Economic comparison between cranes with single or double engines

Nowadays, in the market, there is a debate over whether a truck crane should use a single engine (referred to as a single engine) or use separate engines for lifting and traveling, that is, a dual-engine system (referred to as a dual-engine system). As for which is better, everyone has their own opinions. So, what is the truth? Whether to send single or double messages should ultimately be considered from the user's perspective. Only by considering the overall situation and being able to maximize the product's usage benefits and minimize the process usage costs for users can the best choice be made.

Generally speaking, from purchase to use until final scrapping, the corresponding costs for users to consume a truck crane include purchase cost (usually calculated as a one-time payment), usage cost (mainly including fuel cost and maintenance cost), and residual value (residual value is regarded as income and can be calculated as negative cost). This article starts by examining the main consumption costs of the product to reveal the cost differences caused by the adoption of engine layout.

The following table shows the relevant comparison parameters of three types of cranes: QY70K, LT1070 and LTM1070-4.1.

In the above table: The specific power, as defined in GB7258-2004 "Technical Conditions for the Operation Safety of Motor Vehicles", is the ratio of the maximum net power of the engine (or 0.9 times the rated power of the engine or 0.9 times the rated power of the engine) to the maximum allowable total mass of the motor vehicle. The GB7258-2004 standard requires that this value must be greater than 5.

To ensure consistency in the comparison, the following text will only conduct a corresponding analysis of the changed parts. Taking Model One with a single engine, Model Two with a dual engine, and the additional configurations that must be added to both as examples, it will illustrate the cost difference between using a single engine or a dual engine in the design.

1. Purchase cost comparison

The purchase cost includes the procurement cost of outsourced and purchased parts as well as the production and manufacturing cost.

Due to the different numbers of engines used (single or double engines), the overall layout, structural form and other aspects are also different, which will inevitably lead to differences in the required components, thus resulting in a significant difference in the procurement cost of outsourced and purchased parts compared to self-made parts. This article only considers the differences caused by different engines, and the manufacturing costs during the production process are temporarily disregarded.

Necessary additional components for Model One (single engine) :

The central rotating body and pipelines cost approximately 4,000 yuan and weigh about 120 kilograms.

Necessary additional components for Model Two (twin-engine) :

The lower vehicle hydraulic oil tank (with a capacity of approximately 70 liters), oil filter, stop valve, outrigger hydraulic oil pump, upper vehicle engine, air filter, muffler, radiator, transfer case, fuel tank, battery, engine control mechanism, and the brackets and protective devices provided for installing the above components will require an additional cost of 105,000 yuan, with an additional weight of approximately 1,500 kilograms.

According to the specific power regulations in the GB7258-2004 standard, generally, as the weight of the entire vehicle increases, the required engine power should also increase accordingly. Therefore, when dual engines are adopted, due to the increase in weight, the engine power must be correspondingly enhanced. After the engine power is increased, measures such as increasing the load-bearing capacity of the transmission system and enhancing the output torque of the braking system must be taken during the design process. As a result, the corresponding additional costs during subsequent operation are not a negligible amount (omitted here due to the complexity of the calculation).

The additional cost of using dual engines is a one-time investment at the time of purchase. Therefore, considering the interest on capital, there will be more expenses for those using dual engines. Here, it is approximately calculated as:

101000× (1+ 5%) 10≈ 164,500 (ten thousand yuan)

Among them: 5% is the average interest rate for commercial loans.

Summary 1: Using a single engine saves at least 164,500 yuan in cost compared to using a dual engine, and the weight is reduced by 1,380 kilograms.

2. Comparison of usage costs:

The usage cost mainly includes fuel expenses and maintenance and repair costs.

2.1 Comparison of fuel costs

The state stipulates that the life cycle of each motor vehicle is 10 years (which can be extended to a maximum of 12 years). Considering the overall level of cranes in our country, the calculation in this article takes 10 years into account. Throughout the entire service life, the ratio of the crane's lifting operation time to its traveling time is between 7:3 and 8:2. In this paper, the calculation is based on 7.5:2.5, that is, (3:1).

Calculate the lifetime service life of the crane: 10×305×8 = 24,400 hours; Among them, the 10-year usage period is calculated as 305 working days per year and 8 working hours per day.

The lifetime usage time of the vehicle: 24,400 × 3/4 = 18,300 hours.

The lifetime usage time of the vehicle: 24,400 × 1/4 = 6,100 hours.

For the same lifting operation conditions, the power consumed by single and dual engines is basically the same. However, when a single engine is used, power consumption will increase due to two reasons, that is, the fuel consumption will increase. First, the accessories that come with the engine itself, such as fans, power steering oil pumps, and generators, have a greater output power than the dual-engine vehicle engine. Under the same conditions, they consume more additional power. Secondly, when the operator is performing lifting operations, the output power of the engine and the absorbed power of the load cannot be reasonably matched. To prevent sudden engine stalling and other reasons, the operator will operate the engine at a higher speed, resulting in a single engine having a greater output power than a dual-engine upper vehicle engine, thereby consuming more fuel.

According to Table 1: The rated power of the engine used in the LT1070 vehicle is 112 kw. When the vehicle engine is in operation, its average output power is generally calculated at 75% of the rated power, that is, 112 kw× 75% = 84 kw.

Due to the above two reasons, a single engine consumes 10% more fuel than a dual engine (5% more in each aspect). Therefore, the average additional fuel consumption of a single engine throughout its entire lifting operation life cycle is:

18300×210×84× 10% ÷1000÷ 0.9 = 35,868 (liters)

Among them: 210 - The average fuel consumption of the engine adopted (the average fuel consumption of the engines listed above is between 200 and 220g/kw.h, and the value here is 210g/kw.h);

0.9 is the specific gravity of the fuel.

