Hydrostatic transmission

Claim 2

A hydrostatic transmission assembly comprising a fluid pump, a fluid motor, first fluid conduit means for conducting fluid between said pump and motor upon operation of said pump to thereby operate said motor, second fluid conduit means for connecting said first fluid conduit means in fluid communication with a source of fluid, and valve means connected in fluid communication with said first and second fluid conduit means and operable between open and closed conditions under the influence of pressure differentials of relatively long duration between said first and second fluid conduit means to thereby control fluid flow between said first and second fluid conduit means, said valve means including means for discharging fluid from said valve means into said first fluid conduit means under the influence of a relatively short duration decrease in the pressure in said first fluid conduit means to a pressure below the pressure in said second fluid conduit means and for accepting fluid from said first fluid conduit means at the end of the relatively short duration decrease in the pressure in said first fluid conduit means to thereby tend to minimize the effect of the relatively short duration decrease in the fluid pressure in said first fluid conduit means.

Claim 3

A hydrostatic transmission assembly as set forth in claim 1 wherein said valve means includes a valve body defining a chamber connected in fluid communication with said first and second fluid conduit means and a movable valve element located in said chamber, said chamber including a first portion having a cross-sectional area which is substantially the same as the cross-sectional area of said valve element and a second portion having a cross-sectional area which is substantially larger than the cross-sectional area of said valve element, said first portion of said chamber and said valve element cooperating to block a flow of fluid between said first and second fluid conduit means and to form a cavity which is contractable and expansible by movement of said valve element relative to said valve body to provide said means for discharging and accepting fluid.

Claim 4

A hydrostatic transmission as set forth in claim 1 wherein said means for discharging and accepting fluid includes cavity means which is contractable from a first condition to a second condition to discharge fluid from said valve means into said first fluid conduit means and is expandable from said second condition to said first coNdition to accept fluid from said first fluid conduit means.

Claim 5

A hydrostatic transmission assembly as set forth in claim 1 wherein said valve means includes a valve body defining a chamber having a first portion of a relatively large cross-sectional area, and a valve element movable in said first portion of said chamber to provide for said discharging and accepting of fluid, said valve element being movable from said first portion to said second portion of said chamber to provide for operation of said valve means from said closed condition to said open condition.

Claim 6

A hydrostatic transmission as set forth in claim 1 wherein said valve means includes a valve body defining a chamber having an inlet connected in fluid communication with said second fluid conduit means and an outlet connected in fluid communication with said first fluid conduit means, a valve element movable in said chamber, said means for discharging and accepting fluid including an expansible cavity formed in a portion of said chamber by said valve element and connected in fluid communication with said outlet, said valve element being movable in a first direction upon the occurrence of a relatively short duration decrease in the pressure in said first fluid conduit means to a pressure below the pressure in said second fluid conduit means to contract said cavity and discharge fluid from said valve body, said valve element being movable in a second direction opposite from said first direction at the end of the relatively short duration decrease in pressure to expand said cavity and accept fluid from said first fluid conduit means.

Claim 7

A hydrostatic transmission assembly comprising a fluid pump, a fluid motor, first fluid conduit means for conducting fluid between said pump and motor upon operation of said pump to thereby operate said motor, second fluid conduit means for connecting said first fluid conduit means in fluid communication with a source of fluid, and valve means connected in fluid communication with said first and second fluid conduit means for controlling fluid flow between said first and second fluid conduit means, said valve means including a body connected in fluid communication with said first and second fluid conduit means and means responsive to a short duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said second fluid conduit means for blocking fluid flow from said second fluid conduit means into said first fluid conduit means and discharging fluid from said body into said first fluid conduit means during the short duration decrease in fluid pressure in said first fluid conduit means and for blocking fluid flow from said first fluid conduit means into said second fluid conduit means and accepting fluid from said first fluid conduit means at the end of the short duration decrease in the fluid pressure in said first fluid conduit means to thereby at least partially compensate for the short duration decrease in fluid pressure in said first fluid conduit means, said means responsive to a short duration decrease in the fluid pressure in said first fluid conduit means also being responsive to a relatively long duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said second fluid conduit means to enable fluid to flow from said second fluid conduit means to said first fluid conduit means.

