초록 ▼

A hydrostatic transmission including a main pump, two main ducts serving respectfully as feed and as discharge for first and second hydraulic motors that serve to drive disposed one after the other. A bypass valve can take up a reduced-speed position in which the feed main orifices are connected to

A hydrostatic transmission including a main pump, two main ducts serving respectfully as feed and as discharge for first and second hydraulic motors that serve to drive disposed one after the other. A bypass valve can take up a reduced-speed position in which the feed main orifices are connected to the discharge main duct, and an increased-speed position in which one of the motors is bypassed, the feed main orifice of the motor being connected to the discharge main duct via a bypass link, while the other main orifices continue to have their respective links. The apparatus further includes a constriction suitable for being activated to restrict the flow of fluid through the bypass link.

대표청구항 ▼

1. Hydrostatic transmission apparatus for a vehicle having at least two drive members disposed one after the other in a direction of travel of said vehicle, the apparatus comprising at least two hydraulic motors suitable for driving respective ones of said drive members, each hydraulic motor having

1. Hydrostatic transmission apparatus for a vehicle having at least two drive members disposed one after the other in a direction of travel of said vehicle, the apparatus comprising at least two hydraulic motors suitable for driving respective ones of said drive members, each hydraulic motor having two main orifices serving respectively as feed and as discharge in a preferred direction of travel of the vehicle, a main hydraulic pump connected to two main ducts that serve respectively as feed and as discharge in the preferred direction, and a bypass valve suitable for taking up a reduced-speed position in which the feed main orifices of the motors are connected to the feed main duct, while the discharge main orifices are connected to the discharge main duct, and an increased-speed position in which at least one motor is bypassed, the feed main orifice of said bypassed motor being connected to the discharge main duct via a bypass link, while the other main orifices continue to have their respective links, said apparatus further comprising constriction means suitable for being activated to restrict the flow of fluid through said bypass link, so as to put the two main orifices of said bypassed motor at different pressures. 2. Apparatus according to claim 1, wherein the bypass link extends between the discharge main duct and the bypass valve. 3. Hydrostatic transmission apparatus for a vehicle having at least two drive members disposed one after the other in a direction of travel of said vehicle, the apparatus comprising at least two hydraulic motors suitable for driving respective ones of said drive members, each hydraulic motor having two main orifices serving respectively as feed and as discharge in a preferred direction of travel of the vehicle, a main hydraulic pump connected to two main ducts that serve respectively as feed and as discharge in the preferred direction, and a bypass valve suitable for taking up a reduced-speed position in which the feed main orifices of the motors are connected to the feed main duct, while the discharge main orifices are connected to the discharge main duct, and an increased-speed position in which at least one motor is bypassed, the feed main orifice of said bypassed motor being connected to the discharge main duct via a bypass link, while the other main orifices continue to have their respective links, said apparatus further comprising a constriction valve suitable, in a free configuration, for enabling fluid to flow substantially freely in said bypass link when the fluid pressure in said link is less than a pressure threshold, and, in a constricted configuration, for restricting the flow of fluid in said link when said pressure is greater than said pressure threshold, so as to put the two main orifices of said bypassed motor at different pressures. 4. Apparatus according to claim 3, wherein the bypass link extends between the discharge main duct and the bypass valve. 5. Apparatus according to claim 3, wherein the constriction valve is disposed in the bypass link. 6. Apparatus according to claim 3, further comprising a check valve that is disposed in parallel with the constriction valve so as to allow free flow in the bypass link, in the non-preferred direction of travel. 7. Apparatus according to claim 3, further comprising a constriction bypass valve disposed in parallel with the constriction valve and suitable for taking up a constriction bypassed position allowing free flow in the bypass link, and a constriction active position in which the flow of fluid in the bypass link goes via the constriction valve. 8. Apparatus according to claim 3, wherein the constriction valve is prevented from going into said constricted configuration when the non-preferred direction of travel is detected. 9. Apparatus according to claim 1, further comprising an electronic control unit that is suitable for acting on the basis of information relating to the conditions of travel of the vehicle either to allow the constriction means to go into a constricted configuration or to prevent it from going into a constricted configuration. 