JP4953507B2 - How to maintain engine braking - Google Patents

Description

[0001]
The present invention relates to a method for maintaining the engine braking action of a vehicle traveling downhill by actively electronically controlling braking intervention of at least one wheel.
[0002]
In the case of known road vehicles, the driving state of the vehicle can be influenced by the settable pressures of the individual wheel brakes and by intervening in the engine management of the drive torque, independent of the driver. A device is provided. In this case, this device is equipped with a brake slip control system (ABS) that prevents locking of individual wheels during braking, a traction slip control system (TCS) that prevents idling of driven wheels, a front axle and a rear axle of a vehicle. An electronic braking force distribution system (EBD) that controls the ratio of braking force between the two and an electronic driving stability control system (ESP) that produces a stable running state when passing a curve.
[0003]
That is, in this connection, the vehicle relates to a motor vehicle with four wheels equipped with a hydraulic brake device. When an assembly device such as an electronic device, a wheel rotational speed sensor, an acceleration sensor, a solenoid control valve, etc. provided in this vehicle is necessary for a method for controlling the traveling speed of the vehicle while traveling downhill Are used together to carry out this method. Of course, this known assembly device can also be used only for the method of maintaining the vehicle engine braking action during downhill travel.
[0004]
From WO 96/11826 A1 a vehicle with a so-called hill descent control system (HDC) is known. The driver can activate this hill descent control system by means of a switch. This control system can keep the vehicle at a constant low speed on a steep slope by active braking control without the driver operating the brake. This system is particularly provided for off-road vehicles that run on steep hills where the engine brakes are not sufficient to slow down the vehicle even at low gears. The speed controller compares the target speed with the actual speed and calculates the brake pressure for all four wheels, taking into account various limiting conditions.
[0005]
Furthermore, a system for a four-wheel drive vehicle with a center differential gear is known from German Patent Application Publication No. 19817212. The system includes a device for brake control, by which braking force is applied to a free rotating wheel or both front wheels that do not transmit force to the road. Thereby, in the case of a permanent four-wheel drive vehicle, the unexpected acceleration based on the freely rotating wheels is avoided. This is because, under this condition, engine brake torque is not transmitted when the center differential gear is not locked by the center differential lock mechanism.
[0006]
The problem underlying the present invention is to provide a method for maintaining the engine braking action of a vehicle running on a hill that reliably prevents the rotation of the wheel opposite to the running direction and the acceleration of the vehicle.
[0007]
This problem is solved by the features of claim 1.
[0008]
Advantageous embodiments are described in the dependent claims.
[0009]
In a method for maintaining the engine braking action of a vehicle traveling downhill by actively electronically controlling the braking intervention of at least one wheel, the state of the wheel is defined as “stable wheel” and “unstable” If the at least one wheel is unstable, all stable wheels are braked, and if the wheels are unstable, the following conditions are met: A _instabil <−0.4 h and V _instabil <K _i × V _ref
Where V _instabil = unstable wheel speed, V _ref = stable wheel filtered intermediate wheel speed, K _i = correction factor (K _i <1), A _instabil = unstable Due to the wheel acceleration, the engine drive torque is transmitted to the unstable wheel via the differential gear, thereby preventing the reverse rotation of the unstable wheel. This is because the unstable wheel can rotate in the opposite direction to the stable wheel only when the engine driving torque does not act on the unstable wheel. In the present invention, the engine speed is the same and the gear ratio of the differential gear is constant, so the sum of the four wheel speeds is the same. Based on the perception of stopping and reversing. In the case of μ-split-slope, both low μ wheels are reversed.
[0010]
The state of the wheel is the following formula: V _ref −Kb <V _stable <V _ref + Kb
It is determined according to, wherein _{a V ref} = stable wheel the filtered intermediate wheel speeds of, Kb = correction _{coefficient, V stabil} = stable wheel.
[0011]
At that time, when the wheel speed is within the band around the intermediate wheel speeds, i.e. above or below the intermediate wheel speed 2.5km / h, it is determined in particular by the correction coefficient Kb in the band of 1.3km / h The wheels are stable when they are in the band. When the wheel speed is outside the above band, the wheel is unstable.
