GB1600123A - Hydraulic systems - Google Patents

Description

(54) IMPROVEMENTS IN HYDRAULIC SYSTEMS (71) We, GIRLING LIMITED, a British Company of Kings Road, Tyseley, Birmingham 11, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to hydraulic pressure-producing systems.

An hydraulic pressure-producing system usually comprises a pump, an accumulator and a reservoir.

It is essential to ensure that, in such systems, the accumulator can be unloaded to prevent it being overcharged. Once unloaded the fluid medium from the pump must still circulate back to the reservoir and this places an unnecessary amount of work on the fluid, especially if the pump is driven by the prime mover of a vehicle, and the vehicle is suitable for high speed cruising, for example on motorways.

According to our invention in an hydraulic pressure-producing system for making available pressure medium for hydraulic drives in a motor vehicle, comprising a pump, an accumulator, a one-way valve located in a line through which the hydraulic medium under pressure is supplied to the accumulator from the pump, and an actuating device responsive to pressure of hydraulic medium in the accumulator for selectively rendering the pump operative and inoperative whereby when in use the pump is actuated intermittently, the actuating device is a cut-off piston which is subjected to accumulator pressure for the purDose of rendering the pump inoperative, and a spool valve is included for controlling the supply of accumulator pressure to the cut-off piston.

Some embodiments of our invention are illustrated in the accompanying drawings in which: Figure I is a layout of one hydraulic system: Figure 2 shows a different pump and modified pump drive for use in the system of Figure 1: Figure 3 shows another pump and pump drive; and Figure 4 shows yet another pump and pump drive.

The hydraulic system illustrated in Figure 1 of the accompanying drawings incorporates a pump comprising a pump plunger 1 which is reciprocably driven in a bore 2 in a housing 3 to draw hydraulic fluid from a reservoir 4 and discharge it through a one-way valve 5 and an output port 6.

The plunger 1 is reciprocated by an eccentric drive 7 acting on the plunger 1 through a lever 8 which is pivotally connected at an intermediate point in its length to a fixed pivot 9 in the housing 3. An actuating device in the form of a slave cut-off piston 10 working in a cylinder bore 11 in the housing 3 is carried by a piston-rod 12 which is held out of engagement with a lever 8, by means of a spring 13, when a chamber 14 in the bore 11 on the opposite side of the piston 10 from the piston rod 12 is de-pressurised.

A control valve 15 is located between the pump and an hydraulic accumulator 16.

The control valve 15 comprises a housing 17 having an inlet port 18 to which the output port 6 is connected through a supply line 19, an outlet port 20 connected to the hydraulic accumulator through a pipe-line 21, an exhaust port 22 connected to the reservoir 4 through a pipe-line 23, and a diverted port 24 connected to a restricted port 25 in the housing 3 which leads into the chamber 14 through a pipe-line 26.

A spool valve 27 is located in the housing to control communication between the various ports. As illustrated the valve 27 comprises a single spool 28 provided with spaced lands 29 and 30 which work in the longitudinal bore 31 in the housing 17. The port 18 is connected to the port 20 through a one-way valve 32 and the ports 18 and 20 are themselves connected to opposite ends of the bore 31 so that, normally, pressures at these ports act on portions 33 and 34 of smaller and greater effective area resrectively, which are disposed substantially at opposite ends of the spool 28 An extension 35 of reduced diameter extends from the land 30 into an enlarged chamber 36 which accommodates a cut-out spring 37 for urging the spool 28 in the direction shown, in which the ports 22 and 24 lie between the lands 29 and 30 to exhaust not only the chamber 14 to the tank 4 but also the chamber 36 to the tank through a passage 38 which connects the chamber 36 to the port 22. A restrictor 39 provides restricted communication between the bore 31 and the passage 38.

When the pump is operated initially, the spool valve 27 is in the position shown.

