BRPI0709186B1 - VARIABLE DISPLACEMENT SLIDING PUMP PUMP - Google Patents

Abstract

variable displacement sliding vane pump. a variable displacement sliding vane pump comprising a pump body, inlet and outlet holes formed in the pump body, a drive shaft rotatably mounted on the pump body, a drive shaft driven rotor and coaxially aligned therewith, a plurality of radially extended vanes slidably disposed on the rotor, a pivot disposed on the pump body, a pivotably disposed slide on the pump casing and having a central axis eccentric to the rotor axis, a plurality of chambers rotor, vanes, and slide, which are successively connected to the inlet and outlet ports, a spring acting on the slide to induce the slide in one direction, a first chamber and a second chamber each suitable for receiving hydraulic pressure, each being arranged between the pump body and a slide slide; the first chamber in hydraulic communication with a pump outlet discharge pressure, and a valve operable to selectively pressurize, and depressurize, the second chamber.

Description

“VARIABLE DISPLACEMENT SLIDING VAN PUMP”

Field of the Invention

The invention relates to a variable displacement sliding vane pump having a slide whose position is controlled by a differential pressure between a constant pressure source and a variable pressure source, the differential pressure balancing a spring force applied to the slide to establish flow rate and pressure desired.

Background of the Invention

A lubrication system for an engine pressurizes and distributes the lubrication fluid to the engine's lubrication circuits. It uses a rotor and a slide with multiple vanes and cavities that can vary the volume of fluid supplied to the oil circuits.

The slide is displaced eccentrically from the rotor to create fluid chambers defined by the vanes, rotor, and internal surface of the slide. A compression spring positions the slide to create large fluid chambers as the standard. When the engine requires less fluid volume or less oil pressure through the pump, a pressure regulator directs the fluid from the pump outlet line to a regulating chamber in the pump. The pressure in the regulating chamber turns the vane against the spring force to more closely align the centers of the rotor and slide, thereby reducing the size of the fluid chambers. This reduces the amount of fluid drawn into the pump from the fluid reservoir and similarly, the amount of fluid emitted by the pump and thereby also reduces the oil pressure.

There are two ways to control the pump outlet. The first way is to direct the line pressure to the regulator chamber through the pressure regulator to decrease the pump output. The second way is to remove the pressure from the regulating chamber through the pressure regulator using the exhaust fluid to increase the pump output.

Representative of the technique is United States patent 4342545 (1982) by Schuster which discloses a variable displacement vane pump having a pivotably mounted ring element to vary the eccentricity between the rotor and the ring thereby controlling displacement the pump. The ring is positioned on the pivot in such a way that its center is always located in a quadrant in relation to the axes through the pivot point and the center of the pump rotor to continuously maintain the net force of the ring reaction, due to the internal pressure, directed to one side of the pivot connection as opposed to the displacement control pressure, which is forced on a portion of the outer surface of the ring, so the control stability over the entire displacement range is improved.

What is needed is a variable displacement sliding vane pump having a slide whose position is controlled by a differential pressure between a constant pressure source and a variable pressure source, the differential pressure balancing a spring force applied to the slide to establish flow rate and pressure desired. The present invention meets that need.

Summary of the Invention

The main aspect of the invention is to provide a variable displacement sliding vane pump having a slide whose position is controlled by a differential pressure between a constant pressure source and a variable pressure source, the differential pressure balancing an applied spring force the slide to establish a desired flow rate and pressure.

Other aspects of the invention will be highlighted or made obvious by the following description of the invention and the accompanying drawings.

The invention comprises a variable displacement sliding vane pump comprising a pump body, inlet and outlet holes formed in the pump body, a drive shaft rotatably mounted on the pump body, a rotor driven by the drive shaft and aligned coaxially with it, several radially extended vanes slidably arranged on the rotor, a pivot arranged on the pump body, a slide pivotally arranged on the pivot on the pump body and having an eccentric central axis in relation to the rotor axis, several fluid chambers defined by the rotor, the vanes, and the slide that are connected successively to the inlet and outlet holes, a spring acting on the slide to induce the slide in one direction, a first chamber and a second chamber, each suitable for receiving a hydraulic pressure and each one arranged between the pump body and an external surface of the slide, the prime for communication being in hydraulic communication with a discharge pressure from the pump outlet, and a operable valve to selectively pressurize and depressurize the second chamber.

Brief Description of Drawings

The attached drawings, which are incorporated and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.

Figure 1 is a front view of the pump with the outer cover removed.

