Method for determining the mass of a motor vehicle

Abstract

A method for the provisional determination of the mass of a motor vehicle, for controlling a starting operation when the motor vehicle is at rest. The method determines the mass of the motor vehicle as a function of inclination information about the motor vehicle or the road on which the motor vehicle is located, and as a function of a force required for releasing an engaged parking lock while the motor vehicle is at rest.

Claims

1. A method for provisional determination of a mass of a motor vehicle for a purpose of controlling a starting operation from when the motor vehicle is at rest, the method comprising: proceeding with the method when the motor vehicle is stationary and a parking lock of the motor vehicle is engaged, and the parking lock when engaged locking a transmission output shaft; obtaining inclination information of the motor vehicle or a road on which the motor vehicle is located, and the inclination information being obtained from at least one of a sensor device and a navigation device; determining a force required to release the engaged parking lock while the motor vehicle is at rest; determining the mass of the motor vehicle as a function of the inclination information about the motor vehicle or the road on which the motor vehicle is located, and as a function of the force required to release the engaged parking lock while the motor vehicle is at rest; determining a starting gear or shifting characteristics for the starting operation of the motor vehicle based on the determined mass of the vehicle, and starting the motor vehicle using the determined starting gear or the determined shifting characteristics.

2. The method according to claim 1, further comprising determining the mass of the motor vehicle at one of: after each release of the parking lock; after a fresh start of the motor vehicle when the parking lock is released; after the parking lock is released when a control unit is initialized; and when the parking lock is released after the motor vehicle has been stationary for longer than a specifiable time.

3. The method according to claim 1, further comprising, with a parking lock actuator in a form of a piston-cylinder unit having a piston which is acted upon by a pressure medium for releasing the parking lock, determining the force required to release the parking lock as a function of a pressure required to release the parking lock in relation to a piston area of the piston acted upon by the pressure.

4. The method according to claim 3, further comprising acting upon the piston of the piston-cylinder unit, forming the parking lock actuator with a specified set-point pressure which varies either in steps or in a ramp-like manner.

5. The method according to claim 1, further comprising, with the parking lock being an electric actuator through which an electric current flows in order to release the parking lock, determining the force required to release the parking lock as a function of an amount of the electric current.

6. The method according to claim 1, further comprising determining the inclination information of the motor vehicle or the road on which the motor vehicle is located by the sensor device which is in a form of either an inclination sensor arranged on the vehicle or an acceleration sensor arranged on the vehicle.

7. The method according to claim 1, further comprising determining the inclination information of the motor vehicle or the road on which the motor vehicle is located, by the navigation device.

8. A control unit of a motor vehicle, which is designed to carry out the method according to claim 1 for the provisional determination of the mass of the motor vehicle.

9. A non-transitory computer readable medium having a computer program product with program code means, which are stored on a computer-readable data carrier, for provisional determination of a mass of a motor vehicle for a purpose of controlling a starting operation of the vehicle from when the motor vehicle is at rest, the provisional determination including proceeding when the motor vehicle is stationary and a parking lock of the motor vehicle is engaged, obtaining inclination information of the motor vehicle or a road on which the motor vehicle is located from at least one of a sensor device and a navigation device, determining a force required to release the engaged parking lock, determining a mass of the motor vehicle as a function of inclination information about the motor vehicle or the road on which the motor vehicle is located, and as a function of the force required for releasing the parking lock engaged while the motor vehicle is at rest, determining a starting gear or shifting characteristics for the starting operation of the motor vehicle based on the determined mass of the vehicle, and starting the motor vehicle with the determined starting gear or the determined shifting characteristics, and the provisional determination being carried out when the computer program product is run on a control unit of the motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below, the invention is explained in greater detail with reference to the attached figures, which show:

(2) FIG. 1: A schematic representation of a parking lock of a motor vehicle;

(3) FIG. 2: A first pressure variation for controlling a parking lock actuator; and

