Patent Description:
In motor vehicle drivetrains, it is possible for various clutches, which are hydraulically actuated, to be present. Examples are friction clutches, as are used in transmissions which can be shifted in an automated manner, dual clutches, which make it possible for a switch to be made from a first gearwheel set to a second gearwheel set without interrupting the transmission of torque in a dual-clutch transmission, clutches for coupling and decoupling an electric motor, etc..

A whole series of requirements are made on a pump unit for actuating such a clutch. Firstly, a fluid flow at a high pressure should be provided, in order that the clutch can be reliably closed or opened. At the same time, the clutch should be actuated as quickly as possible. In the case of some transmissions, it is moreover desired to provide hydraulic fluid to lubricate the transmission and cool the clutch. Finally, the pump unit should use as little energy as possible. The publications <CIT>, <CIT> and <CIT> disclose electrically driven pumps for providing flow with different pressure levels, <CIT> and <CIT> disclose pumps for providing flow with different pressure levels driven by a separate engine.

The object of the invention is to provide a pump unit which meets these requirements.

In order to solve this problem, provided according to the invention is a pump unit for clutch actuation, having a high-pressure port for clutch actuation, a low-pressure port for a lubricant flow, a single drive motor and a dual pump, which is driven by the drive motor and has a high-pressure outlet, which is connected to the high-pressure port by means of a high-pressure line, and a low-pressure outlet, which is connected to the low-pressure port by means of a low-pressure line, wherein a prefilling line which leads from the low-pressure line to the high-pressure line is provided, and which comprises the further features as defined in appended claim <NUM>.

This pump unit makes it possible to provide, with a single pump, a high pressure that is desired for actuation of the pump and also a lubricant flow at low pressure. By virtue of the prefilling line, it is possible to "divert" some of the lubricant flow, with the result that it can be used to prefill an actuator of the clutch.

As soon as this prefilling line is prefilled to a sufficient extent, the further control of the clutch actuator is effected only by means of the high-pressure flow.

The term "dual pump" refers here to a hydraulic pump which has both a low-pressure outlet and a high-pressure outlet. This is a question not of the interconnection of two different pumps, but of one unit comprising a single drive motor. During operation, the dual pump delivers a hydraulic fluid flow at the low-pressure outlet with low pressure but a high volumetric flow rate, while at the high-pressure outlet a hydraulic fluid flow is provided which has a low volumetric flow rate but high pressure. The ratio of the volumetric flow rates may be <NUM>:<NUM>, for example.

According to the invention, it is provided that a check valve, which blocks flow in a flow direction from the high-pressure line to the low-pressure line, is arranged in the prefilling line. The check valve makes it possible, during operation of the dual pump, to supply the high-pressure port of the pump unit with hydraulic fluid also from the low-pressure side of the pump as long as the pressure there is lower than the pressure of the hydraulic fluid at the low-pressure outlet of the dual pump. In this way, a clutch actuator can be prefilled very quickly. As soon as the pressure at the high-pressure port corresponds to the pressure provided by the dual pump at the low-pressure outlet, fluid can no longer flow through the check valve, and the further increase in pressure at the high-pressure port is provided by the high-pressure outlet of the dual pump alone. In this respect, the check valve prevents the high-pressure fluid provided from escaping to the low-pressure side.

A bypass line, in which a throttle or diaphragm is arranged, may be assigned to the check valve. The bypass line makes it possible to increase the return speed for the purpose of emptying the clutch According to the invention, the drive motor is an electric motor which can be driven in two directions of rotation and comprises a control means to control the rotational speed of the drive motor in an open-loop or closed-loop manner, wherein in a normal operating state meaning when the check valve is closed and the high-pressure port is supplied with hydraulic fluid from the high-pressure outlet of the pump, the rotational speed of the drive motor is a rated rotational speed, while for prefilling purposes meaning when the check valve is open, before a pressure corresponding to a back pressure in the low-pressure line is reached on the high-pressure side, the rotational speed of the drive motor is temporarily increased, for example to <NUM> times the rated rotational speed, for a very short time, for example <NUM>.

