WO2005077724A1

WO2005077724A1 - Longitudinal control system for keeping a vehicle stationary, said vehicle being equipped with an automatic gear-box

Info

Publication number: WO2005077724A1
Application number: PCT/FR2004/000033
Authority: WO
Inventors: François Fauvel
Original assignee: Renault S.A.S.
Priority date: 2003-01-10
Filing date: 2004-01-09
Publication date: 2005-08-25
Also published as: KR20060026401A; EP1594729A1; FR2849811B1; FR2849811A1; JP2006520301A

Abstract

The invention relates to a system for automatically keeping a motor vehicle stationary, comprising a heat engine, an automatic gear-box and a service brake which is controlled by an electronic control system (1). The invention is characterised in that it comprises: means for estimating the resistant loads applied to the vehicle; means for calculating the braking torque necessary to keep the vehicle stationary, as a function of the aforementioned estimation; and means for transmitting the braking torque value thus calculated to the service brake control system (1).

Description

The present invention relates to a system for automatically holding a motor vehicle stationary, comprising an automatic gearbox. The development of piloted and decoupled braking systems called "brake by wire" makes possible the appearance of new services useful to drivers of motor vehicles. In situations where a vehicle stops, it is advantageous to immobilize this vehicle by relieving the driver of this task. This reduces his workload and therefore his fatigue; safety is also improved because the vehicle is not likely to move forward or backward without the driver's wish. These systems are particularly useful in the case of automatic gearboxes, where the torque when stationary is quite high (drag) and must almost always be compensated for by pressing the brake pedal. Known parking brake or electronically controlled service brake systems, activated by the driver or automatically when the vehicle is stationary, exert a braking torque which generally takes account of the slope of the road, measured by a sensor. By this means, it is possible to calculate the braking torque necessary to maintain the stop, as well as manage the take-off phases while avoiding any backing up of the vehicle on a hill. In the case of automatic gearboxes, the parking brake can be activated in the D or Drive position of the gearbox control. The transmission is on a forward gear. The braking torque must then compensate for the so-called ramping torque provided by the powertrain (GMP) when stopped, which is quite high. There are solutions without automatic maintenance of the stationary vehicle in which the automatic gearbox can be disengaged if the driver has his foot on the brake pedal. There are solutions with automatic maintenance of the stationary vehicle in which a clutch is automatically opened and the transmission switched to the Neutral position as soon as an automatic braking force is applied (see patent FR-2 809065). When the driver cuts the engine, it is necessary to maintain a braking torque. This is not a problem in the case of cable parking brake systems, which remain applied without energy input. But if the holding is stopped by a braking system requiring an energy supply to provide lasting braking torque (example: Eiectro-Hydraulical Braking, Electro-mechanical Braking), known solutions consist in switching, when the engine is stopped, to a braking system that does not require any energy input. This is for example the case in patent application DE-196 32 863 A1. In the known solutions, the following problems remain. Slope sensors have a high cost. The braking torque is not optimized as a function of the GMP (powertrain) torque when stationary: the stress on the braking system is higher than necessary, which accelerates wear and consumes energy. Having to depress the brake pedal to disengage the automatic transmission when stationary represents undue hardship for the driver, and is not appropriate in the case of an automatic vehicle maintenance system stopped. In the case of patent FR-2 809 065, which proposes an automatic holding system when stationary, the solution proposed for uncoupling the GMP from the wheels applies in practice to robotic mechanical gearboxes comprising a single clutch, and not automatic gearboxes with distributed clutches. In known solutions, the parking brake is applied when the engine is off, while the transmission would be able to immobilize the vehicle alone. An expensive system for controlling the active parking brake without adding energy is therefore systematically used. By extension, it is not possible to remove the parking brake, even if the regulations allow it. All these factors increase the costs of manufacturing and using the vehicle, or limit driving pleasure. The invention thus relates to an automatic holding system when a motor vehicle is stopped, comprising a heat engine, an automatic gearbox and a service brake controlled by an electronic control system. According to the invention, the automatic standstill system is characterized in that it comprises means for estimating the resistant forces applied to the vehicle, means for calculating on the basis of this estimate, the braking torque necessary to maintain the stationary vehicle and means for transmitting the value of the braking torque thus calculated to the service brake control system. The system according to the invention has the following advantages in particular: reduction of the manufacturing cost by removing the sensor, - reduction of the manufacturing cost by eliminating an actuator, - reduction of the electric consumption of the piloted braking system, - reduction of the fuel consumption, - reduction of the wear of the braking system, - improvement of the approval driving. According to a preferred version of the invention, the means for estimating the resistant forces applied to the vehicle take account of the torque exerted by the powertrain, when a ratio of the automatic gearbox, other than the "Park" position, is engaged. Preferably, said means also take into account the slope on which the vehicle is located, wind, the holding torque of the braking system exerted on the wheels, the nominal resistive force of the vehicle, such as its aerodynamic drag and its rolling resistance. According to an advantageous feature of the invention, the system comprises means for controlling the removal of the braking torque, when the "Park" position is engaged. According to another characteristic of the invention, the system comprises means for controlling when the vehicle is stopped, the passage of the automatic gearbox in the disengaged position, including when the driver is not stepping on the pedal. brake. According to another particular feature, the system comprises means for progressively reducing the braking torque, when the automatic gearbox is shifted to the "Park" position. This arrangement allows a comfortable docking in this "Park" position, without oscillations or jolts. Other features and advantages of the invention will appear in the description below. In the appended drawings, given by way of nonlimiting examples: FIG. 1 is the input / output diagram of the vehicle standby controller: version not comprising the strategy c of automatic passage through the Park of the gearbox. automatic speeds, - Figure 2 is the input / output diagram of the vehicle standby controller: version including strategy c, - Figures 3 and 4 are diagrams of the various functions of the vehicle standby controller (with / without strategy c), - Figure 5 is the input / output diagram of the longitudinal force estimator - variant using a longitudinal acceleration sensor - Figure 6 is the input / output diagram of the longitudinal force estimator - variant without acceleration sensor longitudinal, - Figure 7 is the input / output diagram of the standstill strategy when the engine is running outside the Park position of the automatic transmission, - Figure 8 is the input / output diagram of the stop authorization strategy of the engine, - Figure 9 is the input / output diagram of the automatic passage strategy in Park, - Figure 10 is the input / output diagram of the comfortable docking strategy in Park. Figures 1 and 2 show that the system according to the invention comprises a controller (2) for holding the vehicle stationary, in functional relation with a control system (1) of the service brake, a control system (3 ) of the transmission and a control system (4) of the heat engine. The vehicle standstill controller (2) is adapted to receive the following data: position of the accelerator pedal, - position of the brake pedal, - state of the parking brake, - request to stop the vehicle, - position of the automatic gearbox lever, - vehicle speed, From the service brake control system (1): - the brake pressure,

