WO2011133094A1

WO2011133094A1 - Method and system for assessing a driver's braking behaviour

Info

Publication number: WO2011133094A1
Application number: PCT/SE2011/050472
Authority: WO
Inventors: Linus Bredberg; Jonny Andersson; Andreas Jerhammar
Original assignee: Scania Cv Ab
Priority date: 2010-04-21
Filing date: 2011-04-18
Publication date: 2011-10-27
Also published as: KR20130092419A; SE535909C2; SE1050393A1; CN102844231A; RU2012149456A; BR112012025865A2; RU2561400C2; EP2560857A1

Abstract

The invention relates to a method for assessing a driver's braking of a vehicle, comprising determining when a braking cycle begins; determining the time t_engbrake when the vehicle's engine brake is used during the braking cycle; determining the time t_shift for gear changes during the braking cycle; determining when the braking cycle ends; determining the total time t_total for said braking cycle; processing t_total and t_engbrake with respect to t_shift according to predetermined rules, and calculating a braking assessment value BA based on processed values for t_engbrake and t_total. The invention relates also to a system for assessing a driver's braking of a vehicle.

Description

METHOD AND SYSTEM FOR ASSESSING A DRIVER'S BRAKING

BEHAVIOUR

Field of the invention

The present invention relates to a method and a system for assessing a driver's braking behaviour, according to the preambles of the independent claims.

Background to the invention

In running heavy vehicles such as trucks, buses and the like, vehicle economy has become an important factor in trying to reduce the costs of the activity for which the vehicle is used. After its procurement cost, the largest expenditures on the vehicle are fuel and service costs. These costs are often related, i.e. a vehicle which is much used not only consumes more fuel but is also subject to more wear, with consequently higher service costs.

Fuel consumption and wear are greatly influenced by driving style. The difference between drivers as regards a vehicle's fuel consumption is not infrequently more than 10%. The difficulty of recruiting capable drivers makes training an attractive solution. The problem with all training, however, is that its effects may fade over time, and after some months the driver's behaviour may be back to the same level as before the training.

Another problem is identifying how much fuel consumption and wear arises from imprudent driving and how much from unfavourable traffic conditions, e.g.

extremely hilly roads and/or urban traffic.

Imprudent driving results mainly in wear of the vehicle's brake system. A heavy vehicle often has a number of different brake systems, e.g. service brake (foot brake), engine brake, exhaust brake, retarder and other types of auxiliary brakes. Using auxiliary brakes is generally preferable in being usually less arduous for the vehicle. By using auxiliary brakes on heavy vehicles, the driver can reduce the wear on brake linings, brake discs etc. which is associated with using the wheel brakes. If for example the service brake is used alone when a heavily laden vehicle is on a long downhill run, this may have disastrous consequences due to overheated brake drums and/or brake linings. Use of auxiliary brakes should therefore be encouraged with a view to drivers using them more often.

Not all vehicles are equipped with all of the auxiliary brakes which are available. For example, a hydraulic retarder is not always fitted, owing to its cost. In contrast, an exhaust brake, which is also an auxiliary brake, is generally available on a heavy vehicle. However, the problem in evaluating the driver's use of an exhaust brake and encouraging him/her to use it is that using it is unlawful in many countries, often at certain times during the 24 hours, because it is very noisy. It is also difficult to estimate the brake force which may be expected from the exhaust brake in different driving situations. WO 2007/139494 describes a device for determining a driver's ability to choose a brake system. His/her use of the brake system is compared with his/her total use of brake systems during a braking operation, in order to assess his/her ability to use the brake system. The total use of the system is measured in terms of energy consumed or use of the system.

EP 1811481 describes a method and a system for monitoring and analysing a driver's driving style. Various parameters such as engine speed, vehicle speed, gear choice etc. are monitored and used to construct a driver profile representing his/her driving style.