[0012]
The intermediate wheel speed V _ref is then determined from the filtered maximum value of the second fastest wheel and the vehicle speed. That is, the maximum value of the low-pass filtered waveform of the second fastest wheel and the vehicle speed or the ABS reference speed are obtained. Intermediate wheel speed The wheel speed is filtered at 2.5 Hz.
[0013]
The correction coefficient K _i is K _i <1/2. Due to the unstable wheel condition being less than 50% of the intermediate wheel speed, the stable wheel is braked immediately upon detection of the unstable wheel. Unstable wheels do not reverse under conditions that are standard for state determination. This is because in the case of an unstable wheel speed that is slower than 50% of the intermediate wheel speed, the engine drive torque is applied to the unstable wheel before reversing.
[0014]
When the wheel acceleration of the unstable wheel is less than −0.4 g, a risk that the unstable wheel changes the rotation direction is detected.
[0015]
The pressure applied to the brake cylinder of the wheel brake to brake a stable wheel is
reg _p = K × (v _ref −V _{ref nom} ) + Offset
Where is determined according to reg _p = Stable wheel demand pressure, K = 7 bar / (km / h), V _{ref nom} = Average speed of all wheels before detection of unstable wheels, Offset = 5 bar.
[0016]
In this case, the required pressure of the stable wheel is calculated by the difference between the average speed of all the wheels before detecting the unstable wheel and the average speed of the stable wheel together with the correction coefficient and the offset coefficient.
[0017]
Advantageously, the state determination is divided over n time steps and at least the value of the last state determination is stored. According to an embodiment, the demand pressure of the preceding state determination is compared with the demand pressure of the current state determination, and the value of the demand pressure of the current state determination is pK _{p with} respect to the demand pressure of the preceding state determination. The current demand pressure becomes invalid when it differs by a smaller value. At that time, PK _{p of} the reference coefficient Is less than 1 bar. By this means, the operation of the hydraulic valve is prevented in order to increase the control comfort and reduce the noise level.
[0018]
In another embodiment, the preceding unstable wheel is compared to the current unstable wheel, and the pressure increase of this wheel is delayed when the preceding unstable wheel is braked. The delay of the current pressure rise at the preceding unstable wheel takes place within a time of 1-2 seconds, in particular 1.5 seconds. Only when the vehicle speed is less than 30 km / h, in particular less than 20 km / h, and the wheel brake is not acting, the control of the vehicle speed is effective.
[0019]
An embodiment of the invention is shown in the figure. Hereinafter, this embodiment will be described in detail.
[0020]
As shown in FIG. 1, the vehicle 10 includes four wheels 11, 12, 13, and 14. Wheel sensors 15, 16, 17, and 18 are attached to each wheel. The wheel speed is detected by the wheel sensor. The value detected by the wheel sensor is supplied to the electronic control unit E. This electronic control unit controls the wheel brakes 19, 20, 21, 22 attached to the wheels 11-14 via the hydraulic unit H in accordance with the input and calculated state variables. The electronic control unit E is further supplied with values detected by the brake pedal and accelerator pedal sensors 23, 24. Thereby, the sensors 23 and 24 supply the electronic control unit E with an analog signal which depends on the position or angle of the brake pedal or accelerator pedal.
[0021]
As further shown in FIG. 1, the vehicle 10 is a permanent all-wheel drive vehicle. The all-wheel drive vehicle is driven through an engine transmission unit M, a center differential 25, a front axle differential 26, and a rear axle differential 27.
[0022]
Hydraulic brake systems with controllable solenoid valves are known per se and therefore do not need to be described in detail. Only the requirement that all wheel brakes 19 to 22 be separately controllable by the electronic control unit E via the hydraulic unit H must be fulfilled. In normal driving of the vehicle, when the driver operates the brake pedal, the electronic control unit E controls the hydraulic unit E by an anti-lock function in order to prevent the wheels 11 to 14 from being locked. In addition, a traction slip control system is provided. As is well known, both functions are performed by detecting the speed and acceleration of the wheels 11 to 14 and the vehicle speed calculated from the speed of the wheels. The vehicle speed is calculated from the average wheel speed without considering the speed of the locked or slipping wheel.
