WO2021110232A1

WO2021110232A1 - Hydraulic unit for a continuously variable transmission for electric vehicle application and a continuously variable transmission provided with a hydraulic unit

Info

Publication number: WO2021110232A1
Application number: PCT/EP2019/025435
Authority: WO
Inventors: Kilian Cornelis Josephus Maria WEETERINGS; Wilhelmus Johannes Maria Van Wijk
Original assignee: Robert Bosch Gmbh
Priority date: 2019-12-05
Filing date: 2019-12-05
Publication date: 2021-06-10
Also published as: CN114761710A

Abstract

The invention relates to a hydraulic unit (80) for a continuously variable transmission (3) comprising a drive pulley (43), a driven pulley (42) and a flexible drive element (41) that is in friction contact with the pulleys (42, 43) under the influence of respective hydraulic pulley pressures (P52; P53), respectively exerted in a hydraulic cylinder (52; 53) of each pulley (42; 43). The hydraulic unit (80) comprises a hydraulic pump (60) for generating a flow of pressurized hydraulic fluid, an electric motor (61) for driving the hydraulic pump (60), hydraulic valves (62, 63) for regulating the respective hydraulic pulley pressures (P52; P53) and a hydraulic manifold (65) containing the valves (62, 63) and defining flow channels (81, 82, 83, 84, 85). The hydraulic pump (60) and the hydraulic manifold (65) are arranged on a common axis (A) of the hydraulic unit (80), preferably a common central axis (A) thereof.

Description

HYDRAULIC UNIT FOR A CONTINUOUSLY VARIABLE TRANSMISSION FOR ELECTRIC VEHICLE APPLICATION AND A CONTINUOUSLY VARIABLE TRANSMISSION PROVIDED WITH A HYDRAULIC UNIT

The present disclosure relates to a hydraulically actuated continuously variable transmission or CVT, in particular to a hydraulic unit thereof as defined in the preamble of the claim 1 hereinafter. The CVT is generally known in the art, for example from the publication of the European patent application EP 1 482 215 A1 or the international applications WO 2007/141323 A1 or WO 2013/097880 A1 , and is widely applied in the drive line of passenger cars in particular. Although the CVT is currently mostly applied in combination with an internal combustion engine, enabling the comfortable and highly efficient operation thereof, its application in modern electric vehicles provides similar benefits. In addition, the CVT enables a downsizing and associated cost reduction of the electric drive motor and/or of the (traction) battery of the electric vehicle.

It is noted that within the context of the present disclosure the term electric vehicle is to be understood as including only purely electric vehicles, such as battery electric vehicles (BEV) and fuel cell electric vehicles (FCEV). In other words, the presently considered electric vehicle powertrain includes only the electric machine as a prime mover and does, in particular, not include an internal combustion engine that is, or at least can be, connected to the driven wheels in addition to or instead of the electric machine.

The known CVT includes a primary or drive pulley and a secondary or driven pulley, as well as a flexible drive element that is wrapped around and in friction contact with the said pulleys. The pulleys each comprise two (frusto-)conical discs arranged on a shaft, whereof at least one disc is axially moveable and can be urged towards the disc under the influence of a hydraulic pressure exerted in a hydraulic cylinder of that pulley. Together the conical discs of each pulley define a V-shaped circumference groove of variable width, wherein an arc shaped circumference section of the flexible drive element is located at a variable radius of curvature. The flexible drive element comes in several types such as a metal push belt, a metal drive chain or a fibre-reinforced rubber pull belt. In the typical motor vehicle application of the CVT, the drive pulley is connected to -and rotationally driven by- a prime mover of the motor vehicle, such as an electric drive motor or an internal combustion engine, and the driven pulley is connected to -and rotationally drives- the driven wheels thereof.

