The sensing element is situated to align with the magnetic sensor tone ring, integrated with the inboard bearing seal. Each seal contains the magnetic elements arranged in pole-pairs that make up the tone ring. Only one side of the bearing contains the integrated tone ring.
As the wheels rotate, the pole-pairs in the seals induce sinusoidal voltage fluctuations in the wheel sensors (Hall Effect sensors) that are converted into square wave signals. The signal frequency is proportional to the speed of each wheel.
The wheel speed sensors are active sensors. They output a current-based signal that has been converted from analogue form, and processed in the sensor unit before being sent to the ESP control unit. This ensures that disturbances and errors in the raw Hall effect signals are not passed to the ESP processor. The pulse width carries further direction and diagnostic information and is not proportional to vehicle speed.
Inertial Measuring Unitlink
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The Inertial Measurement Unit is an electronic device that measures yaw, roll, and pitch of the vehicle. This is integrated into the Restraints Control Module (RCM) and communicates with the ESP and iBooster over the Chassis CAN network.
The sensor is used for ESP operation and measures the vehicle’s rotation around its vertical axis (yaw rate), while at the same time measuring the acceleration perpendicular to the driving direction. The ESP function uses the sensor inputs to detect the onset of side slip during cornering.
Pedal Assemblylink
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| 1. Brake Pedal Clevis Pin 2. Brake Pedal 3. Brake Switch 4. Accelerator Pedal Sensor Housing 5. Accelerator Pedal |
The brake pedal and accelerator pedal form a single assembly. The brake pedal arm connects to the booster input rod using a clevis. The bracket houses the brake switch which senses when the brake pedal arm is pressed. The accelerator pedal assembly has a housing at its pivot containing an electromagnetic induction device to sense rotation. There are two circuits for redundancy.
System Faultslink
If the ESP system faults, normal braking is maintained. However, braking distances may increase and wheels may lock under heavy braking. The RED brake and/or YELLOW ABS fault indicator lights display in the instrument cluster along with a fault message:
If the vehicle power is interrupted and the Hydraulic Boost Compensation (HBC) is also not available, the iBooster is still able to provide a deceleration through a mechanical push through which provides a direct connection between the pedal and the master cylinder.