[0023]
In order to be able to enter the engine drag torque support mode (DTS-Drag Torque Support), the electronic control unit basically has no yaw torque control working whether the DTS system is available or not. It is checked whether the brake demand pressure setting by the driver is smaller than the demand pressure determined to brake a stable wheel. When the above conditions are met and the vehicle speed is 30 km / h, especially slower than 20 km / h, the DTS system is activated. If one of the start conditions is not fulfilled, i.e. the vehicle speed is 30 km / h or higher, a system error exists, or yaw torque control is active, or the brake demand pressure setting by the driver brakes a stable wheel If so, the DTS system algorithm ends.
[0024]
The initial inspection of the vehicle speed and the vehicle brake operation, which are state variables, is obtained from signals supplied from the sensors 23 and 24 to the electronic control unit E. This sensor detects the position or angle of the accelerator pedal and the brake pressing pedal.
[0025]
Of course, the vehicle speed may be obtained from the signals of the wheel sensors 15 to 18 as described above. When the initial conditions are satisfied, the states of the wheels 11 to 14 are determined. At this time, the wheels 11 to 14 are divided into “stable wheels” and “unstable wheels”.
[0026]
Therefore, the state of the wheels, for example 11-13, is V _ref -K _b <V _stabil <V _ref + K _b Determined according to. Where V _ref = Wheel speed, K _b = Correction factor, V _stabil = Stable wheel. If the wheel speed is outside the above band, the wheel is unstable.
[0027]
Since the correction factor _Kb is in particular 1.3 km / h, the wheels are stable when the wheel speed is in the zone around an intermediate wheel speed of 1.3 km / h in particular. The intermediate wheel speed V _ref is then determined from the maximum value filtered low by 2.5 Hz of the second fastest wheel and the known ABS reference speed determined by the vehicle speed or the ABS controller. In order to ensure that the unstable wheels rotating at high speed are closed out, the maximum value of the second fastest wheel is taken into account to determine the intermediate wheel speed.
[0028]
Therefore, when the conditions V _instabil <K _i × V _ref and A _instabil <−0.4 g occur, the wheel brake of the stable wheel is activated. _{Here, V instabil} = unstable wheel speeds _{of, A instabil} = unstable wheel _{acceleration, V ref} stable wheels the filtered intermediate wheel speed of a _{K i} = correction factor.
[0029]
The wheel speed of the unstable wheel is less than 50% of the average wheel speed, ie the correction factor K _i The required pressure is calculated when <1/2 and the wheel acceleration of the unstable wheel is less than -0.4 g. With this required pressure, all stable wheels are braked by supplying brake pressure to the wheel brakes 19 and / or 21 and / or 22 wheel brake cylinders corresponding to the calculated required pressure.
[0030]
The required pressure for a stable wheel is
reg _p = K × (v _ref −V _{ref nom} ) + Offset
Determined according to. Where reg _p = Stable wheel demand pressure, K = 7 bar / km / h, V _{ref nom} = Average speed of all wheels before detection of unstable wheels, Offset = 5 bar.
[0031]
The required pressure is calculated from the difference of the average speed of the stable wheel to the average speed of all the wheels before detecting the unstable wheel. When the required pressure of the stable wheel is calculated, the brake pressure is supplied to a stable wheel, for example 11-13, corresponding to the calculated required pressure, whereby the engine driving torque is transmitted to the unstable wheel. . By actively increasing the pressure of a stable wheel, i.e., a wheel having a large coefficient of friction, it compensates for an unstable wheel, e.g. 14 engine drag torque losses, thereby accelerating the vehicle 10 and the unstable wheel. For example, the reverse rotation of 14 is reliably prevented. The pressure increase is selectively performed by a return pump attached to the hydraulic unit H or by actively operating a brake booster (booster).
[0032]
In an embodiment of the invention, the state determination is divided over n time steps. In this case, at least the last state determination value is stored. In doing so, the required pressure for the previous state determination is compared with the current required pressure for state determination. In this case, PK _{p with} respect to the required pressure for state determination preceded by the value of the required pressure for current state determination. The current demand pressure is invalid when it differs by a smaller value. At that time, the reference coefficient K _p Is less than 1 bar. By this means, the operation of the hydraulic valve is interrupted in order to increase control comfort and to reduce the noise level.
[0033]
Therefore, when the calculated required pressure is lower than the driver brake required pressure, stable wheel positive braking is not performed.
