GB2355241A - A vehicle hill descent control arrangement - Google Patents

Abstract

In a hill descent control arrangement for a hybrid drive vehicle having a heat engine 1, a generator 2 and a motor 3 for traction wheels 4, the motor 3 provides regenerative braking by supplying a driving electrical power to the generator 2 to drive the engine 1 and so act as an energy sink to facilitate braking of the wheel 4. A controller 6 monitors operation such that a generated electrical power is provided to the motor 3 in order to drive the wheel 4. However, once such generated electrical power is no longer required the controller 6 arranges for the motor 3 to provide the driving electrical power to generator 2 in order to maintain engine speed 1 despite removal of application of fuel to the engine 1. In such circumstances, efficient braking through the motor 3 upon the wheel 4 can be maintained despite a traction battery 5 reaching capacity or that battery 5 can be arranged to dissipate electrical power through driving the generator 3 and so the engine 1 such that at least a proportion of the driving electrical power from the motor 3 during regenerative braking can be provided and stored in the traction battery 5 as required.

Description

2355241 A Vehicle Hill Descent Control Arrangement The present invention

relates to a vehicle hill descent control arrangement and more particularly to such an arrangement used with regard to hybrid vehicles which combine a heat engine with electric motor propulsion.

Clearly, control of a vehicle is highly important in order maintain safety and direction for manoeuvring. Thus, with regard to most vehicles it is common to use so-called engine braking in order to control vehicle speed upon a hill descent.

The present invention relates particularly to so-called hybrid vehicles in which electric motors are used to provide propulsion for the vehicle. Electrical power for these electrical motors is provided either from a generator or a battery or other source of electrical power. It will also be understood that where required these electrical motors can be configured in order to return electrical power to the battery or other storage device in order to provide so-called regenerative braking to conserve and extend vehicle endurance.

Hybrid vehicles can be of a series or parallel configuration. Typically, there is a traction battery included in both series and parallel configurations however, it is possible to have a series hybrid configuration in which there is no traction battery and the heat engine directly drives an electrical generator to provide electrical power to the propulsion motors. Similarly, a traction battery in a hybrid vehicle can be configured as a series string or a parallel string of individual battery cells or units.

In a series configuration as depicted in Figure 1, a heat engine 1 is coupled to an electrical generator 2 such that electrical power is provided to electrical motors 3 for each respective wheel 4 and/or to a traction battery 5 in order to store the excess electrical power provided by the generator 2. Operation of the engine 1, generator 2 and motor 3 is controlled by a controller 6. Thus, it will be appreciated that the propulsion provided through the motor 3 to the wheel 4 can be specifically controlled to meet vehicle driver demands and operating conditions.

A parallel hybrid configuration is depicted in Figure 2. Thus, a heat engine is 5 coupled to a transmission 20 through which a parallel electric motor 30 can be driven. Thus, depending upon the powertrain configuration, it is possible for either the heat engine 10 or the electric motor 30 to provide traction to wheels 40 via appropriate propulsion distribution means 70 either exclusively or as a composite blend from both the engine 10 and the motor 30. The electric motor 30 also can provide excess electrical power for storage in a traction battery 50. In such circumstances, the vehicle powertrain comprising the engine 10, transmission 20, motor 30 and propulsion distribution means 70 along with the battery 50 can be appropriately managed by a controller 60 to achieve the best performance in view of current operational conditions and vehicle driver demands.

It will be understood in both a series and a parallel hybrid configuration, it is possible for the respective electric motors 3, 30 to provide traction through the wheels 4, 40 in both the direction of movement of a vehicle, against the direction of movement of the vehicle and generate electric power when the vehicle is braking through a regenerative process with regard to the electric motors 3, 30.

It is known particularly with regard to off-road hill descent, in order to control vehicle speed during the descent, that the vehicle driver will select a low enough gear ratio in the transmission to provide a suitable multiplication of engine overrun torque to sustain the vehicle speed within the desired limit. In hybrid vehicles this engine torque overrun braking operates in several different ways. In a parallel hybrid configuration it is possible to provide additional overrun torque by regenerating via the electric motors 3, 30 electrical power for storage in the traction battery 5, 50. In a parallel configuration that has an electrical only mode of operation, and in traction battery fitted series configurations, there is no physical connection between the heat engine and the vehicles wheels so overrun torque has to be provided solely by electrical regeneration and storage.

It will be understood that a particular problem with regard to hill descent with respect to either hybrid configuration is that there is a limitation placed upon the overrun torque defined by the storage capacity of the traction battery.

Essentially, as the traction battery reaches full power its ability to provide adequate retardation force reduces and thus the vehicle win tend to accelerate. In a series hybrid configuration where there is no traction battery it will be understood without some form of electrical energy dissipation mechanism the vehicle cannot be braked electrically. Such dissipation mechanisms can add significantly to weight and if based upon coolant heating can themselves be limited by the heat capacity and dissipation rate of such coolant through the coolant system of the vehicle.