According to one embodiment of the invention, a throttle or diaphragm is provided in the low-pressure line downstream of the branch of the prefilling line. This ensures a certain back pressure, with the result that a sufficient volumetric flow is "diverted" from the low-pressure side of the pump unit to the high-pressure side for the purpose of prefilling.

In the low-pressure line, a control valve may also be provided downstream of the branch of the prefilling line. The control valve makes it possible to build up hydraulic fluid actively, in order that the high-pressure side of the pump unit is prefilled with the volumetric flow from the low-pressure side. When the prefilling has concluded or if it is not necessary, the control valve can be completely opened, so that a pressure drop is not created.

A control valve may be provided in the prefilling line, in order to be able to actively control the flow cross section of the prefilling line as an alternative or in addition to the passive check valve.

According to one configuration of the invention, a pressure-controlled switching valve, which makes it possible to connect the high-pressure line directly to a reservoir, is provided in the high-pressure line. This switching valve makes it possible to increase the speed at which hydraulic fluid can be discharged from the high-pressure side, such that the clutch is opened more quickly.

According to one configuration, a pressure-controlled switching valve, which makes it possible to switch between a throttled throughflow and a free throughflow, is provided in the low-pressure line downstream of the branch of the prefilling line. This makes it possible to suitably build up the hydraulic fluid on the low-pressure side as required, with the result that it is diverted to the high-pressure side, while during operating phases in which this is not required the hydraulic fluid on the low-pressure side can flow away unimpeded to the lubricant port.

According to one embodiment of the invention, it is provided that the drive motor can be driven in two directions of rotation. This makes it possible to draw fluid into the high-pressure port of the pump unit, with the result that a clutch actuator connected to the high-pressure port can be emptied very quickly. Accordingly, the clutch can be opened very quickly.

According to one embodiment of the invention, the dual pump is a rotary vane pump, in which in each case one low-pressure chamber is delimited between adjacent rotary vanes and in each case one high-pressure chamber is delimited between a rotor and the face side of the rotary vane received in the rotor. This design is distinguished by a particularly compact configuration. As an alternative to a rotary vane pump, it is also possible to use a pump in which two rotors are arranged next to one another on a common drive shaft, wherein the rotors are designed differently in terms of the conveyed volume and the delivery pressure. For example, two toothed-gear pumps (also referred to as gerotor pumps) or two external-gearwheel pumps may be arranged next to one another.

The invention will be described below on the basis of various embodiments which are illustrated in the appended drawings, in which:.

<FIG> schematically shows a pump unit <NUM> which comprises a housing <NUM> and, received therein, a drive motor <NUM> and a dual pump <NUM>.

The housing <NUM> may be a dedicated housing or part of a superordinate assembly, for example a transmission housing, which is part of a drivetrain of a motor vehicle.

The drive motor <NUM> is an electric motor, which can be driven in both directions of rotation. A control means (not shown here), which also makes it possible to control the rotational speed of the drive motor <NUM> in an open-loop or closed-loop manner, is provided.

The dual pump <NUM> is a hydraulic-oil pump, by means of which a hydraulic fluid can be conveyed. The specific characteristic feature of the dual pump <NUM> is that it has a high-pressure outlet <NUM> and a low-pressure outlet <NUM>.

At the high-pressure outlet <NUM> the hydraulic fluid is provided with high pressure but a low volumetric flow rate, while at the low-pressure outlet <NUM> the hydraulic fluid is provided with a large volumetric flow rate but low pressure. The volumetric flow rate at the low-pressure outlet <NUM> may be greater than it is at the high-pressure outlet <NUM> by a factor of <NUM>, for example.