1/1000 is the coefficient for converting g to kg.

Based on the current average selling price of about 4 yuan per liter of fuel, the total increase in fuel consumption cost over a period of 10 years using a single engine is:

35,868 liters ×4 yuan/liter = 1435 (ten thousand yuan)

However, on the other hand, according to the provisions of GB7258-2004 Technical Conditions for the Safe Operation of Motor Vehicles, generally, as the weight of the entire vehicle increases, the required engine power should also increase accordingly. The weight of the vehicle with dual engines (only considering the engine variation part) increases by 1380 kg, which will further increase the fuel consumption of the vehicle. The proportion of the additional fuel consumption of the vehicle to the total fuel consumption of the vehicle is: 1380÷ 46,000 = 0.03.

The rated power of the engine used in the LT1070 vehicle is 261kW. When the vehicle is in operation, its average output power is generally calculated at 75% of the rated power, that is, 261 kw × 75% = 195.75 kw.

The approximate calculated value of the increased fuel consumption cost over the past 10 years is:

6100×210× 195.75 × 0.03 ÷1000÷ 0.9 ×4≈ 33,400 (ten thousand yuan)

Taking into account the above two aspects comprehensively: The cost saved by using dual engines compared to using a single engine is: 14.35-3.34 = 110,100 (ten thousand yuan)

2.2 Comparison of maintenance costs

During the normal service life, the engines used in cranes all need to undergo the following inspection, maintenance and upkeep work. For the lubrication system, the diesel engine oil needs to be replaced at least once a year, and the oil filter or filter element also needs to be replaced. For the cooling system, the antifreeze needs to be replaced every two to three years. Before winter each year, the freezing point of the coolant should be checked and adjusted. If there is a water filter, the filter element should also be cleaned or replaced. For the combustion system, the fuel filter elements (including coarse filter and fine filter) should be cleaned or replaced annually. The opening pressure of the fuel injectors should be checked and adjusted, and the fuel injection pump should be inspected and adjusted on the test bench. For the intake system, check the air filter maintenance indicator or indicator light, clean or replace the air filter element (including the main filter element and safety filter element) regularly as required, clean the air filter dust collection cup, inspect and tighten the intake pipe, and check the bearing clearance of the turbocharger. Other maintenance and upkeep work includes the piston and rings, bearing shells, belts, valves and push rods, timing gear chambers, etc.

During the normal service life, one to two major overhauls and two to four medium overhauls of the engine should also be taken into consideration.

Therefore, in terms of maintenance and upkeep, the maintenance cost of using dual engines is higher than that of using a single engine. Calculated at an average annual maintenance cost of 5,000 yuan, an additional engine would require an extra 50,000 yuan in maintenance costs over ten years.

Summary 2: Considering the total fuel consumption and maintenance costs, the cost savings from using a dual engine compared to a single engine are: 11.01 -5 = 60,100 (ten thousand yuan).

Considering the residual value, after ten years, the difference between using a single engine and a dual engine is very small, and it is ignored here.

Summary: The cost savings from using a single engine compared to using a dual engine are: 16.45-6.01 = 1044 (ten thousand yuan).

3. Other explanations:

In terms of engine utilization rate, there is also a significant difference between a dual-engine crane and a single-engine crane. The engine used for the vehicle's movement is only a quarter of the working hours of a single-engine crane. From the perspective of investment efficiency, the utilization rate of funds has not been fully exploited.

In terms of product performance and reliability, for vehicles with a certain curb weight, the weight utilization rate (the ratio of the weight of the counterweight to the curb weight) should also be an indicator for measuring lifting capacity. That is, when the lifting capacity of the crane is fixed at a 3-meter amplitude, the greater the load applied to the counterweight, the better the stability of the long boom working condition, and the corresponding lifting capacity will also be greater. Conversely, when the lifting capacity is constant, the lighter the curb weight of the vehicle, the lower the user's procurement cost and usage cost will be (the author believes that Liebherr Company is a typical example of success in this regard). Under the premise that the functions of the system meet the usage requirements, the simpler the structure of the system, the higher its reliability will be.

In recent years, diesel engines with electronic control injection technology have adopted a series of new technologies, including adding high-pressure injection, turbochargers with control valves, four-valve technology, electronic fuel injection technology, and emission control technology, etc. These can reduce fuel injection volume by nearly 20%, increase engine power by 5% to 7%, reduce fuel consumption by 3%, and lower engine noise by 3 decibels. The engine emissions during operation can meet the Euro III emission standards and even comply with more stringent emission standards in the future.

The most important point is that the ECU (Electronic Control Unit) of the engine can formulate corresponding output power curves (i.e., dual-power curve engines) based on the actual working conditions of the product vehicle. When driving, the engine outputs power in the maximum power mode. During lifting operations, the PTO mode is adopted to output power, ensuring that the engine operates within the set range, including the lowest and highest speeds, rated power, torque, etc. Based on the driver's wishes and the feedback load size, the electronic control injection system supplies fuel in appropriate amounts to eliminate unreasonable phenomena during operation by the operator. Keep the engine always operating in an efficient and economical range, thereby achieving the goals of fuel saving and minimizing operating costs to the greatest extent. The QY80K truck crane launched by Xuzhou Heavy Machinery Co., Ltd. and the LTM1070-4.1 crane of Liebherr Company are typical representatives of the single-engine design mode.

The next step of work is to promote the application of single-engine dual-power curve electronically controlled engines in crane products, further enhancing the technical performance of the products and making it another highlight of the company's technological innovation.