It is an object of the present invention to provide a vehicle hill descent control arrangement which substantially reduces the above mentioned problems.

In accordance with the present invention there is provided a hill descent control arrangement for a vehicle, the arrangement comprising an engine coupled to an electrical generator such that the engine can drive the generator to provide a generated electrical power and a driving electrical power can be provided to drive the electrical generator and so the engine, the generated electrical power being arranged in use to drive an electric motor associated with at least one wheel of a vehicle whilst that motor provides the driving electrical power for the electrical generator and so the engine when not driven by the generated electrical power, the arrangement including a controller arranged to determine when the generated electrical power is not required such that delivery of fuel to the engine is stopped and so that the driving electrical power substantially drives the engine and provision of that driving electrical power by the motor acts as a substantial brake upon the wheel.

Typically, all the wheels of a vehicle will be associated with a respective motor arranged to be driven by the generated electrical power and to provide the driving electrical power as required.

Normally, a traction battery will be provided such that in addition to direct exchange between the electrical generator and the motor, the traction battery acts as a reserve reservoir of electrical power to enable operation of the motor and/or 10 the electrical generator as required.

Generally, the value of the driving electric power provided by the motor to the electrical generator in order to drive the engine is proportional to a desired engine speed for best performance. Thus, the engine speed may be maintained or set as required for better start-up of the engine when required.

An embodiment of the present invention will now be described by way of example and reference to the drawing of Figure 1.

The present invention particularly relates to the series hybrid configuration as described above. Thus, a vehicle controller monitors and manipulates an electric motor or motors to provide braking torque through a regenerative braking 20 technique. The controller will also monitor a traction battery when fitted. However, in accordance with the present invention, the controller is arranged to also utilise the generator 2 as an energy sink. It is known to provide an electrical machine as an electrical generator 2 such that through suitable control strategies and electronics the generator 2 can be electrically driven and so drive the engine 1.

As described previously, generally whilst the engine 1 is being driven by fuel combustion, it will be understood that, an electrical machine acts as an electrical generator 2 to provide generated electric power to the motor 3 in order to drive the wheel 4. Control of the generator 2 and the motor 3 is through a controller 6 such that the traction requirements of a driver of a vehicle can be met within the capabilities of the vehicle. Typically, a battery 6 is also provided to provide storage of electrical power. It is also known to provide so- called regenerative braking whereby the motor 3 can provide an electric power when the vehicle is slowing down.

In accordance with this present invention, the electric power generated by the motor 3 during regenerative braking is constituted as a driving electric power for the generator 2 in order that that generator 2 may drive the engine 1. In such circumstances, it will be appreciated that the generation of the driving electric power by the motor 3 through a conservation of energy consideration acts as a drag upon the wheel 4 in order to substantially brake that wheel 4.

Previously, regenerative braking from the motor 3 has been used to top-up the battery 5 but not to directly drive the generator 2 and so the engine 1 in order to act as a energy sink. The inherent variation in the electrical power produced by the motor 3 during regenerative braking generally being too unreliable to provide a consistent motor force for the generator 2 to provide control of engine 1 speed. However, according to the present invention, the controller 6 can be arranged to specifically alter a configuration of the motor 3 in order to provide a more consistent driving electrical power to the generator 2 to maintain engine 1 speed. Furthermore, the battery 5 also controlled by a controller 6 can be arranged to regulate the driving electric power from the motor 3 by either supplementing or absorbing some of the electrical power provided by the motor 3 in order to provide a consistent braking effect through the generator 2 to the engine 1. In such circumstances, the engine speed of the engine 1 can be maintained and controlled as required.

The ability to drive the generator 2 and so the engine I using electrical power from the motor 3 and the traction battery 5 means that these high power sources can delete a conventional engine 1 starter and give a more reliable starting performance to the engine I in climatic extremes. It will be understood that the traction battery 5 is generally of a much greater power capacity than a normal ignition battery for the engine 1. Furthermore, the ability to take the engine 1 to a higher engine speed before introducing fuel can give improved and lower start-up emissions.

At the core of the present invention is that during periods of vehicle overrun or hill descent the regenerative braking of the motor 3 can be used to drive the generator 2 and therefore the engine in order to dissipate energy and so provide a drag upon the wheel 4 in order to brake that wheel 4. In such circumstances, it will be understood that battery cycling is reduced and there is the ability to regenerate through the motor 3 relatively large amounts of energy for a short period of time and so achieve efficient braking of the wheel 4.

Clearly, it will also be understood that by choice of an appropriate operational strategy, overall efficiency of the generator set in terms of the generator 2 and the motor 3 can be tuned more efficiently and therefore with less energy loss.

