WO2013113600A1

WO2013113600A1 - Stop-start control system for use in vehicles with a stop-start device

Info

Publication number: WO2013113600A1
Application number: PCT/EP2013/051278
Authority: WO
Inventors: Muthukumaraswamy DHARMALINGAM; Vivek VENKOBARAO; Ramasubramanian KRISHNAMOORTHY; Vinay PAWAR
Original assignee: Continental Automotive Gmbh
Priority date: 2012-02-01
Filing date: 2013-01-24
Publication date: 2013-08-08

Abstract

The invention relates to a stop-start control system (SSCS) for use in vehicles that comprise a stop-start device (SSD), at least one energy storage device (ESD) to power the stop-start device (SSD), and at least one engine control unit (ECU) operating a set of parameters in at least one operating mode, wherein the stop-start control system (SSCS) comprises a stop-start control unit (SSCU) that is provided to enable or to disable an operation of the stop-start device (SSD), depending on an evaluation of a subset of parameters (12) of the set of parameters from an output signal of the engine control unit (ECU). The automatic start stop is enabled or inhibited as a function of the estimated state of charge SOC of the battery and the estimated battery temperature. The battery temperature is estimated based on engine coolant temperature, ambient temperature, engine rotational speed and vehicle speed, taking account of thermal transfer. The battery SOC is estimated based on the battey voltage, the estimated current drawn due to the starter motor and the estimated current generated due to alternator. A neural network is used for the computation. The invention allows to use less sensors, in particular there is no need to use an expensive intelligent battery sensor.

Description

Stop-start control system for use in vehicles with a stop-start device

It is well known to use stop-start devices in vehicles to extend a vehicle range. For instance, during a red phase of a traffic light, a vehicle engine would be shut off and re-started on demand at a next green phase. An energy storage device is often used for intermediately storing energy, to be released for re-starting. Energy storage devices could be mechanical, like a fly wheel, or electrical, like a battery which may store energy from a recuperation system, or a combination of both. When batteries are involved, it is essential to monitor a battery condition which can be characterized by well-known variables like state of charge (SOC), state of health (SOH), state of function (SOF), and permissible maximum power load. As a stop-start system notably increases a number of engine start-up processes, the battery has to be protected against deep discharge or overcharging. For this purpose, a controller unit may check a current battery state and will only permit the stop-start function to be enabled if determined values of the variables fulfill conditions of pre-set limits.

The condition of the battery may usually be determined by using a current sensor, voltage sensor, temperature sensor, or/and other sensors, in combination with a battery management system. External sensors for the determination of battery conditions are readily available. The Intelligent Battery Sensor (IBS) by Continental or other companies provides these data, reguiring a measurement of battery voltage, current and temperature, e.g. at a positive battery terminal. The IBS can be fully integrated as an intelligent battery cable clamp or on a battery terminal and is available on the market for a lot of years.

However, the higher the number of sensors used for monitoring the battery condition, the higher a probability for failure of the monitoring system is. Further, there is a substantial cost advantage in keeping the number of sensors as low as possible.

It is therefore a desire to keep a number of sensors that are provided for monitoring the battery condition to a minimum.

The invention relates to a stop-start control system for use in vehicles that comprise a stop-start device, at least one energy storage device to power the stop-start device, and at least one engine control unit (ECU) operating a set of parameters in at least one operating mode.

It is an object of the invention to provide a simple, reliabe, and highly versatile stop-start control system.

This object is achieved by the present invention as defined in claim 1.

In one aspect of the present invention, the object is achieved by a stop-start control system for use in vehicles that comprise a stop-start device, at least one energy storage device to power the stop-start device, and at least one engine control unit (ECU) operating a set of parameters in at least one operating mode, wherein the stop-start control system comprises a stop-start control unit that is provided to enable or to disable an operation of the stop-start device, depending on an evaluation of a subset of parameters of the set of parameters from an output signal of the engine control unit . By making use of already available parameters operated by the ECU during engine control, a demand for addition sensors that are exclusively assigned for monitoring a condition of the energy storage device can be diminished or even dispensed with. A probability for failure of the vehicle may therefore be maintained at a high level.

The at least one energy storage device preferably may be an accumulator and/or a battery and/or a power capacitor.