During operation of the CVT the flexible drive element is clamped between the two discs of each pulley by the hydraulic pressure exerted in the respective pulley cylinder, denoted pulley pressure in short. A rotational speed and an accompanying torque can then be transmitted from the one pulley to the other one pulley by means of friction between the flexible drive element and the pulleys. Also by these respective pulley pressures, more in particular by the ratio between the clamping forces that are respectively exerted thereby on the flexible drive element at each pulley, the radii of curvature of the flexible drive element at the pulleys are determined. In turn, these radii of curvature determine a speed ratio of the CVT, which speed ratio can be controlled to an arbitrary value within a speed ratio range provided by the CVT through the appropriate setting of the respective pulley pressures. Hereto, i.e. for generating and regulating the pulley pressures, the CVT further includes a hydraulic unit and an electronic unit respectively. The hydraulic unit comprises a hydraulic pump for generating a flow of pressurized hydraulic fluid, an electric motor for driving the pump, hydraulic valves for regulating respective flows of hydraulic fluid to and from, at least, the respective pulley cylinders and a hydraulic manifold containing the valves and defining the necessary flow channels for the hydraulic fluid between the pump, the valves and the pulley cylinders. The electronic unit comprises a microcontroller or microprocessor that is programmed to determine desired pressure levels, such as at least the pulley pressures, sensor means for detecting corresponding actual pressure levels and actuator means for regulating the pump and/or valves of the hydraulic unit to make the actual pressure levels coincide with the respectively corresponding desired pressure levels.

The present invention aims to provide an advantageous design of the hydraulic unit that requires only a minimal installation space and that can be manufactured relatively easily, possibly utilising additive manufacturing technologies such as 3D printing. The present invention makes use of the circumstances that in the electric vehicle application of the CVT :

- the typical secondary hydraulic functions of the hydraulic unit, such as clutch activation and bearing lubrication, either are absent or are separated from its main function of generating and regulating the pulley pressures; and

- the required CVT speed ratio range is relatively small, i.e. typically lies within the range from 0.5 to 2.

According to the present invention, the pump and the manifold are arranged as part of the hydraulic unit on a (virtual) common axis. In particular, these parts are provided with an overall cylindrical, cuboidal or other right prismatic shape, each defining a respective central axis that coincides with the said common axis, i.e. share a common central axis. This arrangement favourably allows the manifold to be easily connected to, or to be formed even integral with a housing of the pump. Preferably, such common central axis also coincides with a rotation axis of a rotor of the pump that rotates inside the inside the pump housing to displace and pressurize the hydraulic fluid during operation of the CVT. Further, the motor of the hydraulic unit is preferably arranged along the common central axis of the hydraulic unit as well, on the opposite side of the pump housing as the manifold. This latter arrangement favourably allows a housing of the motor to be easily connected to, or to be formed even integral with a housing of the pump.

By such coaxial arrangement of the motor, pump and manifold components thereof, the hydraulic unit is favourably compact. Moreover, the said valves, in particular respective valve spools thereof, are preferably accommodated in the manifold mutually spaced in the direction of the said common central axis and oriented perpendicular thereto. Further, flow channels defined by the manifold between the valves and the respective pulley cylinders are preferably oriented perpendicular to both the said common central axis thereof and the valves/valve spools. Moreover, yet further flow channels defined by the manifold between the valves and an external reservoir for hydraulic fluid, i.e. sump, are preferably also oriented perpendicular to both the said common central axis thereof and the valves/valve spools. This particular arrangement of the valves and the flow channels, makes the manifold ideally suited to be manufactured by means of additive manufacturing technologies.

The valves, in particular the valve spools thereof are preferably directly actuated by a respective electric actuator, also known as a solenoid actuator, of the electronic unit, which electric actuators are physically attached to the manifold next to each other. It is noted that this favourably simple, direct mechanical actuation of the valve spool by the electric actuator is possible in the electric vehicle application of the CVT because of the said small speed ratio range thereof.

The hydraulic unit includes at least one valve and the electronic unit includes at least one corresponding electric actuator. In this ultimately simplified embodiment of the hydraulic unit, the discharge pressure of the pump coincides with one of the pulley pressures that is thus regulated by powering the motor that drives the pump as required to maintain such discharge pressure at the desired pressure level. The respective other one of the pulley pressures is regulating by controlling the said one valve that is thus placed between the pump and the pulley cylinder carrying that other one of the pulley pressures. A second valve and a corresponding second electric actuator can be included in the hydraulic unit and in the electronic unit respectively, such that either:

- the discharge pressure of the pump and hence the said one pulley pressure is regulated by the second valve; or

- the said one pulley pressure is regulated by the second valve separately from the pump discharge pressure (that is regulated by powering the motor that drives the pump as required).

In the former embodiment, the motor that drives the pump is preferably powered to create an excess flow of hydraulic fluid that is passed by the second valve to maintain the desired pump discharge pressure. More preferably, the motor is controlled in dependency on such excess flow, e.g. to the flow passed by the second valve constant. In the latter embodiment, both pulley pressures are regulated by controlling a respective one of the two valves that are placed between the pump and a respective one of the pulley cylinders carrying the pulley pressures.