Claim 8

A hydrostatic transmission assembly comprising a fluid pump, a fluid motor, first fluid conduit means for conducting fluid between said pump and motor upon operation of said pump to thereby operate said motor, second fluid conduit means for connecting said first fluid conduit means in fluid communication with a source of fluid, and valve means connected in fluid communication with said first and second fluid conduit means for controlling fluid flow between said first and second fluid conduit means, said valve means including a body connected in fluid communication with said first and second fluid conduit means and means responsive to a short duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said second fluid conduit means for blocking fluid flow from said second fluid conduit means into said first fluid conduit means and discharging fluid from said body into said first fluid conduit means during the short duration decrease in fluid pressure in said first fluid conduit means and for blocking fluid flow from said first fluid conduit means into said second fluid conduit means and accepting fluid from said first fluid conduit means at the end of the short duration decrease in the fluid pressure in said first fluid conduit means to thereby at least partially compensate for the short duration decrease in fluid pressure in said first fluid conduit means, said means responsive to a short duration decrease in the fluid pressure in said first fluid conduit means also being responsive to a relatively long duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said second fluid conduit means to enable fluid to flow from said second fluid conduit means to said first fluid conduit means.

Claim 9

A hydrostatic transmission assembly as set forth in claim 6 wherein said means responsive to a short duration decrease in the fluid pressure in said first fluid conduit means includes a movable valve element for blocking fluid flow between said first and second fluid conduit means, said valve element being located in a chamber defined by said body and cooperating with said body to define a cavity in said chamber, said valve element being movable in a first direction under the influence of the pressure differential between said first and second fluid condUit means during the short duration decrease in fluid pressure in said first fluid conduit means to contract said cavity and thereby discharge fluid from said vicinity into said first fluid conduit means, said valve element being movable in a second direction opposite to said first direction under the influence of a pressure differential between the first and second fluid conduit means to expand said cavity and to accept therein fluid from said first fluid conduit means at the end of the short duration decrease in fluid pressure in said first fluid conduit means, said valve element cooperating with said valve body during the short duration decrease in fluid pressure in said first fluid conduit means to block fluid flow between said first and second fluid conduit means.

Claim 10

A hydrostatic transmission assembly as set forth in claim 7 wherein said valve element is movable for a relatively large distance in said first direction under the influence of a relatively long duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said second fluid conduit means to move said valve element to a position in which it enables fluid to flow from said second fluid conduit means to said first fluid conduit means.

Claim 11

A hydrostatic transmission assembly as set forth in claim 7 wherein said valve element cooperates with said body to define another cavity in said chamber, said other cavity being connected in fluid communication with said second fluid conduit means and being expanded by movement of said valve element in said first direction during the sort duration decrease in fluid pressure in said first fluid conduit means to accept in said other cavity fluid from said second fluid conduit means during the short duration decrease in fluid pressure in said first fluid conduit means, said other cavity being contracted by movement of said valve element in said second duration at the end of the short duration decrease in fluid pressure in said first fluid conduit means to thereby discharge accepted fluid from said second fluid conduit means back into said second fluid conduit means.

Claim 12

A hydrostatic transmission assembly comprising a fluid pump, a fluid motor, first fluid conduit mean for conducting fluid between said pump and motor, said motor means having an inherent displacement variation during low speed operation resulting in a short duration pressure decrease in said first fluid conduit means, second fluid conduit means for connecting said first fluid conduit means in fluid communication with source of fluid, and compensating means including a body connected in fluid communication with said first and second fluid conduit means, said compensating means being responsive to the short duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said second fluid conduit means for discharging fluid from said body into said first fluid conduit means during the short duration decrease in fluid pressure in said first fluid conduit means and for accepting fluid from said first fluid conduit means at the end of the short duration decrease in the fluid pressure in said first fluid conduit means to thereby at least partially compensate for the short duration decrease in fluid pressure in said first fluid conduit means, said compensating means including a movable element located in a chamber defined by said body and cooperating with said body to define a cavity in said chamber, said element being movable in a first direction under the influence of the short duration decrease in fluid pressure in said first fluid conduit means to contract said cavity and thereby discharge fluid from said cavity into said first fluid conduit means, said element being movable in a second direction opposite to said first direction under the influence of the fluid pressure in said first fluid conduit means to expand said cavity and to accept therein fluid from said first fluid conduit means at the end Of the short duration decrease in fluid pressure in said first fluid conduit means.

