Variable displacement pump control

Claim 2

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member when in relief passage closing position having unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone via said orifice means.

Claim 3

The control means of claim 1 wherein spring means acting on said another valve member assists the fluid pressure acting on said smaller area in moving said another valve member to open said relief passage as aforesaid.

Claim 4

The control means of claim 2 wherein said relief passage is open during start-up of said pump means to purge air from said pump means and is closed by said another valve member as fluid pressure commences to build up following such purging of air.

Claim 5

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; and another orifice means limiting the pressure drop across said orifice means during normal operation of said valve and pilot valve members so that said another valve member is retained in position closing said relief passage except when there is an abnormal increase in pressure drop across said orifice means due to rapid rise of fluid pressure in said high pressure zone; said another valve member having opposed areas respectively exposed to said high pressure zone and to said high pressure zone between said orifice means and said another orifice means.

Claim 6

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; and another orifice means limiting the pressure drop across said orifice means during normal operation of said valve and pilot valve members so that said another valve member is retained in position closing said relief passage except when there is an abnormal increase in pressure drop across said orifice means due to rapid rise of fluid pressure in said high pressure zone; said another valve member having opposed areas respectively exposed to said high pressure zone and to said high pressure zone between said orifice means and said another orifice means.

Claim 7

The control means of claim 4 wherein the opposed areas of said another valve member are unequal, the smaller area being exposed to said high pressure zone and the larger area being exposed to said high pressure zone between said orifice means and said another orifice means.

Claim 8

The control means of claim 5 wherein spring means acting on said another valve member assists the fluid pressure acting on said smaller area in moving said another valve member to open said relief passage as aforesaid.

Claim 9

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said housing assembly comprising a pump housing having an intake port adapted to be communicated with a fluid reservoir, a discharge port, and an adjustment port leading to said fluid pressure operated member; and a valve housing secured to said pump housing and provided with discharge and adjustment passages registering with said discharge and adjustment ports; said valve housing having first and second bores intersecting said discharge passage and respectively containing said valve and pilot valve members and said another valve member and providing such restricted communication between said discharge and adjustment passages and providing openings for reservoir discharge from said bleed and relief passages and from said pilot valve member.

Claim 10

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said housing assembly comprising a pump housing having an intake port adapted to be communicated with a fluid reservoir, a discharge port, and an adjustment port leading to said fluid pressure operated member; and a valve housing secured to said pump housing and provided with discharge and adjustment passages registering with said discharge and adjustment ports; said valve housing having first and second bores intersecting said discharge passage and respectively containing said valve and pilot valve members and said another valve member and providing such restricted communication between said discharge and adjustment passages and providing openings for reservoir discharge from said bleed and relief passages and from said pilot valve member.

Claim 11

The control means of claim 7 wherein said another valve member has opposed areas respectively exposed to fluid pressure in said discharge passage and to fluid pressure downstream of said orifice means via a valve housing passage intercommunicating said first and second bores.

Claim 12

The control means of claim 7 wherein said another valve member has unequal opposed areas of which the smaller area is exposed to fluid pressure in said discharge passage and of which the larger area is exposed to fluid pressure downstream of said orifice means via a valve housing passage intercommunicating said first and second bores.

Claim 13

The control means of claim 9 wherein spring means acting on said another valve member assists the pressure acting on said smaller area in moving said another valve member to open said relief passage as aforesaid.

Claim 14

A control means for a variable displacement hydraulic pump of the type which includes a housing assembly having a pressure chamber to which fluid pressure from the high pressure zone of said pump is conducted by way of a restricted passage to act on a pump displacement varying means in said chamber; said control means comprising a pilot operated valve assembly in said housing assembly having a pilot valve member which opens and closes communication between the high and low pressure zones of said pump responsive to the fluid pressure in said high pressure zone being greater than or less than predetermined magnitude, and a spring biased main valve member having first opposed areas respectively exposed to said high pressure zone and to said high pressure zone via orifice means, said main valve member being moved to open a bleed passage from said chamber to said low pressure zone when said pilot valve member is open and to close said bleed passage when said pilot valve is closed, said bleed passage when open decreasing the fluid pressure in said chamber for movement of said pump displacement varying means to decrease the displacement of said pump; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member having unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone via said orifice means.

Claim 15

A control means for a variable displacement hydraulic pump of the type which includes a housing assembly having a pressure chamber to which fluid pressure from the high pressure zone of said pump is conducted by way of a restricted passage to act on a pump displacement varying means in said chamber; said control means comprising a pilot operated valve assembly in said housing assembly having a pilot valve member which opens and closes communication between the high and low pressure zones of said pump responsive to the fluid pressure in said high pressure zone being greater than or less than predetermined magnitude, and a spring biased main valve member having first opposed areas respectively exposed to said high pressure zone and to said high pressure zone via orifice means, said main valve member being moved to open a bleed passage from said chamber to said low pressure zone when said pilot valve member is open and to close said bleed passage when said pilot valve is closed, said bleed passage when open decreasing the fluid pressure in said chamber for movement of said pump displacement varying means to decrease the displacement of said pump; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member having unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone via said orifice means.

