Improved start-stop system of a motor vehicle with manual transmission

Abstract

Method for controlling the starting behavior of a motor-driven vehicle with a manual transmission, a clutch, a service brake device actuated by a brake pedal, and an engine control unit designed to stop the drive engine after the vehicle has come to a standstill in a stop step (4), provided that the manual transmission is in neutral (3) and the clutch is engaged (2), and to start the drive engine in a subsequent start step (10) upon pedal actuation, wherein the service brake device is designed to provide a service brake pressure for a predetermined time period (7) immediately after the brake pedal (5) is released in a time interval between the stop step and the start step (10), unless the start step (10) is triggered in the meantime by disengaging the clutch and by actuating the accelerator pedal.

Description

[0001] The present invention relates to a method for controlling the starting behavior of a motor-driven vehicle, hereinafter also referred to as the vehicle, comprising a manual transmission, a clutch, a service brake device operable by means of a brake pedal and an engine control unit designed to stop the drive motor after the vehicle has come to a standstill in a stop step, provided that the manual transmission is in neutral and the clutch is engaged, and to start the drive motor in a subsequent start step upon pedal actuation.

[0002] The aforementioned engine control units designed in this way are also known as stop-start systems or start-stop systems, or start-stop automatic systems, and aim to reduce fuel consumption during stationary phases (e.g., at a traffic light), particularly in urban traffic, by switching off the engine under certain conditions and automatically restarting it. In systems that have been on the market since approximately 2000, the engine is switched off when neutral is engaged and the clutch is engaged (i.e., when the clutch pedal is released, provided it is a manually operated clutch). When the clutch pedal is pressed again, the engine restarts. In automatic transmissions, the reduction of pressure in the brake system when the brake pedal is released leads to the engine restarting. Vehicles with automatic transmissions are not the subject of the present invention.

[0003] German patent application DE 10 2011 080 172 A1 discloses a method for switching a vehicle engine on and off. DE 10 2011 080 172 A1 is based on a known prior art that requires pressure sensors. The use of pressure sensors is to be eliminated, and therefore a pressure-independent signal is to be used to control the vehicle engine. The signal for switching the vehicle engine on and off is the signal from the brake light switch.

[0004] DE 103 17 501 A1 relates to a method for operating a motor vehicle with an internal combustion engine, an automatic start-stop device for the internal combustion engine, wherein the start-stop device automatically stops the internal combustion engine depending on stop conditions and automatically starts it depending on start conditions, a controllable braking device by means of which a braking torque can be applied to the motor vehicle, and a brake pedal that can be actuated by a driver, wherein the braking device is controlled by a control unit. The control unit is intended to be able to increase the braking torque independently of the degree of actuation of the brake pedal. The control unit checks at the beginning and during the automatic stop phase of the internal combustion engine whether the currently acting braking torque is less than a threshold value.If the test result is positive, the braking torque is increased to a value greater than or equal to the threshold value.

[0005] German patent DE 10 2010 042 449 A1 discloses a braking system for a vehicle with an idle stop-and-go device and a control method thereof. The braking system comprises a valve arrangement located in a brake line to supply brake pressure to the wheels by actuating the brake pedal to open or close the brake line; and a control unit that controls the valve arrangement. The brake pressure is thus effectively locked in when the internal combustion engine stops.

[0006] Furthermore, various methods for supporting the braking function of motor vehicles are known from the prior art.

[0007] DE 10 2015 210 696 A1 relates to a method for improving a hill start assist function for a motor-driven vehicle with automatic transmission or automated clutch.

[0008] German patent application DE 199 12 878 A1 discloses a method and a device for assisting the braking of a vehicle. The degree of actuation of a brake actuation device and the vehicle's standstill are detected. Braking that keeps the vehicle stationary is maintained even if a partial or complete release of the brake actuation device is detected while the vehicle is stationary. Such a method is only carried out with the drive motor running in order to reliably maintain braking.

[0009] DE 10 2010 029 432 A1 relates to a method for controlling the restart of an engine in a hybrid electric powertrain. It includes engaging a gear in a transmission, releasing a brake pedal, maintaining fluid pressure at an adaptively determined level in a wheel brake, initiating an engine restart, and reducing the fluid pressure in the wheel brake when the engine restarts.

[0010] German patent application DE 10 2005 011 559 A1 shows a motor vehicle with an electro-hydraulic service brake system. The stationary vehicle can be held in place by the service brake system even without the brake pedal being actuated, provided that clutch actuation is detected.

