The present invention relates to a hydraulically actuated continuously variable transmission for an electric vehicle, as defined in the preamble of the claim 1 hereinafter. Such a transmission is generally known in the art, in particular from the international publication with number WO 2020/177931 A1.

The known continuously variable transmission includes a primary or driving pulley and a secondary or driven pulley, as well as flexible drive element that is wrapped around and in friction contact with these pulleys. Each such pulley comprises 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 the respective pulley. The flexible drive element comes in several types such as a push-type metal drive belt, a drive chain and a (fibre-reinforced) rubber V-belt. In the electric vehicle application of the transmission, the driving pulley is connected to -and rotationally driven by- an electric machine, also known as a motor/generator-unit (MGU) of the electric vehicle and the driven pulley is connected to -and rotationally drives- the driven wheels thereof.

During operation of the continuously variable transmission the flexible drive element is clamped between the two discs of each pulley by exerting a respective hydraulic pressure in a respective one of the two pulley cylinders. 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 cylinder pressures, more in particular by the ratio between the clamping forces that are respectively exerted thereby on the flexible drive element at each pulley, a radius of curvature of the flexible drive element at each pulley, i.e. between the discs thereof, is controlled. In turn, these radii of curvature determine a speed ratio of the transmission, which speed ratio can be controlled to an arbitrary value within a speed ratio range that is determined by the transmission design, through the appropriate setting of the respective cylinder pressures. Hereto, i.e. for generating and controlling the respective cylinder pressures, the transmission further includes an electro- hydraulic control system.

The known electro-hydraulic control system includes a reservoir for hydraulic fluid, a high pressure pump that is driven by an electronically controlled electric motor for supplying pressurised hydraulic fluid from the reservoir to the two pulley cylinders and two controllable hydraulic valves that determine the cylinder pressure in and/or a flow of hydraulic fluid towards or away from a respective one of the said two pulley cylinders. The known control system further includes a low pressure pump for supplying hydraulic fluid from the reservoir for lubrication and cooling of transmission components such as the flexible drive element.

Although the known electro-hydraulic control system is adequately capable of controlling both cylinder pressures during operation, its practical implementation in the electric vehicle does come with certain limitations. In particular, the main components of the known control system are commercially available only for the traditional application thereof in combination with the internal combustion engine, rather than being specifically designed for application in the electric vehicle. Consequently, such main components of the control system, such as in particular the hydraulic pump and its electric motor, are bound by the known, relatively low, source voltages (of 12V DC) and pump pressure/pump flow response times that are less suited for the increased dynamics of the electric machine compared to the internal combustion engine. Especially in relatively high powered (>100kW) electric vehicles, the desired dynamic performance requires hydraulic pressures and flows (e.g. 4-5 litre @ 40 bar and up to 15 litre @ 20 bar) cannot be met by the known electro-hydraulic control system.

A possible solution for overcoming the above limitations of the known electro- hydraulic control system. For example, a second electrically driven high pressure pump could be added in parallel with the existing high pressure pump. However, this solution not only adds the cost of a second electric motor, but also to the complexity of the control system by the then needed parallel control of the two pump motors, while still suffering from relatively low pump response time that is limited by the responsiveness of such pump motors.

Therefore, and in particular for such specific application thereof, the present invention aims to provide a novel continuously variable transmission that provides an improved dynamic performance of its electro-hydraulic control system with respect to the state of the art. According to the present invention, this aim is realised by providing the high pressure pump of the electro-hydraulic control system of the transmission as a variable displacement pump that is capable of increasing or decreasing the volume of hydraulic fluid that is displaced thereby (i.e. of changing the magnitude of the pump flow without changing the speed of the pump motor). Although this latter type of pump is well known, for example from the US patent No. 3924969 that discloses a vane pump with a pump cam that can be moved relative to a pump rotor for varying the volume of hydraulic fluid that is displaced per revolution of the rotor, it is conventionally applied specifically when the (speed of the) pump motor cannot be controlled in relation to the volume of hydraulic fluid that is actually (i.e. instantaneously) required for the actuation of the transmission. For example, the electric motor driving the variable displacement pump may conventionally be powered at a constant voltage, or the variable displacement pump may conventionally be driven by the electric machine (or even a combustion engine) that also drives the vehicle, such that the speed of the pump motor and thus the pump flow are dictated by the vehicle speed. However, the present invention concerns a control system wherein the high pressure pump is driven by its own electric motor that is, moreover, electronically controllable, i.e. which pump motor can drive the high pressure pump at a variable speed to vary the pump flow. Nevertheless, and specifically in the electric vehicle, by applying the variable displacement high pressure pump, the pump flow can respond to changes in the required flow favourably fast. In particular for minimising such response time, both the displacement of the pump and the speed of the electric motor driving the pump are varied simultaneously.

