Group Two

Group Two Elements
These elements relate to the hydraulic system. This system enables the transmission to transmit power and to vary the ratio in a proper way, according to load conditions and driver demand.
- Hydraulic pump
- Hydraulic control unit


Group Two Components
Oil Pump

The pump within the transmission is an externally toothed gear pump. The engine drives it via a shaft through the hollow primary pulley shaft. The pump shaft is splined to the planet carrier, which always runs at engine speed. System pressure reaches 40 bar. The oil pressure is used both for controlling the transmission hydraulically, and for lubrication purposes.


Hydraulic Control
The ECVT is controlled by a number of valves that respond to mechanical, electrical and hydraulic inputs. The control system is designed to control the pulleys and the clutches in the following three ways:
- Flow to and from the primary pulley is controlled to command the correct transmission ratio for all driving conditions.
- Secondary pressure is supplied to the secondary pulley to ensure that there is always adequate clamping force onto the belt for all load conditions. A solenoid valve influences the secondary pressure control valve, optimizing the pressure and hence the belt tension between the primary and secondary pulleys. This pressure optimization improves fuel consumption.
- The clutch control consists of:
- Selection of the correct clutch (forward or reverse). Engagement of forward or reverse gear via the selector mechanism operates the manual valve directing oil to the appropriate clutch.
- Control of the operation needed for take off: A solenoid valve acting on the clutch valve controls the clutch application pressure to ensure smooth clutch engagement and drive away at all throttle openings.

Pilot Pressure
Engine speed and hydraulic pressure monitoring is accomplished through two Pilot Pressure Systems. Each system consists of a pilot chamber and a pilot pipe. The pipe is stationary while the chamber, which is filled with oil and rotating at the speed to be measured.

Hydraulic Control Valves
The Hydraulic Control System consists of the following valves:

- Primary Valve
- Exhaust Secondary Valve
- Cooler Flow Valve
- Constant Pressure Valve
- PWM Solenoid Clutch Valve
- Manual Valve
- Secondary Valve
- PWM Solenoid Secondary Valve
- Exhaust Valve Clutch Pressure
- Supply Valve
- Reverse Inhibitor Valve

Primary Valve
The function of the primary valve is to regulate primary pressure, controlling the primary pulley, and changing the transmission ratio. The pressure in the primary cylinder defines the position of the primary pulley mobile half. The greater the distance between the pulley halves the smaller the primary radius of the belt and the higher the transmission ratio.

Secondary Valve
The secondary valve determines the clamping force on the secondary pulley by regulating the pump pressure. The higher the clamping force, the higher the torque that can be transmitted.

Exhaust Secondary Valve
The exhaust secondary valve regulates overall maximum pressure and controls the secondary pressure in 'Low' for engine speeds up to 1600 - 2000 rpm. This valve improves creep quality that is better at lower secondary pressures. It also creates a smooth transition from the level in creep to the level in low at higher engine speeds. The valve is closed if not in low ratio.

PWM Solenoid Secondary Valve
The PWM solenoid secondary valve influences secondary valve movement, hence belt tension via secondary pulley chamber pressure. The secondary pressure solenoid further modulates the pressure acting on the secondary pressure valve. This optimizes the secondary pressure and hence minimizes losses and improves fuel consumption.

Cooler Flow Valve
The cooler flow valve controls the oil flow through the cooler when D position is engaged. The valve ensures enough oil flow during stall conditions or driving in high ratio for cooling, while ensuring sufficient system pressure is maintained at low engine speeds even under extreme temperatures.

Clutch Valve
This valve regulates the clutch pressure and allows for the adjustment of stall speed. The clutch pressure is derived from the secondary pressure and is controlled by the engine speed pilot, the primary pressure pilot and the clutch PWM solenoid pressure. The clutch valve consists of 1 valve, 2 springs and a plunger.

Exhaust Valve Clutch Pressure
The Exhaust Valve Clutch pressure has two main functions:
- Limit the maximum clutch pressure.
- Protection of the gearbox from abuse.

The clutch pressure is bled into the exhaust valve, otherwise, with increasing engine speed; the pressure would limit the minimum secondary pressure too much, which would adversely affect fuel economy and could lead to damage within the gearbox.

Constant Pressure Valve
The Constant Pressure Valve establishes a base pressure that is used to supply the supply valve. The constant pressure valve acts as a filter for the supply valve and reduces disturbances in the secondary pressure. The constant pressure is also used for the ratio control depending on locking of the clutches. As the ratio approaches overdrive the constant pressure will be supplied to the clutch valve instead of the clutch PWM solenoid pressure.

Supply Valve
The Supply Valve controls the pressure function of the two pilot pressures. A higher engine pilot pressure will cause a higher supply valve pressure and a lower primary pilot pressure will cause a lower supply valve pressure. If both pilot pressures rise by the same amount the supply pressure will also increase. The supply pressure forms an input to the clutch PWM solenoid and is also used for belt lubrication and oil supply to the pilot systems.

PWM Solenoid Clutch Valve
Influences clutch application pressure by biasing the clutch valve. Permits a variety of strategies to be applied to the engagement process.

Reverse Inhibitor Valve
The Reverse Inhibitor Valve prevents the reverse clutch from being energized above a specified forward speed.

Manual Valve
The manual valve has four positions, each corresponding to a position of the selector lever inside the vehicle. Choosing reverse or drive activates one of the two clutches whereas in the neutral and park position both clutches are released. The engine can only be started with the selector lever in the neutral or park position, in all the other positions the starter circuit is inhibited.