Patent Application
20130189126
The present invention relates to the field of control means for variable displacement hydraulic pumps.
It finds particular application for controlling circuits for driving a cooling circuit fan, in the case of cooling a vehicle heat engine for example.
Variable displacement hydraulic pumps are widely used in hydraulic power supply circuits.
These variable displacement hydraulic pumps typically have a variable tilt swashplate, the tilt of this swashplate causing the pump displacement to vary.
The tilt of the swashplate is typically controlled by a single-acting cylinder; this cylinder includes a setting spring and is pressure-controlled directly by tapping the pressure delivered by the pump through a pressure reducer.
Document US 20100132352 shows such a hydraulic circuit, including a variable displacement hydraulic pump, the output whereof is controlled as stated previously.
Such a pump displacement control circuit is an open circuit; some fluid, typically oil, is tapped from the hydraulic circuit and either led to the cylinder control or exhausted through a leak. Fluid is thus tapped from the delivery constantly provided by the hydraulic pump, which generates losses.
In addition, the hydraulic pump is driven by a heat engine, and a control circuit involves driving the hydraulic pump in rotation as soon as the engine starts, which causes difficulty when starting it.
Moreover, the control of the displacement of the hydraulic pump in the event of failure of the control means, for example in the event of failure of the electrical components of the system, poses a safety problem.
The present invention aims to propose a control circuit for the displacement of a hydraulic pump that does not exhibit such disadvantages.
To this end, a hydraulic circuit is proposed including:
As a variation, said pressure reducing means include two flow reducers assembled in series, defining an intermediate pressure which supplies said first chamber.
According to another variation, said proportional pressure reducer is provided with an electrical load control.
As a variation, a flow reducer is located between the proportional pressure reducer and the second chamber of the cylinder.
This circuit finds a particular application in a system wherein said variable displacement pump supplies a motor for driving a cooling circuit fan.
As a variation, said variable displacement pump is an axial piston pump, and the variable displacement is controlled by the tilt of a cam plate.
As a variation, said circuit is provided with a calibrated valve tapping the pressure of said circuit, designed to provide a pressure leak from said circuit when the pressure is greater than or equal to a defined value.
Other features, aims and advantages of the invention will appear from the description that follows, which is purely illustrative and not limiting, and which should be read with reference to the appended drawings, wherein:
In all the figures, common elements are designated with the same numerical labels.
In the hydraulic circuit as shown, a hydraulic pump 1 and a booster pump 2 are driven by a common drive shaft 3 which is typically driven in rotation by a heat engine M.
The hydraulic pump 1 supplies hydraulic fluid, oil for example, to a hydraulic circuit C, and has a variable displacement, typically in the form of a variable tilt swashplate 4 the tilt whereof is controlled by a pump control 5, typically a cylinder 5.
The hydraulic pump 1 is typically an axial piston pump the variable displacement whereof is controlled by the tilting of a cam plate. The hydraulic pump 1 is designed to circulate the hydraulic fluid in a hydraulic circuit C in two circulation directions, depending on the tilt of the cam plate of the pump 1, the hydraulic pump 1 always being driven in the same direction. Two ranges of values are thus defined for the tilt of the plate 4 of the pump 1; a first range of values corresponding to a first fluid circulation direction in the hydraulic circuit C, and a second range of values corresponding to a second fluid circulation direction in the hydraulic circuit C. Zero displacement is achieved for an tilt of the plate 4 of the pump 1 at the transition between the first and the second range of values.
The booster pump 2 supplies a boosting circuit G of the hydraulic circuit C as well as the pump control 5. The booster pump 2 draws the necessary hydraulic fluid, for example, from a reservoir not shown in this figure.
In this embodiment, the pump control 5 is a cylinder including a chamber 52, a rod 53 which controls the tilt of the plate 4 of the pump 1, and an internal partition 54 connected to an elastic return means 55 such as a spring.
The chamber 52 of the cylinder 5 is supplied by the booster pump 2, via pressure regulation means, typically a proportional pressure reducer 21, provided with a control 22.
The control 22 is typically controlled by means of an electronic control unit.
The proportional pressure reducer 21 leads the fluid coming from the booster pump 2 to the second chamber 52 of the cylinder 5 and/or toward a reservoir R which is at substantially ambient or atmospheric pressure, depending on the action exerted by the control 22 on this proportional pressure reducer 21.
An elastic return means 23 and an equalizing line 24 oppose the action of the control 22 on the proportional pressure reducer 21, such that, when the control 22 applies a zero force on the proportional pressure reducer 21, the proportional pressure reducer 21 adjusts the pressure of the chamber 52 so that it is equal to the pressure in the reservoir R.
