FIELD OF THE INVENTION

The present disclosure relates to an engine system and an off-highway vehicle comprising said engine system. More particularly, though not exclusively, the present disclosure relates to an engine system configured to reduce emissions from an off-highway vehicle.

BACKGROUND OF THE INVENTION

Off-highway vehicles use, almost exclusively, combustion engines to provide the energy and power required for operation. Whilst these engines can be efficient and cost effective they emit exhaust pollutants (hydrocarbons, nitrogen oxides and particulate matter), which can be detrimental to health and to the environment.

Various abatement technologies are known for diesel engines, which may be used alone or in combinations, to reduce these harmful emissions. These technologies include the following:

Diesel particulate filters (DPF) are provided to remove particulate matter from engine exhausts. As the particulate matter may accumulate in the filter causing blockages, mechanisms are required to clean the filter. Passive filters use a catalyst to remove accumulations, but need high temperatures to work. This cannot be guaranteed for off-highway applications, because the engine may spend a significant time idling, such that sufficient temperatures may not be achieved passively. An “active” DPF is therefore desirable for the technology to be effective in off-highway applications. Active DPFs periodically burn fuel, either in a fuel burner, or by using the engine management system to increase exhaust temperature by changing the fuel injection strategy to heat the filter to particulate matter combustion temperatures. High reductions in particulate matter are achievable (over 99% in optimal conditions). Disadvantages of active DPFs include an increased specific fuel consumption.

Selective catalytic reduction (SCR) combines the use of a catalyst such as vanadium, tungsten, copper zeolite (Cu-Zeolite), or iron zeolite (Fe-Zeolite) with a reductant such as anhydrous ammonia, aqueous ammonia, or more typically, urea, to convert NO and NO2to nitrogen and water. Urea is typically used as the reductant, but has to be injected into the exhaust somewhat upstream of the SCR catalyst in order to thermally decompose into ammonia by the point at which it enters the SCR catalyst. Urea is preferred over ammonia, as it substantially safer to store and transport. In the USA, commercially available urea for use with SCRs is referred to as Diesel Exhaust Fluid (DEF), whereas in Europe it is referred to as “AdBlue®”. For SCRs to function effectively at the lower end of the temperature spectrum it has hitherto been desirable for there to be a 50:50 split of NO and NO2, although Cu-Zeolite catalysts have been found to improve performance at temperatures of less than 300° C. when there is little NO2available. An advantage of SCR is that it has minimal impact of specific fuel consumption. On the downside, there is a risk that excess injection of urea reductant, or that ammonia resident in the SCR catalyst at lower temperatures and released as the catalyst heats, causes unreacted ammonia to be emitted from the SCR into the atmosphere. This is referred to in the industry as “ammonia slip”.

Such emissions control devices can be very effective at removing emissions (in excess of 99%), but require optimal operating conditions to be effective.

Accordingly, the present disclosure seeks to overcome, or at least mitigate the problems of the prior art. For example, the present disclosure seeks to reduce the emission of exhaust pollutants from off-highway vehicles, e.g. close to zero.

SUMMARY OF THE INVENTION

A first aspect of the invention provides an engine system for an off-highway vehicle, comprising:a diesel engine configured to drive a driveline of the vehicle;an after-treatment arrangement configured to reduce emissions from the engine system;an after-treatment heating element configured to raise an operating temperature of the after-treatment arrangement;an electric energy storage device; anda controller configured to direct energy from the electric energy storage device to the after-treatment heating element in order to raise the operating temperature of the after-treatment arrangement.

In this way, the after-treatment system can be maintained at an optimal operating temperature in which emissions from the engine system are most effectively reduced. This has the advantage of reducing harmful emissions from the engine system (e.g. NOxand particulate matter). As will be described in further detail below, emissions from an off-highway machine, including such an engine system, may be sufficiently low to be considered to be “zero”, enabling use of engine systems in “Zero Emission Zones”. This is achievable whilst providing the efficiency, range and cost of a hydrocarbon fueled combustion engine equipped vehicle.