[0011] In addition to measures concerning energy or fuel consumption and the associated emissions of vehicles, safety and comfort-enhancing support and assistance systems are also desirable in vehicles and still offer significant development potential. For example, systems known as hill start assist or hill start support provide automated assistance that prevents the vehicle from rolling backward when starting on an incline.

[0012] Such systems typically utilize at least part of the existing braking system to temporarily hold the vehicle on an incline by activating it. Here, automated transmissions offer an advantage over manual transmissions in that they provide at least a small amount of creep torque, depending on the situation. In contrast, an automated or manually operated clutch is completely disengaged when it is disengaged. On inclines, the vehicle can then roll a sometimes considerable distance during this time. Particularly on steep inclines, this period is accompanied by an increased feeling of insecurity, even stress.

[0013] With a vehicle equipped with a manual transmission and a start-stop system, the problem arises that a vehicle brought to a stop on an incline can roll backward after the vehicle has come to a halt and the brake pedal has been released, before the engine has restarted. While this is generally irritating for the driver, it is particularly surprising, because it is unfamiliar, if the vehicle is equipped with a hill start assist system, which is specifically designed to prevent such situations but can nevertheless occur. This is because such systems are only activated at a predetermined clutch position or clutch pedal position. Therefore, there is a risk that if the brake is released too quickly and / or the clutch is disengaged too slowly, the hill start assist will engage late, and the vehicle may roll backward.

[0014] In view of these circumstances that arise in practice and the sometimes unreliable use of such automated support systems, vehicles with start-stop technology, especially in combination with hill start assist systems, still offer room for improvement.

[0015] Against this background, the invention is based on the objective of improving a method for controlling the starting behavior of a motor-driven vehicle with a manual transmission, a clutch, a service brake device actuated by means of a brake pedal and an engine control unit designed to stop the drive engine after the vehicle has come to a stop in a stop step, provided that the manual transmission is in neutral and the clutch is engaged, and to start the drive engine in a subsequent start step when the pedal is actuated - the latter is also referred to as start-stop automatic - in such a way that unintentional rolling backward of the vehicle is better avoided.

[0016] This problem is solved according to the invention by a method having the features of claim 1.

[0017] A method for controlling the starting behavior of a motor-driven vehicle with a manual transmission, a clutch, a service brake system actuated by a brake pedal, and an engine control unit is presented. The engine control unit is designed to stop the drive motor in a stop step after the vehicle has come to a standstill, provided that the manual transmission is in neutral and the clutch is engaged, and to start the drive motor in a subsequent start step upon pedal actuation. The service brake system is designed to provide service brake pressure for a predetermined duration immediately after the brake pedal is released within a time interval between the stop step and the start step, unless the start step is triggered in the meantime by disengaging the clutch and by actuating the accelerator pedal.

[0018] Further, particularly advantageous embodiments of the invention are disclosed in the respective dependent claims.

[0019] It should be noted that the features listed individually in the following description can be combined in any technically sensible way and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention.

[0020] A method for controlling the starting behavior of a motor-driven vehicle is provided herein. The method according to the invention relates to vehicles equipped with a manual transmission, for example, a hand-shifted transmission. The term "manual transmission" is to be interpreted broadly and includes transmissions in which a gear change is effected by manual intervention and not automatically, and foot-shifted transmissions are also included according to the invention. As described above, the vehicle includes a clutch. A clutch is understood to be a friction-fit clutch arranged in the vehicle's drivetrain between the engine and the manual transmission, which can be disengaged during operation. According to the invention, this clutch serves to interrupt the power flow between the engine and the manual transmission when a gear is changed or when the vehicle is to be stationary with the engine running.

[0021] As already mentioned, the vehicle also includes a service brake system that can be actuated by means of a brake pedal. A service brake system is understood to be a brake designed to slow down and bring the motor-driven vehicle to a standstill during normal operation. It is graduated and acts on all wheels of the vehicle. A parking brake system that only acts on two of the four wheels is not considered a service brake system within the meaning of the invention.

[0022] Furthermore, an engine control system is provided which, as described above, is designed to stop the drive engine in a stop step after the vehicle has come to a standstill, i.e., is stopped, provided the manual transmission is in neutral and the clutch is engaged, and to restart the drive engine in a subsequent start step upon pedal deactivation. The start step is triggered by deactivation of the accelerator pedal, with the starting process being initiated either exclusively or additionally by deactivation of the clutch pedal.

