CN114761710A

CN114761710A - Hydraulic unit for continuously variable transmission for electric vehicle application and continuously variable transmission equipped with hydraulic unit

Info

Publication number: CN114761710A
Application number: CN201980102755.3A
Authority: CN
Inventors: K·C·J·M·维特林斯; W·J·M·范维克
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-12-05
Filing date: 2019-12-05
Publication date: 2022-07-15
Also published as: WO2021110232A1

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) in frictional contact with the pulleys (42, 43) under the influence of respective hydraulic pulley pressures (P52; P53) respectively applied in hydraulic cylinders (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 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), in particular a common central axis (A), of the hydraulic unit (80).

Description

Hydraulic unit for continuously variable transmission for electric vehicle application and continuously variable transmission equipped with hydraulic unit

Technical Field

The present disclosure relates to a hydraulically actuated continuously variable transmission or CVT, in particular to a hydraulic unit as defined in the preamble of claim 1 below. CVTs are known in the art, for example as disclosed in european patent application EP1482215a1 or international application WO2007/141323a1 or WO2013/097880a1, which are widely used in particular in the drive train of passenger cars. While CVTs are currently used primarily in conjunction with internal combustion engines to achieve comfortable and efficient operation, their use in modern electric vehicles also provides similar benefits. Furthermore, the CVT enables miniaturization and associated cost reduction of the electric drive motor and/or (traction) battery of the electric vehicle.

Background

Note that in the context of the present disclosure, the term electric vehicle should be understood to include only electric-only vehicles, such as Battery Electric Vehicles (BEVs) and Fuel Cell Electric Vehicles (FCEVs). In other words, the electric vehicle powertrain currently under consideration only includes an electric machine as the prime mover, and in particular does not include an internal combustion engine that is connected to, or at least can be connected to, the driven wheels in addition to, or instead of, the electric machine.

A known CVT comprises a primary or drive pulley and a secondary or driven pulley, and a flexible drive element wrapped around and in frictional contact with the pulleys. Each pulley comprises two (frusto-) conical discs arranged on the shaft, wherein at least one disc is axially movable and can be pushed towards the other disc under the influence of a hydraulic pressure exerted by the hydraulic cylinder of the pulley. The conical discs of each pulley together define a V-shaped circumferential groove of variable width, with the arcuate circumferential section of the flexible drive element at a variable radius of curvature. There are various types of flexible drive elements, such as metal push belts, metal drive chains or fiber reinforced rubber pull belts. In a typical motor vehicle application of a CVT, a drive pulley is connected to and rotationally driven by a prime mover (e.g., an electric motor or an internal combustion engine) of the motor vehicle, and a driven pulley is connected to and rotationally drives a driven pulley thereof.

During operation of the CVT, the flexible drive element is sandwiched between the two discs of each pulley by the hydraulic pressure (referred to simply as pulley pressure) applied in the respective pulley cylinder. The rotational speed and accompanying torque can then be transmitted from one pulley to the other by friction between the flexible drive element and the pulley. The radius of curvature of the flexible drive element at the pulleys is also determined by these respective pulley pressures, more specifically by the ratio between the clamping forces thereby exerted on the flexible drive element at each pulley, respectively. These radii of curvature, in turn, determine the ratio of the CVT, which can be controlled to any value within the range of ratios provided by the CVT by appropriate setting of the respective pulley pressures. To this end, in order to generate and regulate the pulley pressure, CVTs also comprise a hydraulic unit and an electronic unit, respectively. The hydraulic unit includes a hydraulic pump for generating a flow of pressurized hydraulic fluid, an electric motor for driving the pump, a hydraulic valve for regulating respective flow rates of hydraulic fluid into and out of at least respective belt cylinders, and a hydraulic manifold containing valves and defining necessary flow passages for the hydraulic fluid between the pump, the valves, and the pulley cylinders. The electronic unit includes: a microcontroller or microprocessor programmed to determine a desired pressure level, e.g., at least pulley pressure; sensor means for detecting a respective actual pressure level; actuating means for adjusting the pumps and/or valves of the hydraulic unit to bring the actual pressure level into agreement with the respectively corresponding desired pressure level.

Disclosure of Invention

The present invention aims to provide an advantageous design of a hydraulic unit which requires only minimal installation space and which can be manufactured relatively easily, possibly using additive manufacturing techniques such as 3D printing. The present invention takes advantage of the fact that the CVT is used in electric vehicle applications:

typical auxiliary hydraulic functions of the hydraulic unit, such as clutch actuation and bearing lubrication, which are either not present or separate from their main function of generating and regulating the pulley pressure; and

the required CVT ratio range is relatively small, i.e. typically in the range of 0.5 to 2.