After-treatment systems, such as SCR and DPF systems can achieve up to 99.9% efficiency under specific conditions, for example, under specific temperature conditions. For example, when an SCR arrangement is cold, NOxemissions may be high e.g. at about 500 ppm. Whereas, in the case of a Cu-Zeolite catalyst, when the SCR reaches a temperature of about 300° C., NOxemissions are reduced to approximately zero. Accordingly, by heating the after-treatment arrangement, greatly reduced NOxemissions are achieved. The performance of an SCR is highly dependent on temperature.

Further, passive DPFs are temperature dependent. Therefore, by heating the after-treatment arrangement, the proportion of passive DPF regeneration which is possible is increased. This reduces the need for “active” regeneration of the DPF, which would require additional burning of fuel to remove accumulated particulate matter. Therefore, decreased fuel consumption is achieved. The after-treatment heating element can also be used as part of the active regeneration of the DPF, where necessary and desirable.

In this way, by heating the after-treatment arrangement, reduced or negligible emissions are produced from the engine system, whilst still achieving the efficiency and cost benefits associated with diesel engines. In particular, reduced or negligible emissions are produced at a much lower cost than a purely electric engine system.

The EU stage V exhaust emissions standards will come into force on Jan. 1, 2019, for engines below 56 kW and above 130 kW. They will take effect a year later, on Jan. 1, 2020, for engines in the 56 to 129 kW range. Regulation 2016/1628 specifies emission requirements for all categories of compression ignition (diesel) and positive ignition mobile non-road engines, replacing Directive 97/68/EC and its amendments. It has been found that, by using the engine system disclosed herein, it is possible to achieve emissions many times lower than the Stage V standard.

Further, emissions at the point of use are sufficiently low as to be insignificant and classified as “zero”, enabling use of engine systems in “Zero Emission Zones”.

By way of example, the engine system disclosed herein is advantageous in reducing emissions upon vehicle start-up. In such instances, the electric energy storage device can be used provide energy to the after-treatment heating element in order to raise the operating temperature of the after-treatment arrangement to a temperature where the efficiency is optimised. Accordingly, there is no requirement to start the diesel engine in order to heat the after-treatment arrangement. In this way, emissions can be reduced from engine start-up, and throughout use of the engine.

In some embodiments, the off-highway vehicle is a hybrid energy off-highway vehicle.

Optionally, the system further comprises an engine heating element configured to heat the diesel engine, wherein the controller is configured to direct energy from the electric energy storage device to the engine heating element in order to raise the temperature of the diesel engine.

In exemplary embodiments, the engine is heated by heating the coolant and/or oil and/or air inducted into the engine. For example, the oil and/or coolant may be heated to a temperature in the range of 40-80° C., e.g. about 60° C. For example, the inducted air may be heated to a temperature in the range of 10-40° C., e.g. about 25° C.

Again by way of example, the engine system disclosed herein is advantageous in reducing emissions upon vehicle start up. In such instances, the electric energy storage device can be used to provide energy to the engine heating element in order to raise the temperature of the diesel engine, for example an optimal operating temperature at which emissions are reduced. Therefore, the engine can be preheated prior to starting the engine. This means that the engine does not need to be run in before it gets up to temperature.

Optionally, the system is configured to heat the after-treatment arrangement and/or the engine prior to the controller directing the diesel engine to drive the driveline.

In this way, when the after-treatment system and/or the diesel engine are up to temperature, the engine is started and used to drive the driveline. This ensures that emissions will be minimised right from the point of engine start up.

Optionally, after the controller directs the diesel engine to drive the driveline, the controller directs the electric energy storage device to cease supply of energy to the after-treatment heating element and/or the engine heating element.

In most circumstances, temperature of the after-treatment system and/or the engine is maintained by virtue of operation of the engine itself.

Optionally, the controller directs the electric energy storage device to gradually cease supply of energy to the after-treatment heating element and/or the engine heating element.

In some circumstances, the supply of energy to heat the after-treatment arrangement may be stopped prior to or after the supply of energy to heat the engine is stopped. In this way, heating can be tailored so that the required temperature of the after-treatment arrangement and/or the engine is maintained.

