Electric drive system of a hybrid or electric vehicle

Abstract

Electric drive system of a hybrid or electric vehicle comprising at least a first and a second battery pack, said first battery pack being formed by a first plurality of equal cells, wherein a cell of said first plurality of cells identifies a first predetermined C-rate coefficient (power/capacity) and said second battery pack being formed by a second plurality of equal cells, wherein a cell of said first plurality of cells identifies a second predetermined C-rate coefficient (power/capacity) higher than said first predetermined coefficient, and wherein the drive system comprises at least a first and a second set of electromagnetic induction windings, respectively independently powered by said first and second battery pack by means of relative first and second inverter.

Claims

1. An electric drive system of a hybrid or electric vehicle comprising a transmission and at least a first (BA) and a second (BB) battery pack, said first battery pack being formed by a first plurality of cells, equal between each other, wherein one cell of said first plurality of cells identifies a first predetermined C-rate coefficient, namely a first predetermined cell power/capacity ratio, and said second battery pack is formed by a second plurality of cells, equal between each other, wherein one cell of said second plurality of cells identifies a second predetermined C-rate coefficient, namely a second predetermined cell power/capacity ratio greater than said first predetermined C-rate coefficient, and wherein the drive system comprises at least a first (CA) and a second (CB) set of electromagnetic induction windings to cause at least one rotor (RT) connected with said transmission to rotate, respectively independently powered by said first and by said second battery pack via respective first (IA) and second (IB) inverters, wherein the first battery pack (BA) drives the first inverter (IA) and the second battery pack (BB) drives the second inverter (IB), wherein the first inverter is always active delivering all power levels comprised between 0 and a predetermined threshold that is a fraction of a maximum power deliverable by the first battery pack, and the second inverter is activated for supplementing the first inverter when the first battery pack has reached the predetermined threshold.

2. The system according to claim 1, wherein said first (CA) and said second (CB) electric induction windings are wound on a single ferromagnetic core of a single electric motor (M), sharing the same magnetic circuit, or are wound on two independent ferromagnetic cores of as many first and second electric motors (EM1, EM2).

3. The system according to claim 2, wherein when said first (CA) and said second (CB) electric induction windings are wound on the same ferromagnetic core and when both said first and said second inverters are active, they are mutually synchronised in order to generate respective magnetic inductions that are isofrequential with the same phase between one another.

4. The system according to claim 3, wherein when said second set of windings is spatially phase-shifted with respect to said first set of windings, said second inverter is configured to compensate said spatial phase-shift by means of a time phase-shifting of the voltages and currents to obtain that respective magnetic inductions are isofrequential with the same phase between one another.

5. The system according to claim 2, wherein said single electric motor (M) or said first and said second electric motors (EM1, EM2) has/have a radial or axial flux, or said single electric motor (M) or said first and said second electric motors (EM1, EM2) is/are separately excited synchronous motors or brushless DC motors.

6. The system according to claim 2, wherein said first set of magnetic induction windings have a number of phases different from a number of phases of said second set of magnetic induction windings.

7. A control method for a drive system according to claim 1 by means of a processing unit, the method comprising the steps of; (I) constantly activating said first inverter and activating said second inverter when a required power exceeds the predetermined threshold that is the fraction of a maximum power that can be delivered/received by said first battery pack, and (II) varying said threshold in order to obtain a predetermined ratio between charging states of said first and said second battery pack.

8. The method according to claim 7, wherein said first and said second steps are carried out both in the discharging phase and in the regenerative charging phase of said first and said second battery pack.

9. A computer program comprising program-coding means adapted to carry out the steps (I-II) according to claim 7, when said program is run on a computer.

10. Computer readable means comprising a stored program, said computer readable means comprising program-coding means adapted to carry out the steps (I-II) according to claim 7, when said program is run on a computer.

