Starting device for heavy vehicles

A vehicle comprising:

• an engine comprising an engine-output shaft,
• a transmission shiftable in steps by means of friction clutches and having an input shaft operatively connected to the engine-output shaft and an output shaft operatively connected to the driven wheels of the vehicle, the driving connections from the engine to the transmission and to the driven wheels defining a power transmission path,
• a starting unit in said power transmission path comprising a planetary gear having at least three components, a first component, a third component located downstream from the first component, a third component located downstream from the first component in the power transmission path and a second component operatively engaged with at least one of the first and third components to effect drive between said first and third components,
• a braking device having at least one braking member connected with saiad second component so as to either rotate therewith or hold it against rotation relative to a stationary structure, said braking member including at least one brake lamination and including brake rings with braking surfaces facing said brake lamination for the purpose of braking it, actuating means for actuating the braking device and coolant means for passing liquid coolant to the sides of the brake rings opposite from said braking surfaces so as to liquid cool the braking device,
• and an actuating system for controlling operation of said braking device, said actuating system having means for providing a first mode of operation for holding the brake member fixed relative to the stationary structure so that power can be transmitted between said first and third components, and a second mode of operation for releasing the brake member relative to the stationary structure, and said actuating system including means for holding the brake lamination in sliding engagement with the braking surfaces of the brake rings during movement from the second mode to said first mode so as to suppress shocks produced during starting of the vehicle and shifting of the transmission,
• said braking device being a hydraulically actuated brake having a pressure chamber and said brake laminations being movable axially under the pressure of fluid in the pressure chamber to engage the brake ring by means of pressure fluid in the pressure chamber, said actuating system comprising a hydraulic pressure line connected to said pressure chamber and maintaining a pressure therein during the first mode of operation so that the brake laminations are applied to the brake ring providing driving engagement between the first and third components to drive the wheel, said actuating system further comprising a pedal and a valve in said pressure line, which valve blocks the pressure line when the pedal is in operating position for said second mode of operation, relieving the pressure chamber so that the brake is released, and providing during the return movement of the pedal into inoperative position for starting operation the pressure chamber with increasing oil pressure via said valve providing said sliding braking of said brake laminations on said brake ring, and said actuating system further comprising a control means in said line and a lever with various positions corresponding to the speed ratios, the said control means being operable to briefly reduce the pressure in the pressure chamber during said first mode of operation when the lever is moved between the said two positions so that the brake is briefly released suppressing the shifting shocks.