Dual planetary gear transmission controlled by combined parking and service brakes

A transmission arrangement, comprising:

• a first planetary gear set comprising a first set of planetary members, the first set of planetary members comprising a first sun gear, a first ring gear and a first planet carrier carrying a first set of planet gears, the first set of planet gears being in meshing engagement with the first ring gear and the first sun gear,
• a second planetary gear set comprising a second set of planetary members, the second set of planetary members comprising a second sun gear, a second ring gear and a second planet carrier carrying a second set of planet gears, the second set of planet gears being in meshing engagement with the second ring gear and the second sun gear,
• wherein a first member of the first set of planetary members is operatively connected to a first member of the second set of planetary members, and wherein a second member of the first set of planetary members is operatively connected to a second member of the second set of planetary members,
• said transmission arrangement further comprising:
• an input shaft connectable to a prime mover, the input shaft being operatively connected to the first sun gear,
• an output shaft operatively connected to the first planet carrier,
• a transmission housing, and
• a gear selection arrangement comprising a first brake mechanism and a second brake mechanism,
• said first brake mechanism comprising:
• a first brake disc connected to one of the members of the first set of planetary members,
• a first normally disengaged brake attached to the transmission housing and configured to act on the first brake disc to control friction between the first brake disc and the first normally disengaged brake, and
• a first normally engaged brake attached to the transmission housing and configured to act on the first brake disc to control friction between the first brake disc and the first normally engaged brake,
• said first normally disengaged brake being operable by a first fluid pressure (P1) to be forced against the first brake disc by the first fluid pressure (P1), and
• said first normally engaged brake being spring biased against the first brake disc and operable by a second fluid pressure (P2) to be forced away from the first brake disc by the second fluid pressure (P2),
• said second brake mechanism comprising:
• a second brake disc connected to one of the members of the second set of planetary members,
• a second normally disengaged brake attached to the transmission housing and
• configured to act on the second brake disc to control friction between the second brake disc and the second normally disengaged brake, and
• a second normally engaged brake attached to the transmission housing and configured to act on the second brake disc to control friction between the second brake disc and the second normally engaged brake,
• said second normally disengaged brake being operable by a third fluid pressure (P3) to be forced against the second brake disc by the third fluid pressure (P3), and
• said second normally engaged brake being spring biased against the second brake disc and operable by a fourth fluid pressure (P4) to be forced away from the second brake disc by the fourth fluid pressure (P4),
• wherein the transmission arrangement is adapted to assume a first gear ratio when the first brake disc is locked to the transmission housing by the first brake mechanism and the second brake disc is rotatable relatively the transmission housing, and
• wherein the transmission arrangement is adapted to assume a second gear ratio when the second brake disc is locked to the transmission housing by the second brake mechanism and the first brake disc is rotatable relatively the transmission housing.