The pump unit <NUM> draws fluid in from a reservoir <NUM>, wherein a filter <NUM> is provided between a suction port <NUM> of the pump unit <NUM> and the reservoir <NUM>.

The reservoir <NUM> may be an external reservoir, or may be integrated in the housing <NUM>. It may also be the case that the reservoir <NUM> is formed within a transmission housing if the pump unit <NUM> is attached directly to a transmission housing.

The pump unit <NUM> has a high-pressure port <NUM>, which is connected to the high-pressure outlet <NUM> of the dual pump <NUM> by way of a high-pressure line <NUM>. A clutch actuator can be supplied with highly pressurized hydraulic fluid via the high-pressure port <NUM>, for example, in order for example to switch a clutch.

The pump unit <NUM> also has a low-pressure port <NUM>, which is connected to the low-pressure outlet <NUM> of the dual pump <NUM> by way of a low-pressure line <NUM>. A hydraulic fluid flow, which is used to lubricate or cool a clutch or the transmission, may be provided by way of the low-pressure port <NUM>.

A prefilling line <NUM>, which connects the low-pressure line <NUM> to the high-pressure line <NUM>, is provided.

A check valve <NUM>, which opens in a flow direction from the low-pressure side to the high-pressure side and blocks flow in the opposite direction, is arranged in the prefilling line <NUM>.

A diaphragm or throttle <NUM>, which uses a certain flow resistance to counteract a fluid flow towards the low-pressure port <NUM>, is arranged downstream of the branch of the prefilling line <NUM> from the low-pressure line <NUM>.

<FIG> shows an exemplary embodiment of a dual pump <NUM>. Here, this is a rotary vane pump with a stator <NUM> in which there is formed an interior space <NUM> which is surrounded by an inner wall <NUM>.

A rotor <NUM> is arranged in the interior of the stator <NUM> and is mounted on a shaft <NUM> and can be driven by the latter.

The rotor <NUM> is provided with multiple receptacles <NUM>, in which in each case one rotary vane <NUM> is received.

The receptacles <NUM> extend in the axial direction normally from a face side of the rotor <NUM> as far as the opposite face side, and from the outer periphery of the rotor inwards. In the exemplary embodiment shown, the receptacles <NUM> extend in the radial direction. This is not necessary, however.

Here, the rotary vanes are in the form of plates whose dimension in the radial direction is slightly less than the radial depth of the receptacles <NUM>. Each of the plates has a thickness b, which corresponds to the width of the receptacles <NUM>.

As an alternative to plate-like rotary vanes, use may also be made of rotary vanes which are in the form of a cylinder.

The rotor <NUM> has a diameter of <NUM> x r (minus a clearance between rotor and stator that is to be provided in the design), which is less than the diameter r+R of the interior space <NUM> of the stator <NUM>. The rotor <NUM> is arranged eccentrically in the interior space, specifically such that it is (almost) in contact with the inner wall <NUM> on one side (at the <NUM> o'clock position in this case). Accordingly, the maximum spacing to the outer wall of the rotor <NUM> is on the diametrically opposite side.

The rotary vanes <NUM> bear with their radially outer side <NUM> permanently against the inner wall <NUM> of the stator <NUM> (at any rate when the rotor <NUM> is rotating). Consequently, between rotary vanes <NUM> adjacent to one another in the peripheral direction, the inner wall <NUM> of the stator <NUM>, the outer wall of the rotor <NUM> and two side walls which close off the interior space <NUM> at the face sides of the rotor <NUM> (and of which only the "rear" side wall <NUM> can be seen here), in each case one low-pressure chamber <NUM> is delimited.

In the exemplary embodiment shown, there are, since five rotary vanes <NUM> are present, also five low-pressure chambers <NUM> formed. The volume of each individual low-pressure chamber, for one rotation of the rotor <NUM> through <NUM>°, changes from a minimum value (when the low-pressure chamber <NUM> is approximately at the <NUM> o'clock position) via a maximum value (when the low-pressure chamber <NUM> is approximately at the <NUM> o'clock position) and back to the minimum value.

