WO2002081241A1

WO2002081241A1 - A vehicle thermal system comprising an exhaust gas heat exchanger

Info

Publication number: WO2002081241A1
Application number: PCT/GB2002/001618
Authority: WO
Inventors: Adrian Jackson
Original assignee: Calsonic Kansei Uk Limited
Priority date: 2001-04-05
Filing date: 2002-04-05
Publication date: 2002-10-17
Also published as: EP1372997A1

Abstract

An exhaust gas heat exchanger is arranged for heat exchange between engine exhaust gas and coolant fluid in the engine coolant circuit, the engine coolant fluid comprises a substantially glycol-free fluid. A valve arrangement is reconfigurable between a first condition in which engine coolant is directed to the exhaust gas heat exchanger and a second condition in which engine coolant is inhibited from passing to the exhaust gas heat exchanger. Preferably an HVAC heat exchanger arranged for heat exchange between vehicle climate directed air and coolant in the engine coolant circuit. The invention utilises the counter-intuitive step of permitting coolant to boil/vaporise in the exhaust gas heat exchanger. By permitting the coolant to boil, the system can be significantly simplified in terms of both control and operation of component parts.

Description

A VEHICLE THERMAL SYSTEM COMPRISING AN EXHAUST GAS HEAT EXCHANGER

The present invention relates to a vehicle thermal system in particular a vehicle thermal system utilising a vehicle combustion exhaust gas heat exchanger.

Modern vehicles operate with improved engine efficiency. As a consequence, the amount of heat energy dissipated into the engine coolant circuit has reduced. This energy has previously been relied upon to provide a heat source for the interior cabin of the vehicle, thereby facilitating in- vehicle comfort and safety. In response to the trend of heat energy reduction, there has been an increased use of supplementary and auxiliary heat sources within modern vehicles. With the increased sophistication and technology of the modern vehicle, this trend is further supported by heightened consumer expectation demands requiring improved interior vehicle warm-up and windscreen defogging/deicing during winter driving conditions.

Warm-up solutions have mainly concentrated upon introducing additional heat sources, such as electric heating elements, fuel burning heaters or exhaust gas heat exchangers. The use of exhaust gas heat has been used in commercial solutions to introduce heat either directly into the cabin air-flow via a gas-to-air heat exchanger, or indirectly via a gas-to-coolant heat exchanger. The principle disadvantage of the direct gas-to-air solution has concerned safety (to ensure exhaust gases are not allowed ingress into the passenger cabin) whilst the indirect gas- to-coolant systems have required sophisticated control systems to avoid the problems associated with hot ambient driving conditions. During operation of the vehicle in hot ambient conditions, additional heat from the exhaust system is not required, and consequently coolant can vapourise if left stagnant within the exhaust gas heat exchanger. Previous prior art solutions have employed a sophisticated additional by-pass pipe and valve system within the exhaust system to divert the hot exhaust gases past the exhaust gas heat exchanger, and thereby avoid unnecessary heat exchange. The vapourisation of conventional coolants based upon water and glycol mixtures has long been acknowledged within the industry to present problems within vehicle systems. Glycol mixtures have critical flash-points, and evaporation-condensation cycles are known to deteriorate the functionality of the coolant. It is ^'for these reasons that the industry has avoided exhaust gas heat exchange designs that could facilitate localised boiling during vehicle operation.

An improved arrangement has now been devised.

According to the present invention, there is provided a vehicle thermal system comprising:

a) an exhaust gas heat exchanger arranged for heat exchange between engine exhaust gas and a coolant fluid in the engine cooling circuit; and b) a valve arrangement re-configurable between:

i) a first condition in which engine coolant is directed to the exhaust gas heat exchanger; and

ii) a second condition in which engine coolant is substantially inhibited from passing to the exhaust gas heat exchanger;

wherein:

the engine coolant fluid comprises a substantially glycol-free fluid.

The invention utilises the counter-intuitive step of permitting coolant to boil/vapourise in the exhaust gas heat exchanger. By permitting the coolant to boil, the system can be significantly simplified in terms of both control and operation of component parts.