Fluid is drawn from the reservoir 4 and is pumped by the plunger 1 into the accumulator 16 through the one-way valve 5, and through the one-way valve 32. This continues until the pressure in the accumulator 16 which acts on the portion 34 of the spool which is of greater area, attains a predetermined value, say 2000 p.s.i. This pressure is sufficient to apply to the spool a net force greater than the force in the spring 37 plus the force acting in the opposite direction, namely the pump pressure acting over the portion 33 which is of smaller area.This has the result that the spool 28 moves in the bore 31 and relatively into the chamber 36 from the first position into the second position, compressing the spring 37 and placing the accumulator 16 in communication with the chamber 14 to pressurise that chamber, with no time delay as the pressure drop across the restrictor 25 is 2000 p.s.i. The piston 10 is then advanced in the bore 11 and the piston rod 12 moves the lever 8 angularly about the pivot 9 in a direction to urge the plunger 1 away from the drive 7, thereby disabling the pump and preventing further discharge through the output port 6. When the pump pressure falls by a bleed through the restrictor 39, the plunger 29 increases its load on the spring 37 as the pressure in the annular chamber has fallen.

When the accumulator pressure drops to the cut-in pressure, say to 1500 p.s.i., the force produced by that pressure is less than the force acting in the opposite direction, so that the spool 28 is restored to its original first position. Since the chamber 14 is reconnected to the reservoir 4, after a time delay due to the pressure drop across the restrictor 25, which is determined by the spring 13 and the area of the piston 10, the piston 10 retracts under the influence of the spring 13 and the plunger 1 is again reciprocated by the drive 7.

The pressure applied to the smaller area portion 33 of the spool in opposition to the pressure of the accumulator may alternatively comprise the accumulator pressure.

In the modified construction illustrated in Figure 2 the drive 7 is surrounded by as eccentric housing 40 which is pivotally connected at its upper end to a fixed part 41 by means of a pivot 42, and the lower end of the housing 40 is urged into engagement, in a drive position, with a stop 43 adjacent to the piston rod 12, by means of a spring 44.

When the chamber 14 is pressurised, the piston 10 is advanced to urge the housing 40 angularly about the pivot 42 to make it concentric with the drive 7 and therebv disable the pump.

The embodiment of Figure 3 has an epicyclic drive to the pump, and the piston rod 12 again projects from the housing.

The epicyclic gear is normally operated, when the chamber 14 is unpressurised, since an outer ring gear 45 is prevented from rotating within a fixed housing 46 by the piston 12 which is urged into engagement with it by means of the spring 13. When an input drive 47 is operated, since the ring gear 45 is held against rotation, plant gears 48 rotate by travelling around the ring gear 45, and a sun gear 49 comprising the pump output is rotatably driven.

When the chamber 14 is pressurised, the piston 10 is withdrawn against the loading in the spring 13. The ring gear 45 can now rotate within the housing and does so in preference to the sun gear 49, since the torque within the pump is greater than the torque between the ring gear 45 and the planet gears 48. Thus under such conditions the drive to the pump is disabled.

In the embodiment of Figure 4, the pump 50 is driven through a clutch 51, and the piston-rod 12 is operative to disengage the clutch 51 when the chamber 14 is pressurised.

Other features of the embodiments described above form the subject of our copending Patent Application No. 3119/77, Serial No. 1600122, out of which this application is divided.

WHAT WE CLAIM IS: 1. An hydraulic pressure-producing system for making available pressure medium for hydraulic drives in a motor vehicle, comprising a pump, an accumulator, a oneway valve located in a line through which the hydraulic medium under pressure is supplied to the accumulator from the pump, and an actuating device responsive to pressure of hydraulic medium in the accumulator for selectively rendering the pump operative and inoperative whereby when in use the pump is actuated intermittently, in which the actuating device is a cut-off piston which is subjected to accumulator pressure for - the purpose of rendering the pump inoperative, and a spool valve is included for controlling the supply of accumulator pressure to the cutoff piston.