Hydraulic fluid is fed to the low-pressure chambers <NUM> through the inlet <NUM>. Said inlet, as seen in the direction of rotation of the rotor <NUM>, is situated behind the point at which the spacing between the outer surface of the rotor <NUM> and the inner wall <NUM> of the stator <NUM> is minimal.

The hydraulic fluid drawn in by the low-pressure chambers <NUM> via the inlet <NUM> is delivered via a low-pressure outlet <NUM>, which, as seen in the peripheral direction, is behind the position at which the low-pressure chambers <NUM> have the maximum volume, but in front of the position at which the spacing between the outer side of the rotor <NUM> and the inner wall <NUM> of the stator <NUM> is minimal.

The inlet <NUM> and the low-pressure outlet <NUM> are arranged here in one of the side walls <NUM> of the hydraulic pump <NUM> or else, so as to improve the filling, in both side walls <NUM>, so that the hydraulic fluid can be drawn into the low-pressure chamber <NUM>, and pushed out therefrom, from both sides.

Each of the rotary vanes <NUM> delimits together with the rotor <NUM> (and also the side walls <NUM>) in each case one high-pressure chamber <NUM>. Specifically, each radially inner side <NUM> of each rotary vane <NUM> delimits, together with the walls of the receptacle <NUM> and the side walls <NUM> shown, in each case one high-pressure chamber <NUM>.

The volume of the high-pressure chambers <NUM> changes according to the displacement of the rotary vanes <NUM> in the receptacles <NUM>. When the rotary vanes <NUM> move outwards (that is to say during a movement from the <NUM> o'clock position to the <NUM> o'clock position via the <NUM> o'clock position in the exemplary embodiment shown), the volume of the high-pressure chambers <NUM> increases, and when the rotary vanes <NUM> move inwards (that is to say during a movement from the <NUM> o'clock position to the <NUM> o'clock position via the <NUM> o'clock position), the volume decreases.

In this way, there is formed a piston pump in which the radially inner side <NUM> of each rotary vane <NUM> may be regarded as the face surface of a pump piston which is adjusted by means of a curved path (of the inner wall <NUM> of the stator <NUM>). For drawing-in, the pump piston is adjusted outwards under the action of centrifugal force, and for pushing-out, the pump piston is displaced inwards owing to the contour of the inner wall <NUM> of the stator <NUM>.

The high-pressure chamber <NUM> draws in via the same inlet <NUM> as that which provides a supply to the low-pressure chambers <NUM>.

A high-pressure outlet <NUM> which is separate from the low-pressure outlet <NUM> is provided on the pressure side of the high-pressure pump. In the peripheral direction, said high-pressure outlet is arranged approximately at the same position as the low-pressure outlet <NUM>.

The high-pressure outlet <NUM> may be provided either at only one of the side walls <NUM> of the stator <NUM> (and thus also of the rotor <NUM>) or at both face sides.

As an alternative to the rotary vane pump shown in <FIG>, it is also possible to use other pump types which are capable of providing two different hydraulic flows with a single drive motor <NUM>.

Various operating states of the pump unit <NUM> shown in <FIG> will be explained below on the basis of <FIG>.

<FIG> shows the pump unit <NUM> in a state in which there is a requirement to close a clutch connected to the high-pressure port <NUM>. In order that the clutch can be closed quickly, it is desirable to fill the clutch actuator quickly with hydraulic fluid and to bring the clutch to the "kiss point", that is to say the point at which transmission of torque begins.

