JP5652337B2 - Vehicle control device - Google Patents

Description

  The present invention relates to a vehicle control device that is mounted on a vehicle having a plurality of power sources for traveling and performs drive control of the plurality of power sources so as to realize a target acceleration that satisfies a predetermined traveling condition.

  Conventionally, an inter-vehicle control apparatus for a hybrid vehicle having an inter-vehicle control system that has a motor and an engine in a drive system and controls braking / driving force so as to maintain a set inter-vehicle distance from the own vehicle when a preceding vehicle is captured. (For example, refer to Patent Document 1).

JP 2007-168502 A

  The hybrid vehicle described in Patent Document 1 calculates an acceleration (target acceleration) necessary for maintaining a constant inter-vehicle distance from the preceding vehicle, and the target acceleration and a predetermined boundary. Based on the acceleration / deceleration, it is determined whether or not a new power source needs to be driven. If it is determined that a new power source needs to be driven, the vehicle is driven so that the distance between the vehicle and the preceding vehicle is maintained constant. There is a control that drives a new power source in addition to the power source inside.

  For example, when the distance between the vehicle and the preceding vehicle temporarily increases while the motor travels by driving only the motor, and it is determined that the engine needs to be driven in addition to the motor based on the target acceleration and the boundary acceleration The drive control by the motor and engine is performed.

  However, in such control, the target acceleration slightly exceeds the boundary acceleration, and the motor and engine drive control is switched, resulting in a decrease in energy efficiency.

  Therefore, it can be considered that the boundary acceleration during acceleration is set slightly higher. However, if the boundary acceleration is changed in this way, there arises a problem that the acceleration performance deteriorates in all acceleration scenes.

  The present invention has been made in view of the above problems, and an object thereof is to improve energy efficiency without reducing acceleration performance in a full acceleration / deceleration scene.

In order to achieve the above object, an invention according to claim 1 is mounted on a vehicle having a motor and an engine for traveling, calculates a target acceleration / deceleration (Ad) that satisfies a predetermined traveling condition, and performs the target acceleration / deceleration. A vehicle control device that performs drive control of an engine in addition to a motor when it is determined that drive control using the engine is necessary based on a boundary acceleration / deceleration (A 1 ) where the speed (Ad) and acceleration are positive. It is determined whether the difference between the target acceleration / deceleration (Ad) and the positive boundary acceleration / deceleration (A 1 ) is within an acceleration regulation range (ΔAd) defined so that the vehicle speed is wider than the low speed. Even if it is determined that the engine needs to be driven based on the acceleration difference determining means, the target acceleration / deceleration (Ad) and the positive boundary acceleration / deceleration (A 1 ), the acceleration difference determining means determines the target acceleration / deceleration (Ad). , positive border If the difference between the acceleration (A 1) is determined to be the acceleration specified range (? AD), comprising: a target acceleration change means for changing the target acceleration speed (Ad) on the maximum acceleration achievable by the motor, the It is characterized by that.

According to such a configuration, the acceleration regulation range (ΔAd) is defined such that the difference between the target acceleration / deceleration (Ad) and the positive boundary acceleration / deceleration (A1) is wider when the vehicle speed is higher than the low speed. Even if it is determined whether or not the engine needs to be driven based on the target acceleration / deceleration (Ad) and the positive boundary acceleration / deceleration (A 1 ), the acceleration difference determining means determines the target acceleration / deceleration (Ad). And the positive boundary acceleration / deceleration (A1) is determined to be within the acceleration regulation range (ΔAd), the target acceleration / deceleration (Ad) is changed to the maximum acceleration that can be realized by the motor. Energy efficiency can be improved without degrading acceleration performance in an acceleration scene.
By the way, there is a tendency that a change in acceleration / deceleration is less noticeable when the vehicle speed is higher than the low speed.
In the above-described configuration, the acceleration regulation range is defined such that the vehicle speed is wider than the low speed, so that energy efficiency can be improved without making the occupant aware of a decrease in acceleration / deceleration performance. Is possible.

