VEHICLE POWERING SYSTEM

TECHNICAL FIELD

The present invention relates to a vehicle drive system comprising at least one combustion engine that operates with frequency modulation, said engine being provided with at least one cylinder, and a drive shaft of a vehicle, said drive shaft being driven by energy from said engine.

The invention also relates to a method of driving a vehicle, by which mechanical power is generated by means of a frequency modulated operation of a combustion engine.

By engines that operate with frequency modulation the combustion engine, for the enabling of its frequency modulated operation, com- ^' prises freely operable engine valves, in particular the inlet valves, but preferably also the outlet valves, for the introduction of combustion air or combustion air and fuel and for the exhaustion of exhaust gases.

Preferably, said valves are pneumatically, hydraulically or electro magnetically activated.

BACKGROUND OF THE INVENTION

Prior art discloses combustion engines that work with frequency modulation for the propelling of a vehicle. The frequency modulation requires that the cam shaft-driven engine valves of contemporary technique are substituted by freely operable valves. A frequency modulation makes it possible to achieve high efficiency at low engine loads. In urban traffic situations the cam shaft-provided Otto-engines

present, a low efficiency, often down to 5-10%, at low engine loads. By means of a frequency modulation, the efficiency at low engine loads may increase substantially. Within said range of engine loads, the efficiency may even be doubled. The frequency modulation in- eludes that individual cylinders of the engine are permitted to skip power strokes, combustion strokes, in accordance with the momentary need of power or torque. When freely operable engine valves are used, the opening and closure of which can be controlled from a control unit provided with a suitable soft ware, there is, at least theo- retically, no limits for how many power strokes that can be skipped. Those power strokes that occur are powerful and have high efficiency.

By combustion engines that operate with frequency modulation in practice there has, however, been criticism to the fact that the varia- tions of the amplitude of the torque in the driveline becomes large and result in an unacceptably uneven propelling of the vehicle. The problem is of such a magnitude that it is assumed that car drivers will not accept such engine operation, though there is a large saving of fuel.

THE OBJECT OF THE INVENTION

It is an object of the present invention to remedy the problem of uneven propelling of a vehicle that is propelled by a combustion engine working with frequency modulation. At the same time, the substantially higher efficiency of the combustion engine working with frequency modulation should be taken advantage of.

SUMMARY OF THE INVENTION

The object of the invention is achieved by means of the initially defined vehicle drive system, which is characterised in that it com-

prises a generator that is driven by the combustion engine, and an electric motor that is driven by electric power produced by the generator, and that said electric motor propels the drive shaft. In that way the uneven operation of the combustion engine at a low fre- quency of power strokes is not transmitted to the drive shaft, but is absorbed by the generator. The generator, in its turn, provides the electric motor with the electric power that is required at the moment by the latter for the driving of a drive shaft of the vehicle in accordance with the torque or power that has been ordered by the driver or any corresponding function of the vehicle. Suitably, suitable power electronics for this purpose is arranged between the generator and the electric motor. Thanks to the invention, a new variant of a so called serial hybrid, that combines the advantages of a combustion engine operating with frequency modulation and the advantage of electric motor operation is provided.

Preferably the vehicle drive system comprises an electric accumulator and/ or an electric capacitor to which the generator delivers electric energy, wherein the accumulator and/ or the capacitor is /are adapted to, upon request, deliver electric energy to the electric motor.

Thereby, when the need of energy of the electric motor is very small or even reduced to zero, electric energy generated by the combustion engine may by used in an efficient way. Here, one advantage may be that the combustion engine, even if it is permitted to operate at its lowest power, does not need to be completely turned off at such occasions. Preferably, there is power electronics between the accumulator and/ or the capacitor and drive shaft that enables brake energy, i.e. electric energy generated through the braking to be charged in the accumulator and/ or the capacitor, in order to be used later for the propelling of the electric motor.