The object of the invention is to achieve an improved method for evaluating the driver's ability to brake in such a way that wear and fuel consumption are minimised, and in particular to encourage him/her to drive in such a way that wear and fuel consumption are minimised. Summary of the invention

The object described above is achieved by a method for assessing a driver's braking behaviour. The method comprises: determining when a braking cycle commences; determining the time tengbrake when the vehicle's engine brake is used during the braking cycle; determining the time t_Shift taken to engage a gear during the braking cycle; determining when the braking cycle ends; determining the total time ttotai for said braking cycle; processing t_totai and t_engbrake with respect to t_Shift according to predetermined rules, and calculating a braking assessment value BA based on processed values for tengbrake and t_totai_> which rules require that if t_Shift is greater than t_Shiftmax_> which is a settable maximum permissible time for changing gear, then t_totai is processed on the basis that t_totai = ttotai ⁺ t_Sampie_> where t_sampie is a predetermined period of time, and the calculated braking assessment value BA is presented to the driver. According to another aspect, the object is achieved by a system for assessing a driver's braking behaviour. The system comprises: a control unit connected to a first measuring unit adapted to determining when a braking cycle begins; a second measuring unit connected to the control unit and adapted to determining the time t_engbrake when the vehicle's engine brake is used during the braking cycle and to delivering on the basis thereof a second time signal containing t_engbrake; a third measuring unit connected to the control unit and adapted to determining the time tshift taken to engage a gear during the braking cycle, and to delivering on the basis thereof a third time signal containing t_snift; the first measuring unit is adapted to determining when the braking cycle ends, determining the total time t_totai for said braking cycle and delivering to the control unit on the basis thereof a first time signal containing t_totai. the control unit is further adapted to processing t_totai and tengbrake with respect to t_Shift according to predetermined rules, and to calculating a braking assessment value BA based on processed values for t_engbrake and t_totai. which rules require that if t_snift is greater than t_shiftmax. which is a settable maximum permissible time for changing gear, then t_totai is processed on the basis that t_totai = ttotai + tsampie, where t_sampie is a predetermined period of time, and the calculated braking assessment value BA is presented to the driver. The method and the system provide a way of assessing a driver's ability to brake in such a way that wear and fuel consumption are minimised. This type of assessment of how a driver brakes is very general and may be applied on many types of vehicles, e.g. trucks, buses, passenger cars, without substantial requirements about how the vehicle is equipped.

According to an embodiment, the driver can receive direct feedback about his/her braking behaviour and may then rectify behaviour which has adverse

environmental and economic effects. Through constant reminders about desired driving style, the driver may also maintain and improve his/her performance between training occasions.

The driver's behaviour may also be scored, which is a positive way to encourage rivalry and commitment. It may also result in him/her having fun at work while at the same time his/her driving style is improved.

Preferred embodiments are described in the dependent claims and the detailed description.

Brief description of the attached drawings

The invention is described below with reference to the attached drawings, in which:

Figure 1 illustrates schematically an assessment system according to an embodiment of the invention.

Figure 2 is a flowchart of the assessment method according to an embodiment of the invention.

Figure 3 is a flowchart of the assessment method according to another

embodiment of the invention.

Figure 4 illustrates BA scoring in Figure 2.

Figure 5 is a flowchart of the assessment method according to a further embodiment of the invention. Figure 6 depicts an example of how the engine's speed n_eng changes downhill.

Detailed description of preferred embodiments of the invention

Figure 1 depicts schematically a system for assessing a driver's braking

behaviour according to an embodiment of the invention. The system comprises a control unit preferably provided with a processor unit for performing calculations etc., and at least one memory. The control unit is connected to a number of measuring units adapted to determining different variables. The first measuring unit is adapted to determining when a braking cycle begins and ends, determining the total time t_tot_ai for the braking cycle and delivering to the control unit on the basis thereof a first time signal containing t_totai- Depending on the situation to be assessed, the first measuring unit is adapted to monitoring and calculating various parameters and signals such as the vehicle's speed, acceleration, running resistance etc. in order to decide when a braking cycle begins and ends. Figure 1 illustrates this schematically in the form of an arrow pointing to the first measuring unit. The second measuring unit connected to the control unit is adapted to determining the time t_engbrake when the vehicle's engine brake is used during the braking cycle, and to delivering on the basis thereof a second time signal containing t_engbrake- According to an embodiment, the input signals to the second measuring unit are similar to those to the first measuring unit. The third measuring unit is adapted to determining the time t_Shift for gear changes during the braking cycle, and to delivering on the basis thereof a third time signal containing tshift- The third measuring unit then receives for example information from the gear system in the vehicle about when and which gears are used. The control unit is adapted to processing t_tot_ai and tengbrake with respect to t_shift according to

predetermined rules, and to calculating a braking assessment value BA based on the processed values for tengbrake and ttotai- According to an embodiment, the measuring units described are functional units which may be incorporated in the control unit.