The invention according to claim 2, the brake control using the new hydraulic brake in addition to the regenerative braking by the motor based on the objectives acceleration (Ad) and the acceleration is negative boundary acceleration (A 2) If it is determined that it is necessary, the brake control using the hydraulic brake is newly performed in addition to the regenerative braking by the motor . The acceleration difference determination means further includes a target acceleration / deceleration (Ad) and a negative boundary. It is determined whether or not the difference from the acceleration / deceleration (A2) is within the specified acceleration range (ΔAd), and the target acceleration changing means determines whether the motor is based on the target acceleration / deceleration (Ad) and the negative boundary acceleration / deceleration (A 2 ). Even when it is determined that the brake control using the hydraulic brake is newly required in addition to the regenerative brake by the acceleration difference determination means, the acceleration difference determination means sets the target acceleration / deceleration (Ad) and the negative boundary acceleration / deceleration (A 2 ). difference If is it is determined that the acceleration specified range (? AD), is characterized in that changing target acceleration a (Ad) on the maximum deceleration that can be achieved by regenerative braking.

According to such a configuration, it is determined based on the target acceleration / deceleration (Ad) and the negative boundary acceleration / deceleration (A 2 ) that braking control using a hydraulic brake is newly required in addition to the regenerative braking by the motor. Even when the acceleration difference determination means determines that the difference between the target acceleration / deceleration (Ad) and the negative boundary acceleration / deceleration (A 2 ) is within the acceleration regulation range (ΔAd), the target acceleration / deceleration (Ad ) is because it is changed to the maximum deceleration that can be achieved by regenerative braking, without reducing the decelerating performance in total slowing scene, it is possible to improve the energy efficiency.

  The running condition may be such that the inter-vehicle distance from the preceding vehicle is kept constant as in the invention described in claim 4, and the vehicle speed of the vehicle is kept constant as in the invention described in claim 5. The maximum vehicle speed of the vehicle may be held constant as in the invention described in claim 6.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a figure which shows the structure of the vehicle control apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating boundary acceleration / deceleration. It is a figure for demonstrating the change of a target acceleration. It is a figure for demonstrating the relationship between an acceleration regulation range and a vehicle speed. It is a flowchart of inter-vehicle control ECU.

  FIG. 1 shows a configuration of a vehicle control device according to an embodiment of the present invention. The vehicle control apparatus 1 is mounted on a hybrid vehicle that uses a motor and an engine as a driving power source, and performs drive control of the motor and the engine so as to maintain a constant inter-vehicle distance from the preceding vehicle.

  The vehicle control device 1 includes an inter-vehicle control ECU 10 and an acceleration control ECU 20. An inter-vehicle distance sensor 30 and a vehicle speed sensor 31 are connected to the inter-vehicle control ECU 10.

  The inter-vehicle distance sensor 30 is for measuring the inter-vehicle distance between the host vehicle and the preceding vehicle. In this embodiment, a laser radar is used to measure the inter-vehicle distance between the host vehicle and the preceding vehicle by transmitting laser light and detecting reflected light reflected by the preceding vehicle. The inter-vehicle distance sensor 30 periodically measures the inter-vehicle distance from the preceding vehicle, and the inter-vehicle distance data representing the inter-vehicle distance is transmitted from the inter-vehicle distance sensor 30 to the inter-vehicle control ECU 10.

  The vehicle speed sensor 31 outputs a signal for specifying the vehicle speed of the host vehicle. The vehicle speed sensor 31 outputs a vehicle speed signal corresponding to the rotational speed of the wheel of the host vehicle to the inter-vehicle control ECU 10.

  The inter-vehicle control ECU 10 is configured as a computer including a CPU, a memory, an I / O, and the like. The CPU of the inter-vehicle control ECU 10 performs various processes according to a program stored in the memory.

  The inter-vehicle control ECU 10 includes a signal corresponding to the driver's accelerator pedal operation amount from an accelerator pedal operation amount sensor (not shown) and a driver's brake pedal operation amount from a brake pedal operation amount sensor (not shown). A signal corresponding to the signal is input.

  The inter-vehicle control ECU 10 calculates a target acceleration / deceleration Ad requested by the driver based on a signal input from the accelerator pedal operation amount sensor and a signal input from the brake pedal operation amount sensor, and accelerates the calculated target acceleration / deceleration Ad. It is sent to the control ECU 20.

