# Drive Unit

## Overview

### Component Location

1. Drive inverter

2. Motor

3. Driveshaft LH

4. Gearbox

5. Driveshaft RH

1. Drive inverter

2. Drive inverter breather

3. Gearbox breather

4. Gearbox rear mounting

5. Motor

6. Motor encoder sensor

7. Coolant manifold

8. Coolant inlet

9. Motor side mounting

10. Driveshaft LH

11. Gearbox oil drain plug

12. Gearbox oil fill plug

13. Gearbox front mounting

14. Driveshaft RH

1. Breather line

2. High voltage cable inlet

3. High voltage cable connection cover

4. 12V connector

5. Coolant outlet port

6. Gearbox cooler

### General

The motor, gearbox, and drive inverter make up the drive unit assembly. The component parts of the assembly are highly integrated, leveraging shared interfaces and interconnects to reduce system complexity and improve reliability. The three component parts cannot be separated in the field, and must only be opened in a clean environment with appropriate tools and test equipment.

WARNING: Follow all high voltage safety requirements anytime the drive unit is part of a vehicle repair. The drive unit contains 1.2mF of internal capacitance, enough to be lethal if the internal discharge functions are not working properly. Always use a multimeter to confirm that no dangerous voltage is present on the DC input connector of the drive inverter.

The drive unit assembly is attached to the rear sub-frame by front and rear gearbox mounts that are integrated into the gearbox case, and a third mount bolted onto the motor housing.

#### Theory of Operation

All spinning motors must have a changing magnetic field to induce rotation and generate torque. Brushed motors do this by mechanically switching wire coils on and off as the rotor spins. AC induction motors do not have brushes; instead, they use an AC waveform to vary the magnetic fields in the motor and create torque.

The drive inverter converts the direct current (DC) from the battery pack into three alternating currents (AC) in the motor stator. The current waveforms are 120° out of phase with each other and create a rotating magnetic field in the stator. This stator field induces current in the rotor. The induced rotor current creates a second magnetic field that opposes the stator field. The two fields working against each other produce motor torque.

The speed of the motor depends on the frequency of the AC supplied by the drive inverter. The torque of the motor depends on the amplitude of the AC.

#### Top Level Drive Unit Specifications

The motor has a maximum rotor speed of 16000 rpm.

- Base: 415 Nm of torque and 270kW for a motor shaft speed between 6,500 rpm and 9,000 rpm.

- Performance: 590 Nm of torque and 310kW for a motor shaft speed between 5,500 rpm and 9,000 rpm.

The drive inverter delivers 900A rms to the motor in a Base drive unit, and 1200A rms in a Performance drive unit.

The gearbox is a single speed 9.73:1 reduction.

## Component Descriptions

### Motor

1. A, B, and C field windings

2. Rotor bearing

3. Motor encoder

4. Motor encoder sensor

5. Rotor

6. Stator

The 3-phase AC induction motor consists of a stator and a rotor housed in an aluminum casting that is shared with half of the gearbox housing. This level of integration makes it impossible to separate the motor from the gearbox. The advantage of the integration is that the total cost and mechanical volume of the drive unit system is reduced.

The stator consists of a stack of steel laminations. Within the stator, slots contain the conductive motor windings and various layers of insulating film. The stator temperature sensors are buried inside the windings. The stator is connected directly to the drive inverter, and uses no motor cable or connectors. The connection can be accessed behind the orange phase-out cover on the gearbox. Eliminating the motor cable reduces system cost, failure modes, radiated emissions, and mass. Reduced resistive losses in the cable and connections also helps improve drive unit efficiency and vehicle range.

The rotor consists of a stack of steel laminations with evenly spaced copper conductor bars around the circumference. The rotor is mounted on a central shaft, supported at either end by bearings to allow smooth rotation.

#### Motor Speed Sensor

The motor speed is measured using a two-channel Hall effect sensor. The sensor monitors the rotation of the teeth of the encoder wheel that is attached to the rotor shaft. The sensor output is two square waves that are 90 degrees out of phase from each other. The drive inverter control board uses the frequency of the encoder signal to determine motor speed, and the phase of the two signals to determine the motor direction.