11. A composition method of said first (BA) and said second (BB) battery pack according to claim 1, comprising the following steps: acquiring a first target value CT of a total capacity given by the sum of the capacities of said first and said second battery packs; acquiring a second target value PT of a total deliverable power given by the sum of the powers deliverable by said first and by said second battery pack; acquiring a first capacity value C1 and a first power value P1 of a cell of said first plurality; acquiring a second capacity value C2 and a second power value P2 of a cell of said second plurality, wherein the first capacity value C1 is lower than the second capacity value C2; calculating a first amount A of said first plurality and a second amount B of said second plurality according to the following system of two equations 1) and 2) in two unknowns A and B:
A*C1+B*C2=CT  1)
A*P1+B*P2=PT,  2) wherein the first inverter is substantially always activated, whereas when the required electric power exceeds the first battery pack the second inverter driven by the second battery pack is activated to supplement the first inverter up to a maximum total deliverable power.

12. An electric or hybrid terrestrial vehicle comprising a first axle (A1) and a second axle (A2) and at least a drive system according to claim 1 associated with at least one of said first and second axles.

13. A hybrid vehicle according to claim 12, comprising an internal combustion engine (ICE) configured for driving a first axle (A1) into rotation by means of a first transmission and wherein a single electric motor (M) is operatively associated to said first transmission.

14. The hybrid vehicle according to claim 12, comprising an internal combustion engine (ICE) configured for driving a first axle (A1) into rotation by means of a first transmission and wherein a single electric motor is operatively associated to a second vehicle axle (A2) different from said first axle (A1).

15. The hybrid vehicle according to claim 12, comprising an internal combustion engine (ICE) configured for driving a first axle (A1) into rotation by means of a first transmission and wherein said two or more set of windings are wound on two independent ferromagnetic cores of as many first and second electric motors (EM1, EM2), wherein said first electric motor (EM1) is operatively associated to said first transmission and said second electric motor (EM2) is operatively associated to a second vehicle axle (A2) different from said first axle (A1).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further objects and advantages of the present invention will become clear from the following detailed description of an embodiment thereof (and its variants) and from the annexed drawings given purely by way of explanatory and non-limiting example, in which:

(2) FIG. 1 shows an exemplary scheme of an electric drive system of a hybrid or electric vehicle according to the present invention;

(3) FIG. 1a shows a detail of FIG. 1.

(4) The same reference numbers and letters in the figures identify the same elements or components.

(5) FIG. 2 shows an exemplary diagram of the system of FIG. 1, also showing the recharging section of the relative batteries;

(6) FIGS. 3a and 3b show two different arrangements of sets of windings wound on a same ferromagnetic core;

(7) FIG. 4 shows an example of implementation in a hybrid all-wheel drive car.

(8) In the context of the present description, the term “second” component does not imply the presence of a “first” component. These terms are in fact used only for clarity's sake and are not to be meant in a restrictive manner.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) A battery pack must be supposedly sized to store an electric energy of 16 kWh, needing a power of 150 kW.

(10) The C-rate corresponds to 150/16=9.375.

(11) In the hypothesis in which all the cells, regardless of the relative C-rate, have the same nominal voltage (50% of SOC), e.g. 3.68 V, this means that a total storage capacity of about 16 kWh is required.

(12) Supposedly, there is a cell of a first type characterized by a storage capacity of 257 Wh and a power of 1.08 kW and a cell of a second type characterized by a storage capacity of 96 Wh and a power of 2.16 kW.

(13) The first battery expresses a C-rate of 1080/257=4.2 and the second battery expresses a C-rate of 2160/96=22.5.

(14) Two equations with two unknowns are obtained:
A*96+B*257=16  1)
A*2.16+B*1.08=150  2)

(15) A represents the number of cells of the first type, whereas B represents the number of cells of the second type.

(16) The resolution of a system formed by the preceding two equations 1) and 2) identifies the two unknowns A and B, in which A=45 and B=46.

(17) Such two battery packs allow obtaining the desired performance regardless of the availability of cells having that corresponding C-rate.