[0023] Such a functional design of the engine control unit is hereinafter also referred to as start-stop automatic. In addition to the aforementioned mandatory conditions for triggering the stop sequence, further conditions may be required. For example, one or more additional temperature parameters, such as those relating to the coolant temperature, the passenger compartment temperature, or the outside temperature, or a battery voltage parameter, or a vacuum parameter of the service brake system, in particular the brake booster, may be defined to specify one or more additional conditions that prevent the start-stop sequence from being triggered.

[0024] As mentioned above, the service brake system is designed to provide service brake pressure for a predetermined duration immediately after the brake pedal is released within a time interval between the stop and start phases, unless the start phase is triggered in the meantime. During this time interval, the engine is off, no gear is engaged, and the clutch is engaged. Disengaging the clutch and / or engaging a gear would trigger the next phase: starting the engine. Service brake pressure is defined as the braking force of the service brake system sufficient to hold the vehicle stationary for a certain period of time, even with the brake pedal released. The service brake pressure can be determined based on the vehicle's tilt, as measured by an inclination sensor, and adjusted to the specific stopping situation.The service brake pressure acts preferentially on the brakes of all wheels of the motor-driven vehicle.

[0025] Preferably, the service brake system is an electro-hydraulic system. In this system, the driver's braking request is electronically detected using sensors. A displacement sensor measures the time course of the brake pedal travel and, from this, the pedal speed and acceleration. Additionally, a pressure sensor detects the pressure curve in the control circuit. From this, the control unit derives the driver's braking request (partial braking, emergency braking, etc.) and calculates the required target pressure for each wheel brake in the current driving situation. The control unit regulates a hydraulic unit that can generate an individual service brake pressure for each wheel. Pressure sensors in each wheel line measure the actual pressure, allowing the target pressure for each wheel to be adjusted individually.

[0026] The inventive method prevents the vehicle from rolling backwards for a predetermined period of time before the engine starts, even with the brake pedal released and especially during delayed clutch disengagement. This improves the starting behavior of a vehicle with a manual transmission and start-stop system during the time interval between the stop and start phases.

[0027] Maintaining service brake pressure is understood to mean any service brake pressure profile sufficient to hold the vehicle for a certain subsequent period after the initial release of the brake pedal, provided that the brake pressure drops more slowly than the pressure drop achievable by releasing the brake pedal without hindrance. However, the preferred method is the constant maintenance of a specific service brake pressure value over a predetermined period after the brake pedal release is initiated.

[0028] Preferably, the specified time duration is at least 200ms or more.

[0029] Preferably, the maintenance of a service brake pressure is further supported by at least one measured value from an internal vehicle sensor, for example, an inclination sensor. For instance, the pressure is maintained only when the sensor reading reaches and / or exceeds a predetermined value. The aim is, for example, to detect whether the now-stationary vehicle is on an incline. In other words, the system looks for indications that the vehicle is inclined relative to the horizontal in its longitudinal direction. For this purpose, an inclination sensor is preferably used, which provides a value indicating the vehicle's current inclination. As soon as the returned value is not zero, the vehicle is on an incline.If a vehicle's inclination detected while stationary is identified as being above a threshold, for example 1%, and the brake pedal has been released, a positive decision to maintain the service brake pressure is generated.

[0030] Preferably, the motor-driven vehicle further comprises a device for providing hill start assist, which is designed to provide service brake pressure when the brake pedal is released and the vehicle is stationary, depending on clutch engagement, in particular depending on the position of the clutch pedal, and optionally upon fulfillment of further conditions, such as exceeding a predetermined vehicle inclination. Preferably, the activation of the hill start assist requires at least reaching a predetermined depressed position of the clutch pedal from its unactuated rest position, i.e., reaching or at least nearly reaching the disengaged state of the vehicle's clutch.In combination with such a hill start assist, the inventive method, namely preventing the vehicle from rolling backward during the stop phase of a start-stop system, advantageously complements the comfort-enhancing and driving safety-enhancing effect of the hill start assist. The subsequent, optional activation of the hill start assist extends the duration of the service brake pressure maintenance, for example by a further 250 ms.