In accordance with a preferred embodiment of the invention, one parameter of the subset of parameters is a temperature of a vehicle coolant. A sufficiently precise estimate of the battery condition may be made using the coolant temperature as a basis, as an energy storage device temperature change is dependent on the coolant temperature .

According to another preferred embodiment of the invention, one parameter of the subset of parameters is an ambient temperature. A sufficiently precise estimate of the energy storage device condition may be made using the ambient temperature as a basis, as an energy storage device temperature starting point may be represented by the ambient temperature.

According to yet another preferred embodiment of the invention, one parameter of the subset of parameters is a voltage that is related to the energy storage device. A sufficiently precise estimate of the energy storage device condition may be made by making use of the voltage that is related to the energy storage device. Preferably, the voltage that is related to the energy storage device is a momentary voltage.

According to yet another preferred embodiment of the invention, one parameter of the subset of parameters is a vehicle engine speed. The phrase "vehicle engine speed", as used in this application, shall be understood particularly as a parameter that characterizes a point of operation of the engine within an operating range of the engine. For instance, when the engine is formed by an internal combustion engine, the vehicle engine speed may be given by a number of revolutions per time. A sufficiently precise estimate of the battery condition may be made using the vehicle engine speed as a basis, as a battery temperature change is dependent on the vehicle engine speed.

In another preferred embodiment of the invention, one parameter of the subset of parameters is a vehicle speed. The phrase "vehicle speed", as used in this application, shall be understood particularly as a parameter that characterizes a speed of the vehicle relative to a ground the vehicle is moving on. A sufficiently precise estimate of the battery condition may be made using the vehicle speed as a basis, as a battery temperature change is dependent on the vehicle speed due to heat convection.

According to another preferred embodiment of the invention, the stop-start control system further comprises a neural network provided to evaluate the subset of parameters . A change of the temperature of the battery can advantageously be represented in a non-linear way as a polynomial, coefficients of which can be computed using the neural network, which is adaptive.

The invention further relates to a stop-start system for use in vehicles comprising an embodiment of a stop-start control system of the invention, a stop-start device and at least one energy storage device to power the stop-start device, and an engine control unit (ECU) operating a set of parameters in at least one operating mode.

In the drawings,

Figure 1 shows a schematic overview of a stop-start system;

Figure 2 schematically shows a flow of data between an engine control unit and a stop-start control unit of a stop-start control system;

Figure 3 shows a flow diagram of an evaluation of a subset of parameters comprising a vehicle coolant temperature and an ambient temperature; and Figure 4 shows a flow diagram of an evaluation of a subset of parameter formed by a battery voltage and a vehicle engine speed. Fig. 1 schematically illustrates a stop-start system SSS for use in a vehicle with an internal combustion engine (ICE) . The stop-start system SSS comprises a stop-start device SSD which is not shown in more detail, represented by an alternator, and an energy storage device ESD which comprises a flywheel and a rechargeable battery, both of which are not further described as the one of skills in the art is guite familiar with those, for powering the stop-start device SSD. The battery may, for instance, be a lithium-ion battery or a lead-acid battery, or any other type of battery that appears to be appropriate to the one of skills in the art.

Moreover, the stop-start system contains an engine control unit ECU which is formed by a power train energy management system. In an operating mode, the engine control unit ECU is provided to operate a set of parameters which are derived from signals of sensors that are distributed all over the vehicle.

The cut-out part of the stop-start system illustrated in Figure 2 is formed by a stop-start control system SSCS having a stop-start control unit SSCU.

The stop-start control unit SSCU is provided to enable or to disable an operation of the stop-start device SSD as will be described later on, depending on an evaluation of a subset of parameters 12 of the set of parameters from output signals of the engine control unit ECU. The data transfer between the engine control unit ECU and the stop-start control system SSCS can be realized via CAN bus (not shown), which is a common bus system widely used in vehicles, or with any other bus system the one of skills in the art considers to be suitable.

