POWERTRAIN WITH A CONTINUOUSLY VARIABLE TRANSMISSION FOR AN ELECTRIC VEHICLE AND METHOD FOR OPERATING SUCH POWERTRAIN

Abstract

The invention relates to a powertrain for a fully electric vehicle comprising an electric machine (1), a driven wheel (2) and a gearing (3) that is arranged between the electric machine (1) and the driven wheel (2) and that provides a driving connection there between, which gearing (3) includes at least a first speed reduction stage (31) providing a fixed first speed ratio, a variator unit (40) providing a variable speed ratio and a second speed reduction stage (32) providing a fixed second speed ratio between an input gear wheel (35) and an output gear wheel (36) thereof, whereof the input gear wheel (35) rotates as one with the output shaft of variator unit (40). According to the invention, a maximum overall speed ratio provided by the gearing (3) between the electric machine (1) and the driven wheel (2) amounts to at least 20:1.

Claims

1. A method for operating a powertrain for or in a fully electric vehicle, which powertrain comprises an electric machine (1), a driven wheel (2) and a gearing (3) that is arranged between the electric machine (1) and the driven wheel (2) and that provides a driving connection there between, which gearing (3) includes a first speed reduction stage (31) providing a fixed first speed ratio between an input gear wheel (33) and an output gear wheel (34) thereof, whereof the input gear wheel (33) rotates as one with the electric machine (1), which gearing (3) further includes a variator unit (40) providing a variable speed ratio between an input shaft and an output shaft thereof, whereof the input shaft rotates as one with the output gear wheel (34) of the first speed reduction stage (31), and which gearing (3) yet further includes a second speed reduction stage (32) providing a fixed second speed ratio between an input gear wheel (35) and an output gear wheel (36) thereof, whereof the input gear wheel (35) rotates as one with the output shaft of variator unit (40), in which method, during operation of the powertrain, the electric motor (1) is controlled to generate a torque level between zero and a peak torque in dependence on one or more operating parameters of the electric vehicle, characterized in that the peak torque is independent of a controlled rotational speed of the electric motor (1) in a range between zero and at least 50% of a maximum controlled rotational speed of the electric motor (1).

2. The method for operating a powertrain for or in a fully electric vehicle according to claim 1, characterized in that the peak torque is independent of a controlled rotational speed of the electric motor (1) in a range between zero and at least 80% of a maximum controlled rotational speed of the electric motor (1).

3. The method for operating a powertrain for or in a fully electric vehicle according to claim 1, characterized in that the peak torque is, or at least can be, generated in an entirety of an operational speed range of the electric motor (1).

4. A powertrain for or in a fully electric vehicle, which powertrain comprises an electric machine (1), a driven wheel (2) and a gearing (3) that is arranged between the electric machine (1) and the driven wheel (2) and that provides a driving connection there between, which gearing (3) includes at least a first speed reduction stage (31) providing a fixed first speed ratio between an input gear wheel (33) and an output gear wheel (34) thereof, whereof the input gear wheel (33) rotates as one with the electric machine (1), which gearing (3) further includes a variator unit (40) providing a variable speed ratio between an input shaft and an output shaft thereof, whereof the input shaft rotates as one with the output gear wheel (34) of the first speed reduction stage (31), and which gearing (3) yet further includes a second speed reduction stage (32) providing a fixed second speed ratio between an input gear wheel (35) and an output gear wheel (36) thereof, whereof the input gear wheel (35) rotates as one with the output shaft of variator unit (40), characterized in that a maximum overall speed ratio provided by the gearing (3) between the electric machine (1) and the driven wheel (2) is at least 20:1.

5. The powertrain according to claim 4, characterized in that the fixed first speed ratio provided by the first speed reduction stage (31) is in the range from 3:1 to 4:1.

6. The powertrain according to claim 4, characterized in that the fixed first speed ratio provided by the first speed reduction stage (31) is larger than the fixed second speed ratio provided by the second speed reduction stage (32).

7. The powertrain according to claim 4, characterized in that a ratio coverage of the variator unit (40), as defined by the mathematical quotient between a largest speed ratio and a smallest speed ratio thereof, is between 3.5 and 4.5.

8. The powertrain according to claim 7, characterized in that the largest speed ratio of the variator unit (40) is larger than an inverse value of the smallest speed ratio thereof.

9. The powertrain according to claim 8, characterized in that a diameter of the output shaft of the variator unit (40) is larger than a diameter of an input shaft of the variator unit (40).

10. The powertrain according to claim 8, characterized in that the variator unit (40) comprises an input pulley (42) on its input shaft, an output pulley (43) on its output shaft and a drive belt (41) that is wrapped around and in frictional contact with the input and output pulleys (42, 43) and in that an outer diameter of the input pulley (42) is smaller than an outer diameter of the output pulley (43).

11. (canceled)

12. The method for operating a powertrain for or in a fully electric vehicle according to claim 2, characterized in that the peak torque is independent of a controlled rotational speed of the electric motor (1) in a range between zero and at least 90% of a maximum controlled rotational speed of the electric motor (1).

13. The method for operating a powertrain for or in a fully electric vehicle according to claim 2, characterized in that the peak torque is independent of a controlled rotational speed of the electric motor (1) in a range between zero and at least 95% of a maximum controlled rotational speed of the electric motor (1).

