Modes of Operation

Modes of Operation

The transmission control is incorporated into the EMS2000. The EMS2000 does not control the transmission ratio directly but does provide all of the intelligence relating to the required position of the ratio control motor. It also provides the intelligence for how fast it should be operated.

The EMS2000 controls the transmission in one of four modes:
- Drive mode (normal ECVT driving).
- Sport ECVT mode.
- Manual mode.
- Fault mode.

In the CVT modes, the control system operates by deriving a target engine speed based on current vehicle speed and driver demand. In manual mode, the system derives a target engine speed based on the vehicle speed and the current gear ratio. Having obtained an engine speed target, the system calculates the appropriate ratio control motor position and instructs the GIU to deliver this position.

The engine load calculation will depend on two factors:

1. The vehicles road speed.

2. The driver's demand (throttle position).

The EMS2000 also needs to control the speed of the ratio control motor in order to protect the transmission from damage due to drive belt slippage. This is more likely to occur at low transmission oil temperatures, and when the transmission is delivering a large change in ratio (for example, after a manual gear change, or sudden throttle movement in Drive mode).

Four speeds are used by the Ratio Control Motor. The motor is accelerated as appropriate to ensure the motor does not lose its reference, thereby compromising system control. The EMS2000 also knows the maximum torque that the belt can transfer across all possible ratio ranges. It is extremely important that the belt is not allowed to slip on the pulleys, as this would cause excessive wear.

Target Engine Speed
The target engine speed is critical in deciding the position of the ratio control motor. The EMS2000 will keep changing the ratio of the motor to achieve the target engine speed. The target engine speed is mapped inside the EMS2000 against Road speed and Driver demand (throttle angle).

The map is not linear. To achieve good driving characteristics the engine target speed map is programmed to overcome.
- The initial engine speed required to build pressure within the hydraulic clutch.
- The hydraulic profile of the transmission itself.
- The engines power and torque profile.

When the transmission is operating in the D mode (drive), the driver does not experience full engine power until the road speed reaches 50 mph.

Sports Mode
The EMS2000 uses the same map programmed into the EMS2000 as it uses for normal Drive mode but applies a scalar function to the throttle angle. For example if the driver selects sports mode and has the throttle applied by 40%, the scalar function will be applied so that the EMS2000 uses a throttle angle of 60% to calculate its target engine speed. The instrument cluster display will change from 'D' to 'SD'.

Manual Mode
As soon as the EMS2000 receives one of the "+ or -" switched inputs via the GIU, the EMS2000 stops displaying 'S', and changes to one of six gear position displays.

Fault Mode
When the EMS2000 or GIU detects a fault, the EMS2000 will try to position the ratio control motor so that the engine speed in most driving conditions is around 2800-3200 rpm. In this position the vehicle still has reasonable driving characteristics. For certain failure modes, where the EMS2000 cannot command the position of the motor, the GIU will set the motor position to 130 steps (full range of travel is 0-214 steps). In this case, the engine speed in most driving conditions will be 3750-4000 rpm.

The EMS2000 will instruct the instrument cluster to display 'EP', or the Engine MIL depending on legislative requirements. There are certain faults that when stored will not cause the EMS2000 to default the transmission into its limp home position.
These are:

- Gear lever + switch failure.
- Gear lever - failure.
- Steering wheel + switch failure (if fitted).
- Steering wheel - switch failure (if fitted).
- Shift interlock system fault.
- Center Console LED fault.

A gearbox default is not necessary for these failures because the control of the gearbox is not compromised; it is only necessary to warn the driver. The EMS2000 will not operate the sequential gear changes in manual mode if these switches are faulty.