WO1998052783A1

WO1998052783A1 - Method and arrangement for heating a motor vehicle provided with a retarder

Info

Publication number: WO1998052783A1
Application number: PCT/SE1998/000919
Authority: WO
Inventors: Lars-Gunnar Hedström; Sven-Anders Melin
Original assignee: Scania Cv Aktiebolag
Priority date: 1997-05-21
Filing date: 1998-05-18
Publication date: 1998-11-26
Also published as: SE507451C2; SE9701876L; DE19880762B4; DE19880762T1; SE9701876D0

Abstract

A motor vehicle is provided with a hydraulic retarder (5) which during vehicle operation is cooled by the engine coolant and thereby heats the latter. The vehicle's air-conditioning system (19) can via a control unit (9) for the retarder cause the latter to be switched on for heating purposes when the coolant temperature is too low to meet the heat requirement of the air-conditioning system at the time. The control unit decides whether and when switching on can take place.

Description

Method and arrangement for heating a motor vehicle provided with a retarder

The present invention relates to a method and an arrangement of the kind indicated in the preambles to patent claims 1 and 7 respectively.

State of the art

A known practice is to provide motor vehicles and, in particular, heavy-duty motor vehicles such as trucks and buses with a hydrodynamic auxiliary brake incoφorated in the driveline between the engine and the driving wheels of the vehicle. Such a hydraulic retarder is primarily intended to be able to be operated when needed to help to retard the vehicle. The fact that a greater or lesser proportion of the braking work required for the intended retardation of the vehicle can thus be carried out by means of the retarder makes it possible to a corresponding extent to spare the vehicle's ordinary driving brakes, resulting in the latter's brake linings being subject to less wear and hence having a longer life. Cooling of such a retarder is usually by means of coolant in the engine cooling system.

A practice known from SE 8400164-3 is the use of a retarder at low engine load to hasten heating of the engine coolant. This involves using the accelerator pedal position to control the extent of heating provided by the retarder so that heating decreases as the acceleration applied increases.

In the case of trucks where the engine is a diesel engine with computer-controlled or electronically controlled fuel injection (such as, for example, Scania's EDC system) it is possible to control continuously the fuel quantity injected into the cylinders with regard to a number of operating parameters so that the engine always operates optimally with regard to the relevant operating parameters and the driver's wishes. Examples of these operating parameters, which are continuously monitored and detected by various sensors, include the accelerator pedal position, the charge air pressure in the engine, the coolant temperature, the engine speed, the vehicle's velocity and its constant velocity desired by the driver and set by means of the vehicle's automatic constant speed maintenance. The fuel injection control system, which is in this manner connected to various sensors, thus contains information about the vehicle's current operating state. This information can also be used for other computer-based control systems incoφorated in the vehicle, such as a control system for the vehicle's retarder. The retarder control system is usually designed in a conventional manner to control the retarder optimally on the basis of various operating parameters. The programming of the retarder control system includes, for example, interlocks which prevent the retarder being activated at the same time as the driver applies acceleration. Such a mode of driving with simultaneous acceleration and brake activation is not normally advantageous.

A practice known from SE 9201893-6 in such a context is to use a retarder right from the starting of the engine in order to hasten the heating of the engine coolant. When necessary, the driver activates manually a special heating function which causes retarder braking which in normal situations is not allowed at the same time as acceleration. The engine's working temperature can thus be raised more quickly than would otherwise be the case.

Vehicle air-conditioning systems normally utilise for heating puφoses heat from the engine coolant. Experience has shown that even with the known solutions indicated it may be difficult to achieve quickly enough a desired temperature level in the vehicle.

Object of the invention

The object of the invention is to make it possible by means of a retarder to reach more easily and more quickly than hitherto a sufficiently high temperature in the vehicle driver's space even at low engine load and when the outside temperature is low.

Description of the invention

The object of the invention can be achieved if the method and the arrangement of the kind indicated in the introduction also include respectively the adoption of the measures indicated in the characterising part of patent claim 1 and the form of the arrangement being in accordance with the characterising part of patent claim 7.

Further developments of the invention are indicated by the dependent claims associated with said patent claims.

The basic idea of the invention is thus to use the vehicle's air-conditioning system in order to bring about retarder braking as necessary for heating puφoses. It is in this respect advantageous to make it only possible to switch on the retarder if the other operating conditions at the time make it advantageous to do so.

Switching on the retarder should therefore not be possible, for example, during full acceleration, when the whole engine output is required for driving the vehicle. Nor should it be possible to switch on the retarder when the vehicle is standing still. It is also possible to vary the acceleration as a function of the extra load which switching on the retarder imposes on the engine, with a view to not affecting the running of the vehicle.

Having the air-conditioning system control the operation of the retarder not only makes it possible to reach quickly and easily the desired temperature in the driving cab but also means that in cases where extra heating is required the engine itself also reaches a higher temperature more quickly, which is advantageous inter alia with regard to exhaust emissions. A further advantage is of course to reduce the driver's workload.

Description of the drawing

Fig. 1 shows schematically an arrangement on a vehicle engine whereby an air- conditioning system is connected to a control unit for a retarder belonging to the engine.

Description of an embodiment

The attached drawing in Fig. 1 depicts schematically an arrangement according to the invention whereby a vehicle engine 1 via a clutch 2 and a gearbox 3 drives an output shaft 4 which in its turn transmits driving power in a conventional manner to the vehicle's driveline. A hydraulic retarder 5 associated is with the engine 1 and can be switched on and off can be used as a hydrodynamic auxiliary brake. The retarder 5 has associated with it an oil pump 6, an accumulator 7 and an oil cooler 8 which is subsequently connected for cooling puφoses to the engine's coolant system (not depicted).