[0034]
After the unstable wheel stabilization has been achieved, the predetermined unstable wheel is compared with the current state determining wheel to prevent it from becoming unstable again. During braking of a simple wheel, this wheel pressure increase takes place within a period of 1-2 seconds, in particular 1.5 seconds.
[0035]
All wheels 11 to 14 at least one second, when rotated in a state of stable particular between 1.5 seconds, i.e. whether or vehicle wheel speed at all wheels are within the band around the intermediate wheel speed <2. When the speed is 5 km / h, the DTS mode does not work.
[Brief description of the drawings]
FIG. 1 shows a simplified apparatus according to the invention.
FIG. 2 is a flowchart of a method for controlling the engine braking action of a vehicle traveling downhill.

Claims (12)

In a method for maintaining the engine braking action of a permanent all-wheel drive vehicle traveling downhill by actively electronically controlling braking intervention of at least one wheel,
a) When the following conditions are satisfied, the wheel is “stable wheel”, and when it is not satisfied, the wheel (11, 12, 13, 14) is “stable” as “unstable wheel”. The process of judging by dividing into "wheel" and "unstable wheel",
V _ref −Kb <V _stab <V _ref + Kb
_{Here, V ref} intermediate wheel speed of the stable wheels, Kb is the correction _{coefficient, V stabil} a stable wheel wheel speed of,
b) for "unstable wheels", checking whether the following conditions are satisfied;
V _instabil <K _i × V _ref
Where V _instabil is the wheel speed of the unstable wheel, V _ref is the intermediate wheel speed of the stable wheel, K _i is the correction factor, and K _i <1.
c) Brakes all stable wheels (one or more of 11, 12, 13, 14) if at least one unstable wheel satisfies the above condition V _installable <K _i × V _ref Process,
A method characterized by. The method according to claim 1, wherein the correction factor Kb is Kb = 2.5 km / h or Kb = 1.3 km / h.   Between the maximum value in the low-pass filtered waveform of the wheel speed of the second fastest wheel with the intermediate wheel speed Vref of the stable wheel and the vehicle speed calculated as the average value of the wheel speed excluding the locked or slipping wheel 3. The method according to claim 1 or 2, characterized in that it is determined as the larger of. Instead of the vehicle speed, ABS reference speed obtained by the ABS controller is used and wherein the Rukoto The method of claim 3. At least one unstable wheel is stable when the correction factor K _i <1/2 and the condition of V _instabil <K _i × V _{ref and} the condition that the wheel acceleration is less than −0.4 g. 5. A method according to any one of the preceding claims, characterized in that all wheels (one or more of 11, 12, 13, 14) are braked . The required pressure for a stable wheel is: reg _p = K × (V _ref −V _{ref nom} ) + Offset
Where reg _p = stable wheel demand pressure, V _{ref nom} = average speed of all wheels before detection of unstable wheels, K = 7 bar / (km / h), Offset = 5 characterized in that it is a bar, the method according to any one of claims 1-5. The time slot in which one execution cycle of the present method is divided into n times is determined by dividing the state of the wheel (11, 12, 13, 14) into “stable wheel” and “unstable wheel”. 7. The method according to claim 6 , characterized in that it is carried out every time slot and at least the determined wheel condition and the required pressure value for the stable wheel are stored. The required pressure determined in one time slot is compared with the required pressure determined in the previous time slot, and the required pressure value determined in that one time slot is determined in the previous time slot. for values of required pressure, when they differ by PK _p value less than, characterized in that the required pressure determined by the one time slot is invalid, the method according to claim 7. 9. Method according to claim 8 , characterized in that the reference coefficient PK _p is less than 1 bar. The state of a wheel determined to be unstable in one time slot is compared with the state determined in the next time slot of that wheel, and the wheel determined to be unstable in that one time slot is The method according to any one of claims 7 to 9 , characterized in that when the vehicle is determined to be stable in the next time slot and is braked, the pressure rise of the wheel is delayed. Delay in the pressure increase of the wheel, characterized in that between the time of two seconds, The method of claim 1 0. The vehicle speed is less than 30 km / h, there engine drag torque support system in an operable state, the yaw torque control is not applied, and to brake pressure set value by the driver to brake the stable wheels when less than the determined required pressure, characterized in that it features a method of supporting an engine braking method according to any one of claims 1 to 1 1.

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