A third valve and a corresponding third electric actuator can be included in the hydraulic unit and in the electronic unit respectively. In this particular embodiment, both the pulley pressures and the pump discharge pressure are separately regulated by a respective valve. Similar to in the said formed embodiment, the motor that drives the pump is preferably powered to create an excess flow of hydraulic fluid that is passed by the third valve to maintain the desired pump discharge pressure. More preferably, the motor is controlled in dependency on such excess flow, e.g. to the flow passed by the third valve constant.

The hydraulic unit according to the present disclosure is explained in more detail hereinafter by means of non-limiting, illustrative embodiments thereof and with reference to the drawing, in which:

- figure 1 is a schematic representation of the functional arrangement of the main components of a known electric vehicle powertrain with an electric machine and a continuously variable transmission;

- figure 2 is a schematic representation of an electro-hydraulic actuation system of the continuously variable transmission;

- figure 3 depicts a physical embodiment of the hydraulic unit of the electro-hydraulic actuation system in accordance with the present invention; and

- figure 4 depicts the internal hydraulic connections of a hydraulic manifold of the electro-hydraulic actuation system in accordance with the present invention. Figure 1 shows a basic example of a known powertrain for an electric vehicle such as a passenger car. The known electric vehicle powertrain comprises an electric machine (EM) 1 , also known as a motor/generator device, two driven wheels 2 of the electric vehicle and a continuously variable transmission (CVT) 3 that drivingly connects the EM 1 to the driven wheels 2. The known a continuously variable transmission (CVT) 3 includes a variator unit 40, providing a continuously variable speed ratio between an input shaft and an output shaft thereof, is included therein. The variator unit 40 is as such well- known, in particular in the form comprising a drive belt 41 that is wrapped around and in frictional contact with both an input pulley 42 on the input shaft and an output pulley 43 on the output shaft of the variator unit 40. An effective radius of the friction contact between the drive belt 41 and a pulley 42, 43 can be varied in mutually opposite directions between the two pulleys 42, 43 by means of a control and actuation system 50 (see figure 2) of the CVT 3, such that a speed ratio provided by the CVT 3 between its input and output shafts can be continuously varied with a certain speed ratio range between a most decelerating CVT speed ratio, i.e. Low, and a most accelerating CVT speed ratio, i.e. Overdrive.

By including the CVT 3 in the electric vehicle powertrain several advantages and/or optimisation strategies are unlocked. For example, the take-off acceleration and/or top speed of the electric vehicle can be increased thereby. Alternatively, these performance parameters of the vehicle can be maintained at the same level, but while applying a smaller, i.e. downsized EM 1 .

The actuation system 50 of the CVT 3 is schematically illustrated in figure 2 and includes both a hydraulic unit and an electronic unit. In the presently illustrated example thereof, the hydraulic unit is composed of:

- a hydraulic fluid reservoir 64

- a hydraulic pump 60 for generating a flow of pressurized hydraulic fluid

- an electric motor 61 for driving the pump 60,

- two hydraulic valves 62, 63 for regulating respective flows of hydraulic fluid to and from respective pulley cylinders 52, 53, each associated with a respective pulley 42, 43, and

- a hydraulic manifold containing the valves 62, 63 and defining the necessary flow channels 84, 81 , 82, 83 between the reservoir 64, the pump 60, the valves 62, 63 and the pulley cylinders 52, 53.

In the presently illustrated example thereof, the electronic unit is composed of:

- a microcontroller 70 that is programmed to determine desired pressure levels, such as a pump pressure P60 and pulley pressures P52, P53 in the respective pulley cylinders 52, 53, based on input signals h, i_å, i_n that, for example, represent respective, actual pressure levels,

- sensor means for detecting corresponding actual pressure levels (not illustrated), and

- regulator means 71 , 72 under control of the microcontroller 70 for regulating the electric motor 61 of the pump 60 and for operating the valves 62, 63 of the hydraulic unit to make the actual levels of the said pump pressure P60 and the said pulley pressures, P52, P53, coincide with the respectively corresponding desired pressure levels.