  The inter-vehicle control ECU 10 obtains the vehicle speed of the host vehicle based on the vehicle speed signal input from the vehicle speed sensor 31 when a signal instructing to start traveling at a constant inter-vehicle distance is input in response to an occupant's switch operation. Based on the vehicle speed and the inter-vehicle distance data input from the inter-vehicle distance sensor 30, a target acceleration / deceleration (target acceleration or target deceleration) Ad is calculated so that the inter-vehicle distance from the preceding vehicle is constant, and the calculated target acceleration / deceleration is calculated. The speed Ad is output to the acceleration control ECU 20.

  The acceleration control ECU 20 is configured as a computer including a CPU, a memory, an I / O, and the like. The CPU of the acceleration control ECU 20 performs various processes according to a program stored in the memory.

  The acceleration control ECU 20 acquires information representing the driving torque range from the engine ECU 40 and the motor ECU 41, acquires information representing the braking torque range from the brake ECU 42, and converts the information representing the driving torque range and information representing the braking torque range. Based on this, the boundary acceleration / deceleration is defined.

  The driving torque range is determined by the maximum torque that can be realized by engine driving and motor driving, and the braking torque range is determined by the maximum torque that can be realized by regenerative braking by hydraulic regeneration and hydraulic braking.

  The engine ECU 40 controls the driving of the engine so that a driving torque according to the driving instruction from the acceleration control ECU 20 is generated on the axle, and the motor ECU 41 generates a driving torque according to the driving instruction from the acceleration control ECU 20 on the axle. The motor is driven and controlled as described above.

  In addition, the brake ECU 42 controls the motor and the hydraulic brake so that a braking torque corresponding to the braking instruction from the acceleration control ECU 20 is generated on the axle.

  Further, the acceleration control ECU 20 sends an instruction to the engine ECU 40, the motor ECU 41, and the brake ECU 42 so as to realize the target acceleration / deceleration Ad input from the inter-vehicle control ECU 10. Specifically, the engine ECU 40 and the motor ECU 41 are instructed to generate a driving torque for realizing the acceleration required by the driver, and the brake ECU 42 is provided with the deceleration required by the driver. An instruction is sent to generate braking torque.

  The acceleration control ECU 20 determines whether or not a new power source is necessary based on the target acceleration / deceleration Ad input from the inter-vehicle control ECU 10 and a predetermined boundary acceleration / deceleration, and the motor and engine are determined according to the determination result. Drive control and braking control using a motor and a brake.

  The acceleration control ECU 20 preferentially operates the motor within a drive torque range that can be generated by the motor, and operates the engine ECU 40 and the engine ECU 40 so as to operate the engine when the drive torque that can be generated by the motor is exceeded. The motor ECU 41 is instructed.

  Further, the acceleration control ECU 20 preferentially activates the regenerative brake within the braking torque range that can be generated by the motor, and further activates the hydraulic brake when the braking torque that can be generated by the motor is exceeded. The ECU 42 is instructed.

  Specifically, as shown in FIG. 2, at the time of acceleration, when the target acceleration is less than the boundary acceleration / deceleration A1, only the motor drive is controlled. When the target acceleration is equal to or higher than the boundary acceleration / deceleration A1, Implement engine drive control. This makes it possible to obtain energy necessary for realizing the target acceleration.

  Also, during deceleration, if the target deceleration is greater than the boundary acceleration / deceleration A2, braking control of only the regenerative brake by the motor is performed. When the target deceleration becomes the boundary acceleration / deceleration A2 or less, in addition to the regenerative braking by the motor Implement braking control by hydraulic brake. Thereby, the energy required for realizing the target deceleration can be obtained.

  In the present embodiment, the boundary acceleration / deceleration A1 is set to a point at which the operation mode using only the motor as the power source is switched to the operation mode using the motor and the engine as the power source. The boundary acceleration / deceleration A1 is a value that is lower by a certain amount than the maximum acceleration Am that can be achieved by the motor so that the motor does not become overloaded.

  The boundary acceleration / deceleration A2 is set to a point at which the regenerative brake by the motor regeneration is switched to the regenerative brake and the hydraulic brake. This boundary acceleration / deceleration A2 is set to the same value as the maximum deceleration Am that can be realized by regenerative braking by motor regeneration.

