Hydraulic transmission system for zero-turn vehicle

A hydraulic transmission system for a zero-turn vehicle, comprising:

• first and second transaxles each of which includes:
• an axle,
• a casing supporting the axle,
• a fluid sump provided in the casing,
• first and second ports provided on the casing and opened outward from the casing,
• a hydraulic motor for driving the axle,
• a hydraulic pump for delivering fluid to the hydraulic motor,
• a hydraulic circuit disposed in the casing to fluidly connect the hydraulic pump to the hydraulic motor,
• a charge pump disposed in the casing so as to suck fluid from the fluid sump and so as to deliver fluid to be charged to the hydraulic circuit, and
• a charge passage disposed in the casing so as to supply the hydraulic circuit with fluid delivered from the charge pump;
• a first charge pressure regulation valve disposed in the casing of the first transaxle and connected to the charge passage of the first transaxle so as to regulate a pressure of fluid in the charge passage of the first transaxle, wherein the first transaxle is configured so that fluid released from the first charge pressure regulation valve is drained to the fluid sump of the first transaxle;
• a first orifice disposed in the casing of the first transaxle so as to branch from the charge passage of the first transaxle at an upstream side of the first charge pressure regulation valve so that fluid passed through the first orifice is supplied to the first port of the first transaxle;
• a first pipe disposed outside of the casings of the first and second transaxles so as to connect the first ports of the respective first and second transaxles to each other;
• a first drain passage disposed in the casing of the second transaxle so as to connect the first port of the second transaxle to the fluid sump of the second transaxle, whereby part of the fluid flowing in the charge passage of the first transaxle is drained to the fluid sump of the second transaxle via the first orifice, the first pipe and the first drain passage;
• and
• a second pipe disposed outside of the casings of the first and second transaxles so as to connect the second ports of the respective first and second transaxles to each other, whereby overflowing fluid of the fluid sump of the second transaxle is released to the fluid sump of the first transaxle via the second pipe.