The connection between the sensor and the drive inverter is external to the drive unit and routes through the rear subframe harness. The drive inverter provides power to the encoder, as well as the ground return for the sensor. The motor speed sensor can be replaced in the field by unplugging the harness and removing the mounting screw.

### Drive Inverter

1. Drive inverter

2. High voltage cable inlet

3. High voltage cable connection cover

4. 12V connector

The drive inverter translates driver commands from the gear selector, accelerator, and brake pedal into alternating currents that are applied to the motor to generate the correct speed, torque, and direction of rotation to move the vehicle.

The drive inverter is a bi-directional system. It converts battery current to motor current with current flowing in either direction, and with output torque in either direction. Regenerative braking is achieved using the drive inverter to produce negative torque and corresponding current flow from the motor to the battery. Regenerative braking is only allowed when the stability control and ABS systems are active. Traction control is implemented in the stability control system in Model S, with torque limiting commands sent to the drive inverter when traction is reduced.

The drive inverter contains two digital signal processors (DSPs) on the control board. The main DSP controls the motor, monitors the health of the drive unit system, and processes driver requests. The second DSP (referred to as the Pedal Monitor) is a safety monitor that can stop all torque generation if the motor currents, speed, or accelerator pedal conditions indicate that the main DSP is not operating correctly. A field programmable gate array (FPGA) on the control board manages a variety of hardware level safety and protection circuits. An EEPROM on the controller stores the serial number of the drive unit, allowing the pedigree and build history of the drive unit to be tracked using the vehicle log system. The two DSPs and the FPGA can be reprogrammed over the CAN interface.

The drive inverter monitors the temperatures of the motor and power electronics. It sends cooling requests for the motor and internal drive inverter electronics to the thermal controller. There is no direct control over the coolant flow or fan speeds from the drive inverter; the thermal controller manages the system to targets that are optimized for range and efficiency.

If thermal limits are exceeded, the drive inverter limits motor torque until the temperatures are back within nominal operating range.

### Gearbox

1. Ring gear

2. Gearbox casing

3. Differential gears

4. Intermediate shaft gear

5. Oil pump

6. Driveshaft seal

7. Differential bearing

The drive unit features a single speed gear reduction gearbox, located between the motor and the drive inverter. The gearbox is connected to the rear road wheels via the two equal length driveshafts.

The gearbox uses a three shaft layshaft arrangement with two stage gear reduction. The cast aluminum gearbox casing features a gearbox and inverter breather and oil fill/level and drain plugs.

There is no mechanical linkage between the gear selector and the gearbox. The gearbox gear set is in constant mesh. The gearbox has no mechanical neutral or reverse gear, and no parking pawl. Reverse drive is achieved by reversing the polarity of motor torque. Neutral is achieved by de-energizing the motor.

#### Oil Lubrication

The gearbox incorporates a gerotor-type oil pump that is driven by the differential during forward motion of the vehicle. The design of the gearbox allows for adequate lubrication when driving in reverse, as the oil pump is not driven.

Oil is scavenged from the bottom of the gearbox casing via a scavenge pipe and distributed to the gears and bearings. The scavenge pipe strainer is made from a wire mesh, to prevent solid contaminants from contacting the oil pump, gears and bearings. Following lubrication of the gears and bearings, any excess oil drains back to the bottom of the gearbox casing. A magnet in the sump, as well as magnetic drain plugs, keep ferrous material out of the gear meshes.

#### Differential

The differential is of conventional design with a differential housing bolted to the final drive gear. The housing supports the differential pin, side gears, and pinion gears. The differential assembly is supported in the gearbox assembly using deep groove ball bearings.

The differential allows the road wheels to turn at different speeds while providing an equal amount of torque. The integral spline on the output shaft meshes with the final drive gear on the differential assembly. When the output shaft rotates and the wheels are traveling at the same speed, torque is applied to the complete assembly; the pinion gear does not rotate. Torque is transmitted to the road wheels through the drive shafts. During cornering, the inner wheel travels a shorter distance at a lower speed. This results in the pinion gears rotating about the outer wheel side gear, therefore increasing the speed of the outer wheel.