The control unit comprises preferably a processor unit adapted to performing calculations etc., and at least one memory. According to an embodiment, the calculated braking assessment value BA is presented for the driver on a display. The BA value may for example be

expressed in the form of a numerical value or in the form of symbols. The BA value may also be fed back acoustically to the driver. According to an

embodiment, the BA value may be saved in the memory in the control unit or be sent to a central unit external to the vehicle for further analysis.

According to an embodiment, the system comprises a fourth measuring unit adapted to determining the engine's speed n_eng during the braking cycle. The measuring unit is thus adapted to receiving signals from the engine which indicate its speed. The fourth measuring unit is illustrated in Figure 1. In this embodiment, the control unit is adapted to processing t_totai and t_engbrake with respect to t_Shift and n_eng according to predetermined rules, and to calculating a braking assessment value BA based on processed values for tengbrake and t_totai- The driver's use of correct gear for the situation can thus be assessed and he/she may be provided with feedback about his/her choice of gears.

The invention relates also to a method for assessing a driver's braking behaviour. The method is explained below with reference to the flowchart in Figure 2. A first step S21 determines when a braking cycle begins. This may vary depending on the particular braking situation to be assessed, as will be explained below. A second step S22 determines the time tengbrake when the vehicle's engine brake is used during the braking cycle. A third step S23 determines the time t_snift for gear changes during the braking cycle. A fourth step S24 determines when the braking cycle ends, which, as at step S21 , may vary in different situations. A fifth step S25 determines the total time t_totai for the braking cycle, and a sixth step S26 processes t_totai and t_engbrake with respect to t_shift according to predetermined rules. A seventh step S27 calculates a braking assessment value BA based on the processed values for t_engbrake and t_totai- According to an embodiment, BA is calculated on the basis that BA = t_engbrake / ttotai- The result is a BA value of between 0 and 1 , and the percentage of engine brake use time can be calculated as depicted in Figure 4. A braking cycle may begin in different ways depending on the situation in which the vehicle is at the time. We describe below a number of braking situations in which a driver can actively take corrective measures to reduce vehicle wear and also fuel consumption, and how these measures can be detected and assessed. Situation A

In this situation, the driver brakes actively to lower the vehicle's speed. A skilful driver consistently downshifts to contribute as much engine brake force as possible and also to avoid the engine having to idle during braking, which would cost fuel. Nor should the vehicle's gearbox be put into a neutral state during braking, except at very low vehicle speeds.

Detecting and assessing the driver's braking behaviour in situation A involves using the system explained with reference to Figure 1 and the method explained with reference to Figure 2. A braking cycle begins, for example, when the driver starts to brake after a period of driving during which the vehicle's speed has not been lowered by more than a predetermined threshold value. The braking cycle is regarded as ended when the driver accelerates or the vehicle's speed is below a given threshold value. The time t_engbrake when engine brake is used is

determined, and when, for example, there is clutch use a permissible time for changing gear is given. According to an embodiment, the rules then require that if tshift is greater than t_Shiftmax. which is a settable maximum permissible time for changing gear, then t_totai is processed on the basis that t_totai = ttotai + tsampie, where tsampie is a predetermined period of time. This is illustrated in Figure 3. When the vehicle is braked by engine brake, t_engbrake and t_totai are increased by t_sampie- When the vehicle changes gear, t_engbrake and ttotai are not increased until a maximum time tshiftmax for changing gear has passed. If the maximum time has passed but no gear has yet been engaged, then only t_totai is increased by t_sampie- This is repeated until a gear is engaged or the braking cycle has ended.

