Description And Operation: Overview
The ZF 8HP45 transmission is an electronically controlled, hydraulically operated, eight speed automatic unit.
A single unit known as the Mechatronic valve block is located inside the transmission. The Mechatronic valve block contains the following control components:
- Hydraulic control elements
- Electronic control elements
- TCM.
The 8HP45 is a smaller version of the 8HP70 automatic transmission, with the same power flow and control strategies. The 8HP70 transmission is specified for high power and high torque applications. The 8HP45 transmission is optimized for efficiency and weight with a saving of 5kg over the 8HP70, and is specified for lower torque and power capacity applications.
The ZF 8HP45 transmission has the following features:
- Designed to be maintenance free
- Automatic Transmission Fluid (ATF) is 'fill for life'
- The torque converter features a controlled slip feature with electronically regulated control of lock-up, creating a smooth transition to the fully locked condition
- Shift programs controlled by the TCM
- Adaptive Shift Strategy (ASIS), to provide continuous adaptation of shift changes to suit the driving style of the driver, which can vary from sporting to economical
- Connected to the Powertrain Control Module (PCM) via the FlexRay systems bus for communications
- Default mode if major faults occur
- Diagnostics available from the TCM via the FlexRay systems bus.
The transmission selections are made using the rotary Transmission Control Switch (TCS) in the floor console.
For additional information, refer to: EXTERNAL CONTROLS .
On vehicles featured with the stop/start system, the 8HP45 automatic transmission is fitted with a Hydraulic Impulse Storage (HIS) device. The HIS makes sure pressurized Automatic Transmission Fluid (ATF) is available to the shift elements as quickly as possible when the engine is started.