  The inter-vehicle control ECU 10 according to the present embodiment determines that a new power source is necessary only when the target acceleration slightly exceeds the boundary acceleration / deceleration, and switches to drive control of the motor and the engine. In order to solve the problem that energy efficiency is reduced by switching to braking control with regenerative brake and hydraulic brake, etc., it is determined that a new braking means is necessary just by falling below the boundary acceleration / deceleration. A process of changing the target acceleration / deceleration Ad to the maximum acceleration Am realizable by the driving power source according to the conditions is performed.

  FIG. 3 shows an enlarged view of part B of FIG. Even when it is determined that the driving of a new power source is necessary based on the target acceleration / deceleration Ad and a predetermined boundary acceleration / deceleration A1, the inter-vehicle control ECU 10 is in driving with the target acceleration / deceleration Ad as shown in FIG. When it is determined that the difference from the maximum acceleration A1 that can be achieved by the power source is within the predetermined acceleration regulation range ΔAd, as shown by the arrow C in the figure, the power source that is driving the target acceleration / deceleration Ad The maximum acceleration A1 that can be realized is changed.

  In the present embodiment, the acceleration regulation range ΔAd changes according to the vehicle speed. FIG. 4 shows the relationship between the acceleration regulation range and the vehicle speed. In the figure, the positive side of the vertical axis is the acceleration regulation range during acceleration, and the negative side of the vertical axis is the acceleration regulation range during deceleration. In the memory of the inter-vehicle control ECU 10, information that defines the relationship between the vehicle speed and the acceleration regulation range is stored.

  As shown in this figure, when the vehicle speed is less than a certain value (for example, 40 kilometers per hour), the acceleration regulation range is defined to become wider as the vehicle speed increases. This is based on the driver's characteristic that high speed is less likely to notice acceleration / deceleration changes than low speed.

  FIG. 5 shows a flowchart of the inter-vehicle control ECU 10. The inter-vehicle control ECU 10, the acceleration control ECU 20, the engine ECU 40, the motor ECU 41, the brake ECU 42, and the like are in an operating state in response to an operation on the start button provided in the driver's seat. And if the signal which instruct | indicates the start of driving | running | working with constant inter-vehicle distance is input into inter-vehicle control ECU10 by a driver | operator's switch operation, inter-vehicle control ECU10 will implement the process shown in FIG. 5 regularly.

  First, target acceleration and target deceleration are calculated from the inter-vehicle distance and the vehicle speed (S100). Specifically, the vehicle speed of the host vehicle is obtained based on the vehicle speed signal input from the vehicle speed sensor 31, and the inter-vehicle distance from the preceding vehicle is determined based on the vehicle speed and the inter-vehicle distance data input from the inter-vehicle distance sensor 30. The target acceleration / deceleration (target acceleration or target deceleration) Ad is calculated so as to be constant.

  Next, the boundary acceleration / decelerations A1 to An are acquired from the acceleration control ECU 20 (S102). In the present embodiment, the boundary acceleration / deceleration A1 and the boundary acceleration / deceleration A2 shown in FIG. 2 are acquired.

  Next, an acceleration range ΔAd is set (S104). Specifically, the acceleration range ΔAd corresponding to the vehicle speed of the vehicle is specified with reference to the memory.

  Next, among the boundary acceleration / decelerations A1 to An, the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad is specified, and it is determined whether Am ≧ Ad−ΔAd is satisfied (S106).

  Here, it is assumed that the boundary acceleration / deceleration A1 is the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad. In this case, it is determined whether A1 ≧ Ad−ΔAd is satisfied.

  Here, if the target acceleration / deceleration Ad slightly exceeds the boundary acceleration / deceleration A1 and A1 ≧ Ad−ΔAd is satisfied, the determination in S106 is YES, and then the target acceleration / deceleration Ad is changed (S108). . Specifically, the target acceleration / deceleration Ad is changed to the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad.

  Next, the target acceleration / deceleration Ad is output to the acceleration control ECU 20 (S110). That is, motor drive is maintained and engine drive is not started.

