This invention relates to a method and an arrangement of the types in the preambles to claims 1 and 7 respectively.

State of the art

A method of prior art is to equip motor vehicles, particularly heavier vehicles such as trucks and buses, with a hydrodynamic auxiliary brake incorporated in the drive line between the engine and the driving wheels of the vehicle. Such a hydraulic retarder is intended primarily to be switched on when necessary to help retard the vehicle. Thus because a variable proportion of the braking work required for the intended retardation of the vehicle can be performed by the retarder, it will be possible to be economic in the use of the ordinary service brakes of the vehicle, whose linings will not therefore be subject to excessive wear and their life will be extended.

A further method of prior art is to use a retarder for a purpose other than merely to retard the vehicle.

As an example this mention may be made of DE 3 408 057, which describes a design in which a retarder is used to increase the load on the driving engine of the vehicle. The objective is then to increase the temperature of the exhaust gases from the engine, thereby burning away deposits formed in a soot filter in the exhaust system.

GB 2 134 245 describes a hydrodynamic brake which is used to accelerate the heating of the coolant in the engine cooling system at low load.

In the case of trucks with diesel engines and computer controlled or electronically controlled fuel injection (e.g. Scania\'s EDC system), it is possible to regulate the amount of fuel injected into the cylinders continuously on the basis of several operating parameters, so that the engine is working to its optimum at all times in terms of the operating parameters concerned and the driver\'s requirements.

Among these operating parameters, which are monitored and sensed continuously by different transmitters, mention may be made of the accelerator pedal position, the charging air pressure in the engine, the coolant temperature, engine speed, driving speed of the vehicle and the constant driving speed required by the driver and set by the automatic cruise control in the vehicle.

The fuel injection control system, which is connected in this way to different transmitters, therefore contains information on the current operating condition of the vehicle. This information can also be used for other computer-based control systems incorporated in the vehicle, such as the control system for the vehicle retarder. The retarder control system is normally and conventionally designed for optimum control of the retarder according to different operating parameters. The retarder control system may have programmed in it, for example, blocks which prevent the retarder from being activated at the same time that the driver actuates the throttle. Such driving behaviour, with simultaneous throttle and brake activation, is normally inappropriate.

Objective of the invention

The objective of the invention is to be able to use the hydraulic retarder in a motor vehicle for accelerating engine heating. The requirement here is to be able to switch on the retarder acting as a hydrodynamic brake when the

vehicle is started so that the power of the retarder developed during braking can be used as soon as possible to heat the coolant in the engine cooling system. This heating is achieved firstly because the engine is now forced to operate at an increased load due to the braking action of the retarder, which increases the heat developed during combustion, and secondly because of the braking effect which the retarder "brakes away", and which results in heating of the retarder hydraulic oil whose heat is absorbed by the engine coolant via a heating exchanger acting between the retarder hydraulic oil and the coolant.

Such driving, however, with simultaneous braking using both the retarder and throttle, is not normally possible with a modern diesel fitted with an electrically controlled retarder, as explained above.

Description of the invention

This problem can nevertheless be solved, and the above-mentioned objective is achieved if the method and arrangement of the type indicated in the preamble also involves taking the measures indicated in the characterising part of claim 1 , and designing the arrangement according to the characterising part of claim 7.

Further developments of the method are described in the independent claims 2 - 5, and further developments of the arrangement are described in the independent claims 8 - 9.

The principle concept of the invention is therefore to eliminate the blocking function preventing driving with simultaneous throttle and retarder braking incorporated in the computer controlled retarder control system using the proposed method and arrangement. The retarder can therefore be set to perform braking work at the same time that the engine is throttled, thereby

increasing the engine load and accelerating heating of the engine coolant, both due to the increased loading of the engine and absorption of heat from the retarder hydraulic fluid.

In other words, the engine heating function of the engine through management of heat developed by the retarder when it is performing braking work, means that operation of the accelerator pedal (throttle) is prevented from deactivating or switching off the retarder. This enables the engine and the retarder to be "run" simultaneously (i.e. the engine operates under throttle whilst the retarder performs braking work), which results in rapid heating of the coolant in the vehicle cooling system and therefore rapid heating of the engine, as well a heating of the interior of the vehicle, because this is in turn heated by the engine coolant.

A further advantage of rapid heating of the engine is that it reaches its operating temperature more quickly, with a correspondingly faster reduction of its exhaust emissions. In cold starts and during heating diesel engines emit so-called white smoke, and rapid heating reduces the nuisance this causes in a shorter time.

The elimination of the above-mentioned blocking function, preventing driving with simultaneous braking by means of the retarder and throttle, can suitably be achieved by simultaneously activating a separate heating function when the engine is started. This can be activated by means of a manually actuated control mechanism, for example a special button, which can be combined advantageously with an existing control connected to the retarder control system. The use of an existing control has the advantage that no further components are required and the modification can be limited to software in the retarder control system.