According to a preferred embodiment the combustion engine corn- prises a plurality of cylinders, which are arranged to individually and singularly be set in operation for the driving of the generator or be turned off. In that way, it will be possible to, upon need thereof, pro- gram a control unit that, for example, controls the inlet and outlet valves of the individual cylinders, to individually exclude one or more cylinders, thereby permitting the remaining cylinder or cylinders to operate in an optimum range of rotations per minute with optimum power strokes with regard to the energy yield. An optimum power stroke is here referred to as a stroke by which the work that is performed during the power stroke, with regard to the economical, environmental and other practical facts, is as large as possible in relation to the consumed amount of fuel for said work. By providing the mo ^¬ mentary need of torque with a frequency of optimum power strokes, a best possible driving economy is achieved.

An optimum power stroke during a four-stroke operation includes that the inlet valves are permitted to close relatively early in relation to what is common in contemporary engines, and that the outlet valves are permitted to open relatively late in relation to what is common. Accordingly Miller and Atkinson cycles become a natural part of the operation. By means of an engine experiment it is possible to check the individual setting that the included parameters and control values should have at each rotational speed of the engine. As an alternative, the control system may be adapting, that is self- teaching.

At least one of said cylinders is arranged so as to operate with frequency modulation. In those cases when not all cylinders are arranged so as to operate with frequency modulation, and one or more of the cylinders are arranged to be turned off in connection to a low or none need of power, it is preferred that the cylinders that are

not arranged to operate with frequency modulation are excluded first from operation.

According to a preferred embodiment, all cylinders of and a combus- tion engine are arranged to operate with frequency modulation. When the need of power of the electric motor decreases below a certain level, it is preferred that each of these cylinders is permitted to operate with a reduced frequency of power strokes. For example, if the engine has four cylinders, each of said cylinders may skip each forth power stroke (in other words, this may be regarded as that an intake stroke is displaced one rotation as the inlet valves are not opened until next rotation of the engine) whereby a so called empty stroke is obtained, in order to achieve a total decrease of the number of power strokes per time unit, instead of reducing the speed of each cylinder. Thereby, the engine may, in accordance with the principle of frequency modulated operation, operate with an optimum rotation of speed with regard to the energy efficiency, even when the need of energy of the electric motor becomes extremely small.

In order to achieve a suitable, preferably optimum, control of the operation of the combustion engine, the fuel drive system comprises a control unit that, based on the ordered power from the electric motor, decides the rotational speed of the combustion engine and how many cylinders that are to be activated for the driving of the generator and/ or with which frequency of power strokes that the individual cylinders are to operate.

According to a preferred embodiment, the vehicle drive system according to the invention comprises a first and a second combustion engine, a corresponding first and second generator wherein the first combustion engine drives the first generator and the second combustion engine drives the second generator, and a first and a second

electric motor, wherein the first generator delivers electric power to the first electric motor and the second generator delivers electric power to the second electric motor, and the first electric motor drives a first drive shaft of the vehicle and the second electric motor drives a second drive shaft of the vehicle. Thanks to this solution it will be possible, for example in a car, to either have a separate driving of the front shaft and the rear shaft or to have a separate driving of the front wheels or the rear wheels. It is also conceivable with a plural wheel-driven vehicle, for example a four wheel drive vehicle, in which a separate driveline comprising a combustion engine, a generator, an electric motor and a drive shaft is arranged for each of the wheels.

Preferably, said combustion engine is arranged so as to operate with a varying rotational speed and a varying load depending on the mo- mentary need of electric power of the electric motor. In that way, the need of a large accumulator of electric energy and/ or a large electric capacitor for charging of energy from the combustion engine is reduced.

The object of the invention is also achieved by a method as initially defined, characterised in that the combustion is used for the driving of a generator for the generation of electric energy to an electric motor that drives a drive shaft or a plurality of shafts of the vehicle.

Further features and advantages of the vehicle system according to the invention will be shown in the following, detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, by way of example, the invention will be described more in detail with reference to the annexed drawing, on which:

Fig. 1 is an oversight view showing important parts of a vehicle drive system according to the invention.

Fig. 2 is an oversight view of an alternative embodiment of the vehicle drive system according to the invention.

Fig. 3 is an oversight view showing somewhat more in detail the vehicle drive system according to fig. 1.