  Therefore, although acceleration performance is somewhat reduced, engine driving is not started, which can contribute to improvement in energy efficiency.

  Further, when the boundary acceleration / deceleration A1 is the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad, the target acceleration / deceleration Ad greatly exceeds the boundary acceleration / deceleration A1, and A1 ≧ Ad−ΔAd is not satisfied. The determination in S106 is NO, and the target acceleration / deceleration Ad is output to the acceleration control ECU 20 without changing the target acceleration / deceleration Ad.

  In this case, it is possible to quickly switch to motor + engine driving, and to perform drive control without degrading acceleration performance.

Further, the boundary acceleration / deceleration A2 is the boundary acceleration / deceleration Am that is closest to the target acceleration / deceleration Ad, and the target acceleration / deceleration Ad is slightly lower than the boundary acceleration / deceleration A2, so that A 2 ≧ Ad−ΔAd is satisfied. If YES, the determination in S106 is YES, and then the target acceleration / deceleration Ad is changed (S108). Specifically, the target acceleration / deceleration Ad is changed to the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad.

  In this case, the regenerative brake is maintained. Therefore, although the braking performance is somewhat reduced, it contributes to the improvement of energy efficiency.

Further, the boundary acceleration / deceleration A2 is the boundary acceleration / deceleration Am that is closest to the target acceleration / deceleration Ad, and the target acceleration / deceleration Ad greatly falls below the boundary acceleration / deceleration A2 due to sudden braking, and satisfies A 2 ≧ Ad−ΔAd. If not, the determination in S106 is NO, and the target acceleration / deceleration Ad is output to the acceleration control ECU 20 without changing the target acceleration / deceleration Ad.

  In this case, the brake control is quickly switched to the regenerative brake and the hydraulic brake. Therefore, the braking control can be performed without reducing the braking performance.

  According to the above configuration, it is determined whether or not the difference between the target acceleration / deceleration Ad and the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad among the boundary acceleration / deceleration An is within the acceleration regulation range ΔAd. And the boundary acceleration / deceleration An, the difference between the target acceleration / deceleration Ad and the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad of the boundary acceleration / deceleration An is the acceleration. If the target acceleration / deceleration Ad is determined to be within the specified range ΔAd, the target acceleration / deceleration Ad is changed to an acceleration that can be realized by the driving power source, so that the energy efficiency can be improved without degrading the acceleration performance in the entire acceleration scene. Can be planned.

  Even when it is determined that a braking control using a hydraulic brake is newly required in addition to the regenerative braking by the motor based on the target acceleration / deceleration Ad and the boundary acceleration / deceleration An, the target acceleration / deceleration Ad and the boundary acceleration / deceleration When it is determined that the difference from the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad in the An is within the acceleration regulation range ΔAd, the target acceleration / deceleration Ad is changed to a deceleration that can be realized by regenerative braking by the motor. Therefore, energy efficiency can be improved without degrading the deceleration performance in all deceleration scenes.

  In addition, the acceleration regulation range is defined such that the vehicle speed is wider than the low speed, so that it is possible to improve energy efficiency without making the occupant aware of a decrease in acceleration / deceleration performance. .

  In addition, this invention is not limited to the said embodiment, Based on the meaning of this invention, it can implement with a various form.

  For example, in the above embodiment, the target acceleration / deceleration Ad is changed to the boundary acceleration / deceleration Am closest to the target acceleration / deceleration Ad among the boundary acceleration / decelerations An in S108. It is not necessary to change to the speed Am, and it may be configured to change to an acceleration that can be realized by a driving power source. For example, you may comprise so that it may become a value a little smaller than the boundary acceleration / deceleration Am nearest to the target acceleration / deceleration Ad.

  In the above embodiment, the inter-vehicle control device 1 is configured by the inter-vehicle control ECU 10 and the acceleration control ECU 20, but the inter-vehicle control device 1 may be configured by using the inter-vehicle control ECU 10 and the acceleration control ECU 20 as one ECU.

  In the above embodiment, the inter-vehicle distance sensor 30 is configured using a laser radar, but is not limited to the laser radar, and may be configured using, for example, a millimeter wave radar, a two-camera CCD, or the like.