The pump draws in hydraulic fluid via the suction port <NUM>. The hydraulic fluid is conveyed to the high-pressure port <NUM> via the high-pressure outlet <NUM> and the high-pressure line <NUM>. At the same time, hydraulic fluid is conveyed into the low-pressure line <NUM> via the low-pressure outlet <NUM>. Some of the hydraulic fluid flows through the low-pressure port <NUM>. On account of the diaphragm <NUM>, however, a certain back pressure is obtained in the low-pressure line <NUM>, with the result that some of the low-pressure hydraulic oil flow flows to the high-pressure line <NUM> via the prefilling line <NUM> and the opening check valve <NUM> and arrives at the clutch actuator via the high-pressure port <NUM>. Said clutch actuator is thus filled by an overall volumetric flow which consists of a high-pressure volumetric flow and some of the low-pressure volumetric flow.

As soon as a pressure corresponding to the back pressure in the low-pressure line <NUM> is reached on the high-pressure side, a volume can no longer be conveyed to the high-pressure side via the prefilling line <NUM>. The check valve <NUM> then closes, and the pump unit <NUM> is in its normal operating state, as shown in <FIG>. In this operating state, the high-pressure port <NUM> is supplied with hydraulic fluid from the high-pressure outlet <NUM> of the dual pump <NUM>, and the further closing of the clutch is controlled in an open-loop or closed loop manner via a control valve (not shown here).

In the normal operating state, provided at the low-pressure port <NUM> of the pump unit <NUM> is a lubricant flow or coolant flow, by means of which the clutch can be cooled or else bearing points of the transmission can be lubricated.

In the normal operating state, the rotational speed of the drive motor <NUM> is a rated rotational speed, while for prefilling purposes the rotational speed of the drive motor can be temporarily increased, for example to <NUM> times the rated rotational speed. For prefilling purposes, it is sufficient to maintain the increased rotational speed for a very short time, for example <NUM>.

When the clutch should be reopened, the rotational speed of the drive motor <NUM> can be reduced even further. It is also possible to temporarily drive the drive motor <NUM> in the opposite direction of rotation (see <FIG>), with the result that the hydraulic fluid is drawn in at the high-pressure port <NUM>. Accordingly, the clutch actuator is actively emptied. This makes it possible to realize shorter actuation times when opening the clutch.

<FIG> shows an operating state of the pump unit in which no high-pressure fluid for actuating the clutch, but merely a coolant flow or lubricant flow, is provided. The rotational speed of the drive motor <NUM> is lowered far enough here that the hydraulic oil pressure provided at the high-pressure port <NUM> is not sufficient to close the clutch.

Visible in the figures is a branch <NUM>, by means of which hydraulic fluid can be conducted from the low-pressure side into the high-pressure chambers <NUM>. This supports the drawing of hydraulic fluid into the high-pressure chambers <NUM> and ensures that the rotary vanes <NUM> reliably bear against the inner wall <NUM>.

<FIG> shows a second embodiment of the invention. The same reference signs are used for the components known from the first embodiment, and, in this respect, reference is made to the explanations above.

The difference between the first and the second embodiment is that provided in the second embodiment is a bypass line <NUM>, in which a diaphragm or throttle <NUM> is arranged.

The bypass line <NUM> increases the return speed at which the clutch actuator can be emptied if the clutch should be opened.

As an alternative to the bypass line <NUM>, the dual pump <NUM> can also be designed with higher internal leakage, for example by way of an increased axial clearance, with the result that the clutch actuator can be emptied through the dual pump <NUM> when the pump is at a standstill.

<FIG> shows a third embodiment of the invention. The same reference signs are used for the components known from the preceding embodiments, and, in this respect, reference is made to the explanations above.

The difference between the third and the first embodiment is that in the third embodiment a control valve <NUM>, by means of which the back pressure in the high-pressure line <NUM> can be controlled in the desired manner, is provided instead of the throttle or diaphragm <NUM>. When the intention is for hydraulic fluid to flow from the low-pressure side to the high-pressure side via the prefilling line <NUM>, the control valve <NUM> is closed, and therefore the high-pressure line <NUM> and the clutch actuator connected to the high-pressure port <NUM> can be prefilled to a maximum extent by the pressure of the low-pressure outlet <NUM> of the dual pump <NUM>. After this, the control valve <NUM> is opened, so that the coolant flow and lubricant flow can be provided via the low-pressure port <NUM> without a pressure drop.