(18) The method can be summarized by the following steps: acquisition of a first CT target value of total capacity given by the sum of the capacities of the first and of the second battery pack; acquisition of a second target value PT of total deliverable power given by the sum of the powers that can be supplied by the first and by the second battery pack; acquisition of a first capacity value C1 and of a first power value P1 of a cell of the first plurality of cells defining the first pack; acquisition of a second capacity value C2 and of a second power value P2 of a cell of the second plurality of cells defining the second pack; calculation of a first numerosity A of said first plurality and of a second numerosity B of said second plurality according to the following system of two equations 1) and 2) in two unknowns A and B:
A*C1+B*C2=CT  1)
A*P1+B*P2=PT;  2)

(19) FIG. 1a shows an example of an electric drive system according to a preferred example of the present invention. It is clear that the first battery pack BA is connected to a corresponding inverter IA, which feeds a first set CA of windings wound on a ferromagnetic core of an electric motor M. Moreover, the second battery pack BB is connected to a corresponding separate inverter IB and is separated from the inverter IA to feed a second set CB of windings wound on the same aforementioned magnetic core of an electric motor M.

(20) Preferably, said magnetic core defines a stator of said electric motor M.

(21) Therefore, FIG. 1a schematically shows a single electric motor M with the two sets of windings CA and CB that are wound on it. The fact that the set CB is represented externally with respect to the set CA is not to be considered limiting.

(22) With reference to FIGS. 3a and 3b, a rectified stator is shown. The windings belonging to the two sets CA and CB can share the same slots or alternate in adjacent slots. They can also share the same slots and be arranged so that they are alternately proximal to the air gap (solution not shown).

(23) Since the battery packs are characterized by different powers, the sets of windings can also be sized to support these respective powers. For example, the number of turns, their cross-section and the respective amounts of copper can vary freely between one set of windings and another, in addition to the fact that each set can have a different number of phases. For example, the first set consists of three phases, while the second set consists of four phases. The inverters are configured to generate two respective synchronized magnetic fields, i.e. so that the relative rotary phasors are constantly superposed on top of each other.

(24) FIG. 1 further shows that each inverter is connected to the electric motor M by means of a three-wire line. Also this is not to be considered limiting, since each set of windings CA and CB can have any number of phases.

(25) In the case in which the number of the phases of a set differs from the number of phases of the other set of windings or, despite having the same number of phases, if it were not possible to arrange a first phase of the first set in the same angular position as the first phase of the second set as a whole, as shown in FIG. 3a, the inverters are driven so as to compensate for this structural angular displacement by means of a time displacement of the generated relative rotary magnetic field.

(26) It is now assumed that in the drive system of the present invention the first BA battery pack is formed of cells having a first C-rate, i.e. a ratio between power (instantaneously deliverable energy) and energy storage capacity lower than the second C-rate that characterizes the cells of the second BB battery pack.

(27) According to a preferred method of operation of the present drive system, the first inverter, associated with the first battery pack, is always active delivering all power levels comprised between 0 and a predetermined threshold that is a fraction of the maximum power deliverable by the first battery pack. The second inverter, on the other hand, is activated for supplementing the first inverter when this latter has reached said predetermined threshold. For this reason, this threshold is hereinafter referred to as the “overlap threshold”.

(28) For example, said “overlap threshold” can be permanently set to the value 0.95 of the maximum power deliverable by the first battery pack.

(29) Assuming that the driver has a very moderate driving style, it is likely that the first battery pack will run out, leaving the second battery pack fully charged. Since very intense current flows can be generated in abrupt regenerative braking, it is advisable to guarantee a certain capacity in the second battery pack to store them. Therefore, the overlap threshold must be such as to guarantee a certain capacity even in the second battery pack.

(30) The different discharging and recharging dynamics of the two battery packs depends on the overlap threshold, on the difference between the total capacities of the battery packs, on the driver's driving style.

(31) These factors are all interrelated with each other.

(32) The greater the difference between the two overall capacities, the higher the overlap threshold must be, and vice versa, the more similar the capacity of the two battery packs, the lower the overlap threshold must be.

(33) The more aggressive the driving style, the higher the overlap threshold must be to avoid a sudden discharging of the second battery pack and a consequent sudden reduction in the vehicle performance.