Brief description of the drawings

The invention will now be illustrated and explained in greater detail with reference to an arrangement shown in the drawings for implementing the method according to the invention.

In the drawing figures, Fig. 1 shows very diagrammatically the components, essential to the invention, of an arrangement for controlling the engine heating function of a diesel engine driven vehicle with a retarder system designed to accelerate engine heating. Fig. 2 shows in block diagram form a flow chart of the engine heating function.

Description of embodiment

Fig. 1 shows diagrammatically an arrangement which enables the heating of a diesel engine to be accelerated in a motor vehicle equipped with a switchable hydraulic retarder 2, which can be used either as a hydrodynamic auxiliary brake for retarding the vehicle, or as an aid to accelerating the engine heating. The motor vehicle itself is shown in Fig. 1 only in the form of an engine driven crankshaft 4 which, via a coupling 6, transmits the driving force of the engine to a gearbox 8. From gearbox output shaft 10 the driving force is then transmitted by conventional means to the subsequent components of the vehicle drive line not shown here. An oil sump 12, an accumulator 14 and an oil cooler 16 are also connected to hydraulic retarder 2.

The activation (switching on) and deactivation (switching off) of retarder 2 is controlled electrically by a computer based control 18, which is connected to retarder 2 by a signal cable 20. A method of prior art is known where such a control unit 18 incorporates a blocking function which prevents the retarder from being activated at the same time as the engine is throttled.

The blocking function also means that when the retarder is switched on it is automatically switched off as soon as the throttle is activated. The arrangement shown is therefore normally incorporated essentially in a vehicle equipped with a retarder, but it is also used according to this invention to enable the retarder to be activated when the engine is started, so that the engine load is increased by the same even when the throttle is activated, thereby accelerating heating of the coolant in the ordinary engine cooling system. This heating function is activated by eliminating the blocking function preventing driving with simultaneous retarder braking and throttle incorporated in the computer controlled retarder control system.

For controlling retarder 2, both when driving with the heating function activated and not activated, computer 18 must have knowledge of a number of relevant control parameters. Computer 18 obtains information on these control parameters via signal cables from the units.and transmitters shown in Fig. 1 , among other things. The control system for retarder 2 interacts closely with the control system for the electronically controlled engine fuel injection. In practice both these control systems are designed as separate units, but because of their close interaction they have been integrated into control unit 18 in Figure 1.

The controls operated by the driver, such as clutch pedal 22, brake pedal 24 and accelerator pedal 26, are of course controls whose effect on the operation of the vehicle and the engine are highly significant in this connection. Adjusting devices, not shown in greater detail here, which transmit state signals to control unit 18 via signal cables 28, 30 and 32 respectively, are therefore connected to these pedals. An engine speed transmitter 48 and a coolant temperature transmitter 50 are also connected to control unit via signal cables 49 and 51 respectively. Because this is an electrical control system control unit 18 is also connected via a cable 34 to a switch 36, whose actuation switches on the electricity supply to the

system. This switch 36 can suitably be operated with the starting key.

The above-mentioned blocking function preventing driving with simultaneous throttle and braking with the retarder is eliminated in the arrangement shown by switching on a heating function stored in control unit 18. The heating function can be activated automatically when starting or by means of a special control. In this example activation takes place as follows. Retarder control unit 18 incorporates a known constant speed (cruise control) function which, when activated, ensures that the vehicle braked to a constant speed, e.g. when driving downhill. This constant speed (cruise control) function is activated by means of a control switch 38 which can be activated by the driver. In this example this control switch 38 is also used for activating the heating function. One advantage of this is that this component already exists, and the modification required is limited to the software of control unit 18. The heating function is in this case switched on by simultaneously activating control switch 38 and starting the engine. Control unit 18 incorporates software which detects this simultaneous activation of control switch 38 and starter 36. When only control switch 38 is activated, it operates only as designed, i.e. for activating the constant speed (cruise control) function.

In the embodiment shown control switch 38 can be activated via a control button mounted at the outer free end of a iever 40, whose position setting operates an adjusting device 42 which controls the activation of retarder 2 via signal cable 44 and computer 18. The figure shows five alternative setting positions of Iever 40. These positions are designated 0, 1 , 2, 3 and 4, and correspond to gradually increasing braking moments generated by retarder 2. These braking moments may, for example, be 500 Nm, 1000 Nm, 2000 Nm and 3000 Nm for Iever positions 1 , 2, 3 and 4 respectively.

In the alternative embodiment, where a special control is used to switch on

the heating function, no simultaneous activation of starter 36 is required. Instead the function is switched on by the control directly, regardless of whether the engine is switched on or not. In the second alternative embodiment, in which the heating function is activated automatically when the engine is started, this takes place appropriately at the same time that the system is switched on with the starting key.

An indicator 53, which indicates when the heating function has been switched on, is suitably mounted on the engine instrument panel.

The operations of switching the engine heating function, generated by means of retarder 2, on and off, will now be illustrated by means of the flow chart shown in Fig. 2.