2. An hydraulic pressure-producing sys

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. extension 35 of reduced diameter extends from the land 30 into an enlarged chamber 36 which accommodates a cut-out spring 37 for urging the spool 28 in the direction shown, in which the ports 22 and 24 lie between the lands 29 and 30 to exhaust not only the chamber 14 to the tank 4 but also the chamber 36 to the tank through a passage 38 which connects the chamber 36 to the port 22. A restrictor 39 provides restricted communication between the bore 31 and the passage 38. When the pump is operated initially, the spool valve 27 is in the position shown. Fluid is drawn from the reservoir 4 and is pumped by the plunger 1 into the accumulator 16 through the one-way valve 5, and through the one-way valve 32. This continues until the pressure in the accumulator 16 which acts on the portion 34 of the spool which is of greater area, attains a predetermined value, say 2000 p.s.i. This pressure is sufficient to apply to the spool a net force greater than the force in the spring 37 plus the force acting in the opposite direction, namely the pump pressure acting over the portion 33 which is of smaller area.This has the result that the spool 28 moves in the bore 31 and relatively into the chamber 36 from the first position into the second position, compressing the spring 37 and placing the accumulator 16 in communication with the chamber 14 to pressurise that chamber, with no time delay as the pressure drop across the restrictor 25 is 2000 p.s.i. The piston 10 is then advanced in the bore 11 and the piston rod 12 moves the lever 8 angularly about the pivot 9 in a direction to urge the plunger 1 away from the drive 7, thereby disabling the pump and preventing further discharge through the output port 6. When the pump pressure falls by a bleed through the restrictor 39, the plunger 29 increases its load on the spring 37 as the pressure in the annular chamber has fallen. When the accumulator pressure drops to the cut-in pressure, say to 1500 p.s.i., the force produced by that pressure is less than the force acting in the opposite direction, so that the spool 28 is restored to its original first position. Since the chamber 14 is reconnected to the reservoir 4, after a time delay due to the pressure drop across the restrictor 25, which is determined by the spring 13 and the area of the piston 10, the piston 10 retracts under the influence of the spring 13 and the plunger 1 is again reciprocated by the drive 7. The pressure applied to the smaller area portion 33 of the spool in opposition to the pressure of the accumulator may alternatively comprise the accumulator pressure. In the modified construction illustrated in Figure 2 the drive 7 is surrounded by as eccentric housing 40 which is pivotally connected at its upper end to a fixed part 41 by means of a pivot 42, and the lower end of the housing 40 is urged into engagement, in a drive position, with a stop 43 adjacent to the piston rod 12, by means of a spring 44. When the chamber 14 is pressurised, the piston 10 is advanced to urge the housing 40 angularly about the pivot 42 to make it concentric with the drive 7 and therebv disable the pump. The embodiment of Figure 3 has an epicyclic drive to the pump, and the piston rod 12 again projects from the housing. The epicyclic gear is normally operated, when the chamber 14 is unpressurised, since an outer ring gear 45 is prevented from rotating within a fixed housing 46 by the piston 12 which is urged into engagement with it by means of the spring 13. When an input drive 47 is operated, since the ring gear 45 is held against rotation, plant gears 48 rotate by travelling around the ring gear 45, and a sun gear 49 comprising the pump output is rotatably driven. When the chamber 14 is pressurised, the piston 10 is withdrawn against the loading in the spring 13. The ring gear 45 can now rotate within the housing and does so in preference to the sun gear 49, since the torque within the pump is greater than the torque between the ring gear 45 and the planet gears 48. Thus under such conditions the drive to the pump is disabled. In the embodiment of Figure 4, the pump 50 is driven through a clutch 51, and the piston-rod 12 is operative to disengage the clutch 51 when the chamber 14 is pressurised. Other features of the embodiments described above form the subject of our copending Patent Application No. 3119/77, Serial No. 1600122, out of which this application is divided. WHAT WE CLAIM IS:

1. An hydraulic pressure-producing system for making available pressure medium for hydraulic drives in a motor vehicle, comprising a pump, an accumulator, a oneway valve located in a line through which the hydraulic medium under pressure is supplied to the accumulator from the pump, and an actuating device responsive to pressure of hydraulic medium in the accumulator for selectively rendering the pump operative and inoperative whereby when in use the pump is actuated intermittently, in which the actuating device is a cut-off piston which is subjected to accumulator pressure for - the purpose of rendering the pump inoperative, and a spool valve is included for controlling the supply of accumulator pressure to the cutoff piston.

2. An hydraulic pressure-producing sys

tem as claimed in claim 1, in which the pump has a piston drivable by an eccentric, and the actuating device has a coupling for rendering the eccentric drive ineffective.

3. An hydraulic pressure-producing system as claimed in Claim 2, in which the piston is drivable by a camshaft.

4. An hydraulic pressure-producing system as claimed in Claim 1, in which the pump has a rotary drive and the actuating device has a coupling device for rendering the rotary drive ineffective.

5. An hydraulic pressure-producing system as claimed in Claim 4, in which the cut-off piston is only longitudinally movable.

6. An hydraulic pressure-producing system as claimed in Claim 4 or Claim 5, in which the rotary drive is performed by a cam shaft.