(34) It is therefore evident that the overlap threshold can be a function of several variables, among which the difference (or the ratio) between the overall energy storage capacities of the two battery packs and their charging state, which depends on the driving style of the driver.

(35) In other words, the overlap threshold can be continuously varied so as to constantly maintain a predetermined ratio between the charging states of the two battery packs.

(36) Advantageously, during regenerative braking, having the possibility of storing energy in both the battery packs, it is advantageous to continue distributing the available energy between the two battery packs so as to keep said ratio between the charging states unchanged.

(37) It is also advantageous to size the battery packs in such a way as to supply the same rated voltage. This makes also the management of the inverters easier.

(38) FIG. 2 shows a variant of the diagram of FIG. 1, in which the portion relating to the recharging of the batteries is also evident through a “Charger” power supply connected to an external electric network.

(39) If the two battery packs have the same rated voltage, then the operations of connection and disconnection from the power supply can be carried out directly by the electronics on board the battery packs.

(40) The present invention can be validly applied both to pure electric vehicles, i.e. not equipped with further prime engines with respect to the electric motors supplied by the present drive system, or to hybrid vehicles, namely in combination with an internal combustion engine.

(41) The electric motor may be operatively associated to the same transmission to which the crankshaft of the internal combustion engine is connected or it can be connected to a dedicated transmission. For example, the internal combustion engine is operatively connected to the rear axle of a vehicle, whereas the electric motor M is operatively connected to the front axle of the same vehicle.

(42) According to another preferred variant of the invention, the two sets of windings CA and CB are respectively wound on the ferromagnetic cores of as many different motors EM1 and EM2.

(43) With reference to FIG. 4, in which a VHE vehicle is schematically shown, the first electric motor EM1 is associated with a first axle A1, while the second electric motor EM2 is associated with a second axle A2.

(44) Optionally, an internal combustion engine ICE is also connected to the second axle, equipped with a relative transmission GB, for example, shared with the second electric motor EM1.

(45) FIG. 4 is schematic and the fact that the transmission GB is shown between the internal combustion engine ICE and the electric motor EM1 does not mean that this latter cannot be arranged between the heat engine and the gearbox GB.

(46) From the configuration shown in FIG. 4 different variants can be obtained, e.g. by associating the first motor EM1 to the first battery pack (not shown) with a C-rate greater than the second battery pack, in turn associated with the second electric motor EM2, or vice versa.

(47) The examples shown here are based on the use of two battery packs, but it is possible to use any number of battery packs made up of cells characterized by a C-rate different from the one of the cells that make up the other battery packs, in which each battery pack has a relative inverter that feeds one and only set of magnetic induction windings, namely its own.

(48) This can be advantageous, for example, when the shape of some batteries is better suited to form a battery pack suitable for being housed in a predetermined vehicle compartment.

(49) The operation of the inverters can be managed by a dedicated processing unit or can be managed by the on-board control unit. The same functionality can also be introduced in the ECU (Engine control unit), which oversees the operation of the internal combustion engine in the case of hybrid vehicles.

(50) The present invention can be advantageously manufactured by means of a computer program, which comprises coding means for carrying out one or more steps of the method, when this program is run on a computer. Therefore, it is intended that the scope of protection extends to said computer program and also to computer readable means comprising a recorded message, said computer readable means comprising program-coding means for carrying out one or more steps of the method when said program is run on a computer.

(51) Modifications to the embodiments of the described non-limiting example are possible without departing from the scope of the present invention, including all equivalent embodiments for a person skilled in the art.

(52) From the above description, the person skilled in the art is able to manufacture the object of the invention without introducing further manufacturing details. The elements and features shown in the various preferred embodiments, including the drawings, may be combined with each other without however departing from the scope of protection of the present application. What has been described in the part relating to the state of the art only requires a better understanding of the invention and does not represent a declaration of existence of what has been described. Moreover, if not specifically excluded in the detailed description, what has been described in the part relating to the state of the art is to be considered as an integral part of the detailed description.