Figure 2 is an exploded view of the pump.

Figure 3 is a front view of the pump body without the outer cover, slide, rotor and vane.

Figure 4 is a top / plan view of the pump rotor.

Figure 5 is a plan view of the pump slide.

Figure 6 is a schematic diagram of the pump fluid circuit.

Figure 7 is a graph illustrating pump performance including pump flow rate and pressure.

Figure 8 is a side view of an electric valve.

Figure 9 is a graph illustrating the pump's performance including pump flow rate and pressure.

Detailed Description of the Preferred Mode

Figure 1 is a front view of the pump with the outer cover removed. The inventive pump 100 comprises the body 10. The body 10 defines a cavity 11 within which the slide 12 is arranged, and the rotor 13. Several sliding vanes 14 are arranged radially around the rotor 13. Each van 14 extends radially to from a slot 15 in the rotor 13. Each vane 14 is movable within each slot 15.

The pump shaft 16 is pivotally mounted on the body 10. A cooled end 160 of the pump shaft 16 engages the rotor 13. When the rotor 13 rotates the vanes 14 are pushed outwardly by a pair of vane control rings 17 and by the centripetal force for a sliding engagement with the inner surface 120, of the slide 12.

The slide 12 is pivotally engaged with the body on a pivot element 18. The slide 12 rotates on the pivot element 18 within the cavity 11 thereby describing an arc that defines the movement operating range of the slide 12.

The position of each vane 14 is a function of the position of the slide 12 with respect to ring 17. Ring 17 occupies a space determined by the ends of the vanes 14. Ring 17 is substantially concentric with the inner surface 120.

The position of the ring 17 with respect to the rotor 13 determines the radial position of each vane 14 in each slot 15, which in turn determines a determined position of the slide 12 compared to the position of the rotor 13 rotation axis. The ratio determines the volume of each of the chambers 21 between the inlet 19 and the outlet 20 for a given motor speed and therefore a specific slide position 12.

Body 12 defines a pair of kidney-shaped holes 19, 20 comprising an inlet and an outlet port, respectively, for pump 100. Several chambers 21 are formed by vanes 14, rotor 13 and inner surface 120. The chambers 21 rotate with the rotor 13 and expand and contract during rotation, as is well known in vane pumps.

Inlet port 19 accepts fluid from a source or reservoir such as an engine oil system, not shown, and passes the fluid to chambers 21 in turns as rotor 13 rotates. The vanes 14 move the fluids in the chambers 21 from the orifice 19 to the orifice 20. As can be seen in Figure 1, if the pump impeller 13 is rotating in a counterclockwise direction, the chambers 21 are expanding continuously in this way creating a region of low pressure which causes an inflow of fluid in the area of the inlet orifice 19 and are contracting in this way increasing the pressure of the fluid causing an outflow of fluid in the area of the orifice output 20.

The position of the slide 12 is established by the combined effect of the control pressure in each of two chambers, that is, the chamber 22 and chamber 23 acting in balance with the spring force from the spring 31. The chamber 22 extends in around a portion of the outer circumference of the slide 12, from the sealing element 24, arranged in a groove 26 to the sealing member 25 arranged in a groove 27, each formed in the slide 12. Each of the sealing elements , 24 and 25, is driven outwardly against the surface 28 by a flexible support element 29, 30, respectively. The chamber 23 extends around a portion of the outer circumference of the slide 12 from the sealing member 24 to the pivot member 18.

The spring 31 acts in opposition to the sum of the fluid pressures in chambers 22 and 23 in such a way that when the total pressure in chambers 22 and 23 increases and therefore the torque of the slide around the pivot element increases, the pump slide 12 will move clockwise around the pivot element 18. The combined torque caused by pressure in the chamber 22, 23 is balanced by the spring force of the spring 31.

The hydraulic pressure in chamber 22 is provided by the fluid in final communication with the outlet port of the pump 100 and, therefore, is subject to the outlet pressure of the pump 100 and from a return channel to the motor gallery, see Figure 5. The hydraulic pressure in chamber 23 is provided by fluid communication with a second pressure source also connected to outlet port 20 of pump 100. The hydraulic pressure in chamber 22 is proportional to the outlet pressure of pump 100. Hydraulic pressure in chamber 23 it depends on the speed of the pump 100, that is, for certain operating regimes below a predetermined speed of the pump the pressure in the chamber 23 is automatically vented to the environment, for example, an oil storage tank. Above a predetermined speed the pressure in chamber 23 is equivalent to the pressure in chamber 22. This is also referred to as the “switching point” and can be adjusted at any speed depending on the application. The sum of the pressures and, therefore, the torque in the chambers, 22 and 23, determines the position of the slide 12. The position of the slide 12 determines the outlet pressure and the flow rate of the pump.

