Method for controlling a brake system

Abstract

A method for controlling a brake system in an agricultural work vehicle, wherein the work vehicle comprises a drive train having a drive engine, an adjustable ratio transmission, which is arranged downstream of the drive engine and via which a driving power generated by the internal combustion engine can be transmitted to the drive axle, a service brake device and at least one auxiliary brake device.

Claims

1. A method for controlling a brake system in an agricultural work vehicle, the work vehicle including a drive train having a drive engine, a variable transmission ratio transmission which is arranged downstream of the drive engine and via which the drive power generated by the drive engine can be transmitted to a drive axle, a service brake device, and an auxiliary brake device, the method comprising: an actuating device receiving a command to decelerate the work vehicle; commanding a deceleration value (a.sub.soll) to the service brake device and auxiliary brake device; and adjusting a transmission ratio of the transmission towards a larger transmission ratio when the auxiliary brake device is being actuated with priority; wherein the actuating device activates the auxiliary brake device with priority relative to the service brake device so long as the deceleration value (a.sub.aux) provided by the auxiliary brake device is able to cover the commanded deceleration value (a.sub.soll), and the service brake device is activated only if the commanded deceleration value (a.sub.soll), exceeds the deceleration value (a.sub.aux) that can be achieved by the auxiliary brake device; and wherein the auxiliary brake device applies the braking power thereof to a crankshaft of the engine.

2. The method of claim 1, wherein the actuating device is configured to be activated by an operator of the agricultural vehicle.

3. The method of claim 2, wherein the actuating device is a brake pedal or a drive lever of the work vehicle.

4. The method of claim 1, wherein the work vehicle comprises an electronic control unit and the method further comprises the electronic control unit activating the auxiliary brake device when a speed limit of the drive engine is exceeded and a torque limit of the drive engine is undershot.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The method according to the invention will be described with reference to the following figures. Wherein:

(2) FIG. 1 shows an agricultural work vehicle and

(3) FIG. 2 shows a block diagram of components for performing the method according to the invention.

DETAILED DESCRIPTION

(4) FIG. 1 shows an agricultural work vehicle 10 in the form of a tractor. The work vehicle 10 comprises a drive train 12 consisting of a drive engine 14, a transmission 16 with an adjustable transmission ratio and a drive axle 18 having drive wheels 20. The transmission can be a continuously variable transmission, a parallel-shift transmission, an epicyclic gear transmission or a semi-automatic transmission. The work vehicle 10 further comprises a service brake device 30, which comprises an actuating device 32, in the form of a brake pedal for example, arranged in a cab 22 within reach of an operator present there, and a brake unit 34 for applying a braking torque to the drive axle 18, which transmits the braking torque upon actuation to the ground surface currently being driven on. The actuating device 32 can additionally or alternatively comprise a drive lever or a manual throttle lever. The brake unit 34 can be implemented as a wet disk brake, for example. The brake unit 34 can additionally be arranged in a differential housing 24 and thus act on the drive axle 18.

(5) The service brake device 30 can be actuated in the conventional manner, in that the operator actuates the actuating device 32 in the form of a brake pedal and hydraulic fluid is provided by a hydraulic pump of the work vehicle 10 at a braking pressure to the brake unit 34. The position of the brake pedal 32 assumed upon actuation of the service brake device 30 can be detected with a position sensor 36, the generated braking pressure with a pressure sensor 38 and the generated braking deceleration of the work vehicle 10 with an acceleration sensor 40. In addition, an electronic control unit 42, which is connected for data exchange and control purposes to the drive engine 14, the transmission device 16, the service brake device 30 and the sensors 36, 38, 40, is also provided.

(6) The electronic control unit 42 can comprise one or more microcontrollers 42.sub.1, 42.sub.2, wherein at least one microcontroller calculates, from the values position of the brake pedal 32, generated brake pressure and generated braking deceleration of the work vehicle 10, a deceleration value a.sub.soll that characterizes a braking deceleration of the work vehicle 10.