Claim 13

A hydrostatic transmission assembly comprising a fluid pump, a fluid motor, first fluid conduit mean for conducting fluid between said pump and motor, said motor means having an inherent displacement variation during low speed operation resulting in a short duration pressure decrease in said first fluid conduit means, second fluid conduit means for connecting said first fluid conduit means in fluid communication with source of fluid, and compensating means including a body connected in fluid communication with said first and second fluid conduit means, said compensating means being responsive to the short duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said second fluid conduit means for discharging fluid from said body into said first fluid conduit means during the short duration decrease in fluid pressure in said first fluid conduit means and for accepting fluid from said first fluid conduit means at the end of the short duration decrease in the fluid pressure in said first fluid conduit means to thereby at least partially compensate for the short duration decrease in fluid pressure in said first fluid conduit means, said compensating means including a movable element located in a chamber defined by said body and cooperating with said body to define a cavity in said chamber, said element being movable in a first direction under the influence of the short duration decrease in fluid pressure in said first fluid conduit means to contract said cavity and thereby discharge fluid from said cavity into said first fluid conduit means, said element being movable in a second direction opposite to said first direction under the influence of the fluid pressure in said first fluid conduit means to expand said cavity and to accept therein fluid from said first fluid conduit means at the end Of the short duration decrease in fluid pressure in said first fluid conduit means.

Claim 14

A hydrostatic transmission assembly comprising a reversible fluid pump, a reversible fluid motor, first fluid conduit means for conducting high pressure fluid from said pump to said motor during operation of said pump in one direction and for conducting relatively low pressure fluid from said motor to said pump during operation of said pump in an opposite direction, second fluid conduit means for conducting relatively low pressure fluid from said motor to said pump during operation of said pump in said one direction and for conducting relatively high pressure fluid from said pump to said motor during operation of said pump in said opposite direction, third fluid conduit means for connecting said first and second fluid conduit means in fluid communication with a relatively low pressure source of fluid, first valve means connected in fluid communication with said first and third fluid conduit means for controlling fluid flow between said first and third fluid conduit means, second valve means connected in fluid communication with said second and third fluid conduit means for controlling fluid flow between said second and third fluid conduit means, said first valve means including a first body connected in fluid communication with said first and third fluid conduit means and first means responsive to a short duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said third fluid conduit means while said pump is operating in said one direction for blocking fluid flow from said this fluid conduit means into said first fluid conduit means and discharging fluid from said first body into said first fluid conduit means during the short duration decrease in the fluid pressure in said first fluid conduit means while said pump is operating in said one direction and for blocking fluid flow from said first fluid conduit means into said third fluid conduit means and accepting fluid from said first fluid conduit at the end of the short duration decrease in the fluid pressure in said first fluid conduit means while said pump is operating in said one direction to thereby at least partially compensate for the short duration decrease in fluid pressure in said first fluid conduit means, said first means also being responsive to a relatively long duration decrease in the fluid pressure in said first fluid conduit means to a pressure below the fluid pressure in said third fluid conduit means while said first fluid conduit means is conducting relatively low pressure fluid from said motor to said pump during operation of said pump in said opposite direction to enable fluid to flow from said third fluid conduit means to said first fluid conduit means, said second valve means including a second body connected in fluid communication with said second and third fluid conduit means and second mans responsive to a short duration decrease in the fluid pressure in said second fluid conduit means to a fluid pressure below the fluid pressure in said third fluid conduit means while said pump is operating in said opposite direction for blocking fluid flow from said third fluid conduit means to said second fluid conduit means and discharging fluid from said second body into said second fluid conduit means during the short duration decrease in the fluid pressure in said second fluid conduit means while said pump is operating in said opposite direction, and for blocking fluid flow from said second fluid conduit means and accepting fluid from said second fluid conduit means at the end of the short duration decrease in fluid pressure in said second fluid conduit means while said pump is operating in said opposite direction to thereby at least partially compensate for the short duration decrease in the fluid pressure in said second fluid conduit means, said second means also being responsive to a relatively long duration decrease in the fluid pressure in said secOnd fluid conduit means to a fluid pressure below the fluid pressure in said third fluid conduit means while said second fluid conduit means is conducting relatively low pressure fluid from said motor to said pump during operation of said pump in said one direction to enable fluid to flow from said third fluid conduit means to said second fluid conduit means.