Under most operating conditions, the slide axis 12, and therefore the inner surface 120, travels between position 32 during low engine speed conditions to position 33 during high engine speed conditions. When straws 14 are rotated from inlet 19 to outlet 20, a pressure transition occurs with chambers 21.

As the internal surface 120 is subjected to the generation of internal pressure in the chambers 21, the slide 12 is inherently unbalanced during operation. The resulting net reaction force due to the generation of internal pressure passes through the central axis of the inner surface 120. It will be considered that the reaction forces always provide a counterclockwise moment around axis 18 which is opposite to the moment at clockwise generated by the control pressure in chambers 22 and 23.

The pressures in the chamber 22, 23 are balanced against the force of the spring 31 so that the displacement of the pump, and as a result the flow, can be adjusted by varying the pressures of the chamber. The inventive pump controls both displacement and oil flow for two or more levels of outlet pressure based on the outlet pressure of the pump or the pressure of the engine gallery.

Typically, the desired pressure level at the pump for each chamber is the pressure level required to produce the oil flow and pressure itself for all engine speeds and load conditions. In some cases, at lower RPM the mechanism does not require a high level of oil pressure, therefore a somewhat lower pressure is acceptable and therefore the flow is also reduced. The lower operating pressure and flow are obtained by pressurizing the chamber 23.

The required magnitude of the lower oil pressure depends on different engine parameters, including whether it is a gas or diesel driven engine, the complexity of the engine, the engine speed and load.

The inventive pump provides two levels of control. The first is the pressure control over a certain speed range due to the variable function of the vane pump. The second is based on the pump's ability to change between two (or more) pressure levels through the use of two (or more) pressure chambers 22, 23 controlling the position of the slide 12.

The cover 70 is secured to the housing 10 by a plurality of fasteners 37. Leakage from the chambers 21 radially outwardly beyond the cover 70 is prevented by surface-to-surface contact.

Figure 2 is an exploded view of the pump. The position of the ring 17 with respect to the rotor 13 determines the radial position of each reed 14 in each slot 15, which in turn determines a position of the slide 12 compared to the position of the rotor 13 axis of rotation. An inner edge 14a of each vane 14 rests on the outer surface 17a of the ring 17. An outer edge 14b of each vane 14 also rests on and slides over the inner surface 120 of the slide 12. The pump can use a single spring 31, or it you can use, for example, two springs 31a and 31b.

Figure 3 is a front view of the pump body without the outer cover, slide, rotor and vanes. Inlet orifice 19 and outlet orifice 20 are arranged in body 10. Conduit 34 transmits pressure from main oil gallery 204 to chamber 22, see Figure 5. Conduit 35 transmits pressure from oil gallery main 204 for chamber 23, see Figure 5. Duct 34 is exposed to the pump outlet pressure or oil pressure of the engine gallery during all pump operating conditions. The hydraulic pressure in conduit 35 is determined by the position of valve 207, see Figure 1.

Figure 4 is a top plan view of the pump rotor. The rotor 13 comprises slots 15 which are oriented radially around the outer circumference. A reed 14 is slidably engaged in each slot 15. The drive shaft 16 engages the rotor 13 through the splined hole 36. The drive shaft 16 can also be snapped into hole 36. Each slot 15 comprises a radial length sufficient to accommodate the integral range of motion of each vane 14. During operation of the pump each vane 14 travels radially a predetermined distance whose distance depends on the position of the rings 17 with respect to the rotor 13.

Figure 5 is a plan view of the pump slide. The slide 12 comprises the inner surface 120. An outer edge of each vane 14 slidably engages the inner surface 120. The inner surface 120 is cylindrical, but the shape of the surface can be slightly distorted to accommodate design geometries, for example , for an oval shape or an egg shape. Pivot 18 engages detent 121. Groove 26 and groove 27 individually receive sealing elements 24, 25, respectively, to seal a hydraulic pressure within each chamber 23, 22 respectively. The spring 31 rests on the surface 122. Sealing elements 24, 25 can comprise any material having an adequate compatibility with the pump fluid, for example, synthetic and / or natural rubbers.