According to an embodiment, for braking to be assessed at all, a certain total brake time ttotai, which may depend on the vehicle's speed, is required.

The driver is preferably given a BA value in the form of a score based on the time tengbrake when engine brake was used relative to the total brake time t_totai, as illustrated in Figure 4. The expected proportion of engine brake use, i.e. the BA value, may depend on the vehicle's speed. Figure 4 shows the BA value limits as Fiow( o) and F_high(v₀), i.e. the limits for engine brake force at a certain vehicle speed v₀. When the driver's performance has been assessed, it is displayed to him/her, e.g. in the form of symbols and/or point scores. If a particular behaviour is detected, e.g. the driver disengaged the clutch and braked at high vehicle speeds, he/she may be presented with a hint on the display to encourage him/her not to use the clutch but use engine brake instead.

The driver scores well when the vehicle speed is lowered when he/she makes consistent downshifts, resulting in no need for fuel injection and less wear on the service brakes. According to an embodiment, account is also taken of whether the vehicle's exhaust brake is used, with consequent positive impact on the driver's braking method score.

Situation B

In this situation the driver wishes to maintain the vehicle's speed downhill and therefore ensure that it does not increase. A skilful driver will take care to downshift and maintain a higher engine speed which helps to reduce wear on the brakes. Exhaust brake use is also preferable in these situations. The primary consideration is to reduce wear on the service brakes, but also to reduce the risk of brake overheating which might lead to failure. Detecting and assessing the driver's braking behaviour in situation B involves applying the method explained with reference to Figure 2, with some further method steps illustrated in Figure 5. A braking cycle begins, for example, when the vehicle commences a downhill run. There are many ways of detecting downhill runs. One is to calculate the vehicle's running resistance on the basis of expected acceleration at a certain engine output. All the external forces on the vehicle may then be combined as running resistance, comprising inter alia gravitation, rolling resistance and air resistance. The braking cycle is regarded as ended when the driver accelerates or the vehicle's speed is below a given threshold value or the running resistance is below a certain value.

The driver's gear choice is analysed during the braking cycle and two times are calculated, t_engbrake and t_tot_ai- Fig. 5 t_totai increasing by t_sampie when there is no use of engine brake, i.e. when no gear is engaged. Preferably, a certain time t_Shiftmax is allowed here for changing gear, as in situation A. According to an embodiment, when a braking cycle has begun and the vehicle is engine-braking, the engine's speed n_eng is determined during the braking cycle. t_totai and t_engbrake are then processed with respect to t_Shift and n_eng according to predetermined rules, and a braking assessment value BA is calculated on the basis of the processed values for t_engbrake and ttotai- The assessment thus takes into account the speed of the engine and also how much time the driver takes to change gear. According to an embodiment, said predetermined rules require comparison of n_eng with limit values n_enghi_gh and n_engiow for the engine's speed, n_enghi_gh being an upper limit value and n_engi₀w a lower limit value. This provides a way of assessing the driver's choice of gear. According to another embodiment, the rules require that if n_eng is greater than n_enghi_gh, then t_tot_ai is processed on the basis that t_totai = t_totai ⁺ tsampie, and t_engbrake on the basis that t_engbrake = t_engbrake + tsampie- The driver is then assessed as having engaged correct gear for the situation, with necessary engine brake use.

According to an embodiment, if n_eng is less than or equal to n_enghigh> a check is done to see whether the driver uses exhaust brake during the braking cycle. If so and if n_eng is greater than n_enge haustbrake. then ttotai is processed on the basis that ttotal ⁼ ttotai ⁺ tsampie, and tengbrake ΟΠ the baSIS that t_engbrake ⁼ tengbrake ⁺ tsampie, Where nengexhaustbrake is an engine speed limit value related to the exhaust brake. If the control unit receives a signal to the effect that that the vehicle's exhaust brake has been used during the braking cycle and n_eng is greater than n_engexhaustbrake. then t_totai is processed on the basis that ttotai ⁼ totai ⁺ tsampie, and t_engbrake on the basis that tengbrake = tengbrake ⁺ tsampie- This makes it possible to evaluate also the driver's use of the exhaust brake during the braking cycle. Accordingly, according to an embodiment, if n_eng is greater than n_engiow and smaller than n_enghi_gh, then t_totai is processed on the basis that t_totai = ttotai ⁺ tsampie, and tencjbrake O the baSIS that t_en_gbrake ⁼ tencjbrake tsampie ( en_g-nenglow) (nencjhigh- n_engiow)- The driver thus engine-brakes, but the gear choice is not the best for the situation. Downshifting is therefore appropriate, and according to an embodiment this is suggested to the driver in the display. A suitable gear may then be calculated and suggested.