It is noted that, in case of the valves 62, 63 and in the context of the present invention, the respective regulator means 72 are preferably provided in the form of an electric actuator 72 that acts directly on a respective valve 62, 63, in particular on a moveable core, i.e. valve spool thereof. Moreover, the microcontroller 70 and the regulator means 71 of the electric motor 61 of the pump 6 can be mutually integrated. Either way, the regulator means 71 of the electric motor 61 of the pump 60 are preferably located between the electric motor 61 and the pump 60 (not illustrated), such that these are cooled by the hydraulic fluid that is circulated by the pump 60. According to the present invention, the pump 60 and the manifold 65 are arranged as part of the hydraulic unit 80 along a common central axis A. Such a novel hydraulic unit 80 is illustrated in figure 3, both in an isometric 3D view and in a top elevation in 2D. The manifold 65 is favourably formed integral with a housing of the pump 60. In addition, the said electric motor 61 is arranged on the said common central axis A as well, however, on the opposite side of the pump 60 relative to the manifold 65. As a result, a compact hydraulic unit 80 is obtained that, moreover, is suited for additive manufacturing techniques such as 3D printing.

The electric actuators 72 for operating the valves 62, 63 of the hydraulic unit 80 are attached to the manifold 65, mutually spaced along the said common central axis A, each oriented along respective further axes F perpendicular to the common central axis A. The manifold 65 defines respective flow channels 82, 83 between the respective valves 62, 63 and the respective pulley cylinder 52, 53 that are oriented perpendicular to both the said common central axis A and the said further axes F.

The compact design of the hydraulic unit 80 according to the present invention enables flexibility and can easily be adapted to a multitude of different applications.

A favourable layout of the internal hydraulic connections of the hydraulic manifold 65 is illustrated in figure 4. A first hydraulic channel 84 thereof that connects a low pressure or suction port of the pump 60 to the reservoir 64 extends essentially in a radial direction relative to the common central axis A. A second hydraulic channel 81 that connects to a high pressure or discharge port of the pump 60 in parallel with the said common central axis A, includes an intermediate part 81 a that extends perpendicular to the common central axis A and two secondary channel parts 81 b, 81c both extending in parallel with the common central axis A from the said intermediate part 81a thereof.

By applying such two secondary channel parts 81 b, 81c in parallel, a pressure loss between the said discharge port of the pump 60 and the valves 62, 63 is favourably minimised, also when the flow of hydraulic fluid is large, while the manifold 65 remains ideally suited to be manufactured by means of additive manufacturing technologies. To further enhance this effect, both the secondary channel parts 81b, 81c of the second hydraulic channel 81 are connected to both valves 62, 63 via two tertiary channels parts 81 d, 81 e, 81 f, 81 g of that second hydraulic channel 81 each, all four of which tertiary channels parts 81 d, 81 e, 81 f, 81 g extend perpendicular to the common central axis A. Moreover and to the same effect, also the flow channels 85a, 85b, 85c, 85d defined by the manifold 65 extending from the valves 62, 63 towards reservoir 64 are both doubly embodied, i.e. are each embodied by two parallel (sub-)channels, as are the flow channels 82a, 82b, 83a, 83b defined by the manifold 65 extending from the valves 62, 63 towards the respective pulley cylinders 52, 53.

The present invention, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all of the features in the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as a non-limiting example of a respective feature. Separately claimed features can be applied separately in a given product, or in a given process as the case may be, but these can also be applied simultaneously therein in any combination of two or more of such features.

The invention is not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompass(es) straightforward amendments, modifications and practical applications thereof, in particular those that lie within reach of the person skilled in the relevant art.

Claims

1 . A hydraulic unit (80) for a continuously variable transmission (3) comprising a drive pulley (43), a driven pulley (42) and a flexible drive element (41) that is wrapped around and in friction contact with the pulleys (42, 43) that are each provided with two discs arranged on a shaft, whereof at least one disc is axially moveable along the shaft and can be urged towards the other one disc under the influence of a respective hydraulic pulley pressure (P52; P53) exerted in a hydraulic cylinder (52; 53) of the respective pulley (42; 43) to clamp the flexible drive element (41) between the discs, which hydraulic unit (80) comprises a hydraulic pump (60) for generating a flow of pressurized hydraulic fluid, an electric motor (61) for driving the hydraulic pump (60), at least one hydraulic valve (62; 63) for regulating a respective flow of hydraulic fluid to and from a respective hydraulic cylinder (52; 53) and a hydraulic manifold (65) containing the at least one hydraulic valve (62; 63) and defining flow channels (81 , 82, 83, 84, 85) for hydraulic fluid, characterized in that the hydraulic pump (60) and the hydraulic manifold (65) are arranged on a common axis (A) of the hydraulic unit (80).

2. The hydraulic unit (80) according to claim 1 , characterized in that the electric motor (61) thereof is also arranged on the said common axis (A) on the opposite side of the hydraulic pump (60) relative to the hydraulic manifold (65).