Figure 6 is an exemplary schematic diagram of the pump fluid circuit 200. Fluid duct 201 connects pump outlet port 20 to an oil filter 202, oil cooler 203 and a main oil gallery 204. A Main oil gallery 204 is exposed to the outlet pressure of pump 100, subjected to normal friction losses for any fluid system. Main oil gallery 204 is also connected to engine oil system 210. This system is offered as an example only and does not illustrate the varieties of engine oil systems, to which the inventive pump and system can be applied.

Connected to main oil gallery 204 is conduit 205 which connects to chamber 22 through conduit 34, see Figure 1. Connected to conduit 205 is conduit 209. Conduit 209 is connected to electric valve 207, see Figure 7. Valve 207 is used to selectively connect or disconnect conduit 209 through conduit 206 to conduit 35 and chamber 23 in Figure 1, with hydraulic pressure in conduit 205. Valve 207 is preferably contained within body 10. Valve 207 is shown in Figure 5 schematically separated from valve 100 for ease of illustration. However, valve 207 can also be separated from pump housing 100 as shown schematically in Figure 5 to accommodate varying physical constraints as required by system space requirements. Valve 207 may also comprise a mechanical valve known in the art, for example, a valve that regulates a downstream pressure based on an upstream pressure commonly known as a pressure regulating valve.

The total force exerted against the spring 31 by the slide 12 is the sum of the torques created by the hydraulic pressure in the chamber 22 plus the hydraulic pressure in the chamber 23, both acting around the pivot element 18.

At first engine speed or less than the first operating speed, valve 207 is OPEN in this way allowing pressure from the engine gallery to enter chamber 23. Pressure in chamber 23 combined with pressure in chamber 22 causes slide 12 rotates around pivot element 18 at an arcuate distance to a position where the torque caused by the combined pressures in chambers 22, 23 is balanced by the spring force of spring 31. The characteristics of the pump with slide 12 in that position are shown by the “A” portion of Figure 7. The pressure in the chambers, 22 and 23, is proportional to the speed of the pump. As the speed of the motor, and thus the speed of the pump, so does the pressure in the chambers 22, 23. So in this operating condition the pump output is at a flow and pressure that are lower than the flow and pressure of the pump with valve 207 closed (chamber 23 depressurized) at the same speed as the engine. In the “A” portion, the position of the slide 12, and thus of the pump outflow and pressure, is a function of the pressure in both chambers 22, 23.

In an operating condition greater than the first operating speed, valve 207 is thus closed by venting chamber 23 to ambient pressure (approximately 0.98 atm). The pressure in the chamber 22 causes the slide 12 to rotate around the pivot element 18 by an arcuate distance to an equilibrium position where the torque caused by the pressure in the chamber 22 is balanced by the spring force of the spring 31. The slide 12 rotates because as the pump speed increases, the pressure in the chamber 22 also increases, thereby increasing the force exerted against the spring 31. The characteristics of the pump with the slide 12 in that position are shown by portion B of Figure 7. The regime of operation in portion B can also be characterized as a passive mode since the chamber 23 is ventilated to atmospheric pressure and the entire pivot movement and the position of the slide 12 are determined by the pressure level of the chamber 22.

In an alternative embodiment the valve 207 can be opened to a partial position in this causing the slide 12 to move to a position that is the intermediate position A and position B, causing an intermediate outlet pressure and flow. Placing valve 207 in any position between fully open and fully closed allows the pressure in chamber 23 to be variable, thus providing a range of slide positions for a given pump outlet pressure.

In the event of a 207 valve failure, the pump will continue to operate in a passive mode (depressurized chamber 23) while satisfying all engine oil requirements. The passive mode of operation is even more efficient than in a fixed displacement pump. With valve 207 in operation, the present invention provides a reduction in horsepower, incremental, above the passive model.

Figure 7 is an exemplary graph illustrating pump performance including pump flow rate and pressure. A range of motor speeds is plotted on the x-axis and a range of pump outlet pressures is plotted on the y-axis. A range of pump flow rates is also represented on the second y-axis in liters per minute.

The engine speed range is from 0 RPM to 8,000 RPM. The outlet pressure range is 0 atm to 5.92 atm. The flow rate range of the pump is from 0 liters / minute to 90.00 liters / minute.

For the purpose of illustration, an engine speed of -3,500 RPM is selected to demonstrate the characteristics of the inventive pump. The transition between operating conditions "A" and "B" is illustrated as the "switching point" at the center of the curves in the graph.

For engine speeds below -3,500 RPM the maximum pump outlet pressure is approximately 2.56 atm. The maximum flow rate is approximately 20.0 liters / minute.