(4) FIG. 3: A second pressure variation for controlling a parking lock actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The parking lock fora motor vehicle shown in FIG. 1 comprises a locking pawl 1 which engages in or disengages from a parking lock wheel (not shown here in greater detail) connected to a drive output (not shown) of a transmission, and an axially movable locking element 3 arranged on a connecting rod 4 that extends to an actuating plate 7 for example in the form of a parking plate, which element is in this example in the form of a locking cone. However, the locking element 3 could also be realized by means of appropriate roller elements. In the blocked condition of the parking lock—i.e. when the pawl 1 is engaged with interlock in a tooth gap of the parking lock wheel—the locking element 3 is clamped between the pawl 1 and a guide-plate 2 connected to a housing of the transmission (not shown here), in order to prevent the pawl 1 from being pushed out of the tooth gap of the parking lock wheel. In this case the locking element 3 is spring-loaded on the connecting rod 4 by means of a spring element 5, here for example in the form of a spiral spring, and is prestressed in the axial direction. For that purpose a stop 6 is arranged on the connecting rod 4, against which the spiral spring 5 is supported axially so that it prestresses the locking element 3 in the axial direction against the pawl 1 and the guide-plate 2. When the parking lock is engaged, the pawl 1 is pushed by the locking element 3 toward the parking lock wheel. If during this the pawl 1 encounters a tooth gap, then it engages therein and locks the drive output. In contrast if the pawl 1 encounters a tooth of the parking lock wheel, then it is prestressed by the spring element 5 so that when the drive output rotates, with the help of the prestressing force the pawl 1 engages in the next tooth gap of the parking lock wheel.

(6) The parking plate 7 is connected to a parking lock actuator 8, which according to FIG. 1 is in the form of a piston-cylinder unit. To disengage the parking lock the parking lock actuator 8 is acted upon by pressure. In this case the piston-cylinder unit can be in the form of a hydraulic or a pneumatic piston-cylinder unit and is accordingly acted upon by a hydraulic or pneumatic pressure medium.

(7) For this, under the control of a solenoid valve 12 pressure is delivered from a pressure medium supply line 13 to a cylinder 9 of the parking lock actuator 8, whereby a piston 10 of the parking lock actuator 8 is displaced axially in the cylinder 9 and the locking element 3 between the pawl 1 and the guide-plate 2 is pulled out by virtue of the parking plate 7 and the connecting rod 4 connected to the piston rod of the parking lock actuator 8.

(8) To engage the parking lock, by means of the solenoid valve 12 the pressure supplied to the cylinder 9 is cut off and the cylinder space is vented by way of an outflow line 14 leading to a pressure medium sink 15. The parking lock actuator 8 or the piston 10 of the parking lock actuator is prestressed by means of a spring element to a locking position, whereby when a pressure drop takes place the parking lock changes to its engaged position and thereby a transmission output shaft is blocked. The spring element for prestressing the parking lock can for example be in the form of a compression spring 11 arranged inside the cylinder 9 of the parking lock actuator 8, which exerts a corresponding force on the piston 10 of the parking lock actuator 8. Alternatively or in addition to the spring element 11 shown in FIG. 1, the parking lock can also be prestressed by a prestressed leg-spring (not shown here) on the parking plate 7, by means of which the piston 10 of the parking lock actuator 8 is displaced in the “Parking” direction so that the parking lock is engaged. Such leg-springs for prestressing a parking lock have long been known.

(9) The solenoid valve 12 is connected to a control unit 16 and is controlled in accordance with a selector lever position P, R, N, D. If the selector lever is in selector lever positions R, N or D the solenoid valve 12 is energized and the parking lock actuator 8 is pressurized, so that the parking lock is disengaged. In position P of the selector lever, in contrast, the solenoid valve 12 is not energized and the parking lock is engaged by means of the locking element 3.

(10) In the engaged condition of the parking lock—i.e. when the locking pawl 1 is engaged with interlock in a tooth gap of the parking lock wheel—the locking element 3 of the parking lock is clamped between the pawl 1 and the guide-plate 2 of the parking lock, so that a torque applied from the drive wheels to the drive output side of the transmission is supported by the pawl 1 and the drive-train is thereby braced.

(11) A torsional moment in the parking lock wheel produces, by virtue of the teeth between the parking lock wheel and the pawl 1, a force which presses the pawl 1 against the locking element 3. The larger the torsional moment, the larger is the force acting upon the locking element 3 and consequently the larger is also the force required for releasing the parking lock or the pressure required in the parking lock actuator 8 for releasing the parking lock.

(12) Since the force required for releasing the parking lock engaged when the motor vehicle is at rest is related to the downhill-slope force acting on the motor vehicle, it follows that from the force required for releasing the parking lock the downhill-slope force can be deduced.

(13) The current inclination of the motor vehicle or of the road on which the motor vehicle is located is determined by means of a device for determining the inclination, which can be in the form of an inclination sensor, an acceleration sensor or a navigation device.

(14) Thus, the mass of the vehicle can be determined from the force required for releasing the parking lock, which is related to the downhill-slope force, and from the inclination information about the motor vehicle or the road on which the motor vehicle is located.