From the transmission control system (3): - the nature of the gear engaged, From the engine control system (4): - the engine torque, - the situation with the engine stopped. The vehicle standstill controller (2) is further adapted to transmit the following commands: to the service brake control system (1): - the set braking torque setpoint, to the transmission control system (3): - the clutch release request, to the engine control system (4): - the engine stop authorization, - the engine torque limitation. In the case (see FIG. 2) where the automatic gearbox includes an automatic device in the "Park" position, the controller (2) for keeping the vehicle stationary is further adapted to transmit to the control system (3) the order to move to the Park position. The present invention comprises the following four elements: - an estimate of the longitudinal forces exerted on the vehicle, - a strategy for keeping the vehicle stationary, engine running, outside the Park position of the automatic gearbox, - a shift strategy automatic transmission in Park when the engine is stopped, - a comfortable approach strategy in Park position, a. Estimation of the forces exerted on the vehicle (see also Figures 5 and 6).

We write the fundamental equation of the dynamics applied to the center of gravity of the vehicle:

CC resist nom ~ ^t ~ resist suppl (1) rr ^~ with: M: Mass of the vehicle (kg) r Longitudinal acceleration (ms ^"2 ) CGMP '- Traction torque of the powertrain, exerted on the wheels (Nm) Cprei _n • ' _Holding torque of the braking system, exerted on the wheels (Nm) F _reS isi_nom' - Nominal resistance force (aerodynamic drag, rolling resistance of tires, resistance of bearings, etc.) (N) Fresist_suppi - Additional resistant forces (slope, wind, etc.) (N) r: radius of the wheels (m)

Part of the longitudinal forces exerted on the vehicle is known or can CC be estimated or measured: ^GMP , ^Frem , F _resis t_ _πom . A part is unknown: rrr _es ist_suppl • To estimate this unknown term F _resisLsUpp i, four different solutions are described below, which constitute as many variants of this invention. a.1 Method using a derivation of the speed and an estimation of the traction torque and the braking torque.