It will be understood in previous series hybrid configurations when the vehicle switches from driving the wheel 4 to braking that wheel, the generator 2 will either go into a no load idle condition or switch off. In the present invention the controller 6 acts to monitor this driving to braking and vice versa in order to maintain engine I speed by driving that engine 1 through the electrical generator i.e., generator 2 using the braking energy from the motor 3. Thus, by simple removal and application of fuel to the engine 1 during braking and traction respectively a significant dissipation of energy from the motor 3 in regenerative braking will be achieved in order to brake the wheel 4. However, once fuel is again applied to the engine 1 then this engine 1 will provide its own motive power and so again through the generator 2 provide the generated electric power in order to drive the motor 3 and therefore the wheel 4. In such circumstances, the engine I can quickly come on and off the load for best efficiency. Furthermore, the engine 1 will require the minimum application of fuel as the potential for it to accelerate the engine 1 up to its desired engine speed is removed, the engine speed being maintained by the generator 2 using the driving electric power from the motor 3 as described previously.

It will be understood that with the engine 1 consistently operating at a higher engine speed with less transients, engine ancillaries can also operate more efficiently. Thus, ancillaries such as the cooling pump will maintain operation and the most efficient performance criteria. For example, it will be appreciated that during hill descent, vehicle speeds are relatively slow and troublesome but there is still a need to dissipate residual heat from the vehicle and in particular the engine 1 from previous duty.

It will be understood that generally all the wheels of a vehicle will be coupled either to individual specific electric motors 3 or possibly an electric motor to drive two wheels upon the same axle. In any event, in accordance with the present invention, typically all the wheels and in particular the electric motors associated with those wheels will be used in order to provide the driving electric power to be supplied to the generator 2 in order to maintain engine 1 speed etc. Similarly, the driving electric power from the motor or motors associated with all the wheels of a vehicle may be supplemented or stored as required in order to drive the engine 1 in the traction battery 5.

Clearly, the necessary driving electric power to be applied to the generator 2 in order to maintain or achieve a desired engine speed will vary. Thus, the controller 6 will be configured to provide a proportional response dependent upon desired engine speed 1 as necessary. In such circumstances, the driving electric power from the motor 3 may be supplemented by power from the traction battery 5 in order to achieve the desired driving electric power applied to the generator 2 to maintain or achieve the desired engine 1 speed. Conversely, the traction battery 5 may be arranged to receive under the control of the controller 6 a proportion of the driving electric power from the motor 3 subject that traction battery 5 having capacity and the desired energy losses as a result of maintaining engine 1 speed is achieved. In such circumstances, it will be appreciated that the controller 6 will generally monitor the engine 1, generator 2, traction battery 5 and motor 3 along with the status of a vehicle including the hill descent control arrangement in terms of whether that vehicle is braking or descending a hill such that the braking effect as a result of the motor 3 through regenerative braking providing the driving electric power for the generator 2 is consistent with the desired operation of the vehicle.

As indicated previously, maintenance of engine speed or appropriation of a desired engine speed allows a degree of consistency of operation for the engine 1 and the powertrain of a vehicle such that the powertrain can be tuned for best efficiency at that maintained engine speed or desired engine speed for longer periods of time with inherent improved efficiency and performance.

Claims (7)

-9CLAIMS

1. A hill descent control arrangement for a vehicle, the arrangement comprising an engine coupled to an electrical generator such that the engine can drive the electrical generator to provide a generated electrical power and a driving electric power can be provided to drive the electrical generator and so the engine, the generated electrical power being arranged in use to drive an electric motor associated with at least one wheel of a vehicle whilst that motor provides the driving electric power for the electrical generator and so the engine when not driven by the generated electrical power, the arrangement including a controller arranged to determine when the generated electrical power is not required such that delivery of fuel to the engine is stopped and so that the driving electrical power substantially drives the engine and provision of that driving electrical power by the motor acts as a substantial brake upon the wheel.

2. An arrangement as claimed in claim I wherein there is more than one wheel and each wheel has its own respective motor in order to provide a constituent part of the driving electrical power for the electrical generator.

3. An arrangement as claimed in claim 1 or claim 2 wherein the arrangement includes a battery arranged to either provide additional electrical power to supplement that driving electrical power provided by the or each motor or receive a proportion of the driving electrical power from the or each motor so that only an appropriate value of driving electrical power is provided to the electrical generator.

4. An arrangement as claimed in any preceding claim wherein the controller is arranged to only supply at least a proportion of the driving electrical power from the motor to the electrical generator in order to drive the engine at a desired engine speed.

5. An arrangement as claimed in any preceding claim wherein the controller is arranged to maintain a desired engine speed for the engine by providing an appropriate value of driving electrical power from the motor to the electrical engine to maintain the engine speed desired.

6. A hill descent control arrangement substantially as hereinbefore described with reference to the accompanying drawing.

7. A vehicle including a hill descent arrangement as claimed in any preceding claim.