In a more detailed embodiment of the present invention, a further high pressure pump is included in the electro-hydraulic control system, which further high pressure pump is also driven by the said electric motor of the control system, i.e. is driven in common with the other, first-mentioned variable displacement high pressure pump by the same electric motor. In this way, a higher pump flow (e.g. double the pump flow if the pumps are identical) becomes available, without adding a further pump motor, or the additional electric cabling and parallel pump motor control mentioned hereinabove. Preferably, but not necessarily, this further high pressure pump is also provided as a variable displacement pump.

In another more detailed embodiment of the present invention, the variable displacement high pressure pump or pumps is/are provided as a reversible pump. Also this latter type of pump is, as such, well-known in the art, which pump type is capable of reversing the pump displacement (i.e. of reversing the pump flow without reversing the rotation of the pump motor), in addition to begin capable of varying the pump displacement. In this latter embodiment of the invention that can be applied alternative to or in combination with the former embodiment thereof. In this embodiment the pump or pumps may be hydraulically connected directly to a (respective) pulley cylinder, i.e. favourably without requiring the said controllable hydraulic valve to determine the cylinder pressure therein.

The hydraulically actuated continuously variable transmission according to the present invention 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 powertrain of an electric vehicle including a continuously variable transmission;

- figure 2 schematically illustrates an electro-hydraulic control system of the continuously variable transmission in a known embodiment thereof;

- figure 3 schematically depicts a variable displacement pump;

- figure 4 presents a novel embodiment of the electro-hydraulic control system according to the present invention;

- figure 5 schematically depicts a reversible variable displacement pump; and

- figure 6 presents a further novel embodiment of the electro-hydraulic control system according to the present invention.

Figure 1 shows a basic example of a known powertrain for an electric vehicle. In addition to a battery and power electronics (not shown) for powering an electric machine 1 and/or for storing electric power generated by the electric machine 1 , the known powertrain further comprises a gearing 3 that drivingly connects the electric machine 1 to driven wheels 2 of the vehicle via respective half shafts 38. In the specific embodiment of figure 1 thereof, the known gearing 3 includes a continuously variable transmission 40 that provides a continuously variable speed ratio between an input shaft 44 and an output shaft 45 thereof. The known gearing 3 further includes a differential 37 for allowing the driven wheels 2 to rotate at different speeds, an input speed reduction 31 between the electric machine 1 and the continuously variable transmission 40 and an output speed reduction 32 between the continuously variable transmission 40 and the differential 37. Each such speed reduction 31 , 32 is composed of a pair of meshing gears 33, 34 and 35, 36 respectively, for increasing the operating speed of the electric machine 1 relative to the driven wheels 2.

The continuously variable transmission 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 a primary pulley 42 on the input shaft 44 and a secondary pulley 43 on the output shaft 45. 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 to vary the said speed ratio thereof between a most decelerating ratio, i.e. Low, and a most accelerating ratio, i.e. Overdrive, under the influence of respective, i.e. primary and secondary (hydraulic) pressures exerted in respective hydraulic cylinders associated with the primary pulley 42 and the secondary pulley 43. These primary and secondary cylinder pressures are generated and controlled by an electro-hydraulic control system of the continuously variable transmission 40. By including the continuously variable transmission 40 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 vehicle performance parameters can be maintained at the same level, while applying an electric motor 1 that is downsized in terms of, for example, its maximum torque generating capability.