If the total engine brake force F_engbrake at the recommended engine speed n_engreq is greater than the composite brake force F_totbrake, no lower gear is required and no corrective measure is taken, since the driver should not be recommended to brake more than necessary. Braking more than necessary is of course needless and ultimately costs fuel. The composite brake force F_totbrake therefore includes service brakes. The recommended engine speed n_engreq is a threshold value which represents for example the lowest engine speed required in order to actively lower the vehicle's speed during engine braking. According to an embodiment, if the total engine brake force F_engbrake at the recommended engine speed n_engreq is less than or equal to the composite brake force Ftotbrake, and/or if n_eng is less than or equal to n_engiow. then t_totai is processed on the basis that t_totai = ttotai + t_sampie. where t_sam_Pie is, as previously mentioned, a predetermined period of time. Preferably, downshifting is then suggested to the driver. Here again a suitable gear may be calculated and suggested.

Figure 6 depicts an example of how the engine's speed n_eng varies during a period of time t when the driver wishes to maintain the same vehicle speed on a downhill run, i.e. situation B. The diagram also shows when the vehicle's exhaust brake is on or off during the same period of time. Table 1 shows how t_totai and t_engbrake will be calculated, depending inter alia on the driver's gear choice during the period t.

Table 1

Period Description Corrective measures ti Engine braking - engine speed more ttotal ^— ttotal ~*~ tsamplei

than n_enghigh tengbrake- tengbrake tsample t₂ Engine braking - engine speed less than ttotal ^— ttotal ⁺ tsample

n_enghi_gh but more than n_engiow tengbrake ⁼ tsample (neng- nenglow) / (nenghigh~nenglow) t₃ Engine braking - engine speed less than ttotal ⁼ ttotal tsample

Nengiow

U Changing gear (maximum permissible None

time: t_shift)

t₅ Engine braking - engine speed more ttotal ⁼ ttotal tsample)

than n_enghigh tengbrake- tengbrake tsample te Engine braking - engine speed less than ttotal ^— ttotal tsample

n_enghigh but more than n_englow tengbrake ⁼ t_sample (neng" nenglow) (nenghigh-nenglow) t₇ Exhaust braking - engine speed more ttotal ^— ttotal ~*~ tsamplei

than n_engexhaustbrake tengbrake⁼ tengbrake tsample te Exhaust braking - engine speed less ttotal ⁼ ttotal ⁺ tsample

than Or equal tO n_engexhaustbrake tengbrake ^— tsample (l"leng~

Engine braking - engine speed less than Henglow)

nenghigh ut ΓΠΟΓβ than n_englow

t₉ Engine braking - engine speed less than ttotal ⁼ ttotal ⁺ tsample

Denglow

According to an embodiment, t_sam_Pie is equal to the respective periods ti to t_g in the various situations above. After the braking operation, the driver's performance is scored in the same way as in situation A, but possibly with other parameters, as in Figure 4. Hints may also be given to the driver afterwards about he/she might handle a similar situation next time. Situation C

In this situation the driver wishes to freewheel, with consequently no acceleration and no braking. This may for example arise on a gentle downhill run, in which case a gear also needs to be engaged instead of depressing the clutch pedal or using neutral gear. There are several reasons for this. For example, with no gear engaged the engine will idle, involving fuel consumption. There is often great risk that the extra energy gained by freewheeling might have to be braked away.

