One problem when speed regulating a truck in accordance with the foregoing is that the driving runs the risk of becoming jerky, since the control system continuously tries to adapt the speed to changes in the position of the speed control lever. Due to the fact that a regulation never can be done perfectly, the system tends to overreact to changes in the position of the speed control lever, something which is perceived as unpleasant by the operator. Another problem is that the fuel consumption of the truck runs the risk of becoming high, partly since the control unit is allowed to alternately increase the braking action and the engine speed at one

and the same speed, bringing about that the engine is forced to work against the increasingly activated brake, and partly since the control unit tends to force the engine speed up to an unnecessarily high level. Yet another problem is that the operator cannot influence the characteristics of the braking action of the brake, since this is determined in the control system.

The object of the present invention is to achieve a truck reducing the above-mentioned problems.

The truck according to the invention is characterized in that the regulating range includes a first subrange, within which the control unit is arranged for bringing the brake to generate a braking torque by means of said brake regulating control signal, and a second subrange, within which the control unit is arranged for bringing the brake to be inactive by means of said brake regulating control signal.

In the following, the invention will be described in greater detail with reference to the following figures.

Figure 1 is a schematic illustration of a system for speed regulating a truck according to the invention.

Figure 2 shows a pedal-shaped speed control lever in three different positions.

Figure 1 shows a system for regulating the speed of a truck. The system includes a speed control lever 1, which can be operated manually by the operator of the truck in order to regulate the truck speed. The speed control lever 1, preferably being in the form of a foot-operated pedal (see Figure 2), can be operated freely within a

regulating range A-B between a first extreme position A and a second extreme position B. The first extreme position A corresponds to a speed of 0 km/h of the truck, and the second extreme position B corresponds to the maximum speed at which the truck can or may be operated.

In other words, extreme position A corresponds to 0% and extreme position B corresponds to 100% of the maximum truck speed. Preferably, the system is arranged so that the speed increases substantially linearly with increased control lever deflection. Accordingly, by means of operating the speed control lever 1 between the extreme positions A and B, the operator can regulate the truck speed. The maximum truck speed can be for example 30 km/h.

According to the invention, the speed control lever 1 exhibits an intermediate control lever position C, dividing the regulating range A-B into a first subrange A-C and a second subrange C-B. The control lever position C corresponds to a predetermined desired speed value of the truck in the speed interval within which the truck can or may be operated. Accordingly, the predetermined desired speed value is within the interval 0-100% of the maximum speed. The predetermined desired speed value can be for example 50% of the maximum speed, in which case the control lever position C corresponds to a speed of 15 km/h if the maximum speed is 30 km/h.

Furthermore, the system includes a control unit 2, a gear box 3, an engine 4 and a brake 5. The control unit 2 is arranged for receiving information continuously about the position of the speed control lever 1 and for computing and transmitting gear ratio and speed regulating control signals, as a function of this position, to the gear box 3 and the engine 4, respectively, as well as brake

regulating control signals to the brake 5. The speed control lever 1 is preferably electronic and connected to the control unit 2 via a first communication line 6, wherein said information has the form of a voltage signal within a predetermined voltage interval, said voltage signal being a function of the position of the speed control lever 1. Preferably, the speed control lever 1 is arranged so that the voltage signal varies linearly with the control lever deflection. For example, the voltage interval can be 0-5 volts, wherein 0 volt corresponds to extreme position A and 5 volts corresponds to extreme position B.

The control unit 2 preferably includes a computer unit, being arranged for processing the voltage signal and computing said control signals. For the distribution of the control signals, the control unit 2 is connected to the gear box 3 via a second communication line 7, to the. engine 4 via a third communication line 8 and to the brake 5 via a fourth communication line 9. The gear box 3, the engine 4 and the brake 5 include devices for the physical regulation of the respective unit as a response to the respective control signal. Preferably, a proportional valve is used for the regulation of the gear box 3 and a servo-motor for the regulation of the engine 4. Preferably, a magnetic valve is used for the regulation of the brake 5.

