The present invention relates to an Electronical Control Unit (ECU) for a drive train system in a vehicle, a drive train system comprising such an ECU, the control of such a drive train system, a computer program product and a storage medium, such as a computer memory to be implemented in the ECU. In particular, the invention relates, in an aspect thereof, to the control of drive train systems of hybrid vehicles comprising an Internal Combustion Engine (ICE) and an Electrical Motor/Generator (EMG).
Because of the desire to manufacture vehicles with less impact on the environment when driving, e.g. lower fuel consumption and less noxious exhaust gases, there has been an increased interest in hybrid vehicles having a propulsion system comprising an Internal Combustion Engine (ICE) as well as an Electric Motor/Generator (EMG). The ICE and the EMG work in a complementary way such that the electric motor preferably is used in low speed conditions where there are frequent start and stops, e.g. in a city environment, while the ICE for example is preferably used when driving at relatively constant high speeds, e.g. on a high way.
One problem associated with the kind of propulsion system described above is that the complete system occupies more space than ordinary propulsion systems such as an ordinary vehicle only having an ICE or a purely electric vehicle. In addition to provide the vehicle with two propulsion units there is also a need of providing the vehicle with a system and devices for controlling the propulsion units and the drive train system in an efficient way which implies that further details are to be added to the vehicle. Hence, the arrangement of the drive train units in a hybrid vehicle is thus more space demanding and requires a more advanced control system in order to be able to take advantage of the benefits of having two separate propulsion units.
However, the hybrid vehicle will have certain benefits over both the vehicles mentioned above. The purely electric driven vehicle is not in general able to travel as long distances as an ordinary ICE driven vehicle due to limits of the maximum stored energy and the electric motor is usually not as strong as the ICE with slower accelerations and worse performance when a large torque is required, e.g. when starting and driving a heavy loaded vehicle, in steep uphills or when a fast acceleration is desired, for example at overtaking. The hybrid vehicle will thus not have these disadvantages since it may use the ICE when desired. Furthermore, the hybrid will have similar advantages as the electrical vehicle when there is a desire to drive the vehicle with low emissions and the hybrid vehicle may be driven by the electric motor under for example repetitive start and stop conditions or in a city environment where it is particularly desirable to lower the noxious emissions such as nitrogen oxides, carbon oxides or particles. Hence, the hybrid vehicle will have the benefit of lower fossil fuel consumption than ordinary vehicles using combustion engines and have a wider operating range and better driving characteristics, e.g. acceleration and power, than electric vehicles of today. Due to the above stated benign effects of using two propulsion units and an overall great potential in the future for hybrid vehicles, there is a desire to develop hybrid vehicles in spite of the more advanced and costly drive train system.
A number of different drive train systems and drive train control systems are described in for example U.S. Pat. No. 5,637,987; U.S. Pat. No. 6,887,180; U.S. Pat. No. 7,089,095; or GB 2 359 865. These systems thus provide different solutions about how to control a hybrid drive train system. However, the above described systems are rather complicated and it is a general desire when designing a hybrid drive train system and control features thereof to provide a compact system in order to avoid an unnecessary bulky and heavy construction.
A proposed solution to the problem of providing a compact system for a hybrid vehicle which at the same time is relatively simple in its set up is for example described in US 2007/0095584 wherein a hybrid drive mechanism having a single clutch is described. The system comprises an Internal Combustion Engine (ICE) having a drive shaft coupled to the shaft of an electric machine, i.e. an Electric Motor/Generator (EMG), via a clutch. The EMG is further connected to an input shaft of a mechanical transmission which in turn is connected via its output shaft to a differential transmission which distributes the driving force to the wheels on each side of the driven axle. However, one possible problem with such a compact system may be to manage to control the drive train system with a desired accuracy.
Hence, an important feature of the hybrid system is the control of the propulsion units and the drive train system so as to be able to benefit from the advantages of the two propulsion units. One major problem to deal with concerns the energy storage capacity of the electric motor and the regeneration of electricity. There is an almost constant need to generate electrical energy and store it in a battery or the like energy storage device since the capacity of the battery generally is rather limited. It is thus desirable to be able to manage the propulsion units in an efficient way such that the engine respectively the motor/generator may be used in an optimal way and that they are controlled in dependence of the State OF Charge (SOC) of the battery or energy storage device.
In addition to control the drive train system with such concerns as fuel efficiency, exhaust gas pollutions, e.g. carbon dioxide and NOx, and control the State Of Charge (SOC) of the battery, it is also desirable to keep the driving parameters such as acceleration properties, engine response to control actions and smoothness in gear shifting etc. at the same level as for ordinary vehicles, i.e. vehicles provided with only a ICE. Hence, there is a need of a new and improved control strategy in order to satisfy the demands for good drivability, energy efficient driving, control of the SOC of the battery and managing these desired properties while using a compact hybrid drive train system.