According to the invention, the pump and the manifold are arranged on a (virtual) common axis as part of the hydraulic unit. In particular, these components are provided with an overall cylindrical, cubic or other regular prismatic shape, each defining a respective central axis coinciding with said common axis, i.e. sharing a common central axis. This arrangement advantageously allows the manifold to be easily connected to, or even integrated with, the housing of the pump. Preferably, such common central axis also coincides with the axis of rotation of the rotor of the pump, which rotates inside the housing of the pump to move and pressurize the hydraulic fluid during operation of the CVT. Furthermore, preferably, the electric motor of the hydraulic unit is also arranged on the opposite side of the pump housing from the manifold along the common central axis of the hydraulic unit. The latter arrangement advantageously allows the housing of the electric motor to be easily connected to, or even integrated with, the housing of the pump.

By this coaxial arrangement of the electric motor, the pump and its manifold member, the hydraulic unit is advantageously compact. Furthermore, the valves, in particular their respective spools, are preferably accommodated in a manifold, the valves being spaced apart from each other in the direction of the common central axis and oriented perpendicular to the common central axis. Furthermore, the flow passage between the valve defined by the manifold and the respective band wheel cylinder is preferably oriented perpendicular to the common central axis and the valve/spool thereof. Furthermore, further flow channels between the valve defined by the manifold and an external reservoir for hydraulic fluid, i.e. an oil sump, are preferably also oriented perpendicular to said common central axis and the valve/spool. This particular arrangement of valves and flow channels makes the manifold well suited to fabrication by additive manufacturing techniques.

The valves, and in particular the spools thereof, are preferably directly actuated by respective electric actuators (also called electromagnetic actuators) of the electronic unit, which are physically attached to the manifold adjacent to each other. It is noted that due to the small speed ratio range described, in electric vehicle applications of a CVT, such an advantageous simple, direct mechanical actuation of the spool by the electric actuator is possible.

The hydraulic unit comprises at least one valve and the electronic unit comprises at least one corresponding electric actuator. In this final simplified embodiment of the hydraulic unit, the discharge pressure of the pump coincides with one of the pulley pressures, and therefore the pressure can be adjusted as needed by powering the electric motor driving the pump to maintain this discharge pressure at the desired pressure level. The respective other pulley pressure is regulated by controlling the one valve, which is thus placed between the pump and the pulley cylinder carrying the other pulley pressure.

The second valve and the corresponding second electric actuator may be respectively comprised in the hydraulic unit and the electronic unit, so that:

the discharge pressure of the pump and therefore the one pulley pressure is regulated by a second valve; or

The one pulley pressure is regulated by the second valve, separately from the discharge pressure of the pump (which is regulated as required by powering the electric motor driving the pump).

In the former embodiment, the motor driving the pump is preferably powered to produce an excess flow of hydraulic fluid that flows through the second valve to maintain the desired pump discharge pressure. More preferably, the electric motor is controlled in dependence of such an excess flow, e.g. a constant flow through the second valve. In the latter embodiment, the two pulley pressures are adjusted by controlling a respective one of the two valves that is placed between the pump and a respective one of the pulley cylinders that carries the pulley pressures.

The third valve and the corresponding third electric actuator may be comprised in a hydraulic unit and an electronic unit, respectively. In this particular embodiment, both the pulley pressure and the pump discharge pressure are independently regulated by respective valves. Similar to in the formed embodiment, the motor driving the pump is preferably powered to generate an excess flow of hydraulic fluid that flows through the third valve to maintain the desired pump discharge pressure. More preferably, the motor is controlled in dependence of such an excess flow, e.g. a constant flow through the third valve.

Drawings

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

figure 1 is a schematic diagram of the functional arrangement of the main dog members of a known electric vehicle powertrain with an electric machine and a continuously variable transmission;

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

figure 3 shows a physical embodiment of the hydraulic unit of the electro-hydraulic actuation system according to the present invention; and

figure 4 shows the internal hydraulic connections of the hydraulic manifolds of the electro-hydraulic actuation system according to the present invention.