We apply the following formula: t name

where: C _βMP : Estimated _powertrain traction torque (Nm), expressed at wheel C: Estimated braking system torque (Nm), expressed at wheel F. '' Estimated nominal resistive forces (Nm) Vm _es _m - Speed measured using a speed sensor and digitally filtered (ms ^"1 )

C _GMP can be estimated from the torque of the heat engine and the knowledge of the transmission reduction ratio over the current ratio. CGMP = C * " ^• ratio _trans ^ou: C _mot • 'estimate of the engine torque ratiojtrans: gear reduction ratio of the transmission C _word is calculated conventionally from an observation of the air pressure in the intake manifold or of the throttle angle or of the fuel flow as well as of the engine speed. Alternatively, a direct measurement of the torque or tensile force can be used by a sensor. In the case where the GMP is driven from a wheel torque setpoint, it is possible to use a prediction of the traction force of the GMP calculated from the wheel torque setpoint, possibly delayed by a duration representative of the time of GMP response.

& P _{brake could} ^be estimated from a quantity representative of the clamping force of the brake calipers. In the case of a hydraulically controlled braking system, the following formula can be used: 4 C _Brake = _J 2P s _l -c _i -ri where: P; : pressure in the wheel brake cylinder / S; : section of the wheel brake cylinder / C _/ : friction coefficient pad / disc of the wheel / η: mean friction radius disc / pad of the wheel / In the case of a torque-controlled braking system, we can make a prediction of the braking torque from the braking torque setpoint, possibly delayed by a duration representative of the response time of the braking system. The nominal resistance forces can be calculated conventionally from an empirical relationship or from a mapping involving the speed of the vehicle: F _res i _st _ _ncm = f (ScX, M, V _mes ) where: Scx: coefficient aerodynamic drag

^F _res i _{st Supp} ι ^{esi ensu} filtered ^you to remove noise associated with signal measurements. a.2 Method using a derivation of speed and a measurement of longitudinal acceleration.

This variant uses a characteristic property of a conventional construction accelerometer (of the strain gauge type for example) placed in the longitudinal axis of the vehicle. This sensor actually measures the difference between the actual acceleration of the vehicle and the pseudo-acceleration of gravity due to the slope: Mr = MT _acceleration + F _slope or 'acceleration acceleration given by the accelerometer • slope • longitudinal force due to the slope

It is therefore possible to estimate F _slope by the following formula

Now Fpente has a preponderant share in F _resist _ _SU ppi. We therefore assume F _slope ι ~ resist_suppi- U OR:

As in p ¹ récédente Alternatively, E resi .st _sιφpl, must then be filtered P ^r our eliminate noise associated with signal measurements. a.3 Method using an observer and an estimate of the traction torque and the braking torque This variant uses a Luenberger observer, the principle of which is known to automation specialists. It can be used when there is a measurement of the vehicle speed (v _mes ) and a measurement or estimate of the traction torque of the GMP C _GMP and the braking torque c. We start by writing a simplified model of the longitudinal dynamics of the vehicle: F. d) gives: v = E. . + resist _suppl (2)

OR . I nominal acceleration which would be that of the vehicle if r ^' disturbances ~ 0 with] C GMP + ι _. C ^ FF „rreeimn_ ₊ p ^• nominal M \ ^{rr ~} On the other hand, we will assume that the variations of F _perturbat i _0ns are relatively slow compared to the dynamics of the vehicle. This allows to write: perturnatlons = 0 (3)

From equations (2) and (3), we can write the model in the following state form:

X = AX + BU Y = CX + DU with: X = system state vector | _ resist _suppl J LV = Γ nominal system input system output

A = o - M B =; C = [l 0]; D = [0] 0 0

We construct a Luenberger observer, which will allow us to estimate the states v and F _perturbat io _nS from the measured speed v _mes and a prediction of r _nom ; _{na e} . We therefore pose: C GMP ein ^• nominal + - c Fr + E .., M

The observer equation is as follows: X = AX + BU + L (Y - CX - DU) with: estimation of the state vector X vector of the gains of the observer y = v; A =; C = [l 0]; £> = [0]