In this particular embodiment, the pump 1 is at full displacement by default, and the user can use the control 22 in order to lead fluid into the chamber 52 of the cylinder 5 and thus to alter the displacement of the pump 1 by lowering it to 0, and by continuing to increase the pressure in the chamber 52 of the cylinder 5 in this direction up to full reverse displacement.
In the event of a breakdown of the control 22, the pump 1 is at full displacement, which ensures the operation of the hydraulic circuit C supplied by the pump 1.
In this embodiment, the pump control 5 is a double-acting cylinder, including a first chamber 51 and a second chamber 52, a rod 53 that controls the tilt of the plate 4 of the pump 1, and two internal partitions 54 connected by an elastic return means 55 such as a spring, said internal walls being located between the two chamber 51 and 52.
The two chambers 51 and 52 of the cylinder 5 are supplied by the booster pump 2, via pressure and flow control means.
The first chamber 51 of the cylinder 5 is supplied with pressure by the booster pump 2 via pressure reducing means, including two restrictions 11 and 12 assembled in series and producing singular pressure drops. The restrictions 11 and 12 are typically flow limiters with drainage of the excess flow, also called sprinklers. As a variation, the restrictions 11 and 12 can also be replaced by a pressure reducer as will be shown later.
The first restriction 11 taps fluid distributed by the booster pump 2, while the second restriction 12 opens into a reservoir R at ambient pressure, typically atmospheric pressure.
The restrictions 11 and 12 assembled in series define an intermediate pressure in the portion of the hydraulic circuit between these two restrictions 11 and 12, which is led to the first chamber 51 of the cylinder 5. The intermediate pressure defined by the two restrictions 11 and 12 has a value comprised between the pressure delivered by the booster pump 2 and the pressure in the reservoir R.
The second chamber 52 of the cylinder 5 is supplied with pressure by the booster pump 2 via a proportional pressure reducer 21, provided with a control 22, as previously described.
The pressures in the two chambers 51 and 52 of the cylinder 5 oppose each other, and the position of the cylinder 5 resulting from these pressures defines the tilt of the plate 4 of the hydraulic pump 1, and hence its displacement. When the pressures within the two chambers 51 and 52 are equal, then the cylinder 5 is in an equilibrium position and the plate 4 of the hydraulic pump 1 defines a zero displacement.
By increasing the pressure in one or the other of chambers 51 and 52 of the cylinder 5, the cylinder 5 is displaced which drives the plate 4 of the hydraulic pump 1 in a given direction of rotation of the cam plate of the pump 1, which corresponds either to a first delivery direction or to a second delivery direction in the closed loop.
For example, consider an initial condition wherein the chambers 51 and 52 of the cylinder 5 are both at a pressure P0. For example upon starting the system, P0 can be equal to zero. Upon starting the booster pump 2, the pressure in 51 will increase.
By increasing the pressure within the first chamber 51 of the cylinder of the cylinder 5, for example to a value P1 such that P1>P0, the displacement of the hydraulic pump 1 is increased in a first delivery direction of the closed loop of the hydraulic circuit C corresponding to the first range of values of tilt of the plate 4 of the hydraulic pump 1. Then, by controlling the control 22 of the proportional pressure reducer 21, the pressure within the chamber 52 is made to vary to as to attain a value P2 such that P2>P1. The displacement of the hydraulic pump will then decrease until it has zero displacement when the two chambers 51 and 52 are at pressure P1, then as the pressure continues to increase in the chamber to reach the value P2, the tilt of the plate 4 of the hydraulic pump 1 reaches the second range of values that correspond to the second fluid circulation direction in the hydraulic circuit C, the delivery whereof increases as the pressure in the chamber 52 increases. The hydraulic pump 1 then supplies the hydraulic circuit C in the second delivery direction, opposite to the first delivery direction mentioned previously.
The displacement of the pump 1 is therefore controlled thanks to a pump controller 5 constituted here by a double-acting cylinder 5, supplied with pressure by the booster pump 2 through pressure control means. These pressure control means therefore enable a user to regulate the displacement of the variable displacement pump 1.
When the drive shaft 3 is not driven in rotation by the heat engine M, and the system is therefore stopped, the hydraulic pump 1 and the booster pump 2 do not supply the circuit C and the booster circuit G with fluid.
The pressure in the first chamber 51 and the second chamber 52 is then equal to the ambient or atmospheric pressure, the control 22 applied to the proportional pressure reducer 21 then having no effect.
The cylinder 5 is thus in a position of equilibrium, corresponding to a tilt of the plate 4 for which the displacement of the hydraulic pump 1 is zero.