Detailed Description

Fig. 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 referred to as a motor/generator arrangement, two driven wheels 2 of the electric vehicle and a Continuously Variable Transmission (CVT)3 drivingly connecting the EM 1 to the driven wheels 2. A known Continuously Variable Transmission (CVT)3 includes a transmission unit 40 that provides a continuously variable transmission ratio between an input shaft and an output shaft included therein. The transmission unit 40 is well known and in particular comprises a form of a drive belt 41 which belt 41 is wrapped around and in frictional contact with an input pulley 42 on an input shaft and an output pulley 43 on an output shaft of the transmission unit 40. The effective radius of frictional contact between the drive belt 41 and the

pulleys

42, 43 can be varied in speed ratios in mutually opposite directions between the two

pulleys

42, 43 by the control and actuation system 50 (see fig. 2) of the CVT3, such that the CVT3 provides a speed ratio between its input and output shafts that can be varied continuously over a particular range of speed ratios between a maximum deceleration CVT ratio, i.e. a low speed and a maximum acceleration CVT ratio, i.e. an overspeed.

By including the CVT3 in the electric vehicle powertrain, multiple advantages and/or optimization strategies may be unlocked. For example, the starting acceleration and/or the maximum speed of the electric vehicle can thereby be increased. Alternatively, these performance parameters of the vehicle may be kept at the same level, but at the same time a smaller, i.e. reduced size, EM 1 is applied.

The actuation system 50 of the CVT3 is schematically shown in figure 2 and comprises a hydraulic unit and an electronic unit. In the presently illustrated example, the hydraulic unit includes:

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 into and out of

respective belt cylinders

52, 53, each valve being 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, the electronic unit includes:

a microcontroller 70 programmed to base an input signal i representative of the corresponding actual pressure level₁、i₂、i_nDetermining a desired pressure level, such as pump pressure P60 and pulley pressures P52, P53 in the respective

belt wheel cylinders

52, 53;

sensor means (not shown) for detecting the respective actual pressure level; and

adjusting means 71, 72 for adjusting the electric motor 61 of the pump 60 and for operating the

valves

62, 63 of the hydraulic unit under the control of the microcontroller 70 to bring the actual level of the pump pressure P60 and the pulley pressures P52, P53 into agreement with the respective desired pressure level.

It should be noted that in the case of

valves

62, 63 and in the context of the present invention, the respective regulating device 72 is preferably provided in the form of an electric actuator 72 which acts directly on the

respective valve

62, 63, in particular on the movable core, i.e. the spool of the valve. Furthermore, the microcontroller 70 and the regulating device 71 of the motor 61 of the pump 60 can be integrated with one another. Either way, the adjustment means 71 of the electric motor 61 of the pump 60 are preferably located between the electric motor 61 and the pump 60 (not shown), so that they are cooled by the hydraulic fluid circulated by the pump 60.

According to the invention, the pump 60 and the manifold 65 are arranged along a common central axis a as part of a hydraulic unit 80. This novel hydraulic unit 80 is shown in figure 3 in an isometric 3D view and a 2D top view. The manifold 65 is advantageously formed integrally with the housing of the pump 60. In addition, the electric motor 61 is also arranged on the common central axis a, but on the opposite side of the pump 60 with respect to the manifold 65. Thus, a compact hydraulic unit 80 is obtained, which is furthermore suitable for additive manufacturing techniques such as 3D printing.

Attached to the manifold 65 are electric actuators 72 for operating the

valves

62, 63 of the hydraulic unit 80, spaced from each other along said common central axis a, each electric actuator being oriented along a respective further axis 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 cylinders

52, 53, which are oriented perpendicularly to said common central axis a and to said further axis F.

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

An advantageous layout of the internal hydraulic connections of the hydraulic manifold 65 is shown in fig. 4. A first hydraulic passage 84 connecting the low pressure or suction port of the pump 60 to the reservoir 64 extends substantially radially with respect to the common central axis a. The second hydraulic passage 81, which is connected to the high pressure or discharge port of the pump 60 in parallel to the common center axis a, includes a middle portion 81a extending perpendicular to the common center axis a and two

sub-passage portions

81b, 81c extending from the middle portion 81a in parallel to the common center axis a.

By arranging such two

secondary channel portions

81b, 81c in parallel, the pressure losses between said discharge port of the pump 60 and the

valves

62, 63 are advantageously suppressed to a minimum, even in the case of particularly large flows of hydraulic fluid, while the manifold 65 is very suitable for being manufactured by additive manufacturing techniques. To further enhance this effect, the two

secondary channel portions

81b, 81c of the second hydraulic channel 81 are connected to the two

valves

62, 63 via two

tertiary channel portions

81d, 81e, 81f, 81g of the second hydraulic channel 81, respectively, all four of the

tertiary channel portions

81d, 81e, 81f, 81g extending perpendicularly to the common central axis a. Furthermore and for the same effect, the

flow channels

85a, 85b, 85c, 85d defined by the manifold 65 extending from the valve 62 towards the reservoir 64 are all embodied doubly, i.e. each as two parallel (sub-) channels, similarly to the

flow channels

82a, 82b, 83a, 83b defined by the manifold 65 extending from the

valves

62, 63 towards the

respective belt cylinders

52, 53.