### Driveshaft

The equal length driveshafts feature a Constant Velocity (CV) joint at both ends, each with a rubber boot to protect the joint from contamination. The outer CV joint features external splines that locate into the internally splined drive flange. The externally splined inner CV joints locate into the internally splined gearbox output shafts. A serviceable driveshaft seal is fitted to the gearbox casing on each side, to seal the casing and prevent the entry of dirt and moisture.

### Cooling

1. Air bleed pipe

2. Transmission breather

3. Coolant pipe

4. Coolant inlet

5. Coolant manifold

6. Rotor cooler

7. Stator cooling jacket

8. Transmission oil drain plug

9. Transmission oil fill/level plug

1. Coolant bleed pipe

2. Coolant pipe

3. Transmission Cooler

4. Coolant outlet

The motor, gearbox, and drive inverter share a common liquid cooling system. Coolant enters the motor side of the drive unit and flows through the gearbox and drive inverter through a series of internal passageways.

The drive unit is cooled using a glycol/water mix that is circulated by the drive unit cooling loop. Coolant passes from the radiator, through the charger(s), to the coolant manifold. The internal coolant loop is split into two flow paths by the manifold on the motor end bell casting.

Coolant from the bottom of the manifold is channeled into the stator cooling jacket in the housing. From the stator, coolant flows through the drive inverter before exiting the drive unit through the coolant outlet. Heat is transferred from these components to the coolant. Coolant returns to the radiator where the temperature of the coolant is reduced by air flowing across the radiator fins before it flows around the circuit again. The system operates at pressures between 5 psi (35 kPa) and 19 psi (130 kPa). System temperature is maintained below 85°C (185°F).

Coolant from the center of the manifold is sent to the rotor shaft, which is hollow. Coolant flows into the shaft, returning back along the inside wall. This direct rotor cooling is a new innovation for Model S. The coolant returning from the rotor exits the top of the manifold and flows through the coolant pipe to the gearbox cooler, then exits through the coolant outlet.

The air bleed pipe connecting the top of the stator cooling jacket and the coolant outlet removes any air pockets present in the drive unit.

See the Thermal Management Theory of Operation for further detail.

## Operation

### Gear Selection

The gear selector stalk forms part of the Steering Column Control Module (SCCM) located on the steering column. The SCCM sends high-speed 500 kBd chassis CAN signal to the Tesla Gateway depending on the selected gear: P, R, N, or D. The CAN signal is then relayed to the drive inverter through the high-speed powertrain CAN at 500 kBd.

#### Neutral

Select Neutral and apply the parking brake if the vehicle needs to be stationary for a period of time, such as at a traffic signal. When the car is in Neutral, no torque is commanded to the motor. The brake must be used when shifting out of Neutral into Drive or Reverse.

When Neutral is selected, the vehicle transitions into electrical neutral and commands zero torque to the motor. The drive inverter enters standby mode.

#### Drive

Drive can be selected whenever the vehicle is stationary or moving forward. Drive can also be selected if the vehicle's reverse speed is less than 5 mph.

If the vehicle has been in Neutral for more than 1 second and the vehicle is moving at less than 5 mph, the brake pedal must be depressed in order to enter Drive or Reverse.

If Drive is selected from Neutral when the vehicle is stationary and the accelerator pedal is depressed, no torque is commanded until the accelerator pedal is released.

If the vehicle has been in Neutral or Park for more than 1 second and the vehicle is moving at less than 0.5 mph, the brake pedal must be depressed and the accelerator pedal released in order to enter Drive or Reverse.

In European vehicles, an invalid gear selection causes the car to shift into Neutral. For all other markets, an invalid gear selection does not change the active gear.

#### Reverse

Reverse drive is selectable whenever the vehicle’s forward speed is less than 5 mph. The maximum speed in reverse is limited to 15 mph.

If Reverse is selected from Neutral when the vehicle is stationary and the accelerator pedal is depressed, no torque is commanded until the accelerator pedal is released.

NOTE: This behavior also occurs when shifting from Reverse to Drive.