Upon starting the system, the heat engine M is started in order to drive the drive shaft 3 in rotation.
The drive shaft 3 drives in rotation the hydraulic pump 1 and the booster pump 2.
The booster pump 2 then delivers a boost pressure, which will supply with pressure the booster circuit G as well as the chambers 51 and 52 of the cylinder 5.
The chamber 52 is supplied with pressure by the booster pump 2 depending on the action of the control 22 on the proportional pressure reducer 21.
The chamber 51 is supplied with pressure by the booster pump 2 according to the flow rates defined by the flow limiters 11 and 12, and the intermediate pressure that they define.
The establishment of pressure by the booster pump 2 is not instantaneous; the pressure builds progressively in the lines supplying the chambers 51 and 52 of the cylinder 5.
The delivery coming from the booster pump 2 which is established between 11 and 12 defines an intermediate pressure. This intermediate pressure is applied to the first chamber 51 of the cylinder 5. A variation in pressure at the inlet of restriction 11 will cause a progressive change in the flow rates through the restrictions 11 and 12 until a new dynamic equilibrium is reached, which will define a new pressure between the restrictions 11 and 12. If the delivery is zero, the pressure is that of the reservoir R.
Consequently, upon starting the hydraulic pump 1, the two chambers 51 and 52 of the cylinder 5 are at ambient pressure for a given duration, during which the cylinder 5 is in a position of equilibrium and the displacement of the hydraulic pump 1 is nil. The torque to be supplied when starting the heat engine M to drive the hydraulic pump 1 is therefore nil or substantially nil.
Once the booster pump 2 has established pressure in the chambers 51 and 52 of the cylinder 5, the tilt of the plate 4 of the hydraulic pump 1 is altered, which causes the hydraulic pump 1 to begin delivery.
By way of example, considering that the heat engine M starts within substantially 2 seconds of a start instruction from a user, the time needed for the booster pump 2 to build up boost pressure can be chosen to be substantially equal to 2 seconds, the hydraulic pump therefore remains at zero displacement for substantially 4 seconds from the start command. In this manner, starting of the heat engine M is facilitated. This time can be adjusted by selecting the sizing of the restrictions 11 and 12.
In this variation, the restriction 14 makes it possible to damp the entering and leaving flow in the second chamber 52 of the cylinder 5 in order to avoid a too sudden resumption of delivery of the hydraulic pump 1.
Circuits such as those described previously find a particular application for controlling fans performing the cooling of a radiator of a heat engine.
By way of an example, vehicles such as trucks, buses or urban transportation vehicles, public works machinery, agricultural machinery or lifting machines, which include a heat engine and a radiator requiring cooling, can be mentioned.
In this embodiment, the hydraulic pump 1 supplies the hydraulic circuit C including an hydraulic motor 6 which drives in rotation a shaft 61 whereon is assembled a fan 62, typically designed to cool an element such as the radiator of a heat engine.
The tilt of the cam plate of the hydraulic pump 1 determines the direction of circulation of the fluid in the hydraulic circuit C, and therefore the direction of rotation of the fan 62.
Thus a high-pressure branch HP of the hydraulic circuit C is defined, which is the branch of the circuit C upstream of the hydraulic motor 6, and a low-pressure branch BP of the hydraulic circuit C which is the branch of the circuit C downstream of the hydraulic motor 6.
As shown, the booster circuit G includes non-return means 71 providing for the boosting of the hydraulic circuit C in the event of insufficient pressure, and pressure limiters providing for the drainage of fluid in the event of overpressure in the hydraulic circuit C. The booster circuit G also includes a pressure limiter 73 allowing fluid to drain to a reservoir R at ambient or atmospheric pressure when the boost pressure exceeds the desired value.
In the event of a failure of the control 22 of the proportional pressure reducer 21 controlling the pressure in the second chamber 52 of the cylinder 5, the proportional pressure reducer 21 is returned to its initial position by the elastic return means 23 and the equalizing line 24, such that the pressure within the second chamber 52 of the cylinder 5 decreases. Only the first chamber 51 of the cylinder 5 is then supplied with pressure by the booster pump 2, which results in an increase of the displacement of the hydraulic pump 1, hence the driving of the hydraulic motor 6 and the fan 62.
The control circuit as proposed therefore makes it possible to ensure the operation of the fan 62 in the event of a failure of the control 22, the hydraulic pump then be advantageously at maximum displacement to drive the hydraulic motor 6 which drives in rotation the fan 62.
This figure illustrates in particular the reservoir R from which the booster pump 2 draws hydraulic fluid in order to inject it into the hydraulic circuit C.