10. Apparatus according to claim 3, further comprising an electronic control unit that is suitable for acting on the basis of information relating to the conditions of travel of the vehicle either to allow the constriction valve to go into said constricted configuration or to prevent it from going into said constricted configuration. 11. Apparatus according to claim 3, wherein the constriction valve is a pressure-reducing valve. 12. Apparatus according to claim 3, wherein the constriction valve is a variable constriction valve that is controlled proportionally. 13. Apparatus according to claim 1, wherein the bypass valve is controlled hydraulically. 14. Apparatus according to claim 13, wherein, in order to control the bypass valve, said apparatus further comprises a pilot duct suitable for being connected or not connected to a pressure source. 15. Apparatus according to claim 3, wherein the bypass valve is controlled hydraulically. 16. Apparatus according to claim 3, wherein, in order to control the bypass valve, said apparatus further comprises a pilot duct suitable for being connected or not connected to a pressure source. 17. Apparatus according to claim 1, further comprising at least one additional motor that, in the reduced-speed position, has respective feed and discharge main orifices thereof connected respectively to the feed and discharge main ducts and that, in the increased-speed position, has the feed main orifice thereof connected to the discharge main duct via an additional bypass link, whereas the discharge main orifice of said additional motor remains connected to the discharge main duct, and said apparatus further comprising additional constriction means suitable for being activated to restrict the flow of fluid in said additional bypass link. 18. Apparatus according to claim 3, further comprising at least one additional motor that, in the reduced-speed position, has respective feed and discharge main orifices thereof connected respectively to the feed and discharge main ducts and that, in the increased-speed position, has the feed main orifice thereof connected to the discharge main duct via an additional bypass link, whereas the discharge main orifice of said additional motor remains connected to the discharge main duct, and said apparatus further comprising an additional constriction valve suitable for being activated to restrict the flow of fluid in said additional bypass link. 19. Apparatus according to claim 1, further comprising at least one additional motor that, in the reduced-speed position, has respective feed and discharge main orifices thereof connected respectively to the feed and discharge main ducts and that, in the increased-speed position, is bypassed by having the feed main orifice thereof connected to the discharge main duct via the bypass link, which link is common to said bypassed additional motor and to said at least one bypassed motor, whereas the discharge main orifices of said bypassed motors are connected to the discharge main duct, wherein the constriction means are suitable for being activated to restrict the flow of fluid in said common bypass link. 20. Apparatus according to claim 3, further comprising at least one additional motor that, in the reduced-speed position, has respective feed and discharge main orifices thereof connected respectively to the feed and discharge main ducts and that, in the increased-speed position, is bypassed by having the feed main orifice thereof connected to the discharge main duct via the bypass link, which link is common to said bypassed additional motor and to said at least one bypassed motor, whereas the discharge main orifices of said bypassed motors are connected to the discharge main duct, wherein the constriction valve is suitable for being activated to restrict the flow of fluid in said common bypass link. 21. Apparatus according to claim 3, further comprising control means for controlling the constriction valve, which control means are suitable for controlling said valve as a function of the stroke of a control member. 22. Apparatus according to claim 3, further comprising a controller for controlling the constriction valve, which controller is suitable for causing said valve to move in such a manner as to servo-control a variable representative of operation of the vehicle to a setpoint. 23. Apparatus according to claim 22, wherein the controller comprises a memory for storing the setpoint and an electronic control unit suitable for receiving the detected value for the representative value, for comparing said value with the stored setpoint, and for responding to said comparison by issuing a control signal. 24. Apparatus according to claim 3, further comprising a controller for controlling the constriction valve, which controller is chosen from among electrical means, mechanical means, and hydraulic means. 25. Apparatus according to claim 24, wherein the controller is a hydraulic controller including a pressure reducer. 26. Apparatus according to claim 24, wherein the controller is a hydraulic controller including a pressure regulator. 27. Apparatus according to claim 3, wherein the constriction of the bypass link is progressive, depending on the position of the constriction valve.