The operation of the retarder 5, i.e. its switching on and off, is controlled electrically by means of a computer-based control unit 9 which is connected to the retarder 5 via a signal line 10. The control unit 9 cooperates with a control system 11 for the engine's electrically controlled fuel injection. These two units 9 and 11 may also with advantage be combined as one unit.

A number of sensors for various control parameters are connected to the control unit 9, in this case a sensor 12 for coolant temperature, a sensor 13 for engine speed, a sensor 14 for clutch pedal position, a sensor 15 for brake pedal position and a sensor 16 for accelerator pedal position. There may possibly be further sensors. These sensors 12-16 provide the control unit 9 with information on the vehicle's operating state.

In order in a known manner to be able to switch on the retarder manually for braking puφoses, there is a control device 17 by means of which various degrees of braking can be set. In this context reference is made to the aforesaid SE 9201893-6. The control unit's power supply can be switched on by means of a starting switch 18 which is advantageously operated by means of the ignition key.

The vehicle's air-conditioning system 19 by means of which the desired air-conditioning can be set in the driver's space is also connected to the control unit 9. The puφose of this according to the invention is to enable the air-conditioning system 19 to demand via the control unit 9 the automatic switching on of the retarder 5 in order to raise the engine coolant temperature when the latter is not high enough to generate in the air-conditioning system the temperature desired at the time. This can in practice be arranged so that compliance with the demand of the air-conditioning system 19 for temperature increase by means of the retarder 5 is subject to certain conditions determined by the control unit 9. As switching on the retarder 5 imposes an increased load on the engine 1 , it must only be possible when the engine is running at less than full acceleration, since otherwise the vehicle's running characteristics may be affected, e.g. when travelling uphill, with consequent impairment of performance. It is also advantageous, with a view to maintaining good drivability of the vehicle, for it to be possible for the retarder 5 to be switched on during normal vehicle movement when the accelerator pedal is depressed to a certain extent. It must therefore be possible for the usual interlock function intended to prevent the retarder being switched on during acceleration to be disconnected when the requirements of the air-conditioning system 19 have to be met. An advantageous limitation in this respect, however, is that the vehicle has to be in motion for it to be possible to switch on the retarder. On the basis of information from the various sensors 12-16 the control unit 9 can decide when the vehicle's operating state allows the retarder to be switched on. If so desired, an indicator 20 connected to the control unit 9 can provide the driver with information on whether the retarder 5 is on.

The need to switch on the retarder 5 for heating puφoses normally occurs when the engine is running at low load, particularly if the outside temperature is low. In such circumstances, it is desirable from the drivability point of view for the increased engine load due to greater acceleration arising from the retarder being on to be automatically compensated by means of the control unit 9. This means that the driver need not adapt his driving to the current state of the retarder but can concentrate on the traffic situation.

It is advantageous for the control unit 9 to be programmed to cater for various requirements with regard to the functioning of the retarder in a certain order of priority. The first priority to be met is requirements concerning the vehicle's safety and drivability and only secondly should the air-conditioning system's requirements regarding driver comfort be met. It may therefore happen that a driver's space temperature increase demanded by the air-conditioning system has to wait until other requirements have been met.

Claims

Patent claims

1. Method for heating a motor vehicle provided with a hydraulic retarder (5) whereby the retarder takes the form of a hydrodynamic auxiliary brake whose hydraulic fluid is cooled by the engine coolant and whereby the retarder is controlled under the influence of an electrical control unit (9) on the basis of various operating parameters in order to perform braking work for a heating function so that the engine coolant is heated not only by the engine but also by the hydraulic fluid of the retarder, characterised in that the vehicle's air-conditioning system (19) emits signals to the control unit (9) to activate the heating function when the coolant is at too low a temperature for the air-conditioning system's heat requirement, and that the heating function is activated as a function of the load on the engine at the time.

2. Method according to claim 1, characterised in that activation of the heating function only takes place while the vehicle is in motion.

3. Method according to claim 1 or 2, characterised in that activation of the heating function takes place at the same time as acceleration of the vehicle.

4. Method according to claim 3, characterised in that activation entails greater acceleration of the engine to compensate for the increased load caused by switching on the retarder.

5. Method according to any one of claims 1-4, characterised in that activation takes place only when the engine is running at less than full load.

6. Method according to claim 2, characterised in that activation takes place preferably when the load on the engine is low.

7. Arrangement for heating a motor vehicle provided with a hydraulic retarder (5) whereby the retarder takes the form of a hydrodynamic auxiliary brake whose hydraulic fluid is cooled by the coolant of the engine (1) and whereby the retarder (5) is controlled under the influence of an electrical control unit (9) on the basis of various operating parameters, and the control unit has a heating function whereby the retarder can be switched on to increase the heating of the coolant, characterised in that the vehicle's air-conditioning system (19) is connected to the control unit (9) and is arranged to demand switching on of the retarder (5) when the coolant is at too low a temperature for the prevailing heat requirement, and that in such circumstances the control unit (9) is arranged to activate switching on of the retarder as a function of the load on the engine at the time.

8. Arrangement according to claim 7, characterised in that only when the engine is operating at partial load is the control unit (9) arranged to activate switching on of the retarder (5).

9. Arrangement according to claim 7 or 8, characterised in that the control unit (9) is arranged to increase the acceleration of the engine when the retarder (5) is on, in order to compensate for the engine load increase caused by the retarder.