A flow of data between the engine control unit ECU and the stop-start control unit SSCU is indicated in Fig. 2. The set of parameters is given by existing signals from the engine man- agement system without reguiring any additional hardware, i.e., in particular, without reguiring any additional sensors. The set of parameters comprises a voltage that is related to the energy storage device ESD, described as a battery voltage V_B. Further, the set of parameters comprises an ambient temperature T_AM, a coolant temperature T_∞ of the vehicle, a vehicle speed S_v, and a vehicle engine speed N which is represented by a number of rotations per minute (rpm) of the vehicle ICE. The stop-start control unit SSCU comprises signal output lines for an estimated battery temperature Τ_ΒΑτ, a net battery current I_BAT flowing into or out of the battery, and an output signal 10 representing a result of the evaluation of the state of charge of the battery SOC_BAT · This state-of-charge output signal 10 can be used as an input signal to an electronic logic circuit (not shown) that is provided to enable or disable an operation of the stop-start device SSD by controlling a supply of electric power to the stop-start device SSD. Description of the evaluation of the subset of parameters 12:

The evaluation of the subset of parameters 12 is carried out in three steps by using an algorithm that is residing in the stop-start control unit SSCU.

In a first step, the battery temperature T_BAT is estimated from the subset of parameters 12 from the engine control unit ECU. The estimate of the battery temperature T_BAT is based on thermal transfer and physical parameters of the vehicle, like coolant temperature T_Co, ambient temperature T_AM vehicle engine speed N and the vehicle speed S_v (Fig. 3) .

The battery temperature T_BAT is an important criterion for deciding on enabling or disabling the battery charging control. The battery temperature Τ_ΒΑτ is reguired to determine the accurate Electronic Voltage Regulator (EVR)-set point for proper battery charging. If the heat generated from chemical reaction is neglected, the change in the battery temperature Τ_ΒΑτ is mainly defined by conduction, convection and radiation from heat sources surrounding the battery and the battery itself. The heat conduction in the evaluation is defined as the instantaneous rate of heat flow which can be mathematically represented as the product of heat transfer due to conduction, convection and radiation .

The theoretical models of heat convection, conduction and radiation can be used for the temperature estimate. For vehicles eguipped with an ICE, the main heat source is the ICE itself. The temperature of the engine can be related to the coolant temperature Too- Based on this theory, the temperature is derived.

The temperature function is divided into two phases (Fig. 3) . Phase 1: The coolant temperature T_∞ is lower than or egual to 90°C.

The battery temperature T_BAT in this region is a summation of the heat produced due to conduction, convection and radiation. Battery Temperature T_BAT = T_AM + change in heat (conduction, convection, radiation) [10]

The round brackets are used to indicate a functional dependence. At start the term "change in heat" is zero. Based on the vehicle speed S_v, the change in heat is updated.

Phase 2: The coolant temperature is higher than 90°C.

The battery temperature T_BAT is taken as a sum of ambient temperature T_AM with an added correction. The correction added is proportional to the vehicle engine speed N for a given battery temperature Τ_ΒΑτ, stored at a previous instant, and the coolant temperature T_∞ ·

Battery Temperature Τ_ΒΑτ = TAM + f (N, T_co, (Τ_ΒΑΤτ -ι) [11]

The correction is given by f (N, Ί_∞, (Τ_ΒΑττ -ι) · This implementation is represented as a polynomial; i.e. in a non-linear way. The coefficients of the polynomial are computed using neural networks, which are adaptive. This helps in achieving the correct temperature prediction as the coolant temperature T_∞ does not vary above 90°C.

In a second step, a net stop-start system current is estimated (Fig. 4) .

The arrangement comprising the battery, the engine and its accessories, is viewed as a controlled energy system. The energy required to crank the engine is provided by the battery; with this an estimate is developed by which current I _BAT drawn from the battery is obtained. Once the engine has been started, the battery is recharged by the alternator that is driven by the engine.

A starter energy from the battery is equal to the integral of the product of the battery voltage V_B and the battery current I _BAT over time. For illustration purposes, variables are assumed to be constant over time, although the actual solution comprises an integration over time t :

V_BAT*lBAT*t = engine potential energy + engine kinetic energy

[1]

The current is predicted in two phases with reference to the battery .

Phase 1: Current is being drawn due to starter motor Potential Energy (Static load):

The fly wheel, a starting friction of engine pistons, and an initial spring stiffness of various valves are manifested as a starting inertia of the engine. This is the potential energy equivalent load, to be overcome by the starter motor powered by an energy source such as the battery. Energy to overcome engine and flywheel inertia = Energy consumed by the starter motor [2]

Kinetic Energy (Dynamic load) :

After the engine inertia is overcome by starter motor, the further sustenance of the engine is provided by the kinetic energy through the fly wheel . Energy to sustain engine friction + load = Energy of flywheel driven by starter motor [3]

A current at start eguals a sum of contributions [2] + [3] , divided by an instantaneous battery voltage V_B . current at start = ([2] + [3]) / instantaneous battery voltage V_B [4]

Phase 2 : Current returned due to alternator

This current is estimated based on the energy balance method, expressed by eg. [1], using system parameters like characteristics of the starter motor, the alternator and engine specific data like the flywheel data, and transmission ratio. No battery specific parameters need to be taken into account.