For engine speeds greater than -3,500 RPM the pump outlet pressure changes rapidly to a minimum outlet pressure of approximately 4.83 atm at 7,500 RPM. The flow rate changes to a maximum of approximately 28.0 liters / minute at 7,500 RPM.

At the transition point the gradual change in pressure is approximately 1.57 atm. The gradual change in flow is approximately 5 l / min.

The performance transition is caused by the slide 12 rotating around the pivot 18 caused by the deactivation of the valve 27 ventilating the chamber 23 for ambient atmospheric conditions. The 207 valve is controlled by an electrical signal transmitted by an engine ECU, for example. Upon reaching the predetermined engine speed, in this case -3,500 RPM, ECU 208 (see Figure 6) signals valve 207 to close, thereby pressurizing chamber 23 with hydraulic pressure equal to that in the main oil gallery 204.

As previously described, the pressures in the chambers 22, 23 create a torque and therefore force that is greater than the combination of the spring force 31 and the fluid force in the chambers 21, thereby causing the spring 31 to be compressed. This causes slide 12 to rotate. By turning clockwise the flow rate and the outlet pressure are individually substantially decreased at the predetermined speed of the motor because the displacement of the pump is reduced.

For comparison, the dashed lines in portion A of Figure 7 below approximately 3,500 RPM illustrate the behavior of the outlet pressure and the flow rate of a pump in the case where the position of slide 12 is controlled only by a single chamber pressure. In the case of the single chamber, at relatively low engine speeds, say just slightly higher than idling (-1,500 RPM), the pump would operate at a comparatively high outlet pressure and flow rate otherwise not required by the engine. This is inefficient. The inventive pump provides only the required amount of flow and pressure for efficient operation at reduced engine speeds. This means considerable energy savings in the system. However, at high engine speeds the pump can change quickly and precisely to the higher flow rates and outlet pressures needed to meet the demands of the engine.

Figure 8 is a side view of an electric valve. The 207 valve is engaged with the pump body 10. The 207 valve is connected to the electrical network of the engine or vehicle (not shown). An electrical connector (not shown) engages valve 207 in socket 208. When valve 207 is deactivated, pressure is vented from chamber 23, thereby causing the pump to operate in region “A”. When valve 207 is activated, hydraulic pressure is admitted to chamber 23 from nozzle 211, thereby causing the pump to operate in the “B” region. To avoid engine failure caused by inadequate fluid pressure at high speed, the valve must be electrically deactivated to vent the pressure from chamber 23. This results in the safe situation against failure at high speed, that is, chamber 23 is ventilated from electrical failure of valve 207.

Figure 9 is a graph illustrating the performance of the pump including the flow rate and pressure of the pump. A range of motor speeds is plotted on the x-axis, and a range of pump outlet pressures are plotted on the y-axis. A range of pump flow rates is also represented on the second y-axis.

The engine speed range is from 0 RPM to 8,000 RPM. The outlet pressure range is 0 atm to 5.92 atm. The flow rate range of the pump is 0 l / min. at 90 l / min.

For the purpose of illustration an engine speed of -2,000 RPM is selected to demonstrate the characteristics of the inventive pump. The transition between operating conditions "A" and "B" is illustrated as the "switching point" at approximately 2,000 RPM.

In this example, valve 207 is OFF at startup and for engine speeds below 2,000 RPM, that is, chamber 23 is depressurized and ventilated to the environment. For engine speeds below approximately 2,000 RPM the maximum pump outlet pressure (Line Pressure) is approximately 3.55 atm. The maximum flow rate (Flow Rate) is approximately 25 l / min.

For engine speeds greater than approximately 2,000 RPM the pump outlet pressure (Line Pressure) changes rapidly to a minimum outlet pressure of approximately 2.36 atm at 2,000 RPM to 3.15 atm at approximately 7,500 RPM. The flow rate (Rate and Flow) changes to a maximum of approximately 23 l / min. at 7,500 RPM.

At the transition point the gradual change in pressure is approximately 1.38 atm. The gradual change in flow is approximately 5 l / min.

The performance transition in this example is caused by slide 12 rotating around pivot 18 caused by activation of valve 207 thereby pressurizing chamber 23. Valve 207 is controlled by an electrical signal transmitted by an engine ECU, for example. Upon reaching the predetermined speed of the engine, in this case approximately 2,000 RPM, ECU 208 (see Figure 6) signals valve 207 to close, thereby pressurizing chamber 23 with hydraulic pressure equal to that in the main oil gallery 204. In the case of a failure of valve 207 to chamber 23 would thereby depressurize by placing the pump in high discharge pressure mode.