Claim 15

A hydrostatic transmission assembly comprising a reversible fluid pump, a reversible fluid motor, first fluid conduit means for conducting high pressure fluid from said pump to said motor during operation of said pump in one direction and for conducting relatively low pressure fluid from said motor to said pump during operation of said pump in an opposite direction, second fluid conduit means for conducting relatively low pressure fluid from said motor to said pump during operation of said pump in said one direction and for conducting relatively high pressure fluid from said pump to said motor during operation of said pump in said opposite direction, third fluid conduit means for connecting said first and second fluid conduit means in fluid communication with a relatively low pressure source of fluid, first valve means connected in fluid communication with said first and third fluid conduit means for controlling fluid flow between said first and third fluid conduit means, second valve means connected in fluid communication with said second and third fluid conduit means for controlling fluid flow between said second and third fluid conduit means, said first valve means including a first body connected in fluid communication with said first and third fluid conduit means and first means responsive to a short duration decrease in the fluid pressure in said first fluid conduit means to a fluid pressure below the fluid pressure in said third fluid conduit means while said pump is operating in said one direction for blocking fluid flow from said this fluid conduit means into said first fluid conduit means and discharging fluid from said first body into said first fluid conduit means during the short duration decrease in the fluid pressure in said first fluid conduit means while said pump is operating in said one direction and for blocking fluid flow from said first fluid conduit means into said third fluid conduit means and accepting fluid from said first fluid conduit at the end of the short duration decrease in the fluid pressure in said first fluid conduit means while said pump is operating in said one direction to thereby at least partially compensate for the short duration decrease in fluid pressure in said first fluid conduit means, said first means also being responsive to a relatively long duration decrease in the fluid pressure in said first fluid conduit means to a pressure below the fluid pressure in said third fluid conduit means while said first fluid conduit means is conducting relatively low pressure fluid from said motor to said pump during operation of said pump in said opposite direction to enable fluid to flow from said third fluid conduit means to said first fluid conduit means, said second valve means including a second body connected in fluid communication with said second and third fluid conduit means and second mans responsive to a short duration decrease in the fluid pressure in said second fluid conduit means to a fluid pressure below the fluid pressure in said third fluid conduit means while said pump is operating in said opposite direction for blocking fluid flow from said third fluid conduit means to said second fluid conduit means and discharging fluid from said second body into said second fluid conduit means during the short duration decrease in the fluid pressure in said second fluid conduit means while said pump is operating in said opposite direction, and for blocking fluid flow from said second fluid conduit means and accepting fluid from said second fluid conduit means at the end of the short duration decrease in fluid pressure in said second fluid conduit means while said pump is operating in said opposite direction to thereby at least partially compensate for the short duration decrease in the fluid pressure in said second fluid conduit means, said second means also being responsive to a relatively long duration decrease in the fluid pressure in said secOnd fluid conduit means to a fluid pressure below the fluid pressure in said third fluid conduit means while said second fluid conduit means is conducting relatively low pressure fluid from said motor to said pump during operation of said pump in said one direction to enable fluid to flow from said third fluid conduit means to said second fluid conduit means.

Claim 16

A hydrostatic transmission assembly as set forth in claim 11 wherein said first and second valve means each include a valve element movably mounted in a chamber defined by the body of the associated valve means, and said hydrostatic transmission assembly further includes a connector element operatively interconnecting said valve element of said first and second valve means in such a manner that when said first valve means is in an open condition enabling fluid to flow from said third fluid conduit means to said first fluid conduit means said second valve means is in a closed condition blocking fluid flow from said third fluid conduit means to said second fluid conduit means and such that when said second valve means is in an open condition enabling fluid to flow from said third fluid conduit means to said second fluid conduit means, said first valve means is in a closed condition blocking fluid flow from said third fluid conduit means to said first fluid conduit means.