  In the above-described embodiment, the configuration in which the acceleration regulation range changes according to the vehicle speed is shown. However, for example, the acceleration regulation range can be changed by setting the occupant, such as energy saving priority, standard, and acceleration priority. Good. In this case, the acceleration regulation range may be defined so as to be narrowed in the order of energy saving priority, standard, and acceleration priority. Moreover, you may comprise so that an acceleration regulation range may be changed according to a vehicle speed and a setting of a passenger | crew.

  In the above-described embodiment, an example in which the distance between the preceding vehicle and the preceding vehicle is kept constant as the travel condition is shown. However, for example, the vehicle speed of the vehicle may be kept constant, and the maximum vehicle speed of the vehicle may be maintained. May be held constant.

  Moreover, in the said embodiment, although the structure which mounted this vehicle control apparatus in the vehicle carrying a motor and an engine was shown, it is not limited to such a structure, For example, the vehicle carrying two engines, The present invention can also be applied to a vehicle equipped with two motors, a vehicle equipped with two motors and two engines, and the like.

  The correspondence between the configuration in the above embodiment and the configuration of the claims will be described. S106 corresponds to acceleration difference determination means, and S108 corresponds to target acceleration change means.

1 vehicle control device 10 inter-vehicle control ECU
20 Acceleration control ECU
30 Inter-vehicle distance sensor 31 Vehicle speed sensor 40 Engine ECU
41 Motor ECU
42 Brake ECU

Claims (6)

A target acceleration / deceleration (Ad) that is mounted on a vehicle having a motor and an engine for traveling and satisfies a predetermined traveling condition is calculated, and the boundary acceleration / deceleration (A 1 ) where the target acceleration / deceleration (Ad) and acceleration are positive. When it is determined that the drive control of the engine is necessary based on the vehicle, the vehicle control device performs the drive control of the engine in addition to the motor ,
Whether the difference between the target acceleration / deceleration (Ad) and the positive boundary acceleration / deceleration (A 1 ) is within an acceleration regulation range (ΔAd) defined such that the vehicle speed is wider than the low speed. Acceleration difference determining means for determining
Even when it is determined that the engine needs to be driven based on the target acceleration / deceleration (Ad) and the positive boundary acceleration / deceleration (A 1 ), the acceleration difference determination means determines the target acceleration / deceleration (Ad) and the When the difference from the positive boundary acceleration / deceleration (A 1 ) is determined to be within the acceleration regulation range (ΔAd), the target acceleration change for changing the target acceleration / deceleration (Ad) to the maximum acceleration realizable by the motor Means for controlling the vehicle. If it is determined before Symbol target acceleration and (Ad) and acceleration is required braking control using the new hydraulic brake in addition to the regenerative braking by the motor based on the negative boundary acceleration (A 2), the motor In addition to the regenerative braking by, the brake control using a hydraulic brake is newly implemented,
The acceleration difference determination means further determines whether or not a difference between the target acceleration / deceleration (Ad) and the negative boundary acceleration / deceleration (A2) is within the acceleration regulation range (ΔAd),
The target acceleration changing means needs to newly perform a braking control using a hydraulic brake in addition to the regenerative braking by the motor based on the target acceleration / deceleration (Ad) and the negative boundary acceleration / deceleration (A 2 ). even when it is determined, the target acceleration (Ad) by the acceleration difference determining means, a difference between the negative boundary acceleration (a 2) is determined to the the acceleration specified range (? AD) case, the vehicle control apparatus according to claim 1, characterized in that changing the target acceleration speed (Ad) on the maximum deceleration that can be achieved by the regenerative brake. The acceleration specified range, the vehicle control apparatus according to claim 1 or 2, characterized in that is adapted to be stepwise changed according to an occupant of the setting. The vehicle control apparatus according to any one of claims 1 to 3, wherein the traveling condition is to maintain a constant inter-vehicle distance from a preceding vehicle. The running condition, the vehicle control device according to any one of claims 1 to 3, characterized in that is to hold the vehicle speed of the vehicle constant. The vehicle control apparatus according to any one of claims 1 to 3, wherein the traveling condition is to keep a maximum vehicle speed of the vehicle constant.

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