3. The hydraulic unit (80) according to claim 1 or 2, characterized in that the hydraulic manifold (65) thereof is formed integral with a housing of the hydraulic pump (60).

4. The hydraulic unit (80) according to claim 1 , 2 or 3, characterized in that the electric motor, the hydraulic pump (60) and the hydraulic manifold (65) are provided with an overall cylindrical, cuboidal or other right prismatic shape, each having a respective central axis (A) that coincides with the said common axis (A).

5. The hydraulic unit (80) according to a preceding claim, characterized in that the hydraulic valve (62; 63), in particular a valve spool thereof is directly mechanically actuated by a respective electric actuator (72) that is attached to the hydraulic manifold (65) in line with the valve (62; 63)/valve spool.

6. The hydraulic unit (80) according to a preceding claim including a further hydraulic valve (62; 63) for regulating a respective flow of hydraulic fluid to and from a further hydraulic cylinder (52; 53), characterized in that the hydraulic valves (62, 63) thereof are oriented perpendicular to the said common axis (A), while being mutually spaced along such axis (A) and in that the flow channels (82, 83) embodied by the hydraulic manifold (65) between the hydraulic valves (62, 63) and the respective hydraulic cylinders (52, 53) are oriented perpendicular to both the said common axis (A) and the hydraulic valves (62, 63).

7. The hydraulic unit (80) according to a preceding claim 6, characterized in that the hydraulic valves (62, 63), in particular respective valve spools thereof are directly mechanically actuated by respective electric actuators (72) that are attached to the hydraulic manifold (65) next to each other in line with the respective valves (62, 63)/valve spools.

8. The hydraulic unit (80) according to a preceding claim, characterized in that the flow channels (81 , 82, 83, 84, 85) embodied by the hydraulic manifold (65) between the pump (60) and the valves (62, 63) and/or between the valves (62, 63) and the hydraulic cylinders (52, 53) and/or between the valves (62, 63) and a reservoir (64) for hydraulic fluid consist, at least in part, of at least two flow channels (81 b, 81c; 81 d, 81 e; 81 f, 81 g; 82a, 82b, 83a, 83b; 85a, 85b; 85c, 85d) running in parallel each.

9. The hydraulic unit (80) according to a preceding claim, characterized in that regulator means (71) for operating the electric motor (61) are provided therein, located between the electric motor (61 ) and the pump (60).

10. A continuously variable transmission (3) for an electric vehicle comprising a drive pulley (43), a driven pulley (42) and a flexible drive element (41 ) that is wrapped around and in friction contact with the pulleys (42, 43) that are each provided with two discs arranged on a shaft, whereof at least one disc is axially moveable along the shaft and can be urged towards the other one disc under the influence of a respective hydraulic pulley pressure (P52; P53) exerted in a hydraulic cylinder (52; 53) of the respective pulley (42; 43) to clamp the flexible drive element (41 ) between the discs, which transmission (3) further comprises hydraulic unit (80), in particular according to a preceding claim, with a hydraulic pump (60) for generating a flow of pressurized hydraulic fluid, with an electric motor (61) for driving the hydraulic pump (60), with one hydraulic valve (62; 63) for regulating a respective flow of hydraulic fluid to and from a respective one of the hydraulic cylinders (52; 53), and with a hydraulic manifold (65) containing the one hydraulic valve (62; 63) and defining flow channels (81 , 82, 83, 84, 85) for hydraulic fluid, characterised in that the transmission (3) further comprises an electronic unit with an electric actuator (72) for directly mechanically actuating the said one hydraulic valve (62; 63), hence controlling the respective one pulley pressure (P52; P53) exerted therein.

11. The continuously variable transmission (3) according to claim 10, with a further hydraulic valve (62; 63) and with a further electric actuator (72) for directly mechanically actuating the said further hydraulic valve (62; 63) to regulate a respective other one pulley pressure (P52; P53).

12. The continuously variable transmission (3) according to claim 10 or 11 , with a further hydraulic valve (62; 63) and with a further electric actuator (72) for directly mechanically actuating the said further hydraulic valve (62; 63) to regulate a discharge pressure of the pump (60), while powering the electric motor (61) to create an excess flow of hydraulic fluid that is passed by the further hydraulic valve (62; 63) to maintain such discharge pressure.

13. The continuously variable transmission (3) according to claim 12, characterized in that the electric motor (61 ) is controlled in dependency on the excess flow passed by the further hydraulic valve (62; 63).