We discretize this equation to obtain an expression of the states at time N + 1 from the states and measurements at time N: X _{N + l} = (A -st + l) X _N + (B -st) u + (L -sή- (γ-CX-Du) whence finally

^ + 1 = 1 - k ^{• S} ΦN + 77 ^'F resist_suppl _N + st _{nomiπale N} + t _j ^• st ^• v _{mes N} M' resist _suppl N + l ~ ^ 2 ^"S * ' ^V N ^" * ^" ^ resist _suppl N ^ ^ 2 ^'S ^ ^{' V} mes N There is no need to filter the measured speed or additional _resist F, the information obtained being naturally little noisy thanks to the use of an observer. using an observer and a measure of longitudinal acceleration

In this variant, we assume that F _slope ≈ F _resist _ _SUpp i, as for variant a.2. We replace equation (2) by the following equation: E 'resi .st _suppï αccèîêro (4) M The construction of the observer is analogous to variant a.3, by replacing

'nominal by I accelerated •

From where ^V N + 1 ~ V ^S * rN ⁺ , ^' * ^' 'resist _suppl N ^{+ S} * ^' accelerates N ^" * ^"'S ^ ^{' V} mes NZ resist _sιφpl N + _l ⁼ ~ ^ 2 'St' V _N + J _resist _ _{supp! N} + 1 ₂ ^• St ^• V _{mes N}

It is not necessary to filter the measured speed or additional _resist F, the information obtained being naturally little noisy. b. Strategy to keep the vehicle stationary, engine running, out of Park position of the automatic gearbox. The vehicle is stopped when the vehicle speed is observed. The service brake and the automatic gearbox are then controlled so as to minimize the energy consumption and wear of the various systems.

An authorization to stop the engine or inform the driver strategy is also applied, in the event that it is not possible to automatically control the engagement of the Park position of the transmission. b.1 Calculation of the service brake torque setpoint, The value of E resi .st _suppl is used, calculated by one of the methods described above to calculate the braking torque just necessary to maintain the vehicle at l 'stop. The following two strategies are applied simultaneously: Anti-advance: the braking torque preventing the vehicle from moving forward is calculated as follows: C αnti_αvαnce = -C GMP —F resist_suppl - r - F resist_nom - m 1 where: C _ant i_ _ram page: Braking torque preventing the vehicle from moving forward C _GMP : Estimated GMP torque m ₁ : Safety margin

This torque is canceled if the driver presses the accelerator, which means that he wants the vehicle to move forward. Thanks to the term F _{resist suppl} , the braking torque is optimized with respect to non-nominal resistive forces (in particular the slope). Thanks to the term C _GMP , it is optimized in relation to the torque exerted by the GMP. In particular, in the Neutral and Disengaging position when stationary, C _GMP is practically zero; the anti-advancing torque is therefore automatically reduced. In reverse, C _GMP is negative, the anti-advance torque is also reduced. • Anti-kickback

C anti_return = —C GMP - F resist _suppl - r - F resist_nom + m 2 where: C _ant i_ _received i 'Braking torque to prevent the vehicle from rolling back m ₂ : Torque safety margin In this expression, the convention used is that the couples and the efforts are positive when they tend to move the vehicle forward, negative otherwise. According to this convention, the anti-kickback torque must be positive. Note that F _resjst _ _nom is negative when the vehicle tends to move forward, positive when it tends to move back. Like the anti-forward torque, the anti-reverse torque is optimized according to the state of the GMP and the disturbances exerted on the vehicle. The safety margin m ₂ is reduced when the driver has his foot on the accelerator, in order to minimize the response time at takeoff. The anti-reverse torque is canceled as soon as take-off has been detected (vehicle speed not zero). Final braking torque: To simplify the expressions, we now consider that the torque requested from the braking system is always negative. Finally, the torque required for the function “keeping the vehicle stationary outside the Park” is as follows: Jarret ~

ti-back)