Detecting and assessing situation C involves applying the method and system described with reference to Figures 1 and 2. According to an embodiment, a braking cycle begins when the running resistance is calculated at a certain value which indicates that the vehicle is commencing a gentle downhill run. The braking cycle is regarded as ended when the driver accelerates or the vehicle's speed is below a given threshold value or the running resistance is below a certain value. According to an embodiment, the system is adapted to receiving information about, and catering for, a coming traffic situation. This information may for example be received via radio messages containing information about the location of the traffic situation. The driver may thus be made aware of traffic situations in which the vehicle's speed needs to be lowered, e.g. traffic accident or queue, and may adapt the vehicle's speed accordingly. Information about a coming road situation may also be received via map data about the itinerary and the vehicle's location. The vehicle's location may for example be received via a GPS unit in the vehicle. The driver may thus be made aware of traffic situations in which the vehicle's speed needs lowering, e.g. a roundabout, an intersection etc., and may adapt the vehicle's speed accordingly. A further example of a road situation is a speed limit requiring the driver to lower the vehicle's speed.

The driver is preferably encouraged to use engine brake in order to lower or adapt the vehicle's speed before the coming traffic situation. According to an

embodiment, where the driver uses only engine brake during the braking cycle to lower the vehicle's speed, this is rewarded by maximum braking assessment value BA and an encouraging hint is presented to him/her via the display. The driver is preferably given a score based on the time t_engbrake when engine brake was used relative to the total brake time t_tot_ai, as illustrated in Figure 4. The expected proportion of engine brake use may depend on the vehicle's speed. Where the vehicle exceeds a certain speed with no gear engaged, the driver is preferably given a hint via the display to encourage him/her to engage a gear or release the clutch pedal. In this case he/she is preferably also given a certain time tshiftmax to change gear, as in situations A and B. Where a gear is engaged, the driver is rewarded by the addition to t_engbrake of as much time t_sampie as to t_totai , which means that the calculated braking assessment value BA will be higher.

The invention relates also to a computer programme product comprising computer programme instructions for enabling a computer system in a vehicle to perform steps according to the method described above when the computer programme instructions are run on said computer system. The invention comprises also a computer programme product which has the computer programme instructions stored in it on a medium which can be read by a computer system. The present invention is not confined to the embodiments described above.

Sundry alternatives, modifications and equivalents may be used. The above embodiments therefore do not limit the scope of the invention, which is defined by the attached claims.

Claims

1. A method for assessing a driver's braking behaviour,

c h a r a c t e r i s e d in that the method comprises:

- determining when a braking cycle begins;

- determining the time tengbrake when the vehicle's engine brake is used during the braking cycle;

- determining the time t_Shif taken to engage a gear during the braking cycle;

- determining when the braking cycle ends;

- determining the total time t_tot_ai for said braking cycle;

- processing t_totai and tengbrake with respect to t_Shift according to predetermined rules, and calculating a braking assessment value BA based on processed values for tengbrake and t_totai, which rules require that if t_sriift is greater than tshiftmax. which is a settable maximum permissible time for changing gear, then t_totai is processed on the basis that t_totai = ttotai + t_sampie, where t_sampie is a predetermined period of time, and the calculated braking assessment value BA is presented to the driver.

2. A method according to any one of the foregoing claims, in which BA is calculated on the basis that BA = t_engbrake / ttotai-

3. A method according to any one of the foregoing claims, which method comprises

- determining the engine's speed n_eng during the braking cycle,

- processing ttotai and tengbrake with respect to t_sampie and n_eng according to

predetermined rules, and

- calculating a braking assessment value BA based on processed values for tengbrake and ttotai -

4. A method according to any one of the foregoing claims, in which said predetermined rules require comparison of n_eng with limit values n_enghigh and n_engiow for the engine's speed, n_enghigh being an upper limit value and n_engiow a lower limit value.