[0031] The invention further relates to a motor-driven vehicle with a manual transmission, a clutch, a service brake system actuated by a brake pedal, and an engine control unit designed to stop the drive engine after the vehicle has come to a stop in a stop step, provided the manual transmission is in neutral and the clutch is engaged, and to start the drive engine in a subsequent start step upon pedal actuation. The service brake system provided according to the invention is designed to perform one of the methods described above. The inventive procedure prevents the vehicle from rolling backward for a predetermined period before the engine starts, even with the brake pedal released and, in particular, in the case of delayed clutch disengagement.This improves the starting behavior of a vehicle with a manual transmission and start-stop system in the time interval between the stop and start phases.

[0032] Preferably, the service brake system is an electro-hydraulic service brake system.

[0033] Further advantageous embodiments of the invention are disclosed in the dependent claims and the following description of the figures. It shows: Fig. 1 A schematic diagram of the method according to the invention.

[0034] Let the following starting point A be assumed: Prior to the method according to the invention, the vehicle is first braked to a standstill in step 1 with a service brake pressure by actuating a brake pedal acting on a service brake device.

[0035] If, in step 2, the clutch pedal was depressed (i.e., actuated), thus disengaging the clutch, normal operation of the vehicle continues in step E. However, if the clutch pedal was released in step 2 and the clutch engaged, and the driver then selects neutral in step 3, the inventive stop step 4 of the engine control is executed, and the engine driving the vehicle is stopped.

[0036] If the conditions of steps 2 and 3 are not met, the normal operation of the vehicle, which is not in accordance with the invention, is continued in step E.

[0037] If the driver releases the vehicle's service brake system in the subsequent step 5 by releasing the brake pedal, the service brake pressure applied and stored in step 1 is maintained for a predetermined period of time, for example, 200 ms, in step 6. Compliance with this time limit is monitored by a timer function in step 7.

[0038] If, according to step 9, the clutch is not disengaged by actuating it (i.e., by pressing the clutch pedal), the service brake pressure in the service brake system is only released after the specified time period in step 8 has elapsed. The vehicle is then unbraked and returns to normal operation in step E.

[0039] If, in step 9, the clutch pedal is activated and the clutch reaches the specified position, the engine control's start step 10 is triggered and the vehicle's additional hill start assist is activated in step 11.

[0040] The activation of hill start assist in step 11 and the maintenance of service brake pressure in step 6 may also depend on other conditions resulting from the vehicle situation, as shown in the diagram. Fig. 1 is not shown in detail. Preferably, the activation, i.e., the execution of both steps, depends on a measured value obtained from an inclination sensor provided in the vehicle.

Claims

[1] Method for controlling the starting behavior of a motor-driven vehicle with a manual transmission, with a clutch, with a service brake device that can be actuated by means of a brake pedal, and with an engine control system that is designed to stop the drive engine running in a stop step (4) after the vehicle has come to a standstill, provided that the manual transmission has been put into neutral (3) and that the clutch has been engaged (2), and to start the drive engine running in a subsequent start step (10) upon pedal actuation, wherein the service brake device is designed to provide a service brake pressure for a predetermined period of time (7) immediately after the brake pedal (5) is released in a time interval between the stop step and the start step (10), unless the start step (10) is triggered in the meantime by disengaging the clutch and by pedal actuation of the accelerator pedal. [2] Method according to claim 1, characterized by that a service brake pressure applied immediately before the brake pedal (5) is released is maintained for the specified time. [3] Method according to claim 1 or 2, characterized by that the service brake pressure is maintained constant. [4] Method according to one of the preceding claims, characterized by that the service brake pressure is provided as a function of at least one measured value from a vehicle-internal sensor. [5] Method according to claim 4, characterized by that the vehicle's internal sensor is an inclination sensor. [6] Method according to one of the preceding claims, characterized by that the specified time period is at least 200ms or more. [7] Method according to one of the preceding claims, characterized by that the starting step (10) is triggered by a pedal actuation (9) of a clutch pedal of the clutch. [8] Method according to one of the preceding claims, characterized by that the service brake pressure is provided by an electro-hydraulic service brake device. [9] Method according to one of the preceding claims, characterized by that the motor-driven vehicle further comprises a device for providing a hill start assist, which is designed to provide a service brake pressure (10) when the brake pedal (9) is released and when the vehicle is stationary, as a function of a clutch engagement, in particular as a function of a position of the clutch pedal, and optionally when further conditions are met, such as when a predetermined vehicle inclination is exceeded.

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