Where: C _stops : torque required to keep the vehicle stationary C _au tres_s stè _m es: torque possibly requested by other driving assistance systems When the transmission status changes, the braking torque requested can be modified (example: Neutral shift <- »Drive ). In this case, any increase in torque demand (in absolute value) must be applied immediately to ensure that the vehicle remains stationary. On the other hand, if a reduction in torque (in absolute value) is requested, it must be applied gradually to allow the transmission time to change state. To this end, the _stop torque C is filtered with a filter of low time constant in the direction of growth (in absolute value), and a larger time constant in the direction of decrease. Take-off phase: When taking off in forward, the driver presses the accelerator, which immediately suppresses the anti-advance torque. The estimated GMP torque increases, which results in a reduction and - if the driver accelerates sufficiently - cancellation of the anti-kickback torque. The vehicle then takes off comfortably and without reversing, and with a minimum delay time compared to the driver's request. As soon as the effective takeoff has been detected, the anti-reverse and anti-advance strategies are eliminated. They are reactivated as soon as the vehicle stops next. b.2 Checking the automatic gearbox, outside the Park position (see figure

7). Some Automatic Gearboxes (BVA) allow automatic disengagement of the transmission when the vehicle is stopped with the engine running in the Drive position. This allows a big reduction in consumption in town and in traffic jams, by canceling the resistant torque exerted by the transmission on the engine. This stopping clutch mode is achieved by opening one or more of the distributed clutches of the automatic gearbox. Known strategies for controlling this declutching when stationary require the driver to have his foot on the brake pedal. This ensures that the driver wishes to keep the vehicle stationary, and prevents the risk of the vehicle rolling backwards when declutching. With an automatic hold-to-stop system, there are other ways of determining the driver's will, and of preventing the vehicle from rolling back. In addition, the the driver no longer has to step on the brake pedal to keep the vehicle stationary. The strategy proposed by this invention is as follows: when the automatic standstill system is active, the clutch is controlled when the automatic gearbox is stopped if the following conditions are simultaneously verified: Accelerator pedal not pressed - Vehicle stopped - Gearbox control unit in Drive position - Time since vehicle stopped above a threshold The clutch is re-engaged when one of the following conditions is satisfied: Accelerator pedal pressed - Vehicle in movement - Gearbox control unit in a position other than Drive To avoid suddenly during re-engagement, cause of discomfort and wear of the automatic gearbox, the engine torque is limited as long as the forward gear is not engaged.

b.3 Engine stop authorization strategy (see figure 8). This strategy applies in the case where there is no system allowing the Park position to be automatically engaged. If the driver requests the engine to stop, for example by pressing a Start / Stop button while the transmission is not in the Park position, or a parking brake has not been previously activated, it It is not possible to guarantee that the vehicle will remain permanently stationary. Consequently, for safety reasons, it is prohibited to stop the engine in these situations, which indicates to the driver that he must use one of the systems making it possible to keep the vehicle permanently stopped with the engine stopped. This strategy is also applied to prohibit any automatic engine shutdown that would be required by a so-called Start / Stop strategy aimed at reducing consumption, polluting emissions and noise. In the event that the engine stops unexpectedly following a fault, the driver is informed by an audible and visual warning signal ("driver alert") that it is imperative to engage the parking brake or the Park position of the automatic gearbox to ensure the vehicle is immobilized. vs. Strategy for automatic transmission changeover in Park when the engine stops (see Figure 9). This strategy applies if there is an automatic gearbox with an electric control enabling the Park position to be activated without the driver's intervention. In this case, when the driver or a Stop / Start strategy cuts the engine and the vehicle is stationary, the Park position of the automatic gearbox is immediately selected, in order to allow the vehicle to be maintained at judgment. The same applies during an unplanned engine shutdown following a technical incident, if the vehicle is stopped. When the engine is restarted, the driver must select forwards or backwards himself so that the gearbox leaves the Park position.

This avoids the driver having to activate the Park position or a parking brake himself when the engine is stopped, while ensuring that the vehicle remains stationary. This strategy also eliminates the need for an expensive parking brake control system. If the regulations allow it, it is even possible to envisage the complete elimination of the conventional parking brake system. d. Comfortable approach strategy in the Park position of the automatic gearbox (see Figure 10). When this position is selected by the driver or activated automatically, it is no longer necessary to maintain a braking torque to immobilize the vehicle, whether it is the torque exerted by a parking brake or that of a brake. piloted service. However, the existence of games and stiffness in the transmission, as well as elastic connections between the GMP and the body may cause the vehicle to move a few centimeters, then a jerk and unpleasant oscillations if we abruptly cancels the braking torque after engaging the Park position. This is why we use a strategy of progressive reduction of the torque, in order to achieve a comfortable docking in the Park position. This strategy applies when the engine is running. It is also used in the event that the engine is stopped by the driver or by an automatic Stop / Start type system shortly after the Park position is engaged. Indeed, the energy reserve usable by the piloted service brake system (coming from an active booster or from a pressure accumulator or a battery) is sufficient for this short-term operation.