5. A method according to claim 4, in which the rules require that if n_eng is greater than n_enghigh, then t_totai is processed on the basis that ttotai = ttotai + tsamplei and tengbrake ΟΠ the baSIS that tengbrake ⁼ tengbrake tsamplei

if n_eng is greater or equal to n_engiow and smaller than or equal to n_enghigh, then t_totai is processed on the basis that ttotai ⁼ ttotai ⁺ tsampie. and t_engbrake on the basis that tengbrake ^— tengbrake tsample (neng-nenglowV(nenghigh-nenglow)! and

if n_eng is less than n_engiow> then t_totai is processed on the basis that t_totai = t_totai + tsamplei

where t_sampie is a predetermined period of time.

6. A method according to any one of claims 3-5, under which method , if the vehicle's exhaust brake was used during the braking cycle and n_eng is greater than n_engexhaustbrake> then ttotai is processed on the basis that t_totai = ttotai ⁺ t_sampie, and tengbrake ΟΠ the baSIS that tengbrake ^— tengbrake ⁺ tsamplei where n_engexhaustbrake is an engine speed limit value related to the exhaust brake.

7. A system for assessing a driver's braking behaviour,

c h a r a c t e r i s e d in that the system comprises a control unit connected to a first measuring unit adapted to determining when a braking cycle begins; a second measuring unit connected to the control unit and adapted to determining the time t_engbrake when the vehicle's engine brake is used during the braking cycle, and to delivering on the basis thereof a second time signal containing t_engbrake; a third measuring unit connected to the control unit and adapted to determining the time tshift taken to engage a gear during the braking cycle, and to delivering on the basis thereof a third time signal containing t_snift; the first measuring unit is adapted to determining when the braking cycle ends, determining the total time t_totai for said braking cycle and delivering to the control unit on the basis thereof a first time signal containing t_totai. the control unit is further adapted to processing t_totai and tengbrake with respect to tshift according to predetermined rules, and to calculating a braking assessment value BA based on processed values for t_engbrake and ttotai. the rules require that if t_Shift is greater than tshiftmax. which is a settable maximum permissible time for changing gear, then t_totai is processed on the basis that t_totai = ttotai ⁺ tsampie, where t_sampie is a predetermined period of time, and the calculated braking assessment value BA is presented to the driver on a display.

8. A system according to claim 7, in which BA is calculated on the basis that BA = tengbrake ttotai-

9. A system according to either of claims 7 and 8, which system comprises a fourth measuring unit adapted to determining the engine's speed n_eng during the braking cycle; and the control unit is adapted to processing t_totai with respect to t_shift and n_eng according to predetermined rules, and to calculating a braking assessment value BA based on processed values for tengbrake and t_totai-

10. A system according to any one of claims 7 to 9, in which said predetermined rules require comparison of n_eng with limit values n_enghigh and n_engiow for the engine's speed, n_enghigh being an upper limit value and n_engiow a lower limit value.

1 1 . A system according to claim 10, in which the rules require that if n_eng is greater than n_enghigh, then t_totai is processed on the basis that t_totai = t_totai ⁺ tsamplei and tengbrake ΟΠ the baSIS that tengbrake ⁼ tengbrake ⁺ tsampie.

if n_eng is greater or equal to n_engiow and smaller than or equal to n_enghigh, then t_totai is processed on the basis that ttotai ⁼ ttotai ⁺ tsampie. and t_engbrake on the basis that tengbrake ⁼ tengbrake tsampie (neng-nenglow)/(nenghigh-nenglow). and

if n_eng is less than n_engiow, then t_totai is processed on the basis that t_totai = ttotai + tsamplei

where t_sampie is a predetermined period of time.

12. A system according to any one of claims 9-1 1 , in which, if the control unit receives a signal to the effect that the vehicle's exhaust brake was used during the braking cycle and n_eng is greater than n_engexhaustbrake, then t_totai is processed on the basis that ttotai ⁼ ttotai ⁺ tsampie, and t_engbrake on the basis that teng rake = t_engbrake ⁺ t_Sampie, where n_engexhaustbrake is an engine speed limit value related to the exhaust brake.

13. A computer programme product comprising computer programme instructions for enabling a computer system in a vehicle to perform steps according to the method of any of claims 1-6 when the computer programme instructions are run on said computer system.

14. A computer programme product according to claim 13, in which the computer programme instructions are stored on a medium which can be read by a computer system.