(15) FIG. 2 shows a first variation of a specified set-point pressure for controlling the parking lock actuator 8 in the form of a piston-cylinder unit, when the parking lock is to be released. If the selector lever is moved away from the P selector lever position to some other selector lever position R, N or D, then the solenoid valve 12 is energized by the control unit 16 and a pressure is delivered to the parking lock actuator 8 in accordance with the set-point pressure specification.

(16) First, the piston 10 of the parking lock actuator 8 is acted upon for a first specifiable time period t.sub.1 with a first pressure value p.sub.start, which is needed in order to be sure that the parking lock is disengaged when the motor vehicle is on level ground and is unloaded. This pressure value is substantially lower than a maximum pressure value p.sub.max, and can for example be within a range between 3 and 5 bar. The time period t.sub.1 can for example be chosen such that the pressure in accordance with the set-point pressure specification can build up in the cylinder 9 of the parking lock actuator 8. If the pressure bunt up in the cylinder 9 of the parking lock actuator 8 and acting upon the piston 10 is not sufficient to pull the locking element 3 out from between the pawl 1 and the guide-plate 2, then in accordance with the set-point pressure specification the pressure in the cylinder 9 is increased in a ramp-like manner for a second time period t.sub.2. The pressure ramp can for example be implemented by way of a gradient specification or a target-value specification.

(17) The increase of the specified set-point pressure now takes place until the parking lock is released or a maximum pressure value p.sub.max has been reached. The release of the parking lock can be detected by means of a parking lock sensor. The maximum pressure value p.sub.max is preferably chosen such that it is sufficient to release the parking lock when the motor vehicle is fully loaded and is located on an incline steeper than 15%. For example, the maximum pressure value p.sub.max can be within a range of 15 to 18 bar.

(18) By virtue of the ramp-like set-point pressure specification the pressure required for releasing the parking lock and hence the force required for releasing the parking lock can be determined very accurately. Consequently the mass of the motor vehicle can also be determined relatively accurately, so that the appropriate starting gear or the appropriate shifting characteristic for a starting operation can be chosen.

(19) FIG. 3 shows a second variation of a specified set-point pressure for controlling the parking lock actuator in the form of a piston-cylinder unit when the parking lock is to be released. If the selector lever is moved away from the selector lever position P to some other selector lever position R, N or D, then here too the solenoid valve 12 is energized by the control unit 16 and a pressure in accordance with the set-point pressure specification is supplied to the parking lock actuator 8.

(20) In this case, however, the specified set-point pressure does not vary in a ramp-like manner, but rather, the set-point pressure is here increased in steps. First, the piston 10 is acted upon for a first specifiable time period t.sub.3 by a first pressure value p.sub.start, which is required in order to release the parking lock reliably when the motor vehicle is on level ground and is not loaded. This pressure value is substantially lower than a maximum pressure value p.sub.max and can for example be within a range between 3 and 5 bar. The time t.sub.3 can for example be chosen such that the pressure in the cylinder 9 of the parking lock actuator 8 can build up in accordance with the set-point pressure specification. If the pressure built up in the cylinder 9 of the parking lock actuator 8 and acting on the piston 10 is not sufficient to pull the locking element 3 out from between the pawl 1 and the guide-plate 2, then in accordance with the set-point pressure specification the pressure in the cylinder 9 is increased in steps until the parking lock is released or until a maximum pressure value p.sub.max has been reached. The pressure values p.sub.2, p.sub.n between the first pressure value p.sub.start and the maximum pressure value p.sub.max are in turn maintained for times t.sub.4, t.sub.5 in order to enable the parking lock to be released at these set-point pressures. The maximum pressure value p.sub.max is preferably chosen such that it is sufficient to release the parking lock when the motor vehicle is fully loaded and is located on an incline steeper than 15%. For example, the maximum pressure value p.sub.max can be within a range of 15 to 18 bar.

(21) With a set-point pressure specification than increases in steps it is advantageous for the step intervals of the set-point pressure specification p.sub.start-p.sub.2, p.sub.2-p.sub.n to be made small. The smaller the step intervals p.sub.start-p.sub.2, p.sub.2-p.sub.n of the set-point pressure specification, the more accurately can the pressure required to release the parking lock, and hence too the force required to release the parking lock, be determined, so that the mass of the motor vehicle can also be determined more accurately.

INDEXES

(22) 1 Locking pawl 2 Guide-plate 3 Locking element 4 Connecting rod 5 Spring element 6 Stop 7 Parking plate 8 Parking lock actuator 9 Cylinder 10 Piston 11 Spring element 12 Control valve 13 Pressure medium supply line 14 Outflow line 15 Pressure medium sink 16 Control unit