Although a form of the invention has been described here, it will be obvious to those skilled in the art that variations can be made in the construction and relationship of the parts without departing from the spirit and scope of the invention described here.

Claims (10)

1. Sliding vane pump with variable displacement, FEATURED for understanding: a pump body; inlet and outlet holes in the pump housing; a drive shaft rotatably mounted on the pump body; a rotor driven by the drive shaft; a plurality of radially extended vanes slidably arranged on the rotor; a pivot arranged on the pump body; a slide pivotally arranged on the pivot and having a central axis eccentric to the rotor axis; a plurality of fluid chambers defined by the rotor, the vanes, and the slide, which are connected successively to the inlet and outlet holes; a spring acting on the slide to induce the slide in a direction of increasing displacement; a first chamber and a second chamber, each one to receive hydraulic pressure and each one arranged between the pump body and an external surface of the slide, the first chamber and a second chamber configured to act in combination against the elastic force of the spring to pivot the slide to reduce displacement; the first chamber connected to a discharge pressure from the pump; and an operable valve to selectively pressurize the second chamber for a hydraulic pressure greater than an ambient atmospheric pressure condition. 2. Variable displacement pump, according to claim 1, CHARACTERIZED by also comprising a second spring acting parallel to the spring. 3. Sliding vane pump with variable displacement, according to claim 1, CHARACTERIZED by the fact that the valve is electric and controlled by an ECU (Electronic Control Unit) of the engine. 4. Sliding vane pump with variable displacement, according to claim 1, CHARACTERIZED by the fact that the discharge flow rate of the pump outlet decreases after the depressurization of the second chamber. 5. Variable displacement sliding vane pump according to claim 1, CHARACTERIZED by the fact that the second chamber is pressurized to a pressure greater than ambient atmospheric pressure for engine speeds below a predetermined engine speed and is depressurized to an ambient pressure Petition 870180168675, of 12/28/2018, p. Atmospheric 8/12 for engine speeds greater than the engine's predetermined speed. 6. Sliding vane pump with variable displacement, according to claim 1, CHARACTERIZED by the fact that the first chamber and the second chamber are both in hydraulic communication with a discharge pressure from the pump outlet. 7. Sliding vane pump with variable displacement, FEATURED for understanding: a pump body; inlet and outlet holes in the pump housing; a drive shaft rotatably mounted on the pump body; a rotor driven by the drive shaft and aligned coaxially with it; a plurality of radially extended vanes slidably arranged on the rotor; a pivot arranged on the pump body; a slide pivotally arranged on the pivot in the pump body and having a central axis eccentric to the rotor axis; a plurality of fluid chambers defined by the rotor, the vanes, and the slide, which are connected successively to the inlet and outlet holes; a spring acting on the slide to induce the slide in one direction; a first chamber and a second chamber, each in hydraulic communication with a pump discharge oil pressure and each disposed between the pump body and an external slide surface; and a valve operable at a predetermined pump speed in which the second chamber is selectively switched between ambient atmospheric pressure and a pump discharge oil pressure. 8. Sliding vane pump with variable displacement, FEATURED for understanding: a pump body; inlet and outlet holes formed in the pump body; a drive shaft rotatably mounted on the pump body; a rotor driven by the drive shaft and aligned coaxially with it; a plurality of radially extended vanes slidably arranged on the rotor; a pivot arranged on the pump body; a slide pivotally arranged on the pivot in the pump housing and having a Petition 870180168675, of 12/28/2018, p. 9/12 central axis eccentric to the rotor axis; a plurality of fluid chambers defined by the rotor, the vanes, and the slide, which are connected successively to the inlet and outlet holes; a spring acting on the slide to induce the slide in one direction; a first chamber and a second chamber, each of which is suitable for receiving hydraulic pressure and each of which is arranged between the pump housing and an external surface of the slide; the first chamber in hydraulic communication with a discharge pressure from the pump outlet; and an operable valve to selectively pressurize and depressurize the second chamber. 9. Variable displacement sliding vane pump according to claim 8, CHARACTERIZED by the fact that the second chamber is pressurized to a pressure greater than ambient atmospheric pressure for engine speeds below a predetermined engine speed and is depressurisable to ambient atmospheric pressure for engine speeds greater than the engine's predetermined speed. 10. Sliding vane pump with variable displacement, according to claim 8, CHARACTERIZED by the fact that the second chamber is pressurizable to approximately an outlet pressure of the pump.