It is preferred that the vehicle thermal system includes an HVAC heat exchanger arranged for heat exchange between vehicle climate directed air and coolant in the engine coolant circuit.

It is preferred that the engine coolant fluid is a water- based substantially glycol-free fluid. Beneficially the engine coolant fluid is a water-based mixture including carboxylic acid based inhibitor compound. The engine coolant circuit preferably includes a common flowpath portion for directing coolant to the HVAC heat exchanger for engine coolant passing via the exhaust gas heat exchanger and also for engine coolant inhibited from passing via the exhaust gas heat exchanger. The fluid line branch preferably directs coolant from the valve arrangement via the exhaust gas heat exchanger, returning the coolant past the exhaust gas heat exchanger to a second flowline exiting out of the value arrangement.

Beneficially, in both first and second valve arrangement configurations, the coolant fluid is directed to the HVAC heat exchanger .

Downstream of the HVAC heat exchanger the engine coolant is preferably directed to pass along the main engine coolant portion of the circuit. The main engine coolant portion of the circuit includes, typically, the water pump, thermostat, radiator (including expansion tank) and engine. Vapourised coolant can be permitted to be directed back into the engine circuit or, alternatively, the coolant flowline intermediate the valve arrangement and the exhaust gas heat exchanger may include a vent line provided to direct vapourised fluid to the expansion vessel of the primary coolant circuit. In this embodiment, it is preferred that engine coolant is permitted only to carry vapourised fluid to the expansion vessel when the valve arrangement is in the second condition (i.e. when engine coolant is not being directed into the exhaust gas heat exchanger) . One way valve is typically provided in the vent line to facilitate this result.

The invention will now be further described in specific embodiments, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of a first embodiment of vehicle thermal system in accordance with the invention; and

Figure 2 is a schematic representation of a second embodiment of vehicle thermal system in accordance with the invention.

Referring to the drawings, and initially to Figure 1, the vehicle thermal system comprises the following main components :

1. Engine . Component (1) represents an automotive internal combustion engine.

2. Heater Core. This heat exchanger (2) facilitates heat transfer to the air passing across it. Ambient air is directed into the cabin air distribution system (12) via vents and fans and allowed to pass across this component, thereby taking heat from the hot engine cooling fluid flowing within it (13) , and consequently heating the cabin air.

3. Exhaust Gas Heat Exchanger. This component is located within the exhaust system (7) , to provide a heat source. It is preferable if this component be closely positioned behind any catalytic converter to ensure the maximum gas heat available, without detracting from the converter performance. This exchanger (3) takes heat from the exhaust gas stream, heating the coolant within it. This heated coolant can then pass into the heater circuit and subsequently through the heater core (2) , thereby giving up this heat to the in-cabin airflow.

4. Water Pump. This component (4) functions as the pump within the engine cooling circuit, circulating fluid through all components within the circuit under the influence of a created fluid pressure difference.

5. Radiator. This heat exchanger (5) facilitates heat transfer to the air passing across it. Ambient air is directed into the engine bay via grills and vents and allowed to pass across this component, thereby taking heat from the hot engine cooling fluid flowing within radiator (18) , and consequently cooling this circuit fluid.

6. Expansion Tank. This component (6) acts as a fluid reservoir for the engine cooling circuit, thereby facilitating fluctuating fluid volume demands within the circuit as a consequence of variation in operating condition. 7. Exhaust System. This component (7) schematically represents the vehicle pipework carrying the hot exhaust gas from the engine and out to atmosphere. It is anticipated that the exhaust gas heat exchanger (3) will be connected within or around this exhaust system.

8. Thermostat . This valve (8) is generally responsible to engine cooling fluid temperature, and controls flow through the front radiator component (5) and the radiator by-pass circuit .

9. Two-Way Valve. This valve (9) allows fluid flow through itself in the two directions shown (as indicated in the direction of the arrowhead graphics) .

10. One-Way Valve. The valve shown (10) allows fluid flow through itself in the one direction shown (as indicated, only in the direction of the arrowhead graphic) .