Reverse motion is achieved by reversing the direction of motor rotation. If Reverse is selected when wheel speed indicates the vehicle is traveling at more than 5 mph in a forward direction, the gear selection is denied.

#### Park

The Electronic Park Brake (EPB) is engaged to prevent the vehicle from rolling. The EPB disengages automatically when shifting from Park to Drive, Reverse or Neutral.

The gearbox has no mechanical parking pawl.

#### Denied Shift Requests

Any gear position can be selected at any time; however, inappropriate gear selections are prevented until the required conditions are met. An audible alert indicates an invalid gear selection.

#### Creep Torque

If the vehicle is in Drive or Reverse and the accelerator pedal is not depressed, a fixed amount of torque is commanded to maintain a creep effect similar to vehicles with automatic transmissions.

The creep torque feature can be switched on or off by the customer, using the touchscreen.

### Driving Modes

Model S provides the following selectable driving modes:

- Standard

- Range

The difference between the two modes is the amount of energy consumed by the thermal management system.

In Standard, the thermal management system is fully operational to keep the occupants at the desired humidity and temperature, while maintaining the battery temperature within its nominal operating range.

Range mode reduces vehicle power consumption by modifying the thermal management strategies:

- It allows the HV battery to operate within a wider nominal temperature range, which reduces the energy consumed for cooling and heating of the battery.

- It restricts cabin heating and cooling capacity, which reduces energy used by the AC compressor, PTC heater, and blower motor.

Powertrain performance and behavior are not affected. Once Range mode is selected, it remains engaged until Standard mode is re-selected.

NOTE: This mode is only applicable to driving, and is distinct from the charging system’s Range mode. Driving Range mode and charging Range mode can be used together or individually, depending on the driver’s requirements.

### Torque Management

The traction control system reduces motor torque to reduce rear tire slip during acceleration and deceleration. Traction control operates by comparing front tire speed (as measured by the front Anti-lock Braking System, or ABS, wheel speed sensors) to rear tire speed (as measured by motor speed and transmission gear, or by the rear ABS wheel speed sensors). Traction control is automatically enabled every time the vehicle enters Drive. The vehicle monitors wheel speed and controls motor torque to minimize wheel slip.

If the vehicle is in Drive, torque is limited to avoid exceeding the motor’s maximum speed.

Unrestricted drive torque is available when:

- The system is in drive mode.

- The battery and drive inverter status are both OK.

- The gear selector is in Drive or Reverse and the EPB is released.

Drive torque is restricted but available if:

- The battery and/or drive inverter temperatures are outside the defined limits.

- The drive inverter loses communication with the HV Battery.

- Motor temperatures are above full-power maximum allowable temperature.

- Traction control is active. Torque is limited to control wheel slip when required. This is true for drive torque and regenerative braking torque.

- The battery voltage is at a level where power usage under high torque demand causes the voltage to drop below the minimum allowable charge level. Torque is limited to ensure voltage stays in a safe range.

- The battery state of charge is at a level where the regenerative torque could cause the battery to exceed the maximum allowable voltage. Regenerative torque is limited to ensure cell voltages stay in a safe range.

NOTE: Prior to total loss of torque, the driver is informed via the touchscreen as torque is progressively limited.

Drive torque is restricted to zero torque (though not always immediately) when:

- The battery and/or drive inverter status is not OK.

- The EPB is engaged.

- Selecting gears.

- A gear selection request is denied.

If the brake pedal is pressed and held while the accelerator is pressed, an accelerator pedal override drops torque to zero after two seconds.

### Cruise Control

Cruise control enables a constant road speed to be maintained without using the accelerator pedal, compensating for road gradient and vehicle loading conditions. The system is useful on journeys where a constant speed can be maintained for long periods.

The cruise control system can be in one of four states:

- Off

- Standby

- Active

- Failsafe

Cruise control is operated using the control stalk on the left of the steering column, and only engages at speeds above 20 mph.

The cruise control stalk is a direct input to the steering column control module, which converts the signals it receives into CAN messages that it broadcasts on the chassis bus. The gateway module routes these messages to the drive inverter via the powertrain bus. The drive inverter controls motor torque according to the torque requests it receives from the cruise control.

