Functional Description - Hydraulic Impulse Solenoid (His)
A hydraulic impulse solenoid is installed on the transmission, inserted in the transmission housing close to the mechatronic unit solenoid valves. The HIS provides a hydraulic pressure reserve, to be sent to the mechatronic unit during engine starting due to the Engine Stop Start (ESS) function. The component is used for the ESS function as it allows the gear to be engaged in just 350 milliseconds from starting the engine, so that the driver does not perceive the engagement delay. The HIS charges when the engine is running, since the pump sends part of the oil to the HIS, in addition to sending it to the mechatronic unit.
| 1 - Hydraulic Impulse Solenoid |
The HIS is fixed to the transmission housing. It receives and accumulates about 1 liter of oil from the transmission oil pump through a connector. The oil sent to the HIS by the pump, must pass through a regulating valve. The HIS is composed of a piston with a small hole and a spring. During accumulation, the oil only passes through the small hole in the piston. When the oil enters the HIS, the pressure overcomes the force of the spring. The spring is compressed and allows the piston to withdraw and attach to a blocking point controlled by a solenoid valve. If the HIS is powered or the oil pump is operating, the piston will remain blocked.
During Start & Stop operation, namely when the engine is off, the HIS is powered in order to keep the piston blocked, even when the oil is no longer being pumped. When the vehicle is restarted, the HIS will no longer be powered and the spring will be able push the piston, which will send the oil under pressure to the mechatronic unit to engage the gear. When the piston pushes the oil, the regulating valve spring compresses, opening the valve fully to allow the oil at the HIS outlet to pass.