11. Cabin Air Conditioning- and Distribution System. This comprises components including 2, assembled into housings which are shaped to enable vehicle fit and required airflow function into the cabin.

12. Engine Cooling Fluid (Coolant) . This represents the fluid flowing within the engine cooling system shown.

Operation of Preferred System Configurations The following modes of operation for the proposed system describe its beneficial designs:

During operation under cold ambients, there is a requirement for supplementary vehicle heating, from the exhaust gas heat exchanger. Under action of the two-way valve (9) , coolant is allowed to flow into the exhaust gas heat exchanger (3), become heated by the exhaust gases and subsequently flow back to the heater core (2) .

During operation under hot ambients, there is no requirement for supplementary vehicle heating from the exhaust gas heat exchanger. Under action of the two-way valve (9) , coolant is allowed to by-pass the exhaust gas heat exchanger (3) to the heater core (2) , and subsequently back to the water pump (4) . The coolant will be stagnant within the exhaust gas heat exchanger (3) , and could consequently boil. It is proposed to use a glycol-free coolant, such as those based upon water with carboxylic acid inhibitor additions as the engine cooling fluid (13) . Such coolants are inherently stable and could tolerate prolonged evaporation-condensation cycles without detriment to their properties. Thus vaporised coolant could be allowed to escape back into the coolant circuit, via the one-way valve (10) .

An alternative embodiment could make use of an expansion line between the exhaust gas heat exchanger and the expansion tank, controlled via an additional valve (13) , to allow vapourised coolant to be released into the expansion tank if this was preferred. The valve (13) could be configured to open only when the two-way valve (9) was selected to by-pass the exhaust gas heat exchanger.

It is further considered that the two-way valve (9) should default into the position that opened flow to the exhaust gas heat exchanger when the vehicle engine is inoperable for a set period of time. This would allow automatic pressure relief when the vehicle is not in operation.

Claims

CLAIMS :

A vehicle thermal system comprising:

a) an exhaust gas heat exchanger arranged for heat exchange between engine exhaust gas and coolant fluid in the engine coolant circuit; and

b) a valve arrangement reconfigurable between:

wherein, the engine coolant fluid comprises a substantially glycol-free fluid.

2. A vehicle thermal system according to claim 1, wherein the vehicle thermal system further includes an HVAC heat exchanger arranged for heat exchange between vehicle climate directed air and coolant in the engine coolant circuit.

3. A vehicle thermal system according to claim 1 or claim 2, wherein the engine coolant fluid is a water based substantially glycol-free fluid.

4. A vehicle thermal system according to any preceding claim, wherein the engine coolant fluid is a water based mixture including carboxylic acid based inhibitor compounds.

5. A vehicle thermal system according to any of claims 2 to 4, wherein the engine coolant circuit includes a common flowpath portion for directing coolant to the HVAC heat exchanger for engine coolant passing via the exhaust gas heat exchanger and for engine coolant inhibited from passing via the exhaust gas heat exchanger .

6. A vehicle thermal system according to any of claims 2 to 5, wherein in both first and second valve arrangement configurations, the coolant fluid is directed to the HVAC heat exchanger.

7. A vehicle thermal system according to any preceding claim, wherein downstream of the HVAC heat exchanger the engine coolant is directed to rejoin the main engine coolant portion of the circuit .

8. A vehicle thermal system according to any preceding claim, wherein vapourised coolant is directed back into the coolant circuit.

9. A vehicle thermal system according to any preceding claim, wherein in the coolant flowline intermediate the valve arrangement and the exhaust gas heat exchanger a vent line is provided to direct vapourised fluid to an expansion vessel of the primary coolant circuit .

10. A vehicle thermal system according to claim 9, wherein the vent line is permitted only to carry vapourised fluid to the expansion vessel when the valve arrangement is in the second condition.

11. A vehicle thermal system according to claim 9 or claim 9, wherein a one-way valve is provided in the vent line to permit coolant flow only in the permitted direction.

12. A vehicle thermal system substantially as herein described with reference to the accompanying drawings.