<FIG> shows a fourth embodiment of the invention. The same reference signs are used for the components known from the preceding embodiments, and, in this respect, reference is made to the explanations above.

The difference between the fourth and the first embodiment is that in the fourth embodiment a control valve <NUM>, which can actively represent the mode of operation of the passive check valve <NUM>, is provided instead of the check valve <NUM>. Therefore, when the intention is for hydraulic fluid to flow from the low-pressure side to the high-pressure side via the prefilling line <NUM>, the control valve <NUM> is opened, and when the intention is for the clutch actuator to be closed in a controlled manner by the hydraulic fluid provided from the high-pressure outlet <NUM>, the control valve <NUM> is closed. In order to quickly dissipate pressure on the high-pressure side, the valve can be reopened, and the volume can escape to the low-pressure side.

<FIG> shows a fifth embodiment of the invention. The same reference signs are used for the components known from the preceding embodiments, and, in this respect, reference is made to the explanations above.

The difference between the fifth and the first embodiment is that provided in the fifth embodiment is a pressure-controlled switchover valve <NUM>, which can make a switch between a state with throttled throughflow and a state with free throughflow. This makes it possible to implement the function of the throttle or diaphragm <NUM> for the purpose of prefilling the clutch actuator, while a free throughflow is possible whenever fluid is not intended to be diverted from the low-pressure side to the high-pressure side.

<FIG> shows a sixth embodiment of the invention. The same reference signs are used for the components known from the preceding embodiments, and, in this respect, reference is made to the explanations above.

The difference between the sixth and the first embodiment is that in the sixth embodiment there is provided in the high-pressure line <NUM> a pressure-controlled switching valve <NUM>, which can be switched between a state in which the high-pressure outlet <NUM> is connected to the high-pressure port <NUM> and an emptying state, in which the high-pressure port <NUM> is connected to an emptying line <NUM>, which leads to the reservoir <NUM>. In this way, the clutch actuator can be emptied particularly quickly.

Claim 1:
Pump unit (<NUM>) for clutch actuation, having a high-pressure port (<NUM>) for clutch actuation, a low-pressure port (<NUM>) for a lubricant flow, a single drive motor (<NUM>) and a dual pump (<NUM>), which is driven by the drive motor (<NUM>) and has a high-pressure outlet (<NUM>), which is connected to the high-pressure port (<NUM>) by means of a high-pressure line (<NUM>), and a low-pressure outlet (<NUM>), which is connected to the low-pressure port (<NUM>) by means of a low-pressure line (<NUM>), wherein a prefilling line (<NUM>) which leads from the low-pressure line (<NUM>) to the high-pressure line (<NUM>) is provided, characterised by a check valve (<NUM>) which blocks flow in a flow direction from the high-pressure line (<NUM>) to the low-pressure line (<NUM>) is provided in the prefilling line (<NUM>), wherein the drive motor (<NUM>) is an electric motor which can be driven in two directions of rotation and comprises a control means to control the rotational speed of the drive motor (<NUM>) in an open-loop or closed-loop manner, wherein the pump is configured such that in a normal operating state meaning when the check valve (<NUM>) is closed and the high-pressure port (<NUM>) is supplied with hydraulic fluid from the high-pressure outlet (<NUM>) of the dual pump (<NUM>), the rotational speed of the drive motor (<NUM>) is a rated rotational speed, while for prefilling purposes meaning when the check valve (<NUM>) is open, before a pressure corresponding to a back pressure in the low-pressure line (<NUM>) is reached on the high-pressure side, the rotational speed of the drive motor (<NUM>) is temporarily increased, for example to <NUM> times the rated rotational speed, for a very short time, for example <NUM>.