The invention relates, according to an aspect thereof, to a drive train system for a hybrid vehicle comprising an Internal Combustion Engine (ICE) located upstream in the drive train system of an Electric Motor/Generator (EMG). The ICE may be of any desired type, e.g. an Otto-engine or diesel-engine. The EMG may also be of any desired kind but should have the ability of working as an electric motor as well as a generator. The ICE is connected to the EMG via a Main Clutch (MC). The arrangement may thus be exemplified by an output shaft of the ICE connected to an input shaft of the EMG via a MC. The MC may be a friction clutch, such as a disc clutch, or a positive engaging clutch, e.g. a dog clutch. In general, a positive engaging clutch is desired in this position since a positive engaging clutch generally contributes with less energy losses than a friction clutch. The drive train system further comprises a mechanical transmission provided with at least one synchronized gear. The mechanical transmission is located downstream of said EMG and upstream of end actuators (wheels). In this context, the mechanical transmission is considered to involve any stepped gear selection device or transmissions which are able to change a speed ratio of an incoming shaft and an outgoing shaft. The transmission may for example be only a main gearbox or a main gearbox with one or several auxiliary gearboxes such as a split and/or range gear shift arrangements as described in EP 1 852 635. The drive train system is further connected to an Electronic Control Unit (ECU) for control of the drive train system. The drive train system according to an aspect of the invention is thus an automatic or semiautomatic system which receives control signals from the ECU. The invention is characterised, according to an aspect thereof, in that the ECU is programmed to perform a control sequence comprising the steps of:
a) Setting the drive train system in a generating mode when the vehicle is at standstill with its ICE running and there is a signal indicating that electric generation is desired. An indication of desired energy generation may for example be the State Of Charge (SOC) of the battery, an indicator of time at standstill conditions or a manually triggered signal indicating that electricity generation is desired. This standstill or idle generating mode includes the features of setting the MC to be engaged such that the EMG is rotating in a generating mode and the end actuators are decoupled by the use of a synchronized gear of the mechanical transmission set in neutral mode. The ICE and EMG are preferably controlled such that the ICE is working in an optimal manner concerning such aspects as (fuel) efficiency and low concentrations of noxious components in the exhaust gases while the rotational speed of the EMG preferably is optimised concerning an efficient generation of electricity. This is usually achieved by controlling the rpm of the ICE and the load on the EMG. Even though it would be possible to incorporate some kind of gear or transmission arrangement between the output shaft of the ICE and the input shaft of the EMG, in order to set the rotational speed of the input shaft for optimal generation of electricity at the desired idling speed of the ICE at regeneration, the gear ratio between the output shaft of the ICE and the input shaft of the EMG is usually 1:1, e.g. by using a positive engaging clutch such as a dog clutch, in order to avoid friction losses while keeping the system compact and simple.
b) Starting the change of mode from idle to driving as a response to an input signal to the ECU indicating that a motion of the vehicle is desired. This signal may for example be triggered by a gear change from neutral to forward or rear, pressing down of the accelerator pedal or release of a service brake/parking brake or any other suitable indication of a status or change of status of a relevant parameter.
c) Disengage the MC such that the ICE and EMG are disengaged from each other. By disengaging the ICE from the EMG, the rotational speed of the EMG may be decreased rather quickly. Furthermore, the synchronization arrangement of the above mentioned synchronized gear, which was used to decouple the end actuator (e.g., vehicle wheels) from the EMG and ICE, is engaged. By engaging the synchronization arrangement of the gear, which earlier was set in neutral mode, it will be possible to transmit a torque to the end actuators from for example the inertial forces while retarding the rotational speed of the EMG. An advantageous feature by using this control method is that there will be a faster response of the start up of the vehicle in response to a signal indicating that a motion of the vehicle is desired. As described in the control method in US 2007/0095584, there is a waiting time from the point of time it is indicated that a change from a generative, still standing mode to moving of the vehicle is desired due to the waiting for the slow down of the EMG to zero or close to zero before the gear is shifted from neutral to a selected gear. This waiting time may be annoying for the driver who is used to feel a response directly to his control actions. Hence, the present control method will make the vehicle start to move more quickly as a response to an appropriate input signal indicating a motion of the vehicle is desired. Hence the synchronization procedure and the synchronized gear will be used in order to transmit a torque from the EMG, (preferably via inertial forces of the EMG and associated shafts), to the end actuators, e.g. wheels in the case of an ordinary car, truck or bus. In addition to be able to use the energy stored as inertia forces in the system to provide an immediate response to the desire to move, it will also have the benefit of using mechanical energy directly without the need of converting it to electrical energy before it is reconverted to mechanical energy or, still worse, brake the rotation of the EMG by the use of a friction brake or the like device such that the inertial energy is lost as friction. The overall energy efficiency may thus be improved by the use of the control strategy herein described. Still another advantage is that the retardation of the rotational speed of the EMG while setting the vehicle in motion by the use of the synchronization arrangement will also contribute to a smooth start of the vehicle. Hence, the EMG will retard due to the braking force of the synchronization of the mechanical transmission and at least a part of the inertial energy of the EMG will be transferred to the end actuators and the vehicle will smoothly start to move.