(7) FIG. 1 additionally shows that the work vehicle 10 comprises an auxiliary brake device 50 that, in a first embodiment of the work vehicle 10, is designed as a retarder, to which the method of the invention for controlling a brake system is applicable. The retarder can operate according to a hydrostatic functional principle and can be arranged in a front region on the drive engine 14 and driven by a crankshaft 26 of the drive engine 14. The auxiliary brake device 50 can be actuated by operating means arranged separately in the cab 22, which are not illustrated in the present case, however. Alternatively, the auxiliary brake device 50 can be actuated by the actuating device 32 already described in relation to the service brake device 30.

(8) FIG. 2 schematically shows, in a block diagram, the interaction of individual components necessary for performing the method according to the invention. The actuating device 32, by means of which a braking deceleration of the work vehicle 10 can be commanded, is listed first. The actuating device 32 has a control connection to the microcontroller 42.sub.1, which is part of the electronic control unit 42. Driving strategies, which include stored transmission shifting strategies, for example, are stored on the microcontroller 42.sub.1. The microcontroller 42.sub.1 takes on the control of subsystems such as the activation of a front-wheel drive that can be switched on as needed, or the activation of the transmission 16 based on a shifting strategy. A microcontroller 42.sub.2 is connected for control purposes to the actuating device 32 and the microcontroller 42.sub.1. The microcontroller 42.sub.2 is used for controlling the auxiliary brake device 50. The method according to the invention has the effect, depending on the availability and the respective driving state, of initially executing the braking deceleration commanded by the operator by using the auxiliary brake device 50, until the braking deceleration a.sub.aux that can be achieved with the auxiliary brake device 50 is below a value a.sub.soll of the braking deceleration. The auxiliary brake device 50 is controlled by the microcontroller 42.sub.2. If the commanded braking deceleration a.sub.soll cannot be provided or cannot be provided completely by the auxiliary brake device 50, the microcontroller 42.sub.1 activates the service brake device 30.

(9) The method according to the invention can additionally extend to adjusting the transmission 16 in the direction of a larger transmission ratio by means of a transmission ratio lever, where the transmission ratio lever can be comprised by the actuating device 32. Additional braking power is provided by the auxiliary brake system 50 due to the adjusted higher transmission ratio of the transmission 16. For this purpose, the relevant transmission variables such as engine speed or current transmission ratio and additional conditions are checked by the microcontroller 42.sub.1.

(10) The method according to the invention can also be used for an engine speed regulation of the drive engine 14. In this case the auxiliary brake device 50 is operated in overrun mode. This allows an over-rotation protection by automatically activating the auxiliary brake device 50 when an engine rotational speed limit is exceeded with simultaneous undershooting of a torque limit.

(11) By activating the auxiliary brake 50 during a warm-up phase of the drive engine 14, faster heating of the drive engine 14 and a hydraulic system of the work vehicle 10 can be achieved, since an artificial load is produced by the auxiliary brake device 50.

(12) A hydrostatic retarder was described in connection with FIG. 1 as a possible embodiment of the auxiliary brake device 50. Either alternative systems or additional systems in parallel can be used. These include a variable turbine geometry of an exhaust gas turbocharger, an eddy current brake, an exhaust brake, a hydraulic system brake, a combination of a generator, an inverter and a brake resistor, or an electrical drive axle operated in generator mode in a towed implement. The auxiliary brake device 50 can also be arranged on the work vehicle 10 itself or on an attached implement. Each of said auxiliary brake devices can be used both autonomously and as a single or multiple combination with other auxiliary brake devices. In principle, any connectible power consumer that exerts a load on the drive engine can be used as an auxiliary brake device. The load can be connected via an electrical path, a mechanical path or a hydraulic path. All auxiliary brake devices at least indirectly draw their braking power from the crankshaft of the drive engine.