The engine 4 is arranged for delivering a driving torque to the truck via the gear box 3, as a function of said gear ratio and speed regulating control signals, and the brake 5 is arranged for delivering a braking torque to the truck as a function of said brake regulating control signal. By means of the gear ratio and speed regulating control signals, the control unit 2 is arranged for

bringing the gear box 3 and the engine 4 to generate a driving torque within the entire regulating range A-B. In other words, the system is arranged for generating a driving torque within the entire regulating range A-B.

According to the invention, however, the system is arranged for activating the brake 5 only within the first subrange A-C, but not within the second subrange C-B. In other words, the control unit 2 is arranged for bringing the brake 5 to generate a braking torque within the first subrange A-C, but not within the second subrange C-B by means of the brake regulating control signal.

Accordingly, the first subrange A-C can be considered as a braked, and the second subrange C-B as an unbraked regulating range, and consequently, in principle, the speed control lever 1 functions as a combined throttle and brake control lever. Accordingly, within the first subrange A-C, the driving torque and the braking torque are interacting in order to give the truck the desired speed, i. e. the speed corresponding to the present control lever position. Within the second subrange C-B, the driving torque is acting alone in order to give the truck the speed corresponding to the present control lever position. It is true within both subranges A-C and C-B that the control unit 2 will regulate the speed of the engine 4 and/or the gear ratio of the gear box 3 when an the load on the truck is increased, for example in an upward slope, so that the speed corresponding to the present control lever position is maintained.

The braking torque is arranged in order to assume its maximum value in extreme position A in order to then decrease with increased control lever deflection and to assume its minimum value in extreme position C. For example, said maximum value is 100% of the available braking torque, i. e. the maximum braking torque which the

brake 5 can deliver, and said minimum value is 0% of the available braking torque. Preferably, the reduction of the braking torque takes place substantially linearly with an increased control lever deflection from extreme position A to control lever position C. The driving torque is arranged to assume its minimum value in extreme position A where, in principle, it is zero, and its maximum value in extreme position B.

Since each position of the speed control lever 1 corresponds to a predetermined braking action, decreasing with the control lever deflection within subrange A-C and being zero within subrange C-B, a uniform regulation of the truck speed which is pleasant to the operator is obtained. Furthermore, the situation that the control unit 2 alternately increases the braking action and the engine speed is avoided. In that way, a low fuel consumption is obtained.

Preferably, the system includes a terminal 10, being connected to the computer unit of the control unit 2, by means of which the operator via a communication bus 11 can modify the way the control unit 2 computes said brake regulating control signal for the purpose of adapting the characteristics of the braking action to himself.

Preferably, the operator is given a possibility to adjust the desired braking torque in extreme position A, said braking torque being for example 10-100% of the maximum braking action. Conveniently, this is done by means of allowing the operator to select a braking program amongst a predetermined number of braking programs, for example nine such programs, wherein braking program one implies that the braking torque in extreme position A is 10% of the maximum braking action and braking program nine implies that the braking torque in extreme position A is

100% of the maximum braking action. In the remaining braking programs two to eight, the braking torque is uniformly distributed between 0% and 100% of the maximum braking action. Preferably, the operator is also given a possibility to adjust the control lever position C, i. e. the extent of subrange A-C. For example, the operator could select control lever position C from a predetermined interval, for example 20-60% of the maximum speed at which the truck can or may be operated.

In the foregoing, the invention has been described starting from a specific embodiment. It will be appreciated, however, that variants and modifications are possible within the scope of the invention. For example, the system. can include a separate foot-operated brake, by means of which the operator, in an emergency situation, can bypass the control unit 2 and operate the brake 5 directly.

In this patent application, truck relates to a counterweight truck (for example a fork truck), a side- stacking truck, a container truck or a similar vehicle for loading, unloading and handling goods in general.