d) When the EMG has slowed down enough such that the rotational speed is within the speed limit to engage the positive coupling of the synchronized gear, the EMG and the end actuators will be connected by the positive coupling of the synchronized gear. Hence, the EMG may now start to work as a motor and be the power source of the vehicle during start and acceleration of the vehicle.
The above described drive train system may of course work for a variety of hybrid vehicles and is for example suitable for a vehicle provided with such a system as described in US 2007/0095584. However, it most advantageous use may be for vehicles which have frequent starts and stops, e.g. local buses, mail van or a refuse lorry.
The invention, in an aspect thereof, also relates to a method for the control of a drive train system of a vehicle. The drive train system comprises an Internal Combustion Engine (ICE) located upstream in the drive train system of an Electric Motor/Generator (EMG). The ICE is connected to the EMG via a Main Clutch (MC). The drive train system further comprises a mechanical transmission (MT) provided with at least one synchronized gear. The mechanical transmission is located downstream of the EMG and upstream of end actuators, e.g. wheels. The drive train system is further connected to an Electronic Control Unit (ECU) for control of the drive train system. The method for control of the drive train system comprises the steps of:
a) Setting the drive train system in a generating mode when the vehicle is at standstill or idle with its ICE running while the MC is engaged such that the EMG is rotating in a generating mode and the end actuators are decoupled by the use of a synchronized gear set in neutral mode.
b) Preparing a control sequence for the change of driving mode from idle to driving as a response to a signal in the ECU indicating that a motion of the vehicle is desired. The signal indicating that a motion of the vehicle is desired may be received as such a signal by the ECU or computed by the ECU from sensed conditions in the drive train system and/or parameters relevant to the driving conditions and the condition of the vehicle in general.
c) Disengaging the MC such that the ICE and EMG are disengaged from each other and engaging the synchronization arrangement of the above mentioned synchronized gear, which were used to decouple the end actuator from the EMG and ICE, in order to transmit a torque from the rotating EMG and associated axles to the end actuators while the EMG is slowing down. Preferably, the MC is disengaged before the synchronization arrangement of the gear is engaged in order to avoid wear of the MC and/or the synchronization arrangement. However, these operations may slightly overlap if the MC and synchronization arrangement are dimensioned for such a control strategy and it is desired to speed up the procedure and make the change occur more rapidly.
d) Engage the positive coupling of the synchronized gear when the rotational speed of the EMG and the shaft connected to the end actuators are within the engaging speed limits. When this step is finished it is of course possible to once again allow the vehicle to be powered by the ICE, provided that the rotational speed of the EMG is within the range where the ICE may be connected to the EMG, by connecting the output shaft of the ICE to the input shaft of the EMG by engaging the Master Clutch. In order to control the acceleration of the vehicle, it is important to select the gear such that a desired gear ratio is achieved. Generally, a low gear, or in most cases, the lowest gear, is to be selected when starting to move the vehicle from a still standing, generating mode. The selection of an appropriate gear at start up follows in general essentially the same gear shift pattern as used for a hybrid starting up with its EMG as the power source or the limits for the gear shift pattern may be slightly amended to shift up to start at a higher gear due to the additional starting force from the inertial energy from the EMG.
Still another feature which is important for the acceleration force is the pressure by which the shift fork is pressed against the synchronization cone. On one hand, there is of course a desire to use a high pressure in order to achieve a fast response to start the moving of the vehicle. On the other hand, the fork pressure in the synchronization arrangement should not be too high to avoid a jerky or abrupt start which may be inconvenient for drivers or passengers and such an abrupt start may also cause wear of the drive train system due to large reaction forces when starting. In addition, the wear of the synchronization arrangement and the surfaces of the cones should be considered such that the synchronization arrangement is not worn out too fast. It may of course be possible to use different synchronization arrangements if there are several synchronization arrangements available in the mechanical transmission in order to not wear out one, single synchronization arrangement too fast.