The present invention relates to and includes all the features of the appended claims, except for all the details of the foregoing description and accompanying drawings. The inclusion of a reference in parentheses in the claims does not limit the scope thereof but is merely provided as a non-limiting example of a corresponding feature. The features claimed individually may be applied individually in a given product or in a given process as the case may be, but these may also be applied simultaneously in any combination of two or more such features.

The present invention is not limited to the embodiments and/or examples explicitly mentioned herein, but also includes direct modifications, variations and practical applications thereof, particularly those modifications and applications which would be understood by a 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) wound around and in frictional contact with the pulleys (42, 43), each provided with two discs arranged on a shaft, wherein at least one disc is axially movable along the shaft and can be urged towards the other 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 sandwich the flexible drive element (41) between the discs, the hydraulic unit (80) comprising 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 into and out of the respective hydraulic cylinder (52; 53) and at least one hydraulic valve comprising(s) 62; 63) and a hydraulic manifold (65) 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) is also arranged on the common axis (a), on the opposite side of the hydraulic pump (60) with respect to the hydraulic manifold (65).

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

4. Hydraulic unit (80) according to any one of claims 1, 2, 3, characterized in that said electric motor, said hydraulic pump (60) and said hydraulic manifold (65) are provided with an overall cylindrical, rectangular parallelepiped or other regular prismatic shape, each having a respective central axis (A) coinciding with said common axis (A).

5. The hydraulic unit (80) according to any one of the preceding claims, characterized in that the hydraulic valves (62; 63), in particular the spools thereof, are directly mechanically actuated by respective electric actuators (72) attached to the hydraulic manifold (65) and in line with the hydraulic valves (62; 63)/spools.

6. The hydraulic unit (80) according to any one of the preceding claims, comprising a further hydraulic valve (62; 63) for regulating a respective flow of hydraulic fluid into and out of a further hydraulic cylinder (52; 53), characterized in that the hydraulic valves (62, 63) are oriented perpendicular to the common axis (A) while being mutually spaced along the common axis (A), flow channels (82, 83) implemented by the hydraulic manifold (65) between the hydraulic valves (62, 63) and the respective hydraulic cylinders (52, 53) being oriented perpendicular to the common axis (A) and to the hydraulic valves (62, 63).

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

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

9. Hydraulic unit (80) according to any of the preceding claims, characterized in that an adjusting device (71) is provided between the electric motor (61) and the pump (60) for operating the electric motor (61).

10. Continuously variable transmission (3) for an electric vehicle, comprising a drive pulley (43), a driven pulley (42) and a flexible drive element (41) wound around and in frictional contact with the pulleys (42, 43), each provided with two discs arranged on a shaft, wherein at least one disc is axially movable along the shaft and can be pushed towards the other 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 sandwich the flexible drive element (41) between the discs, the continuously variable transmission (3) further comprising a hydraulic unit (80), in particular according to one of the preceding claims, having a hydraulic pump (60) for generating a flow of pressurized hydraulic fluid, an electric motor (61) for driving the hydraulic pump (60), a hydraulic motor (61) for driving the hydraulic pump (60), and a hydraulic drive element (41) arranged between the discs, At least one hydraulic valve (62; 63) for regulating a respective flow of hydraulic fluid into and out of 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 continuously variable transmission (3) further comprises an electronic unit with an electric actuator (72) for directly mechanically actuating the at least one hydraulic valve (62; 63) for controlling a respective one of the pulley pressures (P52; P53) exerted therein.

11. Continuously variable transmission (3) according to claim 10, characterized in that it has a further hydraulic valve (62; 63) and a further electric actuator (72) for directly mechanically actuating the further hydraulic valve (62, 63) to adjust the respective further pulley pressure (P52; P53).

12. A continuously variable transmission (3) according to claim 10 or 11, characterized in that it has a further hydraulic valve (62; 63) and a further electric actuator (72) for directly mechanically actuating the further hydraulic valve (62; 63) to regulate the discharge pressure of the hydraulic pump (60) while powering the electric motor (61) to generate an excess flow of hydraulic fluid through the further hydraulic valve (62; 63) to maintain such discharge pressure.

13. Continuously variable transmission (3) according to claim 12, characterized in that the electric motor (61) is controlled in dependence of the excess flow through the further hydraulic valve (62; 63).