Figure 2 illustrates a known embodiment of the electro-hydraulic control system of the transmission 40. The known control system includes two pumps 101, 102 that are each driven by a respective electric motor 111, 112 that can be electronically controlled by an electronic control unit 104 of the control system, determining the flow of hydraulic fluid generated by each pump 101 , 102, i.e. to vary the displacement thereof in relation to the (respective) flow of hydraulic fluid that is required by the transmission 40, i.e. for the operation thereof.

A high pressure pump 101 can supply hydraulic fluid from a fluid reservoir 105 to a main hydraulic line 106 at a relatively high pressure level. The hydraulic pressure in this main hydraulic line 106 that is commonly referred to as the line pressure, is thus determined by the electronic control unit 104 through the controlled (electric) activation of the respective pump motor 111, i.e. in relation to a desired pump pressure. Alternatively, but not illustrated here, a line pressure control valve can be included in the control system for this purpose in a well-known manner, in which case the electronic control unit 104 controls the pump motor 111 of the high pressure pump 101 in relation to a desired pump flow.

The primary cylinder pressure that is exerted in a primary pulley cylinder 107 (i.e. the hydraulic cylinder of the primary pulley 42), is derived from the line pressure in the main hydraulic line 106 by means of a primary pressure control valve 117. The secondary pulley pressure that is exerted in a secondary pulley cylinder 108 (i.e. the hydraulic cylinder of the secondary pulley 43), is derived from the line pressure in the main hydraulic line 106 by means of a secondary pressure control valve 118. These two pressure control valves 117, 118 -and hence the respective cylinder pressures-, are controlled by the electronic control unit 104 in a well-known manner, for example directly, by the controlled activation of a respective electromagnetic valve actuator, or indirectly, by a respective pilot pressure generated by a respective pilot pressure valve.

A low pressure pump 102 can supply hydraulic fluid at a relatively low pressure level to a friction contact 109 between the drive belt 41 and the pulleys 42, 43 and to other rotating parts 110 of the transmission 40, for the lubrication and cooling thereof. Alternatively, but not illustrated here, this low pressure fluid supply can be derived from the main hydraulic line 106 by means of a lubrication control valve in a well-known manner.

In the thus illustrated embodiment of the electro-hydraulic control system, both pulley cylinders 107, 108 are supplied with (pressurized) hydraulic fluid by the high pressure pump 101. Alternatively, but not illustrated here, a further, i.e. second high pressure pump FP driven by a further electric motor EM can be included in the control system, in which case the two high pressure pumps FP, 101 each supplies a respective one of the two pulley cylinders 107, 108 with hydraulic fluid. In such alternative embodiment, the said pressure control valves 117, 118 may be redundant, as the respective cylinder pressures could then potentially be controlled through the independent activation of the pump motors EM, 111 of two high pressure pumps FP, 101 by the electronic control unit 104.

To improve the known electro-hydraulic control system, in particular in terms of its responsiveness to a change in the volume of hydraulic fluid required for the actuation of the transmission 40, i.e. for pressurizing the pulley cylinders 107, 108, the high pressure pump is provided as a variable displacement pump 201 that is known as such and whereof figure 3 provides a schematically depicted and simplified example.

The variable displacement pump 201 of figure 3 is a so-called rotary vane pump 201 with a annular pump cam 202 and with a pump rotor 203 inside the cam 202, carrying radially oriented, sliding vanes 204 that are in contact with the cam 202 in a sealing manner and that thus divide the space between the rotor 203 and the cam 202 into a number sealed chambers 205. Due to an off-centred position of the cam 202 relative to the rotor 203 that is illustrated on the left side of figure 3, the said chambers 205 grow and shrink in volume when the rotor 203 is rotated (as indicated by the arrow R). At the side of the pump 201 where the said chambers 205 grow in volume, i.e. its suction side SS, a low pressure is generated and hydraulic fluid is sucked from the reservoir 105, whereas at the other pump side the said chambers 205 shrink in volume, i.e. the pump’s discharge side DS, the hydraulic fluid is discharged into the main line 106 of the electro-hydraulic control system and a high pressure is, or at least can be, generated. Now, when the cam 202 is moved from the said off-centred, i.e. positive displacement position thereof, into a concentric position relative to the rotor 203 that is illustrated on the right side of figure 3, the said volume of the chambers 205 is the same between all chambers 205, i.e. does not change when the rotor 203 is rotated. As a result, in such concentric, i.e. zero displacement position of the cam 202, no flow of hydraulic fluid can be generated by the pump 201 from the reservoir 105 to the main line 106.