When the engine has started and is able to sustain, the starter motor is not engaged anymore with providing energy to the engine. At this instance, the engine starts to drive the flywheel which in turn engages the alternator. Now this engine energy, stored in the flywheel, will provide the energy to recharge the energy that was consumed during start-up. The available energy to recharge is a function of the vehicle engine speed N. Simultaneously, energy is being consumed by other accessories in the engine and the vehicle, like sensors, actuators, ECU, lights, and so on. This will account for the draining of the energy from the energy storage device ESD. Energy from the engine/flywheel = Energy by alternator (vehicle engine speed N)

[5]

Energy consumed by accessories I² * R * t [6]

Herein, R is meant to be an eguivalent effective resistance representing the accessories .

The energy that is stored into the battery is given by the difference of the energy contributions [5] and [6] : energy stored in battery = [5]-[6] [7]

Based on the energy produced and consumed, the current I_BAT into the battery is estimated:

IBAT = [7] / V_B [8] Finally, the net current is obtained by net current = [4] +[8] [9]

In a third step, a potential employment of the stop-start device SSD is evaluated.

The evaluation is carried out by making use of an estimate of the charge that has been utilized from the battery, and subtracting it from a rated charge of the battery at a given battery temperature T_Bat · The so-called SOC-eguation is

SOC_BAT = 1 - (total charge utilized / rating of battery at T_Bat)

If the SOC_BAT function value is higher than or egual to a pre-set value, the stop-start control unit SSCU produces an adeguate output signal 10 at one of the signal output lines (Fig. 2) that is connected to an electronic logic circuit in the energy storage device ESD that enables and releases a provision of powering of the energy storage device ESD to the stop-start device SSD. If the SOC_BAT function value is lower than or equal to the pre-set value, the stop-start control unit SSCU produces an adequate output signal 10 at the one of the signal output lines (Fig. 2) that is connected to an electronic logic circuit in the energy storage device ESD that disables and prevents a provision of powering of the energy storage device ESD to the stop-start device SSD, and, by that, protects the battery from deep discharge.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments .

Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

Claims

1. Stop-start control system (SSCS) for use in vehicles that comprise a stop-start device (SSD), at least one energy storage device (ESD) to power the stop-start device (SSD), and at least one engine control unit (ECU) operating a set of parameters in at least one operating mode, wherein

the stop-start control system (SSCS) comprises a stop-start control unit (SSCU) that is provided to enable or to disable an operation of the stop-start device (SSD), depending on an evaluation of a subset of parameters (12) of the set of parameters from an output signal of the engine control unit (ECU) .

2. Stop-start control system (SSCS) as claimed in claim 1, wherein one parameter of the subset of parameters (12) is a vehicle coolant temperature ( T_Co ) ·

3. Stop-start control system (SSCS) as claimed in claim 1 or 2, wherein one parameter of the subset of parameters (12) is an ambient temperature (ΤΆΜ ) .

4. Stop-start control system (SSCS) as claimed in one of the preceding claims, wherein one parameter of the subset of parameters (12) is a voltage (V_B) that is related to the energy storage device (ESD) .

5. Stop-start control system (SSCS) as claimed in one of the preceding claims, wherein one parameter of the subset of parameters (12) is a vehicle engine speed (N) .

6. Stop-start control system (SSCS) as claimed in one of the preceding claims, wherein one parameter of the subset of parameters (12) is a vehicle speed (S_v) .

7. Stop-start control system (SSCS) as claimed in one of the preceding claims, further comprising a neural network provided to evaluate the subset of parameters (12) .

8. Stop-start system (SSS)for use in vehicles, comprising a stop-start control system (SSCS) as claimed in claims 1 to 6, a stop-start device (SSD) and at least one energy storage device (ESD) to power the stop-start device (SSD) , and an engine control unit (ECU) operating a set of parameters in at least one operating mode .