The driver can perform several different actions with the control stalk:

- Push on/off: The driver pushes the cruise control stalk toward the steering column. The inner detent position is off; the outer detent position is on. System ON is indicated by an amber LED on the stalk, and by a white pointer icon on the speedometer. Pushing while cruise control is active turns it off and set speed is cleared from memory.

- Tap the stalk up to the first detent and release immediately: Initializes set speed or increases the set speed by 1 mph increments. If vehicle speed is greater than set speed, the vehicle speed becomes the set speed.

- Tap the stalk up to the second detent and release immediately: Initializes set speed or increases the set speed by 5 mph increments. If vehicle speed is greater than set speed, the vehicle speed becomes the set speed.

- Hold the stalk up to the first or second detent: Initializes set speed and steadily increases the set speed by 2 mph/second until released.

- Tap the stalk down to the first detent and release immediately: Initializes set speed or decreases the set speed by 1 mph increments. If vehicle speed is less than set speed, the vehicle speed becomes the set speed.

- Tap the stalk down to the second detent and release immediately: Initializes set speed or decreases the set speed by 5 mph increments. If vehicle speed is less than set speed, the vehicle speed becomes the set speed.

- Hold the stalk down to the first or second detent: Initializes set speed and steadily decreases set speed by 2 mph/second until released.

- Pull the stalk toward the driver: Previous set speed is resumed. If no previous speed was set, it is initialized.

- Push the stalk away from the driver: The motor torque command tapers gracefully (soft cancellation), and the cruise control state transitions from active to standby. The set speed is retained in memory.

Other actions the driver can perform to influence cruise control operation are:

- Press the brake pedal: Instantly transitions from active to standby (hard cancellation), set speed is retained in memory.

- Press the accelerator pedal: If the accelerator pedal is pressed to a position that corresponds to a commanded torque that exceeds the torque commanded by cruise control, the torque appropriate for that pedal position is commanded.

- Move the gear shift lever: If cruise control is active, selecting any gear besides Drive causes it to transition to standby.

- Push Park or parking brake buttons: If cruise control is active, it transitions to standby. Applying the parking brake also clears the set speed from memory.

- Power down the vehicle: Exiting drive mode turns cruise control off.

If the cruise control state transitions from active to standby while attempting to meet a new set speed, speed is set to the current vehicle speed at the time of the transition. If the cruise control state transitions from active to standby while attempting to meet a resume speed request, the set speed does not change.

Vehicle speed changes should not take place at a rate greater than 2 mph/second. If the vehicle’s speed is less than the set speed and the vehicle speed does not increase for 4 seconds, cruise control transitions to standby. If set speed reaches a value below 20 mph for any reason, the set speed clears from memory and cruise control transitions to standby. If cruise control is active and any signal goes missing, or is determined as irrational such that cruise control functionality cannot be provided, it enters failsafe state. In this state, all driver inputs are ignored and the indicator on the instrument panel turns yellow.

### Regenerative Braking (Regen)

Regeneration operates on the principle that the electric motor can also operate as an electrical generator. This places a load on the motor, which in turn provides an additional braking effect.

The amount of regen torque generated is proportional to vehicle speed, battery SOC, and the accelerator pedal position. The pedal provides maximum available regen torque when fully released, then proportionally less as the pedal is depressed. The motor delivers zero regen torque when the accelerator pedal reaches its neutral torque position, which varies depending on driving conditions.

The drive inverter converts this torque command into the appropriate 3-phase voltage and current waveforms to produce the commanded torque in the motor in the most efficient way. The torque command can be positive or negative. When the torque is used to slow the vehicle, energy is returned to the battery to create regenerative braking.

The maximum regeneration braking profiles take speed and corresponding drag into account to aim for a target total deceleration rate. Regeneration braking profiles are tailored to everyday driving conditions, and typically provide higher deceleration rates at lower speeds.

NOTE: A failure of the ABS or ESP system disables regenerative braking. A notification is displayed on the touchscreen. Regen is limited or disabled if battery SOC is too high.