Claim 16

The control means of claim 11 wherein spring means acting on said another valve member assists the fluid pressure acting on said smaller area in moving said another valve member to open said relief passage as aforesaid.

Claim 17

The control means of claim 12 wherein said another valve member, upon start-up of said pump, purges air therefrom through said relief passage until fluid pressure builds up to actuate said another valve member to overcome said spring means to close said relief passage.

Claim 18

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member having unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone via said orifice means.

Claim 19

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member having unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone via said orifice means.

Claim 20

The control means of claim 14 wherein spring means acting on said another valve member assists the pressure acting on said smaller area in moving said another valve member to open said relief passage as aforesaid.

Claim 21

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said housing assembly comprising a pump housing having an intake port adapted to be communicated with a fluid reservoir, a discharge port, and an adjustment port leading to said fluid pressure operated member; and a valve housing secured to said pump housing and provided with discharge and adjustment passages registering with said discharge and adjustment ports; said valve housing having first and second bores intersecting said discharge passage and respectively containing said valve and pilot valve members and said another valve member and providing such restricted communication between said discharge and adjustment passages and providing a sensing passage opening and openings for reservoir discharge from said bleed and relief passages and from said pilot valve.

Claim 22

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said housing assembly comprising a pump housing having an intake port adapted to be communicated with a fluid reservoir, a discharge port, and an adjustment port leading to said fluid pressure operated member; and a valve housing secured to said pump housing and provided with discharge and adjustment passages registering with said discharge and adjustment ports; said valve housing having first and second bores intersecting said discharge passage and respectively containing said valve and pilot valve members and said another valve member and providing such restricted communication between said discharge and adjustment passages and providing a sensing passage opening and openings for reservoir discharge from said bleed and relief passages and from said pilot valve.

Claim 23

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member having opposed areas respectively exposed to said high pressure zone and to said high pressure zone via said orifice means.

Claim 24

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member having opposed areas respectively exposed to said high pressure zone and to said high pressure zone via said orifice means.

Claim 25

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member when in relief passage closing position having unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone via said orifice means.

Claim 26

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; said another valve member when in relief passage closing position having unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone via said orifice means.

Claim 27

The control means of claim 18 wherein spring means acting on said another valve member assists the fluid pressure acting on said smaller area in moving said another valve member to open said relief passage as aforesaid.

Claim 28

The control means of claim 19 wherein said relief passage is open during start-up of said pump means to purge air from said pump means and is closed by said another valve member as fluid pressure commences to build up following such purging of air.

Claim 29

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; and another orifice means limiting the pressure drop across said orifice means during normal operation of said valve and pilot valve members so that said another valve member is retained in position closing said relief passage except when there is an abnormal increase in pressure drop across said orifice means due to rapid rise of fluid pressure in said high pressure zone.

Claim 30

Control means for a variable displacement hydraulic pump of the type including a housing assembly having pump means, high and low fluid pressure zones, and a fluid pressure operated member operatively engaged with said pump means to vary the displacement thereof, said fluid pressure operated member having restricted fluid communication with said high pressure zone; said control means comprising a valve member movable in said housing assembly to open and close a bleed passage from said fluid pressure operated member to said low pressure zone and having first opposed areas including an area on one side thereof exposed to fluid pressure in said high pressure zone and an area on the other side exposed to fluid pressure in said high pressure zone via orifice means; spring means in said housing assembly biasing said valve member to bleed passage closing position; and a pilot valve in said housing assembly opened upon increase of fluid pressure in said high pressure zone to predetermined magnitude to bleed fluid pressure acting on the area on said other side of said valve member to said low pressure zone whereby predominant fluid pressure upstream of said orifice means acting on the area on said one side of said valve member is effective to move it to a position to open said bleed passage for movement of said fluid pressure operated member to decrease the capacity of said pump means; said valve member having second opposed areas respectively exposed to said high pressure zone and to a pressure sensing passage which is communicated with the downstream side of a variable area orifice in the pressure feed path from said high pressure zone to a fluid motor actuated by fluid under pressure flowing through said variable area orifice from said high pressure zone, said valve member, while said pilot valve is closed, being moved to bleed passage opening position against said spring means when the fluid pressure differential acting on said second opposed areas exceeds a predetermined value; and another valve member movable in said housing assembly responsive to opening of said pilot valve and to abnormal increase in pressure drop across said orifice means to open a relief passage from said high pressure zone to said low pressure zone; and another orifice means limiting the pressure drop across said orifice means during normal operation of said valve and pilot valve members so that said another valve member is retained in position closing said relief passage except when there is an abnormal increase in pressure drop across said orifice means due to rapid rise of fluid pressure in said high pressure zone.

Claim 31

The control means of claim 21 wherein said another valve member has opposed areas respectively exposed to said high pressure zone and to said high pressure zone between said orifice means and said another orifice means.

Claim 32

The control means of claim 21 wherein said another valve member has unequal opposed areas of which the smaller area is exposed to said high pressure zone and of which the larger area is exposed to said high pressure zone between said orifice means and said another orifice means.

Claim 33

The control means of claim 23 wherein spring means acting on said another valve member assists the fluid pressure acting on said smaller area in moving said another valve member to open said relief passage as aforesaid.