Optionally, the system further comprises a motor generator configured to drive the driveline of the vehicle, such that the engine system is configured to drive the driveline of the vehicle via the motor generator in an electric mode, via the diesel engine in an engine mode, or a combination of both modes.

In this way, the driveline of the vehicle can be operated when the engine has not yet been started by using the motor generator to drive the driveline of the vehicle. This means that the vehicle may still be used whilst the engine and/or the after-treatment arrangement are being brought up to temperature.

This also has the advantage that, under very high load demands, both the diesel engine and the motor generator can be used to drive the driveline of the vehicle.

In other circumstances, where there is a low load demand on the vehicle, the driveline of the vehicle may be driven only using the motor generator.

Optionally, prior to and/or during heating of the after-treatment arrangement and/or the engine, the controller directs energy from the electric energy storage device to the motor generator to drive the driveline in the electric mode.

In this way, the vehicle can still be used by using the motor generator to drive the driveline of the vehicle whilst the after-treatment system and/or the engine are getting up to temperature. This means that use of the vehicle is not impeded, whilst still ensuring minimal or zero emissions are produced by the vehicle.

Optionally, upon receipt of an input corresponding to a request to start the vehicle, the controller directs energy from the electric energy storage device to the motor generator to drive the driveline in the electric mode.

This ensures that the engine is not started until it is determined that a sufficient load demand has been placed on the vehicle and so ensures that the engine is not started unnecessarily. Further, this ensures that the engine is only started once the engine and after-treatment arrangement have been brought up to temperature.

Optionally, the system is configured to determine a load demand on the system, wherein, when the system is running in electric mode, if the demand is determined to be below a lower load threshold, then the controller directs the system to continue to drive the driveline in the electric mode.

In exemplary embodiments, the lower load threshold may be 10-30%, e.g. 20%.

In other words, where a low load demand has been placed on the vehicle, the engine system is configured to drive the driveline in the electric mode and so not start the engine. The engine will therefore only be started when the load demands are great enough to necessitate this. Accordingly, unnecessary use of the engine is avoided.

Additionally, when the engine is running at a light load demand, exhaust gases from the engine will be at a relatively low temperature and so the temperature of the after-treatment arrangement will not be optimal for minimising emissions. Accordingly, running in the electric mode avoids the engine system running in non-clean modes.

Optionally, the controller is configured to direct the system to switch from the electric mode to the engine mode, wherein switching from the electric mode to the engine mode comprises:pre-heating the after-treatment arrangement and/or the engine, andfollowing pre-heating, the controller is configured to cause the engine to drive the driveline in the engine mode.

Advantageously therefore, the engine system is only switched from electric mode to engine mode when the after-treatment arrangement and/or the engine have been brought up to temperature e.g. met a respective predetermined temperature. In this way, the use of the engine is limited to when emissions can be most effectively reduced i.e. when the after-treatment arrangement and/or the engine are operating at an optimal temperature. Further, the vehicle can be used in either electric mode or engine mode, to optimise emission levels, without interfering with the use of the vehicle.

Optionally, the pre-heating the after-treatment arrangement and/or the engine comprises the controller directing energy from the electric energy storage device to the after-treatment heating element and/or the engine heating element for a respective pre-determined time period.

In exemplary embodiments, the respective pre-determined time period is selected to correspond to the time period required for the engine and/or the after-treatment system to reach a respective predetermined temperature.

Optionally, the pre-heating the after-treatment arrangement and/or the engine comprises the controller directing energy from the electric energy storage device to the after-treatment heating element and/or the engine heating element until the after-treatment arrangement and/or the engine reach a pre-determined temperature.

Optionally, the system is configured to determine a load demand on the system, and wherein, when the system is running in electric mode, if the demand is above the or a lower load threshold, the controller directs the system to switch from the electric mode to the engine mode.

Therefore, the engine is only started when the load demand is great enough to require it. When the demand is greater than a lower load threshold, the engine is then started since this is more efficient for such loads.