The flow chart contains six function blocks 52, 54, 56, 58, 60 and 62 arranged in sequence.

In the top block 52 it is established whether the power has been switched on in the system, i.e. whether the power supply to the system has been switched on by turning on starter 36, which is the case if the starting key has been turned to the power on position. At the same time the system senses whether control switch 38 has been activated, i.e. whether its control button has been pressed. If this is the case the next stage of the heating function follows, namely the step indicated in block 54, whereby sensing takes place to determine whether the coolant temperature is below

70°C. If, however, the answer to the question in block 52 is "No", the preparations for activating the heating function are interrupted immediately. Similarly, if the coolant temperature exceeds 70°C (and the answer to the question in block 54 is therefore "No"), the preparations for activating the heating function are also interrupted immediately.

If, on the other hand, the answer to the question in block 54 is "Yes", the next measure indicated in block 56 follows, namely activation of the heating function. This means that the blocking function preventing simultaneous retarder braking and throttle for the engine is disconnected. The retarder can therefore be set to brake with the moment corresponding to the position of Iever 40, in which case accelerator pedal 26 can also be used conventionally to control the engine throttle. If the retarder is not set to brake, the retarder is not activated either and the heating function is not used in this case. When the retarder has been switched on the monitoring of the coolant temperature indicated in the next block 58 commences. As long as this coolant temperature remains below a predetermined value, preferably the value corresponding to normal engine operating temperature, which in this example is 85°C, the heating function will remain switched on, but as soon as the coolant temperature reaches or exceeds 85°C (implying that the required engine heating has been completed), the next step indicated in block 60 follows, namely disconnection of the heating function, which leads to termination of the process according to the invention, as indicated in block 62. This also means that the blocking function of the retarder is reactivated.

To summarise it may be stated that an activation of the heating function operation of accelerator pedal 26, as when throttling by pressing the accelerator pedal, does not disconnect retarder 2 but instead enables the engine and retarder to operate simultaneously, thereby achieving an acceleration of the engine heating due both to the engine\'s own increased heat development and the heat generated during braking of the retarder, which contributes to rapid heating of the coolant in the engine cooling system and therefore to rapid heating of the engine itself and hence also the interior of the vehicle.

The implementation of the method according to the invention has been

described above by examining the function of the activation of the heating function controlled by computer 18. As a supplement to this a description will now finally be given of how the driver proceeds to implement the method according to the invention, i.e. when he wants to use the heating i function to accelerate the heating of the vehicle engine by means of the retarder. To achieve this the driver proceeds appropriately as follows:

1. If the vehicle engine is already running, the driver begins by switching off the engine and ignition.

2. The driver then activates control switch 38 by pressing its control button and keeping it pressed.

3. The driver then switches on the ignition and starts the engine by means of the starting key, so that starter 36 is activated at the same time as control switch 38 is activated.

4. The engine is then allowed to idle for a few seconds, e.g. for three seconds.

5. The driver then deactivates control switch 38 by releasing the control button pressed until that point.

6. The driver then sets the vehicle in motion with a suitable throttle by pressing accelerator pedal 26 so that the vehicle gains speed.

7. The driver then commences braking, at the first most suitable opportunity, by means of retarder 2, which is activated by setting Iever 40 to the desired braking moment position whilst at the same time increasing the throttle by pressing accelerator pedal 26. The heating power developed by the retarder (which contributes to

increasing the temperature of the coolant) is determined by the position to which Iever 40 is set (see Fig. 1 ), i.e. by the braking moment set for the retarder.

8. When the vehicle engine has reached the desired operating temperature, i.e. when the temperature of the coolant has reached a predetermined value, the heating function is switched off. However, this takes place automatically and therefore requires no special effort on the part of the driver.

It is assumed that when there is a need to accelerate heating of the interior of the vehicle, the driver will also activate the air-conditioning system of the vehicle, at a suitable opportunity, to heat the ventilation air supplied to the interior of the vehicle. Heat for this purpose is taken conventionally from the engine coolant via a heat exchanger.

The entire heating process takes place - once initiated by the driver - by means of the retarder control system shown in Fig. 1. The most important component in this system is of course control unit 18 based on microcomputer technology. The control laws which enable the method according to the invention to be implemented could in practice be established by suitable modification of the software incorporated in retarder control system 18. Alternatively the required program control can be arranged in a separate control unit.

Essentially the description of this embodiment has only discussed the function which takes place when the heating function is activated. Obviously control unit 18 and the arrangement described is designed to operate conventionally to control the retarder and engine in all other operating conditions when the heating function is not activated. In this case the blocking function incorporated in the control unit is active, and if the driver

activates the accelerator pedal in this case braking with the retarder is automatically disconnected (provided that the retarder has been activated).

The description relates to an advantageous embodiment in which the diesel engine fuel injection is controlled electrically. In simpler, alternative embodiments of the invention the fuel injection can be controlled mechanically, but this requires such an arrangement to be supplemented by the components necessary for sensing the operating parameters concerned.