With the provision of the variable displacement pump 201 therein, the electro- hydraulic control system, in particular the electronic control unit 104 thereof, can change the flow generated by that pump 201 , by controlling its displacement volume (per rotor revolution) through the position of the cam 202 (relative to the rotor 203) or by controlling the (rotational) speed of an electric motor driving it and possibly by both such methods simultaneously. In other words, a relatively fast hydraulic response can be favorably achieved with this control system by a combination of pump motor speed change with the simultaneous cam displacement.

As a further improvement of the electro-hydraulic control system, a further, i.e. second high pressure pump 301 may be included therein that driven by the same electric motor 111 as the first high pressure pump 201. In this way, more hydraulic fluid can be delivered to the main line 106 while keeping the size of the high pressure pumps 201, 301 small and without adding a further pump motor, additional electric cabling or parallel pump motor control. This latter novel arrangement of the electro- hydraulic control system is schematically illustrated in figure 4, however, without (also) illustrating the electronic control unit 104, the low pressure pump 102, its electric drive motor 112 and lubrication circuit 109, 110.

Such second high pressure pump 301 can be either of the fixed-displacement- type, to limit the cost and complexity of the control system, or of the variable- displacement-type, to maximise the responsiveness and flexibility thereof.

As yet a further improvement of the electro-hydraulic control system, the variable displacement high pressure pump 201 or pumps 201 , 301 are provided as a reversible variable displacement pump 401 , whereof figure 5 provides a schematically depicted and simplified example. Similar to the variable displacement, rotary-vane-type pump high pressure pump 201 depicted in figure 3, the cam 402 of the reversible variable displacement pump 401 can be moved relative to its rotor 403. However, in this case, the cam 402 can be moved from the said concentric position relative to the rotor 403 that is illustrated in the middle of figure 5, to two, mutually opposite off-centred positions that are respectively illustrated on the left and right sides of figure 5. As before, when the cam 402 is moved off-centre to the left of the rotor 403, a positive displacement, i.e. a flow of hydraulic fluid from the reservoir 105 to the main line 106, is generated by the pump 401. However, when the cam 402 is moved off-centre to the right of the rotor 403, the flow of hydraulic fluid becomes opposite or negative, i.e. from the main line 106 into the reservoir 105, in particular without changing the (direction R of) rotation of the rotor 403. By incorporating such reversible variable displacement pump 401 in the electro- hydraulic control system, such pump 401 can be directly connected to a respective one of the two pulley cylinders 107, 108, i.e. without a pressure control valve being necessary there between. In particular and as illustrated in figure 6, two such reversible variable displacement pumps 401, 402 are provided that are driven in common by a single electric motor 111 and that are individually connected to and in fluid communication with a respective one of the two pulley cylinders 107 ,108. In this case, the electro-hydraulic control system, in particular the electronic control unit 104 thereof, can change the cylinder pressure, respectively generated by a respective one of the two reversible variable displacement pumps 401, 402 in a respective pulley cylinder 107, 108, by controlling the displacement volume (per rotor revolution) and displacement direction thereof through the position of the cam 402 (relative to the rotor 403). Additionally, the (rotational) speed of the pump motor 111 an electric motor driving it and possibly by both such methods simultaneously.

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

The invention is not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompasses variants, modifications and practical applications thereof that lie within reach of the person skilled in the relevant art.