14. The powertrain according to claim 4, characterized in that the maximum overall speed ratio provided by the gearing (3) between the electric machine (1) and the driven wheel (2) is at least 30:1.

15. The powertrain according to claim 4, characterized in that the fixed first speed ratio provided by the first speed reduction stage (31) is 3.6:1.

16. The powertrain according to claim 6, characterized in that the fixed second speed ratio provided by the second speed reduction stage (32) is 3.5:1.

17. The powertrain according to claim 7, characterized in that the ratio coverage of the variator unit (40), as defined by the mathematical quotient between a largest speed ratio and a smallest speed ratio thereof, is about 4.

18. The powertrain according to claim 8, characterized in that the largest speed ratio of the variator unit (40) is equal to 2.4:1 with the smallest speed ratio being equal to 1:1.67.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be explained in more detail by means of non-limiting, illustrative embodiments thereof and with reference to the drawing, in which:

[0013] FIG. 1 is a schematic representation of the functional arrangement of the main components of a known electric vehicle powertrain;

[0014] FIG. 2 is a schematic representation of the functional arrangement of the main components of a novel electric vehicle powertrain in accordance with the present invention; and

[0015] FIG. 3 is a graph illustrating the peak torque vs rotational speed characteristic of two differently specified electric machines.

DETAILED DESCRIPTION

[0016] 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 1 (EM), also known as a motor/generator device, two driven wheels 2 of the electric vehicle and a gearing 3 that drivingly connects the EM 1 to the driven wheels 2. In the embodiment of FIG. 1 the known gearing 3 provides a fixed speed ratio between the EM 1 and the driven wheels 2 by means of a gear train consisting of two speed reduction stages 31, 32 of two meshing gear wheels 33, 34; 35, 36 each that are arranged in series. An upstream gear wheel 33 of a first, i.e. upstream speed reduction stage 31 is directly driven by, i.e. rotates as one with the EM 1, preferably by being placed on a rotor shaft thereof. A downstream gear wheel 34 of the first speed reduction stage 31 rotates as one with an upstream gear wheel 35 of a second, i.e. downstream speed reduction stage 32, typically by being placed on a common shaft. A downstream gear wheel 36 of the second speed reduction stage 32 drives the driven wheels 2 through a differential gearing 37 for distributing a driving power between two or more driven wheels 2 of the electric vehicle through a drive shaft 38. Actually, the second speed reduction stage 32 can be embodied by a pinion wheel and a crown wheel of the differential gearing 37, i.e. as an integral part of the differential gearing 37.

[0017] The overall speed reduction ratio provided by the gearing 3 determines, on the one hand, a maximum attainable speed of the electric vehicle and, on the other hand, a maximum attainable torque level at the driven wheels 2 of the electric vehicle at standstill. In this respect it may be observed that, at least in theory, only a single speed reduction stage could be applied in the known electric vehicle powertrain. However, because of the relatively high maximum rotational speed of the EM 1, the speed reduction ratio that is required between the EM 1 and the driven wheels 2 would require an impractically sized gear wheels. In particular, a speed reduction ratio of more than 10:1, typically of around 12:1 is required from the gearing 3 overall.

[0018] As an improvement of the known electric vehicle powertrain of FIG. 1 and in accordance with the present invention, a variator unit 40, providing a continuously variable speed ratio between an input shaft and an output shaft thereof, is included therein, for example in the manner illustrated in FIG. 2. 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 of the variator unit 40 (not shown), such that a speed ratio provided by the variator unit between its input pulley 42 and its output pulley 43 can be continuously varied with a certain range. For example, in a largest speed ratio within such variator speed ratio range, a rotational speed of its output pulley 43 is maximally reduced relative to a rotational speed of its input pulley 42 by the drive belt 41 contacting the input pulley 42 at a small effective radius and the output pulley 43 at a large effective radius.

[0019] Evidently this latter, novel arrangement of the electric vehicle powertrain and of its gearing 3 in particular is more complex than the known arrangements without variator unit 40. However, according to the present invention, the novel arrangement favourably allows for a downsizing of the EM 1, such that the overall cost of manufacturing and/or the overall operating efficiency of the novel powertrain can in fact be improved.

[0020] In the graph of FIG. 3, a specific example is provided of the EM downsizing that is attainable with the novel powertrain. In particular, in the specific example of FIG. 3, a peak torque level of the EM 1 is reduced from 225 Nm in the known powertrain to 100 Nm in the novel powertrain. Moreover, the peak torque level of the downsized EM 1 is largely unrelated to its rotational speed. Additionally, in the specific example of FIG. 3, a maximum operating speed of the EM 1 is reduced from 16,000 rpm in the known powertrain to 12,500 rpm in the novel powertrain. To the contrary, the peak power of the downsized EM 1 in the novel powertrain has remained the same as that of the known powertrain at 120 kW.

[0021] To enable the EM downsizing illustrated in FIG. 3, the gearing 3 is specified as follows: [0022] the largest speed ratio of the variator unit 40 is 2.4; [0023] the ratio coverage of the variator unit 40 is 4; [0024] the speed reduction ratio of the first speed reduction stage 31 equals 3.6; and [0025] the speed reduction ratio of the second speed reduction stage 32 equal 3.5.

[0026] 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.

[0027] 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.