Claim 17

A hydrostatic transmission assembly comprising a fluid pump, a fluid motor, first fluid conduit means for conducting fluid between said pump and motor upon operation of said pump to thereby operate said motor second fluid conduit means for connecting said first fluid conduit means in fluid communication with a source of fluid, and valve means connected in fluid communication with said first and second fluid conduit means and operable between open and closed conditions under the influence of pressure differentials of relatively long duration between said first and second fluid conduit means to thereby control fluid flow between said first and second fluid conduit means, said valve means including means for retaining fluid flowing from said second fluid conduit means into said valve means under the influence of a relatively short duration variation in the pressure differential between said first and second fluid conduit means and for discharging the retained fluid from said valve means back into said second fluid conduit means at the end of the relatively short duration variation in the pressure differential between said first and second fluid conduit means to thereby tend to minimize the effect of relatively short duration variations in the pressure in said first fluid conduit means on the operation of said motor.

Claim 18

A hydrostatic transmission assembly comprising a fluid pump, a fluid motor, first fluid conduit means for conducting fluid between said pump and motor upon operation of said pump to thereby operate said motor second fluid conduit means for connecting said first fluid conduit means in fluid communication with a source of fluid, and valve means connected in fluid communication with said first and second fluid conduit means and operable between open and closed conditions under the influence of pressure differentials of relatively long duration between said first and second fluid conduit means to thereby control fluid flow between said first and second fluid conduit means, said valve means including means for retaining fluid flowing from said second fluid conduit means into said valve means under the influence of a relatively short duration variation in the pressure differential between said first and second fluid conduit means and for discharging the retained fluid from said valve means back into said second fluid conduit means at the end of the relatively short duration variation in the pressure differential between said first and second fluid conduit means to thereby tend to minimize the effect of relatively short duration variations in the pressure in said first fluid conduit means on the operation of said motor.

Claim 19

A hydrostatic transmission assembly as set forth in claim 13 wherein said valve means includes a valve body defining a chamber connected in fluid communication with said first and second fluid conduit means and a movable valve element located in said chamber, said chamber including a first portion having a cross-sectional area which is substantially the same as the cross-sectional area of said valve element and a second portion having a cross-sectional area which is substantially larger than the cross sectional area of said valve element, said first portion of said chamber and said valve element cooperating to substantially block a flow of fluid between said first and second fluid conduit means and to form a cavity which is expansible and contractable by movement of said valve element relative to said valve body to provide some means for retaining and discharging fluid, said second portion of said chamber and said valve element cooperating to enable fluid to flow between said first and second fluid conduit means.

Claim 20

A hydrostatic transmission assembly as set forth in claim 13 wherein said means for retaining and discharging fluid includes cavity means which is expansible from a contracted condition to an expanded condition to hold fluid which flows into said valve means from said second fluid conduit means and to dischargE fluid from said valve means into said first fluid conduit means, said vicinity means being contractable from the expanded condition to the contracted condition to discharge fluid from said valve means into said second fluid conduit means and to enable fluid to flow from said first fluid conduit means into said valve means.

Claim 21

A hydrostatic transmission assembly as set forth in claim 13 wherein said valve means include s a valve body defining a chamber having an inlet connected in fluid communication with said second fluid conduit means and an outlet connected in fluid communication with said first fluid conduit means, and a valve element movable in said chamber, said means for retaining and discharging fluid including an expansible cavity formed in a portion of said chamber by said valve element and connected in fluid communication with said second fluid conduit means through said inlet, said valve element being movable in a first direction upon the occurrence of a relatively short duration variation in the pressure differential between said first and second fluid conduit means to expand said cavity while blocking a flow of fluid from said inlet to said outlet to thereby retain fluid flowing into said valve body from said second fluid conduit means, said valve element being movable in a second direction opposite from said first direction at the end of the relatively short duration variation in the pressure differential between said first and second fluid conduit means to contract said cavity while blocking a flow of fluid from said inlet to said outlet to thereby discharge retained fluid from said cavity into said second fluid conduit means.

Claim 22

A hydrostatic transmission assembly as set forth in claim 16 wherein said valve element is movable through a relatively short distance in said first direction under the influence of a relatively short duration variation in the pressure differential between said first and second fluid conduit means and is movable through a relatively large distance in said first direction under the influence of a pressure differential of a relatively long duration between said first and second fluid conduit means to thereby move said valve element into a position enabling fluid to flow from said inlet to said outlet.