Fig. 4 is an oversight view showing a further embodiment of the vehicle drive system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 is a oversight view showing important parts of a vehicle drive system according to the invention. The drive system comprises a combustion engine 1 operating with frequency modulation, a generator 2 driven thereby, an electric motor 3 which is provided with electric power from the generator, and a drive shaft 4 driven by the electric motor 3 for the propelling of one or more wheels 5 of the vehicle.

Further, the system comprises a torque order gauge or power order gauge 6, in this case represented by a driver-operated gas pedal of a vehicle. Other types of torque order gauges are, of course, also possible, and they need not be directly controlled by a driver. As an example, this might be a speed control function or function in which the need of torque is automatically controlled upon basis of, for example, the distance to a vehicle in front of the vehicle in question or upon basis of a speed limit registered by the vehicle and its components.

The vehicle drive system also comprises a control unit 7, that may be any type of central computer unit provided with a suitable software for the control of a plurality of functions in the system. Suitably the control unit 7 is operatively connected to the torque order gauge 6, and to the combustion engine 1 , for example for the control of the valves thereof, to the generator 2 and to the electric motor 3. The functions, or the control of these components will, basically, be regulated through the torque order gauge 6. In more advanced systems, in which the roll of the driver may be of minor importance, it is conceived that the torque order gauge forms a part of the control unit or a part of the soft ware of the latter.

Fig. 2 shows an alternative embodiment of a vehicle drive system, that comprises a plurality of modules each of which comprises a combustion engine 1 operating with a frequency modulation and a generator 2 driven thereby. The generators 2 of all modules are connected to a common electric motor 3. In accordance with the torque or power ordered by the torque order gauge 6, the control unit 7 regulates how many of the modules that, at the moment, are to oper- ate actively to provide energy to the electric motor 3. The disengagement of a module may comprise that the combustion engine 1 connected thereto is turned off. According to a preferred embodiment, each of the combustion engines 1 is provided with only one cylinder 10. One or more, preferably all of these engines 1, are arranged so as to operate with frequency modulation. Since the inlet and outlet valves of the engines 1 are not connected to any cam shaft, but are, for example, pneumatically operated, the individual positioning of the cylinders 10 may differ from the one that is common of contemporary engines provided with cam shafts. As an alternative to what is shown in fig. 2, it is conceivable that a plurality of or all the engines are connected to a common generator, which, in its turn, feeds one or more electric motors.

Fig. 3 shows somewhat more in detail, an embodiment of a part of a vehicle drive system according to the invention. Apart from what has been shown in figs. 1 and 2, fig. 3 also shows the existence of an electric accumulator formed by a battery 8, and power electronics 9 suited for the transmission of electric power between the generator 2 and the electric motor 3. The battery is, preferably, arranged to accumulate surplus energy from the generator 2, i.e. such energy that is not immediately required for the operation of the electric mo- tor 3. Further, the battery 8 may, upon basis of control signals from the control unit 7, be arranged to deliver energy to the electric motor 3 as a supplement to the electric energy that is delivered to the latter by the generator 2. The battery 8 may also, in a way known per see, act as an energy source for the driving of a start engine (not shown) for the starting of the combustion engine 1. The invention also comprises embodiments in which the battery 8 is periodically the only distributor of the electric power to the electric motor 3. The battery 8 may, if there are only low requirements on its capacity, be replaced by a capacitor.

The power electronics 9 comprises electronics known per see required between a battery 8 and the electric motor 3 and between a generator 2 and the electric motor 3 for the transmission of the electric power provided by the battery or the generator to a form suitable for the driving of the electric motor. Such electronics may for example comprise rectifiers etc. It may also comprise such components that are required for the transmission of energy obtained during motor braking to the battery 8.

Fig. 4 shows a further embodiment of the invention, by which there are two separate drivelines, from the combustion engine 1 to the output shaft 4 of the electric engine 3, wherein said drivelines drive two

separate wheels 5 of one and the same vehicle. The battery 8 also forms a component shared by the two drivelines. As to the rest, the drivelines do not differ from the ones described previously.