The following four phases are applied: Decision to remove the braking torque:

Two situations must be distinguished: 1. Engine running: The following conditions must be met to authorize the reduction of the braking torque. - Vehicle stopped - \ F _r esist_suppi \ below a threshold, to keep braking on a steep slope - No depressing on the brake pedal - Delay elapsed since the vehicle stopped and no depressing on the brake pedal 2 Engine stopped: In this case, the decision to reduce the braking torque is taken immediately without further conditions, during the period of time during which there is available energy. Gradual reduction of the braking torque: The braking torque is first rapidly reduced from the value calculated in paragraph b.1 to the minimum value allowing the vehicle to be stationary (the safety margins m-, and m ₂ are deleted). Then it is gradually reduced to zero. This development takes account of the slope, and adopts a profile which ensures comfortable docking of the vehicle in the parking position. Restoring the braking torque Here again, two cases must be distinguished: 1. The engine had remained running. The braking torque is reactivated instantly as soon as the driver presses the brake pedal. This ensures that the vehicle will remain stationary if the driver engages the transmission in a position other than Park; there is no risk that this last action is carried out without pressing the brake, because the gearbox lever then conventionally remains locked in the Park position. 2. The engine was stopped The braking torque is reactivated instantly when the engine is started.

Claims

1. System for automatically keeping a motor vehicle stationary, comprising a heat engine, an automatic gearbox and a service brake controlled by an electronic control system (1), characterized in that it comprises means for estimating the resistant forces applied to the vehicle, means for calculating on the basis of this estimate, the braking torque necessary to keep the vehicle stationary and means for transmitting the value of the braking torque thus calculated towards the system of service brake control (1).

2. System according to claim 1, characterized in that the means for estimating the resistant forces applied to the vehicle take account of the torque exerted by the power train, when a ratio of the automatic gearbox, other than the position " Park ”, is engaged.

3. System according to claim 2, characterized in that said means also take into account the slope on which the vehicle is located, wind, the holding torque of the braking system exerted on the wheels, the nominal resistance force. of the vehicle, such as its aerodynamic drag and its rolling resistance.

4. System Sefon one _of, claims 1 to _3? characterized in that it further comprises means, for controlling the removal of the braking torque, when the, "Park" position is engaged.

5. System according to one of claims 1 to 4, characterized in that it further comprises means for controlling when the vehicle is stopped, the passage of the automatic gearbox in the disengaged position, including when the driver does not have your foot on the brake pedal.

6. System according to claim 5, characterized in that it further comprises means for controlling a reduction of the braking torque taking into account the removal of the torque exerted by the power train.

7. System according to one of claims 1 to 6, characterized in that it further comprises means for gradually reducing the braking torque, during the passage of the automatic gearbox towards the "Park" position.

8. System according to one of claims 1 to 7, characterized in that it comprises a controller (2) for keeping the vehicle stationary, in functional relation with a control system (1) for the service brake, a transmission control system (3) and a combustion engine control system (4).

9. System according to claim 8, characterized in that the controller (2) for keeping the vehicle stationary is adapted to receive the following data: a. position of the accelerator pedal, b. brake pedal position, c. parking brake condition, d. request to stop the vehicle, e. position of the automatic gearbox lever, f. vehicle speed,

From the service brake control system (1): g. brake pressure, From the transmission control system (3): h. the nature of the gear engaged, From the engine control system (4): i. the engine torque, j. with the engine stopped, the vehicle standstill controller (2) is further adapted to transmit the following commands: to the service brake control system (1): k. the braking torque setpoint when stopped, at the transmission control system (3): I. the clutch release request, at the engine control system (4): m. authorization to stop the engine, n. limitation of the engine torque.

10. System according to claim 9, characterized in that in the case where the automatic gearbox comprises an automatic device in the "Park" position, the controller (2) for keeping the vehicle stationary is further adapted to transmit to the transmission control system (3) the order to move to the Park position.