Optionally, when the system is running in electric mode, if the amount of charge in the electric energy storage device is below a first predetermined amount, the controller directs the system to switch from the electric mode to the engine mode.

In exemplary embodiments, the first predetermined amount is between 10-50%, e.g. 20%. This ensures that there is sufficient power to drive the driveline of the vehicle. Further, in such instances, the engine may be directed by the controller to also charge the electric energy storage device, via the motor generator, and so increase the load demand on the system e.g. to above the lower load threshold.

Optionally, the system is configured to determine an operating temperature of the after-treatment system and, when the system is operating in the engine mode, when the operating temperature is determined to be decreasing and/or when the operating temperature determined to have reached a pre-determined minimum temperature, the controller is configured to direct the engine to also provide mechanical energy to the motor generator, for conversion to electrical energy and storage in the electric energy storage device.

For example, if the load demand on the system is not very high, the operating temperature of the after-treatment system may decrease. Therefore, by directing the diesel engine to also charge the electric energy storage device, the load demand on the engine is increased and so the temperature of exhaust gases produced is also increased. This raises the operating temperature of the after-treatment arrangement.

Optionally, when the system is operating in the engine mode, when the operating temperature is determined to be decreasing and/or when the operating temperature determined to have reached a pre-determined minimum temperature, and when the amount of charge in the electric energy storage device is determined to be above a second predetermined amount, the controller directs the system to run in the electric mode.

In exemplary embodiments, the second predetermined amount is between 50-100%, e.g. 90%.

In this way, when the operating temperature of the after-treatment arrangement is likely to fall to below an optimal temperature, and therefore fall outside the optimal operating conditions, the engine is stopped so to ensure that emissions are kept to a minimum. In the meantime, the vehicle is run in the electric mode.

Optionally, the operating temperature of the after-treatment arrangement is determined based on a temperature of the exhaust gases from the diesel engine.

Optionally, the system is configured to determine a load demand on the system, and wherein if the demand is above an upper load threshold, the controller directs the system to run in both the electric mode and the engine mode.

This ensures that there is sufficient power to meet high load demands. For example, the upper load threshold is above the load demand which can be satisfied by the engine alone.

Optionally, the system is configured to determine an amount of charge in the electric energy storage device, and wherein when the system is running in the engine mode and upon receipt of an input corresponding to a request to stop the vehicle:if the amount of charge is above a third predetermined amount, the controller directs the engine to switch off; andif the amount of charge is below a third predetermined amount, the controller directs the engine to keep running to provide mechanical energy to the motor generator, for conversion to electrical energy and storage in the electric energy storage device.

In exemplary embodiments, the third predetermined amount is between 50-100%, e.g. 90%.

This ensures that there is sufficient charge in the electric energy storage device when the vehicle is started up again at a later time. This ensures that the vehicle will be able to operate whilst keeping emissions to a minimum.

Optionally, the motor generator is configured to generate electrical energy from engine overrun and/or vehicle braking and transfer this to the electric energy storage device.

Optionally, the controller is configured to direct energy to the after-treatment heating element and/or to the engine heating element upon receipt of an input corresponding to a request to start the vehicle.

Upon vehicle start-up, the after-treatment arrangement and/or the engine are likely to be at a relatively low temperature and so the system may act to immediately increase these temperatures to enable the engine to be started as soon as possible.

Optionally, the system is configured to determine an operating temperature of the after-treatment arrangement and/or an engine temperature of the diesel engine, wherein, when the determined operating temperature of the after-treatment system and/or the determined engine temperature meet a respective predetermined threshold, the controller directs the diesel engine to drive the driveline.

Optionally, the after-treatment arrangement comprises a Diesel Particular Filter (DPF) and/or a Selective Catalytic Reduction (SCR) arrangement, optionally wherein the after-treatment heating element is configured to raise the operating temperature of the after-treatment arrangement by heating an exhaust from the diesel engine and/or by heating an SCR catalyst.

Optionally, heating the engine comprises heating a coolant and/or an oil and/or air inducted into the engine.

A second aspect of the invention provides an off-highway vehicle comprising the engine system of as disclosed herein.