By way of example, the circulation direction of the hydraulic fluid in the hydraulic circuit C has been shown with arrows at the inlet and outlet of the hydraulic pump 1 and the hydraulic motor 6. A high-pressure branch HP of the hydraulic circuit C and a low-pressure branch BP of the hydraulic circuit C are thus defined.
The high-pressure branch HP corresponds to the branch of the hydraulic circuit C upstream of the hydraulic motor 6, while the low-pressure branch BP corresponds to the branch of the hydraulic circuit C downstream of the hydraulic motor 6.
It is easy to understand that in the event of a change in the direction of circulation of the fluid in the hydraulic circuit due to the control of the plate of the hydraulic pump 1, the branches HP and BP are reversed.
In the circuit illustrated in
The second chamber 52 of the cylinder 5 is, for its part, connected to the booster pump 2 through a proportional pressure reducer 21 equipped with a control 22 and allowing a variable pressure to be applied in said second chamber 52 of the cylinder 5. In the embodiment shown, this proportional pressure reducer 21 is assembled in series with a restriction or sprinkler 14.
The pressure in the chambers 51 and 52 of the cylinder 5 is determined according to the control and/or setting of the pressure reducers 13 and 21.
In the embodiment shown, the second chamber 52 of the cylinder 5 is also connected to the hydraulic circuit C, for example at the outlet of the hydraulic pump 1 via a pressure limiter 25 provided with setting means that can be controlled.
This pressure limiter 25 enables the implementation of protection of the hydraulic circuit C, and more precisely a protection of the hydraulic pump 1. Indeed, in the case where the pressure in the high pressure branch HP of the hydraulic circuit C exceeds the set value of the pressure limiter 25, this pressure limiter 25 directs some flow into the branch between the restriction of the sprinkler 14 and the second chamber 52. The flow creates a pressure drop when passing through the sprinkler 14, thus creating a pressure in the second chamber 52, which decreases the tilt of the plate 4.
The tilt of the plate 4 of the pump 1, and hence the displacement of the hydraulic pump 1, is thus decreased, which makes it possible to avoid overloading the hydraulic pump 1 or more generally the hydraulic circuit C. Unlike prior solutions which consist of creating a leak or losses in the hydraulic circuit in order to limit the pressure there, the proposed circuit thus makes it possible to obtain maximum efficiency from the hydraulic pump 1.
In this particular embodiment, it is therefore the combination of control of the proportional pressure reducer 23 and of the pressure limiter 25 which determines the pressure within the second chamber 52 of the cylinder 5.
As shown in
The embodiment shown in
The booster pump 2 provides for the replacement of this fluid which is tapped from the hydraulic circuit.
It is thus possible to tap hydraulic fluid having a high temperature due to its circulation in the hydraulic circuit C and to re-inject hydraulic fluid at ambient temperature, which makes it possible to avoid the danger of overheating the circuit.
It will be well understood that in the case where the direction of circulation of the hydraulic fluid in the circuit C is reversed, the exchange takes place in a similar fashion because the pressure-compensated flow limiter is able to exchange on an HP branch in the same manner as on the low pressure branch BP.
The compensated flow limiter could just as well be placed on ether of the two branches, high pressure HP or low pressure BP; for better efficiency, however, it is advantageous to place it on the branch that will be the low pressure BP branch in normal operation.
This exchange system is simplified compared with a usual, more complicated and costly, exchange valve, connected both to the high pressure HP and low pressure BP lines and selecting the low pressure BP line (for example by means of a slide valve selector) to carry out the exchange.
The invention as previously described thus exhibits several advantages.
Starting of the heat engine M is carried out with the hydraulic pump having zero delivery, which therefore greatly facilitates its starting by reducing the torque that it must supply. The start of delivery of the pump 1 occurs a few seconds after starting of the heat engine, for example in order to provide for its cooling in the case where the pump 1 enables the driving of a cooling circuit fan. In this particular application, it is well understood that driving the fan as soon as the engine starts is not imperative, due to the fact that the temperature rise in the circuit to be cooled occurs progressively.
The displacement control circuit of the hydraulic pump 1 also enables the implementation of a safety function in the event of failure of the control 22, by providing maximum cooling due to the resulting maximum displacement of the hydraulic pump 1.
Control of the displacement of the hydraulic pump 1 does not cause any loss of power, because instead of controlling a leak at the power output of the pump in an open loop, a minimum tapping is carried out on the boosting delivery, and not on the drive pump.
The hydraulic and mechanical efficiency is therefore superior.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1156989 | Jul 2011 | FR | national |
